Knee Medial Compartment Joint Loads In Stationary Cycling With Increased Q-factor

Abstract

As Q-Factor (QF: inter-pedal width) is increased, the knee abduction moment also increases. Though the knee abduction moment has been associated with knee medial compartment joint load, it is not a direct measure of joint contact forces. In the absence of in vivo measurement using an instrumented knee implant, musculoskeletal modeling simulations may provide a viable option for estimation of knee joint contact forces. PURPOSE: To estimate the total knee joint compressive force (TCF) and knee medial compartment joint compressive force (MCF) in stationary cycling with increasing QF using musculoskeletal simulation. METHODS: Five recreationally active males cycled on a stationary ergometer at a workrate of 80 Watts and a cadence of 80 rotations per minute at two QF: original QF (150mm), and wide QF (276mm). Wide QF was increased using pedal extenders. Three-dimensional kinematic data (240 Hz, Vicon) and pedal reaction forces using two custom instrumented bike pedals (1200 Hz, Kistler) were collected. A modified gait2392 model with a knee that includes hinge joints for the medial and lateral compartments was used to estimate muscle forces with static optimization and TCF and MCF with joint reaction analysis (3.3 OpenSim, SimTK, Stanford University). Paired samples t-test and Cohen’s d were used to detect differences between conditions. RESULTS: Peak TCF increased from original to wide QF (960.2 ± 258.2 N to 1117.3 ± 202.1 N ; p = 0.299; d = 0.54) and MCF increased from original to wide QF (792.2 ± 98.4 N to 1029.2 ± 315.5 N; p = 0.116; d = 0.89). CONCLUSION: Large standard deviations and small sample size may account for the lack of statistical significance, yet medium and large effect sizes may allude TCF and MCF increases with greater QF (Figure 1). It appears the majority of TCF is born by the medial compartment; TCF and MCF ranged from 1.46 and 1.14 BW for original and 1.75 to 1.42 BW for wide QF, respectively. These loads are much smaller than 2.0-2.5 BW found in walking and 4.0 BW in jogging.