Purpose: Knee sagittal plane dynamic joint stiffness (DJS) is the interaction between the external knee flexion moment and knee flexion joint excursion, quantified as the slope of the linear regression line of the external knee flexion moments with respect to flexion angles, during the loading response phase of gait. DJS represents muscle and capsuloligamentous resistance during joint motions and is a mechanical marker of sagittal plane dynamic knee stability during walking. Persons with knee OA often walk with altered knee sagittal plane mechanics, however, the role of sagittal DJS in knee OA is not well understood. In theory, knees with more severe OA may have higher DJS due to decreased joint excursion and/or DJS may in turn contribute to further progression by altering load distribution. Greater DJS may also be an attempt to stabilize/stiffen the joint to lessen knee pain. We hypothesized that greater sagittal plane DJS is associated with more severe disease and less severe knee pain in persons with knee OA. Methods: Participants all had knee OA (defined as K/L grade > 2) in at least one knee. Three-dimensional knee kinematics and kinetics during ambulation on a 35 x 4 foot walkway were captured at a rate of 120 Hz, using external passive reflective markers, an 8-camera Digital Real-Time Eagle motion analysis system, and 6 AMTI force plates. Participants walked in their own walking shoes at a self-selected comfortable speed without assistive devices. Inverse dynamics were used to compute the external knee flexion moment, normalized to body weight and height. Sagittal DJS was computed as the slope of the fitted linear regression line for external knee flexion moments vs. flexion angles during the loading response phase, beginning at the time when the flexion moment started to increase and ending at the time when maximum flexion angle was recorded. Disease severity was assessed using K/L grade from the AP weight bearing image acquired in a semi-flexed position with fluoroscopic confirmation. Pain was assessed by both WOMAC score and pain after 20-meter walk. We stratified analyses by gait speed (> 1.20 vs. < 1.20 m/s) to assess the association between DJS and disease severity and pain, using linear regression with generalized estimating equations (GEE) to account for correlations between the 2 limbs of each individual, adjusting for age, gender, strength, and when appropriate, disease severity and pain. Results are reported as regression coefficients and 95% confidence intervals (CIs). Results: The study sample consisted of 482 knees from 248 persons: mean age 64.8 years (SD 10.3); BMI 28.6 kg/m2 (5.6); 187 (75.4%) women. 24 (5.0%) knees were K/L grade 0, 84 (17.4%) grade 1, 219 (45.4%) grade 2, 72 (14.9%) grade 3, and 83 (17.2%) grade 4. Mean sagittal DJS was 0.23% body weight*height/degree (SD 0.06); gait speed 1.19 m/s (0.20). Mean WOMAC pain was 4.75 (3.55) on a scale of 0-20 and pain after 20-meter walk was 1.92 (1.60) on a scale of 1-10, higher indicating worse pain. As shown in Table 1, higher K/L grade was associated with greater DJS regardless of gait speed. Table 2 shows that greater DJS was associated with less severe pain, both by WOMAC and pain after 20-meter walk, in the faster speed group, but not in the slower group. Conclusions: More severe knee OA was associated with greater knee sagittal DJS; in theory, this may reflect compensatory activity to stabilize the joint, disease-related diminished joint motion, and/or DJS influence on load distribution. Greater DJS was associated with less knee pain in persons with faster walking speed; during faster walking, greater DJS may reflect successful compensation to reduce knee pain. Future longitudinal studies will help to elucidate the direction of the relationships between DJS and pain, function, and disease progression. (Table Presented).
Chang, A. H., Chmiel, J. S., Almagor, O., Moisio, K. C., Belisle, L., Zhang, Y., … Sharma, L. (2015). Association between knee sagittal plane dynamic joint stiffness during gait and disease severity and pain in knee osteoarthritis (OA). Osteoarthritis and Cartilage, 23, A94–A95. https://doi.org/10.1016/j.joca.2015.02.803