Abstract
Category:
Ankle Arthritis; Ankle.
Introduction/Purpose:
Ankle arthritis is a painful disease resulting in limited function, mobility, and quality of life.1 Total ankle arthroplasty (TAA) a widely accepted treatment to reduce pain while maintaining joint motion.2,3 There are two common types of implants: fixed bearing (FB) and mobile bearing (MB). Comparisons of these implants have shown similar patient and clinical outcomes;4 however, post-operative gait kinematics from a multi-segment foot and ankle model have not been compared. This study assessed multi-segmental foot and ankle gait kinematics between persons following TAA with MB and FB implants and compared them to control data of adult ambulators without lower extremity pathology.
Methods:
This was a prospective analysis of persons who had previously underwent TAA with a MB (n=6; average follow-up period of 2.5 years) implant. After consenting to the IRB-approved study, participants were fitted with reflective markers for the Milwaukee Foot Model (MFM).5 Participants walked barefoot along a 30-foot walkway at a comfortable, self-selected pace for a minimum of ten trials while twelve infrared motion capture cameras recorded data. Kinematic data from the MB group and historical data from a FB population who underwent the same protocol with the MFM (n=7; average follow-up period of 2 years) were compared to control data (n=37). Welch’s two-tailed t-tests were used to calculate statistical significance at an alpha level of 0.05. Deviation from control data was compared between both implant groups.
Results:
In the MB group, sagittal motion of the hindfoot, forefoot, and hallux were significantly different from control for the majority of stance. The only significant MB group swing phase differences were early swing sagittal kinematics in the tibia, forefoot, and hallux segments. The FB data differed significantly for the majority of stance phase for sagittal tibia motion, all hindfoot planes, sagittal and coronal forefoot motion, and all hallux planes. The FB group kinematics also significantly differed throughout most of swing phase across all planes and segments, except coronal hindfoot motion. All FB kinematic data deviated further from control than the MB data except stance phase coronal tibia and transverse forefoot motion, where the data overlapped (Figure 1).
Conclusion:
Multi-segment foot and ankle gait kinematics following TAA showed the MB implant better restores healthy ambulatory motion than the FB implant. Abnormal stance phase kinematics lead to altered joint loading. This can accelerate adjacent joint arthritis, which has been seen following ankle arthrodesis.6 Both populations showed diminished forefoot plantarflexion throughout gait, compensating for decreased hindfoot dorsiflexion. Because the joints are not heavily loaded during swing phase, the primary concerns of alterations are regarding ground clearance and foot position prior to the next step. The MB implant better restores normal gait, minimizing compensations and likely decreasing arthritis-inducing stress on adjacent joints.
