Short Achilles Lever Arm is a Risk Factor of Achilles Tendinopathy in Obese Patients

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Achilles tendinopathy is one of the most prevalent tendon disorders in obese people. Etiology of Achilles tendinopathy is complex. Multiple biomechanical risk factors were identified including high calcaneal inclination, foot pronation, etc. However, However, the relationship between Achilles lever arm length and Achilles tendinopathy remains unexplored. Purpose of study: To investigate if the length of Achilles lever arm is a risk factor of Achilles tendinopathy in obese patients. Methods: A retrospective review of 101 obese patients (BMI>30) with Achilles tendinopathy and 47 obese patients (BMI>30) without Achilles tendinopathy as control from 2020 through 2024 was completed at our institution. The Achilles lever arm is defined as the distance from Achilles insertion to the perpendicular line across the center of ankle’s rotation (line B in Figure 1). Three other lever arms were measured as well, including the arm length from the center of first metatarsal head to the perpendicular line across the center of ankle’s rotation (line A in Figure 1), and the arm length from the center of first metatarsal head to the insertion of Achilles tendon insertion (line C in Figure 1), and the arm length from Achilles insertion to the center of ankle’s rotation (line D in Figure 1). Statistical analyses, including Student’s t-test and Chi-square test, were performed using STATA. Results: 148 patients with BMI >30 were included. Mean age 52 years (range 23.4 - 84). Mean BMI 37.4 (range 30.1 - 57.6). 101 patients were included in Achilles tendinopathy group with mean BMI 38.1, and 47 patients without Achilles tendinopathy were included in control group with mean BMI 35.7. The difference of BMI in Achilles tendinopathy group and control group was not significant (BMI 38.1 vs 35.7. P>0.05). However, the length of the Achilles lever arm (line B, figure 1) in Achilles tendinopathy group was significantly shorter than that in control group (59mm vs 62.8mm, P< 0.01). The difference of other lever arm length of line A (132.6mm vs 136.3mm), line C (191.4mm vs 199.4mm) and line D (66.6mm vs 68.9mm) were not significantly different (P < 0.05). Conclusion: A shorter Achilles lever arm is a significant risk factor of Achilles tendinopathy in obese patients. This finding has important clinical relevance, suggesting that surgical techniques aiming at lengthening the Achilles lever arm may be a potential treatment option for Achilles tendinopathy.