Peri-acetabular external fixation for hip disease: an anatomical study

Hip distraction using cross joint articulated external fixation has been used by a number of orthopaedic centres for the treatment of osteoarthritis, chrondrolysis, and osteonecrosis, as an alternative to hip arthroplasty or arthrodesis in the adolescent and young adults. The hip, however, is problematic with respect to external fixation, as it lies deep, surrounded by powerful muscles and in intimate contact with major neurovascular structures and intrapelvic organs. The numbers of patients treated by this technique to date remains small and the technical detail and potential complications, with respect to the application of the external fixation, unclear. In this study we used anatomical information from CT scans combined with computer modelling of the hip and pelvis to identify safe screw positions in the periacetabular region. The surgical insertion of the pins was then performed on five cadavers and anatomical dissections undertaken to confirm the structures at risk. This study indicated that whilst there are a number of anatomic constraints, it is still possible to insert three pins with good divergence into the limited bony corridor of the peri-acetabular region recognising that the more posterior of the laterally inserted pins poses a potential risk to the sciatic nerve if not inclined away from the sciatic notch.