Fig. 1

Muscle strength, CSA, activation (EMG) and FI of GM, TFL, VL and RF in the affected and contralateral limb of HOA patients. a Strength of the hip abductor, hip flexor and knee extensor muscles. b CSA of the GM, TFL, VL and RF. c EMG during hip abduction, hip flexion and knee extension. d Relative fatty infiltrated area on MRI fat fraction maps in GM, TFL, VL and RF in both limbs. e Fat fraction map generated from the transverse Dixon MR-sequence of the left hip in a 74-y old patient, indicating the three GM-regions (GM-ant, GM-mid, GM-pos) at the level of the upper border of the acetabular rim: The signal intensity of each pixel is directly proportional to the relative fatty infiltrated area of the muscle. ^x p < 0.1, ^xx p < 0.05, ^xxx p < 0.005 compared to the affected limb. * p < 0.05, ** p < 0.005, *** p < 0.0005 compared to the GM. CSA, cross sectional area; EMG, electromyography; FI, fatty infiltration; GM, gluteus minimus; HOA, hip osteoarthritis; RF, rectus femoris; TFL, tensor fascia latae; VL, vastus lateralis;