Medial Calcar Erosion Is Associated With Synovial Thickness in Patients With ASR XL Total Hip Arthroplasty.

BACKGROUND:Medial calcar erosion is considered a late finding in patients with severe adverse local tissue reactions (ALTRs) after total hip arthroplasty (THA) with dual modular neck stems. Although calcar erosion has been associated with dual modular neck stems, one would expect similar findings in standard stems owing to analogous corrosion at the taper junction. The aim of this study was to evaluate whether medial calcar erosion is also associated with ALTR in patients with standard stems in metal-on-metal (MoM) THA. METHODS:A total of 96 patients (108 hips) with MoM THA had radiographs and a magnetic resonance imaging of the hip performed at a mean time of 5.7 years after surgery. Calcar erosion was assessed from radiographs. ALTR Anderson grade, diameter, volume, and synovial thickness were assessed from magnetic resonance imaging. RESULTS:Calcar erosion was present in 54 hips (50%) and was associated with ALTR synovial thickness but not with Anderson grade, diameter, or volume. Most of the hips with calcar erosion (n = 45) had an ALTR (positive predictive value 0.83, 95% confidence interval 0.70-0.92). The relative risk of having a synovial thickness > 3 mm increased by a factor of 3.0 (95% confidence interval 1.3-6.5) if calcar erosion was observed. CONCLUSION:Subtle erosions of the medial calcar after MoM THA may be an early indicator of an adverse reaction to wear particles warranting cross-sectional imaging. Synovial thickness may also be more relevant than absolute size in the classification of ALTR severity and collateral tissue damage.