Abstract
Introduction
Bi-Metric® cementless primary stem is tapered, rounded conical shaped and coated with plasma spray porous to one-third from the proximal. Fixation is achieved by a press-fit insertion in the Metaphyseal-diaphyseal junction. From 1986 until now, nearly 700 Bi-Metric® stems have been implanted at our hospital. The purpose of this study was to present the clinical and radiological findings including a survival analysis of a consecutive Bi-Metric® stems series followed for over 10 years.
Materials and methods
112 primary cementless THAs in 96 patients using the Bi-Metric® femoral tapered stem were available for clinical and radiological evaluation with a minimum follow-up of ten years. Malloy-Head 4-fined acetabular cup was used in all hips. Follow-up was at a mean of 13 years. We applied THA in 84 patients for osteoarthritis, in 6 avascular necrosis for the femoral head and in 6 for rheumatoid arthritis. The mean age of the patients was 59.5 years. Clinically, pain ROM walking and ADL were evaluated according to the Japanese association hip (JOA) score, and complications and survivorship were investigated. Radiographic results were described according to the 7 femoral Gruen zones. Stem fixation in accordance with the method of Engh at al, cancellous condensation, reactive line, osteolysis, stem subsidence, and bone atrophy with stress shielding were examined. Wear was measured according to the method described by Livermore et al., and the effect of the wear on osteolysis was investigated.
Results
The mean JOA score at follow-up was 93.5 points. No early loosening and no fracture of the implant were found. Tow hips underwent revision surgery, one for a late deep infection, and another one for recurrent dislocation. The overall survival was 98.2% at 13 years. Survival with femoral revision for aseptic loosening as an endpoint was 100%. No subsidence was seen in follow-up period. The mean Engh score for fixation was 9.3 and for stability was 16.8. Focal osteolysis was noted in 20.6% of the hips. In most cases, they were located proximally in zones 1 and 7. The appearance of osteolysis was correlated with PE linear wear.
Discussion
The results for mid- to long-term survival with this femoral component are encouraging. However focal osteolysis attributed to PE wear was seen in one-fifth of the hips and there is a concerned risk that progressing osteolysis causes the loosening in the future. We believe that if the PE wear is reduced, further longevity of this stem will be realized.
