Research suggests that obesity influences the development of Achilles tendinopathy to a greater degree than other types of foot and ankle pain. This phenomenon will become increasingly important to lower extremity practitioners as global obesity rates continue to rise.
By Ryan T. Scott, DPM, AACFAS, and Christopher F. Hyer, DPM, MS, FACFAS
Obesity is a rising epidemic in the US. A recent report published by the Centers for Disease Control and Prevention noted that more than one-third of adults (35.7%) and 17% of adolescents were classified as obese (body mass index [BMI] higher than 25)1 and, in July 2013, the American Medical Association formally recognized obesity as a disease.2 Significant complications associated with an increase in BMI are well documented, and include hypertension, diabetes, and musculoskeletal conditions. In 2008, medical costs associated with obesity were $147 billion, and annual medical costs for people who are obese were $1429 higher than those of normal-weight individuals.1
The World Health Organization currently recommends attention and further investigation into the emerging relationship between obesity and tendinopathy.3,4 According to Schweitzer, in both traumatic injury and tendinopathy, the Achilles tendon is the most frequently injured tendon in the musculoskeletal system.5 Achilles tendinopathy is a common condition characterized by pain during activities that place load on the Achilles tendon.6 Holmes and Lin found that 59% of men and 64% of women complaining of Achilles tendinopathy had a BMI of more than 30.7
Achilles tendon pain can have multiple presentations, including insertional and noninsertional tendinitis (Figure 1). Insertional tendinopathy, which results from recurrent stress on the attachment site of the Achilles tendon, is classically considered the hindfoot etiology more commonly associated with increased BMI. Changes in vascularity, hypertrophic inflammatory tissue, and chronic tearing of the distal Achilles tendon typically characterize this type of tendinopathy. As chronic insult and overuse to the Achilles tendon continues, researchers have noted a loss of healthy type 1 collagen and an increase in inflammatory type 3 collagen that leads to further tendinopathy.8,9 Because of the mechanical recruitment of the hindfoot in the push-off phase of ambulation, insertional tendinopathy is more common than noninsertional pathology.
Recent evidence suggests the amount of fat distribution may be a risk factor for Achilles tendinopathy.4,10 Abate et al noted that overweight sedentary individuals showed Achilles tendon thickness values significantly higher than normal-weight sedentary individuals.11 They found Achilles tendon sonographic abnormalities were more frequently observed in the obese population than in their nonobese counterparts. They also noted that intratendinous microvessels were more common among overweight individuals compared with normal-weight individuals.
Possible etiologic factors
Our clinical observations lead us to believe that the increased thickness in the Achilles tendon is most likely due to chronic inflammation from the overload syndrome typically associated with an increase in BMI. It is also possible that increased thickness is a conversion of healthy type I collagen to inflammatory type III collagen secondary to chronic damage to the Achilles tendon.
Increases in central fat distribution are closely related to insulin resistance and other metabolic abnormalities.6 Impaired insulin sensitivity has been linked to systemic chronic low-grade inflammation, which can potentially disrupt tendon healing.6 Diabetes has been shown to cause degeneration of tenocytes, vascular proliferation, and chondrocyte-like tendon cells in a histological study performed on the Achilles tendon of leptin-deficient mice.12
Abate et al have also examined the plantar fascia and Achilles tendon in patients with increased BMI and diabetes.11 They noted a weak correlation between BMI and Achilles tendon thickness in patients with type 2 diabetes. They found a stronger correlation, however, between BMI and the thickness of the plantar fascia in the same cohort. The researchers concluded the chronic inflammatory syndrome associated with diabetes has potential to increase the thickness of both tendons and ligaments.
As pathologic changes continue in the Achilles tendon, inflammation and pain increases, reducing the likelihood that the patient will engage in physical activity. Decreased activity levels lead to increased adiposity, creating a vicious circle. Studies report that, due to inactivity, 40% of patients with Achilles tendinopathy gained an average of roughly 10 pounds a year.13,14
Our recent publication demonstrated an association between BMI and Achilles tendinopathy.15 We retrospectively reviewed charts for 197 patients with Achilles tendinosis or tendinitis, and compared the BMI for those patients to the BMI for 100 random new patients, excluding Achilles pathology, plantar fasciitis, and surgical consults. There were 84 women and 113 men in the Achilles tendinopathy group, and 38 men and 62 women in the control group. The Achilles group had a mean age of 52.77 ± 11.8 years (range, 21 years to 82 years), while the control group had a mean age of 42.74 ± 12.1 years (range, 21 years to 78 years). We used InStat software for the statistical analysis.
We hypothesized that increasing BMI would be correlated with a higher incidence of Achilles tendon pathology. BMI in the Achilles tendinopathy group was 34.69 ± 7.54 (17.9–75.9), compared with 30.56 ± 7.55 (19.7–61.5) in the control group. It should be noted that age difference between the two cohorts was statistically significant (52.77 years vs 42.74 years, p < .001), perhaps reinforcing the involvement of age-related degenerative changes. However, the patients with Achilles pathology exhibited a significantly higher BMI than non-Achilles patients (p < .001) even after controlling for age.
Klein et al performed a case-control study that included 472 patients with a diagnosis of Achilles tendinopathy seen from 2002 to 2011.16 Those patients were matched with 472 patients who presented to the same clinic with other types of foot pain. The Achilles tendon patients had a significantly higher BMI than those in the control group (30.2 ± 6.5 vs 25.9 ± 5.3, p < .001). Overweight and obese patients were 2.6 to 6.6 times more likely to present with Achilles tendinitis than those with normal BMI. An elevated risk of presenting with Achilles tendinitis was also noted at higher BMI categories. However, BMI did not appear to affect treatment outcomes, whereas age did. Patients in the Achilles tendinitis group older than 65 years were at the greatest risk of not responding to conservative care. The authors concluded that BMI plays a role in the development of Achilles tendinopathy but does not appear to influence patient response to conservative treatment.
These findings lead us to believe that overuse and age are the most significant factors contributing to pathology of the Achilles tendon. Klein et al’s similar findings reinforce this hypothesis.16 Our findings and those of Klein et al are consistent with the findings of Holmes and Lin, who found that obesity was significantly associated with Achilles tendinopathy in both men and women (with p-values of .025 and .001 respectively).7
Interventions and BMI
Operative and nonoperative treatments for Achilles tendinopathy have been well documented in the literature.
According to Paavola, conservative measures are usually attempted in combination for three to six months, but may be unsuccessful in up to 25% of patients.17 Physical therapy, activity modification, nonsteroidal anti-inflammatory medications, custom orthotic devices, heel lifts, night splints, and immobilization are some of the most commonly utilized nonoperative modalities.18
Verrall et al showed promising outcomes following an aggressive course of eccentric stretching of the posterior muscle group (gastrocnemius and soleus) in athletes with either insertional or noninsertional Achilles tendinopathy.19 Wasielewski and Kotsko evaluated the effectiveness of eccentric stretching for the treatment of Achilles and patellar tendinopathy.20 A systematic review compared eccentric stretching, concentric stretching, night splinting, and physical agents. The researchers noted that, in most trials, tendinosis-related pain was reduced with eccentric exercise over time. The Achilles tendon study by Wasielewski and Kotsko demonstrated that eccentric stretching decreased pain relative to the control group. They concluded that eccentric stretching may reduce pain and improve strength for the treatment and management of Achilles tendon pathology.20
The authors of this paper utilize similar physical therapy protocols for obese patients and nonobese patients, and have not noted any difference in the efficacy of physical therapy associated with BMI. As noted above, Klein et al16 found that BMI did not influence response to conservative treatment in 472 patients presenting with Achilles tendinitis. In addition, a 2008 study by Knobloch et al21 found that BMI did not influence the likelihood that a patient with Achilles tendinopathy would or would not be compliant with a 12-week eccentric training program.
Some studies suggest, however, that exercise interventions for Achilles tendinopathy may be more effective in athletic patients than in sedentary patients, including those with elevated BMI. A 2007 study by Sayana and Maffuli22 assessed the effectiveness of a 12-week eccentric calf strengthening exercise program in 34 sedentary patients (average BMI, 28.6). They found that nearly half (15) of the patients did not improve with exercise, and seven patients who had completed six months of conservative therapy without significant improvement ended up undergoing surgery.
The findings of a 2013 study by Wearing et al23 may offer an explanation for the apparent discrepancy. This study used sonography to assess Achilles tendon thickness before and immediately after weight-bearing ankle exercises in 20 healthy men who were categorized as “low normal weight” (BMI less than 23) or overweight (BMI higher than 27.5). They found that the acute transverse strain response (calculated based on change in tendon thickness) of the Achilles tendon in the overweight group was almost half that of the low normal weight group, and hypothesized that the structural tendon changes associated with obesity impair the tendon’s ability to respond to load.
On the other hand, surgical intervention has been widely accepted for the treatment of Achilles tendinosis (Figure 2). It has been noted in the literature that up to 85% of symptomatic patients who undergo open repair for Achilles tendinopathy fare better than those treated with conservative therapy.17 There is also limited published evidence suggesting that BMI does not adversely affect surgical outcomes in patients with Achilles tendinopathy. Maffuli et al24 found that female patients who underwent surgery for chronic recalcitrant Achilles tendinopathy experienced more prolonged recovery, more complications, and a higher risk of subsequent surgery than male patients, but there was no significant difference in BMI between the two groups.
Surgical procedures include excision of the retrocalcaneal bursa, resection of the prominent retrocalcanal exostosis, debridement of degenerative and calcific areas within the Achilles tendon, flexor hallucis longus (FHL) fasciotomy, and FHL tendon transfer. Achilles tendon debridement can be accomplished through the surgeon’s preferred approach. Recently, Nunley et al demonstrated the central tendon splitting exposure allows direct access to the posterior superior bony growth, as well as visualization of the most diseased aspect of the tendon.25 This method is advantageous as it spares both the medial and lateral insertion slips of the Achilles tendon into the calcaneus. FHL tendon transfer has been associated with a loss of overall plantar flexion strength, with ranges reported from 3.9% to 30%.26
As obesity continues to rise, we as clinicians will face an epidemic of foot and ankle injuries and tendinopathies. An appropriate algorithm and a multidisciplinary approach for the management of Achilles tendinopathy will lead to improved clinical outcomes for patients.
Ryan T. Scott, DPM, AACFAS, is a fellowship-trained foot and ankle surgeon in private practice at the CORE (Center for Orthopedic Research and Education) Institute in Phoenix, AZ. Christopher F. Hyer, DPM, MS, FACFAS, is a fellowship-trained foot and ankle surgeon in private practice at Orthopedic Foot and Ankle Center in Columbus, OH.
1. Overweight and Obesity. Centers for Disease Control and Prevention website. http://www.cdc.gov/obesity Accessed January 3, 2014.
2. AMA Adopts New Policies on Second Day of Voting at Annual Meeting. American Medical Association website. http://www.ama-assn.org/ama/pub/news/news/2013/2013-06-18-new-ama-policies-annual-meeting.page Published June 18, 2013. Accessed January 3, 2014.
3. Obesity: Preventing and managing the global epidemic. Report of a WHO consultation. World Health Organ Tech Rep Ser 2000; 894:i-xii, 1-253.
4. Gaida JE, Cook JL, Bass SL. Adiposity and tendinopathy. Disabil Rehabil 2008;30(20-22):1555-1562.
5. Schweitzer ME,Karasick D. MR imaging of disorders of the achilles tendon. AJR Am J Roentgenol 2000;175(3):613-625.
6. Gaida JE, Alfredson H, Kiss ZS, et al. Asymptomatic achilles tendon pathology is associated with a central fat distribution in men and a peripheral fat distribution in women: A cross sectional study of 298 individuals. BMC Musculoskelet Disord 2010;11:41.
7. Holmes GB, Lin J. Etiologic factors associated with symptomatic achilles tendinopathy. Foot Ankle Int 2006;27(11):952-959.
8. Józsa L, Balint BJ, Reffy A, Demel Z. Fine structural alterations of collagen fibers in degenerative tendinopathy. Arch Orthop Trauma Surg 1984;103(1):47-51.
9. Maffulli N, Ewen SW, Waterston SW, et al. Tenocytes from ruptured and tendinopathic achilles tendons produce greater quantities of type III collagen than tenocytes from normal achilles tendons. An in vitro model of human tendon healing. Am J Sports Med 2000;28:499-505.
10. Gaida JE, Ashe MC, Bass SL,Cook JL. Is adiposity an under-recognized risk factor for tendinopathy? A systematic review. Arthritis Rheum 2009;61(6):840-849.
11. Abate M, Schiavone C, Di Carlo L, Salini V. Achilles tendon and plantar fascia in recently diagnosed type ii diabetes: Role of body mass index. Clin Rheumatol 2012;31(7):1109-1113.
12. Ji J, Wang Z, Shi D, Gao X, Jiang Q. Pathologic changes of Achilles tendon in leptin-deficient mice. Rheumatol Int 2010;30(4):489-493.
13. Hill JO, Wyatt HR. Role of physical activity in preventing and treating obesity. J Appl Physiol (1985) 2005;99(2):765-770.
14. Olsen RH, Krogh-Madsen R, Thomsen C, et al. Metabolic responses to reduced daily steps in healthy nonexercising men. JAMA 2008;299(11):1261-1263.
15. Scott RT, Hyer CF, Granata A. The correlation of Achilles tendinopathy and body mass index. Foot Ankle Spec 2013;6(4):283-285.
16. Klein EE, Weil L, Jr, Weil LS Sr, Fleischer AE. Body mass index and Achilles tendonitis: A 10-year retrospective analysis. Foot Ankle Spec 2013;6(4):276-282.
17. Paavola M, Kannus P, Järvinen TA, et al. Achilles tendinopathy. J Bone Joint Surg Am 2002;84-A(11):2062-2076.
18. Irwin TA. Current concepts review: insertional achilles tendinopathy. Foot Ankle Int 2010;31(10):933-939.
19. Verrall G, Schofield S, Brustad T. Chronic achilles tendinopathy treated with eccentric stretching program. Foot Ankle Int 2011;32(9):843-849.
20. Wasielewski NJ, Kotsko KM. Does eccentric exercise reduce pain and improve strength in physically active adults with symptomatic lower extremity tendinosis? A systematic review. J Athl Train 2007;42(3):409-421.
21. Knobloch K, Schreibmueller L, Longo UG, Vogt PM. Eccentric exercises for the management of tendinopathy of the main body of the Achilles tendon with or without an AirHeel brace. A randomized controlled trial. B: Effects of compliance. Disabil Rehabil 2008;30(20-22):1692-1696.
22. Sayana MK, Maffuli N. Eccentric calf muscle training in non-athletic patients with Achilles tendinopathy. J Sci Med Sport 2007;10(1):52-58.
23. Wearing SC, Hooper SL, Grigg NL, et al. Overweight and obesity alters the cumulative transverse strain in the Achilles tendon immediately following exercise. J Bodyw Mov Ther 2013;17(3):316-321.
24. Maffuli N, Testa V, Capasso G, et al. Surgery for chronic Achilles tendinopathy produces worse results in women. Disabil Rehabil 2008;30(20-22):1714-1720.
25. Nunley JA, Ruskin G, Horst F. Long-term clinical outcomes following the central incision technique for insertional achilles tendinopathy. Foot Ankle Int 2011;32(9):850-855.
26. Decarbo WT, Hyer CF. Interference screw fixation for flexor hallucis longus tendon transfer for chronic Achilles tendonopathy. J Foot Ankle Surg 2008;47(1):69-72.