Predicting tibiotalar and subtalar joint angles from skin-marker data with dual-fluoroscopy as a reference standard

Abstract

Evidence suggests that the tibiotalar and subtalar joints provide near six degree-of-freedom (DOF) motion. Yet, kinematic models frequently assume one DOF at each of these joints. In this study, we quantified the accuracy of kinematic models to predict joint angles at the tibiotalar and subtalar joints from skin-marker data. Models included 1 or 3 DOF at each joint. Ten asymptomatic subjects, screened for deformities, performed 1.0 m/s treadmill walking and a balanced, single-leg heel-rise. Tibiotalar and subtalar joint angles calculated by inverse kinematics for the 1 and 3 DOF models were compared to those measured directly in vivo using dual-fluoroscopy. Results demonstrated that, for each activity, the average error in tibiotalar joint angles predicted by the 1 DOF model were significantly smaller than those predicted by the DOF model for inversion/eversion and internal/external rotation. In contrast, neither model consistently demonstrated smaller errors when predicting subtalar joint angles. Additionally, neither model could accurately predict discrete angles for the tibiotalar and subtalar joints on a per-subject basis. Differences between model predictions and dual-fluoroscopy measurements were highly variable across subjects, with joint angle errors in at least one rotation direction surpassing 10° for 9 out of 10 subjects. Our results suggest that both the 1 and 3 DOF models can predict trends in tibiotalar joint angles on a limited basis. However, as currently implemented, neither model can predict discrete tibiotalar or subtalar joint angles for individual subjects. Inclusion of subject-specific attributes may improve the accuracy of these models.

Subject-Specific Axes of Rotation Based on Talar Morphology Do Not Improve Predictions of Tibiotalar and Subtalar Joint Kinematics

“…7,29,33 However, defining these additional degrees-of-freedom may require new subject-specific approaches, as our previous work has demonstrated that a generic model with three degrees-of-freedom at both the tibiotalar and subtalar joints does not improve predictive accuracy. 23 Alternatively, incorporating a multi-segment foot model may be necessary to accurately discriminate between tibiotalar and subtalar joint motion. This recommendation is supported by previous studies that have concluded a rigid-foot model cannot precisely capture motion of individual foot and ankle bones because the forefoot and midfoot violate the rigid-body assumption.…”

“…23,29 Briefly, ten healthy, young adults (5 male, 5 female; age 30.9 ± 7.2 years; height 1.72 ± 0.11 m; weight 70.2 ± 15.9 kg) participated in this study. Each subject provided written informed consent and the experimental protocol was approved by University of Utah's Institutional Review Board (IRB#65620).…”

The Turmell-Metre: Using Draw Wire and Inertial Sensors for an In Vivo Ankle Kinematics Study

“…The most accepted approach for modeling the ankle is the biaxial movement model [42]- [63]. In this model, the ankle is considered as two rotational joints in series.…”

The Turmell-Meter: In Vivo Ankle Kinematics by Using Draw-Wire and Inertial Sensors

“…In vivo studies for articulated boots were performed in [54], subject-specific in [55], and the axes of rotation were calculated in [56]. Dual fluoroscopy for the ankles from markers was performed in [57]. The most complex joint is the subtalar axis, and important contributions are shown in [58]- [65].…”