Joint Stiffness in ACL-R and OA on Normal and Uneven Surfaces

Individuals with knee musculoskeletal injury and disease may stiffen their lower limb, particularly the knee, to safely traverse a challenging uneven surface. This study quantified leg, torsional knee and ankle joint stiffness for individuals with knee injury (ACL-R) and disease (knee OA) during an overground walk task over a normal flat and an uneven surface. Leg, knee, and ankle stiffness were submitted to an RM ANOVA to test the main effect and interaction between cohort (ACL-R, knee OA and healthy controls) and surface (normal or uneven). Surprisingly, surface but not cohort impacted knee (p = 0.011) and ankle (p = 0.033) joint stiffness. Participants exhibited a 54% increase in knee stiffness and a similar 36% decrease in ankle stiffness, when walking over the uneven surface. Contrary to our expectations, neither group nor surface impacted leg stiffness (p > 0.05). All participants may modify their limb stiffness, by adopting a stiffer knee and more compliant ankle to traverse the challenging, uneven surface type. But, considering how healthy controls exhibited greater variability of leg stiffness on the uneven surface (CV of 1.77 vs CV < 0.88), individuals with knee injury and disease may compensate for limb instability with rigid movement patterns.