Patent Publication Number: US-6656113-B2

Title: Surgical instruments and procedures for stabilizing a localized portion of a beating heart

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 09/305,813 filed May 4, 1999, now U.S. Pat. No. 6,290,644, which is a continuation-in-part of U.S. application Ser. No. 08/931,158 filed Sep. 16, 1997, now U.S. Pat. No. 6,036,641, which is a continuation-in-part of U.S. application Ser. No. 08/789,751 filed Jan. 27, 1997, now U.S. Pat. No. 6,346,077, which is a continuation-in-part of U.S. application Ser. No. 08/603,758 filed Feb. 20, 1996, now U.S. Pat. No. 5,894,843. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to surgical instruments, and more particularly to surgical retractor, instrument mount, and tissue stabilizer devices for use during coronary artery bypass graft surgery. 
     BACKGROUND OF THE INVENTION 
     Diseases of the cardiovascular system affect millions of people each year and are a leading cause of death throughout the world. The cost to society from such diseases is enormous both in terms of the number of lives lost as well as in terms of the costs associated with treating patients through traditional surgical techniques. A particularly prevalent form of cardiovascular disease is a reduction in the blood supply leading to the heart caused by atherosclerosis or other condition that creates a restriction in blood flow at a critical point in the cardiovascular system that supplies blood to the heart. 
     Treatment of such a blockage or restriction in the blood flow leading to the heart is, in many cases, treated by a surgical procedure known as a coronary artery bypass graft (CABG) procedure, more commonly known as a “heart bypass” operation. In the CABG procedure, the surgeon “bypasses” the obstruction to restore normal blood flow to the heart either by attaching an available source vessel to the obstructed target coronary artery or by removing a portion of a vein or artery from another part of the body, to use as a graft, and installing the graft between a point on a source vessel and a point on a target artery. 
     To restore the flow of blood to the heart, the CABG procedure requires that a fluid connection be established between two vessels. This procedure is known as an “anastomosis.” Typically, a source vessel, such as a source artery with an unobstructed blood flow, i.e., the left internal mammary artery (LIMA), or a bypass-graft having one end sewn to an unobstructed blood source such as the aorta, is sewn to a target occluded coronary artery, such as the left anterior descending (LAD) artery or other vessel, that provides blood flow to the muscles of the heart. 
     Although the CABG procedure has become relatively common, the procedure itself is lengthy and traumatic and can damage the heart, the cardiovascular system, the central nervous system, and the blood supply itself. In a conventional CABG procedure, the surgeon makes an incision down the center of the chest, cuts through the sternum, performs several other procedures necessary to attach the patient to a heart-lung bypass machine, cuts off the blood flow to the heart, and then stops the heart from beating in order to complete the bypass. The most lengthy and traumatic surgical procedures are necessary, in part, to connect the patient to a cardiopulmonary bypass (CPB) machine to continue the circulation of oxygenated blood to the rest of the body while the bypass is completed. 
     In recent years, a growing number of surgeons have begun performing CABG procedures using surgical techniques especially developed so that the CABG procedure could be performed while the heart is still beating. In such procedures, there is no need for any form of cardiopulmonary bypass, no need to perform the extensive surgical procedures necessary to connect the patient to a cardiopulmonary bypass machine, and no need to stop the heart. As a result, these beating heart procedures are much less invasive and the entire procedure can typically be achieved through a small number, typically one or two, comparatively small incisions in the chest. 
     Despite the advantages, the beating-heart CABG procedure is not universally practiced, at least in part, because of the difficulty in performing the necessary surgical procedures using conventional surgical instruments. For example, it has been difficult for the surgeon to access the required areas of the heart requiring revascularization. In addition, the various surgical steps that are required to be performed on the heart itself are more difficult to perform because the heart muscle continues to move and contract to pump blood throughout the duration of the procedure. 
     The specific portion of the surgical procedure that creates the anastomosis in the beating-heart CABG procedure is particularly difficult. Completion of the anastomosis requires placing a series of sutures through extremely small vessels on the surface of the heart while the heart muscle continues to beat. Moreover, the sutures must be carefully placed to ensure that the source vessel or graft is firmly attached and will not leak when blood flow through the vessel is established. In cases where the target coronary artery is temporarily obstructed, for example, to improve the surgeon&#39;s visibility and avoid excessive blood loss, it is also important that the anastomosis procedure be performed rapidly to avoid ischemic damage to the heart. 
     Further adding to the difficulty of the procedure is the fact that the working space and visual access are often quite limited. The surgeon may be working through a small incision in the chest, for example, or may be viewing the procedure on a video monitor if the site of the surgery is viewed via surgical scope. The vessel, and particularly the arteriotomy to which a source vessel is to be anastomosed, may also be very difficult for the surgeon to see as it may be obscured more or less by layers of fat or other tissue. 
     The beating-heart CABG procedure could be greatly improved if the heart could be accessed and stabilized during the procedure such that the motion of the heart, particularly at the site of the anastomosis, is minimized even though the heart continues to beat and supply blood to the body. The beating-heart CABG procedure could be further improved if the target vessel, and specifically the arteriotomy was presented to the surgeon in a way that allows sutures to be easily placed. 
     In view of the foregoing, it would be desirable to have improved devices for accessing and effectively stabilizing the beating heart at the site of the anastomosis. It would be desirable to have a low-profile, atraumatic stabilizing device that stabilizes the beating heart at the site of the anastomosis and provides a favorable presentation of the target vessel and the arteriotomy. It would be further desirable to provide a mount for the stabilizing device, or other instruments, that allows the stabilizing device to be easily maneuvered to the desired position and orientation, fixedly secured until the procedure is completed, and then easily removed from the site of the anastomosis. It would also be desirable to have a retractor system for use in conjunction with the stabilizer that provides unobstructed and organized access to the areas of the heart requiring revascularization. 
     SUMMARY OF THE INVENTION 
     The present invention will be described for use in stabilizing the beating heart during CABG surgery, but the invention is not limited thereto, and is contemplated to be useful for other surgical procedures requiring body tissue or organs to be immobilized or stabilized. 
     The present invention involves various aspects of tissue stabilizer devices, and in particular a tissue stabilizer for use in immobilizing or stabilizing a portion of the beating heart using a compressive force delivered to the heart via the tissue stabilizer. The stabilizer may include a stabilizer base and a shaft. The shaft may be secured within an appropriate instrument mount preferably fixed to a retractor or other stable platform. The stabilizers of the present invention provide improved access to a surgical site at a target vessel on the surface of the heart and may include features which facilitate optimal presentation of the target vessel. 
     One aspect of the present invention involves an apparatus for stabilizing a localized portion of a beating heart comprising a base member having a wire frame coupled to the base member. The base member is preferably substantially rigid having at least one contact area adapted to frictionally engage the surface of the beating heart adjacent a first side of a target vessel. The wire frame may have a frame portion adapted to engage the beating heart adjacent a second side of said target vessel opposite to the first side and at least one leg portion connecting the frame to the base member. Preferably, the leg portion is substantially perpendicular to the frame portion. In a preferred embodiment, the frame portion is parallel to a central axis of the base member. 
     The leg portion is preferably flexible relative to the base member and may have a vertically relieved portion in the area where it would cross over the vessel between the contact area and the frame portion. In a preferred embodiment, the leg portion is formed from a unitary length of wire material. The wire material may be selected from stainless steel or titanium and may have a round or square cross-section. In one embodiment, the frame portion is vertically offset from the contact area, preferably by a distance of about 0.05 inches to about 0.2 inches. The contact area may be planar or curved to conform to the surface of the heart. The base member may have more than one contact area and most preferably two contact areas separated by an open space. 
     A shaft may be connected to the base member. Preferably, the base member of the stabilizer is operably connected to the distal end of the shaft. The shaft may be any configuration suitable for delivering the required compressive forces to the base member, but is preferably a substantially rigid shaft. The shaft may be straight, or more preferably, curved. 
     Preferably, the wire frame is moveable relative to the base member. In one embodiment, the base member includes a channel for slidably receiving at least a portion of the leg portion. The leg portion may have a plurality of detented positions with the channel. The detented positions may result from the channel having a plurality of teeth and the leg portion having a plurality of mating teeth adapted to engage the channel teeth. The position of the wire frame relative to the base member may be manually positioned between the detented positions. 
     The wire frame may be also be moveable using a rack and pinion arrangement, a threaded shaft and collar arrangement, or other like driving mechanism. In one embodiment, the base member includes a pinion gear having a plurality of gear teeth and the leg portion includes a rack having a plurality of mating teeth adapted to engage the gear teeth on the pinion. The wire frame can be moved in and out relative to the base member by rotating the gear. In another embodiment, the base member includes a threaded shaft rotatably coupled to the base member and the leg portion includes a collar having a threaded interior adapted to receive the threaded shaft. In that case, the wire frame can be moved in and out relative to the base member by rotating the threaded shaft causing the collar to move along the shaft. 
     The frame portion may have a first end and a second end each having a leg portion extending therefrom. Each leg portion may be removably attached to said base member. The base member may include a first and second channel for slidably receiving each leg portion. The wire frame may preferably be attached to from either side of the base member. When the wire frame is attached to the base member using two leg portions, the wire frame is preferably detachable from said base member to facilitate its removal from a completed anastomosis on the target vessel. 
     In another aspect of the present invention, an apparatus for stabilizing a localized portion of beating heart may include a base member having a post which is offset from the center of the base member. In a preferred embodiment, a substantially rigid base member is formed from a unitary piece of sheet material having a first side and second side. The base member may have a first section adapted to contact the surface of the beating heart and a second section at a fixed angle relative to the first section. The first section defines a first contact surface, a second contact surface and an open space between said first and second contact surface. A first end of the post is connected to the second section at a location which is offset from the open space between the first and second contact surfaces. A second end of the post terminates with at least a portion of a ball extending therefrom. 
     A shaft may be connected to the second end of the post. Preferably, the distal end of the shaft has a socket operably engaged with the portion of the ball at the end of the post. Preferably, the shaft is curved and substantially rigid. 
     In one embodiment, the angle between the first section and the second section may be from about 75 degrees to about 105 degrees, most preferably about 90 degrees, and the post is attached to and extends from the first side of the sheet material. In another embodiment, the angle is more than about 120 degrees and the post is attached to and extends from the second side of the sheet material. 
     In another aspect of the present invention, the apparatus for stabilizing a localized portion of a beating heart includes a substantially rigid base member having at least one surface adapted to contact the surface of the heart and a post having a first end moveably coupled to the base member and a second end having a ball or a ball-shaped member extending therefrom. A shaft, preferably a rigid shaft, may be provided with a distal end having a socket operably engaged with the ball. 
     In one embodiment, the base member has a first section having at least one surface for contacting the surface of a heart and a second section adjacent the first section. Preferably, the moveable post is attached to the second section. The second section may be at an angle relative to the first section. The second section may have a slot adapted to receive the first end of the post which is moveable within the slot from a first position to a second position. 
     In another embodiment, at least a portion of the base member has a curved outer profile and the post is mounted to a top member having an interior profile adapted to engage and concentrically rotate about the curved outer profile. The base member may have at least one elongate slot. The top member may have one or more extending features or tabs engaged within the slot or slots. Preferably, the interior profile of the top member is close fitting with the curved outer profile of the base member. Most preferably, the top member encircles more than 180 degrees of the base member thereby capturing the base member within the top member. 
     In another aspect of the present invention, the apparatus for stabilizing a localized portion of a beating heart includes a base member having a post attached to a pivotable link member. Pivoting the link to one or more different positions correspondingly moves the post to one or more different positions, including positions offset from the center area of the base member in a right or left direction. In a preferred embodiment, the base member has at least one surface adapted to contact the surface of the heart. The link member may be pivotably coupled to the base member at a predetermined pivot point and has a first link end spaced a distance away from the pivot point. A first end of the post is attached to the first link end and a second post end includes at least a portion of a ball extending therefrom. A shaft, preferably a rigid shaft, may be operably coupled to the ball. Preferably, the shaft has a socket an a distal end which engages the ball. 
     The link member may also have a second link end opposite the first link end. The second link end may be releasably locked to said base member to substantially prevent relative movement of the link member relative to the base member. The second link end is releasable such that the link member can be pivoted about the pivot point to allow the post to be moved from one position to another. Preferably, the link member pivots about a pivot pin extending from the base member. The base member may have a first contact surface, a second contact surface and an open space therebetween. The link member preferably provides a first position where the post is laterally offset from the open space in a first direction and second position where the post is laterally offset from the open space in a second direction. Thus, the post can be advantageously moved from a left-hand position to a right-hand position. 
     These and other features of the present invention will become more fully apparent from the following description and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view illustrating a cardiac surgery system according to the principles of the present invention. 
     FIG. 2 is a perspective view illustrating a retractor assembly according to the principles of the present invention. 
     FIG. 3 is a perspective view illustrating a preferred retractor drive assembly. 
     FIG. 4 is a perspective view illustrating an exemplar bar assembly. 
     FIG. 5 is a perspective view illustrating a moveable housing associated with the retractor drive. 
     FIG. 6 is a perspective view illustrating a retractor drive handle assembly. 
     FIG. 7 is a top plan view illustrating a preferred platform blade and retractor drive assembly in an unengaged position. 
     FIG. 8 is a top view in partial cross-section illustrating the platform blade and retractor drive assembly in an engaged position. 
     FIG. 9 is a cross-sectional view taken along line  9 — 9  shown in FIG.  8 . 
     FIG. 10 is a partial top view illustrating a preferred suture stay arrangement associated with a platform blade. 
     FIGS. 11A,  11 B, and  11 C illustrate a preferred platform blade latch. FIGS. 11A and 11B are top and front plan view, respectively. FIG. 11C is a cross-sectional view taken along line  11 C— 11 C as shown in FIG.  11 B. 
     FIG. 12 is a perspective view showing a preferred suture lock. 
     FIG. 13 is a perspective view illustrating an instrument mount assembly according to the principles of the present invention. 
     FIG. 14 is an exploded assembly illustration of the instrument mount assembly of FIG.  13 . 
     FIGS. 15A and 15B are perspective views illustrating the assembly of the mount cam to the mount base. 
     FIGS. 16A and 16B are top and front plan views, respectively, illustrating a preferred mount cam. 
     FIG. 17 is a front plan view illustrating a preferred mount hinge. 
     FIG. 18 is an exploded view illustrating the assembly of the mount body to the mount base. 
     FIG. 19 is an exploded view illustrating the assembly of the instrument clamp to the mount body. 
     FIG. 20 is a cross-sectional view taken through a horizontal plane of the instrument shaft grip of FIG.  19 . 
     FIG. 21 is a front plan view showing an assembled instrument mount operably positioned on a platform blade according to the principles of the present invention. 
     FIGS. 22A and 22B are front and top plan views, respectively, of an alternate instrument mount assembly according to the principles of the present invention. 
     FIG. 23 is a cross-sectional view taken along line  23 — 23  as shown in FIG.  21 . 
     FIG. 24 is an offset cross-sectional view taken along line  24 — 24  as shown in FIG. 22 illustrating the mount assembly of FIGS. 21 and 22 in the closed position. 
     FIG. 25 is an offset cross-sectional view illustrating the mount assembly of FIGS. 21 and 22 in the open position. 
     FIG. 26 is an exploded assembly view showing selected components of a preferred closing mechanism. 
     FIG. 27 is a perspective view illustrating a preferred instrument mount cam post. 
     FIG. 28 is a perspective view illustrating a preferred instrument mount release button. 
     FIG. 29 is a perspective view illustrating a preferred instrument mount follower post. 
     FIG. 30 is a perspective view of a preferred instrument mount shaft clamp. 
     FIG. 31 is a perspective view of a preferred instrument mount conical clutch. 
     FIG. 32 is a perspective view of a threaded collar associated with the instrument mount shaft clamp. 
     FIGS. 33 and 34 are exploded perspective and cross-sectional views respectively of a handle mechanism of a preferred tissue stabilizer. 
     FIG. 35 is an exploded perspective view of a contact member of the stabilizer shown in FIGS. 33 and 34. 
     FIG. 36 is a rear plan view of the contact member of FIGS. 33,  34  and  35 . 
     FIG. 37 is a cross-sectional view of the contact member of FIG. 36 taken along line  37 — 37 . 
     FIG. 38 is a perspective view illustrating a stabilizer base embodiment having an offset shaft connection. 
     FIG. 39 is a perspective view illustrating an alternative offset stabilizer base in use over a target vessel. 
     FIGS. 40A and 40B are respectively front and side plan views of the offset stabilizer base embodiment of FIG.  39 . 
     FIG. 41 is a perspective view of a tissue stabilizer having a moveable ball/post. 
     FIG. 42 is a perspective view illustrating another tissue stabilizer embodiment having a moveable ball/post. 
     FIG. 43 is a partial cross-section taken through the ball/post of FIG. 42 showing a spring biased ball/post. 
     FIG. 44 is a partial cross-section showing the ball/post of FIG. 43 utilizing a locking clip to secure the ball/post. 
     FIG. 45 is a perspective view of the locking clip of FIG.  44 . 
     FIG. 46 is a perspective view illustrating another moveable ball/post stabilizer embodiment. 
     FIG. 47 is a front perspective exploded view of a stabilizer base assembly having an adjustable ball/post position. 
     FIG. 48 is a rear perspective view of the stabilizer base of FIG.  47 . 
     FIGS. 49A and 49B are front and rear perspective views of the stabilizer base assembly of FIG.  47 . 
     FIG. 50 is a partial cross-sectional view through a portion of the rear guide slot of the stabilizer base of FIG.  47 . 
     FIG. 51A is a perspective view of a stabilizer base embodiment having a single contact member and bail construction. 
     FIG. 51B is an end plan view of the stabilizer embodiment of FIG.  51 A. 
     FIGS. 52A and 52B are perspective views illustrating another stabilizer base embodiment having a single contact member and bail construction. 
     FIGS. 53 and 54 are perspective views illustrating stabilizer base embodiments having a single contact member and a bail having a mechanical drive. 
     FIG. 55 is a perspective view of a preferred cardiac surgery system during operation according to the principles of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention involves surgical instruments stabilizing the heart and methods for their use. The present invention may also include a mount that allows various instruments to be easily positioned within the surgical working space, locked or secured into a desired position for the duration of a particular surgical procedure, and then easily and safely removed from the working space. The present invention may also involve a retractor system or assembly for accessing the heart. 
     Although the instruments and methods of the present invention may have application in both conventional stopped-heart and beating heart procedures, they are preferably used to access and stabilize the beating heart during a minimally invasive coronary artery bypass graft (CABG) operation which has been specially developed to facilitate completion of an anastomosis, typically between a target artery and a bypass graft or source artery, without requiring cardiac arrest such as cardioplegia or fibrillation and without cardiopulmonary bypass (CPB). Further, although the instruments for accessing and stabilizing the beating heart can be applied in a number of different surgical contexts involving various incisions and surgical approaches to the heart as are known in the art, the instruments and devices described herein are most advantageously employed in a CABG procedure wherein the heart is accessed through only one or two minimally invasive incisions in the chest. 
     Although the particular source vessel and target artery of the anastomosis are determined clinically, a common minimally invasive bypass procedure on the beating heart includes an anastomosis which forms a connection between the left internal mammary artery (LIMA) as the source artery, and the left anterior descending artery (LAD) as the target artery. To complete the anastomosis, the surgeon must dissect a portion of the LIMA by separating it from the internal chest cavity. Once dissection of the LIMA is achieved, the surgeon may attach the dissected LIMA to the target coronary artery, i.e., the LAD by way of creating an anastomosis. 
     In this example, the present invention may involve a number of discreet components that facilitate access to the anastomosis site, allow various instruments or devices to be maneuvered and secured in place, and provide stabilization of the heart. The various stabilizer embodiments of the present invention may be used to stabilize the beating heart during at least the portion of the procedure during which the surgeon completes the anastomosis of the LIMA to the LAD. The mount of the present invention may be used to facilitate convenient manipulation of the stabilizer, and other instruments or devices, to their desired position and allows the devices to be secured in that desired position. The retractor of the present invention may be used to provide access to the anastomosis site of the target artery on the heart itself. Although the LIMA to LAD anastomosis is provided as one example, it is readily appreciated that the techniques and instruments described herein may be applied to other procedures depending on the clinical diagnosis and the patient&#39;s anatomy. 
     Although each component of the present invention may be used separately with great benefit, the components are preferably used in unison to provide a surgical system which provides an unobstructed and organized surgical field, exceptional instrument maneuverability and access to the heart facilitating total revascularization of the heart if required, and effective vessel stabilization during the anastomosis procedure. Although the present invention will have application whether access to the heart is achieved by way of a full-sternotomy, mini-sternotomy, para-sternotomy, thoracotomy or other known approach, the exemplar embodiments described below will be generally described with reference to a coronary artery bypass procedure using a mid-sternal approach. 
     Referring to the figures wherein like numerals indicate like elements, an exemplar surgical system for performing a mid-sternal surgical procedure on the beating heart is illustrated in FIG.  1  and includes retractor assembly  10 , mount assembly  20  and stabilizer assembly  30 . 
     Retractor assembly  10  generally includes a pair of opposing blades adapted to engage opposite sides of a sternal incision, or other incision, and a drive mechanism constructed to force the blades, and thus the sternum apart. Using the drive mechanism, the sternum may be spread to the desired opening, thus providing the desired access and direct visualization of the thoracic cavity. If desired, the heart may be positioned or oriented to best present the target vessels for anastomosis. This positioning may be established, for example, through the strategic placement and tensioning of sutures in the pericardial sac, by appropriately placing the patient in the Trendelenburg position, or by using a heart positioner in the form or a strap or pad or the like. 
     Once the target vessel is in the desired position, at least one component of stabilizer assembly  30  is brought into contact with the beating heart adjacent the target site of the anastomosis. The surgeon then applies a stabilizing force to the beating heart via the stabilizer assembly  30  which may then be fixed in place, preferably to the retractor assembly  10  by way of mount assembly  20 . The stabilizing force supplied by the stabilizer assembly substantially eliminates movement of the heart in the area of the anastomosis so that the surgeon may accurately and efficiently perform the required anastomosis (or other surgical procedure). After the anastomosis has been completed, the stabilizing force is released and the contacting component of stabilizer assembly  30  is removed from the anastomotic site. 
     Each of the principal components, the preferred surgical system, and their methods of use are separately described in detail below. A preferred retractor is described below with reference to FIGS. 2-12. A preferred stabilizer or instrument mount according to the principles of the present invention is described below with reference to FIGS. 13-32. Preferred stabilizer embodiments according to the principles of the present invention are described below with respect to FIGS. 33-44. A preferred surgical system and methods for performing a coronary artery bypass on a beating heart according to the principles of the present invention is described below with respect to FIG.  45 . 
     The Retractor 
     The preferred retractor generally involves a drive mechanism and a pair of opposing blades adapted for insertion into an incision and for engaging opposite sides of the incision. The drive mechanism functions in some manner to urge the opposing blades apart, thus forcing opposite sides of the incision open to allow surgical access through the incision. For purposes of performing a coronary artery bypass, the incision may be any suitable incision which provides the desired access to the thoracic cavity, and more specifically a desired area of the heart. For purposes of example only, the retractor of the present invention will be described with respect to a mid-sternal incision, however skilled artisans will recognize that many aspects the invention are equally applicable to other surgical approaches to the heart, for example, by way of a thoracotomy, or other suitable access approach. 
     When the heart is accessed by way of an incision through all or a portion of the sternum, the opposing blades are adapted to be inserted into and engage opposite sides of a sternal incision such that the severed sternum may be forced apart by the action of the opposing blades to create a working space for operating on the heart. Typically, the drive mechanism is constructed to spread the opposing blades apart in a generally parallel fashion, however, the parting motion may also have a significant curvilinear or angular component as well. 
     In one embodiment, the blades may be permanently, integrally, or inseparably formed with a drive mechanism. Preferably however, at least a portion of the blades are separable from the drive mechanism. That is, at least some of the features and functions associated with the retractor blades are allocated to a structural component which is separate, separable, or otherwise detachable from the drive mechanism. The separate component and the drive mechanism may be manufactured independently and then subsequently assembled at the factory or, more preferably, at the point of use. 
     A retractor construction having a separable component allows the features and functions of the drive mechanism to remain separate from the remainder of the retractor assembly and vice versa. This allows a greatly simplified or depopulated drive mechanism and allows the separable component to have a much more sophisticated construction with increased features and functionality. Accordingly, the simplified drive mechanism, which is typically required to be made from a hardened steel, is easier and more economical to manufacture and easier to maintain, clean and sterilize post surgically. Moreover, the separate component can be economically made from materials or processes that allow for the intricate structural features which provide superior functionality. 
     In a preferred embodiment, the drive mechanism is constructed to be resterilized and reused a relatively large number of times, and the feature-rich separate component is constructed to be disposable, i.e. discarded after a single surgical use. Thus, the depopulated drive mechanism, which will be used over and over, can afford to be constructed to be quite robust with a view to materials and manufacturing processes that will support the rigors of such extended surgical service. The separable component, free from the typical functional requirements of the drive mechanism and the service requirements of extended surgical re-use, may preferably be constructed from any number of engineering materials to produce an economical component having the desired features and which may be discarded after a single use if desired. 
     In a preferred embodiment, retractor assembly  10  comprises a drive  12  and first and second platform blades  14  and  16  detachably connected to drive  12 , as illustrated in FIG.  2 . Preferably first platform blade  14  and second platform blade  16  each have one or more channels or engaging members  18  adapted to engage opposite sides of an access incision. Activation of drive  12  forces apart first and second platform blades  14  and  16  thereby causing engaging members  18  to correspondingly force the incision open to provide access to the desired surgical site. 
     In the example of a sternal approach to the heart, engaging members  18  are adapted to engage each side of the incised sternum to reliably hold and engage the sternum as the sternum is forced open to expose the thoracic cavity and ultimately the heart. As best seen in FIG. 9, which illustrates a cross-section of second platform blade  16 , engaging member  18  is generally in the form of a channel or the like, preferably having a U-shape, curved shape, or other shape suitable for engaging the incised sternum. 
     Preferably, engaging member  18  generally has a concave interior profile  17  for engaging and holding the sternum and a corresponding convex exterior profile  19  that is relatively smooth so as not to interfere with other surgical instruments, snag sutures or create other such difficulties. The engaging members  18  are preferably constructed to have sufficient strength to withstand the loads required to spread the sternum yet maintain a suitably low profile to facilitate easy insertion into the access incision and to require as little space within the working incision as possible. 
     It may be desirable to provide engaging members  18  with features to reduce trauma to the incision site, increase the traction against the sides of the incision, or both. A thin pad or layer of non-slip or atraumatic material (not shown) may be fixed, by way of an adhesive or other suitable fastening technique, to the interior profile  17  if desired to reduce slippage and trauma to the severed sternum or surrounding tissue. Alternatively, the desired features may be integrally fabricated into engaging members  18 . For example, when platform blades  14  and  16  are injection molded components, traction features such as raised bumps, ribs, indentations, or the like can be molded integral into engaging members  18 . 
     Referring to FIGS. 2-6, drive  12  is preferably constructed to force the platform blades apart in generally opposite directions. Any type of drive mechanism which provides the desired separating action of the blades may be suitable. A common, substantially straight-line parting motion may be provided by a ratchet or rack arrangement as is generally known in the art. FIG. 3 illustrates a preferred drive  12  which involves a bar  15 , moveable housing  22  and handle assembly  24  which facilitates movement of moveable housing  22  relative to bar  15 . A first end of first blade  14  may be operably attached to moveable housing  22  and second blade  16  to bar  15 . 
     In a preferred embodiment, bar  15  is a substantially rigid bar having a stationary or fixed housing  21  assembled thereto and thus forming bar assembly  23 . Fixed housing  21  may be fastened to one end of bar  15  using one or more mechanical fasteners, an interference fit, suitable adhesive or bonding compounds, welding, or any other suitable fastening technique. A first end of second blade  16  is preferably operably attached to fixed housing  21 . As with moveable housing  22 , fixed housing  21  may be of any configuration which provides for the structural attachment of first and second platform blades  14  and  16 . 
     Bar  15  preferably includes a number of teeth  13  evenly spaced along at least a portion of its length. Teeth  13  may have substantially parallel side portions  11  and may have radiused tops  25 . The exterior edges of teeth  13  may be broken or radiused or have a chamfer  26  as shown. Handle assembly  24  preferably includes a means for engaging teeth  13  so as to drive moveable housing  22  relative to bar  15  to any desired position under load where it remains so positioned against the load without need for any applied input or holding force. The means for engaging teeth  13  could be any suitable gear, ratchet, cog or like mechanism. Bar  15  may also be adapted and used for receiving an instrument mount, such as those described in detail below. 
     In a preferred embodiment, moveable housing  22  is driven using one or more drive pins which may successively engage teeth  13  in a cogging manner. Handle assembly  24  includes drive handle  29  connected to first and second cylindrical drive bearings  31  and  32 . Drive bearing  31  preferably has a raised boss  34  extending from one end to which drive handle  29  may be pivotally connected by way of pin  33 . At the opposite end, drive bearing  31  has first drive pin  27  and second drive pin  28  extending therefrom and terminating at second drive bearing  32 . First and second drive bearings  31  and  32  are spaced apart a distance  35  which is selected to be slightly greater than the thickness  38  of bar  15  such that a portion of bar  15  may be received between first and second drive bearings  31  and  32 . The outside diameters of drive bearings  31  and  32  are selected so as to fit within guide holes provided in moveable housing  22 . For example, the outside diameter of second drive bearing  32  is sized to accurately rotate within guide hole  36 . 
     Moveable housing  22  has a bore  37  extending therethrough for receiving bar  15 . Bore  37  generally has a shape corresponding to the dimensions of the cross-section of the portion of the bar  15  which is to pass through bore  36 . With handle assembly  24  properly positioned within the guide holes provided in moveable housing  22 , it may be assembled to bar  15  by placing the end of bar  15  within bore  36  and turning handle  29  such that first and second drive pins  27  and  28  become engaged with teeth  13 . Once assembled in this manner, moveable housing  22  may be forced one way or the other along the length of bar  15  by turning handle  29 , and thus drive bearings  31  and  32 , to cause first and second drive pins  27  and  28  to progressively engage teeth  13  along bar  15 . 
     As mentioned above, first and second platform blades  14  and  16  may be removably assembled to moveable housing  22  and fixed housing  21 , respectively. Platform blades  14  and  16  may be attached in any suitable fashion including, for example, threaded connections or other mating features on the platform blades and housings themselves, ordinary or specialized mechanical fasteners, and cam or latching mechanisms adapted to secure the platform blades to the housings. In a preferred embodiment, both moveable housing  22  and fixed housing  21  are constructed with features that engage, secure and support first and second platform blades  14  and  16  in an operable position on drive  12 , thus providing an assembled retractor  10  which is ready for surgical use. 
     Referring to FIGS. 7 and 8, second platform blade  16  is shown before and after assembly onto fixed housing  21 . Preferably, at least one of the platform blade  16  or the fixed housing  21  has an extending protuberance, post or like feature which can be receivably engaged by the other of the platform blade or housing. In a preferred embodiment, fixed housing  21  is preferably constructed to have a latch post  42  adapted to be received within latch post cavity  45  provided in platform blade  16 . Latch post  42  may have a hole, notch, protuberance, or other feature formed therein which may be engaged in any convenient manner by the platform blade  16  so that platform blade  16  becomes releasably locked in place for use. 
     In a preferred embodiment, latch post  16  has a notch which defines latch surface  51  and stop surface  52 . Platform blade  16  has a latch member  48 , best seen in FIGS. 11A-11C, having a latch body  50  constructed with surfaces  53  and  54  for engaging latch surface  51  and stop surface  52  respectively. Generally transverse to latch post cavity  45 , platform blade  16  has a latch body cavity  56  having an opening towards upper surface  57  of platform blade  16  for receiving latch body  50  of latch  48 . 
     Latch  48  is preferably constructed to engage and disengage latch post  42  by manual rotation of latch knob  49 . Latch body  50  includes cylindrical portion  55  which provides for controlled rotation within latch body cavity  56 . Latch body  50  may be biased towards the engaged position shown in FIG. 8 by way of any suitable spring element. Preferably, latch post  42  is provided with an angled tip  43  having a lead-in angle  44  which allows angled tip  43  to slide against second engaging surface  54  as latch post  42  begins to be received within latch post cavity  45 . As latch post  42  is advanced further within latch post cavity  45 , angled tip  43  causes latch  48  to rotate out of the way about cylindrical portion  55 . Near the end of the advancement of latch post  42  within latch post cavity  45 , the angled tip is advanced beyond latch body  50 , and latch  48  (which is biased towards an engaged position) rotates into the engaged position with second engaging surface  54  biased against stop surface  52 . 
     With latch  48  and latch body  50  snapped into the engaged position, any separating force encountered between platform blade  16  and fixed housing  21  is resisted by action of first engaging surface  53  against latch surface  51 . With this configuration, the reaction force at first engaging surface  53  is advantageously borne by latch body  50  primarily in compression. Thus, since the loading is primarily compressive in nature, a high strength material is not required, and latch  48  can be made from standard engineering polymers, for example, such as polycarbonate. 
     When it is desired to remove platform blade  16  from drive  12 , the operator simply turns latch knob  49 , causing latch body  50  to be placed in a disengaged position relative to latch post  42 . With latch  48  disengaged, latch post  42  of fixed housing  21  is free to be removed from latch post cavity  45  of platform blade  16 . As is apparent from the Figures, a mirror image of the latch assembly described with reference to platform blade  16  and fixed housing  21  is provided to releasably attach platform blade  14  to moveable housing  22 . 
     When the retractor assembly is used to gain access to the thoracic cavity, a good deal of force must be generated to create the desired opening. For example, a separating force in excess of 100 pounds may be required to be generated at each engaging member  18  to achieve the desired separation of a particular sternum. Such loads must be carried by the engaging members and transmitted to drive  12  by way of platform blades  14  and  16 . Since platform blades are preferably made from a suitable engineering polymer (for example, a glass filled thermoplastic polyurethane resin), it may be desirable to provide a reinforcing member for each of platform blades  14  and  16  to ensure that platform blades  14  and  16  will not break or otherwise rendered inoperable as a result of the loads encountered during use. 
     Although the reinforcing members may be a permanent or removable members within the platform blades themselves, the reinforcing members are preferably one or more substantially rigid members extending from each of the fixed housing  21  and the moveable housing  22 . In a preferred embodiment, fixed and moveable housings  21  and  22  have a pin extending therefrom which may be received within a mating cavity within first and second platform blades  14  and  16 . The pin operates to spread the load developed in the mechanism over a larger internal area within the platform blades  14  and  16  and reduces the effective beam length of unreinforced platform blade material subjected to the operating loads. The pin may be straight pin  40 ′ illustrated in FIG.  3 . More preferably, fixed and moveable housings  21  and  22  have tapered pins  40  and platform blades  14  and  16  have mating tapered cavities  41  for receiving tapered pins  40 . The tapered construction tends to allow the user to easily align pin  40  with cavity  41  and allows the pins  40  to fit relatively snugly within cavities  41  without significant binding during insertion that could otherwise occur between elongate pins and mating cavities which are designed to be very close fitting. 
     To provide sufficient load bearing reinforcement, the reinforcing pins  40  are preferably constructed of a substantially rigid material, such as steel, and are preferably at least about 0.75 inches long, more preferably at least about 1.125 inches long, and most preferably between about 1.25 inches to about 2.25 inches long. In a preferred embodiment, reinforcing pins  40  are made from AISI 420 stainless steel having a length of about 1.5 inches, an outside diameter near the housing of about 0.25 inches, and a 2 degree taper angle decreasing towards the free end of the reinforcing pins  40 . 
     In the preferred embodiments just discussed, platform blade  16  can be removed from drive  12  with a substantially straight-line relative motion as indicated by arrow  46 . This engagement action not only provides for simple and intuitive assembly in the operating room, but also represents a significant safety feature. Under certain rare circumstances, for example where the drive through neglect or misuse has become sufficiently damaged during use that it is unable to close and disengage from the sternum, an extremely dangerous situation can be created for the patient. In such exigent circumstances, the configuration described above may allow the drive to be separated from the in situ platform blades by releasing the latches and applying a sufficient amount of force in the direction indicated by arrow  46 . Once the drive has been removed, the detached platform blades may be easily removed from the patient. 
     In addition to engaging members  18 , detachable platform blades  14  and  16  may incorporate a wide variety of additional features which enhance the performance of the retractor system. For example, one or both of platform blades  14  and  16  may have mounting features to which various instruments used during the procedure can be secured. In the case where a stabilizer is to be secured to a retractor for operating on a beating heart, it is critical to minimize or substantially eliminate the amount of flex and motion attributable to each component and each connection between each component, from the component engaging the beating heart to the component which provides the sternal attachment. To this end, the engaging features  18  which engage the sternum are preferably part of a unitary platform blade structure which also includes mounting features to which a stabilizer and other instruments can be mounted. Since the mounting features and the sternal engaging features are part of the same component, and therefore there is no mechanical connection between the two, the stability of an attached instrument against the forces of a beating heart is greatly improved. 
     In a preferred embodiment, each of first and second platform blades  14  and  16  include mount features in the form of rails. The rails allow one or more instruments to be positioned at any desired location along the operable length of the rail. Preferably, the rails are oriented in a direction generally perpendicular to the direction of separation, in this case perpendicular to bar  15 . The rails may be a recessed feature within the body of platform blades  14  and  16 . More preferably, the mounting rails extend upwardly from the body of platform blades  14  and  16 . 
     Referring to FIGS. 7-9, right platform blade  16  has rail  60  extending over at least a portion of the length of platform blade  16 . Rail  60  may have a top portion and a bottom portion having a narrowed region adjacent said top portion. In one embodiment, Rail  60  preferably has a T-shaped cross-section. The T-shaped configuration has a top portion  61  and a narrowed portion  62 , thus forming mounting tabs  63  and  64  which can be gripped by a number of appropriately constructed mounts. 
     The rail may be straight, curved, or a combination of straight and curved portions. Preferably, at least a portion of the T-shaped rail is curved in a manner which more closely follows the profile of the access or incision site (as seen, for example, see FIG.  45 ). In a curved rail configuration, instruments extending perpendicular to a generally central axis  67  of rail  60  will naturally point more towards a central area between the platform blades  14  and  16 , and thus may require less positional adjustment or manipulation from their normal, natural or beginning position. In addition, all or a portion of top portion  61 , and more specifically mounting tabs  63  and  64 , may be tilted or angled inwardly at an angle  65  as shown. 
     Platform blade  16  may be also be provided with a number of suture holders or stays which can be used to organize or capture various sutures used in the course of a particular surgery. Since certain sutures are placed near the beginning of a CABG procedure, such as pericardial sutures used to position the heart, the placement of the suture stays in a manner which does not interfere with subsequent procedures and instruments is an important aspect of the present invention. Preferably, the suture stays are positioned such that placing and manipulating the sutures or the various instruments and instrument mounts employed during surgery can be accomplished without interfering with each other. Preferably, the location of the suture stays position the sutures below the level of the mounting tab  63  and  64  so that a mating instrument mount may traverse the entire operable length of rail  60  without interfering with the sutures. 
     Rail  60  may have one or more grooves, channels, slots or passageways for receiving a suture. In addition, a suture lock may be provided in the rail or elsewhere on platform blade  16  so that the suture may be fixed in place. To accommodate the use of pericardial sutures, which are often subjected to a significant amount of tension when used to position the heart, the suture locks must be adapted to hold the suture material even while under a significant amount of tensile loading. 
     In a preferred arrangement for organizing and locking sutures, and in particular tensioned pericardial sutures, rail  60  has at least one open slot or passageway formed therein for receiving the free end portions of a surgically placed suture. The passageways preferably extend across rail  60  and have a depth which allows the suture to lay at an elevation sufficiently below mounting tabs  63  and  64  so as not to interfere with an instrument mount sliding along rail  60 . In a preferred embodiment the passageways extend through at least a portion of narrowed portion  62 . Thus, the height  66  of narrowed portion  62  may be selected not only to provide sufficient space for a desired instrument mount to attach, but also to ensure that mounting tabs  63  and  64  are sufficiently raised above the surrounding features of platform blade  16  so that an instrument mount may be positioned and repositioned along rail  60  without disturbing or disrupting the sutures within the various passageways. 
     The passageways may be a single channel for receiving both free ends of a surgically placed suture or each end may have a separate channel. In a preferred embodiment, rail  60  has a number of bifurcated channels  70  at predetermined intervals along its length. Referring to FIG. 10, bifurcated channel  70  has a single entrance channel  71  which bifurcates into first and second exit channels  72  and  73 . Entrance channel  71  and either one of exit channel  72  or  73  can be used in the same manner as a single channel, with both free ends  76  and  77  being routed together. Alternatively, both suture ends may be received within entrance channel  71  and then separated, one end within exit channel  72  and one end within exit channel  73 . 
     A means for clamping the suture against movement within the suture channels may be provided on any of entrance channel  71  or exit channels  72  or  73 . Preferably, suture locks are provided on each exit channel  72  and  73 . This allows the surgeon to positively identify and unlock a desired suture end for further tension adjustments or other manipulation without unlocking or loosening the other end of the suture. In addition, placing each suture end  76  and  77  in separate exit channels  72  and  73 , each with a dedicated suture lock, increases the maximum amount of tension that can be applied to a given suture. Exit channels  72  and  73  may have recesses  74  and  75 , respectively associated therewith for receiving a suture lock adapted to secure the suture material within the channels. 
     A preferred suture lock  80  is illustrated in FIGS. 10 and 12. Suture lock  80  has a relatively rigid body  83  having a fixed or pivot end  81  which allows body  83  to pivot within the mating profile of recess  74  or  75 . Pivoting the body  83  about pivot end  81  selectively engages and disengages free end  84  against the wall  78  of exit channel  72  or  73 . Alternatively, suture lock  80  may be made from a more flexible material which, by nature of the elastic properties of the material, tends to flex about its fixed end instead of rotate. In a preferred embodiment, fixed or pivot end  81  is substantially cylindrical and recesses  74  and  75  have mating cylindrical surfaces. 
     Preferably, the suture lock is angled relative to the wall  78  so that it is self-locking in one direction. That is, the suture ends  76  or  77  (or both) operate on the free end  84  in such a way as to force it towards wall  78 , and thus against the suture material, in proportion to the tension, T encountered by suture ends  76  or  77 . Thus, within practical limits, the higher the tension the harder free end  84  will press or bite against the sutures placed therein. Conversely, when the suture ends are pulled in the direction indicated by arrow  79 , the suture forces tend to pivot body  83  about pivot  81  such that free end  84  is rotated away from wall  84  allowing the suture to move relatively freely. Preferably, angle  79  between body  83  and wall  78  is nominally about 1 degree to about 30 degrees, more preferably about 5 degrees to about 15 degrees, most preferably about 10 degrees. Of course, angle  79  is greater as body  83  pivots to accept a suture placed within the suture channel. 
     Suture lock  80  may be biased towards the locked position, preferably using a small spring between the suture lock and the recess  75 . In a preferred embodiment, a piece of resilient closed cell foam  85  is fixed to body  83  to provide the desired biasing effect. Free end  84  may optionally have a number of teeth or ridges  82  to ensure acceptable traction against the suture material. 
     Platform blades  14  and  16  may also be provided with soft tissue retainers to help control and retain the incised tissue and fat in the immediate vicinity of the blades. Referring to FIGS. 8 and 9, platform blade  16  includes integrally attached tissue retainer  85 . Tissue retainer  85  is generally at a small distance  88  above the top of the engaging members  18 . Tissue retainer  85  may be made from a flexible material, such as an elastomer, preferably a polyurethane elastomer having a durometer in the range of about 45 to about 75 Shore D, more preferably about 55 Shore D. In a preferred embodiment tissue retainer  85  is injection molded over the platform blade to form a permanent and inseparable assembly. Tissue retainer  85  may have a raised outer lip  86  and optionally having a plurality of slots  87  formed therein to receive and organize any loose suture ends. Tissue retainer  85  ensures that the tissue surrounding the access incision does not interfere with the operation of rail  60  or the suture holders and also provides a convenient location for attaching surgical drapes of the like without interfering with the operation of the retractor assembly. 
     Although some of the features of the present invention have been described, for illustration only, with respect to only one of the platform blades  14  and  16 , it should be apparent that both platform blades  14  and  16  may have similar or identical features. Although not necessarily so, first platform blade  14  and second platform blade  16  are preferably substantially mirror images of each other. 
     The retractor assembly just described, provides a simplified drive mechanism for use in conjunction with multi-featured platform blades. In addition, a number of different platform blades may be provided for use with a single drive, for instance, tailored to different sized anatomy or the specifics of different surgical procedures. Thus, a number of platform blade configurations can be provided to an operating room and, based upon pertinent prevailing clinical factors, the proper configuration can be selected, mounted to drive  12 , and used as described above to provide access to a desired location. Also, with the modular configuration new features and advancements can be rapidly incorporated into the platform blades and immediately introduced for use with existing simplified drives already in place in the operating rooms. 
     The platform blades themselves represent a surgical platform that allows instruments to be mounted and stabilized in virtually any position, even over already placed and secured sutures from the surgical site accessed by the retractor assembly. Described below are preferred instrument mounts for use in conjunction with rail  60  to secure a beating heart stabilizer or other instruments such as heart positioners, saline or medical air blowers, suction devices, surgical clamps, or vessel occluders. 
     The Instrument Mount 
     Referring to FIG. 13, a preferred instrument mount assembly  20  is shown for mounting an instrument, such as stabilizer assembly  30 , to an instrument mounting rail such as described above with respect to rail  60  of platform blades  14  and  16 . Mount assembly  20  includes mount base  115  having features to secure mount assembly  20  at a desired position on an appropriately configured mating rail or other suitable structure and includes a shaft locking mechanism for controlling and securing an instrument shaft in a desired position and orientation. 
     One important aspect of instrument mount assembly  20  is to provide the necessary degrees of freedom to allow the tissue stabilizer or other instrument to be easily maneuvered to whatever position may be required by a particular procedure. As discussed above, an additional aspect with respect to stabilizing the beating heart is to eliminate or minimize the flex or motion attributable to the various components and connections of instrument mount assembly  20 . As will be discussed in more detail below, instrument mount assembly  20  is uniquely suited for use in stabilizing the beating heart because it allows sufficient degrees of freedom to easily manipulate the position of an instrument secured thereto, allows the degrees of freedom to be frozen or locked in place and, once locked in place, does not significantly flex or allow movement at any of the mechanical joints or connections. 
     Instrument mount assembly  20  provides a number of different controllable joints that, when in a released condition, allows motion in one or more predetermined directions or about one or more degrees of freedom. Although instrument mount assembly  20  may be used to secure any mounting shaft configuration from straight or curved substantially rigid shafts to multi-link or segmented ball and socket type shafts which are relatively flexible until themselves locked in some manner at each joint along the shaft length, it is most advantageously constructed to provide the joints or connections required to position an instrument having a straight or curved rigid shaft. 
     In a preferred embodiment, instrument mount assembly  20  has three releasable joints or connections for controlling the location and position of the instrument mount assembly and instrument attached thereto. The mount base may be positioned at a desired location along an appropriate rail and secured by rail grips  114  and  116 . The position and orientation of the instrument is then determined by ball joint (or ball and socket joint)  112  between mount base  125  and mount body  110 , a rotational joint  157  between mount body  110  and shaft hub assembly  160 , and a shaft clamping mechanism within shaft hub assembly  160  which may allow translation, rotation, or both of shaft  3  relative to shaft hub assembly  160 . 
     Ball joint  112  is preferably of the ball and socket type having 3 rotational degrees of freedom. Rotational joint  157  allows rotation of shaft hub assembly  160  about axis  121  as indicated by arrow  113 . The shaft clamping mechanism allows translation of instrument shaft  3  as indicated by arrows  111  as well as rotation about the shaft itself as indicated by arrow  117 . As will be discussed later, a further ball-joint type connection  201  may be employed between shaft  3  and the particular end-effector of the instrument. 
     Instrument mount assembly  20 , having the particular joints and connections identified above, allows all the required areas of the heart to be conveniently and intuitively accessed by a stabilizer connected to one end of a substantially rigid shaft. Certainly, instrument mount assembly  20  could be provided with more or less degrees of freedom for maneuvering a particular instrument. For example, to add additional degrees of freedom rotational joint  157  could be replaced with a ball joint and to eliminate degrees of freedom shaft  3  could be keyed within shaft hub assembly  160  or ball joint  112  could be replaced with a rotation only joint. However, it should be noted that excessive degrees of freedom may tend to make instrument adjustment increasingly difficult and cumbersome to control while too few degrees of freedom may not allow the instrument to be easily placed in the desired position or orientation. 
     In one embodiment, the various joints and connections are locked into a desired position by way of a series of knobs. The degrees freedom provided by ball joint  112  is locked by activation of top mount knob  120 . Both rotational joint  157  and the shaft clamping mechanism of shaft hub assembly  160  is locked in place by the activation of side mount knob  118 . Base  125  is locked in position on the rail by activation of mount lever  122 . Ball joint  201 , as will be discussed in greater detail below, may be locked in position by activation of knob  504 . This particular sequence of knobs used to lock down the degrees of freedom associated with instrument mount assembly  20  tends to allow the user greater precision in positioning the instrument because degrees of freedom unnecessary to a particular desired maneuver of the instrument can be locked down. Most commonly, mount body  110  is placed at a desired angle or orientation and then fixed in place by locking ball joint  112 , leaving final adjustment to take place using rotational joint  157  and the shaft movement allowed by the shaft clamping mechanism of shaft hub assembly  160 . 
     FIGS. 14-20 show in greater detail the various mechanisms which lock and release the joints or connections associated with instrument mount assembly  20 . FIG.  14  shows an exploded assembly illustration of instrument mount assembly  20 . Instrument mount assembly  20 , and more specifically mount base  125  to which all the other components are ultimately secured, is preferably constructed to engage and lock in position on a rail or other suitable feature. 
     Preferably, instrument mount assembly  20  has a fixed rail grip  114  adapted to engage mounting tab  64  of rail  60  and a moveable rail grip  116  adapted to engage mounting tab  63  or rail  60 . Rail grips  114  and  116  may generally have hook-like features for gripping mounting tabs  63  and  64 . Rail grip  114  is part of mount base  125  and moveable rail grip  116  is part of articulating hinge member  115 , which is pivotally attached to mount base  125  by way of hinge pins  123  and  124 , or other suitable fastener. Articulation of hinge member  115  and rail grip  116  in clamping manner towards rail grip  114  on mount base  125  effectively clamps mount base  125  onto rail  60  at mounting tabs  63  and  64 . 
     Hinge member  115  may be articulated using any suitable mechanism capable of pivoting hinge member  115  to a closed position and holding it there. In a preferred embodiment, best illustrated in FIGS. 15A-17, hinge member  115  includes follower surface  155  which may be acted upon by any suitable cam device to drive hinge member  115  about hinge pins  123  and  124 , thus urging rail grip  116  towards rail grip  114 . 
     In a preferred embodiment, hinge member  115  is articulated by action of cam  145  having cam surface  152  which acts upon follower surface  155 . Cam  145  has a center, C about which cam  145  rotates. Preferably, cam  145  has bore  127 , having its central axis coincident with center, C. Mount base  125  may have a cam guide  153  around which bore  127  rides for smooth rotation of cam  45  about center, C. Cam surface  152  has a varying radius, illustrated by exemplar radial lines R 1 , R 2 , R 3 , R 4 , and R 5 . Thus as cam surface  152  is rotated past follower surface  155 , from example from R 1  to R 2 , it pushes the follower surface a greater distance away from center, C, thus causing hinge member  115  to pivot about hinge pins  123  and  124 , thus causing rail grip  116  to move closer to rail grip  114 . 
     The varying radius of cam surface  152  may be configured to place hinge member  115 , and thus rail grip  116  in a variety of positions. A first portion of cam surface  152  may be configured such that follower surface  155  biased against cam surface  152  is placed in an position characterized in that rail grip  116  is sufficiently spaced apart relative to rail grip  114  to allow assembly onto a rail or other structure. A second portion of cam surface  152  has an increasing radius such that rotation of cam  145  moves rail grip  116  towards rail grip  114  to an intermediate position. In the intermediate position, rail grip  116  has been moved close enough to rail grip  114  so that it becomes captured on a rail but remains loose enough to slide along the rail. A third portion of cam surface  152  has an increasing radius such that the rotation of cam  145  moves rail grip  116  further towards rail grip  114  to a completely locked position wherein relative motion between rail grips  114 ,  116  and the rail is essentially no longer possible. 
     Cam  145  is generally provided with a handle or lever  122  to allow the user to easily turn cam  145  relative to mount base  125 . Cam  145  may be captured onto mount base  125  by operation of retaining hook  150  on cam  145  which rides within exterior groove  151  on mount base  125  on one side, and projection  154  which is engaged below undercut  156  generally opposite to retaining hook  150 . Projection  154  also serves to work against undercut  156  to return hinge member  115  to the open position as cam  145  is rotated in the opposite (open) direction. Hinge member  115  preferably has first and second end stops  158  and  159  between which the motion of projection  154  (and thus the rotation of cam  145 ) is limited. Cam  145  may also have a protective extended portion or cover  163  which shields the area of groove  151  when assembled over mount base  125 . 
     The assembly of cam  145  and hinge member  115  to mount base  125  is illustrated in FIGS. 15A and 15B. Cam  145  is placed in position relative to hinge member  115  with projection  154  in place below undercut  156 . In roughly that position, cam  145  and hinge member  115  are brought over mount base  125  until bore  127  is properly seated over cam guide  153  and retaining hook  150  is positioned within groove  151 . Pins  123  and  124  are then pressed in place through holes provided in both mount base  125  and hinge member  115 . 
     Ball joint  112  is generally created between ball  129  provided at the top of mount base  125  and a socket or mating cavity within mount body  110  adapted to receive at least a portion of ball  129 . Preferably ball  129  includes a generally spherical portion, although other curved shapes providing the desired degrees of freedom may also be suitable. Base post  130  extends vertically upward through bore  126  of mount base  125  and vertical passageway  128  of mount body  110  until enlarged end portion  130  become biased against mount base  125 . Top mount knob  120  may then be threaded onto threaded shaft  132  whereby mount base  125  and mount body  110 , with ball  129  received within mount base  125 , becomes captured between top mount knob  120  and enlarged end portion  130 . Continued tightening of top mount knob  120  over threaded shaft  132  forces ball  129  harder against mount body  110  until the friction between mating surfaces on ball  129  and mount body  110  become so great as to effectively resist any relative movement, thus locking ball joint  112 . 
     The assembly of rotational joint  157  and shaft hub assembly  160  are shown in FIG.  19 . Rotational joint  157  is in the form of a conical clutch formed between frustoconical surface  138  of clutch member  135  and mating frustoconical surface  139  in mount body  110 . Shaft hub assembly  160  is generally formed as upper and lower shaft locks  136  and  137  are advanced over shaft grip  140  and against instrument shaft  3  which is positioned between shaft locks  136  and  137  and outer shaft guide  144 . As clutch member  135  is received over the outside diameter of grip housing  141  of shaft grip  140  tang  164  becomes engaged between upper shaft lock  136  and lower shaft lock  137  thereby preventing relative rotation between clutch member  135  and shaft grip  140 . 
     Side mount knob  118  having threaded shaft  119  extends through mount body  110  (and consequently through transverse bore  131  in central portion  167  of base post  130 ), clutch member  135  and into interior threads  142  within grip housing  141  of shaft grip  140 . Tightening of side mount knob  118  clamps the assembly together. Thus, translation and rotation of instrument shaft  3  is prevented as shaft grip  140  and clutch member  135  are forced together to clamp or trap instrument shaft  3  between shaft locks  136  and  137  and outer shaft guide  144 . Also, relative rotation between frustoconical surface  138  of clutch member  135  and mating frustoconical surface  139  in mount body  110  is prevented as clutch member  135  is forced against mount body  110 . One or both of frustoconical surface  138  and mating frustoconical surface  139  may include a number of teeth, ridges, or other features to prevent rotation when clutch member  135  is forced against mount body  110 . 
     So that the shaft does not become too loose as side mount knob  118  is loosened, a minimum amount of friction between instrument shaft  3  and the clamping surfaces  146  of outer shaft guide  144  is preferably maintained by providing a biasing load against shaft  3 . Referring to FIG. 20, shaft biasing member  147  is provided within shaft grip  140  to maintains a biasing load against shaft  3 . Shaft biasing member  147  has a first portion  148  which slides within counterbore  143  in shaft grip  140 . Shaft biasing member  147  may optionally have a second portion  149  having external dimensions sized to be received within the inside diameter of compression spring  133 . Compression spring  133  urges end  134  of shaft biasing member  147  against shaft  3  to force shaft  3  against clamping surfaces  146 . The amount of force is selected to allow instrument shaft  3  to be easily positioned by hand but would generally not allow instrument shaft  3  to slide relative to shaft grip  140  under only its own weight. 
     Referring to FIG. 21 a preferred instrument mount assembly  20  is shown fixed to a preferred platform blade  16  having rail  60 . As discussed above, rail  60  has mounting tabs  63  and  64  over which rail grips  114  and  116  may be secured. Instrument mount assembly  20  can be positioned, maneuvered, and removed virtually anywhere along rail  60  without disturbing suture  166  locked in place by free end  84  of suture lock  80  below the operating features of instrument mount assembly  20  within any one of the suture channels provided in platform blade  16 . In addition, rail  60  is placed in close proximity to engaging member  18  and thus close to the surgical opening into the patient providing a more direct access to the heart by an instrument mounted to instrument mount assembly  20 . Since the rail  60  moves in unison with platform blade  16 , this relationship between rail  60  and engaging member  18  is maintained no matter how much or how little platform blades  14  and  16  have been spread to create the desired surgical opening. 
     FIGS. 22A-32 illustrate a preferred embodiment of an alternative instrument mount assembly  220 . Preferably, the degrees of freedom available for maneuvering instrument mount  220  are substantially the same as that of instrument mount assembly  20 . Instrument mount assembly  220  preferably has ball joint  112  between mount base  221  and mount body  222 , a rotational joint  157  between mount body  222  and clutch member  225 , and a shaft hub assembly  227  which allows rotation and translation of an instrument shaft held between shaft grip  226  and clutch member  225  of shaft hub assembly  227 . Instrument mount assembly  220 , however, has a different mechanism for controlling or locking the various joints and connections and may also provide a means for releasing and removing the shaft from the bulk of the remainder of instrument mount assembly  220 . 
     As just mentioned, the joints and connections themselves are quite similar between instrument mount assemblies  20  and  220 . As before, ball joint  112  is a ball and socket configuration created between generally spherical ball  224  provided at the top of mount base  221  and a mating cavity within mount body  222  adapted to receive and slide against at least a portion of ball  224 . Rotational joint  157  may be in the form of a conical clutch formed between frustoconical surface  243  of clutch member  225  and mating frustoconical surface  244  in mount body  222 . An instrument shaft may be clamped in place within shaft hub assembly  227  by forcing together shaft grip  226  and clutch member  225  thus closing clamp surface  239  of outer shaft guide  233  towards V-shaped channels  273  on shaft locks  231  and  232 . 
     Instead of locking the joints and connections by way of multiple knobs as described above with respect to instrument mount assembly  20 , instrument mount assembly  220  preferably uses a mechanism which releases each of ball joint  112 , rotational joint  157 , and the shaft clamping mechanism of shaft hub assembly  227  by activation of a single knob, lever, or other suitable manual interface. Generally speaking, this is accomplished by utilizing the clamping motion required to lock one or more of the joints or connections along a first axis to also lock the remainder of the joints or connections along remaining axes. 
     In a preferred embodiment, ball  224  of mount base  221  is locked in place relative to housing  222  by operation of base post  230 . Base post  230  is assembled through mount base  221  and mount body  222  from the bottom until bottom flange  259  (see FIG. 27) is resisted against mount base  221 . At the top of base post  230  is upper link portion  256  having pivot hole  257 . Cam  235  is attached through pivot hole  257  at off-center link pivot  238  using a pin or other suitable fastener and is supported by contact surface  236  associated with mount body  222 . Contact surface  236  may be an integral feature of mount body  222  or may be in a separate mount body cover  254  which may be selected to have superior wear characteristics. 
     With cam  235  in a closed position, as shown in FIG. 24, link pivot  238  is drawn to its maximum distance  251  (or slightly less than the maximum if the cam is constructed to rotate over center) from contact surface  236  thus increasing the clamping force between mount body  222  and ball  224  as the assembly is clamped between cam  235  on the top and bottom flange  259  on the bottom. With cam  235  in the closed position, ball joint  112  is effectively locked. 
     By rotating cam  235 , by way of handle  237 , to an open position as illustrated in FIG. 25, link pivot  238  is withdrawn to a position closer to contact surface  236  at a distance  252 , thus reducing or relaxing the clamping forces between mount body  222  and ball  224  of mount base  221 . With cam  235  in the open position, the friction at ball  224  is reduced to a level that allows the user to easily manipulate mount body  222  relative to mount base  221 . 
     Mount base  221  may have an insert  253  secured in the bottom thereof against which bottom flange  259  is caused to seat as upper link portion  256  is drawn upwards by operation of cam  235 . Preferably, insert  253  includes recess  255  for receiving compression spring  248  captured about base post  230 . Compression spring  248  operates between insert  253 , and thus mount base  221 , and bottom flange  259  to bias base post  230  towards the unlocked position. 
     That same motion of base post  230 , created by operation of cam  235 , is preferably also used to lock both rotational joint  157  and the instrument shaft clamping mechanism of shaft hub assembly  227 . Instead of using a threaded shaft to clamp instrument mount assembly along this axis as did the previous embodiment, instrument mount assembly  220  preferably utilizes tie pin  240  which is driven in the direction of arrow  245  causing shaft grip  226  and clutch member  225  to be forced together to clamp an instrument shaft placed therein and also causing frustoconical surface  243  of clutch member  225  to forced against frustoconical surface  244  in mount body  222 . 
     Tie pin  240  preferably has a generally cylindrical back portion  261  and a front portion which is connected in some manner to shaft grip  226 . Preferably, the front portion includes forward extending first and second flexible prongs  262  and  263 . Cylindrical back portion  261  is slidably received within blind hole  272  of release button  242  and is preferably biased in the unlocked direction indicated by arrow  270  by compression spring  247  positioned within blind hole  272  behind tie pin  240 . 
     Tie pin  240  is preferably driven in the direction of arrow  245  by the movement of base post  230  which is assembled in the space between first and second prongs  262  and  263  of tie pin  240 . Preferably, base post  230  has an angled cam or ramp  258  that engages back wall  269  at the base of first and second prongs  262  and  263 . As base post  230  is drawn upwards in the direction of arrow  271  by cam  235  from the open position of FIG. 25 to the closed position of FIG. 24, ramp  258  progressively forces back wall  269 , and thus tie pin  240 , in the direction of indicated by arrow  245 . 
     Tie pin  240 , connected at its front end to shaft grip  226 , locks an instrument shaft in place and locks rotational joint  157  in the same manner as did threaded shaft  119  of instrument mount assembly  20 . In sum, tie pin  240  urges shaft grip  226  towards clutch member  225  and mount body  222 . The movement of shaft grip  226 , having tang  236  engaged between upper and lower shaft locks  231  and  232  of clutch member  225 , closes together in a clamping fashion surfaces  239  on shaft grip  226  and V-shaped channels  273  on clutch member  225 . At the same time, shaft grip  226  pushes against clutch member  225  to force frustoconical surface  243  against mating frustoconical surface  244  with sufficient force to frictionally lock the surfaces together, thus preventing relative motion therebetween. 
     The operation of cam  235  has been described as generally moving between an open position, in which the various joints and connections of instrument mount assembly  220  are free to be easily manipulated about their respective degrees of freedom, and a closed position in which the joints and connections resist any relative movement and are thus effectively locked in position. However, the outer cam profile of cam  235  operating against contact surface  236  may be given a profile that has one or more intermediate positions such that link pivot  238  is placed at an intermediate distance from contact surface  236 . In an intermediate position, the joints and connections may be in a stiffened or partially locked state which allows some positional and orientational manipulation with somewhat higher operator forces that the completely released condition. In addition, the action of base post  230  may be such that ball joint  112  becomes fully locked before tie pin  240  has completely locked the remaining degrees of freedom. Thus, cam  235  may have a completely released position where manipulation about all degrees of freedom is easily accomplished, an intermediate position in which only ball joint  112  is fully locked and the remaining degrees of freedom are unlocked or may be partially locked, and final closed position in which all degrees of freedom are locked. 
     Instrument mount assembly  220  may optionally be provided with a release mechanism allowing shaft grip  226 , and thus the instrument shaft slidably assembled therein, to be released from instrument mount assembly  220  preferably by activation of release button  242 . This allows instruments associated with instrument mount assembly  220  to be quickly and conveniently removed and replaced or exchanged. 
     In a preferred embodiment, first and second prongs  262  and  263  of tie pin  240  have first and second projections  267  and  268  which releasably attach tie pin  240  to shaft grip  226 . Grip housing  274  of shaft grip  226  is covered with a sleeve having a deep counterbore  278  and small through hole  279 . The depth of counterbore  278  is longer than the exterior of grip housing  274  so as to form internal space  290  (see FIG. 25) when assembled. First and second prongs  262  and  263  can be flexed to position projections  267  and  268  relatively close together for insertion through hole  279  where projections  267  and  268  can then expand apart locking projections  267  and  268  behind surface  280 . 
     Preferably, projections  267  and  268  have lead-ins  291  and  292  which urge projections  267  and  268  together as they are advanced through hole  279  so that shaft grip  226  can simply be aligned with lead-ins  291  and  292  and then snapped into place without any further action. Alignment of hole  279  is generally quite simply accomplished as the cylindrical exterior surface  277  of sleeve  260  is slidably received in a substantially coaxial arrangement within center bore  219  of clutch member  225 . Clutch member  225  may optionally have first and second flexures  281  and  282  having first and second retaining features  283  and  284  so that it may be snapped in place and thereafter retained within mount body  222 . 
     As mentioned above, shaft grip  226  may be released from tie pin  240 . To separate tie pin  240 , it is necessary to flex first and second prongs  262  and  263  together so that projections  267  and  268  will again be positioned to fit through hole  280 . This may be accomplished by providing a raised portion  264  having a ramp  266  on tie pin  240 . A sliding member may be advanced up tie pin  240  and over ramp  266  and raised portion  264  thus flexing prongs  262  and  263  inwards. Preferably, the sliding member is a tip portion  289  of release button  242 . Tie pin  240  is slidably received within blind hole  272  of release button  242 . The internal diameter of blind hole  272  is small enough so that when it is advanced over ramp  266  and/or raised portion  264 , prongs  262  and  263  are flexed inwards. Preferably, the entrance to blind hole  272  has an internal chamfer  288  so that ramp  266  is smoothly engaged as release button  242  is advanced. 
     Release button  242  preferably has a generally cylindrical body  285  which is slidably received within mating bore  294  (see FIG. 25) of mount body  222 . Release button  242  is retained in place, and its sliding travel limited, by release button flange  241  on one end and spring clip or e-clip  293  assembled within e-clip groove  286  on the other end. Spring material  246 , such as a wave spring washer or foam material, may be disposed between release button flange  241  and mount body  222  to bias release button  242  outwards. Transverse to blind hole  272  tip portion  289  also has a clearance slot  287  through which base post  230  passes. 
     For clarity only, FIGS. 22A-25 have illustrated instrument mount assembly  220  without hinge member  115  and cam  145  attached. However, hinge member  115  having rail grip  116  is preferably pivotally mounted, with cam  145  in place, by way of pins or the like at hinge mount  228  as described above with reference to instrument mount assembly  20 . As discussed above, cam  145  may be rotated about cam guide  223  using base lever  122  to secure the instrument mount to a rail or other suitable structure. 
     The retractor and instrument mounts described above can be used to mount and stabilize a great number of instruments for use during surgery. Preferably, the retractor and instrument mounts are used to mount a mechanical stabilizer for stabilizing at least a portion of the beating heart during CABG surgery or the like. Described below are a number of mechanical stabilizer embodiments that are particularly beneficial for stabilizing the beating heart, especially when used in conjunction with the retractors and instrument mounts described above. 
     Tissue Stabilizers 
     Once access to the heart is achieved, and the heart is positioned if necessary, a means for stabilizing the beating heart is introduced through the opening created and at least one component of the stabilizing device of the present invention is brought into contact with the beating heart. The surgeon then applies a stabilizing force to the beating heart via the stabilizing means which may then be fixed in place by attachment to a fixed support. When a retractor or platform is fixed in an open position to expose the heart, the retractor platform may also provide the stable support structure to which the stabilizing means is affixed. When the position of the stabilizing means is fixed by attachment to a stable support or to the retractor platform, the stabilizing force is maintained for the duration of the procedure. 
     The structure of the portion of-the stabilizing means which contacts the heart may include one or more contact members which exert a stabilizing force on the heart proximate to the site of the anastomosis. A pair of contact members may be plates or rectangular members which are placed on either side of the target coronary artery at the site of the anastomosis and which may have friction means or tissue spreading or compressing apparatus associated therewith. The contact members may also be provided by a platform which may be substantially planar or which may be contoured to fit conformingly on the surface of the heart. The stabilizing means may also include a shaft means having several alternative embodiments to facilitate adjusting the position and orientation of the instrument. For example, the shaft means may have an adjustable length and the axis of the shaft means may have at least one ball joint disposed within its length such that the orientation of the shaft means relative to another structure such as the contact members or stable support may be continuously varied. As is apparent from the description of the several embodiments, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments. 
     Referring to FIGS. 33-37, a preferred stabilizer assembly for stabilizing the beating heart is comprised of a foot or base portion  553  attached to a rigid or semi-rigid shaft means or connecting shaft  3 . Base portion  553  typically has one or more contact members  1  adapted to contact the heart adjacent the site desired to be stabilized. The contact members  1  may be substantially planar, may be slightly curved to conform to the shape of the heart, or may be a non-conforming curve to establish contact between only a portion of the contact member  1  and the beating heart. The shape of the contact members may be varied depending on the clinical assessment by the surgeon, the design of the other features of the stabilizing means, or the design of other instruments used to complete the anastomosis. In some embodiments the contact members  1  may have apertures, openings or attachments to facilitate connection with sutures or other devices to achieve the requisite stabilization, occlusion of the target vessel, or exposure of the target vessel. Examples of suitable base portions and contact members can be found, for example, in co-pending U.S. patent application Ser. No. 08/931,158 filed on Sep. 16, 1997, entitled “SURGICAL INSTRUMENTS AND PROCEDURES FOR STABILIZING THE BEATING HEART DURING CORONARY ARTERY BYPASS GRAFT SURGERY”, the entirety of which is herein incorporated by reference. 
     Referring to FIGS. 33 and 34, the proximal end of connecting shaft  3  has handle mechanism  468  assembled thereto which, among other things, provided the user with a means for locking an end effector operably attached to the distal end of connecting shaft  3 . The mechanism  468  is rotatably secured to the proximal end of the shaft means  3  and is formed at a selected angle to the shaft means to permit a surgeon to swivel the mechanism to a preferred position where the knob  504  is more readily accessible to allow quickly locking the shaft means  3  in the orientation selected. In addition, the angled axis of the knob  504  relative to the shaft means  3  reduces the tendency of the shaft means  3  to rotate about its axis when a surgeon applies torque to the knob  504  to lock the associated locking mechanism. The knob  504  is secured to a screw  539  by suitable means such as press fitting, bonding, etc. Right and left handle covers  540 ,  541  comprise the handle  503  and provide the support for the handle mechanism. When assembled, the covers define generally a cylinder formed with a selected curvature. A secondary inner molding, generally indicated at  542 , includes various integrally formed annular walls and shoulders for supporting and containing the knob  504  and screw  539 , as well as a cooperating nut  543 , and arcuate wedge  544 , a shaft retaining ring  545 , the proximal end of the shaft means  3 , and a proximal end of the translatable pushrod  505 . The proximal end of the shaft means  3  includes an annular retaining ring slot  546  which secures the proximal end of the shaft means  3  within suitable annular walls in the corresponding end of the handle covers  540 ,  541  when the retaining ring  545 , confined by shoulders in the inner molding  542 , is snapped into the slot  546  and the covers are assembled. The nut  543  is confined by shoulders in the inner molding  542 , and the arcuate wedge  544  is slidably confined by correspondingly arcuate walls  547  also formed in the inner molding. 
     As may be seen, rotation of the threaded screw  539  within the confined threaded nut  543 , causes translation of the screw, pivoting and thus translation of the translatable wedge  544  which abuts the screw, and translation of the pushrod  505  which abuts the translatable wedge. As is further described relative to FIGS. 35-37, any tightening or loosening of the screw  539 , however slight, will cause a corresponding translation of the pushrod  505  into or out of the shaft means  3 . 
     As depicted in the Figures, the shaft means  3  and thus the pushrod  505 , are formed with a slight arcuate configuration, which permits additional degrees of freedom and movement and orientation of the distal end of the shaft means  3  and thus of the heart contact member  1 . Rotation of the shaft means  3  about the axis of confinement within the shaft grip  495  or  495   a , moves the distal end of the shaft means  3  through a circular path while changing the angles through which the contact member  1  can be oriented. This allows a surgeon to conveniently achieve a wider range of positions and orientations of the contact member relative to the patient&#39;s heart, while keeping the proximal end of the shaft means  3  and handle mechanism  468  out of the way as much as possible. 
     FIGS. 35-37 illustrate an associated mechanism for maneuverably supporting the various embodiments of the contact member  1  and for cooperatively assisting in the quick locking of the contact member by a partial rotation of the knob  504  once the member is positioned. To this end, the distal end of the shaft means  3  is provided with exterior threads matching interior threads in a ball/socket  548 . The distal end of ball/socket  548  is provided with slots  549 , whereby the remaining material comprises short extended tips  550  which, when bent in or inwardly formed, form a socket. A ball/post  551  includes a ball at one end and a post at the other. When the mechanism is assembled, the ball/post  551  is inserted into place within the ball/socket  548  with the ball in the socket and the post protruding from the ball socket. A mechanism for providing a preloaded source, such as a compression spring  552 , is coupled to the ball/socket  548  abutting the ball. The spring  552  is urged by the distal end of the shaft means  3  to exert a preloaded or constant minimum force against the ball of the ball/post  551 . The post of the ball/post  551  is solidly fixed as by pressing fitting, welding, etc., to the contact member  1 . The distal end of the pushrod  505  passes through the spring  552  to abut the ball of the ball/post  551 . Thus when the screw  539  is not tightened, the distal end of the pushrod  505  exerts a slight pressure against the ball, however the spring  552  maintains a preloaded force against the ball sufficient to maintain the contact member  1  at any orientation set by a surgeon. When the screw  539  is tightened, the pushrod  505  is forced against the ball to prevent any further movement of the contact member  1 . As may be seen, the contact member  1  can be tilted to assume many orientations since the narrow center of the post can tilt into any of the four slots in the ball/socket  548 . In addition, simultaneous rotation of the curved shaft means  3  provides a surgeon with an even greater variety of orientations of the contact member relative to a patient&#39;s heart. 
     The contact member  1  includes a preferred configuration which improves the size of the area of the heart which is visible to a surgeon while still providing the required suppression of heart movement necessary to enable the efficient construction of the anastomosis. More particularly, the pair of spaced-apart contact members  1  extend from a common base portion  553 , which uniquely first extends back away from the tips of the contact members at the point of attachment to the post, as shown at reference number  554 . The spaced contact members  1  then curve downward away form the common base portion  553  and back past the post and away from the shaft means  3 . As may be seen in the FIGS. 35-37, the contact member  1  of this embodiment uniquely is attached to the post on the same surface as the surface that bears against the surface of the beating heart. Since the members  1  separate at the base portion  553  at a point  555  behind the distal end of the shaft means  3 , a surgeon has an unobstructed and thus optimum view of the heart even below the distal end of the shaft means  3 . 
     The contact members preferably include friction means  556  selectively secured to the bottom surfaces thereof to more securely engage a beating heart. In addition, the tips of the contact members are bent upward in the form of “ski tips” to lessen their impact when the contact members are firmly pressed against a beating heart to suppress the anastomotic site. 
     Although screw means  539 / 504 / 543  is illustrated herein as a locking mechanism of the handle mechanism  468 , it is to be understood that other mechanisms may be employed. For example, a cam/lever mechanism may be attached to a rod which in turn imparts a pivoting movement or translation to a suitable bellcrank or pivotable member, which in turn imparts translation to pushrod  505  of the shaft means  3 . Thus, locking mechanisms other than those specifically described herein may be used. 
     The basic configuration as just described with reference to base portion  553  provides the maneuverability necessary to access and stabilized any desired vessel on the surface of the beating heart. However, the exact manner and position in which the stabilizer may be placed relative to the vessel and the surgical techniques preferred by an individual surgeon may vary significantly. Accordingly, there is some potential that certain combinations of stabilizer positioning may interfere somewhat with the preferred surgical technique of a particular surgeon. The embodiments illustrated below with respect to FIGS. 38-40B alleviate any such problems. 
     One useful variation, as illustrated in FIG. 38, connects connecting shaft  3  to the base portion of the stabilizer at a position which is generally offset from the center or off-center. Base portion  710  is again typically formed of a unitary piece of sheet material and has a curved back portion in which connecting shaft  3  is attached to an extension of the same surface which carries the contacting members, except that the connecting point  718 , to which ball/post  551  is attached is positioned away from the center and therefore away from the space between contact members  712  where the anastomosis would be performed. This configuration tends to ensure that connecting shaft  3  will not interfere with the surgical access to the center area of the base portion. Of course, the connection can be offset from the central region in either direction. 
     In addition, base portion  710  illustrates a number of features for improving the traction and vessel presentation during a CABG procedure on a beating heart. Contact members  712  of base member  710  have portions  713  having an increased width and which are preferably substantially flat or slightly curved to conform to the heart. This configuration provides a larger area for coined regions  715 , which represent indentations on the bottom surface for receiving a traction material, thus providing greater traction against the surface of the heart. 
     Further, base portion  710  provides a smaller open space between contact members  712 . In a preferred embodiment, the spacing  716  between contact members  712  is less than about 0.350 inches, more preferably less than about 0.300 inches, and most preferably about 0.25 inches. This minimized spacing provides stabilization closer to the vessel and, in some instances, the compressive forces applied through contact members  712  actually tend to present the vessel upwards between contact members  712  in a more favorably pronounced manner. The tip portions  714  of contact members  712  are angled upwards from the surface of the heart to minimize any possible trauma to the heart during use. 
     As just discussed, the base portions ( 550  or  710 ) can be manipulated or oriented relative to the end of the connecting shaft  3  by virtue of the ball and socket joint between base portion  553  and connecting shaft  3 . The amount of angular manipulation or travel available is somewhat limited as ball/post  551  eventually bottoms out or stops against either the bottom of slots  549  or extended tips  550 . Thus, the contact members have a limited range of movement relative to connecting shaft  3  based upon the nominal mounting relationship between the contact members and the ball/post. Accordingly, for some procedures, it may be desirable to have a different nominal relationship between the contact members and the ball/post to shaft connection. 
     Referring to FIGS. 39-40B, base member  720  illustrates an alternative orientation of ball/post  551 . Instead of being angled away from the contact members, base member  720  has a back portion  721  which allows ball/socket  551  to be mounted generally parallel to contact members  722 . Ball/post  551  preferably extend towards contact members  722  as shown, but may also extend the opposite direction away from the contact members. The connecting point  723  is preferably offset a distance  724  from the central area between the contact members  722 . The connecting point  723  is also off set a greater distance  726  from the contacting place of contact members  722 . In nominal position of base portion  722  relative to ball/post  551 , this configuration tends to keep the connecting shaft  3  clear from the central portion between contact members  722 . Furthermore, relative to connecting shaft  3 , contact members  722  can be maneuvered through a range of motion different from base member  553  due to the initial orientation of ball/post  551 . 
     Because the preferred location of the attachment of the connecting shaft  3  to the base portion may be different from surgeon to surgeon and from procedure to procedure, it may be desirable to have the ball/post moveable to more than one location. In one embodiment shown in FIG. 41, for example, ball/post  562  has threaded end  561  which may be threaded into any desired threaded receiving hole  563  provided in stabilizer base  560 . Ball/post  562  is preferably provided with one or more flats  564  on the exterior thereof to facilitate tightening or loosening of the threaded connection. In the embodiment shown, stabilizer base  560  has threaded receiving holes  563  to provide center, offset right, and offset left connecting positions. 
     Referring to FIGS. 42 and 43, ball/post  572  may be captured within slot  571  formed in stabilizer base  570 . Slot  571  preferably has two or more positions where the ball/post can be positively locked. In a preferred embodiment, slot  571  preferably has two or more key-hole openings  573 . Key openings  573  are sized to receive first post portion  577  having an outside diameter which closely matches the inside dimension of key opening  573 . First post portion  577  of ball/post  572  is released from key hole  573  by pulling ball post in the direction indicated by arrow  579  until second post portion  578  is positioned within keyhole  573 . Second post portion  578  is sized to have an outside diameter small enough to fit and traverse through slot  571 . Ball/post  572  may then be traversed along the path defined by slot  571  until the next desired key hole is reached, which may then be engaged by first post portion  577  to secure ball/post  572  in position on stabilizer base  570 . 
     First post portion  577  may be kept in engagement with keyholes  573  by any convenient manner. For example, ball/post  572  may be spring biased in the locked position between upper flange  574  and lower flange  575 , preferably using spring washers  576  as shown. Ball/post  572  may also be locked into operating position within keyholes  573  by using a retaining or locking clip, such as locking clip  580  illustrated with reference to FIGS. 44 and 45. Locking clip  580  has slot  584  adapted to slide over second post portion  578 . Locking clip  580  includes a thin portion  585 , a thick portion  583 , a transition ramp  582  between thin portion  585  and thick portion  583 , and a grip or handle portion  581 . With locking clip  580  in the open position shown in FIG. 44, ball post  572  is free to move upwards in the direction of arrow  579 , thus releasing first post portion  577  from key hole  573 . When locking clip  580  is moved in the direction indicated by arrow  586 , the outer thickness of thick portion  583  is wedged between lower flange  575  and stabilizer base  570 , thus locking ball/post  572  in place within keyhole  573 . 
     Stabilizer base  590  in FIG. 46 has ball/post  592  mounted to an articulating member which is moveable between two or more positions. Preferably, ball/post  592  is mounted on first end  594  of pivoting link  591  which is pivotably attached to stabilizer base  590  at pivot pin  596 . Preferably, pivot pin  596  is centrally located on pivoting link  591 . At second end  593  of pivoting link  591 , a locking knob  595  may be provided to engage stabilizer base  590 . Preferably, locking knob  595  has a threaded shaft or other such fastening or locking feature which engages mating threaded holes (typically one positioned under locking knob  595  and one under ball/post  592 ) in stabilizer base  590 . The ball/post  592  and locking knob  595  are preferably spaced equal distances from pivot pin  596  such that when pivoting link  591  is rotated as indicated by arrow  597 , the position of ball/post  592  and locking knob  595  are reversed. 
     Another embodiment of a tissue stabilizer having an adjustable attachment position of the connecting shaft is illustrated in FIGS. 47-50. Stabilizer base assembly  625  includes top member  605  and stabilizer base  600 , having contact members  606  and  607  and notch or relief  603  under which a vessel may safely pass without being occluded. At least a portion of stabilizer base  600  has outer profile  601  which is generally curved or circular at a predetermined radius. Top member  605  has a mating interior curvature such that stabilizer base  600  and top member  605  concentrically rotate relative to each other, preferably about a common center point. Ball/post  602  may be attached at a convenient position, typically centered, on top member  605 . Rotation of top member  605  relative to stabilizer base  600 , as indicated by arrows  620  and  619 , thus adjusts the position of ball/post  602  along an arcuate path relative to contact members  606  and  607 . 
     To facilitate the secure attachment and smooth rotation of top member  605  relative to stabilizer base  600 , top member  605  may be provided with one or more projections adapted to be received within guide slots provided in stabilizer base  600 . In a preferred embodiment, top member  605  has side projections or rails  608  and  609  which snap into lower slots or channels  611  and  610  in stabilizer base  600  as top member  605  is urged into a concentric position over stabilizer base  600 . Rails  608  and  609  slide within channel  611  and  610  to maintain a secure attachment and controlled rotation of top member  605  and stabilizer base  600 . Top member  605  may optionally have tab  612  adapted to be received within upper slot  604  on stabilizer base  600 . Upper slot  604  may have a plurality of detents or teeth which form a desired number of detented positions as tab  612  is rotated around the path of upper slot  604 . In a preferred embodiment, detented position  617  is formed between tooth  613  and slot end  616  and detented position  618  is formed between tooth  614  and tooth  615 . Of course, detented positions may be created at any desired location using a variety of alternate constructions. Preferably, the detent action of tab  612  allows the operator to manually select a position of ball/post  602 , but then holds the position of top member  605  relative to stabilizer base  600  against movement during use to ensure effective stabilization of a target vessel on the beating heart. 
     In addition to the critical function of stabilizing the beating heart, it is also important for the tissue stabilizer to present the stabilized coronary artery in a manner which allows sutures to be easily placed around the mouth of the arteriotomy as required to create the anastomosis. FIGS. 51A-54 illustrate a tissue stabilizer embodiment involving a base portion having a single contacting surface for stabilizing a target vessel on the beating heart and a mechanical bail element to facilitate optimal vessel presentation. 
     Referring to FIGS. 51A and 51B stabilizer base  740  is shown attached to connecting shaft  3  using ball/post  730 . Connecting shaft  3  is shown connected generally to the center of stabilizer base  740  at approximately a right angle, however, as discussed above, the ball/post  730  could be connected at any desired offset or orientation or the position of ball/post  730  could be adjustable. Stabilizer base  740  preferably has a single contacting surface  742  which may be flat or curved to at least partially conform to the surface of the heart. Contacting surface  742  is sized to provide sufficient contacting area such that sufficient compressive force can be applied to the beating heart to achieve effective immobilization or stabilization of a target coronary artery. 
     Stablizer base  740  preferably has an extending frame member or bail  745  attached thereto. Bail  745  may be a thin, round or square cross-sectioned member, and is preferably a stainless steel wire. Bail  740  has a bail portion  756  which is generally parallel to stabilizer base  740  and may have relieved sections  747  formed therein so as not to occlude the vessel during use. Bail portion  756  may have tissue gripping features, such as teeth  755 . In an optional embodiment, bail portion  756  may be provided with rotating cover or a spiral wound thread (not shown) so that bail portion may be more easily repositioned, under a stabilizing load, over the surface of the heart as discussed below. 
     In a preferred embodiment, bail  745  is moveable relative to stabilizer base  740 . Bail  745  can be moved in or out in the direction indicated by arrow  750  to cause bail section  756 , which is generally parallel with stabilizer base  740 , to compress tissue towards stabilizer base  740  or stretch tissue away from stabilizer base  740 . Thus, bail  745  can be moved in and out to compress or stretch the tissue surrounding a coronary artery until the optimum presentation for performing the anastomosis is achieved. The generally parallel portion may be vertically offset from contacting surface  742  by a distance  757  which is typically about 0.050 inches to about 0.200 inches. 
     Although bail  745  may be attached in a number of ways, bail  745  is preferably formed with first and second end portions  748  and  749  having detents or teeth  746 . Stabilizer base  740  preferably has channels  751  and  752  for receiving end portions  749  and  748  respectively. Channels  751  and  752  preferably have internal mating teeth  753  for engaging teeth  746 . End portions  748  and  749  can be incrementally advanced into channels  752  and  751  as teeth  746  deflect and release from a mated position relative to teeth  753  and then successively engage the next mated position. Stabilizer base  740  may include cover  754  over channels  751  and  752 . So that the stabilizer can be removed from around a completed anastomosis, at least one end of bail  745  is detachable from stabilizer base  740 . In a preferred embodiment, stabilizer base  740  is substantially symmetrical allowing bail  745  to be assembled from either side in a right or left handed configuration. 
     Bail  745  is preferably flexible or semi-flexible relative to stabilizer base  740 . As a result of its inherent flexibility, bail  745  applies a predetermined force against the heart that, under operating conditions, may be generally independent of the stabilizing force applied to stabilizer base  740  to stabilize the beating heart. That is, once stabilizer base  740  is forced against the surface of the heart, the force applied by bail  745  is a function of its mechanical spring rate relative to stabilizer base  740 . 
     FIGS. 52A and 52B illustrate another single contact stabilizer base having a bail  762  which is secured at only one end. Stabilizer base  760  may have a housing  765  having a series of internal teeth (not shown). Bail  762  has a toothed end  766  which is received within housing  765  to engage with the mating teeth provided therein. As with the embodiment above, bail  762  has a generally parallel portion  763  which is moveable relative to stabilizer base  760  in the direction generally indicated by arrow  767  to stretch or compress the surrounding tissue for optimum vessel presentation. Bail  762  may have tab  761  to facilitate grasping by an instrument, such as for example forceps  799 . The free end  764  of bail  762  is preferably rounded or somewhat bulbous so as to be atraumatic. Because bail  762  attaches only at one end, the stabilizer can be easily removed from the completed anastomosis without removing bail  762  from stabilizer base  760 . 
     In another embodiment of the stabilizer, the wire frame member or bail may have a drive mechanism for moving the bail relative to the stabilizer base. Referring to FIG. 53 stabilizer base  770  has housing  771  which is constructed with guide channel  774  having gear  775  mounted for rotation therein. Bail  772  has a toothed end  773  which may be assembled within guide channel  774  such that rotation of gear  775  causes bail  772  to be moved in and out in the direction indicated by arrow  777 . Gear  775  may be driven by any suitable tool, for example, gear  775  may have a drive hole  778  for engagement by a suitable drive tool  776 . 
     Another driven bail stabilizer is shown in FIG.  54 . In this embodiment, stabilizer base  780  has threaded shaft  781  preferably supported at its end portions by bushings or bearings  783  and  784 . One end of the threaded shaft is connected to a flexible drive  785  through a flexible or universal joint  791 . The flexible drive may be routed up connecting shaft  3 . Preferably flexible drive  785  is secured to connecting shaft  3  by way of a thin polymeric coating. Bail  782  is connected to threaded collar  787  which cooperates with threaded shaft  781  to move bail in and out relative to stabilizer base  780  in the general direction indicated by arrow  790 . The screw and collar drive mechanism is preferably concealed by housing  788  which has only a small slotted opening  786  allowing passage of bail  782 . 
     With each of the flexible bail embodiments described above, stabilization and vessel presentation are relatively independent. First, the beating heart is typically stabilized using a compressive force delivered by way of the single contacting surface provided by the stabilizer base. The bail may then be manipulated in or out to obtain the optimum presentation of the vessel for whatever surgical procedure is underway. For example, one bail position may be optimal for creating the arteriotomy, another bail position for insertion of a shunt or like device (should one be used), another bail position for creating the anastomosis, and so on. All the while, the stabilization of the beating heart itself remains optimized by the contacting surface of the stabilizer base. 
     The Stabilization System 
     Preferred embodiments for each of the retractor, the instrument mount and the tissue stabilizers have been discussed in detail above. While each component may be utilized separately, superior access and stabilization can be achieved when the multiple components are used together for performing a minimally invasive cardiac surgery, preferably through a sternotomy approach. Referring to FIG. 55, retractor assembly  900 , including drive mechanism  910  and first and second platform blades  915  and  920 , may be used to spread the sternum, providing access and direct visualization to the thoracic cavity. Retractor assembly  900  also allows sutures to be fixed or organized. Stabilizer assembly  800  isolates and provides local immobilization of the target vessel on the beating heart. Instrument mount assembly  850  facilitates precise maneuvering of the stabilizer and ensures a stable, motion free mount at the desired position and orientation. 
     To begin a typical beating heart CABG procedure using the preferred stabilization system illustrated in FIG. 55, drive mechanism  910  is preferably placed in the fully closed position with moveable housing  925  positioned against or adjacent fixed housing  930 . First platform blade  915  is then assembled to moveable housing  925  and a second platform blade  920  is assembled to fixed housing  930 . After ensuring that platform blades  915  and  920  are fully and securely attached to drive mechanism  910 , engaging members  935  of platform blades  915  and  920  are securely seated on the incised sternum created using standard surgical procedures. Drive handle  940  may then be rotated clockwise to separate platform blades  915  and  920 , thus creating the desired opening for accessing the beating heart. 
     If positioning the heart using sutures to position the heart, the sutures may be placed through the tissue at the desired location and secured to platform blades  915  and  920 . Sutures  945  may be slid into suture holder slots  950  to engage the suture. To ensure proper a proper hold, only one suture strand is preferably engaged within each suture holder slot  950 . Sutures  945  are released from platform blades  915  and  920  by concurrently pulling back and up on suture  945  while pulling the suture through the suture holder slot  950 . 
     With the heart positioned as desired, instrument mount assembly  850  may be assembled to platform blade  920  (or  915 ) by hooking stabilizer mount base  955  onto rail  960  (or  961 ) at the desired location and moving the base lever (not visible in this view) clockwise to the closed position to secure instrument mount assembly  850  onto rail  960 . Mount body  110  may be oriented to the desired angle by way of ball joint  965  and locked into place by turning the top mount knob  855  clockwise. 
     Stabilizer base  810 , having contact members  812  and  814 , may then be positioned on the epicardium of the beating heart by gently lowering connecting shaft  820  using one hand to guide stabilizer base  810  onto the target area on the heart. Incremental pressure is applied to stabilizer base  810  situated on the epicardium until the desired immobilization or stabilization is achieved. Connecting shaft  820  is secured in the desired position by turning side mount knob  860  clockwise and stabilizer base  810  is secured in the desired position relative to connecting shaft  820  by turning the stabilizer shaft knob  830  clockwise. With the beating heart stabilized the anastomosis, or other desired procedure, is completed. 
     To remove stabilizer base  810 , connecting shaft  820  is held with one hand while side mount knob  860  is loosened with the other hand. Stabilizer base  810  is then carefully removed from the anastomotic site. The base lever is moved to the open position to release instrument mount assembly  850 , and stabilizer assembly  800  mounted thereto, from rail  960  on platform blade  920 . When the entire bypass procedure is completed, drive handle  940  is rotated in the counter clockwise direction to close drive mechanism  910  and platform blades  915  and  920 . Retractor assembly  900  may then be gently removed from the access incision. To remove platform blades  915  and  920  from moveable housing  925  and fixed housing  930 , respectively, release latches  970  are manually activated and platform blades  915  and  920  may be pulled generally straight away from drive mechanism  910 . Drive mechanism  910  may then be sterilized and prepared for use in a subsequent procedure. 
     While certain embodiments are illustrated in the drawings and have just been described herein, it will be apparent to those skilled in the art that many modifications can be made to the embodiments without departing from the inventive concepts described. For purposes of illustration only, the principles of the present invention has been generally described with reference to a coronary artery bypass procedure, but may readily be applied to other types surgical procedures not specifically described. Many other uses are well-known in the art, and the concepts described herein are equally applicable to those other uses. Further, the different components of the various exemplar embodiments described above can be combined in any desirable construction. Accordingly, the invention is not to be restricted except by the claims which follow.