ADAPTER FOR ACETABULAR COMPONENT POSITIONING

Abstract

An adapter for a tripodal stereotactic reference frame for use in arthroplastic surgery mounts a third leg of the frame at an angle with respect to the other two legs to facilitate use of said frame with varying surgical exposures.

Description

BACKGROUND INFORMATION

The above application (“the '545 application”) describes a method and apparatus for determining acetabular component positioning, particularly for use in connection with hip arthroplasty. The method establishes a coordinate frame for the ipsilateral hip, and an apparatus is disclosed that rapidly and reliably establishes the desired frame. A preferred form of the apparatus is shown in FIG. 4 of the '545 application, and comprises a manual stereotactic instrument in the form of a tripod having of a pair of extensible arms extending from a common hub about which the arms can be rotated. First and second legs or cannulas, respectively, extend from an end of the respective arms remote from the hub and generally perpendicular to the plane formed by the arms, and a third leg or cannula extends from the hub, also generally perpendicular to that plane. The tips of the legs remote from the plane themselves are then positioned by the surgeon or by the instrument itself.

One of the tips is placed at the root of the ischium, a short distance (e.g., 20 millimeters or so) above the infracotyloid notch; this establishes a “basepoint” of Anchor point for proper docking of the instrument to the hip. A second tip is placed by the surgeon on the lateral side of the iliac wing, adjacent to the anterior superior iliac spine. The third tip then lands on the surface of the lateral ilium, anterior to the sciatic notch; the precise location is determined by the settings of the instrument, in particular, the extensions of the arms and the angle between them. The tips of the three legs, when so positioned, themselves form a plane and provide a reference frame with respect to which the orientation of the hip may be referenced. The procedure is fast and accurate, and has significantly improved the accuracy of acetabular component positioning. Further details are set forth in the '545 application.

The above configuration is especially useful for procedures in which a patient is oriented in the lateral position. In that position, the instrument readily accommodates to the three commonly used lateral exposures, namely, the posterior exposure, the superior capsulotomy, and the transgluteal exposure. In these exposures, the desired basepoint can readily be observed and directly reached. However, other operative exposures can present difficulties. For example, some surgeons prefer to use an anterolateral exposure for arthroplasty. In this exposure, the gluteus medium and minimus muscles and femur are retracted posteriorly instead of anteriorly, and therefore these muscles, together with skin and subcutaneous tissue, lie in the path of the basepoint cannula.

SUMMARY OF THE INVENTION

As discussed above, the configuration of FIG. 4 of the '545 application is especially useful for exposures in which the patient is oriented in the lateral position, where the desired basepoint for fixing one of the legs of the instrument can readily be observed and directly reached. (As used herein and in the claims, the term “leg” should be understood to encompass not only solid legs, but hollow legs such as cannulas as well). However, in other operative exposures used in hip arthroplasty, such as an anterolateral exposure, the positioning of skin, muscles and tissue obstruct direct access to a desired basepoint or Anchor point, which is preferably located in the region of the ischium as it joins the lower wall of the acetabulum. I have resolved this problem by enabling repositioning of the basepoint leg so that it may approach the desired basepoint at an angle to that at which it would otherwise approach it, thus avoiding the obstructions otherwise interposed by the anterolateral exposure.

Accordingly, it is an object of the invention to extend the capabilities of the method and apparatus of the '545 application to encompass a greater variety of surgical exposures

Further, it is an object of the invention to extend the capabilities of the method and apparatus of the '545 application to encompass surgical exposures in which access to the desired basepoint is at least partially blocked or restricted.

The foregoing and other and further objects and features of the present invention will be understood on reference to the following detailed description of the invention, when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a modified version of FIG. 4 of the '545 application;

FIG. 1A is a partial sectional view of conduit 107;

FIG. 2 is a view in perspective of a preferred embodiment of a basepoint adapter is as described herein;

FIG. 3 is a side view of the adapter of FIG. 2 on which a cannula has been mounted; and

FIG. 4 shows one form of leg for mounting on adapter 10.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Turning now to FIG. 1, a modified version of FIG. 4 of the '545 patent application is shown. The reference numbers of that application have been retained for ease of reference to it. Basically, the figure shows a manual stereotactic instrument in the form of a tripod having of a pair of extensible arms 102, 104 extending from a common hub 105 about which the arms can be rotated. Hollow bore conduits 107 and 109 are carried on the ends of arms 102 and 104, respectively, as well as at the hub 105 which itself includes a hollow bore conduit. Legs or cannulas 114, 116, extend downwardly from conduits 109, 105, respectively.

In the preferred embodiment of FIG. 4 of the '545 application, these legs are parallel to each other and are perpendicular to a plane formed by the arms 102, 104. In that application, a third leg or cannula 112 is fitted into, and extends downwardly from, the conduit 107, parallel to the legs or cannulas 114, 116. In accordance with the present invention, however, the leg 112 and its accompanying rod segment 106 of FIG. 4 of the '545 application is not used; accordingly, it has been removed as shown in FIG. 1 of the present application. In its place I insert an adapter, a preferred form of which is shown in FIG. 2.

The adapter 10 comprises an arm 12 having a first connector 14 at one end thereof and a second connector 16 at the other end. In the embodiment shown, the connector 14 takes the form of a cylindrical plug which is fixed to arm 12 by a screw 20 inserted through the bottom of arm 12 into the bottom of connector 14; see FIG. 3. The connector 16 has a split collar 16a having a bore 16b extending through it. A leg or cannula will be inserted into the collar 16, and will be held firmly in it on tightening a thumbscrew 18 which compresses slit 16a.

In use, the connector 14 is inserted into the bottom of conduit 109, and held there by any of a number of well-known means, such as by a set-screw of the like. In order to seat the connector at a fixed distance into the conduit 107, the conduit preferably has an inner lip 107a against which the top face of connector 14 butts when inserted into it; see FIG. 1A.

As seen more readily in FIG. 3, arm 12 has a curved, sinuous shape. As a result, an axis 22 extending along the centerline of collar 16 is oriented at an angle θ with respect to an axis 24 extending along the centerline of connector 14. For anterolateral arthroplasty procedures, I have found that an angle of from approximately 20 to 30 degrees is appropriate. Further, these axes are coplanar, and converge to a point P. This is the basepoint or Anchor point described in the '545 application. Thus, when connector 14 is mounted on conduit 107, a leg or cannula 26 mounted on connector 14 can be directed to the same point P (FIG. 3) as one that would have been directed to that point along the axis 24 had there been no intervening muscles, skin, tissue, etc. (indicated figuratively as element 28) blocking access along axis 24. Accordingly, the instrument described in the '545 application for arthroplasty procedures using a lateral exposure can readily be adapted to accommodate arthroplasty procedures using an anterolateral exposure.

FIG. 4 shows one form of leg or cannula for mounting on adapter 10. Cannula 26 has an elongated hollow body 26a extending from and through a shoulder 26b. The upper end of the cannula is threaded, 26c, and connects to a ferrule 26d having one or more compression slits 26e in it. An internally threaded cap 26f mates with the threads 26c when assembled. Cannula or leg 26 is mounted on arm 12 by sliding it upwardly (referring to FIG. 3) through the aperture 16b of collar 16 until shoulder 26g of cannula or leg 26 butts against the bottom of arm 12. Cap 26f is then inserted over ferrule 26d onto threads 26c, the cap being rotated until the ferrule is compressed sufficiently to secure the cannula or leg 16 onto the arm. Protuberances 26h provide a grip to assist in securing and releasing the cannula or leg 26.

CONCLUSION

It will be understood that the foregoing description and drawings are directed to a preferred embodiment of the adapter, and that other forms of the adapter will readily be constructed, given the description of the issues and the formulation of the solution set forth herein, it being understood that the foregoing is intended as illustrative only as to the problem and its solution, the scope of the invention being more fully defined in the claims appended hereto.

Claims

1. An adapter for an instrument having three legs which define a reference frame for arthroplastic surgery, said adapter comprising an arm having a first connector thereon for connection to said instrument in place of one of said legs and having a second connector thereon, spaced from said first connector, for mounting a leg at a defined angle with respect to the two other legs, whereby surgical approaches not appropriate for said instrument when all three legs are parallel may be used.

2. An adapter according to claim 1 in which said adapter mounts said leg at an alignment such that its axis intersects with the axis of the instrument leg that said leg replaces, to thereby reach the same basepoint as would have been reached by the replaced leg.