Background: The extended trochanteric osteotomy was introduced as a
safe and effective exposure technique for revision hip surgery; however,
intraoperative iatrogenic femoral fractures have been reported. This study
examined the effects of the extended trochanteric osteotomy on the torsional
strength of the femur with use of cadaver bones. We hypothesized that repair
of the osteotomy fragment would restore the torsional strength to that of an
intact femur and that an osteotomized femur containing a well-fixed stem would
have the same torsional strength as an intact femur with a stem.
Methods: Fifty-eight cadaveric human femora were divided into five
groups, according to the repair technique, to examine the effects of the
extended trochanteric osteotomy: intact, osteotomy, repaired osteotomy,
implant, and implant-repaired osteotomy. Osteotomy fragments were reattached
with use of three double-looped 18-gauge wires. A femoral stem was cemented
into the last two groups. Specimens were tested mechanically in rotation until
failure. Rotational properties were compared with one-way analysis of variance
followed by post hoc pairwise comparisons. Linear regression analysis was
performed for bone mineral density and torsional strength.
Results: Torque to failure was reduced by 73% for the specimens in
the osteotomy group compared with the intact group (p < 0.0001). Repair of
the osteotomy did not improve torque to failure (p > 0.99). Femora in the
implant-repaired osteotomy group displayed significantly improved
torque-to-failure values compared with the specimens in the osteotomy and
repaired osteotomy groups (p < 0.0001). However, the strength of the femora
in the implant-repaired osteotomy group remained significantly less than that
of the specimens in the implant group (p < 0.007). A significant linear
relationship was observed between bone mineral density and torque to failure
for femora in the intact (p < 0.006), osteotomy (p < 0.002), and
repaired osteotomy (p < 0.001) groups.
Conclusions: The extended trochanteric osteotomy reduces torsional
strength by 73% even when the osteotomy fragment is repaired. Bone mineral
density directly affects absolute femoral strength in this model.
Clinical Relevance: In this in vitro cadaver study, the extended
trochanteric osteotomy resulted in a significant reduction of torsional
strength and energy required for fracture. Femoral stem insertion with
osteotomy repair significantly improved torsional strength; however, this
construct remained significantly weaker than that of a femur that had an
implant without an osteotomy. This finding suggests that postoperative
rehabilitation protocols should be even more restrictive with regard to
weight-bearing and the use of abduction braces after revisions with use of an
extended trochanteric osteotomy than after revisions that do not require an
extended trochanteric osteotomy.