The range of motion was measured for the ankle joints in vivo for 20 subjects using the 3D CT stress-test. Motion of the tibia and calcaneus relative to the talus for eight extreme foot positions were described by helical parameters.
High consistency for finite helical axis orientation (n) and rotation (θ) was shown for: talocrural extreme dorsiflexion to extreme plantarflexion (root mean square direction deviation (η) 5.3° and θ: SD 11.0°), talorucral and subtalar extreme combined eversion–dorsiflexion to combined inversion–plantarflexion (η: 6.7°, θ: SD 9.0° and η:6.3°, θ: SD 5.1°), and subtalar extreme inversion to extreme eversion (η: 6.4°, θ: SD 5.9°). Nearly all dorsi – and plantarflexion occurs in the talocrural joint (θ: mean 63.3° (SD 11°)). The inversion and internal rotation components for extreme eversion to inversion were approximately three times larger for the subtalar joint (θ: mean 22.9° and 29.1°) than for the talocrural joint (θ: mean 8.8° and 10.7°). Comparison of the ranges of motion of the pathologic ankle joint with the healthy subjects showed an increased inversion and axial rotation in the talocrural joint instead of in the suspected subtalar joint.
The proposed diagnostic technique and the acquired database of helical parameters of ankle joint ranges of motion are suitable to apply in clinical cases.