Background/Purpose:  Few studies have evaluated risk factors for patterns of foot pain in the general population, let alone over time.  An understanding of the possible predictors is the first step towards evidence-based interventions.  The purpose of this study was to examine risk factors for the onset and persistent of severe foot pain in men and women of the population-based Framingham Foot Study (FFS).

Methods: The longitudinal FFS included 648 participants who attended baseline (BL, 2002-5) and follow-up (FU, 2005-8) exams. The presence of foot pain at both BL and FU was queried using the question “On most days, do you have pain, aching, or stiffness in either of your feet?” If participants had foot pain, severity was then queried as mild, moderate or severe.  We dichotomized pain severity into 2 pain groups: moderate/severe versus none/mild for each foot.  Two separate analyses were done to examine 1) onset of moderate/severe pain versus none/mild pain and 2) persistent severe/moderate pain versus resolving severe/moderate pain. Two per-foot analyses using logistic regression and generalized estimating equations were used to examine the association between onset versus no foot pain and persistent versus resolving foot pain with potential risk factors (age, sex, body mass index (BMI), current smoking, knee pain, hip pain, and low back pain). Models were also examined by sex.

Results: At BL, average age was 65 years (range 36-86, SD=9), BMI was 29 kg/m² (SD=5), 51% were female and mean follow-up time was 3 years (range 1-6).  85% had no pain, 5% had onset, 7% had resolving, and 3% had persistent pain.  Female sex and current smoking was associated with a 2-3 fold increased odds of onset of pain.  Increased BMI was associated with a 16-20 fold increased odds of persistent versus resolving pain (Table).

In the sex-specific models, current smoking maintained its effect with onset pain, but was non-significant (OR_men=3.4, p=.07; OR_women=2.4, p=.11). The elevated odds of persistent pain remained for overweight (OR=14, p=.20) and obese men (OR=7, p=.10) but not for women. These non-significant results are not surprising given the small numbers in individual cells.

Conclusion: A larger study with longer follow-up is needed to identify risk factors and patterns of foot pain over time. Looking at foot disorders, in addition to pain, is also of interest. Nevertheless, in our study current smoking regularly appears to be linked with onset of moderate to severe foot pain, which is in agreement with common clinical observations that smokers develop more foot problems than non-smokers.  Additionally, increased BMI was suggestively linked to persistent moderate to severe foot pain compared to those whose pain resolved.