Foot Posture and Ankle Dorsiflexion as Risk Factors for Developing Achilles Tendinopathy and Plantar Fasciitis: A Case-Control Study

Abstract

Background: Plantar fasciitis (PF) and Achilles tendinopathy (AT) are common injuries that primarily affect people engaged in sport or occupational weightbearing activities. Identifying modifiable risk factors is important for the treatment and prevention of these injuries. The purpose of this study was to evaluate whether foot posture or ankle dorsiflexion are risk factors for developing AT or PF, and if there were any differences between PF and AT patients.

Methods: This was a case-control study of 108 patients with PF and 114 patients with AT, compared to the same number of referred patients in 2 control groups never having had these injuries, matched for sex, age, body mass index (BMI), sport, and occupational weightbearing activities. Included patients were 20-65 years with ultrasonographic-verified PF or midsubstance AT. Foot posture was assessed using Foot Posture Index (FPI) classifying the feet into 3 categories: FPI 0-5 normal foot, 6-12 hyperpronated, <0 hypopronated. Ankle dorsiflexion was measured with a goniometer in weightbearing with straight and bent knee.

Results: Abnormal foot posture was associated with an increased risk for sustaining both AT (odds ratio [OR] 3.4-4.1) and PF (OR 3.2-3.8). Hyperpronation being the major reason for this association with ORs 5.4-5.5 compared with hypopronation with ORs 2.6-2.9. However, decreased dorsiflexion was not a risk factor: instead, there was an increased ankle dorsiflexion in patients with AT or PF compared with their control groups. Comparison between PF and AT patients demonstrated that PF affected mostly women, and AT mostly men, PF patients were 2.4 years (CI 0.2-4.5) younger, and had 25% more occupational weightbearing than AT patients. However, no differences in BMI or weightbearing physical activity was demonstrated.

Conclusion: Hypopronation and hyperpronation but not limited ankle dorsiflexion was associated with increased risk for AT or PF.

Keywords: Achilles tendinopathy; Achilles tendon tightness; ankle dorsiflexion; foot posture; foot posture index; plantar fasciitis.