Implant/bone constructs in femoral neck osteotomy. An autopsy study

Previous studies have suggested that three rather than two screws may give better results in the treatment of femoral neck fractures. In the present study, the strength of various screw/bone constructs in femoral neck osteotomy was analyzed. Transverse osteotomies on 65 cadaver femora were fixed with two or three screws of two types: one with a shank diameter of 6 mm and thread diameter of 8 mm, and a prototype screw with equal shank and thread diameter of 7 mm. The femoral heads were subjected to static and cyclic loads in the one-legged stance position. Single-energy quantitative computed tomography measurements were correlated to load. The two experimental models resulted in different patterns of failure of the bone/implant constructs, otherwise the results were similar. Three of the prototype screws gave the strongest construct, while two of the other screw type were stronger than three. The explanations for the diverging properties of the different bone/implant constructs may be that large threads destroy too much of the bone trabeculae, and that screw threads larger than the shank may destroy the drill canal and produce an unstable situation compared with screws with equal shank and thread diameter.