Background/Purpose:

Common risk factors of low back/lower extremity (LB/LE) joint pain are age, gender and body mass index (BMI), with women, older adults and overweight/obese individuals at increased risk. However, as foot motion during gait influences the movement pattern through the kinetic chain, foot structure and function may also be associated with lower extremity joint pain. Thus, the aim was to evaluate the relations of LB/LE pain to foot structure and function in a population-based study.

Methods:

Framingham Foot Study members with complete data on pain in the LB/LE joints as well as foot structure and function were included.

LB/LE joint pain was determined by the response to the NHANES-type question, “On most days do you have pain, aching or stiffness in your [low back, hips, knees, ankles, or feet]?” Bilateral and unilateral pain were weighted the same; responses were dichotomized to yes or no.

A pressure mat (Matscan, Tekscan Inc.) yielded foot structure and function data during bipedal standing, and while walking, using the two-step method. From these data, modified arch index (MAI), a measure of foot structure, and center of pressure excursion index (CPEI), a measure of foot function, were calculated.

Foot structure classification used MAI, with participants who had a foot in the top or bottom 20% of these values considered low arch or high arch, respectively, with the middle 60% the referent. Foot function classification used CPEI, with those who had a foot in the top or bottom 20% of these values denoted as supinators or pronators, respectively, with the middle 60% the referent.

Crude and adjusted (age, gender, BMI) logistic regression analysis (SAS, v. 9.3) determined associations of LB/LE pain to foot structure and function. Alpha was set to p≤0.05.

Results:

There were 1856 participants (age: 63.8 ± 8.9 years; BMI: 28.6 ± 5.6 kg/m²; 56% women). Of the sites assessed, low back pain was the most common at 34.1%, followed by knee pain at 29.4%; ankle pain was the least prevalent at 11.2% (Table 1).

Those with high arch foot structure had 26% lower odds of low back pain, whereas those with low arch structure had higher odds of knee (57%) and ankle (47%) pain. Supinated foot function during gait was associated with a 31% reduced odds of hip pain. After adjustment, odds ratios were attenuated and confidence intervals widened.

Conclusion:

A low arch structure, but not high arch structure or foot function, is associated with greater odds of lower extremity joint pain. The results suggest that differences in the kinetic chain may exist between those with high, low, and normal arch structure, and future studies should evaluate if differences in movement patterns are related to foot structure. Further, as this study is cross-sectional, longitudinal studies are needed to determine the cause-effect relations between foot structure and function to LB/LE pain.