Tibiofibular junction of the South African ostrich (Struthio camelus australis)

The tibiofibular junction of the South African ostrich (Struthio camelus australis) consists of the Ligg. tibiofibularia caudale, craniale proximale and distale, obliquum, and interosseum. The motion range of the fibula, respective to the tibiotarsus, averaged 35 degrees. This junction is, however, not freely mobile as there is a resting position from which the fibula can be pronated an average of 14 degrees (counterclockwise motion of the right fibula from the proximal view) and supinated an average of 21 degrees. Flexion and inward rotation of the tibiotarsus causes fibular supination. This behavior is induced by the lateral meniscus (which follows the movements of the femur on the plateau of the tibiotarsus) and the femorofibular joint surfaces. As the fibular attachment of the popliteus muscle cannot migrate medially, due to its relative fixation by the femorofibular joint surfaces, fibula supination (tibiotarsus pronation), caused by contraction of the popliteus muscle leads to an inward rotation of the tibiotarsus relative to the femur. The ligaments impede excessive pro- and supination. Except for the Lig. tibiofibulare craniale distale, all ligaments also comprise fibers taut in intermediate positions-the Ligg. obliquum and interosseum each have a fiber bundle that is taut in all positions. Tibiotarsus and fibula have no joint surfaces for a common articulation. Hence, the proximal junction should not be termed ''articulation'' (especially with regard to the distal ''syndesmosis''). (C) 1996 Wiley-Liss, Inc.