Background Recent osteoarthritis (OA) studies propose vastus medialis (VM) muscle surface as a variable associated with cartilage volume loss over time. However, such muscle area may also include a significant proportion of fatty infiltration which may influence the knee mechanics/metabolism.

Objectives We contrasted the muscle fatty infiltration with cartilage volume loss and changes in bone marrow lesions (BMLs) assessed by MRI using data from a recent randomized clinical trial in knee OA¹.

Methods A subgroup of 143 patients from the according-to-protocol population of a 2-year randomized clinical trial evaluating the impact of licofelone vs. naproxen and having MRI acquisitions at baseline and 2 years were studied. MR images of the VM (mm²) were evaluated semi-automatically and VM percentage of fatty infiltration (%Fat) by a fully automated software. Univariate and multivariate analyses were performed to assess the relationship between VM area and its %Fat, cartilage volume loss, and BML change over 2 years.

Results The average %Fat/VM surface area was 6.3±3.9%. In the VM, the median baseline %Fat (5.1%) was chosen to separate patients with high vs. low fat content. Female (p=0.004) and higher BMI (33.2±5.7 vs. 30.2±5.3, p=0.001) and disability (WOMAC function 59±18 vs. 53±15, p=0.04) were associated with a higher %Fat. Change at 2 years in %Fat was univariately strongly associated with an increase in the BML score in the global knee (p=0.0002) and cartilage volume loss in the global knee (p=0.01), lateral compartment (p=0.02), plateau (p=0.01), and medial plateau (p=0.03). No correlations were found between %Fat change and change in symptoms over time. Multivariate analyses correcting for age, gender, BMI, and meniscal damage revealed correlations with %Fat for the global knee (p=0.011), plateau (p=0.012), and medial plateau (p=0.019) and condyle (p=0.027). Importantly, %Fat change was independently and strongly associated with BML change (p<0.0001). All the above changes were found irrespective of the treatment the patients had during the clinical trial.

Conclusions These data demonstrated, for the first time, that the %Fat in the VM was strongly associated with cartilage volume loss and the occurrence and progression of BMLs

References

1. Raynauld JP, et al. Ann Rheum Dis 2009;68:938-47.

Disclosure of Interest : J.-P. Raynauld Consultant for: ArthroLab Inc., J.-P. Pelletier Shareholder of: ArthroLab Inc., F. Abram Employee of: ArthroLab Inc., M. Dorais Consultant for: ArthroLab Inc., Y. Wang: None declared, J. Fairley: None declared, F. Cicuttini: None declared, J. Martel-Pelletier Shareholder of: ArthroLab Inc.

DOI 10.1136/annrheumdis-2014-eular.2369