Poincaré analysis detects pathological limb loading rate variability in post-anterior cruciate ligament...

Post-ACLR individuals can experience repeated exposure to variable limb loading, which contributes to development of knee osteoarthritis. Variable limb loading can present as loading rate variability (LRV) and is magnified during tasks like fast walking when the system is stressed. Nonlinear measures that evaluate temporal variability have successfully detected changes in gait variability associated with altered motor control, however, appropriately describing and uncovering the nature of gait variability has been challenging. Here, Poincaré analysis, a nonlinear method unique in its ability to capture different aspects of variability, served to uncover and quantify changes in limb LRV. It was hypothesized that post-ACLR individuals' overloaded limbs would quantitatively and graphically demonstrate greater short-term stride-to-stride and long-term limb LRV during fast walking compared to the underloaded and healthy control limbs.

Fourteen post-ACLR individuals and fourteen healthy controls completed a walking protocol on an instrumented treadmill where they walked at 1.0 m/s and 1.5 m/s for 5-minutes each. A Welch's test was performed to compare differences in short-term and long-term LRV metrics for the post-ACLR individuals' overloaded and underloaded limbs and the healthy controls' right limbs.

Analyses revealed that the post-ACLR individuals' overloaded limb exhibited significantly greater short-term and long-term values compared to the underloaded and healthy control limbs at 1.5 m/s (p<0.05). Additionally, the loading rate data was widely scattered across the plots for the overloaded limb, indicating greater LRV.

Poincaré analysis successfully identified that post-ACLR overloaded limbs exhibited impaired motor control during fast walking based on quantitative and graphical changes in variability. This highlights the clinical applications of Poincaré analysis, with the plots potentially serving as an easy-to-interpret diagnostic tool for pathological limb LRV.