Greater trochanter displacements after Charnley's trochanterotomy, during passive hip movements: a real-time 3D cadaveric approach.

Non-unions of greater trochanter (GT) fractures or osteotomies are the source of frequent complications. Two muscles are involved in the genesis of such non-unions, the gluteus medius and the gluteus minimus. Literature says that, during hip flexion, their terminal insertions on the faces of the GT generate an anterior translation of the GT responsible for contact loosening and healing defect. The main goal of this paper was to assess this hypothesis into the 3D space and to quantify the 3D displacements (three translations and three rotations) of the GT after trochanterotomy during passive motions of the hip joint (flexion, abduction-adduction, internal and external rotation). Therefore, we used 13 fresh cadaveric hips, on which we registered the GT displacements thanks to a 3D infrared localizer. An ultra low weight dynamic reference based has been developed to track the motion of the GT without any interference. The results have shown rotatory displacements of the GT around the three axes. This produces a posterior and lateral opening of the osteotomy site associated with a posterior rotatory shear of the GT. Above 45 degrees of hip flexion these three rotations combine together to exert shear on the osteotomy site which is harmful to the osteosynthesis material and the consolidation potential and may explain implant loosening.