Relationship between individual forces of each quadriceps head during low-load knee extension and cartilage thickness and knee pain in women with knee osteoarthritis

Abstract

BackgroundThis study aimed to clarify the individual forces of each quadriceps head during low-load contractions and to determine the associations between individual muscle force and cartilage thickness and symptoms in female knee osteoarthritis patients. MethodsTwenty-two women with painful knee osteoarthritis and 15 asymptomatic age-matched women (control group) participated in this cross-sectional study. Maximal knee extension strength and the cross-sectional area of each quadriceps muscle were measured. Shear modulus was calculated for each muscle during 20-Nm torque production by shear-wave elastography. Muscle force index was defined as the product of the cross-sectional area and shear modulus. Medial femur cartilage thickness was measured using an ultrasound B-mode image. Knee pain during gait was evaluated using a Numerical Rating Scale. Muscle force index, cross-sectional area, and maximal knee extension strength, which were defined as muscle functions, were compared between groups using the unpaired t-test. Correlation coefficients were calculated using muscle function, cartilage thickness, or pain. FindingsMaximal strength and vastus lateralis force index were smaller in the knee osteoarthritis group than in the control group (p < 0.001 and p = 0.005, respectively). In the knee osteoarthritis group, vastus medialis and vastus lateralis force indexes were positively correlated with cartilage thickness (r = 0.57 and r = 0.45, respectively), whereas the rectus femoris force index was negatively correlated with cartilage thickness (r = −0.45). The vastus lateralis force index was negatively correlated with knee pain (ρ = −0.56). InterpretationVasti force indices were positively associated with cartilage thickness; however, rectus femoris index was negatively associated in female patients with knee osteoarthritis.