Hip involvement in patients with calcium pyrophosphate deposition disease: potential and limits of musculoskeletal ultrasound

OBJECTIVES: To preliminarily explore the diagnostic potential of ultrasound (US) in detecting calcium pyrophosphate crystal (CPP) deposits at the hip joint in a cohort of patients with calcium pyrophosphate deposition disease (CPPD) which were previously evaluated by conventional radiography (CR); to assess the sensitivity and specificity as well as the agreement between US and CR in the evaluation of hip CPP crystal deposits. DESIGN: Fifty consecutive patients with "definite" CPPD and 40 age/sex/body mass index-matched disease controls who had undergone hip CR within the previous six months were enrolled. Bilateral hip US examination was carried out by one of the authors (A.D.M) to assess the presence of CCP crystal deposits at the acetabular labrum fibrocartilage and at femoral head's hyaline cartilage. Two independent radiologists evaluated the presence of hip CPP crystal deposits on CR in both groups. RESULTS: US findings indicative of CPP crystal deposits were found in at least one hip in 45 out of 50 (90.0%) patients with CPPD, in 73 out of 100 (73.0%) hips. CPP crystal deposits were more frequently found at the acetabular labrum fibrocartilage than at femoral head's hyaline cartilage (72% and 17% of the hips in CPPD patients, respectively). US and CR sensitivity was 90% and 86% whereas US and CR specificity was 85% and 90%, respectively. Total agreement between the US and CR findings was 77.8%. CONCLUSIONS: Our results provide new evidence supporting US as a first-line, sensitive, safe and reliable imaging technique in detecting CPP crystal deposits at hip level.