Patent Application
20070191686
None.
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'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.
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'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.
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 102 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.
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.
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.
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.
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
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
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.
As best shown in
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.
The handle 24 is oriented to the side with a horizontal offset 53 providing a minimum clearance 55 (best shown in
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
As best shown in
In most surgical procedures and as depicted in the figures (particularly
As best shown in
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
The preferred clamp 22 permits pivoting of the shaft 16 relative to the support frame 18 through angles θ1 and θ2 (best shown in
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.
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.
During assembly of the preferred clamp 22 as best understood with reference to
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.
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.
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.
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.
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
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'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.
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' 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.
As best shown in
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
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.
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'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
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's body or garments. Even if the support frame 18 is positioned very close or in contact with a patient'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
In the tightened position of the preferred clamp 22 with the most common orientation of the handle/shaft (in the six o'clock position shown in solid lines in
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.
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.
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'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.
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.
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.
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.
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.
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).
In the modeling of
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.
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.
