THE ROLE OF FIBULAR FIXATION IN COMBINED FRACTURES OF THE TIBIA AND FIBULA - A BIOMECHANICAL INVESTIGATION

Objectives: To determine whether adjunctive plating of the fibula with tibial fixation enhanced the stability of the construct under combine d compressive and bending loads in simulated fractures of both the tib ia and fibula. Methods: Each of twelve fresh cadaveric specimens (six pairs) with an intact knee, lower extremity, and foot was mounted on t he table of a materials testing machine. An intramedullary (IM) rod lo cked in the distal femur allowed combined compression, and flexion, va lgus bending, or varus bending loads to be transmitted from the actuat or of the testing machine to the knee. Three displacement measurement transducers were mounted on the tibia at anterior, posterolateral, and posteromedial positions. Intact tibial deformations under load were m easured. Then, in one specimen of each pair a 2 cm osteotomy was creat ed near the tibial midshaft, which was stabilized with an external fix ator. Tibial gap displacements were measured under the following condi tions: (a) intact fibula, (b) osteotomized fibula, (c) fibula fixed wi th a plate, (d) fibula fixed with an Enders IM nail. In the other spec imen of the pair, tibial fixation was performed with an interlocked un reamed IM nail, with the same successive stages of fibular fixation. R esults: Osteotomy of the fibula significantly increased tibial defect motion when external fixation was used, and plating the fibula in this case significantly decreased motion. Using an Enders rod to stabilize the fibula instead of a plate, with tibial external fixation, produce d smaller decreases in tibial defect site motion. With IM rod fixation of the tibia, osteotomizing the fibula had no effect on defect site m otion or on its subsequent stabilization using a plate or LM rod. Conc lusion: Plating the fibula can decrease motion across a tibial defect, but only when less rigid (i.e., external) fixation is used.