FIXATION OF LONG BONE SEGMENTAL DEFECTS: A BIOMECHANICAL STUDY

Abstract

Gaining stable fixation in cases of recalcitrant non-unions can be challenging. These cases can be accompanied by a segmental bone defect and disuse osteopenia. One strategy to gain stable fixation is the use of allografts. Both cortical struts and intramedullary fibular allografts have been used for this purpose in the femur, tibia and humerus. The present study aims to compare the mechanical properties a locking plate, an intramedullary fibular strut allograft and a cortical strut allograft in a femur model of segmental bone defect.

A transverse mid-shaft osteotomy was performed in fifteen third generation large composite femurs. Twelve millimeters of bone was resected to create a segmental bone defect. Fixation was undertaken as follows: Construct F (Fibula): Lateral Non Locking plate and Intramedullary Fibula Allograft Construct LP (Locking Plate): Lateral Locking Plate Constrcut S (Strut): Lateral Non-Locking Plate and Medial Cortical Strut Allograft Axial, Torsional and Bending Stiffness as well as Load-to-Failure were determined using an Instron 8874 materials testing machine.

Overall, construct S was the stiffest, construct F intermediate and construct LP the least stiff. Specifically, the S construct was significantly (p< 0.05) stiffer than the two other constructs in the axial, coronal plane bending, sagital plane bending and torsional modes. Construct F was significantly stiffer than construct LP in the axial and coronal plane bending modes only. Both the S construct (6108 N) and the F construct (5344 N) had a greater Load-to-Failure than the LP construct (2855 N) (p=0.005 and 0.001 respectively).

The construct with a lateral non-locking plate and a medial allograft strut was stiffer and had a higher load-to-failure than the construct consisting of a stand-alone locking plate. An intramedullary fibular allograft with a lateral non-locking plate had intermediate characteristics. Other factors, such as anatomic and biologic considerations need to be considered before choosing one of the above constructs. The allograft procedures should only be used once soft tissue coverage has been obtained and any infection eradicated.