Objective: To detect by magnetic resonance imaging (MRI) the presence and type of knee injuries in non-professional runners after running an ultra-marathon, and to determine whether ultra-marathon running exacerbates pre-existing knee injuries or results in new permanent injuries.
Design: A prospective MRI study of one knee of 10 randomly selected participants who completed the Comrades Marathon between 1997 and 2002. Their knees were scanned 48 hours before the race, and 48 hours and 1 month after the race.
Setting: All scans were performed at the Radiology Department, Wentworth Hospital, Durban, and the University of KwaZulu-Natal.
Main outcome measures: Scores of all knee injuries detected on MRI scans immediately before the race, compared with the scores after the race.
Results: All scanned knees demonstrated an abnormal amount of joint fluid before the race; this increased immediately after the race in 5 runners and remained unchanged in another 5. At 1 month, 5 knees showed decreased joint fluid and 5 remained unchanged, but these were not the same runners as in the post-race groups. There was increased signal intensity in the distal patellar and quadriceps tendons in 4 runners before the race, which increased or remained the same on post-race scans in 6 knees. There was a decrease in signal intensity on scans taken 1 month later in 3 runners, with complete resolution in 2 and no change in 1. Old injuries to ligaments, tendons or other knee structures were unaffected by the race. No bone bruising, cartilage defects or meniscal abnormalities were observed. There was no significant difference in the pre- and post-race or 1-month scan scores.
Conclusions: The race appears to have had a detrimental effect on runners who started the ultra-marathon with tendinopathy, which worsened post-race by MRI criteria. One month after the race, the scan appearance of the overuse injury had either improved or resolved completely. Bone bruising or meniscal damage did not appear to occur, and the presence of increased joint fluid probably relates to stress or injury.