Transverse plane evaluation of the effects of surgical technique on stem positioning and geometry of reconstruction in canine total hip replacement.

OBJECTIVES

To test whether femoral ostectomy level, subtrochanteric bone mass removal, and stemsize selection significantly affect stem positioning in canine total hip replacement, and to determine ability of the femoral stem component to restore geometry of the normal femoral head and neck.

SAMPLE POPULATION

Femurs from 8 adult mixed-breed canine cadavers.

PROCEDURE

Femurs were systematically prepared, using 8 combinations of 3 surgical preparation techniques that included level of ostectomy (cervical isthmus vs lesser trochanter), subtrochanteric bone block removal, and femoral stem size (recommended, undersized). Computer-aided analysis of specimen photographs was used to evaluate femoral head offset and position and variability of femoral stem positioning for each of the preparation combinations.

RESULTS

Original femoral head offset and position were reconstructed to within a mean of 0.052 and 0.031 cm, respectively, using an undersized femoral stem after ostectomy at the level of the lesser trochanter. Implantation of an undersized femoral stem after subtrochanteric bone block removal improved ability to centralize the distal tip of the implant and reduce the angle between the femoral diaphyseal and implant axes. Ostectomy at the level of the cervical isthmus tended to force femoral implants into a varus position, and ostectomy at the level of the lesser trochanter tended to force implants into a valgus position.

CONCLUSIONS

Geometry of normal canine femurs was most closely reconstructed by implantation of an undersized femoral component after ostectomy at the level of the lesser trochanter. Implantation of an undersized femoral component after subtrochanteric bone block removal resulted in the best alignment and centralization of the stem.