USE OF A NON CONSTRAINED TRIPOLAR IMPLANT FOR RECURRENT DISLOCATION OF THA: 59 CASES AT 8 YEARS OF FOLLOW-UP

Abstract

Treatment of recurrent total hip arthroplasty (THA) dislocation is always a surgical challenge. Numerous treatments have been developed, but until now there is no gold standard. The goal of our study was to evaluate the results of a non-constrained tripolar implant (Novae) in this indication.

Material and Methods: The study was retrospective. The inclusion criterion was a dislocated THA which underwent reoperation for changing acetabular stem for a Novae cup. 59 patients were included. Femoral stem was always cemented and was never changed. All patients were reviewed with clinical and radiological examinations. The mean follow up is 8 years (6–11 years). 9 patients died before clinical examination and there was no lost to follow up.

Radiological examination was performed numerically with the software Imagika^®

Results: Only one patient had an early dislocation, treated by external reduction. After reduction, no more dislocation occurred. One patient had a femoral fracture below the femoral stem treated by plate. Dislocation rate in our study was 1.7%. The mean Postel Merle d’Aubigné score was 16.5 (12–18) and the mean Harris score was 86.7 (49–99). Radiologically, there wasn’t aseptic loosening neither implant migration, but 19% of the radiographs showed a radiolucent line (less than 1 mm).

Discussion: We compared the results of our study with the results of the other treatments of dislocation. With a dislocation rate of 1.7%, the efficacy of the tripolar non-constrained implant is much better than that of several other treatments, such as external braces, allograft, re-orientation of acetabular shell, change of liner or acetabular augmentation. Constrained implants have also a low dislocation rate, but they have an increased risk of early aseptic loosening. The high rate of radiolucent lines at the last examination is possibly due to the absence of osteointegrating surface of the shell. New implants with osteointegrating surface have been developed.

Conclusion: The efficacy of the studied non-constrained implant is very good with a re-dislocation rate of 1.7%. At 8 years of follow-up, the clinical and radiological results are excellent. We continue to use this implant in the prevention and treatment of dislocation.