Automatically adjusting patella cutting guide

A patella clamping device has a handle having a first arm and a second arm, the arms each having a first gripping end and a second clamping end. The clamping ends are movable towards the opposite arm by action on the gripping end of each arm. The clamping ends of the first and second arms comprise opposed clamping surfaces. The clamping end of each arm has a body portion having spaced first and second surface defining the opposed surface of each arm. A plurality of pins extend from the first to the second surface. A rotatable toothed jaw member is pivotally mounted on each of the pins. The jaw member has at least one tooth extending outwardly of the opposed surface of each arm for engaging the patella. Each body has a third surface spaced from the second surface to create a slot for receiving a saw blade.

BACKGROUND OF THE INVENTION

The invention relates to a patellar saw guide which has a plurality of rotatable teeth adapted to engage an edge of a patella prior to its preparation for receiving a prosthetic implant.

A patellar clamp and saw guide are used during a total knee arthroplasty procedure to prepare the posterior surface of a patellar bone to accept a prosthetic implant.

Typically, a surgeon will select a patellar prosthesis for implantation either by utilizing a resurfacing technique wherein the prosthetic patella will be resected and resurfaced and/or by an insetting procedure where the prosthetic patella is inserted into the prepared surface of the patella.

The patella is a sesamoid or lens shaped bone which slides in a groove between the condyles of the femur. Its function is to increase the efficiency of the quadriceps muscle by shifting the line of action of the muscle's pull forward. As the knee articulates, the muscles and tendons force the patella toward the condyles of the femur. Consequently, there is considerable relative motion between the patella and the other bones comprising the knee joint.

Because of aging or disease, the articulating surfaces of the knee may degrade. To treat certain pathologies, it has become common to surgically remove the condyles and replace these structures with prosthetic implants. By the same processes, the articulating surfaces of the patella may also degrade. In connection with the implantation of a prosthetic knee, therefore, the articulating surface of the patella may also be replaced. Because of the tendons connected to the patella, it is generally advisable to replace only the articulating surfaces. An ultra high molecular weight polyethylene articulating surface, with or without a metal baseplate or metal backing, will be implanted on the posterior side of the patella, adjacent the femoral condyles.

In either a total resurfacing procedure or a patella insetting procedure, it is important that a sufficient amount of bone stock remain after resection to accept the typical fixation pegs of the patellar prosthesis and maintain the integrity of the remaining patellar bone. Therefore, proper location of the saw blade is important.

As used herein, when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body.

Prior art devices for aiding the surgeon in performing patella resections are well known to those skilled in the art. For example, Peterson, in U.S. Pat. No. 4,673,862, teaches a method and instruments for the installation of a patella button prosthesis which involves performing a patella resection.

In particular, Peterson relates to a saw guide which comprises a pliers-like instrument having a pair of mutually pivotable jaw members. The jaw members are designed so as to enable them to surround part of the outer periphery of the patella with each jaw member having a respective handle, integrally formed therewith, which handles may be pivoted so as to pivot the jaw members to and from engagement with part of the patella periphery. The Peterson device requires that a flat saw blade be guided over the face of the jaw members after the patella has been set to the correct depth between the members.

U.S. Pat. No. 5,147,365 relates to a patella osteotomy guide in which the jaw members include a slot for guiding the flat saw blade and an arm for setting the saw blade depth in the patella.

U.S. Pat. No. 5,486,177 relates to a patella milling instrument having a clamp which contacts the underside of the patella. A similar clamping tool is shown in U.S. Pat. No. 5,284,482.

U.S. Pat. No. 5,222,955 relates to a reaming system designed to cut a conical bore in a patella surface while the patella is being held in a patella clamp similar to that disclosed in U.S. Pat. No. 5,284,482. U.S. Pat. No. 5,941,884 relates to a patella clamp which includes indicia of both the amount of bone resected and the amount of bone remaining.

BRIEF SUMMARY OF THE INVENTION

It is one aspect of the invention to provide an improved apparatus and method for facilitating the preparation of the natural patella to receive a patellar prosthesis.

It is an additional aspect of the invention to provide a clamping system which can hold the patella in position during resection by actuating a pliers like grip.

The cutting guide of the present invention has the ability to clamp variously shaped patellae by automatically adjusting the direction of the clamping teeth to the anatomy of the patella. The intention of this design is to automatically adjust to the edge surface of variously shaped patellae to provide a more secure hold.

The invention works by clamping the patella jaws over the patella bone with multiple teeth embedded in the patella. The patella jaws secure the patella sufficiently to allow a surgeon to use an oscillating surgical saw to resect the patella bone in a well known manner.

The clamping tooth or teeth are located on a plurality of rotatable elements that rotate about a pin such that the teeth will align with the patella edge surface resulting in more holding teeth penetrating the patella bone. The clamp may also have a slot to guide an oscillating surgical saw to cut the clamped patella.

The rotation of the toothed rotatable element is limited by stops placed in a top and/or bottom portion forming the automatically adjusting patella cutting guide. These stops in combination with the stop features cut into each toothed rotatable element limit the amount of rotation of each toothed rotatable element. This limit prevents the 360° rotation of the toothed element about the pin which would allow the teeth to rotate out of contact with the patella bone.

The patella clamping device of the invention has a handle portion having a first arm and a second arm which arms may be coupled by a pivot pin or a linkage system which preferably moves the arms in parallel. The first and second arms each have a first gripping end and a second clamping end. The clamping end of each arm is movable, such as by the pivoting or linkage action, towards the opposite arm by movement of the gripping end of each arm towards one another. The clamping end of the first arm has a clamping surface opposed to a clamping surface on the clamping end of the second arm. The clamping end of each arm includes a body portion having spaced first and second surfaces and a plurality of pins extending from the first surface to the second surface on each arm clamping end. One toothed rotatable jaw member is pivotally mounted on each of the plurality of pins. The rotatable jaw members each have at least one tooth extending outwardly of the opposed surface of each arm towards the opposite arm clamping surface. The opposed clamping surface on the clamping arm defined by the body portion may be arcuate with a concave surface facing towards the patella gripping area. Each body portion preferably has three pins and toothed rotatable jaw members. Each jaw preferably has three teeth but fewer or more teeth can be used. To improve gripping at least two teeth on each jaw may have a different size or shape. Each body portion may include a stop element adjacent each toothed jaw member to limit the rotation of each toothed rotatable jaw member around the pin. The stop member may be a raised portion on at least one of the first and second surfaces adjacent a recessed side surface of the toothed jaw member. The first and second clamping arm bodies have a surface for guiding a saw blade.

DETAILED DESCRIPTION

Referring toFIG. 1, there is shown a patella clamping device generally denoted as10which includes a handle portion including two gripping members12and14. Gripping members12and14engage a pivot section16which is capable of moving a first jaw arm18towards a second jaw arm20. Pivot section16may include one or more pivot pins and/or a linkage system for transferring the action or gripping member12,14to jaw arms18,20. The linkage system may move jaw arms18,20in parallel. The jaw arms18and20may be removably coupled to clamping section16. The handle portion and pivot section of the patella clamping device10are known in the prior art and are shown, for example, in U.S. Patent Application Publication No. 2007/0118141, the disclosure of which is incorporated herein by reference.

Referring toFIG. 2, there is shown a top view of the two clamping jaw arms18and20surrounded and clamping a patella24. Arms18and20are arcuate and have concave surfaces26and28respectively facing inwardly towards patella24which arms include rotatable toothed jaw elements30a,30band30cwhich will be discussed in more detail below. Arms18and20may be separate elements which can be selectively coupled or detached from pivot section16. Referring toFIG. 3, there is shown the clamping jaw arms18and20detached from the handle portion of clamping device10. At the end mounted on the handle10there are coupling elements32and34designed to couple the clamping jaw arms to the handle10in a selectively releasable manner. Preferably two spring loaded detent mechanisms (not shown) which respectively engage recessed portions33and35of elements32and34are mounted in ends17and19of pivot section16. Obviously the jaws could be fixedly attached to the handle10. However, providing a releasable coupling mechanism allows for different size clamping jaws to be used depending on the size of a patella. Preferably each clamping arm18,20includes a series of three pivotable tooth elements30a,30band30ceach having, in a preferred embodiment, three teeth.

Referring toFIGS. 4-8, there is shown bottom portion40(FIGS. 4-7) and top portion42(FIGS. 7 and 8) respectively which, when assembled, form clamping jaw arms18and20. Only one claiming jaw18is described. Clamping jaw is identical in design but concave in the opposite direction. Thus clamping jaw arms18and20are mirror images. Referring toFIG. 4, there is shown a top view of bottom portion40of clamping jaw arms18and20including coupling element32. Bottom portion40includes three raised areas or bosses44,46and48which have a generally triangular shape with the apex directed towards the concave surface26of the arm18. Each boss44,46and48has a bore50,52and54respectively which may be located on a centerline of the raised areas adjacent the apex which bores are adjacent concave surface26. The bosses44,46and48can be seen inFIG. 5which is an elevation view of jaw arm18ofFIG. 4. Also visible inFIG. 5is a cutting blade slot56below an upwardly facing surface41of bottom portion40. Slot56may receive an oscillating saw blade (not shown) adapted to resect the patella in a well known manner.

As best seen inFIG. 5bosses44,46and48are separated by gaps60and62which gaps widen on moving from the outer surface31of jaw arm18to the inwardly facing surface26of bottom portion40of arm18. Referring toFIG. 6there is a bottom view of jaw arm18bottom portion40showing bores50,52and54as well as a recessed edge66which defines an upper surface55of slot56.

Referring toFIGS. 7 and 8there is shown top portion42of clamping jaw arm18. Top portion42includes a downwardly facing surface68which includes three bosses70, and74which again are generally triangular in shape and match the shape of bosses44,46and58. The apexes of bosses70,72and74are adjacent concave surface26and wider portions adjacent outer surface31. Three pin holes76,78and80are located adjacent the apex on each boss. Top portion42includes three small holes82designed to receive holding pins which connect the bottom and top portions (40,42) of arms18and20such as by spot welding or deformation. Top portion42does not include a coupling element32and generally acts to mount and capture rotatable toothed jaw elements30a,30band30c.

Each of the generally triangular shaped bosses44, and48and70,72and74can be aligned prior to the assembly of the top and bottom portions to form clamping jaw arm18. Thus, each aligned pair of bosses have identical angled sides90and92so that upon assembly a smooth side surface of the aligned bosses result. When bosses44,46and are aligned respectively with bosses70,72and74holes50,52and54are also aligned with holes76,78and80so that they may receive a pivot pin112. Side surfaces90and92of each of the six bosses are angled at between 40 and 45 degrees and spaced to form gap60and62. These angles can change based on teeth size and boss size. For example, a larger boss would create a smaller angle. In a preferred embodiment, the alignable bosses44and70as well as alignable bosses46and72have sides90and92angled at 45 degrees while alignable bosses48and74having an angle of sides90and92of 40 degrees. In addition, the lengths of sides90and92of the bosses may vary depending on the location of alignable holes50,52,54and76,78and80which holes, when the top and bottom portions40and42are assembled, align to receive a pivot pin as will be discussed below.

FIG. 8is an elevation view of top portion42ofFIG. 7showing bosses70,72and74spaced by gaps60and62.

Referring toFIGS. 9 and 10, there is shown one of the rotatable toothed elements30a,30band30ceach including three teeth100. While three teeth100are shown, any number of teeth can be utilized.FIG. 9shows one of the toothed element30a,30band30cwhich may be identical and is designated as30including a bore102for receiving a pivot pin and a recessed generally triangular area104facing an upper surface106and, as seen inFIG. 10, a bottom recessed generally triangular area108facing a bottom surface110. Bore102may be located on a centerline of a toothed element30a,30band30c. However, as shown inFIG. 10a, an alternate toothed element130may have a bore102aoffset from a centerline103aso that greater inward rotation of teeth100ais permitted. This result can also be accomplished by leaving bore102ain the center but offsetting the pivot pin holes76,78and80in the bosses.

Toothed elements30a,30b,30cand130are adapted to be mounted between the top and bottom members40,42of clamping jaw arms18,20. The top and bottom recessed areas104and108are shaped to receive bosses44,46,48and70,72and74when the top and bottom jaw arm portions40,42are assembled. However, the generally triangularly shaped recessed areas104,104aand108of toothed elements30a,30b,30cand130are at a wider angle than the 40 to 45 degree included angle of sides90and92of each boss44,46,48,70, and74thus allowing limited rotation of the toothed elements about pivot pin112mounted through holes50,52,54and76,78,80respectively and bore102. The sides of the bosses act as stop surfaces so that toothed elements30a,30b,30cand130cannot rotate out of engagement with the patella.

Referring toFIGS. 11-13, there is shown the assembled clamping jaw arms18or20whereby bottom portion and top portions40,42are assembled capturing toothed elements30a,30band30ctherebetween. Holding pins (not shown) extending through holes82may be spot welded to each top and bottom portion40,42to capture toothed element30therebetween. Three pivot pins112are inserted through holes or bores76,78and80of top portion42, through bore102of each toothed element30a,30b,30cand into bores50,52and54of bottom portion40. Pins112may be spot welded to top member42. Pins112extend partially into bottom member40stopping prior to slot56thus leaving the slot56open to receive an oscillating saw blade (not shown).

In use, clamping jaw arms18and20are mounted on portion16of clamping device10and handles12and14are actuated to clamp the clamping jaw arms18,20around a patella. Upon contacting an edge surface of the patella, at least one of the three toothed jaw elements on each clamping arm18and20will pivot automatically into a position engaging the periphery of patella24. Thus, a plurality of teeth100from one or more of the tooth elements will contact each side of the periphery of the patella.

The teeth100of toothed elements30a,30b,30cor130may be made either identically or may vary in size either on each toothed element30a,30band30bor from one toothed element to another. Again this enhances the ability to have multiple teeth100contacting the edge of patella24. Once the patella24is gripped, a resection may be performed with an oscillating saw in a standard manner.

Referring toFIG. 14, there is shown a jaw member230similar to jaw members30a,30band30cmounted on an arm18,20in a recess232formed thereon. The recess232is similar in shape to the bosses described above. Jaw230is again rotatable on a pivot pin234with contact between sides236and238of jaw member230and sides240and242of recess232acting as a stop system for the rotation of jaw230about pivot pin234.

Referring toFIG. 15, there is shown a jaw member330mount on an arm18,20rotatable about a pivot pin334. In this embodiment there are no bosses or recesses but only two pins336and338for contact side surfaces340and342of jaw330to act as stop elements. Pins336and338would be fixed to members40and42and extend between surfaces41and68thereof.