Biomechanics and functional anatomy of the upper ankle.

Abstract

Dorsoplantar motion in the upper ankle joint is around one "transverse" rotational axis. In relation to the lower leg this axis is oblique joining the tips of the malleoli. Talocrural motion is highly precise compared to other human joints. Most of the stability and undisturbed motion in the loaded joint is afforded by the intimate osteocartilagineous contact. The rule of the collateral ligaments is secondary stabilisation, buffering of abnormal stresses and centering the talus in the extremes of motion. The posterior talofibular ligament is the universal lateral stabilizer, the deep portion of the deltoid ligament is the predominant medial ligament structure. Ligament tension without strain and under valgusabduction load as a rule makes only a difference in a quantitative way. Under varusadduction-stress load patterns are usually changed. Fibula and the distal syndesmotic ligaments, in the presence of valgusabduction- and external rotation stress, predominate over the medial joints structures. Remaining joint steps, especially in Volkmanns triangle (posterior malleolus) are prearthritic deformities. Nevertheless primary traumatic lesion of the cartilage has a major prognostic meaning. In cadaver joints as in vivo permanent lesions of only a singular fasciculus of the deltoid or lateral collateral ligament result in clearly detectable motion abnormalities. Concerning clinical therapy at present as in the past complete reconstruction of all that damaged singular structures must be claimed for. There is generally only a small tolerance against instability and malposition in the upper ankle joint. Even after one hundred years of research today factors defining the individual breadth of tolerance are not fully understood. In the presence of treatment regimes, that stood the test of time, it is therefore difficult to recommend treatment alternatives, relaying on individual biomechanical tolerance.