Biomechanical properties of human cadaveric ankle-subtalar joints in quasi-static loading.

The biomechanical properties of human ankle-subtalar joints have been determined in a quasi-static loading condition. The moving center of rotation was determined and approximated by a fixed point. The moment-angle characteristics of the ankle-subtalar joints about the fixed center of rotation have been measured under four basic movements: dorsiflexion, plantarflexion, inversion, and eversion. The method linearly increases rotation of the calcaneus until failure, and measures the moments, forces, and linear and rotational displacements. Failure was identified as the initial drop of moment on plot showing the moment representing gross injury or microfilament damage. In this study, 32 human ankle-subtalar joints have been tested to failure. The center of rotation of the ankle-subtalar joints was determined for a pure dorsiflexion (9 specimens), plantarflexion (7 specimens), inversion (8 specimens), and eversion (8 specimens). Failure in the joints occurred at an average moment of -33.1 +/- 16.5 Nm in dorsiflexion, 40.1 +/- 9.2 Nm in plantarflexion, -34.1 +/- 14.5 Nm in inversion, and 48.1 +/- 12.2 Nm in eversion. The failure angle was also determined in all four motions. Failure was best predicted by an angle of -44.0 +/- 10.9 deg in dorsiflexion, 71.6 +/- 5.7 deg in plantarflexion, -34.3 +/- 7.5 deg in inversion, and 32.4 +/- 7.3 deg in eversion. Injury was identified in every preparation tested in inversion and eversion, while it resulted in five of the nine preparations in dorsiflexion, and in three of the seven in plantarflexion. Injury occurred at -47.0 +/- 5.3 deg and -36.2 +/- 14.8 Nm in dorsiflexion, and at 68.7 +/- 5.9 deg and 36.7 +/- 2.5 Nm in plantarflexion. The results obtained in this study provide basic information of the ankle-subtalar joint kinematics, biomechanics, and injury. The data will be used to form a basis for corridors of the ankle-subtalar joint responses.