Purpose: Foot pain is common and disabling in older people and a frequent reason for primary care consultation, despite this there are few prospective studies examining the course of foot pain. While there is evidence of distinct progressive trajectories at the knee, hip, and hand, it is not currently known if such trajectories exist at the foot and which patients are at risk of poor outcome. The aim of this study was to investigate foot symptom trajectories over seven years and ascertain whether progressive symptom trajectories are associated with potential generic and foot-specific prognostic factors.
Methods: Study participants were from a large population-based prospective cohort, the Clinical Assessment Study of the Foot (CASF). All adults aged ≥50 years registered with four general practices in North Staffordshire, UK were invited to take part in a postal health survey at baseline (2010/11). Those who reported foot pain in the previous 12 months at baseline were additionally invited to attend a research clinic that included an interview, physical examination including foot posture, anthropometric measures (height, weight) and foot radiographs. Follow-up by postal health survey was undertaken at 18 months, three years, 54 months and seven years.
The health surveys collected data on the severity (0-10 numeric rating scale [NRS]) and impact (Manchester Foot Pain and Disability Index [MFPDI] pain subscale) of foot pain; foot-specific functional limitation (MFPDI function subscale); coping strategies for foot pain; hallux valgus; general health (Short Form-12); physical performance (Short Physical Performance Battery); psychosocial factors (Hospital Anxiety and Depression Scale); and demographic and socioeconomic characteristics.
Symptom trajectories were identified using Latent Class Growth Analysis (LCGA) of repeated measures of self-reported foot pain severity (NRS) as the main analysis but also for foot pain impact and foot function (MFPDI pain and function subscales) as secondary analysis. Logistic regression was used to examine associations between symptom trajectories and baseline foot and person-level prognostic factors with adjustment of odds ratios (OR) for age, sex and body mass index (BMI).
Results: At baseline, 560 people with foot pain attended the research clinics. Response rates were 92% at 18 months, 87% at three years, 93% at 54 months and 85% at seven years. In total, 425 participants had data at baseline and at least two of the four follow-up time points and were included in the analysis.
The optimum LCGA model for foot pain severity in the last month was a 4-class model with the following trajectories: mild improving pain (n=109, 26%); moderate improving pain (n=179, 42%); moderate persistent pain (n=122, 29%); severe persistent pain (n=15, 4%) (Figure 1). Comparable trajectories were obtained for the MFPDI pain and function subscales.
Individuals with moderate and severe persistent foot pain over 7 years (32.2%, n=137) were compared to those with mild and moderate improving foot pain (67.8%, n=288). A persistent foot pain trajectory over 7 years was accompanied by greater foot-specific functional impairment (MPDI function subscale) at 7 years (aOR=1.43 [95%CI 1.16, 1.76]) after adjustment for baseline score, age, sex and BMI compared to those with an improving pain trajectory.
Compared with individuals with mild/moderate improving pain trajectories, those with moderate/severe persistent pain trajectories over 7 years did not differ significantly by age (aOR=1.00 [95%CI 0.98, 1.03]), female sex (0.95 [0.63, 1.43]), foot posture (left foot 0.97 [0.87, 1.09], right foot 0.98 [0.87, 1.09]) or radiographic foot OA phenotype at baseline (1st metatarsophalangeal OA 1.11 [0.65, 1.89], polyarticular OA 1.33 [0.73, 2.44] vs no/minimal OA), but were more likely to be overweight/obese (BMI ≥35.0 2.37 [1.11, 5.07] vs BMI 20.0-24.9). After adjustment for covariates, these less favourable long-term trajectories were associated with having greater foot-specific functional limitation (MFPDI) (1.81 [1.57, 2.08]), self-reported hallux valgus in either foot (2.36 [1.52, 3.64]), lower socioeconomic status (intermediate 2.65 [1.38, 5.09], routine & manual occupation 2.13 [1.23, 3.70] vs managerial & professional), atastrophizing (1.39 [1.26, 1.54]) and poorer physical health (0.93 [0.91, 0.95]) and mental health (0.95 [0.93, 0.97]) at baseline.
Conclusions: Over a 7-year period, one-third of individuals had persistent moderate to severe pain that was accompanied by a decline in their foot-specific functional impairment. Obesity and hallux valgus have been identified as prognostic factors. Further investigation to ascertain whether interventions targeting these factors improves long-term outcomes in people with foot pain are warranted.
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