Poor vastus medialis muscle quality is associated with disrupted cartilage integrity in mild knee osteoarthritis

ObjectiveEarly knee osteoarthritis (KOA) presents as minor structural abnormalities in joint tissues, such as cartilage and subchondral bone, that cannot be assessed radiographically. Identification of a sensitive and convenient marker for early disease has the potential to enhance patient outcomes. This study determined 1) whether fat infiltration in muscle (i.e., muscle quality), as measured by ultrasound, is associated with structural abnormalities seen in early KOA and 2) which quadriceps muscles are appropriate as a novel marker for early KOA. MethodsParticipants with early symptomatic KOA (Kellgren Lawrence grade 1-2) underwent ultrasound assessment to measure the echo intensity of the vastus medialis and rectus femoris. The echo intensity corrected for ultrasound wave attenuation caused by subcutaneous fat was then calculated (i.e., corrected echo intensity). Structural abnormalities were assessed using the whole-organ magnetic resonance score (WORMS). A generalized linear mixed model was used to assess the relationship between the corrected echo intensity and WORMS score. ResultsForty-nine participants (ages: 44-78 years, 65.3% women) with 52 knees were included. After adjustment for covariates, increased corrected echo intensity (i.e., poor muscle quality) in the vastus medialis muscle was significantly associated with greater structural abnormalities, including disrupted cartilage integrity in the medial tibiofemoral joint. The association was not significant in the rectus femoris muscle. ConclusionIndividuals with poor muscle quality in the vastus medialis displayed compromised joint integrity. This study suggests that fat infiltration in vastus medialis assessed by ultrasound is an indicator of early symptomatic KOA.