From 2003 to 2007, we implanted 24 GAP II reinforcement rings in combination with impacted bone allografts for acetabular reconstruction. The specific indications for use of this cage were AAOS Type III or IV bone loss. We performed 51 revisions in 2003 (two GAPs, 4%), 67 in 2004 (0 GAPs), 74 in 2005 (six GAPs, 8%), 80 in 2006 (six GAPs, 7.5%), and 81 in 2007 (10 GAPs, 12%). During the study time, we also implanted the Burch-Schneider cage (Zimmer Inc, Warsaw, IN, USA) (five patients) in AAOS Type III or IV defects and the Kerboull ring (Implantes Fico SRL, Buenos Aires, Argentina) (three patients) in AAOS Type III defects, always in combination with impacted bone allografts. The right hip was affected in 14 patients and the left hip in 10. There were 20 women and four men with an average age of 69 years (range, 41–84 years). Initial diagnosis was osteoarthritis in 15 patients, developmental dysplasia of the hip in five, and rheumatoid arthritis in four. The indication for revision surgery was aseptic loosening in 19 patients, septic failures in three, and periprosthetic fractures in two.
Patients with infection underwent a two-staged protocol [8
]. Three of the 24 patients underwent their index THA at our institution. The preoperative Merle d’Aubigné-Postel score [8
] averaged 4.1 points. The average number of previous surgeries was two for patients without infection and three for those with infection. In 23 of the 24 patients, acetabular revision was combined with a femoral revision. None of the patients died or were lost to followup. The minimum followup was 24 months (mean, 34 months; range, 24–72 months). We had prior approval of our local ethics review board.
We classified acetabular deficiencies radiographically before surgery and confirmed the classification after removal of components during the procedure using the system reported by the AAOS classification [7
] (Table ). Fourteen patients had a Type IV defect and 10 had a Type IIIB defect. All patients underwent the procedure using a posterolateral approach under hypotensive epidural anesthesia in a laminar flow operating room.
We ruled out the presence of active infection during single-stage surgeries or second-stage reimplantations in all patients using intraoperative frozen-section biopsy [17
], bacteriologic studies, and permanent histology of removed tissues. For all implants, we completely removed the polymethylmethacrylate, granulation tissue, and interface and identified the remaining acetabulum to determine the type of bone defect.
We obtained bone allografts from frozen femoral heads from our own bank following the protocol of the American Association of Tissue Banks for the harvesting and processing of grafts [10
]. We made 7- to 10-mm cancellous chips with a grinder from the unwashed bone allografts and mixed for 15 minutes with 1 g dry powdered vancomycin/femoral head, according to the method in previous investigations [2
]. Grafts were impacted according to the technique described by the Nijmegen group [20
] using specific instruments (Exchange Revision Instruments System; Stryker). In cases with a pelvic discontinuity, we impacted the bone allograft until the fracture was stabilized. Once we obtained stability, we fixed the ring to the iliac bone and to the teardrop. All patients had a GAP II implant used in their reconstruction, with a 28-mm polyethylene liner cemented into place. The outer diameter of the liners we used ranged from 48 to 54 mm, with an average of 50 mm. We used an average of five screws/ring (range, four to eight screws). The average operative time was 146 minutes (range, 90–190 minutes).
In patients without evidence of preoperative infection, we prescribed antibiotic prophylaxis with 1 g cefazolin every 8 hours for 48 hours. All patients with a previous infection received the same intravenous antibiotic treatment used after the first stage; antibiotics were stopped when the infection was controlled. Routine prophylaxis for thromboembolic disease was continued for the first postoperative month; this consisted of intravenous heparin during surgery, early postoperative mobilization, 0.4 mg enoxaparin in patients with a high clinical risk of thromboembolic disease (ie, malignancy, particularly if associated with chemotherapy; antiphospholipid syndrome, immobility, or a history of venous thromboembolism; administration of tamoxifen, raloxifene, oral contraceptives, or estrogen; morbid obesity; stroke; atherosclerosis; an American Society of Anesthesiologists physical status classification of 3 or greater), and 325 mg aspirin in patients with a low clinical risk [19
]. We did not routinely prescribe prophylaxis against heterotopic calcification. The mean transfusion requirements were 2.5 concentrated red blood cell units/patient (range, one to five units).
The rehabilitation protocol included early mobilization 48 hours after surgery, ambulation with a walker, and toe-touch weightbearing on the operated side for 90 days. After that, we encouraged patients to progressively increase weightbearing as tolerated with the use of a cane for at least 1 month.
We collected data prospectively using an information sheet that had individual data for each patient. Two authors (MAB, DMD) evaluated patients clinically and radiographically at 15, 45, 90, and 180 days postoperatively and then yearly using the Merle d’Aubigné-Postel scoring system [8
]. We routinely obtained pelvic AP and frog leg lateral views. We evaluated allograft incorporation by the radiographic criteria described by Slooff et al. [22
] and evaluated graft consolidation of the acetabular graft. Consolidation was defined by the presence of trabecular bone crossing the graft-host junction in both views. We defined clinical failure as having had further acetabular revision regardless of the reason. We considered a hip functional when pain was absent or slight during walking (with or without the use of a cane) and when there were no radiographic findings indicating the possibility of future surgery. These radiographic findings were a fractured hook and/or screws, a fracture of any of both plates, and progressive radiolucencies or more than 5 mm of migration [21
]. We defined a stable GAP ring when the device had an intact hook, screws and both plates, and less than 5 mm of migration in the horizontal or vertical plane at latest followup.
We determined survival using the Kaplan-Meier survival method [12
] using acetabular clinical or radiographic failure as the end point with SPSS®
17 (IBM Corp, Armonk, NY, USA).