Abstract:
Devices and methods for sternal retraction that reduces bleeding from the cut edges of a sternum and reduces fracturing of the sternum during retraction. The devices and methods involve the use of sternal retractor blades having a certain geometry and inserts placed inside the sternal retractor blades during retraction of the sternotomy incision. The blades and inserts act to tamponade the blood flow from the cut sternal edge and reduce fracturing of the sternum during retraction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. application 61/609,662 filed on Mar. 12, 2012, and U.S. application Ser. No. 13/786,370 filed on Mar. 5, 2013, both of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to medical devices, and more specifically to a sternal retractor that minimizes blood loss and fractures of the sternum during use of the sternal retractor. 
     Approximately 1,000,000 cardiac surgical procedures are performed worldwide each year. In the vast majority (&gt;95%) of these procedures, access to the heart is achieved by dividing the sternum, a procedure known as a sternotomy. The sternum is the “breast bone”, a flat bone approximately 15 to 25 cm in length, 2 to 3 cm in width, and 8 to 16 mm in thickness. In fact, it consists of three bones connected by fused “joints”: the manubrium is 3 to 6 cm long and is located at the cephalad end, the sternum proper is 12 to 15 cm long, while the xiphoid is 1 to 4 cm long and located at the caudal end. The manubrium and sternum are composed of thin (1 to 2 mm) outer and inner tables of cortical bone and a wafer-like, spongiform center of cancellous bone in which the bone marrow resides. Within this bone marrow are numerous venous sinusoids. 
     Bleeding from the cut sternal edges during a sternotomy can be profuse and prolonged, lasting the duration of the operation, which may be 4 to 8 hours. Cardiac surgical patients are usually given a powerful intravenous anticoagulant, heparin, which prevents the formation of clots during the operation. Total blood loss from the sternal marrow frequently exceeds one liter during a cardiac operation. In conventional operations performed with the use of the heart-lung machine, this shed blood is suctioned up into the venous reservoir of the heart-lung machine and then re-infused into the arterial system of the patient. Fat droplets and other particulate matter is copious within blood shed from bone marrow and these “impurities” are also re-infused into the patient, where they have been implicated as a cause of neurocognitive decline (brain injury), respiratory insufficiency, and renal failure after heart surgery. Recent reports in the literature have advocated discarding this shed blood, yet the sheer volume of blood shed from the sternal bone marrow makes this impractical in most cases. Alternatively, this shed blood may be “washed” in a centrifugal cell scavenge system prior to re-infusing the red blood cell portion. Unfortunately, all other blood components (platelets, coagulation proteins, serum proteins, etc.) are wasted in this system and derangements in the normal clotting ability of the patient often result. In either case, the volume of blood routinely shed from the sternum during cardiac surgery is a major cause of blood transfusion during and after cardiac surgery. 
     Transfusion associated with cardiac surgery is the single largest civilian demand for blood transfusion worldwide. Within the US, cardiac surgery consumes 10 to 15% of all blood provided by the Red Cross. Thus, there is a clear and immediate need for a way to safely reduce the volume of blood shed from sternal bone marrow during surgical procedures performed via sternotomy. 
     When the surgeon performs a sternotomy to access the heart or other mediastinal structures, the cut edges of the sternum are typically pried apart with a mechanical device known as a sternal retractor. This device is typically made of stainless steel and includes left and right arms and a rack and pinion mechanism to move the arms apart or together. The arms have blades attached thereto, which actually contact or grip the cut edges of the sternum to apply the opening pressure exerted by the rack and pinion. While these blades are currently available in different shapes and sizes to accommodate the numerous different available retractor systems, none are designed to reduce or prevent bleeding from the edges of the sternum. 
     Another issue with presently used sternal retractors is the issue of sternal fractures. Presently available blades only contact the central or middle region of the sternal edge. This applies a large amount of pressure against a relatively small surface area of the sternum, which leads to frequent fractures of the sternal edges. These fractures contribute to increased sternal bleeding and are associated with delayed or incomplete healing and increased risk of sternal wound infection. 
     Accordingly, there is a need for a sternal retractor that reduces bleeding from the cut sternal edge and that reduces fracture of the sternum. 
     SUMMARY OF THE INVENTION 
     In one aspect the present invention provides a device and method to reduce bleeding from a cut sternal edge during surgery performed via a sternotomy. In another aspect, the present invention provides a device and method to reduce sternal breakage during surgery performed via a sternotomy. 
     A typical sternal retractor has arms that attach to a rack, wherein one of the arms is fixed and the other is movable via a rack and pinion mechanism. Each arm carries a blade and the blades have sternal engaging surfaces facing away from each other. During a sternotomy, after the cutting of the sternum, the blades are inserted into the chest incision so that they rest against the sternal edges. The rack and pinion is engaged, causing the blades to move away from each other, and forcing the sternal edges to move away from each other. This is continued until a sternal opening is created that is large enough for the surgeon to access the inside of the chest. 
     The present device and method for reducing bleeding from the cut edges of a sternum involves the use of sternal retractor blades having a certain geometry. The blades act to tamponade the blood flow from the cut sternal edge. 
     The present device and method for reducing bleeding from the cut edges of a sternum further optionally involves the use of inserts placed inside the sternal retractor blades during retraction of the sternotomy incision. The inserts preferably conform to the surface of the cut sternal bone and act to tamponade the blood flow from the cut sternal edge. 
     The present device and method for reducing the incidence of sternal fractures during surgical procedures performed via a sternotomy involves the use of sternal retractor blades which extend substantially the length of the sternum and distribute force across substantially the entire sternum during the sternotomy. Because the force applied to the cut sternum is more evenly distributed across the cut edge, the incidence of sternal fracture is reduced. In addition, the present device and method provide a means to create a trapezoidal opening of the sternal cavity, with a wider opening at the caudal end, which also reduces fractures. 
     In a preferred embodiment, the inserts of the invention are used in retractor blades which extend substantially the length of the sternal edge. In a further preferred embodiment, the retractor blades are configured to fit the shape of the cut sternal edge. In a still further preferred embodiment, the inserts are configured to fit the shape of the cut sternal edge. In a preferred embodiment, the retractor provides a trapezoidal opening of the sternal cavity. 
     Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a retractor according to one embodiment of the invention. 
         FIG. 2  is a perspective view of a retractor blade according to one embodiment of the invention showing the insert in exploded view. 
         FIG. 3  is an exploded view of one embodiment of the invention illustrating a pivot attachment of the blade to a retractor arm. 
         FIG. 4  is a view of an embodiment of the invention illustrating pivoting retractor arms. 
         FIG. 5  illustrates the pivot attachment shown in  FIG. 4  in greater detail. 
         FIG. 6  illustrates an embodiment of a retractor having pivoting blades that can be reversibly employed for a patient. 
         FIG. 7  is a perspective view of another embodiment of a retractor blade according to the invention. 
         FIG. 8  is a perspective exploded view showing a preferred embodiment of the attachment of an insert to a blade. 
         FIG. 9  is a perspective view of another embodiment of a retractor and retractor blades as described herein. 
         FIG. 10  is an additional view of aspects of the embodiment of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A typical sternal retractor has arms that attach to a rack, wherein one of the arms is fixed and the other is movable via a rack and pinion mechanism. Each arm carries a blade and the blades have sternal engaging surfaces facing away from each other. During a surgical procedure performed via a sternotomy, after the sternum is cut, the blades are inserted into the cut opening so that they rest against the sternal edges. The rack and pinion is engaged, causing the blades to move away from each other and causing the sternal edges to move away from each other. This is continued until a sternal opening is created that is large enough for the surgeon to access the inside of the chest. 
     The present invention is a sternal retractor that reduces bleeding from the cut edges of the sternum. The present invention also is a sternal retractor that reduces breakage or fracture of the sternum. 
     Note that while the present invention is described as relating to a sternal retractor having two arms, one of which is fixed and the other movable, the invention is applicable to other types of retractors and retractors having different configurations of arms. For example, the sternal retractor could have two movable arms. 
       FIG. 1  illustrates a first embodiment of a sternal retractor according to the invention. The retractor  10  includes a rack  12  having a fixed arm  14  attached thereto. The rack  12  has a second movable arm  16  also connected thereto. Movable arm  16  has a housing  18  on one end thereof containing a pinion gear (not shown). This pinion gear interacts with a number of teeth  20  on rack  12 , functioning as a rack and pinion gear. Rotation of the pinion gear and thus movement of the moving arm  16  along the rack  12  is controlled by knob  22 . 
     Retractor blades  24 ,  25  are attached to the fixed arm  14  and the moving arm  16 , respectively. As shown more clearly in  FIG. 2 , retractor blade  25  includes a rigid frame  26  and an attachment clip  28 . A connector  30  connects the attachment clip  28  to the rigid frame  26 . The frame, connector, and attachment clip can be one integral part, two separate parts, or three separate parts. Desirably the two blades  24 ,  25  are mirror images of each other or they can be different. 
     Rigid frame  26  is sized and shaped to cover a substantial amount of the cut sternal edge. A substantial amount means that the frame extends the entire length of or at least 50% the length of the cut sternal edge. In a more preferred embodiment, the rigid frame covers at least 75% (and up to or over 100%) of the sternal edge. Desirably, rigid frame  26  has a “canoe” shape with a floor  32  and two side walls  34 ,  36  which substantially encase the cut sternal edge. Desirably frame  26  includes a closed cephalad end  38  and an open caudal end  40 . However, the caudal end may also be closed in some embodiments. Floor  32  can be flat or slightly bowed outward or inward. 
     Since the rigid frame  26  is sized and shaped to cover a substantial amount of the cut sternal edge, its preferred size and shape depends upon the size and shape of the individual patient. It may be desirable to provide a variety of blades with differently sized and shaped rigid frames. In general however, the rigid frame  26  desirably has a length from about 7 cm to 25 cm. The rigid frame  26  desirably has a width (from side wall  34  to side wall  36 ) between about 1 cm and 3.5 cm. Side walls  34  and  36  are desirably about 0.25 to 2.5 cm high. Side walls  34 ,  36  can be a consistent height along their lengths or varying heights and can be the same height or different from each other. 
     The cephalad end  38  can be closed with a wall that is the same height as the side walls  34 ,  36 . Alternatively, the cephalad end  38  can have a lower wall or can be open with no wall. In one embodiment, the cephalad end has a notch (not shown) on the floor  32 . The purpose of the closed end  38  or notch is three-fold; first, to signify to the surgeon or other operator that the blade has been inserted and positioned properly; second, to aid in tamponading bleeding from the cut edge of the manubrium; and third, to prevent the retractor blades from sliding caudad when force is applied to them during trapezoidal opening of the sternotomy incision. As described below, during use the closed end  38  or notch provides a signal that the frame  26  has been placed over the cephalad end of the cut sternal edge. 
     Since the angle between the sternum and manubrium (the Angle of Louis) is slightly bent downwards at the cephalad section, the frame  26  is desirably slightly bent at the cephalad end. Desirably, this angle of curvature between the caudal section and the cephalad section is from about 5 to 30 degrees. Desirably the caudal section is about 4 to 20 cm in length and the cephalad section is about 3 to 5 cm in length. The frame may be wider at the cephalad section than the caudal section, to accommodate the greater thickness of the manubrium. 
     Blades  24 ,  25  are attached to the retractor arms  14 ,  16  via one of a number of mechanisms. Blade  24  or  25  can simply be bolted to the arm  14  or  16  through mating holes in the arm and attachment clip  28 . Preferably however, blades  24  and  25  are able to pivot. The sternum is more resistant to spreading at the cephalad end, and if the same force is applied across the entire length of blade frame  26  then the cephalad section is more prone to breaking. Having blades that pivot allows the retractor to open the sternum trapezoidally, wider at the caudal section where the force needed to open the sternum is lower. Desirably the blades pivot at about 5 to 45 degrees. In a preferred embodiment, the caudal aspects of the blades pivot 10 to 30 degrees outwards from the centerline of the retractor. 
     Blades  24 ,  25  are thus preferably attached to the retractor arms  14 ,  16  with a pivot attachment. This can be a single attachment point, such as a single rotating pin extending through both the blade attachment clip  28  and the arm  14 ,  16  (and which can also function as the connector  30 ). Alternately, the blades can be attached with the mechanism shown in  FIG. 3 , in which the blade attachment clip  50  has two pins  52  and  54  extending therefrom. The pins have expanded heads  53 ,  55 . The retractor arm  56  has two corresponding receiving holes, one of which is a circular stationary receiving hole  58  and the other is an oblong shaped sliding hole  60 . The oblong sliding hole  60  is positioned more cephalad and the stationary hole  58  is positioned more caudal. Each of  58  and  60  has a second hole  59 ,  61 , respectively, connected thereto through which the heads  53 ,  55 , respectively can pass. The heads  53 ,  55  cannot pass through holes  58 ,  60 . The pins  52  and  54  are positioned in the holes  58  and  60 , respectively, by inserting pins  52 ,  54  through holes  59 ,  61  and then sliding the pins into holes  58 ,  60 . 
     The blade  48  will pivot when the pin  54  slides in the sliding receiving hole  60 . The range of pivot of the blade is restricted by the length of the sliding receiving hole  60 . The blade  48  is kept in place by the pin heads  53 ,  55  and using a sliding stitch guide  62  that slides into a groove  64  of the retractor arm  56 , thus holding the pins  52  and  54  into position. 
     In another embodiment, trapezoidal opening of the sternum is provided by pivoting retractor arms. As shown in  FIG. 4 , pivot mechanisms  70  and  71  attach the retractor arms  72  and  73  to the rack  74 . Retractor arm  73  is a two piece assembly  76 ,  78  which snaps together and arm  72  preferably has the same configuration. 
       FIG. 5  illustrates the pivot attachment  70  in greater detail. A pin  80  rotatably fastens arm  72  to the housing  82 . A fixed or adjustable pawl  84  mechanically stops the rotation of the arm  72  at the desired angle when it meets tab  86  on the end of retractor arm  72 . When the retractor blades are inserted into the sternotomy incision the blades are parallel and as the retractor opens the angle of the retractor arm  72  can change until tab  86  hits the pawl  84 .  FIG. 5  shows the pawl  84  allowing a range of motion of the arms  72  and  73  from 0 to 25°. The pawl however can allow a range of motion up to about 45°. 
     Desirably, the pivot mechanisms described above or otherwise provided are equipped with an adjustable governor mechanism that allows the surgeon to adjust the desired range of motion of the retractor arms and/or blades either before insertion of the retractor blades into the chest or after insertion, during the spreading of the retractor arms. Desirably this governor allows a range of motion of the arms or blades between about 0 and 45°. 
     In another embodiment, to provide for a trapezoidal sternal opening, the blades can be nonpivoting and the rack can be curved in the cephalad/caudal direction, so that as the retractor arms are spread the blades open the sternum at an angle defined by the curvature of the rack. Desirably, in this embodiment, the rack would be curved such that S linear inches of the rack allow for about 10 to 30 degrees of arc. 
     In addition to allowing for distribution of pressure across the sternum, the trapezoidal sternal opening provided by pivoting blades or arms applies reduced pressure on the clavicles and brachial plexus (a very important set of nerves in the shoulder that innervate the arm). When the sternum is opened the same amount at the manubrium as at the bottom (xiphoid), in a rectangular fashion, excess pressure may be placed on the brachial plexus, which can cause neuropraxia of the brachial plexis. 
     In yet another embodiment, the rack can be bent in the antero-posterior direction at about 10 to 30 degrees, so that it conforms to the rounded anterior surface of the human chest and abdomen. This optional aspect is shown in  FIG. 1 . Of course, the rack may be both curved in the cephalad/caudal direction and bent in the antero-posterior direction. Another optional feature that further provides for beneficial shaping of the retractor to the patient&#39;s torso is a slight downward angling of the retractor arms. This feature is illustrated in  FIGS. 1 and 4 . 
     In another set of preferred embodiments, the arms of the retractor are removably attached to the rack and pinion mechanism, such that the blades (attached to or independent of the arms) may be inserted into the sternal incision individually and independent of the rack and then later connected to a rack and pinion mechanism. This may facilitate the insertion of the blades into the sternal incision at the beginning of the surgical procedure. This embodiment is shown in  FIG. 4  with respect to an embodiment having pivoting retractor arms. However, this feature can also be employed in other embodiments, such as the embodiment shown in  FIG. 1 . 
     Similar to the above described optional embodiment, the blades can be provided removably attached to the retractor arms, such that the blades may be inserted into the sternal incision individually and independent of the arms and rack and then later connected to rack and pinion mechanism. This may facilitate the insertion of the blades into the sternal incision at the beginning of the surgical procedure. 
     The connector  30  provides for spacing of the rigid frame of the blade  26  from the retractor arms  14 ,  16 . The preferred distance of this spacing will vary depending upon the amount of fat anterior to the patient&#39;s sternum. The sternum may be directly under the patient&#39;s skin, thus requiring a very short connector, or there may be an inch or more of fat between the skin and the sternum. It is preferable to use as short a connector as allowed by the patient&#39;s fat layer, since otherwise the retractor attachment clip  28  and arms  14 ,  16  will protrude above the patient and interfere with the surgeon&#39;s access to the exposed area. Preferably, the connector length will range between 1 and 5 cm. Desirably, connectors of various lengths may be available such as at least short (1 cm), medium (2.5 cm), and deep (5 cm) connectors. 
     In one embodiment, as shown in  FIG. 2 , the retractor blade  24  is a single element comprising the frame  26 , connector  30 , and attachment clip  28 . In this embodiment, it may be desirable to provide a plurality of retractor blades having varying connector lengths and blade widths/shapes. Alternatively, the retractor blades can be provided with independent frame, connector, and attachment clip. In this case, it may be desirable to provide connectors of varying lengths so that retractor blades can be assembled having the desired combination of blade width/shape and connector length. The width of the connector may also be variable. A narrow connector will produce less contact with and subsequent traction on the skin edges, while a wider connector will result in more direct contact with and traction on the skin edges. It may be desirable to provide connectors of two widths, a narrow connector of about 1 to 4 cm and a wider connector of about 4 to 12 cm. 
       FIG. 7  illustrates a second preferred embodiment of a retractor blade. Blade  150  includes a rigid frame  152  and an attachment clip  154 . A connector  156  connects the attachment clip  154  to the rigid frame  152 . The frame, connector, and attachment clip can be one integral part, two separate parts, or three separate parts. 
     Rigid frame  152  is sized and shaped to cover a substantial amount of the cut sternal edge. A substantial amount means that the frame extends the entire length of or at least 50% the length of the cut sternal edge. Desirably, rigid frame  152  has a “canoe” shape with a floor  158  and side wall  160 . The caphalad end  164  can be closed with a wall as shown here or can be open with no wall. Caudal end  166  is preferably open as shown in  FIG. 7  or can also be enclosed with a wall. Side wall  162  extends only about 5% of the length of the frame  152  as shown here. Side wall  162  can also be absent or extend the fill length of the frame. Preferably in this embodiment, side wall  162  extends about 5 to 20% the length of the frame  152 . 
     Floor  158  can be flat or slightly bowed outward or inward. Attachment clip  154  includes two pins  168 ,  170  for attaching the blade  150  to a retractor arm. 
     In a preferred embodiment, the device and method for reducing bleeding from the cut edge of a sternum involves the use of inserts fixed to the sternal retractor blades so that when the retractor blades are placed into the sternotomy incision, the inserts contact the cut edge of the sternum forcefully as the retractor is opened and the sternal edges are pried apart. The inserts act to tamponade the blood flow from the cut sternal edge. Preferably, the inserts are sized and shaped to fit within the rigid frame of the retractor blades described herein. Thus, the inserts will have generally the same dimensions as the rigid frame. However, the insert may be sized smaller or larger than the rigid frame. 
     One example of an insert according to the invention is shown in  FIG. 2 . Insert  100  is sized and shaped symmetrically to rigid frame  26 , having a similarly shaped floor  102 , walls  106  and  106 , closed cephalad end,  108  and open caudal end  110 . 
     The insert  100  in the embodiment shown in  FIG. 2  is simply friction fit into the frame  26 . In one embodiment, the frame  26  has an inwardly directly lip (not shown) around the top perimeter and the insert  100  is retained by the lip. The insert  100  could be simply pushed into place or slid into the frame  26 , from the caudal end, so that it slides under the lip. 
     An insert can be attached to the rigid frame  26  in a number of ways. In another embodiment, the insert can be molded to the frame  26 —the frame and insert can be an integral piece. In another embodiment, the insert and frame can each have a fastening material attached thereto which bond to each other, such as Velcro® or double sided tape. Similarly, a snap-on attaching means could securely and removably fasten the insert to the interior of the rigid frame  26  of the retractor blade. 
     If the insert is disposable but the frame is not it is important that no part of the insert material or disposable fastener is left in or on the frame after the insert is removed. 
       FIG. 8  illustrates one preferred method for attaching an insert to a retractor blade frame using one or more mating protrusions and indentations. Protrusions can be in the form of pins and other elements that extend from the blade. Indentations can be in the form of holes or other receptacles. Blade  180  is illustrated in mirror image. Insert  182  is shown exploded from blade  180 . Blade  180  includes elongated slits  184 ,  186 , male pins  188 ,  190 ,  192 , and female indents  194 ,  196 . Insert  182  contains two elongated protrusions  198  (the second is not in view) which mate with blade elongated slits  184 ,  186 ; three female indents  200 ,  202  (the third is hidden from view) which mate with blade male pins  188 ,  190 ,  192 ; and two male pins  204 ,  206  which mate with blade female indents  194 ,  196 . 
     Prior to use, the insert  182  is attached to the blade  180  by snapping the male and female elements together. After use, the insert  182  can simply be peeled off of the frame  180  and disposed. While the blade and insert are shown here having a multitude of attachment points it should be understood that the invention can employ more or less attachment points, and a different variety of attachment means (slits, tabs, extrusions, male pins, female indents, etc.). 
     The insert is desirably made of a material that conforms to the surface of the cut sternal edge so that a seal is created that reduces or eliminates blood flow. The cut sternal edge has a surface which is an uneven, irregular latticework of cancellous bone, containing sharp bony surfaces as well as open pores. Desirably, the insert conforms to the surface so that it tamponades bleeding from the cut surface. By conforms is meant that the insert will adjust its surface to match the surface of the sternal edge so that a maximum amount of surface area of the sternal edge is tamponaded by the insert. 
     In order to provide these functions, the material should exhibit a soft, rubbery, and pliant behavior. Typical materials that are appropriate have a durometer ranging from about 20 to 60 Shore00 or about 10 to 70 Shore A, more desirably between 20 and 40 Shore A. These properties minimize the risk of trauma at the material/body interface and allow for gentle removability. In addition, the insert material cannot shred on the cut bone surface or otherwise leave material on or in the surface of the sternal bone or elsewhere in the surgical incision after use. The insert is desirably made of a material that is self sealing. The insert material must be biocompatible and sterilizable. The thickness of the insert should desirably be between about 0.5 to 20 mm. 
     A number of different materials can be used for the insert, including silicones and thermoplastic elastomers. Other materials that may be appropriate for use include some gels, polyurethanes, and rubbers. Examples of materials include Dynaflex™ G2 706-1000-00 by GLS Corporation, Medalist® MD-110 by Teknor Apex, Elastosil® R 427/30 by Wacker Chemical Corporation, and LC 58220 by Star Thermoplastic Alloys and Rubbers, Inc., and SILASTICS 9252/250P. 
     In one embodiment, the insert is supplied as a material that is tastable or moldable. In other words, the insert is provided in a first state and changes state as it is applied to the cut sternal edge. For example, the material could be a material that changes state in response to a change in temperature, exposure to moisture, or upon light activation. 
     In another embodiment the insert is a dual material—a softer material such as a conformable gel-like material having a tougher skin. In this way the insert can function as desired as a tamponade but is protected from shredding or otherwise leaving particles upon use. 
     The insert may include additives such as pro-thrombic agents, antimicrobial agents, analgesic agents, and osteoblastic agents. These can be linked to the insert via known techniques or absorbed into the insert. Other methods of incorporating additives are known and can be used. 
     It may be desirable in some cases to use the retractor in the opposite orientation than that discussed above, where the rack and pinion mechanism is cephalad to the patient rather than caudal. In this situation it may still be desirable to have retractor blades that rotate and  FIG. 6  illustrates one embodiment of a retractor having this feature. Retractor  120  includes a rack and pinion mechanism  122 . Retractor arms  124 ,  126  have retractor blades  128 ,  130 , respectively, mounted thereon with the two pin pivot mechanism described above. In addition to the circular stationary receiving hole and the oblong shaped sliding hole as described above, this embodiment has a second set of receiving holes, a stationary receiving hole  132  and an oblong sliding hole  134 . If the retractor is used in the direction having the rack and pinion at the cephalad end, the blades are mounted using this second set of receiving holes  132 ,  134 . Other means of providing reversible retractors with pivoting arms can also be provided. 
     In one embodiment, one or more elements of the retractor or blade are disposable. The insert is desirably disposable. The retractor blade can also be disposable, whether it is provided as an integral piece with the frame, insert, connector, and attachment clip or whether these parts are provided individually. In another embodiment, the retractor blade can be provided as a single piece with the frame, insert, connector, and retractor arm and the entire assembly may be disposable. 
       FIG. 9  illustrates another preferred embodiment of a retractor  220 . The retractor  220  includes a rack  222  having a fixed arm  224  attached thereto. The rack  222  has a second movable arm  226  also connected thereto. Movable arm  226  has a housing  228  on one end thereof containing a pinion gear (not shown). This pinion gear interacts with a number of teeth  230  on rack  222 , functioning as a rack and pinion gear. Rotation of the pinion gear and thus movement of the moving arm  226  along the rack  222  is controlled by knob  232 . 
     Retractor blades  234 ,  235  are attached to the fixed arm  224  and the moving arm  226 , respectively, through attachment clips  236 ,  237 , respectively. Attachment clip  236 ,  237  each is topped with two extending pins;  238 ,  239  on clip  236  and  240 ,  241  on attachment clip  237 . In a preferred embodiment, pins  238  and  240  have larger heads than pins  239  and  241 . As shown more clearly in  FIG. 10 , retractor arm  226  includes an elongated receiving trough  242  with floor  243  and walls  244 ,  246 . Walls  244 ,  246  are each topped with a retaining lip. In a preferred embodiment, wall  244  is slightly shorter than wall  246 . 
     Four grooves are cut into floor  243 , grooves  248 ,  250 ,  252 ,  254 . Outer grooves  248 ,  254  are curved towards each other. In a preferred embodiment, outer grooves  248 ,  254  are narrower in width than grooves  248 ,  254  so that they can accept pins  239  and  241  but not pins  238  and  240 . All grooves  248 ,  250 ,  252 ,  254  are open ended at the connection of floor  243  to wall  246 . 
     To mount the blade  235  onto the arm  226  in the direction shown in  FIGS. 9 and 10 , the pin  240  is inserted into groove  250  and the pin  241  is inserted into groove  254 . Note that in the preferred embodiment, the pin  240  will not fit into groove  248  thus ensuring the blade is mounted with the pins  240 ,  241  into grooves  250  and  254 . 
     The curved groove  254  allows for pivoting of the blade  235  up to about 5°. The degree of pivot can be adjusted up to about 15° by changing the distance between the pins  240 ,  241 , and also the distance between grooves  250  and  254 . 
     Pins  240 ,  241  are prevented from slipping out of grooves  250 ,  254  by installation of a sliding suture guard.  FIGS. 9 and 10  illustrate the suture guard  260  in relation to arm  224  and blade  234  but the principle is the same for blade  235  and arm  226 . Suture guard  260  includes a body  262  having on the top surface thereof one or more suture guides  264 . Left gunnel  266  and right gunnel  268  extend along the outside bottom edge of body  262 . In a preferred embodiment, left gunnel  266  is slightly shorter than right gunnel  268 . In a preferred embodiment, the end  280  of the suture guard  260  is curved. 
     Suture guide  260  can be slid into the receiving trough of arm  224 . Similarly to arm  226 , arm  224  includes an elongated receiving trough  270  with floor  271  and walls  272 ,  274 . Walls  272 ,  274  are each topped with a retaining lip. In a preferred embodiment, wall  272  is slightly shorter than wall  274 . 
       FIG. 9  shows blade  234  attached to the arm  224 . The attachment mechanism acts the same as the previously described attachment mechanism for the arm  226  and blade  235 . After blade  234  is attached to the arm  224  using pins  238  and  239 , the suture guide  260  is slid into receiving trough  270 . Note that in the preferred embodiment, suture guide  260  can only be inserted into arm  224 , and not arm  226 , since the taller right gunnel  268  of the suture guide  260  will not fit under the retaining lip of the shorter wall  272  of the arm  224 . Insertion of the right-arm suture guide into the left retractor arm is, for example, prevented. 
     When suture guide  260  is in place the gunnel  268  blocks the pins  238 ,  239  from sliding out of the grooves. However, the suture guide  260  allows free pivoting movement of the pin  239  within the groove. Similarly, when the corresponding suture guide is inserted within the receiving trough of arm  226  the pins  240 ,  241  cannot slide out of the grooves  250 ,  254  but the pin  241  can freely move within groove  254  and allow pivoting of the blade  235 . 
     Note that this embodiment of the retractor can be used reversibly, as discussed above for other embodiments. In other words, typically a sternal retractor is used with the rack towards the patient&#39;s feet. However on occasion it might be desirable to position the retractor with the rack closer to the patient&#39;s head. In this case, the blades  234 ,  235  can be reversed so that blade  235  is attached to arm  224  and blade  234  is attached to arm  226 . In the preferred embodiment where the pin  238  is larger and the grooves  248  and  254  are smaller, blade  234  can only be positioned one way on arm  226  (with pin  238  in groove  252  and pin  239  in groove  248 ). Accordingly the blade will be able to pivot. 
     In one embodiment of the retractor and blade, there is a single pin on the blade that engages a groove on the retractor arm such that the blade can pivot on the single pin as the retractor is used to force the sternal edges apart during surgery. The location of the groove on the retractor arm is chosen to optimize the even distribution of force on the retractor blade as the retractor is cranked open. All other elements of the retractor, rack and pinion, blade and inserts could be as described elsewhere in this application. In this one-pin design, reversibility of the retractor blade is accomplished simply by switching the left and right blades on the right and left retractor arms. 
     The retractor is put into use after the sternum has been divided with a sternal saw or other means. In order to minimize the length of the post-operative scar, the skin incision may be made shorter than the length of the sternum. The skin incision is then undermined at its cephalad and caudal ends in order to provide access to divide the entire sternum. In this way, an incision of only 4 to 6 inches is made instead of 8 to 12 inches. However, although this shortens the length of the scar it makes more difficult the insertion of the long retractor blades of the invention into the sternotomy incision. Accordingly, the rigid frame is desirably streamlined so that it easily slides into the incision without getting caught up in the skin on either end of the incision. The frame has smooth and rounded edges and is as thin as structurally possible. 
     To insert the retractor, the surgeon or other operator lifts the skin at the cephalad end of the incision and slides the rigid frames of the blades  24 ,  25  into the incision. The frames are slid until the closed front end  38  of the frame  26  fits over the cephalad end of the manubrial bone. The skin at the caudal end of the incision can be lifted to allow insertion of the caudal end of the retractor blades. The presence of the closed cephalad end  38  or notch as described above provides tactile confirmation that the blade is properly positioned. 
     The method of performing a surgical procedure involving a sternotomy with less bleeding thus involves using a sternal retractor having blades that extend substantially (at least 50% and preferably at least 75%) the length of the cut sternal edge. The method further optionally involves using a sternal retractor having sternal blades including an insert that conforms to the cut sternal edge and preferably also covers substantially all of the cut sternal edge. 
     The method of performing a surgical procedure via a sternotomy with lower incidence of sternal fracture involves using a sternal retractor having blades that extend substantially (at least 50% and preferably at least 75%) the length of the cut sternal edge. The method further optionally involves using a retractor with pivoting blades or arms that open the sternum to provide a trapezoidal sternal opening. 
     The above description is for the embodiment where the retractor is fully assembled before use. As described above, the retractor may be assembled in situ. In such an embodiment, the blades, or just the rigid frame, may be first inserted into the incision and placed between the cut edges of the sternum. In some cases it may be easier to insert just the blades or rigid frame unattached to the retractor arms and rack. Preferably one blade is inserted into place over the sternal cut edge and then the other blade is placed into position. The blades are then connected to the retractor arms via one of the connecting methods described above. If the rigid frames are separate pieces they are now connected to the retractor arms via the connectors and attachment clips. In some embodiments, the retractor arms would then have to be connected to the rack and pinion mechanism. 
     Modifications and variations of the present invention will be apparent to those skilled in the art from the forgoing detailed description. All modifications and variations are intended to be encompassed by the following claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety.