10-YEAR SURVIVORSHIP OF THE ZWEYMULLER PROSTHESIS IN CEMENTLESS PRIMARY TOTAL HIP-ARTHROPLASTY

Purpose of the study To provide clinical and survival results of a con secutive series of primary total hip arthroplasties (THA) performed wi th the Zweymuller grit-blasted titanium total hip prostheses of the 2 last designs (Hg and AIloclassic-SL), and to compare the IO-year survi vorship with those of other prostheses either cemented or cementless. Material and methods Of 238 index THAs, 213 hips have been prospective ly studied with a 2 year minimum follow-up (average, 6.5 years; range, 25 to 146 months). Mean age was 63 years. Hip arthrosis was the main diagnosis (88 per cent).Results Intra-operative fracture rate (n = 238 primary THAs) was 6.3 per cent, 2.9 per cent and 1.3 per cent, for th e greater trochanter, the upper femur, and the acetabulum, respectivel y. Early dislocation rate was 4.6 per cent. Average Postel-Merle d'Aub igne-Charnley Hip Score raised from 11.3 points pre-operatively, to 16 .7 points at last follow-up. Clinical results were graded excellent an d good in 93 per cent of hips, fair in 5.1 per cent, and poor in 1.9 p er cent. At least 19.5 per cent of stems subsided 2-10 mm within the f irst 2 years. Reactive and lucent lines have been noted in 33 hips (15 .5 per cent) in complete Gruen zones 1 and 7, and in 4 hips (1.9 per c ent) extending in zones 2 and 6. 1 Hg and I SL components definitively failed to stabilize, and have been revised, at 5.6 and 2.4 years, res pectively. Proximal mild stress shielding and Brooker III and IV heter otopic bone formation were noted in 11.7 per cent and 12.7 per cent of hips, respectively. Beside one immediate revision, 4 threaded compone nts failed to achieve initial stability. Two migrated within the first 2 years, then stabilized with good clinical results at 8.5 and 5.2 ye ars. The 2 others failed their osseointegration, with only 1 revision thus far. Most immediate post-surgery bone-implant acetabular gaps in 57.8 per cent of hips, have nearly disappeared at last control, with r esidual lucencies around 7 per cent of rings. Annual linear wear rate superior to 0.2 mm per year could be detected in only 1 ceramic-PE bea ring surfaces, but femoral osteolysis was seen in 3 cases. There has b een no ceramic head breakage thus far. At 10 years, survivorship of th e 238 index THAs with ''pain graded < 5'' and ''revision for clinical failure'' (dislocation excluded) as end point was 95.8 per cent and 98 per cent, respectively. With ''definite loosening'' (radiographic fai lure) as end point, 10 year survivorship was 99.1 per cent for the ste ms and 98.6 per cent for the threaded cups. Discussion Once osseointeg ration apparently occured, the authors have never observed any seconda ry migration indicating failure of the bone-implant anchorage. The fem oral implantation technique was critical and improved following an una voidable learning curve. Liner disassociation, evolutive acetabular lu cencies, worrisome wear and osteolysis were not of great concern thus far. Results of these grit-blasted threaded cups are much better than those of former smooth screw rings. Conclusion Ten year survivorships of the Zweymuller cementless prostheses in primary THA are better than those of former cemented or cementless prostheses, and are within the range of the best results published at equivalent follow-up with hybr id reconstructions with use of stems cemented with up to date techniqu e and hemispheric cementless press-fit cups with screw fixation.