Strict component positioning is necessary in hip resurfacing

Hip resurfacing arthroplasty has some advantages, including improved metal-on-metal articulation, a lower dislocation rate and preserved femoral bone. This procedure is a surgical option for younger and more active patients with osteoarthritis and osteonecrosis of the femoral head. Although there have been some reports about the efficacy of this technique, others report serious complications caused by metal debris. Additionally, femoral neck preservation adversely decreases the head-neck ratio and results in postoperative impingement. We evaluated the range of motion after hip resurfacing with various component orientations and optimal component orientations to avoid postoperative impingement using computer simulations in 10 male patients with osteonecrosis. The mean ranges of motion in flexion, extension, abduction, adduction and internal rotation at 90A degrees of flexion were 92.4A degrees A A +/- A 13.8A degrees, 25.7A degrees A A +/- A 13.8A degrees, 38.0A degrees A A +/- A 11.1A degrees, 29.1A degrees A A +/- A 10.0A degrees and 20.9A degrees A A +/- A 11.5A degrees, respectively. The oscillation angle in flexion and extension motion was 118.1A degrees A A +/- A 10.3A degrees. More than 100A degrees of flexion was acquired in 79 of 240 simulations (32.9 %), and more than 20A degrees extension was acquired in 142 simulations (59.2 %). Combined anteversion was significantly correlated with maximal flexion and extension angles. The component safe zone to fulfill the range of motion criteria varied among patients, and 4 of 10 patients had no safe zone. Postoperative impingement occurs relatively frequently in hip resurfacing because of preservation of the femoral neck and component malpositioning. The safe zone of the acetabular component to avoid postoperative impingement is very narrow. Greater care should be taken regarding patient selection, rigorous preoperative planning and accurate component positioning.