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Background:

Gait analysis is a widely used non-terminal method to assess functional recovery following tendon injury. However, differences between treadmill-based systems and free-movement platforms raise concerns regarding comparability of outcomes.

Purpose:

To compare gait parameters obtained from a treadmill-based system and a free-movement arena following murine Achilles tendon injury, and to evaluate the validity of velocity-matched cross-platform comparisons.

Study Design:

Controlled laboratory study.

Methods: Twenty adult C57BL/6 mice underwent unilateral Achilles tendon hemitransection (n = 10) or served as controls (n = 10). Gait was assessed longitudinally at baseline and postoperative days (POD) 3, 14, and 21 using both a treadmill-based ventral imaging system and a free-movement plantar pressure system. Dynamic gait parameters were analyzed using velocity-matched locomotion windows within ±10% of treadmill speeds. Primary outcomes included duty factor, stance duration, swing duration, and peak paw area. Functional asymmetry was quantified using a Functional Deficit Index (FDI) based on contralateral limb comparisons.

Results: Both systems detected significant functional deficits at POD3, characterized by decreased duty factor and stance duration and increased swing duration in the injured limb. Free-movement analysis demonstrated greater sensitivity to early functional changes, with significantly larger FDI magnitudes for duty factor (7.90% vs −0.05%, p = 0.0302) and swing duration (16.92% vs −1.26%, p = 0.0276). Peak paw area demonstrated divergent behavior, with negative FDI values observed in the free-movement system, consistent with compensatory overloading. Despite differences in magnitude, directional trends were preserved across platforms.

Conclusion: Velocity-matched comparisons demonstrate that treadmill-based and free-movement gait analyses capture consistent directional functional deficits following Achilles tendon injury, although free-movement systems exhibit greater sensitivity to early changes.

Clinical Relevance: These findings support the use of velocity-controlled cross-platform comparisons and highlight important differences in sensitivity between commonly used preclinical gait analysis systems.