Purpose. There are concerns of soft-tissue reactions such as metal hypersensitivity or pseudotumors for metal-on-metal (MoM) bearings in hip arthroplasty, however, such reactions around ceramic or polyethylene bearings are incompletely understood. The present study was conducted to examine the capabilities of ultrasound screening and to compare the prevalence of periarticular soft-tissue lesions among various types of bearings. Methods. Ultrasound examinations were conducted in 163 hips (153 patients) with arthroplasty after mean a follow-up of 8.1 years (range, 1–22 years). This included 39 MoM hip resurfacings (M-HR) including 30 Birmingham hip resurfacings (BHR) and 9 ADEPT resurfacings; 36 MoM total hip arthroplasties (M-THA) with a large femoral head including 26 BHR and 10 ADEPT bearings; 21 ceramic-on-ceramic THAs (C-THA) of Biolox forte alumina bearings; 24 THAs with a conventional polyethylene liner (cPE-THA) including 19 Lubeck and 5 Omnifit systems; and 43 THAs with a highly cross-linked polyethylene liner (hxPE-THA) including 28 Crossfire and 15 Longevity liners. All procedures were performed in the lateral position through the posterior approach without trochanteric osteotomy. The M-HR group had a significantly higher frequency of male patients than the C-THA, cPE-THA, and hxPE-THA groups, and the patients in the M-HR group were younger than those in the other four groups. Ultrasound images were acquired as a still picture and in video format as the hip moved in flexion and rotation, and 4 qualitative classifications for periarticular soft-tissue reactions were determined as normal pattern, joint-expansion pattern (marked hypoechoic space between the anterior capsule and the anterior surface of the femoral component), cystic pattern (irregularly shaped hypoechoic lesions), and mass pattern (a large mass extending anterior to the femoral component). Magnetic resonance imaging (MRI) was subsequently performed in 45 hips with high-frequency encoding bandwidths. For the reliability of ultrasound screening, positive predictive value, negative predictive value, and the accuracy of the presence of abnormal patterns on ultrasound were calculated using the abnormal lesions on MRI as a reference. Results. Among the 45 hips that underwent MRI, periarticular abnormal lesions were detected in 26 hips (58%). Using MRI findings as reference, positive predictive value, negative predictive value, and the accuracy of ultrasound examination for the detection of soft-tissue lesions were 83%, 71%, and 78%, respectively. Abnormal ultrasound lesions with joint expansion, cystic, or mass patterns were most frequently observed in the cPE-THA group (50%), followed by the M-THA (25%), hxPE-THA (23%), M-HR (18%), and C-THA groups (14%). Compared to the hxPE-THA group, the frequency of abnormal patterns did not differ significantly in the two MoM groups. A mass pattern was detected in 3 hips of the M-THA group and 1 hip of the C-THA group (Figure 1). Abnormal ultrasound lesions were significantly associated with the presence of symptoms. Conclusion: Various soft-tissue reactions could be observed other than those for MoM bearings, and pseudotumors may not be a specific feature of MoM bearings. Ultrasound examination may be a suitable screening tool for further large prospective investigations of soft-tissue reactions around various types of bearings
