[Reconstruction of the acetabulum during replacement of the aseptically loosened polyethylene cup]

K Koudela, T Malotín
Acta Chirurgiae Orthopaedicae et Traumatologiae Cechoslovaca 2001, 68 (3): 162-7

THE PURPOSE OF THE STUDY: The aim of the study was to verify the method after Slooff in our modification, i.e. "a cemented cup--cancellous bone grafts--a metal net" for the revision surgery of aseptic loosening of cemented polyethylene acetabular cup in combined defects of acetabulum.

MATERIAL: The followed-up group of 52 patients (36 women and 16 men), average age of 65 years (age range, 50-81 years) with aseptic loosened cemented polyethylene Poldi cups included 52 operated on hip joints. The average interval between the primary implantation and the revision surgery was 9 years (2-21 years).

METHOD: We reconstructed acetabulum with combined bone defects (AAOS III Degree--as a result of aseptic loosening and migration of cemented acetabular cups) by means of cancellous bone allografts, a shaped Howmedica metal net, Simplex bone cement and a polyethylene cup.

RESULTS: Average follow-up was 36 months (range, 14-49 months). Clinical evaluation of the group was performed after Harris Hip Score averaging 80 points. Radiological evaluation focused on the density and presence of bridging trabeculae between the grafts and the host bone. Positive finding was in 46 patients, i.e. 90%. Further, we evaluated migration of the cup after Conn. In 4 patients (7.7%) it was less than 2 mm and in 3 patients (5.7%) it was greater than 5 mm. Reconstruction failed in 1 patient (1.9%). Radiolucent line was found in the zone between the host bone and bone grafts only in III zone after De Lee and Charnley in 8 cases (15.3%), in zones I and II it was not encountered in any of the patients in the group. One case required another revision surgery in which Burch-Schneider ring, bone allografts and Müller cemented cup were used for the reconstruction. In two patients of this group there developed a phlebographically verified phlebothrombosis without signs of embolism into pulmonary artery. In two cases there occurred a superficial inflammation of the wound which subsided before the removal of the suture. No deep infection of the wound was encountered. Particular ossifications were assessed after Brooker. Type I occurred in 7 cases and Type II in 1 patient.

DISCUSSION: At present several methods are used for the reconstruction of acetabulum and their choice is limited by the extent of the bone loss. For cavitary defects it is possible to use the combination of bone grafts with cementless cups. In segmental and combined defects the situation is more complicated and it can be solved by the application of a solid bone graft. In case the solid bone graft assumed greater load, the situation logically resulted in the fatigue fracture of screws and failure of the whole reconstruction prior to the bone graft-host bone osteointegration. In cementless cups and solid bone grafts the situation is slightly more favourable. If there is a timely biological (secondary) osteointegration of the cup the reconstruction has a chance to survive. The timeliness of biological (secondary) osteointegration is significantly influenced also by the quality of the applied bone graft and a good contact of the bone graft and the host bone and the surface of the cementless cup. Our method of the reconstruction of acetabulum by means of cancellous bone grafts, metal net and cemented cup allows a relatively good primary stability of the cup. Due to its partial elasticity the metal net does not prevent transmission of forces on the bone grafts which are placed under the net. As a result there occurs a faster union of bone grafts with the host bone.

CONCLUSION: The method of cemented cup--cancellous bone grafts--metal net after Slooff is in our modification one of the accepted options of the reconstruction of acetabulum. Its benefit is the possibility of early weight bearing of the limb operated on. The stress on the bone grafts under an elastic construction conduces to a relatively fast good secondary osteointegration. The method can be recommended for II and III Degrees of acetabular bone loss according to AAOS classification. Of no less importance is also the economic aspect of the whole reconstruction.

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