Pitfalls in the use of acetabular reinforcement rings in total hip revision

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Abstract
Introduction: For the reconstruction of acetabular bone defects different types of acetabular reinforcement rings are being used. In clinical practice, these implants showed to some extent good long-term results. In the present work pitfalls and complications after the implantation of acetabular reinforcement rings as well as possible solutions are being discussed. Material and methods: In the first case recurrent dislocation was caused by the malposition of the acetabular component with an impingement of the protruding bone cement and the anterior edge of the acetabular ring as well as muscle insufficiency as a result of the shortening of the leg length. The second case revealed an impingement of the iliopsoas tendon due to a protruding acetabular reinforcement ring. During revision, bone cement was used to smoothen the protruding anterior edge of the acetabular reconstruction ring in order to obtain a relieved sliding of the tendon. Furthermore, we report on the case of a delayed neuropathy of the sciatic nerve after reconstruction of the acetabulum with an acetabular reinforcement ring. Results: Intraoperatively an impingement of the sciatic nerve at the protruding dorsal edge of the acetabular reinforcement ring and the surrounding scar tissue was found. In a further case an aseptic loosening of an acetabular reinforcement ring caused the formation of an excessive granuloma with a large intrapelvic portion. The granuloma led to persisting senso-motoric deficits of the femoral nerve. In summary, based on these clinical cases possible pitfalls, associated with the use of acetabular reinforcement rings, are shown. The mal-positioning and the intra-operative re-shaping of the implant by the surgeon are pointed out as the substantial factors for the occurrence of an impingement phenomenon and total hip instability. Furthermore, in case of an adequate orientation of the cemented polyethylene insert an improper position of the acetabular ring which results in protruding edges has to be considered as a cause of a prosthetic impingement. Conclusion: The cases presented emphasize the necessity of prevention of such pitfalls intra-operatively as well as accurate analysis of implant failures. Furthermore, they suggest explicit preoperative planning before deciding on the strategy of revision surgery of acetabular reinforcement rings.