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|a Introduction: Gout affects approximately 15% of Maori and Pacific men, these men being at risk of early onset, severe disease with formation of gouty tophi and joint damage. Gout most frequently affects the foot, particularly the big toe and midfoot. This disease initially presents as self-limiting attacks of severe joint inflammation, and in the presence of persistent hyperuricaemia, tophaceous disease may also develop. Tophi are collections of monosodium urate crystals surrounded by chronic inflammatory cells and connective tissue. Tophi typically occur in both subcutaneous tissues and within affected joints, and may cause pain, cosmetic problems, mechanical obstruction of joint movement, and joint destruction. Despite the predilection of gout to the foot, the impact of gout on foot function is currently unknown and only case studies relating to hallux pain, tibial sesamoid pain and longitudinal tears in peroneal tendons have been reported in the literature. The aim of this study is to assess the intra-tester reliability of certain biomechanical tests to evaluate foot structure and function (plantar pressure measurements, gait parameters, range of motion at the ankle and first MTPJ and the foot posture index) in individuals with gout and to assess the differences between disability, impairment, foot structure and function between individuals with gout and non-gout controls. Subjects: A total of 25 patients with chronic gout with a mean age of 61.2 (11.7) years old were recruited from a rheumatology clinic within the Auckland District Health Board. A further 25 age-and sex-matched controls with a mean age of 57.3 (12.2) years old were recruited from AUT University. Methods: Disability, impairment, foot structure and foot function were assessed for the gout and the control group. Disability and impairment was assessed using the Health Assessment Questionnaire, Foot Function Index, Leeds Foot Impact Scale and Lower Limb Task Questionnaire. Foot structure was investigated using the Foot Posture Index, first metatarsophangeal joint (MTPJ) dorsiflexion, ankle dorsiflexion movement, subtalar joint and midtarsal joint motion, Foot Problem Score, tophi count and muscle strength of extrinsic and intrinsic foot muscles. Foot function was investigated using an in-shoe pressure system measuring mean peak plantar pressures and pressure-time integrals. Temporal-spatial gait parameters were evaluated, as well as peripheral sensation and vibration perception threshold. Plantar pressures were assessed using the Tekscan pressure insole system, gait parameters were measured using the Gaitmat walkway system, peripheral sensation and vibration threshold were assessed using 10gm monofilament and biothesiometer respectively. Intra-tester reliability was investigated using ICC, Standard Error of Measurement and Smallest Real Difference in the gout group for key measures (Foot Posture Index, first MTPJ dorsiflexion, ankle dorsiflexion movement, peak plantar pressures, pressure-time integrals and gait parameters). To investigate the significant difference between the groups, the left and right foot in gout were compared with the left foot of the control group using ANOVA with post-hoc comparisons. Non-parametric tests were used for muscle strength, peripheral sensation and Foot Problem Score and motion at the subtalar and midtarsal joints for comparison between the groups. Walking velocity, cadence and disability and impairment scores between the groups were assessed using an independent t-test with 95% confidence intervals. Significance for all these measures was set to 0.05 except for Chi square where a significance of 0.02 was set. Results: The ICC for the intra-tester reliability was excellent with low measurement error for the measured outcomes. The gout group recorded significantly higher disability and impairment scores than controls (p<0.01). Significant differences between the two groups were recorded for vibration pressure threshold, muscle strength, Foot Problem Score, first MTPJ dorsiflexion, foot motion and gait parameters (p<0.05). Significant differences were demonstrated under the toes for mean plantar pressures and under the lateral heel, midfoot and hallux regions for pressure-time integrals in the gout cases (p<0.05). Conclusions: Individuals with gout have reduced quality of life due to greater disability and impairment. The gouty foot is slightly supinated with reduced dorsiflexion at the first MTPJ. Rearfoot and forefoot motions are limited with a high incidence of digital deformities and dermatological lesions. The foot function in gout is characterized by reduced walking velocity, cadence, step and stride length. The plantar pressures are reduced under the toes with increased duration of loading under the hallux, lateral heel and midfoot regions. Further research using three-dimensional gait analysis is recommended to quantify motion at the foot and ankle joints and also to ascertain the role of proximal joints. Future work could be undertaken to evaluate the impact of acute gout on objective measures of foot function, and to determine predictors of poor foot function in patients with this disease. This will allow further work to investigate or formulate a podiatric management plan in conjunction with pharmacological therapy to improve impairment, disability and function in chronic gout.
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