SLR - May 2020 - Tyler K. Sorensen

Compensatory Motion of the Subtalar Joint Following Tibiotalar Arthrodesis: An in Vivo Dual-Fluoroscopy Imaging Study

Reference: Lenz AL, Nichols JA, Roach KE, Foreman KB, Barg A, Saltzman CL, Anderson AE. Compensatory Motion of the Subtalar Joint Following Tibiotalar Arthrodesis: An in Vivo Dual-Fluoroscopy Imaging Study. J Bone Joint Surg Am. 2020 Feb 19.

Scientific Literature Review

Reviewed By: Tyler K. Sorensen, DPM
Residency Program: Regions/HealthPartners Institute – St. Paul, MN 

Podiatric Relevance: Ankle arthritis is a common pathology encountered by the foot and ankle surgeon. Although improvements with  total ankle arthroplasty continue, ankle arthrodesis remains the mainstay procedure selection for many surgeons. One of the largest concerns with ankle arthrodesis is the increased stress that this procedure places on the nearby subtalar joint with long-term risk of concomitant osteoarthritis. It has been clinically postulated that subtalar arthritis is due to subtalar hypermobility following ankle arthrodesis, increasing stress and accelerating degeneration. In vivo measurements of the subtalar joint following tibiotalar arthrodesis have not been quantified. This present study utilized dual-fluoroscopic motion capture in attempts to demonstrate differences in kinematics and increased range of motion when comparing the limb with tibiotalar arthrodesis against the contralateral, untreated, asymptomatic ankle.

Methods: Ten asymptomatic patients who had undergone unilateral tibiotalar arthrodesis at a mean of 4.0 ± 1.8 years were evaluated during walking and double heel-rise test. Evaluation was completed utilizing markerless tracking with dual fluoroscopy integrated with 3-D CT. This allowed for dynamic measurements of dorsiflexion-plantarflexion, inversion/eversion, and internal/external rotation. Range of motion, stance time, swing time, step length, step width were all measured, as well.

Results: Statistical significance was found in early stance phase of walking. In the limb that had been treated with arthrodesis of the ankle joint, the subtalar joint was plantarflexed (4.7o ± 3.3o), whereas the subtalar joint of the untreated limb was dorsiflexed (4.6o ± 2.2o). During early stance phase of walking, eversion of the subtalar joint on the surgically treated limb was less than that of the untreated limb (0.2o ± 2.3o and 4.5o ± 3.2o respectively). Also, during double heel-rise test, the treated limb had increased peak plantarflexion of the subtalar joint (27.1o ± 4.1o) when compared to the untreated limb (0.2o ± 1.8o).

Conclusions: In this present study it was found that, with low-speed activities, a significant increase in subtalar plantarflexion seems to be the primary kinematic compensation following ankle arthrodesis. This compensation agrees with the clinical hypothesis that the motion lost from the ankle joint is transferred to other nearby joints, i.e. the subtalar joint. It is not surprising that the main plane of motion impacted was that of the sagittal plane, as this is the major plane of motion of the now fused ankle joint. There were a number of limitations to this study. This includes evaluating a relatively small sample of patients at self-selected walking speeds. Angle of the ankle fusion and the orientation of the talus in relation to the ground were not measured. No preoperative or pretreatment analysis was conducted to evaluate the preoperative ankle condition. Future studies should include a larger cohort of patients evaluated at multiple walking speeds, while also comparing this group to a healthy non-operative control group. Other metrics could include patient reported outcomes along with preoperative evaluation. Future research should also analyze longitudinal changes in subtalar joint kinematics after ankle fusion to better characterize the potential impact of excessive motion, surgical technique and final positioning of the ankle arthrodesis on the development of subtalar arthritis. Additionally, kinematic assessment of talonavicular compensation should also be assessed as this has been shown to develop adjacent joint osteoarthritis as well. 

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