Purpose

The purpose of the study was to determine the rate of conversion from RSA to THR in a number of Canadian centers performing resurfacings

Purpose: Recently, there has been concern raised on the occurrence of pseudotumors after metal on metal hip resurfacing. A pseudotumor is defined as a local soft tissue mass associated with localized bony and/or tissue (muscle) destruction. The primary purpose of this study is to determine the incidence of this complication in several high volume Canadian academic centres.

Method: Nine of the 11 Canadian academic centres who perform metal on metal hip resurfacings were surveyed. The number of metal on metal hip resurfacing arthroplasties performed at each centre was first determined, as were the number of those who have presented with a pseudotumour, and subsequently gone on to revision surgery. The basic demographics of the group were recorded, as were the radiographic and implant design variables for those cases presenting with a pseudotumour.

Results: A sample of 3,400 hip resurfacing arthroplasties performed between 2002 and December 2008 were surveyed. Demographics were tabulated for a sub-sample of these patients. 76% were male, the mean length of follow-up was 3.02 years, mean BMI was 28.65, and mean age was 52.10 years. Three of 3,400 cases presented with a pseudotumour, an incidence of .09%.

Conclusion: Although pseudotumors remain a concern after metal on metal hip resurfacing, the incidence at short to mid term follow-up is very low in this multi-centre academic survey. This information is significantly lower than what other groups have recently reported. Continued close monitoring is required in order to determine what clinical factors are at play.

Purpose: Femoroacetabular impingement (FAI) results from abnormal abutment between the proximal femur and acetabulum (Ganz et al., 2003). FAI occurs in three forms; cam, pincer and mixed (cam and pincer combined). The cam type has been quantified radiographically (Beall et al., 2005), but pincer FAI is poorly defined. Radiographic measures, including the center-edge angle (Wiberg, 1953), and Sharp’s angle (Sharp, 1961) have been used to define hip dysplasia, but these measures have not been used to define FAI. The purpose was to test these measurements to compare pincer patients with controls.

Method: This study is a retrospective, observational analysis of anterior-posterior pelvic radiographs for control (N=76 hips; 40 patients) and pincer (N=20 hips; 19 patients) groups. Control radiographs were obtained from injury-free pelvic x-rays from the emergency department. Lateral center-edge (CE) angle Sharp’s angle and a proposed measurement of Femoral Head Containment (FHC) were measured using PACS. FHC was defined as the percentage of the 2D area of the femoral head circle covered by the acetabulum, using chord length, height and diameter of the femur head. Non-parametric statistics with post-hoc analyses were used. Pearson’s correlations were calculated for within- and between-observer reproducibility.

Results: Mean (± SD) CE angle was significantly larger in the FAI group [37.4° (±5.2)] compared to controls [31.0° (±3.9)]. Mean Sharp’s angle was significantly less in the FAI group [37.6° (±3.9)] compared to the controls [41.2° (±3.5)]. Mean FHC was significantly larger in the FAI group [26.4% (±5.3)] compared to control group [21.5% (±5.3)]. Intra-observer r-values ranged from 0.86–0.97 and inter-observer correlations ranged from 0.93–0.96. There was significantly greater acetabular overcoverage in the pincer group based on these three measures, suggesting these may be used diagnostically.

Conclusion: Pincer FAI is a debilitating condition that has not been quantified. This study found that CE angle, Sharp’s angle and FHC measures may be useful in diagnosing pincer FAI. A new method of quantifying FHC was proposed, evaluated and appears to be a promising new measure for evaluating pincer FAI. The CE and Sharp’s angles are simple, reproducible measures that can easily be used in a clinic setting to assist with diagnosing pincer FAI.