LONG-TERM FOLLOW-UP OF THE ACETABULAR REINFORCEMENT RING (ARR) IN PRIMARY TOTAL HIP REPLACEMENT

Abstract

Introduction: The Acetabular Reinforcement Ring (ARR) (ME Müller®) was introduced in 1977 as successor of the Endler ring, especially to allow total hip replacement (THR) in patients with congenital hip dislocation, serious dysplasia and revision of loose cups. The Polyethylen (PE)-inlay can be freely oriented in the fixed ARR. It is the first implant with screws having angular stability as the screw-heads are blocked when cementing the inlay in the ring.

Patients and Methods: Out of 2251 primary THR performed between 1984 and 2005 at our hospital the ARR was used in 399 hips (363 patients). The indication for a THR with ARR was mainly a deficient acetabular bone stock as judged by the operating surgeon. 51 % of the patients had osteoarthritis, 22% dysplasia, 7% fractures, 6,5% osteonecrosis, 5% protrusion acetabuli, 4% rheumatoid arthritis and 4,5% other diagnosis. The mean age at operation was 66.4 years, 64% were females.

Intraoperatively, the ARR was placed with its medial border adjacent to the tear drop figure. The weight bearing area was fixed with 3–4 cancellous screws in the acetabular bone stock. Regular clinical and radiological follow-up 3months, 1, 2, 5, 10,15 and 20 years was planned. The radiographs were assessed for osteolysis, radiolucent lines and screw breakage after 15 years. Survival for revision due to aseptic loosening was calculated by Kaplan Meier.

Results: The overall survival regarding aseptic loosening of the cup was 100% after 10 years, 97,2% after 15 and 93,2% after 20 years.

Of the 96 patients (104 rings) operated at least 15 years ago, one was lost for follow-up. Three rings were revised due to aseptic loosening (11, 12, 16 years after implantation) and one was removed due to infection (1,8 years after implantation). 54 patients (with 56 rings) died before they reached the 15 years control. None of them was revised for aseptic loosening of the ring. 37 patients (43 hips) remained for 15-years control, six of them refused to come and were contacted by questionnaire or phone. Two cups were radiologically loose with broken screws but not symptomatic. The mean HHS after 15 years was 80.1.

Conclusion: The ARR shows a very good long term survival even in patients with difficult acetabular situations such as deficient bone stock. The design allows an application in a variety of positions. Even at a teaching hospital good long term results could be reached with this implant.