KNEE JOINT LOADING MAGNITUDE, DISTRIBUTION, AND ASYMMETRY WITH VEST-BORNE LOADS

Abstract

INTRODUCTION: Chronic exposure to high tibiofemoral joint (TFJ) loads can be detrimental to knee joint health and lead to the onset of osteoarthritis (OA). Soldiers who carry heavy loads have greater risk for onset of OA. Load carriage increases TFJ contact forces, but it is unclear how the whole knee joint environment responds to incremental load carriage, relative to bodyweight. Furthermore, kinetic asymmetries between the dominant and nondominant limb are present during gait, but no studies have examined asymmetries in TFJ loading magnitude or distribution. We hypothesized vest-borne loads relative to bodyweight would cause an increase in TFJ contact forces and impulses in healthy young adults during gait, but the increase at the heavier condition would be attenuated by gait adaptations. We also hypothesized that TFJ contact forces and impulses would be greater in the dominant limb as compared to the non-dominant limb as vest-borne loads are added. PURPOSE: The purposes of this study were 1: to compare TFJ loads and walking patterns when walking on an instrumented treadmill while unloaded vs. loaded with a weighted vest at 15% and 30% bodyweight and 2: to compare the dominant and nondominant limbs' TFJ contact forces and impulses in correspondence with increasing load carriage. METHODS: Young healthy adults (n = 24; 18-30 yrs.; 12 Females; 3 left legged; BMI 18 - 24.9) walked for five minutes per conditions of no load, 15% bodyweight load, and 30% bodyweight load on an instrumented treadmill while kinematic and ground reaction force data were recorded. Total, medial, and lateral first peak TFJ contact forces and impulses were calculated via an inverse-dynamics driven musculoskeletal model. One-way repeated measures ANOVAs ([alpha] = 0.05) were used to investigate the loading conditions effect on the dependent variables. Orthogonal polynomial trend analysis was used to test for the present of quadratic trends ([alpha] = 0.05) as evidence of disproportionate change in the dependent variable with increasing load carriage. 2 x 3 repeated measures ANOVAs ([alpha] = 0.05) were used to test for interactions between limb dominance and load carriage. RESULTS: The 30% loading condition drove a disproportional increase in total and lateral TFJ impulses, whereas medial first peak TFJ contact forces and impulses responded in a linear fashion. There were no interactions between leg dominance and load carriage for TFJ contact forces or impulse. However, main effects revealed that the nondominant limb exhibited 6% greater peak medial TFJ contact forces and 9% greater medial impulses, while the dominant limb exhibited 21% greater peak lateral TFJ contact forces and 29% greater lateral impulses. DISCUSSION: These findings suggest that peak total TFJ impulses increased disproportionally at the 30% condition due to kinematic adaptations, such as a large decrease in leg stiffness. The medial knee compartment is not sensitive to increasing load carriage from 15% to 30% bodyweight, but the lateral compartment is sensitive. Lastly, there are variations in the distribution of knee joint contact forces when comparing the dominant and nondominant limb, with the lateral compartment being prominently different.