The pronation capacity of the foot —Its consequences for axial deformity after tibial shaft fractures

Summary

In spite of the fact that discomfort from the subtalar area is common after varus-deformed tibial shaft fractures no plausible mechanism is to be found in the literature. A mechanical analysis of the problems shows that a varus deformity is compensated as pronation of the foot. A limited pronation capacity could thus be the cause of the pain. Pronation capacity was accurately measured in ten osteoligamentous preparations. The average pronation capacity was found to be 9.5° ± 7.0°. There was a marked interindividual variation. In two of the specimens the pronation capacity was less than 1°. Capacity decreased by 0.21° for every degree increase in plantar flexion of the ankle joint. Thus, a small pronation capacity may be the mechanical basis for ankle complaints after varus-deformed tibial shaft fractures. An anterior angulation, compensated as plantar flexion, further decreases the pronation capacity and adds to the risk associated with varus deformities.