A mechanical comparison and review of transverse, step-cut, and sigmoid osteotomies

Successful incorporation of massive allografts for the treatment of bone deficiency demands maximizing biologic and mechanical factors. These factors have yet to be mastered, as evidenced by the 8% to 17% nonunion and the 5% to 20% fracture rate. The current study addresses the allograft incorporation process by examining the three construct geometries: transverse, step-cut, and sigmoid. Specimens were plated and mounted on a mechanical testing machine. A rotational displacement was applied, and torsional stiffness (N-m/ degrees ), maximum torque (N-m), and maximum displacement ( degrees ) were calculated. The sigmoid osteotomies had a torsional stiffness of 1.90 +/- 0.68 N-m/ degrees and maximum torque of 18.85 +/- 6.63 N-m versus 0.99 +/- N-m/ degrees and 14.48 +/- 2.15 N-m for the transverse osteotomies; and a maximum angular displacement of 11.60 degrees +/- 1.78 degrees versus 5.73 degrees +/- 1.6 degrees for the step-cut osteotomies. The step-cut osteotomies consistently failed at the step-cut corners, which acted as stress risers. Computer-aided solid modeling of the contact surfaces showed that the step and sigmoid osteotomy areas were 74% and 44%, respectively, larger than the transverse osteotomy. The sigmoid osteotomy, created with a template and pneumatic drill, seems to offer a mechanical advantage over the transverse and step-cut osteotomies by increasing stability and contact surface area relative to the transverse osteotomy but reducing the stress-riser effect of the step-cut osteotomy.