Biomechanical comparison of methods of fixation of isolated osteotomies of the posterior acetabular column.

Ten fresh frozen specimens of a hemipelvis, including the hip joint, capsule and proximal femur, from elderly cadavers were used to evaluate three methods of internal fixation of isolated posterior column osteotomies. Intact and reconstructed specimens were tested at 30 degrees and 60 degrees of hip flexion in a specially designed joint simulator. The three methods of fixation used were a single 3.5 mm reconstruction plate, two such plates, and a 4.5 mm lag screw with a single plate. Motion at the fracture site in three orthogonal directions, and the overall stiffness of the construct, were recorded simultaneously. No significant differences were noted in stiffness for the three procedures and all retained 80% of the intact stiffness. At 60 degrees of flexion, smaller interfragmentary compliances were allowed by fixation with a lag screw and a neutralisation plate (p < 0.05). At 30 degrees, the position of the load plane relative to the fracture plane allowed less interfragmentary motion, so that no significant differences were found between the 3 methods.