Mechanics of the subtalar joint and its function during walking

Because it does not connect large bones with prominent and palpable landmarks, the subtalar joint is not studied easily in quantitative mechanical terms. The high degree of intersubject variation in the joint mechanics is a second major complicating factor. Even location of the joint axis is difficult without resorting to invasive means; this forms a barrier to the application of conventional gait analysis techniques to study subtalar joint motions, the actions of muscles, and the ground reaction force about the subtalar joint axis. Improvements in motion analysis technology and the application of noninvasive imaging techniques may lead to more productive clinical gait analysis of subtalar joint function. More studies that link subtalar joint function to injuries and movement deformities, such as those described in the previous section, will be possible when better tools exist for making patient-specific studies of the subtalar joint. Because there is no method for location of the subtalar joint in common clinical use, it is impossible to gauge the role of the ground reaction force or of resultant muscle moments in producing normal or abnormal movements and postures. The subtalar joint passes close to the tendons of many extrinsic foot muscles, making the actions of these muscles sensitive to axis location and joint position. The outcomes of treatments designed to alter the frontal plane actions of foot muscles will improve when methods permitting patient-specific assessments of muscle action are developed.