Knee power is an important parameter in understanding medial knee joint load in knee OA

Abstract

Purpose: The progression of knee osteoarthritis (OA) is facilitated by excessive knee loading. Theoretical models of knee joint loads demonstrate that muscular contributions likely relate strongly to the load transmitted through the knee. The relationship between knee loading with muscle strength and muscle power in people with knee OA remains unclear. The purpose of this study was to determine the extent to which the variance in knee extensor strength and power explain variance in loading magnitudes in participants with clinical evidence of knee OA. Methods: Participants between the ages of 40-70 who met the American College of Rheumatology clinical criteria for OA were recruited. The knee adduction moment (KAM) was measured during gait trials using Optotrak Certus position sensors (NDI, Waterloo, Canada) and a synchronized floor-mounted force plate (AMTI, Watertown, MA, USA). Rigid, infrared marker clusters were secured to the sacrum, thigh, shank and foot of the study leg. Participants ambulated barefoot at self-selected speeds until five trials were captured. The KAM waveform was generated using inverse dynamics using commercial software (Visual 3D, C-Motion, Inc., Germantown, MD, USA). Loading magnitude was quantified as the mean non-normalized knee adduction moment impulse to reflect the total medial knee load encountered during gait. Muscular contributions were knee extensor strength and power. For strength, five maximal effort isometric knee extensor (MVIC) contractions were performed with the knee at 60°, where the peak torque value was normalized to body mass (Nm/kg). For power, ten isotonic contractions with the resistance set at 25% of MVIC were performed as quickly as possible to measure power (Watts), where the middle 5 contractions were averaged and represented knee extensor power. Covariates included age, sex, knee pain and obesity. Knee pain was measured using the pain subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS-pain) while obesity was characterized by abdominal circumference (mm). The relationship between loading magnitude with knee extensor strength and power was examined using two sequential forward linear regression models, after controlling for age, sex, knee pain and obesity. Results: Fifty-three adults (61.6 ± 6.3 years, 11 men) participated. Loading magnitude was correlated with sex (r=-0.29, p<0.05), where males had greater loading magnitudes than females (13.61±10.72 and 8.82±4.86; p<0.05). Loading magnitude was also correlated with abdominal circumference (r=0.46, p<0.05), and knee extension power (r=0.44; p<0.05). Regression analysis between loading magnitude and knee extensor strength showed that 22% of the variance in the loading magnitude was explained by the covariates in the model (p=0.003), not knee extensor strength (p=0.66). Regression analysis between loading magnitude and knee extension power revealed that 30.2% of the variance in loading magnitude was explained by the model (p=0.01), with knee power contributing 9.2% (p<0.05). Conclusions: Knee extensor power is a more important parameter than isometric knee strength in understanding loading magnitude during gait in knee OA. Further examination into the relationship between knee power and knee OA may provide insight into loading and muscular changes during symptomatic and structural disease progression.