Role of thigh muscle cross-sectional area and strength in progression of knee cartilage degeneration over 48 months - data from the Osteoarthritis Initiative

Abstract

Objective: To determine in a 48-month longitudinal study the association of thigh muscle cross-sectional area (CSA) and strength on progression of morphologic knee cartilage degeneration using 3T magnetic resonance imaging (MRI).

Design: Seventy Osteoarthritis Initiative (OAI) subjects aged 50-60 years, with no radiographic evidence of osteoarthritis (OA) and constant muscle strength over 48 months as measured by isometric knee extension testing were included. Baseline right thigh muscle CSAs were assessed on axial T1-weighted magnetic resonance (MR) images, and extensor to flexor CSA ratios were calculated. Degenerative knee abnormalities at baseline and 48-months were graded on right knee 3T MRIs using a modified whole organ MRI score (WORMS). Statistical analysis employed Student's t-tests and multivariable regression models adjusted for age, body mass index and gender.

Results: Extension strength was significantly and positively correlated with baseline thigh muscle CSA (r = 0.65, P < 0.001). Greater baseline total thigh muscle CSA was significantly associated with increase of cartilage WORMS scores over 48 months in patellar (P = 0.027) and trochlear (P = 0.038) compartments, but not in other knee compartments. Among specific muscle groups, CSA of extensors (P = 0.021) and vastus medialis (VM) (P = 0.047) were associated with patellar cartilage increase in WORMS. Baseline E/F ratio had a significant positive association with patellar WORMS cartilage score increase over 48 months, P = 0.0015. There were no other significant associations between muscle CSA/ratios and increase in WORMS scores.

Conclusion: Maintenance of proper extensor to flexor muscle balance about the knee through decreased E/F ratios may slow patellofemoral cartilage deterioration, while higher extensor and VM CSA may increase patellofemoral cartilage loss.

Keywords: Cartilage; Extension strength; Knee; MR imaging; Muscle cross-sectional area; Osteoarthritis.

Figure 1

Flowsheet demonstrating patient exclusion criteria.

Figure 2

Full-length femur radiograph (A) demonstrates method of obtaining slice selection in uniform manner that accounted for individual height/body size differences. The length of the femur from the superior aspect of the femoral head to the intercondylar notch was first measured, and the obtained measurement was divided by three to obtain the location of the distal-middle third junction of the femur. This length (18.335 cm) was then correlated with the appropriate axial MR slice (B).

Figure 3

Axial T1-weighted thigh MRIs at the distal one-third junction in patient (A) demonstrates extensor compartment (highlighted in red) and flexor compartment (highlighted in blue) with an E/F ratio of 1.01, in contrast to an axial image in a different patient (B) showing a much larger E/F ratio of 2.17.

Figure 4

Graphical depiction of relationships between various muscle strength (A) and CSA parameters– including total CSA (B), flexor CSA (C), extensor CSA (D), VM CSA (E), and E/F ratio (F)-- and the corresponding mean increase in subcompartmental cartilage WORMS scores associated with each group. Statistical significance was defined as p<0.05 (asterisk). MF=medial femur; LF=lateral femur; MT=medial tibia; LT=lateral tibia; Pat=patella; Tr=trochlea; Max=maximum cartilage score (any compartment); Men=meniscus; BMEP=bone marrow edema pattern.

Figure 5

Baseline sagittal DESS image (A) demonstrating patellar cartilage with small partial-thickness defect (bracket) in patient with high extensor-flexor ratio. 48-month follow-up MRI (B) demonstrates clear progression of the patellar cartilage lesion which is now a large full-thickness defect (arrows).