Relationship between the Magnitude and Location of Thigh-Calf Contact Force in High Flexion and Anthropometric Measures

Abstract

The soft-tissue contact between the thigh and calf during deep knee flexion results in tibiofemoral joint contact force reductions at angles beyond 134º of flexion (Caruntu et al., 2003; Zelle et al., 2009; Hirokawa et al., 2013). Many knee models that predict tibiofemoral joint contact forces in high flexion neglect to account for this force. Very few investigations have attempted to characterize thigh-calf contact force, and even fewer have directly measured thigh-calf contact or attempted to model thigh-calf contact force and contact force location on the tibia (Zelle et al. 2007; Zelle et al. 2009). This study focused on the following four thigh-calf contact parameters: (1) maximum total thigh-calf contact force, (2) the corresponding flexion angle, (3) the corresponding centre of pressure, and (4) the starting angle of thigh-calf contact (the flexion angle at the initiation of thigh-calf contact when transitioning into a kneeling or squatting posture). This study addresses limitations of previous work by investigating how the thigh-calf contact parameters are correlated to anthropometric measures after accounting for correlations between body mass and contact force (by normalizing thigh-calf contact force to body mass), comparing parameters between sexes and activities, and presenting an equation for the average thigh-calf contact force and location from 30 participants as a function of percent thigh-calf contact flexion range (this has only been done previously for a single participant as a function of flexion angle). Anthropometric measurements from 30 healthy participants (16 male and 14 female) were recorded. Instrumentation included opto-electronic markers to track dominant leg motion and an interface pressure mapping system to determine the thigh-calf contact force during three deep flexion movements: dorsi-flexed kneeling, plantar-flexed kneeling, and plantar-flexed squatting. Four two-way (3 activities x 2 sexes) ANOVAs were used to compare the mean values for maximum total thigh-calf contact force (in N/kg), centre of pressure at maximum total force (in cm), flexion angle at maximum total force (in degrees) and the starting angle of thigh-calf contact (in degrees) between sexes and between the three activities. Pearson product-moment correlation coefficients (R) were calculated in order to investigate the relationship between the anthropometric measures and the four outcome parameters. In cases where the R value exceeded 0.5 for one or more of the anthropometric measures for a given outcome parameter, predictive modeling of the outcome parameter based on anthropometric measures was pursued using multivariate linear regression with forward stepwise selection. A mean curve for thigh-calf contact force and a mean curve for centre of pressure were created for all participants for each activity. Equations were fit to the mean curves to express each of the measures as a function of percent range of flexion after contact. Based on the average thigh-calf contact force curve for 30 participants, the maximum thigh-calf contact force occurred at maximum flexion and was 1.1 N/kg (S.D. 0.6 N/kg) during squatting, 2.0 N/kg (S.D. 0.7 N/kg) during dorsi-flexed kneeling and 2.2 N/kg (S.D. 0.9 N/kg) during plantar-flexed kneeling. The average centre of pressure, corresponding to those maximum total thigh-calf contact force values, was found to be closer to the epicondylar axis during squatting (13.7 cm, S.D. 1.6cm) than for dorsi-flexed kneeling (14.9 cm, S.D. 1.7 cm) and plantar-flexed kneeling (14.6 cm, S.D. 1.9 cm). There was a significant difference in the maximum total thigh-calf contact force, centre of pressure at maximum total force, and starting angle of thigh-calf contact between squatting and each of the two kneeling activities, however, for all outcome parameters, dorsi-flexed and plantar-flexed kneeling were not significantly different. There was a significant main effect of sex on the starting angle of thigh-calf contact (p = 0.004), whereas, with all other outcome parameters, there was no sex main effect. Unlike the previous investigation that measured thigh-calf contact (Zelle et al., 2007), there was little correlation between anthropometric measures and maximum total thigh-calf contact force or location of centre of pressure at maximum total thigh-calf contact force. This discrepancy likely occurred because thigh-calf contact force was normalized to body mass in this study, whereas non-normalized contact force was used in the previous study. The joint reaction forces, net joint moment, and joint contact forces at the knee joint in the sagittal plane during static full flexion squatting were calculated for a single participant both with and without the addition of thigh-calf contact force. The addition of thigh-calf contact force into the model reduced the knee joint reaction forces by 101.09 N in the anterior-posterior direction and the net sagittal plane knee joint moment by 13.14 Nm at maximal flexion. Based on a single muscle equivalent estimate, the compressive tibiofemoral joint contact force decreased by 221.78 N in the longitudinal direction and 84.96 N in the anterior-posterior direction.