Second generation metallic bearings in cementless primary fetal hip arthroplasty: rationale, homologation and preliminary results

Purpose of the study Long-term outcome of Charnley low-friction arthroplasty in young active pat ients is impaired worldwide due to wear of the polyethylene (PE) component and osteolysis. In the late eighties, reports of possible low wear with som e former metal on metal total hip arthroplasties led to the reintroduction of metallic bearings. The aims of this work were to examine the rationale f or using metal on metal bearings in primary total hip arthroplasty (THA) an d report preliminary results obtained with cementless Metasul(TM)-Alloclass ic(TM), hips. Materials and methods From January 1994 to March 1997, 64 cementless primary Alloclassic-THA (gri t-blasted titanium SL stems and CSF treaded cups) with 28 mm Metasul bearin gs were performed. Mean age at surgery was 60 years (range, 36-73). Diagnos es were usual, mainly primary osteoarthrosis in 70 p. 100 of the hips. Two bearing surfaces were exchanged for late dislocation at 2.6 and 2.9 years. Thus, 62 hips in 58 active patients (4 bilateral) were reviewed after a min imum 2-year follow-up (mean 3.2 years, range 24-66 months). Results Clinical results according to the Merle d'Aubigne and Charnley rating syste m were graded excellent or good in all 62 hips. Radiologically, calcar, atr ophy and spot welds were noted in 93 p. 100 and 82 p. 100 of hips respectiv ely. Proximal reactive and lucent lines and mild proximal stress shielding were observed in 8 p. 100 and 4.8 p. 100 of hips respectively. No osteolysi s granuloma has thus far been observed in the vicinity of any component. Co balt blood level remained normal, except in 6 cases due to occupational exp osure (n = 1), possible impingement (n = 1) or an unknown cause (n = 4). Al l elevated cobalt levels (range 7 to 25 mug/l) were nevertheless far below the toxic limit. Discussion Dislocation may be due either to the posterolateral surgical approach and/o r early impingement with the first Metasul bearing design (head sleeve). Me tasul acetabular component fixation is not restricted to only cementless me tal-backing, unlike alumina-ceramic cups. The concern about the toxicity of metallic wear debris dissemination and the hematocarcinogenic risk must be taken into consideration as for any metallic THA. Follow-up is too short f or the new polys for significant comparisons. Conclusion Metal on metal tribology is well known in vitro and Metasul(TM) bearings ha ve functioned in vivo for 12 years (120 000 Metasul hips worldwide) as was expected from laboratory tests. Obviously, this friction couple is not the unique answer to PE-wear and THA longevity, but, in light of current data, appears as a trustworthy solution available today.