BORS-OP3: FUNCTIONAL OUTCOME FOLLOWING HIP RESURFACING: THE IMPORTANCE OF COMPONENT SIZE AND ACETABULAR ORIENTATION

Abstract

Optimal cup orientation for metal-on-metal hip resurfacing has yet to be established. Guidance is based on hip replacement data and in vitro studies. We sought to determine the influence of component size and positioning on early clinical outcome.

This study comprises a consecutive series of 200 hip resurfacings. All had Harris Hip Scores (HHS) at one-year review. Acetabular inclination angles were measured on pre-operative radiographs, and cup inclination/anteversion angles on 3-month post-operative films using EBRA. Restoration of anatomy was defined as placement of the cup within +/−5 degrees of pre-operative inclination. The difference between pre-operative acetabular and post-operative cup inclination was termed cup-angle difference (CAD).

HHS inversely correlated with CAD (P=0.023) and anteversion (P=0.003), and directly correlated with femoral head size (P< 0.001). In patients with restoration of inclination anatomy mean HHS at one year was significantly higher at 98.7 compared with cups placed outside the normal anatomy restoration limits (93.8, P=0.003). Patients with anteversion > 20 degrees had a significantly lower HHS (P=0.010) compared with cups anteverted < 20 degrees. 96% of patients with HHS < 90 had malaligned cups (inclination over 45 degrees, anteversion over 20 degrees).

Restoring pre-operative cup inclination, anteverting the cup < 20 degrees and using large femoral heads improves early clinical outcome following MonM hip resurfacing. We recommend accurate pre-operative planning and meticulous attention to intra-operative cup positioning with these results in mind.