Achilles tendinopathy is no different to any other overuse injury in that the cause is the cumulative loads in the tissue are beyond what the tissue can take. There are a number of factors that increases the cumulative loads and make the tissues more susceptible to those loads. One of the factors that is assumed to affect the load on the Achilles tendon is the body mass index (BMI). Today, there are two studies in the same journal on just that topic:
Body Mass Index and Achilles Tendonitis; A 10-Year Retrospective Analysis
Erin E. Klein, Lowell Weil Jr, Lowell Scott Weil Sr, Adam E. Fleischer
Foot Ankle Spec May 17, 2013
Introduction. High body mass index (BMI) has been implicated as an etiologic agent in Achilles tendonitis (AT) and may contribute to poorer treatment outcomes. The purpose of this study was to better elucidate the role of BMI in both the development and treatment of AT.
Methods. A matched case–control (1:1) study design was used. Matching criteria were age, gender, and year of presentation. Consecutive patients who presented with a diagnosis of AT between 2002 and 2011 at a single foot and ankle specialty clinic were identified. Patients who presented with other foot pain at the same clinic served as controls (CG). The AT group was further stratified into treatment responders and nonresponders. The main effect measure for both analyses was an adjusted odds ratio.
Results. A total of 944 patients (472 AT; 472 CG) were included. AT patients had higher BMI than those in the CG (30.2 ± 6.5 vs 25.9 ± 5.3, P < .001). Overweight and obese patients were 2.6 to 6.6 times more likely than those with a normal BMI to present with Achilles tendonitis (P < .001). There was also elevated risk of presenting with AT at higher BMI categories (Mantel–Haenszel χ2 = 8.074, P = .004). However, only age, not BMI, correlated with having failed conservative treatment among the AT group, with patients older than 65 years at the greatest risk (odds ratio = 2.4, 95% confidence interval = 1.5 to 4.1, P < .001).
Conclusion. BMI plays a role in the development of AT but does not appear to influence patient response to conservative treatment.
The Correlation of Achilles Tendinopathy and Body Mass Index
Ryan T. Scott, Christopher F. Hyer, Angela Granata
Foot Ankle Spec May 17, 2013
With this study we intend to determine if there is a correlation between body mass index (BMI) and Achilles tendon pathology. A retrospective chart review of 197 patients was performed with CPT codes of Achilles tendinosis/tendonitis. These 197 patients were then compared with 100 random new patient encounters excluding Achilles pathology, plantar fasciitis, and surgical consults. Statistical analysis was then performed to identify correlation of BMI to incidence of Achilles tendinosis compared with patients without Achilles pathology. A total of 197 Achilles tendon pathology patients (113 male, 84 female) were analyzed and had a mean age of 52.77 ± 11.8 years (21-82) with a BMI of 34.69 ± 7.54 (17.9-75.9). The control group had a mean age of 42.74 ± 12.1 years (21-78) and mean BMI of 30.56 ± 7.55 (19.7-61.5). A significant difference was found in mean BMI between the Achilles tendinopathy group versus the control group (P < .001). There was a very significant difference in age noted between the 2 cohorts (52.77 years vs 42.74 years, P < .001), perhaps reenforcing the involvement of age-related degenerative changes. In this study, patients with Achilles pathology exhibited a significantly higher BMI than non-Achilles patients (P < .001) even after accounting for age.
While both these studies were not exclusive to running and included all cases of Achilles tendinopathy and are of the weaker study design (retrospective case control), they do both confirm what is widely believed that obesity or a higher BMI is associated with Achilles tendinopathy. The mean BMI in the cases in both studies was pretty high (34 & 30; a BMI > 30 is usually considered ‘obesity’), so they were not necessarily very active individuals. The mechanism is assumed to be the increased loads associated with the higher bodyweight, though a previous study suggested that obesity is associated with structural changes in tendon that impairs intra-tendinous fluid movement in response to load. It appears as though a higher BMI not only probably increases the loads, but also affects the ability of the tissues to take the load – a double whammy!