Purpose or Case Report: 1. To determine short-term interval changes in T2 maps of knee cartilage of healthy boys before and after a 2-minute knee-squat exercise at 1.5T and 3T MRI; 2. To determine interval changes in T2 maps pre-exercise at 1.5T vs. 3T, and post-exercise at 1.5T vs. 3T; 3. To determine interval changes pre- and post-exercise among minimal-, moderate-, and high-activity subjects at 1.5T and 3T; and 4. To determine inter- and intra-reader reliability of 1.5 and 3T values.
Methods & Materials: 13 healthy boys (ages: 12-19) with different (8 moderate/high and 5 minimal) World Health Organization-recommended levels of physical activity were asked to follow a knee-squat protocol under supervision. Their knees were scanned at 1.5T and 3T pre- and post-exercise. T2 maps at TE=13,19,28 ms were obtained. 8 ROIs (weight-bearing [WB], non-weight-bearing [NWB], and whole areas) of femurs and tibias were analysed using MATLAB software. Qualitative analysis of gray-scale representations of T2 maps was performed.
Results: At 1.5T, in both medial and lateral ROIs, there were no significant differences observed between pre- and post-exercise T2 values. At 3T, there were significant differences between pre- and post-exercise T2 values in the lateral proximal tibia (P = 0.02), but not in other ROIs. At 1.5T and 3T, there were significant differences between pre-exercise values in medial femoral and tibial ROIs (P = 0.03, 0.002, 0.0002), and between post-exercise values in medial femoral and tibial ROIs (P = 0.006, 0.02, 0.001) and lateral femoral and tibial ROIs (P = 0.01, 0.017, 0.04, 0.0017, 0.0046). Intra-reader reliability of T2 maps was mostly excellent (ICC = 0.76 – 0.99), and inter-reader reliability, mostly ranged from moderate to excellent (ICC = 0.51 – 0.99). No significant differences were observed at any ROIs between pre- and post-exercise T2 values in minimal- vs. moderate- vs. high-activity participants.
Conclusions: Exercise does not have a short-term effect on the direction of cartilage fibers as represented by T2 maps, regardless of weekly activity levels. This suggests that short-term exercise may not deform cartilage significantly in vivo. Further investigation is needed to determine the long-term effects of exercise on the direction of collagen fibers as this information could direct safe integration of exercise into arthropathic treatment regimens.