PELVIC OSTEOTOMY TECHNIQUES AND COMPARATIVE EFFECTS ON BIOMECHANICS OF THE HIP

Abstract

Dysplasia of the hip in children, characterised by a shallow acetabulum and a deficient coverage of the femoral head, generally causes altered biomechanics of the hip joint. A kinematic analysis on the individual and comparative spatial movement of the acetabulum with some of the pelvic osteotomy techniques is performed. The osteotomy providing greater correction in most of the parameters potentially leading to greater reduction in loading is the choice of the surgeon.

Adult saw bone hip models have been used. Points of reference have been carefully chosen and data has been obtained using the Polhemus Electromagnetic measuring system before and after the osteotomy. Five techniques (Chiari, Salter, Steel, Tonnis and Ganz) have been performed, parameters like the Centre-edge angle, Sharp’s angle, Acetabular Head index (Femoral head cover), translation and rotation in 3 planes have been analysed.

Results show an improvement in most of the parameters when the above pelvic osteotomies are performed. Centre-Edge angle improved by a mean (in degrees) of 7.4 (Chiari), 9.6(Salter), 16.9(steel), 28.4(Tonnis) and 31.0(Ganz). There has been marked increase in Femoral head cover with mean 24% with Tonnis and Ganz. Significant changes in rotational parameters in all 3 planes were achieved, particularly with Ganz and Tonnis techniques.

Traditionally acetabular dysplasia correction has been assessed in one or two dimensions by plain radiographs and true three dimensional movement of the acetabulum is difficult to assess with simple techniques. This study describes a simple and reproducible method to compare the various pelvic osteotomies and comparative effects these can produce on the kinematics of the hip joint. It is intended to extend this study to include kinetics to compare the forces and stress distribution changes caused by performing the above techniques and a larger study is recommended, based on this technique and the initial trend of results shown.