Cam versus pincer femoroacetabular impingement. Which type is associated with more hip structural damage? An exploratory cross-sectional study

Abstract

Background: Femoroacetabular impingement (FAI) occurs as a conflict between the proximal femur and the acetabular rim. The purpose of this study was to evaluate MRI findings and look for correlations with pain intensity and duration in each type of FAI separately in an attempt to identify which type is associated with more structural damage. Methods: Forty-four patients (78 hips) diagnosed with either cam or pincer FAI were consecutively recruited in a prospective cohort study. None of our patients had evidence of osteoarthritis (OA) on the initial plain radiography. All patients had contrast-enhanced MRI and CT scans of the hips. All patients filled in a visual analogue scale (VAS) for pain. Results: The frequency of bone marrow edema (BME) was 37% in cam FAI and 20.8% in pincer FAI. In cam FAI, BME positively correlated with pain severity as measured by VAS (P<0.0001), cartilage degradation (P=0.001), pseudocysts (P<0.0001), hip effusion (P=0.013) and reactive synovitis (P<0.0001). However, in pincer FAI, BME only correlated with pain severity (P=0.004) and duration (P=0.011) and did not correlate with other MRI signs of structural hip damage. Conclusions: In cam FAI, BME of the femoral head and neck on MRI positively correlated with chondral damage and synovitis, but not in pincer FAI. This correlation suggests that cam FAI might be associated with a worse long-term prognosis. This finding might have an impact on clinical practice and decision making as it would encourage surgeons to intervene early in cases of cam FAI, thus preventing the possible development of irreversible, established hip OA.