Effect of transtrochanteric rotational osteotomy on impingement and contact state of a femoral implant in conversion total hip arthroplasty - Retrospective simulation study.

BACKGROUND

The transtrochanteric rotational osteotomy is a common osteotomy for osteonecrosis of the femoral head, although the results of conversion total hip arthroplasty after the osteotomy are controversial. We evaluated how deformities in the proximal femur after the osteotomy affect hip impingement and the contact state of the stem in total hip arthroplasty.

METHODS

We retrospectively reviewed 35 hips (24 men) that had undergone the transtrochanteric rotational osteotomy for osteonecrosis of the femoral head (TRO-group) and compared them with 31 contralateral, unoperated hips (Primary group). The distance between the anterior and posterior greater trochanter at the cutting point of the femur, defined as the greater trochanter width and the contact area of the femoral implant surface with cortical bone were measured by CT-based three-dimensional templating software. We also calculated the hip range of motion in conversion total hip arthroplasty and analyzed the correlations between the greater trochanter width and the range of motion.

FINDINGS: The number of bony-impingement cases was significantly greater, and the range of motion in flexion, internal rotation and external rotation was significantly less in TRO-group. There was a significant negative correlation between the greater trochanter width and range of motion of internal rotation. There were no significant differences between two groups in percentages of femoral-implant contact area.

INTERPRETATIONS: The femoral implant fixation appears to be satisfactorily fixed in all zones in conversion total hip arthroplasty. However, the greater attention should be paid to minimizing bony impingement, especially on the anterior side, in conversion total hip arthroplasty.