Kinematic chain between pronation/supination of calcaneus and rotation of shank: efficiency of the kinematics by plantar-dorsiflexed ankle joint position

Abstract

Background: The kinematic chain of pronation/supination of calcaneus and internal/external rotation of shank in standing position provides smooth movement, such as gait, since the kinematic chain has a conversion function between movements of foot and shank on the plane of motion. Purpose: This study was aimed to clarify the change in the kinematic chain of calcaneus and shank by plantardorsiflexed ankle joint position. Methods: Subjects were 108 limbs of 25 healthy young adults (26.4± 3.7 yo) and 29 healthy elderly (73.5± 3.3 yo) without history of orthopedic disease in lower extremities. We measured pronation/supination movement of calcaneus and rotational movement of shank at standing position using 3Dmotion analysis system (VICON-NEXUS, ViconMotion Systems Ltd., UK). We defined the linear regression coefficient between calcaneus angle and shank angle as the kinematic chain ratio (KCR, shank angle/calcaneus angle) in the kinematic chain movement. KCR was measured in three ankle joint positions of neutral, 15◦-plantarflexion and 15◦-dorsiflexion positions. Differences in KCR values with factors of joint positions and ages were analyzed using two-way repeated measures ANOVA and Tukey’s HSD test (significance at p< 0.05). Results: The significant difference in the KCR was observed among three positions of ankle, but not among ages. KCR was 0.9± 0.3 in plantarflexion position, 1.0± 0.2 in neutral position and 1.3± 0.4 in dorsiflexion position. KCR at dorsiflexion position was significantly larger than those at neutral and plantarflexion positions (p< 0.001). Furthermore, the KCR at neutral position was significantly larger than that at plantarflexion position (p< 0.05). Correlation coefficient between changes of KCR and shank anteversion angle was r= 0.01 in flexion or r= 0.41 (p< 0.001) in extension. Conclusion(s): This study reveals that KCR becomes larger along with the ankle movement from plantarflexion to dorsiflexion. Since kinematic chain of calcaneus and shank is caused by complex motion of the subtalar and talocrural joints, the KCRmay be affected by the orientation of responsible joint axis upon motion. When the ankle is dorsiflexed, the angle around major axises of shank and subtalar joint may be decreased in the sagittal plane. Hence, the conversion efficiency of the internal/external rotation of shank against the pronation/supination of calcaneus might be increased at the dorsiflexed ankle joint position, leading to the increased KCR. On the other hand, the decreased KCR at plantarflexed ankle joint position may be due to the increased angle between subtalar joint axis and the major shank axis. Present experiments further suggest that the stability of the talocrural joint affects the chain movement as the stable and rigid joint may lead to the constantly gradual increase in KCR upon ankle dorsiflexion, while inconstant decrease in KCR at the plantarflexion may be associated with the instable talocrural joint. Implications:When analyzing the kinematic chainmovement of calcaneus and shank, it should be noted that the manner of kinematic chain changes along with the alteration of the ankle joint position.