Background: An Achilles tendon rupture (ATR) is known to cause persistent biomechanical deficits such as decreased muscle strength in end-range plantar flexion and reduced tendon stiffness.

Purpose/Hypothesis: This study aimed to examine whether sustained asymmetries were present in dynamic stiffness and kinematic and kinetic variables in gait and single-leg balance at 4.5-year follow-up in conservatively treated patients recovering from an ATR. We hypothesized that patients who had recovered from ATRs exhibit a midterm increase in peak ankle dorsiflexion, a decrease in concentric work, and decreased dynamic stiffness during the stance phase of gait, along with increased single-leg standing sway in the injured leg compared with the uninjured leg.

Study Design: Case series; Level of evidence, 4.

Methods: This study was a cross-sectional medium-term follow-up of conservatively treated patients recovering from ATRs. A total of 34 patients who underwent nonoperative treatment were included for testing 4.5 years after a rupture. The Achilles tendon length was measured using ultrasound. Standard instrumented 3-dimensional (3D) gait analysis and single-leg standing balance were performed using 3D motion capture. Kinematic and kinetic ankle parameters were calculated during gait, and quasi-stiffness was calculated as the moment change per the change in the degree of dorsiflexion during the second (ankle) rocker of the gait cycle. Center of pressure displacement (sway length), along with rambling and trembling, was calculated for the single-leg balance task.

Results: Peak dorsiflexion in stance was 13.4% larger in the injured leg than the uninjured leg (16.9° ± 3.1° vs 14.9° ± 0.4°, respectively; P ≤ .001). Peak dorsiflexion was not associated with the normalized Achilles tendon length (B = 0.052; P = .775). Total positive work in the plantar flexors was 23.9% greater in the uninjured leg than the injured leg (4.71 ± 1.60 vs 3.80 ± 0.79 J/kg, respectively; P = .001). Quasi-stiffness was greater in the uninjured leg than the injured leg during the initial (0.053 ± 0.022 vs 0.046 ± 0.020 N·m/kg/deg, respectively; P = .009) and late (0.162 ± 0.110 vs 0.139 ± 0.041 N·m/kg/deg, respectively; P = .005) phases of eccentric loading. No difference was found in sway length during single-leg stance between the injured and uninjured legs (1.45 ± 0.4 vs 1.44 ± 0.4 m, respectively; P = .955).

Conclusion: Patients treated conservatively have a small increase in peak dorsiflexion, decreased total concentric plantar flexor power, and decreased quasi-stiffness in initial and end-range dorsiflexion in the injured leg. These deviations could not be directly associated with the measured tendon elongation.

Registration: NCT02760784 (ClinicalTrials.gov).