Analysis of Plantar Fasciitis Risk Factors Among Intercollegiate and Recreational Runners: A Matched Case-Control Study
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Context: Plantar fasciitis, the most common cause of inferior heel pain, afflicts as many as 10% of the U.S. population during their lifetimes, and is currently responsible for approximately 1,000,000 physician visits per year. Despite this prevalence, the etiology of plantar fasciitis is not well understood, particularly among physically active populations. Objective: To evaluate known and hypothesized risk factors for plantar fasciitis among running athletes to determine which outcome measures are most predictive. Design: Case-control. Setting: Laboratory setting. Patients or Other Participants: 71 intercollegiate and recreational runners completed all aspects of this study (age, 21.8 ± 3.7 yrs; height, 168.0 ± 11.9 cm; mass, 70.29 ± 18.14 kg). We employed a 2:1 ratio of healthy runners to injured runners with plantar fasciitis for the logistic regression analysis using a subset of 63 participants, creating 21 triads that were matched on sex, age and BMI. Interventions: None. Main Outcome Measurements: Body Mass Index (BMI), dorsiflexion active range of motion (AROM), dorsiflexion passive range of motion (PROM), longitudinal arch angle, navicular drop test, lower leg and foot length, and Foot Function Index-Revised. Statistical Analysis: A Group (2) x Limb (2) MANOVA was used to identify differences between the case and control groups and the involved/uninvolved limbs (α = 0.05). Odds ratios were calculated using conditional logistic regression in an effort to identify independent risk factors for plantar fasciitis. A secondary hypothesis investigated the extent to which reduced ankle dorsiflexion AROM, reduced longitudinal arch angle, and increased BMI were risk factors associated with the incidence of plantar fasciitis ( = 0.05). Results: MANOVA indicated that dorsiflexion AROM and PROM were significantly less in the plantar fasciitis group compared to the healthy control runners (P < 0.05). Injury status accounted for 10.6 % and 16.7% of variance in active and passive dorsiflexion range of motion, respectively. Results of the Cox regression analysis indicated that for the hypothesized model, decreased ankle dorsiflexion AROM, decreased longitudinal arch angle, and increased BMI significantly influenced the risk of incurring plantar fasciitis (χ2 = 11.046; P < 0.05). More specifically, each degree of decreased dorsiflexion AROM increased the risk of plantar fasciitis by 14.6% (OR = 1.146, P < 0.05). Conclusions: Our findings present strong evidence of a link between limited ankle dorsiflexion and plantar fasciitis among physically active individuals. Future research should involve longitudinal, prospective experimental designs with physically active individuals, using these same outcome measures in an effort to establish causal relationships with plantar fasciitis.