Transmissions within the tarsal gearbox.

Background: The dependence of the movements of the calcaneus, cuboid, navicular, and talus on each other have been described as the tarsal gearbox. To provide a basis of its modeling, data on transmissions between tarsal joint rotations within this gearbox are required. The feasibility of tibiocalcaneal rotations to predict tarsal joint rotations is of interest because a meaningful relation would allow the use of common motion analysis with skin markers to investigate rearfoot kinematics.

Methods: We performed linear regression analyses between tarsal joint and tibiocalcaneal rotations on the basis of magnetic resonance imaging of tibia and tarsal bone positions during quasi-static foot pronation and supination.

Results: In the frontal plane and transverse planes, linear models were found to predict tarsal joint rotations quite well (r(2) = 0.83-0.97 for the frontal plane and r(2) = 0.73-0.95 for the transverse plane). For each degree of talocalcaneal rotation, there was 1.8 degrees of talonavicular rotation in the frontal plane and 1.6 degrees in the transverse plane; each degree of talocalcaneal rotation resulted in 0.6 degrees of calcanealcuboid rotation in the frontal plane and 0.7 degrees in the transverse plane; each degree of calcaneocuboid rotation resulted in 3 degrees of talonavicular rotation in the frontal plane and 2.8 degrees in the transverse; each degree of tibiocalcaneal rotation resulted in 0.9 degrees of talocalcaneal rotation in the frontal plane and 0.9 degrees in the transverse plane; and each degree of tibiocalcaneal rotation resulted in 1.6 degrees of talonavicular rotation in the frontal plane and 1.3 degrees in the transverse plane.

Conclusion: The present study provides a basis on which the tarsal gearbox in the frontal and the transverse planes under quasi-static conditions can be modeled. Furthermore, it is concluded that tibiocalcaneal rotations are practical for predicting tarsal joint rotations during quasi-static motions.