[10-year survival of Zweymüller total prostheses in primary uncemented arthroplasty of the hip].

PURPOSE OF THE STUDY

To provide clinical and survival results of a consecutive series of primary total hip arthroplasties (THA) performed with the Zweymüller grit-blasted titanium total hip prostheses of the 2 last designs (Hg and Alloclassic-SL), and to compare the 10-year survivorship with those of other prostheses either cemented or cementless.

MATERIAL AND METHODS

Of 238 index THAs, 213 hips have been prospectively 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 the greater trochanter, the upper femur, and the acetabulum, respectively. Early dislocation rate was 4.6 per cent. Average Postel-Merle d'Aubigné-Charnley Hip Score raised from 11.3 points pre-operatively, to 16.7 points at last follow-up. Clinical results were graded excellent and good in 93 per cent of hips, fair in 5.1 per cent, and poor in 1.9 per cent. At least 19.5 per cent of stems subsided 2-10mm within the first 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 cent) extending in zones 2 and 6. 1 Hg and 1 SL components definitively failed to stabilize, and have been revised, at 5.6 and 2.4 years, respectively. Proximal mild stress shielding and Brooker III and IV heterotopic bone formation were noted in 11.7 per cent and 12.7 per cent of hips, respectively. Beside one immediate revision, 4 threaded components failed to achieve initial stability. Two migrated within the first 2 years, then stabilized with good clinical results at 8.5 and 5.2 years. 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 residual 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 bearing surfaces, but femoral osteolysis was seen in 3 cases. There has been no ceramic head breakage thus far. At 10 years, survivorship of the 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 failure) as end point, 10 year survivorship was 99.1 per cent for the stems and 98.6 per cent for the threaded cups.

DISCUSSION

Once osseointegration apparently occurred, the authors have never observed any secondary migration indicating failure of the bone-implant anchorage. The femoral implantation technique was critical and improved following an unavoidable learning curve. Liner disassociation, evolutive acetabular lucencies, 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 Zweymüller 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 hybrid reconstructions with use of stems cemented with up to date technique and hemispheric cementless press-fit cups with screw fixation.