Abstract
Introduction
Support cages are often used for reconstruction of acetabular bone defects in revision total hip arthroplasty. A Burch-Schneider cage is one of the most reliable systems that has shown good clinical results. It has an ischial flange and an iliac plate for screw fixation to the ilium. It is sometimes necessary to bend the flange or the plate to fit the shape of the peri-acetabulum. However, the frequency, indications, and characteristics of bending the flange or plate have not been reported. To clarify them, a simulation study was conducted.
Materials and methods
Twenty-five cases with acetabular bone defects of Paprosky type 2, 3, or 4 were the subjects of this study. A 3D template surgical simulation was conducted using 3D surface models of the Burch-Schneider cage and acetabulum. The size of the cage was determined by the size of the cavitary bone defect. Placement of the cage was performed in two ways. One was the iliac plate fitting method, in which fitting of the iliac plate to the ilium was performed first, followed by bending of the ischial flange to keep the flange in the center of the ischium. When bending of the flange was needed, it was bent at the base. The other method was the ischial flange fitting method, in which the ischial flange was inserted from the center of the ischium, followed by bending of the iliac flange to adapt to the ilium. When bending of the plate was needed, it was bent at the base. In both methods, the direction and angle of bending were measured.
Results
In the iliac plate fitting method, the cage adapted the acetabulum without bending the ischial flange in 12 cases, and with lateral bending in 11 cases. The bending angle was less than 30° in 8 cases. Three cases required more than 30° of bending and there were also 2 cases which were impossible to fit the acetabulum even with bending the ischial flange. This was due to the large bone defect at the superolateral region of the acetabulum. In the ischial flange fitting method, the cage adapted the acetabulum without bending in 12 cases. The remaining 13 cases required less than 30° of iliac plate lateral bending.
Discussion
The iliac plate fitting method is a clinically oriented method since the insertion position of the ischial flange is determined after fitting the provisional cage with an iliac plate. However, in cases with a large bone defect in the superolateral region of the acetabulum, some were impossible to fit. On the other hand, with the ischial flange fitting method, the cage could fit all types of acetabular defects. This suggests that, even in cases with a bone defect in the superolateral region of the acetabulum, the Burch-Schneider cage is a usable instrument.
Conclusion
The half of the cases required lateral bending of the ischial flange or iliac plate. If there is a large bone defect at the superolateral region of the acetabulum, the iliac plate may need to be bent.
