Background

Adipose tissue has recently gained interest as an independent imaging biomarker for osteoarthritis.

Purpose

To explore 1) cross-sectional associations between local subcutaneous fat (SCF) thickness at the knee and the extent of degenerative changes in overweight and obese individuals and 2) associations between local fat distribution and progression of osteoarthritis over 4 years.

Study type

Retrospective cohort study.

Population

338 obese and overweight participants from the Osteoarthritis Initiative cohort without radiographic evidence of osteoarthritis.

Field strength

3T: 3D-FLASH-WE; 3D-DESS-WE; T1w-SE; MSME.

Assessment

Baseline SCF thickness was measured in standardized locations medial, lateral and anterior to the knee and the average joint-adjacent SCF (ajSCF) was calculated. Right thigh SCF cross-sectional area was assessed. Quantitative cartilage T₂ relaxation times and semi-quantitative whole organ MRI scores (WORMS) were obtained at baseline and 4-year follow-up. WORMS_sum was calculated as sum of cartilage, bone marrow edema, subchondral cyst, and meniscal scores.

Statistical tests

Associations of SCF measures with baseline, and 4-year change in T₂ and WORMS were analyzed using regression models. SCF measurements were standardized using the equation ValueParticipant-MeanCohortStandard deviation . Analyses were adjusted for age, sex, physical activity, and BMI.

Results

Cross-sectionally, significant associations between lateral SCF, lateral compartment WORMS and T₂ were found ( ΔWORMSsum1SDchange in lateralSCF , [95% CI]: 0.53, [0.12-0.95], P < 0.05; ΔT₂ : 0.50, [0.02-0.98], P < 0.05). Moreover, greater lateral SCF was associated with faster progression of lateral WORMS_sum gradings (OR = 1.50, [1.05-2.15], P < 0.05). No significant positive associations were found for thigh SCF and WORMS_sum (P = 0.44) or T₂ measurements (medial: P = 0.15, lateral: 0.39, patellar: P = 0.75).

Data conclusion

Joint-adjacent SCF thickness was associated with imaging parameters of knee osteoarthritis, both cross-sectionally and longitudinally, while thigh SCF was not, suggesting a spatial association of SCF and knee osteoarthritis. Based on these findings, joint-adjacent SCF may play a role in the development and progression of knee osteoarthritis.

Level of evidence

4 TECHNICAL EFFICACY: Stage 5.

Articular cartilage damage and degeneration are among hallmark manifestations of joint injuries and arthritis, classically osteoarthritis. Cartilage compositional MRI (Cart-C MRI), a quantitative technique, which aims to detect early-stage cartilage matrix changes that precede macroscopic alterations, began development in the 1990s. However, despite the significant advancements over the past three decades, Cart-C MRI remains predominantly a research tool, hindered by various technical and clinical hurdles. This paper will review the technical evolution of Cart-C MRI, delve into its clinical applications, and conclude by identifying the existing gaps and challenges that need to be addressed to enable even broader clinical application of Cart-C MRI.