Abstract
Purpose: Massive cavitary and segmental bone defects of the medial wall in revision arthroplasty are usually managed with large auto and/or allograft in association with a cemented or a cementless cup. To obtain a satisfactory hip center reconstruction with such a procedure can be sometimes challenging and the complications rate can be high. One other option is the use of a cup with a medial expansion (“protrusio cup”) to treat the medial bone defect.
Method: We carried out a retrospective study including 21 consecutive acetabular revisions arthroplasties using a cementless Converge Protrusio™ cup (Zimmer, Warsaw, IN, USA). Clinical outcomes were assessed by Harris Hip Score (HHS), WOMAC index and SF-12. Hip centre was assessed on anteroposterior (AP) view and the reconstruction was considered as satisfying when its location was located from − 10 to + 10 mm proximally (y axis) and/or medially (x axis) in comparison with ideal theoretical hip center location. Cup migration and modification of abduction angle were considered as significant when there were respectively > 4mm and to > 4° in comparison with the immediate postoperative AP view.
Results: At the last follow up [radiological data: 71.6 months (24–128.3) and clinical data: 72.1 months (24–129.5)], two patients were died and there were no lost of follow up. The mean HHS was 79.4% (52–100), WOMAC 82% (46–100), SF-12 52 (23–71) and 44 (18–65). Bone defect were filled with cancellous bone chips allograft in 16 cases and bulk bone allograft was used in only two cases to manage a large segmental defect of the roof. Bone graft integration was completed in all cases. The mean abduction cup angle was 43.6° (32–60). A satisfying hip centre positioning was obtained in 19 cases on x axis and in 10 cases on y axis, in all the remaining cases, we noted an improved implant positioning. The complications were: recurrent dislocation in one case (successfully revised with a constrained liner), infection in two cases (1 treated conservatively and the other one revised in two times procedure) and Brooker’s type III and IV ectopic ossifications in three cases. A significant cup migration occurred in only one case at nine years but was not revised because of painless. No case required revision for aseptic loosening.
Conclusion: Protusio cups appear as a reliable procedure to manage bone loss in acetabular revision. The revision procedure is widely simplified by reducing the use of the massive allograft and by promoting a satisfying hip center reconstruction to allow an optimal biomechanical joint functioning. Moreover, the cementless fixation in contact with patient acetabular bone makes more easy bone integration.
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