A Comprehensive Study of Pressure Distribution in the Ankle Joint with Inversion and Eversion

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Abstract
The understanding of load transfer characteristics is the baseline for biomechanics of the ankle joint. Changes in contact patterns of the articular cartilage from the norm may indicate pathologic conditions. Measurement of the contact in human cadaver ankles provides a direct measurement for this understanding. The force transfer characteristics of the three facets of the ankle joint were investigated. Five fresh-frozen cadaver lower extremities were tested in 12 positions under three axial loads of 490, 686, and 980 N. Fuji film served as the pressure transducer and the prints were analyzed by a computerized video digitizer. The results demonstrated that as the foot was moved into inversion or eversion with the ankle in neutral flexion or dorsiflexion, there was a decrease in total contact area and an increase in the average high pressure. In plantarflexion, the contact area was lower and the average high pressure was higher, indicating a greater force per unit area as compared with dorsiflexion and neutral flexion. In plantarflexion, however, little change was noted with inversion or eversion. In dorsiflexion, the total contact area was higher and the average high pressure slightly lower as compared with neutral flexion. With inversion, the contact area of the medial facet of the ankle increased and with eversion it increased on the lateral facet, especially in dorsiflexion. With an increase in loading, the pressure did not significantly increase but the contact area did increase. The centroid of the contact moved anteriorly to posteriorly on the talus as the joint moved from dorsiflexion to plantarflexion. The talar dome facet sustained 77% to 90% of the load, while the medial facet was loaded more during inversion (up to 22%) and the lateral facet was loaded more during eversion (up to 10.5%). No previous study has examined the relative contributions of the three main talar joint surfaces in multiple positions. The new information in this study includes the fibular and medial facet contribution and the variation of the load with position changes and loading increase. This study also provides a comprehensive evaluation of the pressure, contact area, and centroid of the ankle joint in its normal ranges of motion.