Epidemiology of insertional and midportion Achilles tendinopathy in runners: A prospective cohort study.

backgroundAchilles tendinopathy (AT) is a common problem among runners. There is only limited evidence for risk factors for AT, and most studies have not defined the AT subcategories. No study has compared the incidence and risk factors between insertional AT and midportion AT, though they are considered distinct. This study aimed to assess incidence and risk factors of AT based on data from a large prospective cohort. The secondary aim was to explore differences in risk factors between insertional and midportion AT.

methodsParticipants were recruited from among registered runners at registration for running events. Questionnaires were completed at baseline, 1 month before the event, 1 week before the event, and 1 month after the event. Information concerning demographics, training load, registered events, and running-related injuries were collected at baseline. The follow-up questionnaires collected information about new injuries. A pain map was used to diagnose midportion and insertional AT. The primary outcome was the incidence of AT. Multivariable logistic regression analysis was applied to identify risk factors for the onset.

resultsWe included 3379 participants with a mean follow-up of 20.4 weeks. The incidence of AT was 4.2%. The proportion of insertional AT was 27.7% and of midportion AT was 63.8%; the remaining proportion was a combined type of insertional and midportion AT. Men had a significantly higher incidence (5%, 95% confidence interval (95%CI): 4.1%-6.0%) than women (2.8%, 95%CI: 2.0%-3.8%). AT in the past 12 months was the most predominant risk factor for new-onset AT (odds ratio (OR) = 6.47, 95%CI: 4.27 -9.81). This was similar for both subcategories of AT (insertional: OR = 5.45, 95%CI: 2.51-11.81; midportion: OR = 6.96, 95%CI: 4.24-11.40). Participants registering for an event with a distance of 10/10.55 km were less likely to develop a new-onset AT (OR = 0.59, 95%CI: 0.36-0.97) or midportion AT (OR = 0.47, 95%CI: 0.23 -0.93). Higher age had a significant negative association with insertional AT (OR = 0.97, 95%CI: 0.94-1.00).

conclusionThe incidence of new-onset AT among recreational runners was 4.2%. The proportion of insertional and midportion AT was 27.7% and 63.8%, respectively. AT in the past 12 months was the predominant risk factor for the onset of AT. Risk factors varied between insertional and midportion AT, but we could not identify clinically relevant differences between the 2 subtypes.