Compression Hip Screw

This invention relates to a compression hip screw which rigidly connects a femoral head to the remaining portion of the femur despite a fracture in the area of the femur neck.

Heretofore, a compression hip screw provided a lag screw extending through the femur and into the femoral head. An opening was drilled through the femur from an opposite side of the femoral head to receive the lag screw. With the lag screw threadably coupled to the femoral head, a plate was disposed adjacent the femur so that a barrel formed by the plate extended into the opening. The lag screw extended into a bore formed by the barrel so that a compression screw or bolt could threadably engage the lag screw and oppose the barrel to bias the femoral head in the direction of the fracture to take up any spacing at the fracture.

As shown in U.S. Pat. No. 4,432,358 issued Feb. 21, 1984 to Fixel, it is known that a locking assembly can be provided to a keyless assembly to prevent rotation of the lag screw relative to the plate and barrel. In order to accommodate the locking assembly, the barrel is modified to provide additional holes and the lag screw is modified to define a hexagonal hole to receive the locking assembly, which is longer than the lag screw.

During a normal walking cycle for the femur and compression hip screw, the superior side of the barrel is loaded in tension and the inferior side of the barrel is loaded in compression. With the substantial loads imparted to the plate and barrel it is desirable to reduce the possibility of failure. Therefore, if any part of the compression hip screw should fail, it may be necessary for the patient to undergo additional surgery. For this reason, the lag screw and barrel should be designed for optimum load transfer.

The present invention comprises a compression hip screw with a locking device or assembly that is disposed between the lag screw and the barrel on the inferior side of the barrel so that a uniform profile is retained for the superior side of the barrel. The locking device comprises a pin disposed in a groove formed by the barrel and a recess formed by the lag screw.

It is an advantage of the present invention that a compression hip screw can be modified slightly to accommodate a locking assembly without substantially reducing the load carrying capability of the compression hip screw.

In the drawings,

FIG. 1 depicts the compression hip screw in cross section as applied to a femur having a fracture at the neck thereof.

FIG. 2 is a cross sectional view taken along line 2--2 of FIG 1.

FIG. 3 is a side view of the lag screw.

FIG. 4 is an exploded view of the compression screw, barrel and lag screw.

A femur 10 is shown in FIG. 1 with a femoral head 12 and a fracture 14 located at a neck 16. The femoral head 12 forms a hip joint with an acetabular member 18.

A compression hip screw 20 includes a lag screw 22, a compression screw 24 threadably coupled to the lag screw 22, a plate 26 adapted for attachment to the femur via bone screws 25, and a locking pin 28. An opening 30 is formed in the femur to extend from a lateral side of the femur to an internal position within the femoral head. The plate 26 defines an integral barrel 32 disposed in the opening 30. The barrel is formed with a bore 34 extending therethrough. A first end 36 of the lag screw is disposed in the bore 34 when a second threaded end 38 is threaded into the femoral head for fixation therewith. The first end 36 is slotted at 40 so that a screwdriver or the like can be utilized to advance the lag screw into the femoral head. A passage 42 within the lag screw 22 is provided with a threaded internal surface at the first end so that the compression screw 24 is engageable therewith. The compression screw 24 forms a flange 44 which abuts a shoulder 46 on the barrel 32 when the compression screw 24 is fully engaged with the lag screw 22.

In accordance with the invention, the lag screw is provided with a pair of recesses 50 and 52 and the barrel 32 is provided with a groove 54. The pair of recesses 50 and 52 are disposed on opposite sides of the lag screw while the groove 54 is disposed on the inferior side 33 of the barrel. As a result the superior side 35 of the barrel 32, viewing FIGS. 1 and 2, defines a uniform cylindrical profile with a constant radial thickness R. The pin 28 fits within the groove 54 and extends into the bore 34 to also fit within one of the recesses 50 or 52. Preferably, the groove 54 is dimensioned to receive 75% of the pin's diameter and the pair of recesses is dimensioned to receive 25% of the pin's diameter. In order to retain the pin 28 longitudinally in the groove 54, a pair of projections 56 and 58 are formed at the ends of the groove 54. The pair of projections form a slight interference with the pin so that the pin can be forced onto the groove but the pin will not freely withdraw from the groove. Therefore, the pin is yieldably retained in the groove. The wall of the groove 54 partially overlaps the diameter of the pin 28 to prevent radially withdrawal thereof.

The technique described hereinafter is one way to attach the compression hip screw 20 to the femur 10. Other techniques are feasible in view of orthopaedic surgeon preferences and the characteristics of the femur fracture. The opening 30 is provided by a suitable tool, such as a reamer. The lag screw 22 is secured to the femoral head 12 via the opening 30 by rotating the lag screw 22 for advancement in the opening 30 to a predetermined location. For a "keyed" insertion, the pin 28 is disposed in the groove 54 and the barrel 32 is aligned with the lag screw 22 for insertion of the latter in bore 34. If the recesses 50 or 52 are not aligned with pin 28, the barrel 32 and plate 26 are rotated until the pin 28 is free to advance into either recess. With the barrel fully disposed in the opening 30, the plate 26 and barrel 32 are rotated to further secure the lag screw 22 into the femoral head 12. When the plate is adjacent the femur, the bone screws 25 are fastened to the femur to fixedly attach the plate thereto. Thereafter the compression screw 24 is threadably coupled to the lag screw 22 so that the femoral head 12 is biased in compression toward the barrel 32 to eliminate or reduce any spacing at the fracture 14. Alternatively, the compression screw 24 can be secured before the bone screw 25 is fastened to the femur. For a "keyless" insertion, the barrel 32 is advanced into the opening 30 over the lag screw without the pin 28 in the groove 54. With the barrel 32 in the opening 30, the plate 26 and barrel 32 are rotated until the groove 54 is aligned with either recess 50 or 52. The pin 28 is then inserted into the groove 54 and one of the recesses to prevent rotation between the barrel 32 and the lag screw 22. Thereafter, the barrel 32 and plate 26 are rotated to further secure the lag screw 22 to the femoral head 12 and align the plate 26 with the femur 10.

Although the foregoing description proposes use of the pin 28, it is possible to utilize the lag screw 22, the compression screw 24, the plate 26, and the barrel 32 in the absence of the pin 28, should the orthopaedic surgeon prefer a "keyless" compression hip screw. If the orthopaedic surgeon elects to omit the pin 28, the structure for the barrel 32 and lag screw 22 retains the uniform cylindrical profile of constant radial thickness for the barrel 32 so that the tension loads imparted to the barrel are evenly distributed. Moreover, the lag screw 22 provides a robust structure with only minor material removed for the recesses 50 and 52, whether the pin 28 is used or omitted.