Abstract:
A surgical clamp includes a support frame clamp member, a retraction shaft clamp member and a handle linked to the support frame clamp member and the retraction shaft clamp member for moving the clamp members between loosened and tightened positions. The handle includes a cam, and the handle/cam is unitarily formed by metal injection molding. The handle includes relatively uniform thickness throughout to better accept the shrinkage induced by the metal injection molding process. The base used for a bottom position of the cam is adjustable and spring loaded, to better support a wider range of manufacturing tolerances on the cam as well as the other components of the clamp without over stressing the metal injection molded handle during use. The handle includes a gripping portion with a planar portion inducing alignment of the clamping force as desired for best operation of the clamp.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     None.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to the field of surgical tools, and particularly to the design and manufacture of surgical retractor systems. Surgical retractor systems are used during surgery to bias and hold tissue in a desired position. As one example, some surgical procedures require anterior access to the spine, through the patient&#39;s abdomen. Tissue such as skin, muscle, fatty tissue and interior organs needs to be held retracted to the side so the surgeon can obtain better access to the vertebrae structures of primary interest.  
         [0003]     Surgical retraction may be performed by one or more aides using handheld tools, with the most basic retractor apparatus being a tongue depressor. More commonly now in sophisticated operating rooms during abdominal or chest surgery, a surgical retractor system or assembly is used. The retractor assembly may, for instance, include a ring or support frame which is rigidly supported from the patient&#39;s bed above and around the surgical incision location, with a number of clamps and retractor blades to hold back tissue proximate to the surgical incision. Other retraction systems, such as those disclosed in U.S. Pat. Nos. 6,315,718, 6,368,271 and 6,659,944 to Sharratt, incorporated herein by reference, may not include a ring and/or may be directed at other types of surgery. Clamps may also be used to attach the ring or support frame to a support post and/or part of the bed frame.  
         [0004]     One style of surgical clamp which has gained some marketplace acceptance includes a handle which moves a cam or wedge to effect the clamping force for the clamp. Examples include the surgical clamps disclosed in U.S. Pat. Nos. 5,727,899, 5,792,046, 5,888,197, 5,899,627, 6,017,008, 6,042,541 and 6,264,396. The handle provides a torque through a pivoting action, which generally provides a great mechanical advantage to the clamp. For instance, a handle throw of several inches may result in a cam movement of several hundredths of an inch, i.e., a mechanical advantage on the order of 10 2  or more. Though the handle throw force may be only 10 to 50 pounds, the forces and torques sustained by the handle and cam may be considerable, providing the most likely location for clamp failure. In that surgical clamps are used in critical surgery applications, inopportune clamp failure is not a permissible risk. Such handles, and their associated cams or wedges, are typically machined out of stainless steel bar stock and subsequently heat treated, such as a 17-4 stainless steel, precipitation hardened and heat treated to condition H 900.  
         [0005]     In devising a proper clamping structure, the clamp should give the surgeon flexibility in quickly assembling the retraction system and in placement of the various retractors. (The term “surgeon” is used herein including the person operating the clamp, who may or may not be the person performing the actual surgery.) Once the various retractors are in place and oriented and pulled as desired, the retraction system clamps should allow quick and easy tightening so the entire retraction system is maintained fixedly in place. Once tightened the retraction system should be unobtrusive so neither the tissue held retracted nor the retraction system interfere in any way with the surgeon or the surgical procedure. After surgery is completed (or perhaps once or more during surgery), the retraction system should quickly loosen and/or disassemble so as relax the retracted tissue and minimize damage to the retracted tissue. Surgical retractor systems must be robust and strong, as even a slight possibility of failure during use is not tolerated. Surgical retractor assemblies should be readily reusable, including sterilizable, for use in multiple surgeries. Surgical retractor systems should maintain a relatively low cost. Improvements in surgical retractor clamps and systems can be made in keeping with these goals.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     The present invention is a surgical clamp and clamping system using a handle, which, in one aspect, is unitarily formed with the wedge or cam member. The handle/cam is not machined from bar stock or from a casting, but rather is metal injection molded. The metal injection molding process includes a significant shrinkage during manufacture. In one aspect, the handle utilizes the benefits of the metal injection molding process in providing a shaped handle with a double offset, while avoiding non-uniform shrinkage by providing a design with largely uniform thicknesses and volumes. In another aspect, dimensional tolerances on the cam member are increased by having a separate, post-initial assembly manufacturing adjustment for the distance through which the camming action is applied on the other parts of the clamp design. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a perspective view of a preferred surgical clamp in accordance with the present invention.  
         [0008]      FIG. 2  is an exploded perspective view of the clamp of  FIG. 3 .  
         [0009]      FIG. 3  is an elevational side view of the clamp of  FIGS. 1 and 2 , showing the loosened position of the handle in dotted lines.  
         [0010]      FIG. 4  is a plan view of the clamp of  FIGS. 1-3 , showing the range of adjustment of the shaft and handle relative to the support frame.  
         [0011]      FIGS. 5 and 6  are end views of the clamp of  FIGS. 1-4 .  
         [0012]      FIG. 7  is an opposing elevational side view of the clamp of  FIGS. 1-6  in the loosened position.  
         [0013]      FIG. 8  is a side view of the clamp of  FIG. 7  in the tightened position.  
         [0014]      FIG. 9  is a finite element analysis rendering of the handle/cam of  FIGS. 1-8 .  
         [0015]      FIG. 10  is a finite element analysis rendering of the cam of  FIGS. 1-8 . 
     
    
       [0016]     While the above-identified drawing figures set forth one or more preferred embodiments, other embodiments of the present invention are also contemplated, some of which are noted in the discussion. In all cases, this disclosure presents the illustrated embodiments of the present invention by way of representation and not limitation. Numerous other minor modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.  
       DETAILED DESCRIPTION  
       [0017]     The method and apparatus of the present invention will be described with reference to a clamp member  22  as further disclosed in Application No. M1.12-4, incorporated by reference. The clamp  22  primarily includes a tightening handle  24 , a first clamp member  26  (in the lower position as shown in  FIGS. 1-8 , it being recognized that orientation of the clamp  22  may depend upon use) and a second clamp member  28  (in the upper position as shown in  FIGS. 1-8 ). For ease of description, the first or lower clamp member  26  will be called a “frame” clamp and the second or upper clamp member  28  will be called a “shaft” clamp, recognizing that the first clamp  26  may attach to a rod other than the support frame  18  and the second clamp  28  may attach to a rod other than a retractor shaft  16 .  
         [0018]     The frame clamp  26  may be a fulcrum clamp as generally disclosed in U.S. Pat. No. 5,727,899 and in application Ser. Nos. 10/664,195 filed Sep. 17, 2003 and 11/330,625 filed Jan. 12, 2006, all incorporated by reference. The preferred fulcrum clamp  26  thus includes a fulcrum portion  30  extending between an upper leg portion  32  and a lower leg portion  34 . The fulcrum portion  30  allows the size of the frame clamp opening  36  to change based upon biasing the upper leg portion  32  away from the lower leg portion  34 . A wedge or cam  38  (shown in  FIG. 2 ) positioned between the upper and lower leg portions  32 ,  34  is movable to force the upper and lower leg portions  32 ,  34  apart and causes the fulcrum portion  30  to flex. As the fulcrum portion  30  flexes, the frame clamp opening  36  constricts. When the frame clamp opening  36  constricts, the clamp  22  can frictionally attach onto the support frame  18 . The frame clamp opening  36  extends longitudinally on the frame  18  for a sufficient distance to define a rod axis  40  (shown in  FIGS. 1 and 3 ) and orientation of the frame  18  ( FIG. 4 ) in the frame clamp opening  36 . In the preferred embodiment, the frame clamp  26  is about ¾ inch wide. The frame clamp opening  36  is sized to mate with the cross-sectional size and shape of the support frame  18 , such as a ½″ diameter cylindrical shape. In the loosened position, the frame clamp  26  permits substantially unimpeded longitudinal movement of the clamp  22  on any linear portion of the support frame  18 , as well as substantially free rotation of the clamp  22  about the support frame axis  40 .  
         [0019]     The clamping force is provided by a wedge or cam member  38  placing equal and opposite forces on the upper and lower leg portions  32 ,  34 . Once the frame clamp  26  is closed to a tightened position, it does not require further application of force or holding by the surgical staff to remain in the tightened position. The preferred frame clamp cam  38  includes two outer lobes  39  for pushing downward and a central lobe  41  for pushing upward so it can provide a balanced force and for ease of manufacture and assembly. In the preferred embodiment, both the central lobe  41  and the outer lobes  39  are circular with diameters of about ¼ of an inch, and with the axis of the central lobe  41  offset from the axis of the outer lobes  39  by about ⅛ of an inch.  
         [0020]     As best shown in  FIGS. 1, 2 ,  5  and  6 , the shaft clamp  28  primarily includes a stanchion head  42  having a top stanchion  44  extending rigidly from a side stanchion  46 . The inside surfaces of the top stanchion  44  and side stanchion  46  are sized and shaped to mate with the retractor shaft  16 . The shaft clamp opening  48  extends longitudinally on the shaft  16  for a sufficient distance to define a rod axis  50  and orientation of the shaft  16  in the shaft clamp opening  48 . The shaft clamp opening  48  also defines the placement of the bottom and top surfaces  86 ,  88  of the shaft  16 . In the preferred embodiment, the shaft clamp  28  is about inch wide. The shaft clamp opening  48  is sized to mate with the cross-sectional size and shape of the shaft  16 , such as a ⅜″ diameter cylindrical shape. In the loosened position, the shaft clamp  28  permits substantially unimpeded longitudinal movement of the shaft  16  in the shaft clamp opening  48 , as well as substantially free rotation of the shaft  16  about its axis  50  in the shaft clamp opening  48 .  
         [0021]     The shaft clamp  28  is preferably activated by the same handle  24  as the frame clamp  26 . To achieve the simultaneous tightening with a single handle  24 , pivoting movement of the handle  24  not only causes the wedge  38  to increase separation between the upper and lower legs  32 ,  34 , but also moves a pin  52  vertically upward to press the retractor shaft  16  against the top stanchion  44 . The pin  52  translates or slides in a pin bore  54  in the bottom of the shaft clamp  28 . The pin bore  54  intersects the shaft clamp opening  48 , so the pin  52  can be biased against the outer profile of the shaft  16  by sliding the pin  52  in the pin bore  54 .  
         [0022]     The handle  24  is oriented to the side with a horizontal offset  53  providing a minimum clearance  55  (best shown in  FIG. 6 ) relative to the retractor shaft  16  to further facilitate access during surgery to quickly and easily snap the shaft  16  into the clamping opening  48 . The handle  24  includes a grasping portion  57  and an arm portion  59  extending from the cam  38 . The grasping portion  59  is centered relative to the shaft axis  50 , so biasing the handle  24  tighter or looser by the surgeon will result in no net rotational moment of the clamp  22  about the shaft axis  50 . In the preferred embodiment as shown in  FIGS. 1 and 4 , the grasping portion  57  defines a plane with a grasping centerline  61  vertically in line with the shaft axis  50 . The planar nature of the grasping portion  57  helps induce the surgeon to apply the tightening force centered within and normal to the grip plane, which is thereby also normal to the handle pivot axis  43  and centered relative to the cam  38 , such that a naturally oriented tightening force on the handle  24  provides substantially 100% tightening moment, while minimizing non-beneficial stress on the handle  24  and non-beneficial stress on the connection between the frame clamp  26  and the frame  18 .  
         [0023]     The shaft clamp  28  is preferably pivotable relative to the frame clamp  26  about the vertical axis  58 . To achieve the pivoting feature, the shaft clamp  28  is attached to the frame clamp  26  through a rotatable attachment. After the clamp  22  is positioned on the support frame  18  and the shaft  16  is positioned in the shaft clamp  28  but before the handle  24  is moved from the loosened position to the tightened position, the shaft  16  is pivotable about the pivot axis  58 . As shown in  FIG. 3 , an offset  63  between the frame axis  40  and the pivot axis  58  for the shaft  16  is as small as possible, e.g., axis  40  and axis  58  would intersect in the ideal design. In the preferred embodiment, the vertical pivot axis  58  for the shaft  40  intersects the horizontal pivot axis  43  for the handle  24  and cam  38 , and thus has an offset  63  from the frame opening axis  40  of only about ⅞ th  of an inch.  
         [0024]     As best shown in  FIG. 4 , the pivot axis  58  for the shaft  16  is preferably centered to bisect the frame clamp  28 . As best shown in  FIG. 6 , an offset  65  between the pivot axis  58  for the shaft  16  and the shaft longitudinal axis  50  is as small as possible. In the preferred embodiment, the offset  65  between the shaft pivot axis  58  and the shaft longitudinal axis  50  is only about 1/20 th  of an inch. Having an offset  65  between the shaft pivot axis  58  and the shaft longitudinal axis  50  of less than ½ inch or so provides a more balanced feel to the surgeon during pivoting of the retractor shaft  16 , because the retractor shaft  16  seems to pivot rather than swing in an arc about the shaft pivot axis  58 . While the offset  65  could be eliminated by either making a larger stanchion head  42 , by selecting a stronger material for the stanchion head  42  and making the side stanchion  46  smaller, or by positioning the stanchion head  42  (and particularly the side stanchion  46 ) further from the pivot axis  58 , the preferred design is very compact and tight, and the 1/20 th  of an inch size of the offset  65  is negligible to the perception of most users.  
         [0025]     In most surgical procedures and as depicted in the figures (particularly  FIG. 4 ), pivoting of the shaft  16  will take the shaft  16  through a shaft travel path which, in the preferred embodiment, is a substantially horizontal plane. The handle movement direction (i.e., the surface defined by movement of the grasping axis  61  during tightening/loosening pivoting of the handle  24 ) is preferably at a substantial angle to the shaft travel path, such as perpendicular to the horizontal shaft travel plane.  
         [0026]     As best shown in  FIG. 2 , the preferred rotatable attachment has a frustroconical bottom flange  60  formed integrally with the side stanchion  46 . The frustroconical bottom flange  60  mates with a frustroconical recess  62  in a bore  64  within the upper leg portion  32  of the frame clamp  26 . The frustroconical nature of this mating relationship permits pivoting of the shaft clamp  28  relative to the frame clamp  26  so long as the handle  24  is in the loosened position, but frictionally prevents pivoting of the shaft clamp  28  relative to the frame clamp  26  once pressure is applied by the handle  24  in the tightened position.  
         [0027]     The handle  24  is keyed to the shaft clamp  28  so the handle  24  moves with the shaft clamp  28  and controls the pivoting location of the shaft clamp  28  about the vertical axis  58 . The preferred keying structure is through the tightening pin  52 , best shown in  FIG. 2 . A proximal end of the tightening pin  52  includes a non-circular yoke  66 , and the central lobe  41  of the cam  38  resides within the yoke  66 . A non-circular opening (not shown) in the bottom of the stanchion head  42  mates with and receives the non-circular yoke  66 . The preferred non-circular yoke  66  has flats  70  to drive this rotational coupling. When the handle  24  is pivoted about the vertical axis  58 , the cam  38  pivots as part of the handle  24 , causing both the non-circular yoke  66  and the keyed stanchion head  42  to also pivot. After the clamp  22  is on the support frame  18  and while the handle  24  is still in the loosened position, the surgeon can easily select and adjust the orientation of the shaft clamp  28  in two ways: either by grasping the handle  24  and pivoting the handle  24  about the pivot axis  58 , or by placing the retractor shaft  16  in the shaft clamp opening  48  and lightly pivoting the retractor shaft  16  about the pivot axis  58 . Either way, the handle  24  always stays oriented in a vertical plane in line with the retractor shaft  16 . If desired, the handle plane (defined by the movement of the grasping axis  61  during tightening/loosening pivoting of the handle  24 ) could alternatively be offset somewhat from the retractor shaft axis  50 , preferably remaining at least parallel to the retractor shaft axis  50  if not aligned with the retractor shaft axis  50 .  
         [0028]     The preferred clamp  22  permits pivoting of the shaft  16  relative to the support frame  18  through angles θ1 and θ2 (best shown in  FIG. 4 ) before the handle  24  interferes with the frame clamp  26  on either side. These large pivoting angles θ1 and θ2 permit great flexibility for the surgeon to determine the best angle for placement of the shaft  16 . In the preferred embodiment, the counter-clockwise (from above) pivoting angle θ1 is about 45°, which will accommodate the desired angle of securement for the shaft  16  in the vast majority of applications. This high pivoting angle θ1 is achieved by the horizontal offset  53  together with the shape of the arm portion  59  of the handle  24 , which avoids contact between the handle  24  and either the shaft  16  or the frame clamp  26  throughout the complete throw of the handle  24  between the loosened position and the tightened position.  
         [0029]     The clockwise pivoting angle θ2 is even greater, and in the preferred embodiment extends about 90° before the proximal end of the handle  24  (the end of the handle  24  beyond the cam  38 ) interferes with the frame clamp  26 . If desired, the length of the proximal end of the handle  24  could be made shorter or the offset  63  increased slightly to permit an even greater clockwise pivoting angle θ2. With the full pivoting angle θ1+θ2 being greater than 180°, any desired angle of securement is possible. For instance, if the surgeon desires to secure the shaft  16  at a 60° counterclockwise angle to the frame  18 , the handle  24  could be rotated 120° clockwise and the shaft could be snapped into the shaft clamp  28  in a “backwards” orientation, with the handle  24  tightening toward the surgical arena.  
         [0030]     To provide the desired base position for the outer cam lobes  39 , the bearing surface between the cam lobes  39  and the lower leg  34  of the frame clamp  26  is provided by a variable height assembly with an adjustable base height, which includes a C-bearing  68 , a plunger base  74 , a spring  84  and an adjustment plug  82 . The plunger base  74  and C-bearing  68  ride on the spring  84 , which maintains a loosened compressive force (typically only a few pounds) biasing the assembly upwards. Transverse insertion of a properly-sized retractor shaft  16  into the shaft clamp  28  moves the pin  52  slightly downward, which in turn moves the C-bearing  68  and plunger base  74  slightly downward, against this spring force. During tightening of the clamp  22 , first the cam action absorbs the spring deflection until the spring  84  bottoms out. After the spring  84  bottoms out, the remainder of the cam action causes a force loop which: a) forces the pin  52  upward to clamp the shaft  16  against the top stanchion  44 , transferring the cam force through the shaft  16  to the stanchion  42 , which in turn b) forces the bottom flange  60  upward to clamp the shaft clamp  28  against rotation against the recess  62  of the upper leg portion  32 , transferring the cam force to the upper leg portion  32 , which in turn c) forces the frame clamp  26  closed by bending at the fulcrum portion  30 , to clamp the frame  18  against the lower leg portion  34 . The C-bearing  68  follows the outer cam lobes  39 , in an arc relative to the yoke  66  and frame clamp  26 , during the entire throw of the handle  24 .  
         [0031]     During assembly of the preferred clamp  22  as best understood with reference to  FIG. 2 , the stanchion head  42  is inserted into the bore  64  of the upper leg portion  32  from below. An opening  76  in the lower leg portion  34  may be used for access to assist in machining of the upper leg portion  32  and to assist in placement of the stanchion head  42  into the bore  64  from below. An annular groove  80  on the stanchion head  42  is positioned above an upper surface of the upper leg portion  32 . Once assembled in position, the stanchion head  42  is then loosely secured to the frame clamp  26  with a snap ring  78 . The snap ring  78  is disposed within the annular groove  80  and rotatably holds the stanchion head  42  within the upper leg portion  32  of the frame clamp  26 . The pin  52  including the non-circular yoke  66  is then positioned into its keyed opening  54  in the stanchion head  42 .  
         [0032]     The plunger base  74  is positioned into the lower leg portion  34  from above the lower leg portion  34 . The handle  24  is then assembled in place from the side. The handle  24  is first positioned in the C-bearing  68 , and retained in position in the C-bearing  68  with two captivation pins  72 . Side ears  77  on the cam  38  maintain the cam  38  centered side to side in the C-bearing  68 . Once in position, the C-bearing  68  provides stops which limit the throw of the cam  38  in both loosening and tightening to the desired 95° throw angle φ. The keyed yoke  66  is placed over the central lobe  41  of the cam  38  as the handle  24  and C-bearing  68  are slid in from the side, and the upper arm  32  must be sufficiently spaced from the lower arm  34  to enable this side entry of the handle/C-bearing underneath the keyed yoke  66 . Side ears  77  may include flats  75  so side ears  77  do not interfere with the upper arm  32  in the loosened position.  
         [0033]     Assembly is completed by placing a spring  84  and screwing an adjustment plug  82  in from below to bias the plunger base  74  upward. The adjustment plug  82  is raised a sufficient distance to lift the plunger base  74  enough to prevent the handle/C-bearing from withdrawing out of the keyed yoke  66 . Spring  84  preferably has a low spring constant (such as 24 pounds per inch), so it will be fully compressed with a relatively small compression force (such as 4 pounds). The final elevation of the adjustment plug  82  is selected by screwing an appropriate amount to provide the desired loosened and tightened (with spring  84  fully compressed) bottom position spacing for the clamp  22 . The terms “elevation” and “bottom position” as used herein refer to a baseline position and direction for the cam action to generate the clamping force (in the preferred embodiment, reached upon bottoming out the spring  84 ), without regard for the orientation of the clamp  22 . For instance, the elevation of the adjustment plug  82  may be set such that a throw force on the handle  24  of 20 pounds will complete the tightening action about an appropriately sized shaft  16  and frame  18 . Once the desired elevation for the adjustment plug  82  is achieved, the adjustment plug  82  is set at this elevation by upsetting the threads of the adjustment plug  82  through by using an orbital riveting machine through the holes  85  in the bottom arm  34 .  
         [0034]     Because the final seated position of the adjustment plug  82  is not set until after all the component parts are fully manufactured and assembled, the tightening force on the handle  24  is not changed by differing dimensions of the component parts within tolerance. That is, all the clamps  22  manufactured can be set to have the same tightening force, even if, for instance, the cam  38  on one clamp  22  is a mil or two larger than the cam  38  of a different clamp  22 . The spring  84  places a vertically oriented force on the assembly and, together with proper tightening of the adjustment plug  82 , prevents any separation or rattling of parts which might otherwise occur if the dimensional tolerances on any of these parts are not strictly met.  
         [0035]     The preferred clamp  22  accordingly permits a loosened attachment to both the support frame  18  and the retractor shaft  16  which has five degrees of freedom: the clamp  22  can be slid longitudinally on the support frame  18 ; the clamp  22  can be rotated about the longitudinal axis  40  of the support frame attachment portion; the shaft  16  can be pivoted about the vertical axis  58 ; the shaft  16  can be slid longitudinally in the shaft clamp  28 ; and the shaft  16  can be rotated about the longitudinal axis  50  of the shaft attachment portion. When the handle  24  is “thrown” or pivoted from the loosened position to its tightened position, all five of these degrees of freedom are secured. During tightening, both the shaft opening and the frame opening dimensions are slightly decreased to eliminate any rotation or translation of the shaft  16  and frame  18  relative to the clamp  22 . At the same time, the frictional engagement of the mating frustroconical surfaces  60 ,  62  after tightening prevent further pivoting of the shaft clamp  28  relative to the frame clamp  26 .  
         [0036]     The linkage between the handle  24  and the frame clamp  26  and the shaft clamp  28  is fully operated between the fully loosened position and the fully tightened position by a pivoting of the handle  24  through a tightening throw range φ shown in  FIG. 3 . In contrast to prior art devices, the entire tightening range φ for the clamp  22  is targeted to conform to the size and motion appropriate for a surgeon&#39;s hand. To tighten the clamp  22 , the surgeon need only grasp the bottom biasing surface  86  (height shown in  FIG. 3 ) of the shaft  16  with the surgeon&#39;s fingers and the grip portion  57  of the handle  24  with the surgeon&#39;s thumb on the same hand, and squeeze similar to operating a scissors. This scissors squeezing motion is very intuitive, as students have been taught to use scissors since kindergarten. Thus, the top of the grasping portion  57  of the handle  24  is always aligned with and is generally facing away from the bottom biasing surface  86  of the shaft  16 . In particular, the grasping surface  57  of the handle  24  should remain within about six inches or less from the bottom biasing surface  86  of the shaft  16 . The handle  24  should move an entire distance of about five inches or less. To enable the scissors action, the tightening throw should proceed through an angle φ of 120° or less. In the tightened position, the grasping surface  84  of the handle  24  is positioned a distance d of from ½ to three inches from the bottom biasing surface  86 , which enables a strong single handed grasping force to the fully tightened position. In the preferred embodiment, the tightened squeeze distance d is about 1½ inches. The preferred handle  24  extends for a length of about 3 inches, and pivots through a tightening throw range φ of about 95°.  
         [0037]     In the fully tightened position, the grasping portion  57  of the handle  24  extends at a slight angle σ to the shaft axis  50 . This grasping angle σ, though not critical, assists in application of a greater squeeze force by the surgeon&#39;s normal grip, and also assists in providing clearance for releasing the clamp  22 . In the preferred embodiment, the tightened grasping angle σ is about 5°. The bottom side of the grasping portion  57  of the handle  24  provides a spacing  96  of about ¾ of an inch over the top  88  of the shaft  16  for loosening access to the handle  24 .  
         [0038]     At this size, amount of pivoting and location of the handle pivot axis  43 , the grasping surface  57  of the handle  24  is 4 inches away from the bottom biasing surface  86  of the shaft  16  while in the loosened position, and is about ½ inch away from the bottom biasing surface  86  of the shaft  16  when in the tightened position. The handle/shaft combination thus act in conjunction to ergonomically fit the grasp of most surgeons&#39; hands for a single handed, intuitive tightening operation. The surgeon is most commonly standing roughly in line and behind the retractor shaft  16 . Just as when cutting a wide cloth a seamstress will lean over a flatly laid cloth and cut away from his or her body, so too the surgeon tightens the clamp  22  with a natural “cutting” orientation, fingers down and thumb up, similar to a handshake position. While the clamp  22  can be readily tightened with a wide variety of single handed orientations, the most common hand orientation naturally coincides with the most common clamp orientation and strongest grip orientation relative to the person tightening the clamp  22 .  
         [0039]     As best shown in  FIGS. 4-6 , the arm portion  59  of the handle  24  in the preferred clamp  22  is offset with offset  53  relative to the shaft axis  50 , primarily to provide sufficient clearance to maximize the pivot angles θ1 and θ2 and to provide loosened and tightened clearance  55  between the shaft  16  and the handle  24 .  
         [0040]     As commonly desired, the clamp  22  is capable of being used with a vertical plane containing the shaft axis  50  being oriented perpendicular to the support frame axis  40 . For instance, with the shaft/handle of the clamp  22  as shown in the plan view of  FIG. 4 , the entire clamp  22  is generally balanced and largely symmetrical about a bisecting vertical plane.  
         [0041]     When the tightening force is applied in this most common position, the plane defined by the grasping portion  57  tends to orient the tightening force so as to provide the maximum rotational moment on the cam  38  while minimizing any twisting moment of the clamp  22  off the support frame  18 . By having a largely balanced, most-common position, the clamp  22  is less likely to twist off the support frame  18  during tightening.  
         [0042]     Whether in the tightened position or in the loosened position, the grip portion  57  of the handle  24  always resides vertically above the shaft  16 . The shaft  16  is accordingly always in place below the handle  24  for the surgeon&#39;s hand to provide equal and opposite squeeze forces on the clamp  22  and hold the clamp  22  from rotating about the support frame  18  during tightening. Orienting the grip portion  57  of the handle  24  and the shaft  16  always in alignment is particularly important when the shaft  16  is at a non-perpendicular angle to the support frame  18 , so the tightening forces can be carefully and easily controlled, via single-handed operation, without causing the frame clamp  26  to twist off the support frame  18 . To provide this desired orientation of the grip portion  57  of the handle  24 , the arm portion  59  of the handle  24  has a vertical S-curve offset  90  (shown in  FIG. 3 ) and a horizontal S-curve to provide the offset  53  (shown in  FIG. 6 ). In the preferred embodiment, the horizontal offset  53  is about 0.8 inches, and the vertical offset  90  from the handle pivot axis  43  to the top of the grip portion  57  in the tightened position is about 2 inches. This preferred handle/cam combination transmits both the tightening force for the clamp  22  and any pivoting moment about axis  58  keeping the handle  24  aligned with the shaft  16 .  
         [0043]     The “over the top and downward” throw of the handle  24  of the preferred clamp  22  assists in avoiding any interference between the handle  24  and the patient&#39;s body or garments. Even if the support frame  18  is positioned very close or in contact with a patient&#39;s body or garments, the handle  24  will be accessible from above for its complete throw without interference in any way from the support frame  18  or the patient. In the loosened position (shown in  FIG. 3  in dashed lines), the preferred handle  24  projects forward from the frame axis  40  by only a spacing  102  of about 1¼ inches, for a total throw of about 5¼ inches.  
         [0044]     In the tightened position of the preferred clamp  22  with the most common orientation of the handle/shaft (in the six o&#39;clock position shown in solid lines in  FIG. 4 ), the grasping portion  57  of the handle is disposed outward from the surgical arena to provide a very low profile clamping arrangement. This is best understood with reference to  FIG. 3 , wherein: 
        a) the distal end of the handle  24  has a tightened elevation  92  over the shaft  16  of only about 1 inch, and this highest elevation is spaced distally outward from the frame by a spacing  100  of about 4 inches;     b) the stanchion head  42  projects an elevation  94  of less than ¼ of an inch over the shaft  16 , such as a profile elevation  94  of about 0.1 inches; and     c) the bottom surface  86  of the shaft  16  is a distance  98  of only about ¾ of an inch over the support frame  18 . 
 
 With this configuration, the tightened clamp  22  virtually never interferes with the surgeon&#39;s line of sight or access to the surgical arena. 
       
 
         [0048]     In the preferred embodiment, the yoke  66  and the C-bearing  68 , which bear against the cam  38  during tightening and loosening of the clamp  22 , are formed of a strong bearing-grade metal, such as NITRONIC  60  super alloy. The handle  24  is formed by metal injection molding, as further described below. The remaining components may be formed of an appropriately strong sterilizable metal, such as surgical stainless steel.  
         [0049]     The double offset handle  24  of the present invention is difficult to cost effectively manufacture out of stainless steel bar stock using bending and machining operations. Rather than using the forming operations for prior art surgical clamp cams and handles, the present invention utilizes a handle  24  and cam  38  which are unitarily formed by metal injection molding.  
         [0050]     Powdered metal injection molding is known for other uses. The process begins by combining about 80% metal powder with about 20% binder and additives so as to form a homogeneous granular mixture. The preferred metal powder is 17-4PH stainless steel, but other materials such as 316L, alloy steel and ceramic could alternatively be used. To achieve optimum results, the metal powder has an average particle size of less than or equal to about 15 microns. The binder acts as a viscous carrier, when heated under pressure, to help transport the metal powder through the molding machine&#39;s screw feed and into the mold cavity. Binder may include a combination of acetyl, paraffin wax, polypropylene and carnauba wax. Additives may optionally be added to improve the viscosity and moldability of the mixture, as well as to reduce corrosion of the mold tool. Additives may include, for instance, stearic acid and various plasticisers.  
         [0051]     The mixture is heated in a conventional metal injection mold press and forced under pressure into a mold cavity. The resultant ejected part is a “green” part, which is considerably larger but of a similar shape to the desired final handle  24  and cam  38 . If desired, the green handle/cam may be stored for some period of time after it is removed from mold and before its processing is completed. Care should be taken at this point in handling the green handle/cam due to its extreme brittleness and lack of strength. Rough handling may result in a cracked or broken handle/cam.  
         [0052]     The green handle/cam blade is debound by placing parts in a furnace at a temperature of 115° C. with an atmosphere of a catalyst to turn the binder to a vapor. As a result of this debinding step, approximately 85% of the binder and additives are removed from the handle/cam.  
         [0053]     The residual binder and additives are removed from the blade during a pre-sintering temperature warmup. A handle/cam part molded from 17-4PH stainless steel is sintered at a temperature of approximately 1360° C. for one hour, in a hydrogen atmosphere. This causes the metal particles to strongly adhere to one another so as to give the molded part its structural integrity. At the end of sintering, the handle/cam is allowed to furnace cool.  
         [0054]     Removing the binder and additives from the green handle/cam results in a shrinkage of about 10-30%, and dimensional tolerances may be off on the final part by up to 2%. At this point additional minor forming or machining operations may be performed on the sintered part. However, the design of the preferred clamp  22 , and particularly in that the elevation of the adjustment plug  82  and the plunger base  74  are not established until after the handle/cam  24  is manufactured and assembled with the other component parts, allows for a design which is very forgiving in terms of tolerance on the critical cam action. Further, the entire handle  24  is formed with a relatively consistent thickness throughout the part. The opening and consistent near-circular cross-sections in the grip portion  57  in particular enable the handle  24  to provide a wide, flat grip portion  57  while at the same time permitting uniform shrinkage as part of removing the binder and additives from the green part.  
         [0055]     The handle/cam is then heat treated for tempering and hardening. For instance, the sintered handle/cam may be held at 480° C. in a hydrogen atmosphere for approximately one hour followed by air cooling, producing a final handle/cam having a hardness of H-900 (equivalent to a hardness of 40-44 on the Rockwell “C” scale).  
         [0056]      FIGS. 9 and 10  are finite element analysis renderings of the handle/cam of  FIGS. 1-8 .  
         [0057]     In the modeling of  FIG. 9 , the cam  38  was completely restrained, and a 60 pound force (three to four times the tightening force required after properly elevating the adjustment plug  82 ) was applied to the grip portion  57  of the handle  24 . In the modeling of  FIG. 10 , the two outside lobes  39  were completely restrained, and a bearing force of 2000 pounds was applied to the middle cam lobe  41 . Further, the preferred embodiment has been repetition tested through thousands of tightenings without deformation or damage of the handle  24  or other components of the clamp  22 . As shown through this modeling and testing, the preferred design is very robust and strong, without detrimental effects either due to the shrinkage involved with the metal injection molded handle/cam or the dimensional tolerances required of the handle/cam.  
         [0058]     Thus it can be seen that the complex shape of the handle  24  provides several distinct advantages during the surgical procedure which are not provided by prior art clamps. Further, the complex shape of the handle  24  is achieved through metal injection molding together with the cam  38  as a single, integrally molded part. The design of the clamp  22  permits the shrinkage and dimensional tolerances of metal injection molding of the handle/cam  24  through both having an adjustable elevation of the base for the cam  38  and by having a handle design of relatively consistent cross-sectional shapes and dimensions, such as including the opening in the grip portion  57  of the handle  24 .  
         [0059]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For instance, different shapes or offsets in either the handle  24  or cam  38  could be incorporated which utilize the advantages of metal injection molding or other aspects of the present invention once the present invention teaches that metal injection molding is a suitable manufacturing method for handle/cam parts of surgical clamps.