Introduction

Among the marathon runners, the annual incidence of muscle and bone injury is as high as 90%, for which the knee joint is most frequently injured. At present, scholars have different views on the impact of marathon running on knee cartilage. Some believe that repeated excessive stress during marathon running and training could exceed knee joint cartilage load capacities, resulting in cartilage injury and secondary knee osteoarthritis, while others believe that the knee joint can withstand the high impact force of marathon running with no cartilage loss[1]. The knee joint contains hyaline cartilage that does not easily repair. A marathon runner might suffer knee cartilage damage from a high-impact long-distance race, leading to biochemical or morphologic cartilage changes. Magnetic resonance imaging (MRI) is a safe and noninvasive method to image knees, and when combined with post-processing, can quantitatively assess articular cartilage thickness, morphology, and biochemical components changes. Changes in T2* values reflect the combined changes of transverse relaxation time and magnetic field non-uniformities and is sensitive to collagen fiber anisotropy and water content in articular cartilage. Therefore, this method is often used to study early cartilage matrix composition changes. In this study, we assessed the extent to which knee cartilage can be damaged in the marathon runners using T2* mapping and high-resolution 3D MRI. Then, we quantitatively investigated the morphologic changes and biochemical components of knee cartilage.

Methods

We recruited 15 non-professional marathon runners for this study. At last 8 runners (4 males, 4 females) were included. The participants were between 21 and 37 years of age and had a mean body mass index (BMI) of 17.6 -27.2 kg/m2. Inclusion criteria were (1) age between 18- 40 years, (2) a BMI< 28 kg/m2; (3) no history of knee joint trauma, surgery, or infections, and (4) no history of chronic diseases requiring long-term drug therapy. The exclusion criteria were (1) knee joint trauma occurring during the study period; (2) pre-competition images showing morphologic injury of the articular cartilage; (3) knee joint pain or other positive sign; and (4) MRI contraindications. The right knee joint of each participant was examined using a 3 Tesla (3T) MR scanner (MAGNETOM Verio, Siemens Healthcare, Erlangen, Germany) one week before, and 12 hours and 2 months after a race. A 2D gradient multi-echo sequence was used for the T2*mapping. A 3D-double echo steady-state (DESS) sequence was used for high-resolution morphologic imaging. The knee joint cartilage was segmented and divided into 21 subregions using prototypic software (MR Chondral Health, version 2.1, Siemens Healthcare, Erlangen, Germany). The results from the automatic segmentation were manually fine tuned .The subregions are shown in Figure 1, and segmented cartilage partitions are shown in Figure 2. The T2* value and cartilage volume and thickness of each subregion were derived accordingly. A paired t-test was used to compare the cartilage before and after marathon running. P-values<0.05 were considered statistically significant.

Results

A significant difference in the cartilage thickness of the FLC and TLC was found between before and 12 hours after running (P<0.05; Figure 3). The cartilage volume was significantly different in the TLP between before and 12 hours after running (P<0.05; Figure 4). And there is a significant difference in the volume of the FLA and TMA between before and 2 months after running (P<0.05; Figure 4).A significant difference in the T2* value for the FMC, FMA, FLP, FLC, FLA, PLC, PLS,PMI, PMC,PMS, and TMC between before and 12 hours after running (P<0.05; Figure 5). Moreover, a significant difference in the T2* values of the FTM, FLP, and TMA were found between before and 2 months after running (P<0.05; Figure 3).

Discussion

From the results, we found that the significant statistical differences of cartilage volume and thickness was smaller than that of T2* value, maybe indicating that changes in the T2* value were more obvious than volume and thickness measurements when evaluating cartilage. When T2* values were compared before, and 12 hours after marathon running, most values increased, indicating that the water content of the cartilage and the direction of the collagen fibers changed during marathon running[2]. However, by comparing the T2* values before and 2 months after running, we found that most cartilage returned to pre-race levels two months after marathon running and that to a certain degree, changes in cartilage after long-distance running could be recovered. According to our study, the cartilage changes caused by marathon running may be recovered after 2 months resting.

Conclusions

Biochemical imaging is more sensitive than morphologic examinations to study early changes in cartilage. We found that the T2* value of knee cartilage in marathon runners showed a trend of "first rising and then decreasing," suggesting that articular cartilage showed a degree of reversible change during marathon running.

Acknowledgements

None.

References

[1] Hohmann E, Wortler K, Imhoff A B. MR imaging of the hip and knee before and after marathon running[J]. Am J Sports Med, 2004, 32(1): 55-9. [2] Morgan P, Nissi M J, Hughes J, et al. T2* Mapping Provides Information That Is Statistically Comparable to an Arthroscopic Evaluation of Acetabular Cartilage[J]. Cartilage, 2018, 9(3): 237-240.