Pseudotumours, cobalt and clinical outcome in small head metal-on-metal versus conventional metal-on-polyethylene total hip arthroplasty

Abstract

IntroductionTotal hip arthroplasty (THA) has proven to be an excellent treatment for treating osteoarthritis of the hip. Since Sir John Charnley, the metal-on-polyethylene (MoP) bearing has been the gold standard, outperforming 1st-generation metal-onmetal (MoM) THAs like the McKee THA. 1 However, polyethylene (PE) wear leading to particle-induced osteolysis and component loosening has been considered a drawback of the MoP articulation couple. Therefore, in the late 1980s, 2ndgeneration MoM bearings were developed, with improvements in fixation, metallurgy, sphericity and radial clearance. These new MoM designs showed promising wear performance, 2,3 but as there was a lack of comparative clinical trials, Pseudotumours, cobalt and clinical outcome in small head metal-on-metal versus conventional metal-on-polyethylene total hip arthroplasty Abstract Background: Metal-on-metal total hip arthroplasty (MoM THA) is associated with the formation of pseudotumours. Studies mainly concern pseudotumour formation in large head MoM THA. We performed a long-term follow-up study, comparing pseudotumour incidence in small head metal-on-metal (SHMoM) THA with conventional metal-onpolyethylene (MoP) THA. Predisposing factors to pseudotumour formation were assessed. Methods: From a previous randomised controlled trial comparing SHMoM (28 mm) cemented THA with conventional MoP cemented THA, patients were screened using a standardised CT protocol for the presence of pseudotumours. Serum cobalt levels and functional outcome were assessed. Results: 56 patients (33 MoP and 23 MoM) were recruited after mean follow-up of 13.4 years (SD 0.5). The incidence of pseudotumours was 1 (5%) in the SHMoM THA cohort and 3 (9%) in the MoP THA cohort. Prosthesis survival was 96% for both SHMoM and MoP THAs. Serum cobalt levels did not exceed acceptable clinical values (<5 µg/L) whereas no differences in cobalt levels were detected at follow-up between both groups. Oxford and Harris Hip Scores were good and did not differ between SHMoM and MoP THA. Conclusions: This long-term follow-up study shows a low incidence of pseudotumour formation and good functional outcome in cemented head-taper matched SHMoM and MoP THA.

No difference in implant survival between 28-mm M2a RingLoc metal-on-metal and metal-on-polyethylene total hip arthroplasty: results from the Finnish Arthroplasty Register

“…However, when using uncemented Biomet cups (PE+M2a or PE) the liner was attached to the acetabular component by RingLoc mechanism, producing intraoperative modularity comparable to the monoblock Stanmore cup. Implant survival in our study for both M2a and MoP THA groups was slightly inferior compared with those of van der Veen et al ( 12 ) but their study patients initially participated in a single-center trial whereas our data represents nationwide results. Difference in fixation method may also have some minor bias on the results.…”

“…Previous reports focus mainly on devices under the same product umbrella with notable differences. Van der Veen et al ( 12 ) reported similar 96% implant survival rates at 13 years when comparing 23 cemented M2a THAs and 33 cemented MoP THAs. A Stanmore cemented stem was used in both groups.…”

“…M2a bearing surfaces were made of wrought high carbon Co-Cr-Mo alloy in accordance with ASTMF-1537/ISO 5832-12. The M2a RingLoc liner was manufactured by molding a block of conventional polyethylene (ArCom, Biomet) around a highly polished metal alloy bearing insert ( 12 ). The M2a RingLoc THA was the most common SH MoM device in Finland.…”

Haemorrhagic Pseudotumour Following Metal-on-Metal Hip Replacement

“…Although pseudotumours have been studied extensively [5,[12][13][14][15], little is known about their natural history and controversy exists over their management, especially in asymptomatic patients [3,13,16]. Reports in the literature show that pseudotumours can grow in size, remain static, reduce in size and spontaneously resolve [13,16,17].…”