Total Ankle Replacement Provides Symmetrical Postoperative Kinematics: A Biplane Fluoroscopy Imaging Study

Abstract

Background: In vivo measurements of tibiotalar and subtalar joint motion following TAR are unavailable. Using biplane fluoroscopy, we tested the hypothesis that the prosthetic tibiotalar joint and adjacent subtalar joint would demonstrate kinematic and range of motion differences compared to the contralateral untreated limb, and control participants.

Methods: Six patients of 41 identified candidates that all underwent unilateral Zimmer TAR (5.4 ± 1.9 years prior) and 6 control participants were imaged with biplane fluoroscopy during overground walking and a double heel-rise activity. Computed tomography scans were acquired; images were segmented and processed to serve as input for model-based tracking of the biplane fluoroscopy data. Measurements included tibiotalar and subtalar kinematics for the TAR, untreated contralateral, and control limbs. Statistical parametric mapping quantified differences in kinematics throughout overground walking and the double heel-rise activity.

Results: Patients with this TAR performed walking and heel-rise activities symmetrically with no significant kinematic differences at the tibiotalar and subtalar joints between limbs. Compared to control participants, patients exhibited reduced dorsi/plantarflexion range of motion that corresponded to decreased peak dorsiflexion, but only in the late stance phase of walking. This reduction in tibiotalar dorsi/plantarflexion range of motion in the TAR group became more apparent with double heel-rise activity.

Conclusion: Patients with a Zimmer TAR had symmetric kinematics during activities of walking and double heel-rise, but they did exhibit minor compensations in tibiotalar kinematics as compared to controls.

Clinical relevance: The lack of significant kinematic compensation at the subtalar joint may explain why secondary subtalar osteoarthritis is reported as being relatively uncommon in patients with some TAR designs.

Keywords: biplane fluoroscopy; kinematics; subtalar joint; total ankle replacement.

Figure 1.

(A) Biplane fluoroscopy data were collected in 2 calibrated views during dynamic activities (walking shown). (B) Medical imaging consisted of a foot and ankle CT with metal artifact reduction algorithms applied for patients with a TAR. (C) Segmentation was performed to reconstruct 3-dimensional bones adjacent to the TAR implants, avoiding regions with metal artifact present. (D) CAD models were imported, and DRRs (shown in green) were created for the bone and CAD models separately. The DRRs were statically tracked in a standing trial to establish an alignment between the bone and the TAR implants. (E) The bone and CAD models were transformed into the CT coordinate system to resegment the bone-implant interface to create a solid hybrid model of both components. (F) The hybrid model was then used to track dynamic trials (overground walking and heel-rise activities). (G) Tibiotalar and subtalar kinematics were normalized from heel-strike to toe-off for walking. CAD, computer-aided design; CT, computed tomography; DRRs, digitally reconstructed radiographs; TAR, total ankle replacement.

Figure 2.

Line graph showing tibiotalar kinematics (dorsi/plantarflexion, inversion/eversion, and internal/external rotation) during walking for the limbs treated with TAR (blue), the contralateral, untreated limbs (red), and the control participants (green). Results are normalized as the percentage of stance (with 0% indicating initial heel contact and 100% indicating toe off). Portions of the stance phase of walking during which differences were significant (*) as evaluated with statistical parametric mapping are shown with a horizontal bar. The shaded regions indicate the 95% CIs.

Figure 3.

Line graph showing subtalar kinematics (dorsi/plantarflexion, inversion/eversion, and internal/external rotation) during walking for the limbs treated with TAR (blue), the contralateral, untreated limbs (red), and the control participants (green). Results are normalized as the percentage of stance (with 0% indicating initial heel contact and 100% indicating toe-off). Portions of the stance phase of walking during which differences were significant (*) as evaluated with statistical parametric mapping are shown with a horizontal bar. The shaded regions indicate the 95% CIs.

Figure 4.

Line graph showing tibiotalar kinematics (dorsi/plantarflexion, inversion/eversion, and internal/external rotation) during double heel-rise for the limbs treated with TAR (blue), the contralateral, untreated limbs (red), and the control participants (green). Results are normalized as the percent of stance (with 0% indicating initial heel contact and 100% indicating toe off). Portions of the stance phase of walking during which differences were significant (*) as evaluated with statistical parametric mapping are shown with a horizontal bar. The shaded regions indicate the 95% CIs. TAR, total ankle replacement.

Figure 5.

Line graph showing subtalar kinematics (dorsi/plantarflexion, inversion/eversion, and internal/external rotation) during double heel-rise for the limbs treated with TAR (blue), the contralateral, untreated limbs (red), and the control participants (green). Results are normalized as the percentage of stance (with 0% indicating initial heel contact and 100% indicating toe-off). The shaded regions indicate the 95% CIs. TAR, total ankle replacement.