FEMORO-ACETABULAR CUP IMPINGEMENT AFTER TOTAL HIP RESURFACING ARTHROPLASTY

Abstract

Risk of impingement after total hip resurfacing arthroplasty may be great because femoral head-neck unit is preserved and there is little flexibility to adjust limb length and femoral offset, but this potentially worrisome phenomenon has been rarely reported. Impingement between femoral neck and acetabular cup was observed in a cohort of patients who underwent contemporary total hip resurfacing arthroplasty. We then questioned whether patient demographics, component features or suboptimal position of components would be risk factors for impingement.

We reviewed a consecutive series of 51 patients (61 hips) who underwent contemporary total hip resurfacing arthroplasty. The mean age at the time of the index arthroplasty was 38 years (18 to 64). The most common diagnosis leading to the total hip resurfacing arthroplasty was osteonecrosis of the femoral head in 41 hips (67%). All the procedures were performed by single surgeon through an anterolateral approach. All the patients were assessed clinically and radiographically at a mean of 32 months (24 to 53) postoperatively.

Femoro-acetabular cup impingement, defined as the presence of bony spur at the femoral neck corresponding to abutment site of the metallic cup, was observed in seven of the 61 hips (11.5%). Of these, five patients reported limitation of activities due to groin pain. The average postoperative Harris hip score of impingement hips was inferior to those of non-impingement hips (p = 0.004). No significant difference was detected between the impingement hips and non-impingement hips with regard to of patient demographics, component features and radiographic measurements including cup inclination, cup version, femoral component version, anterior femoral offset, stem-shaft angle, femoral offset and limb length discrepancy. Our multivariate analysis revealed that only acetabular cup uncoverage ratio had a significant association with femoro-acetabular cup impingement (p = 0.04, odds ratio 1.385 [95% CI, 1.014 – 1.891]). There was no aseptic loosening of components or femoral neck fracture.

We found a high incidence of impingement between retained femoral neck and metallic acetabular cup after contemporary total hip resurfacing arthroplasty in association with an increased acetabular cup uncoverage ratio. As patients with femoro-acetabular cup impingement showed inferior clinical results, it is crucial to avoid excessive protrusion of acetabular cup beyond bony margin by proper selection of acetabular component size and appropriate positioning.