Introduction: Gout is a chronic inflammatory joint disease characterised by painful flares of inflammatory arthritis which most commonly involve the lower limbs, in particular the first metatarsophalangeal joint (1MTP) and Achilles tendon . People with gout report high levels of foot pain during episodes of acute arthritis which reduces, but does not completely normalise, once the flares resolve [2, 3]. This persistent nature of foot pain is reflected in the ongoing lower-limb and foot-related impairment and disability reported by people with gout [2, 4]. This is emphasised in laboratory based studies which have observed walking difficulties [5, 6], reduced foot and ankle muscle strength  and foot-related structural and functional joint changes in people with gout [4, 8]. However, research related to foot function and disability in gout is limited. Objective: To determine relationship between impaired activity limitation and foot function in people with gout.
Methods: Forty-nine people with gout (45 male, 4 female) participated in the study. Participants were recruited from a rheumatology department at Counties Manukau District Health Board, Auckland, New Zealand. Participants met the 1977 preliminary American Rheumatism Association classification criteria for gout. Demographic and medical data was recorded for all participants. The study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12614001140640). Age, gender, ethnicity, body mass index (BMI), current medications and co-morbidities were recorded for all participants. In addition, gout disease duration, serum urate and the presence of subcutaneous tophi, were recorded for the gout participants. Activity limitation was measured using the Health Assessment Questionnaire (HAQ-II) . General body pain and first metatarsophalangeal joint pain over the past week were assessed using 100 mm Visual Analog Scales. Foot pain and disability was assessed using the 19-item Manchester Foot Pain and Disability Index . Lower limb disability during daily and recreational activities was assessed using the Lower Limb Task Questionnaire . Isometric muscle strength for ankle plantarflexion, dorsiflexion, inversion and eversion was measured using a hand-held dynamometer. Foot type was assessed using the Foot Posture Index. Gait velocity was assessed using the six-meter walk test. Plantar pressure was assessed using a TekScan MatScan® system during level barefoot walking at a self-selected, comfortable walking speed. Peak plantar pressure (kPa) and pressure time integrals (kPa*s) were computed for seven masked regions of the plantar foot. Statistical analysis was performed in SPSS v. 22.0 (SPSS Inc., Chicago, IL, USA). Demographic and participant characteristics were summarised with mean (SD) or n (%). To meet the assumption of independence for the purpose of all inferential analyses, included data were randomly selected from either right or left limbs form each participant. Differences in activity limitation by dichotomous variables were assessed using Mann-Whitney U tests and differences in activity limitation by ordinal variables were assessed using Kruskal-Wallis tests. Relationships were explored between activity limitation and continuous predictor variables using Spearman’s rho coefficients. Significant factors with a value of p < 0.15 were included in a stepwise multiple linear regression model and considered significant if p < 0.05. Preliminary analyses were conducted to ensure no violation of the assumptions of normality, linearity, multicollinearity and homoscedasticity.
Results: Participants had a mean (SD) age of 59 (13) years with a mean (SD) gout disease duration of 17 (13) years. The mean (SD) HAQ score was 0.47 (0.52). Bivariate correlations were found between the HAQ and gender, foot type, tophus count, generic pain, reduced daily and recreational activity, foot impairment, foot disability, reduced ankle plantarflexion, dorsiflexion, inversion and eversion muscle strength, increased pressure time integrals at the midfoot, lateral forefoot, lateral toes and reduced walking velocity. The stepwise regression analysis showed that reduced lower limb disability during daily activity, general body pain and increased pressure time integral at the midfoot were independently associated with the HAQ. Results for the multiple linear regression are summarised in Table 1.
Conclusions: The study identified reduced physical activity, general body pain and increased pressure time integral as predictors of impaired activity limitation. The finding of the significant correlation between and impaired activity limitation and increased midfoot pressure time integral may be reflective of gait adaptation due to the prolonged disease duration. The current study provides further insights into the dynamic function of the foot, which might assist in the development of interventions for pressure-related foot complaints in people with gout.
References: 1. Dalbeth N et al. Ann Rheum Dis 2013, 72:1545-8. 2. Rome K et al. Arthritis Care Res 2012, 64:384-8. 3. Roddy E et al. Rheumatology (Oxford) 2014, 53:163. 4. Stewart S et al. J Foot Ankle Res 2015, 8:41-9. 5. Rome K et al. Clin Biomech 2011, 26:90-4. 6. Stewart S et al. Gait Posture 2015, 44:18-22. 7. Stewart S et al. Clin Biomech 2015, in press. 8. Roddy E et al. Ann Rheum Dis 2007, 66:1374-7. 9. Fries JF et al. Arthritis Rheum 1980, 23:137-45. 10. Garrow AP et al. Pain 2000, 85:107-13. 11. McNair PJ et al. Arch Phys Med Rehabil 2007, 88:993-1001.