MECHANICAL CHARACTERISTICS OF PROXIMAL FEMORAL RECONSTRUCTION AFTER 50-PERCENT RESECTION

Six techniques of proximal femoral replacement were compared in vitro with the use of compression, bending, and torsional testing in a canin e model. One femur of each pair was osteotomized in the midshaft regio n, and the proximal portion was replaced with one of six techniques. T hese techniques included (a) a segmental proximal femoral endoprosthes is cemented into the distal femur with no allograft (technique E(S)); (b) a long-stem endoprosthesis press-fit into an allograft and cemente d into the distal femur with a transverse osteotomy (technique A(T)); (C) the same construct as technique AT, but with a step-cut at the ost eotomy (technique A(S)); (d) a long-stem endoprosthesis interlocked in to an allograft and cemented into the distal femur with a transverse o steotomy (technique A(I)); (e) a short-stem endoprosthesis cemented in to an allograft combined with one plate laterally stabilizing the allo graft to the distal femur with a transverse osteotomy (technique A(P1) ); and (f) the same construct as technique A(P1), but with an addition al plate cranially (technique A(P2)). A long-stem endoprosthesis cemen ted into the contralateral intact femur served as the control. Techniq ues that involved a long-stem endoprosthesis and cementing distally (A (T), A(S), and A(I)) were more resistant in torsion than the plated re placement techniques (A(P1) and A(P2)). The segmental replacement cons truct (E(S)) was equal to or stronger than all other techniques under each testing condition. In torsion, the addition of a step-cut (A(S)) significantly lowered angular displacement of the reconstruction when compared with the reconstruction with a transverse osteotomy (A(T)) (p < 0.05). Bones with one-plate fixation (A(P1)) were significantly wea ker in torsional stiffness and maximum torque and in mediolateral bend ing (p < 0.05) than all other techniques. The addition of a second pla te (A(P2)) increased the mechanical properties of the construct so tha t it was greater than the one-plate method and was equal to (bending a nd compression) or still weaker (torsion) than the other techniques. T he results indicate that segmental replacement methods and allograft/e ndoprosthetic composites that involve long-stem endoprostheses fixed w ith cement are mechanically superior to methods that involve short-ste m endoprostheses with single or double plating at the osteotomy sites.