Quantitative magnetic resonance imaging (QMRI) techniques, including T1ρ and T2 relaxation mapping, are utilized to indirectly assess articular cartilage composition and health. Previous work has quantified the effects of acute loading on articular cartilage composition via T1ρ and T2 mapping in healthy individuals.1–3 One current limitation of the previous work1–3 is a lack of post recovery-based measures of cartilage composition and function. Understanding the effects of acute loading experienced during exercise, as well the recovery rate of cartilage post-exercise, are limited.4 Understanding the ability of cartilage to recover from acute loading as experienced during exercise would prove beneficial in informing safe exercise protocols in populations with pre-existing joint degeneration and symptoms.
In this issue of JMRI, Kessler et al10 measured compositional response of the femoral, tibial, and patellar articular cartilage to exercise-induced loading and compared these compositional changes to intrasession-based repeatability of T1ρ and T2 mapping. This study utilized 10 healthy knee joints to measure the repeatability of T1ρ and T2 relaxation times, with and without knee repositioning, between two successive MRI scans. Baseline T1ρ and T2 imaging of nine healthy knee joints was performed prior to a 5-minute exercise bout consisting of a unilateral stepping-based protocol to acutely load the knee joint. Immediately following exercise, these nine knee joints underwent four rounds of T1ρ and T2 imaging over a 45-minute time span to measure recovery of the cartilage composition.
The authors indicate that repeatability of T1ρ and T2 relaxation values was most affected by repositioning of the knee joint. The authors provided the smallest detectable differences in T1ρ and T2 values as a form of measurement error for use in future studies. Similar to previous work,1–3 the results of this study demonstrated an overall decrease in T1ρ values of the patellar, femoral, and lateral tibia cartilage as well as decreases in T2 values within the femoral and lateral tibia cartilage immediately after exercise. Conversely, medial tibia T1ρ and T2 values as well as patellar T2 values increased immediately after exercise. Post exercise-based imaging indicated slight compositional recovery in T1ρ compared to T2, indicating a potentially more rapid recovery of the proteoglycan concentration than the collagen network of the articular cartilage. The authors suggest that T1ρ may be more sensitive in detecting changes in cartilage composition after acute loading.
Current guidelines5,6 suggest exercise as a form of conservative treatment of osteoarthritis (OA). As the number of clinical trials7–9 to assess the effects of exercise on reducing OA-related symptoms continues to increase, there is a growing need to assess the effects of these exercise-based interventions on cartilage health. More specifically, implementation of QMRI to quantify the effects of these exercise-based interventions on cartilage composition would be beneficial in understanding the long-term clinical outcomes of these interventions on cartilage health in the OA population. This study by Kessler et al10 provides an initial step towards the implementation and clinical interpretation of changes that occur in cartilage composition as an effect of exercise.
References
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