Background/Purpose: The standard treatment for end-stage arthritis of the ankle joint due to rheumatoid arthritis (RA) has been an ankle arthrodesis. Patients with RA who require surgery usually already have degeneration of the subtalar and midtarsal joints. Fusion of the ankle and hindfoot will result in functional problems with gait. Thus, total ankle replacement (TAR) that can relieve pain while retaining ankle movement is important for patients with RA. However, high complication rates and low survivorship are still problematic in TAR, as compared to total knee and hip replacements. This could primarily be due to implant loosening and subsidence induced by excessive articular contact stress during ankle motion. A better understanding of ankle kinematics after TAR may be important to explain the failures in TAR, especially those attributed to loosening and subsidence. The purpose of this paper was to study in vivo kinematics of a three-component mobile-bearing TAR by 3D-evaluation of fluoroscopic imaging of ankle motion.

Methods: We investigated ten ankles in 7 patients with RA implanted with a three-component mobile-bearing TAR (FINE Total Ankle System, Nakashima Medical, Okayama, Japan), which allows not only internal/external rotation but also anteroposterior translation. Fluoroscopic images were obtained while each patient was asked to perform normal gait with full weight-bearing on the implanted ankle. Thereafter tibio-talar motion was analyzed by 2D/3D registration technique; a reproduction method of the spatial position of each component in TAR, from single-view fluoroscopic images by use of computer-assisted design models. We evaluated the dorsi-/plantarflexion angle, internal/external rotation angle and anteroposterior translation between the components.

Results: The average range of tibio-talar motion during the stance phase of gait with full weight-bearing on the implanted ankle was 11.2±2.7°. The average range of internal/external rotation was 3.9±1.4°. However, large intersubject variability resulted in the lack of a uniform pattern of rotational movement. The average absolute amount of anteroposterior translation was 1.6±0.7mm.

Conclusion: The range of motion, with regard to plantar/dorsi flextion, was not so wide as expected, and was almost the same with other non-mobile TAR. As intended by mobile bearing design, however, the tibial and talar components rotated internally/externally with respect to each other. Anteroposterior translation was also observed but was within small amount. These results suggest that mobile bearing TAR should be advantageous in durability with expectation that it could compensate rotational malposition of the components as well as malalignment of the subtalar joint.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/in-vivo-kinematics-of-three-component-mobile-bearing-total-ankle-replacement-for-rheumatoid-arthritis/