Uphill walking unveils hidden instability and biomechanical adaptations in anterior cruciate ligament-deficient...

Using computerised motion analysis, the study investigated possible joint instability and biomechanical adaptations during uphill walking in participants with anterior cruciate ligament deficiency (ACLD) classified as copers based on level walking performance.

Thirteen participants with ACLD and thirteen healthy adults each walked and ascended a 3-meter slope with inclines of 3°, 6°, and 9°. Trunk angular motions, lower-limb joint angles, forces and moments, and tibial inclination angles were calculated. Two-way analyses of variance were used to study between-subject (group) and within-subject (slope angle) effects on the variables, using a significant level of α = 0.05 for all tests.

The ACLD group displayed a compensatory trunk anterior tilt strategy over the stance phase of uphill walking to reduce knee extensor moments and posterior knee forces to accommodate knee instability during uphill walking. Compared to Control, the ACLD group showed increased anterior forces during single-limb support (SLS) and decreased posterior forces at the affected knee during the double-limb support (DLS) of uphill walking. They also demonstrated an increased anterior tibial angle of the affected limb with a decreased extensor moment at the affected knee around the contralateral heel-strike. The trunk anterior tilt was also accompanied by increased extensor moments at both hips and ankle dorsiflexion during terminal DLS.

This study demonstrates that uphill walking uncovers hidden functional instability at the ACL-deficient knee that remains undetected during level walking. This suggests that assessments based solely on level walking may overestimate the functional stability of the ACLD knee during more demanding uphill walking. Incorporating uphill walking into clinical evaluations may help identify compromised movement patterns that could necessitate surgical intervention in ACLD.