PURPOSE: The purpose of this cross-sectional investigation was to determine the influences of alignment and obesity on the knee joint loads of overweight and obese older adults with knee osteoarthritis. Our primary hypothesis was that there would be a significant interaction between knee alignment and Body Mass Index (BMI) on the knee joint load, independent of gender and walking speed.
METHODS: Baseline data from a subset of participants (157 out of 454) enrolled in the Intensive Diet and Exercise for Arthritis (IDEA) clinical trial were utilized for this study. Knee alignment was quantified on all subjects (N = 157) using a full length anteroposterior (AP) radiograph. Varus alignment was defined as an angle greater than 2°, neutral was 0-2°, and valgus was less than 0°. BMI was quantified in all subjects using each participant’s height and weight. Internal knee moments, knee joint forces, and quadriceps, hamstrings, and gastrocnemius forces were calculated using a 3-D gait analysis with a 37-reflective maker set arranged in a Cleveland Clinic full-body configuration, a 6-Camera Motion Analysis system set to sample data at 60 Hz, and a torque-driven musculoskeletal model. Linear regression models were fitted for each kinetic outcome controlling for gender and walking speed.
RESULTS: After adjusting for walking speed and gender, there was not a significant interaction between BMI and knee alignment on the knee joint forces, or on the internal knee abduction moment. However, alignment had a significant (p < 0.0001) association with the internal knee abduction moment, independent of BMI. BMI had significant associations with the peak knee compressive and shear forces and knee muscle forces, independent of alignment.
CONCLUSION: A higher BMI was associated with greater peak knee compressive, shear, and muscle forces, regardless of alignment, and alignment was associated with the internal knee abductor moment, independent of BMI. Hence, BMI and alignment influence different joint loading measures that have both been linked to disease progression.