Matuszak SJ, et al. - Authors reported the progression of acetabular osteolysis during mid-term follow-up in patients treated with metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) and MoM total hip arthroplasty (THA). They also identified the independent predictors of osteolytic lesion progression. A total of 12.2% ASR HRA patients and 11.7% ASR XL THA patients present with osteolytic lesion progression. In ASR HRA, the independent predictors of osteolytic lesion progression were the lower acetabular version angle and elevated whole blood chromium. Physicians were suggested that among the patients implanted with ASR HRA implants, the ones with higher chromium levels and lower version angles should be monitored closely as they were at increased risk for osteolytic lesion progression. And an annual radiographic follow-up on all patients with ASR implants was recommended.