Transfer of movement between calcaneus and tibia in vitro.

Excessive foot eversion and/or abnormal tibial rotation have been associated with knee injuries. The mechanical coupling of leg and foot, which may be related to the aetiology of knee injuries, is still not well understood. The goal of this study was to determine in vitro, as a function of loading and flexion position of the foot, the movement transfer from calcaneal eversion-inversion to tibial rotation and vice versa occurring in the ankle-joint complex. A lower leg holding and loading device with 6 degrees of freedom was used in the investigation. Fourteen fresh-frozen, foot-leg specimens were tested. The movement transfer from calcaneus to tibia and vice versa differed significantly between the specimens. The transferred movement was not the same for all input modes. Specifically, calcaneal eversion resulted in significant internal tibial rotation; however, internal tibial rotation did not induce any calcaneal eversion. Vertical loading of the tibia and foot flexion position had a major influence on this movement transfer. The amount of calcaneal eversion transferred to internal tibial rotation depends on the individual mechanical coupling at the ankle-joint complex. Therefore excessive pronation, in running for instance, is only critical for high knee loading when coupled with a high movement transfer in the ankle-joint complex. The interindividual differences may also signal difficulties for prosthesis design in total ankle-joint replacement and for the design of shoe orthotics.