Cementless cups do not increase osteolysis risk in metal-on-metal total hip arthroplasty

Summary Background Metal-on-metal bearings in total hip arthroplasty (THA) were introduced to reduce the production of wear debris and debris-induced periprosthetic osteolysis. Analysis of various series according to the type of selected acetabular fixation highlights different evolutions: favourable results with uncemented cups contrasting with loosening and radiolucent lines (RLL) evolution for cemented cups. Hypothesis Combining metal-on-metal bearings to uncemented cups does not increase the osteolysis risk at a minimum 5 years’ follow-up. Materials and methods From January 1999 to December 2002, 106 Metasul™ THAs were implanted in 95 patients using a Hardinge anterolateral approach (40 women and 55 men with an average age of 59.2 years). The cups were of cementless, hydroxyapatite-coated Cedior™ type (Zimmer) housing a Metasul™ insert in a polyethylene sandwich. The femoral stem used was the cemented Acora™, then the Exafit™ (Zimmer) type with Metasul™ 28-mm head mounted on a 8/10 Morse taper. Patients were evaluated clinically using the Postel-Merle-d’Aubigne (PMA) scoring system and radiologically using various markers: cup inclination angle, eventual RLL presence, appearance of osteolysis images, ectopic ossifications and finally, eventual implant migration. In the eventuality of suspected RLL evolution or osteolysis, advanced imaging was performed; joint aspiration liquid and cobalt serum level were studied. Results We reviewed 94 prostheses (85 patients) with an average follow-up of 6.4 years (4.3 to 9.3 years, median of 6.3 years). The rate of patient loss from follow-up and death was 12.1%. The PMA score of non-revised patients increased from 11.4 ± 1.5 to 17.6 ± 0.2 at follow-up. We numbered ten re-operations not attributable to the type of bearings used. Three revisions were directly related to the metal-on-metal bearing: two metallosis due to impingement and one case of hypersensitivity. Cup inclination angle was 45.7 ± 5.49°. No implant migration was noted during the follow-up duration. Only one cup undergoing revision presented a substantial osteolysis. On the femoral side, with non-revised implants, we observed 13 cement/bone RLL images around nine femoral stems and six calcar resorptions. The survival rate at more than 6 years was 95.8% (91.8–99.8) for the cups and 94.8% (90.3–99.2) for the femoral stems (95% confidence interval). Discussion The present study confirms our hypothesis: with Metasul™ bearings equipped cementless cups, the rates of aseptic loosening, RLL or acetabular osteolysis are low and remain stable over time, unlike the results observed for Metasul™ series with polyethylene directly cemented on bone. Specific complications, such as metallosis due to impingement and hypersensitivity, can rarely be encountered. These results encourage us to continue employing metal-on-metal bearings with non-cemented cups in active patients. Level of evidence Level IV: Therapeutic study.