THE EFFECTS OF THE INTEROSSEOUS MEMBRANE, AND PARTIAL FIBULECTOMY ON LOADING OF THE TIBIA - A BIOMECHANICAL STUDY

The biomechanical basis for the treatment of delayed union of tibial f ractures by partial fibulectomy has yet to be fully evaluated. To gain further insight into this problem, nine intact cadaveric lower extrem ities were instrumented with strain gauges on the surfaces of the tibi a and fibula. The limbs were then subjected to axial loading with the ankle and subtalar joints placed in multiple positions. The specimens were loaded either through the distal femur or by direct loading of th e tibial plateau. All specimens were first tested intact then after se ctioning of the interosseous membrane and finally after partial fibule ctomy. It was shown that during loading of the leg, the primary effect s of the interosseous membrane sere to stabilize the fibula and constr ain its posterolateral bending. The fibular strains were not reduced t o zero following sectioning of the interosseous membrane. Tibial strai ns measured on the anteromedial and anterolateral surfaces were consis tently in relative tension, indicating a posterior bending force (ante rior bowing) of the tibia. After partial fibulectomy, strains on these surfaces became relatively more compressive. With the ankle and subta lar joints in neutral position (0 degrees flexion, 0 degrees inversion /eversion) the strains on the anterior surface averaged approximately 10% more compressive relative to the intact condition. Tibial strains were observed to vary with the position of the ankle and subtalar join ts. The fact that the anteromedial and anterolateral tibia surfaces we re always in tension may explain why partial fibulectomy has not prove d to be a uniformly successful treatment method for delayed union of t he tibia. Furthermore, it points to the important role of ''fracture p ersonality'' in the selection of treatment.