Selection of fixation devices in proximal femur rotational osteotomy: clinical complications and finite element analysis

Objective. To compare the postoperative stability between large cancellous screws fixation and dynamic hip screws fixation in transtrochanteric rotational osteotomy. Design. Finite element analysis was designed to validate the clinical outcomes of fixation failure in transtrochanteric rotational osteotomy. Background. From 1997 to 2000, transtrochanteric rotational osteotomy had been done in 20 osteonecrotic hips. Fixation with large cancellous screws as suggested by Sugioka had been used in the first five hips. Unfortunately, fixation failures were encountered in all of the five cases. The fixation mode was then shifted to a combination of plate and screws, no fixation failure had been observed postoperatively. A finite element analysis was designed to investigate the causes of fixation failure. Methods. Finite element models for four dynamic hip screw instrumented femora and four large screws instrumented femora simulating four different levels of bone cut were created. The von Mises stress distributions of each model were analyzed and compared for a loading condition simulating single-legged stance. Results. Analysis results confirmed our clinical observation that fixation with screws had higher stress concentration on the proximal femur. Improper bone cut, especially those that are too distal from the intertrochanteric line, had higher risks of fixation failure. Conclusions. Transtrochanteric rotational osteotomy is a technically demanding procedure such that surgical principles should be abided carefully to avoid catastrophic complications.