Abstract
Nearly nothing is known about the consequences of ultra-long-distance running on knee cartilage. In this mobile MRI field study, we analysed the biochemical effects of a 4,486 km transcontinental multistage ultra-marathon on femorotibial joint (FTJ) cartilage. Serial MRI data were acquired from 22 subjects (20 male, 18 finisher) using a 1.5 T MR scanner mounted on a 38-ton trailer, travelling with the participants of the TransEurope FootRace (TEFR) day by day over 64 stages. The statistical analyses focused on intrachondral T2* behaviour during the course of the TEFR as the main outcome variable of interest. T2* mapping (sagittal FLASH T2* weighted gradient echo) is a validated and highly accurate method for quantitative compositional cartilage analysis of specific weightbearing areas of the FTJ. T2* mapping is sensitive to changes in the equilibrium of free intrachondral water, which depends on the content and orientation of collagen and the proteoglycan content in the extracellular cartilage matrix. Within the first 1,100 km, a significant running load-induced T2* increase occurred in all joint regions: 44.0% femoral-lateral, 42.9% tibial-lateral, 34.9% femoral-medial, and 25.1% tibial-medial. Osteochondral lesions showed no relevant changes or new occurrence during the TEFR. The reasons for stopping the race were not associated with knee problems. As no further T2* elevation was found in the second half of the TEFR but a decreasing T2* trend (recovery) was observed after the 3,500 km run, we assume that no further softening of the cartilage occurs with ongoing running burden over ultra-long distances extending 4,500 km. Instead, we assume the ability of the FTJ cartilage matrix to reorganize and adapt to the load.
Highlights
Nothing is known about the consequences of ultra-long-distance running on knee cartilage
The amount of data pertaining to long-distance running has increased in recent decades, little is known about the consequences of ultra-long-distance running, such as multistage ultra-marathon (MSUM), on knee joint cartilage[26]
Consistent with the fact that cartilage areas with regularly high loads are stiffer than areas with lower loads[92], we found significant mean T2* differences between the superficial and deep layers throughout the TransEurope FootRace (TEFR) in all cartilage areas of the femorotibial joint (FTJ)
Summary
Nothing is known about the consequences of ultra-long-distance running on knee cartilage. Prolonged running burden over time is thought to alter the collagen network and lubricating proteoglycans, slowly wear out the articular cartilage, and cause microfractures in the subchondral bone[4,16] This hypothesis has not been proven, and clinical and radiographic cohort studies of regular long-distance running subjects, up to marathons, have shown no significance regarding knee OA incidence and progression in hip and knee joints without knee injury, poor muscle tone, obesity, or proprioceptive deficit[9,17,18,19,20,21,22,23,24]. In the femorotibial joint (FTJ), T2 value inequalities and variabilities between corresponding cartilage regions are correlated with the limited water mobility within an anisotropic rigid matrix[52] They mostly depend on the different degrees of stiffness and creep rates[53] needed in relation to degrees of biomechanical stress and loading (cartilage compression)[54], resulting in regionally different glycosaminoglycan (GAG) content and collagen fibril network orientation[55]. It is widely accepted that load-induced intrachondral T2 increases result from a loss of structural anisotropy of type II collagen matrix (spatial orientation of collagen fibrils) and from an increase in free cartilage water[41,47,56,57]
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