Thirty-seven percent of participants in the present study reported foot symptoms, slightly higher than the proportion reported in studies of adults 65 years of age and older, signifying that foot symptoms are also a common condition in non-elderly adults. Participants with foot symptoms were more likely than those without foot symptoms to report greater difficulty with self-reported and performance-based physical function (as indicated by the 8 foot walk), even when controlling for important covariates. These results among participants aged 45 years and older are consistent with prior studies that have examined adults 62 years and older, demonstrating a persistent relationship association even at younger ages. [2
The measure of self-reported physical function, the HAQ, includes questions about both upper and lower extremity function. A direct relationship between foot symptoms and lower extremity function can be easily appreciated. However, foot symptoms may affect ones overall confidence in his or her ability to complete physical tasks (functional self-efficacy). Thus, inclusion of a measure like the HAQ was important to attempt to reflect the functional self-efficacy associated with foot symptoms. Self-efficacy was not assessed specifically in the present study, but the results were independent of depressive symptoms, which have been shown to contribute to self-efficacy for general physical tasks. [22
Foot symptoms may affect physical function by contributing to altered gait patterns, ultimately reducing gait speed. This may explain the slower completion times noted among participants with foot symptoms during the 8-foot walk. In general, no association was observed between foot symptoms and timed chair stands comparing ≥ 12 to < 12 seconds. However, the presence of obesity positively modified this association; obese participants (BMI >30 kg/m2) with foot symptoms required more time to complete the chair stand task than those without symptoms, but this association was not observed among non-obese participants with and without foot symptoms. Thus, weight reduction may assist in diminishing the impact of foot symptoms on some functional activities.
Strengths of this study include that it is community-based, consists of African American and Caucasian men and women, and includes radiographic OA data and symptoms data of the knee and hip. Additionally, this is the largest study to date that includes assessment of foot symptoms and self-reported and physical function. One limitation of the present study is that conditions contributing to foot symptoms in this population are not known. Foot radiographs were not obtained, but it is unlikely that participants had arthritic and rheumatic conditions other than OA because participants with inflammatory conditions on knee or hip radiographs were excluded. Other conditions that may have contributed to foot symptoms, such as calluses, corns, hallux deformities, toe deformities, pes planus, heel spurs, plantar fasciitis, and neuropathy, were not included in these analyses, but will be the topic of future research. A comprehensive physical assessment of the foot may help identify musculoskeletal origins of foot symptoms in this population, but previous studies have demonstrated that some foot disorders, such as hallux valgus and toe deformities and especially if mild disease, may not be associated with foot symptoms or functional limitations. [5
] Another possible limitation is that results for women are only generalizable to women over the age of 50 because hip radiographs were obtained only for women who were at least 50 years of age due to radiation concerns with reproductive health. However, in contrast to prior comparable studies, [2
] the present study included middle-aged adults (at least 45 years of age). Additionally, whether the foot symptoms were acute or chronic in this population is not known because the duration of foot symptoms was not collected during study interview. Furthermore, a measure of self-reported physical function that was specific to the foot was not collected at baseline. Finally, due to the cross-sectional study design, a temporal relationship between foot symptoms and physical function cannot be inferred. A longitudinal analysis would assist in determining the possible contribution of foot symptoms to functional decline.
In summary, foot symptoms play an important role in poor physical function, independent of knee and hip symptoms and OA. Interventions for foot symptoms, including weight loss, foot orthotics, foot care strategies, and patient education on proper footwear, may be important for helping patients prevent or manage an existing decline in perceived and performance-based functional abilities. Screening strategies may be helpful in identifying patients with foot symptoms who are at risk of the development or progression of functional decline.