Natural History of Adverse Local Tissue Reactions (ALTRs) Around Hip Arthroplasty as Identified by MARS MRI

Purpose: The clinical significance and management of adverse local soft tissue reactions (ALTRs) following total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) continues to be controversial.. The purpose of this study was to evaluate sequential MARS MRIs in patients with painful THA to attempt to establish management criteria.

Methodology: Twenty-three (23) hips in 20 patients had sequential MARS MRIs for pain and were positive for ALTR. The group consisted of 4 MM THA, 3 M-XLPE THA, 1 CM THA and 15 MM HRA. Two musculoskeletal radiologists evaluated all the MRIs using a standardized template. Changes in the size of the lesions were evaluated between initial and final scans. Blood cobalt (Co) and chromium (Cr) levels were measured

Results: 52.2% were cystic fluid filled lesions, 8.7% were solid masses and 43.5% were complex mixed lesions. Mean follow up was 8.4 years (28.8 -337.5 months). The mean time between first and last MRI was 24 months (range f6 to 56 ). Mean initial volume of the ALTRs was 302.85ml and the final volume was 309.81ml. There was 1outlier lesion that measured 808 ml and consisted of a large anterior fluid mass that completely resolved nine months later and was thought to be a psoas bursal lesion. 30.4% increased in size, 34.8% decreased in size and the rest did not change. 9 cases were revised - only 5 were revised for an initially large or progressively enlarging lesion The remaining 4 were revised for femoral neck fracture or aseptic loosening. The relation between classification of the lesion and its progression was not significant. Significant relationship was identified between Co (but not Cr) level in the blood and size / progression of the lesions (P<0.05).

Conclusion: Larger lesions that increase in size over time tend to be more aggressive and can lead to more soft tissue and bony destruction. Stable ALTR should be followed and can be treated conservatively. Cystic fluid filled masses can resolve or decrease spontaneously.