THE EFFECTS OF CONTACT PRESSURE ELEVATIONS AND ASEPTIC NECROSIS ON THE LONG-TERM OUTCOME OF CONGENITAL HIP DISLOCATION

The relationship between excessive articular contact pressure, aseptic necrosis, and the long‐term outcome with unilateral congenital dislocation of the hip (CDH) was studied in a series of 84 patients treated by closed reduction and followed for an average of 29.2 years. Contact stress was estimated from archived radiographs taken at the time of maturity and at several follow‐up visits. At a recent review, each patient was rated both clinically for pain and function and radiographically for deformity, degeneration, and aseptic necrosis. For each of 431 films, articular contact stress (force/area) was estimated mathematically, based upon a frontal plane equilibrium (force) analysis and a landmark‐based inference of three‐dimensional head surface (area). Good correlation with final deformity (Spearman ρ = 0.78) was obtained when the hips were ranked in terms of a new cumulative overpressure index P̂, defined as a time‐pressure product involving years of pressure exposure beyond a 2 MPa pressure damage level. An unsatisfactory outcome occurred in 90.4% of the hips experiencing P̂ > 10 MPa‐years (most of which had aseptic necrosis involvement), whereas the outcome was satisfactory in 80.9% of hips with P̂ < 10 MPa‐years. Copyright © 1990 Orthopaedic Research Society