Clinical Biomechanics

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1 Clinical Biomechanics 26 (2011) Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: Functional and biomechanical characteristics of foot disease in chronic gout: A case-control study Keith Rome a,, David Survepalli a, Alex Sanders a, Maria Lobo b, Fiona M. McQueen b,c, Peter McNair a, Nicola Dalbeth b,c a AUT University, Health & Rehabilitation Research Institute, Auckland, New Zealand b Auckland District Health Board, Auckland, New Zealand c University of Auckland, Auckland, New Zealand article info abstract Article history: Received 28 July 2010 Accepted 9 September 2010 Keywords: Gout Hallux Foot Plantar pressures Walking Disability Pain Objectives: Despite the predilection of gout to the feet, the impact of gout on foot function and biomechanics is currently unknown. The aim of this study was to describe the effects of chronic gout upon function and selected biomechanical parameters associated with gait. Methods: Twenty-five patients with a history of gout were compared with 25 age and gender matched control participants with no history of gout or other forms of arthritis. General function, foot specific disease activity and lower limb activities were determined using the Health Assessment Questionnaire, Foot Function Index (pain domain), and Leeds Foot Impact Scale respectively. Each patient also underwent a gait assessment that included plantar pressure measurements and an evaluation of temporal spatial gait parameters. Findings: Patients with chronic gout had higher levels of general and foot-specific disability, pain and impairment (Pb0.001). Significantly lower peak plantar pressures were observed in the hallux of patients with chronic gout (Pb0.05). Significantly higher pressure time integrals were observed in the cases at the midfoot (Pb0.05), but lower values were observed at the hallux (Pb0.05). Patients with chronic gout walked slower, with longer step and stride lengths compared to the controls. Interpretation: Patients with chronic gout experience pain and disability associated with their feet. Different toe-off strategies may account for functional changes and pain associated with foot problems in chronic gout Elsevier Ltd. All rights reserved. 1. Introduction Corresponding author. Tel.: x address: keith.rome@aut.ac.nz (K. Rome). Gout is a common form of arthritis caused by the inflammatory response to monosodium urate crystals within the joint. Initially, the disease presents as self-limiting attacks of severe joint inflammation, and in the presence of persistent hyperuricaemia, chronic gout may also develop with recurrent flares, tophi and chronic synovitis. It is well documented that gout has a predilection for the first metatarsophalangeal joint (1st MTPJ), with as many as 50 70% of first gout attacks occurring at this site (Grahame and Scott, 1970; Wright et al., 2007). However, the impact of gout on foot function has not been reported. The recent pursuit of objective gait data has yielded a better understanding of foot impairment in chronic disease conditions such as diabetes and rheumatoid arthritis (RA) (Turner and Woodburn, 2008). Objective gait data includes the measurement of temporal spatial parameters of gait such as walking speed, step and stride length. Plantar pressure measurements also provide useful information for clinicians and researchers regarding the structure and function of the foot, general mechanics of gait, and are a helpful tool to evaluate patients with foot conditions (Keijsers et al., 2009). Evaluating the function of the foot in patients with chronic gout may be helpful in understanding the pathways leading from underlying disease processes, to localised impairment and subsequently to loss of function. The aim of this study was to describe the functional and biomechanical characteristics of foot disease in chronic gout. 2. Patients and methods Twenty-five adult patients with a history of documented gout were recruited from the rheumatology outpatient clinics in Auckland, New Zealand. All patients in the chronic gout group had a history of acute gout according to ACR diagnostic criteria (Wallace et al., 1977). Twenty-five age and gender matched participants with no history of gout or other forms of arthritis were recruited as the control group. Although the subjects in the control group were of an age to have osteoarthritis (OA), none of the control participants described pain present on most days of the past month nor did any state any degree of stiffness in their lower limb joints. These criteria are a key part of the ACR diagnostic criteria for individuals with OA. The local ethics /$ see front matter 2010 Elsevier Ltd. All rights reserved. doi: /j.clinbiomech

2 K. Rome et al. / Clinical Biomechanics 26 (2011) and institutional committees approved the study and patients provided written informed consent. Participants were excluded if they were experiencing an acute gout flare at the time of assessment, history of gout or had lower limb amputation or diabetes mellitus. Participants attended a single study visit where a clinical and podiatry assessment was completed. Information relating to age, gender, ethnicity, body mass index (BMI) and disease duration were recorded. Patients completed the Health Assessment Questionnaire (HAQ) (Bruce and Fries, 2005). Foot pain was evaluated using the Foot Function Index, pain domain (Budiman-Mak et al., 1991), which measures pain over the past week. The Foot Function Index is a selfadministered questionnaire consisting of 23 items grouped in three domains: foot pain (nine items), disability (nine items) and functional limitation (five items), that has been validated for patients with RA (Budiman-Mak et al., 1991). All items are rated using 100 mm visual analogue scales, and higher scores indicate greater pain, disability and limitation of activity and thus poorer foot health. Only the foot pain domain was used in the current study. The Leeds Foot Impact Scale (LFIS) was also recorded (Helliwell et al., 2005). The LFIS is a self completed questionnaire that comprises of two subscales for impairment/footwear (LFISIF) and activity limitation/participation restriction (LFISAP). Blood samples were obtained from patients with gout for the measurement of serum urate, creatinine and C-reactive protein on the day of assessment. Two independent podiatric researchers undertook all foot and ankle measurements over a 16-week period. Each patient's plantar pressure measurements were determined on the same day by the same researcher. Plantar pressure readings were obtained using the F-Scan Mobile system (Tekscan Inc., South Boston, MA, USA) which incorporates insoles with 960 different pressuresensing locations (sensels) and a spatial resolution of four sensels/cm 2. The plantar region of the foot was masked into ten regions and the mean peak pressure (KPa) and pressure time integrals (KPa sec) were calculated. The plantar surface of the foot was masked into 10 regions and included the regional division of the foot into lateral and medial heel, midfoot, 1st metatarsal region, 2nd metatarsal region, 3rd metatarsal region, 4th metatarsal region, 5th metatarsal region, hallux and 2nd 5th toes (Rome et al., in press). Manual masking was undertaken based upon the protocols used by automated masking software (Research Foot software, Version 5.24). Before data acquisition, each patient was instructed to walk freely in the laboratory to reproduce their typical gait and to feel comfortable within the clinical setting (Gurney et al., 2009). Prior to the tests, the pressure insoles were calibrated according to the manufacturer's instructions, and before data acquisition, the zero setting procedure was performed as recommended by Tekscan Inc. Following a step calibration routine, the participant undertook a five-stride protocol as suggested by previous studies (Barker et al., 2006). The five strides were averaged from each patient's walking trial. Three trials of the five-stride protocol were recorded. Data analysis was conducted with the F-scan software package (Tekscan Inc, Version 5.24). The GAITMAT II was used to measure the spatial and temporal parameters of gait. This device contains six arrays of sensors encapsulated in a walkway, producing an active area of 1 m wide and 3.7 m long. The patient was asked to walk along its length at his or her own preferred comfortable walking speed (Barker et al., 2006). Three repetitions were performed and a mean was obtained. The following variables were of interest: step and stride length (m); stance and swing phase (%); single and double support (s); velocity (m/s) and cadence (steps/min). 3. Data analysis Data analysis was undertaken to compare significant differences between the two groups. Independent t-tests were used to analyse all demographic characteristics, walking velocity, cadence, Foot Function Index (foot pain), HAQ and Leeds Foot Impact Scale. Independent t- Table 1 Demographic characteristics of cases and controls. Cases Controls P value Age (years), mean (SD) 61.2 (11.7) 57.3 (12.2) Gender: Male, n (%) 19 (75%) 19 (75%) BMI (kg/m 2 ), mean (SD) 32.1 (5.6) 30.3 (6.4) Ethnicity n (%) European Caucasian 14 (56%) 15 (60%) Asian 5 (20%) 2 (8%) Maori 5 (20%) 6 (24%) Pacific 1 (4%) 2 (8%) Disease duration, years, mean (SD) 22.4 (13.2) Flare frequency/year, mean (SD) 3.1 (3.7) Tophus, n (%) 13 (52%) Monosodium urate crystals 11 (44%) confirmed microscopically, n (%) Allopurinol use, n (%) 21 (84%) Serum creatinine (μmol/l), mean (SD) (29.5) Serum urate (mmol/l), mean (SD) 0.40 (0.10) C-reactive protein (mg/l), mean (SD) 4.2 (5.9) tests were also undertaken to look for any significant differences across the gout cases and controls of the right and left feet. These latter analyses were focused upon gait parameters and plantar pressure measurements. All tests were two tailed and Pb0.05 was considered significant. 4. Results Table 1 presents the demographic information of cases and controls. The patients with chronic gout were predominantly middle aged men with prolonged disease duration. In both cases and controls, mean BMI was high. Table 2 presents the comparison of the functional measures between cases and controls. Significant differences (Pb0.001) were demonstrated in the HAQ, Foot Function Index (pain), and Leeds Foot Impact Scale (LFISIF and LSISAP). Peak plantar pressure values for both groups are presented in Table 3. The results demonstrated no significant differences in the peak pressures across the ten regions except for under the hallux (Pb0.05) where a significant decrease in peak pressure was observed in the cases compared to the controls (Fig. 1). Table 4 presents the descriptive information for pressure time integrals. Analysis of the pressure time integrals demonstrated a significant increase under the midfoot in the patients with chronic gout (Pb0.05). Pressure time integrals under the hallux were also significantly reduced in the cases compared to controls (Pb0.05). No consistent differences between groups were demonstrated at other regions of the foot. The temporal spatial gait parameters between the two groups are presented in Table 5. There were significant differences between the cases and controls in walking velocity (P=0.02), cadence (P=0.02), step (P=0.02) and stride length (P=0.02). The results demonstrated patients with chronic gout walked slower, with a reduced step, stride length and cadence. Table 2 Comparison of overall function measures between cases and controls. Controls mean (SD) Cases mean (SD) P value Health Assessment Questionnaire 0.08 (0.2) 0.54 (0.5) b0.001 Foot Function Index (pain) 3.8 (6.9) 28.2 (25.2) b0.001 Leeds Foot Impact Scale (total) 1.0 (3.3) 24.0 (16.3) b0.001 Leeds Foot Impact Scale 0.9 (1.7) 10.0 (6.1) b0.001 (shoes/impairment) Leeds Foot Impact Scale (activity/participation) 0.4 (1.3) 14.7 (10.1) b0.001

3 92 K. Rome et al. / Clinical Biomechanics 26 (2011) Table 3 Comparison of peak plantar pressure measures between cases and controls (KPa). Medial heel (87.2) (98.8) (83.7) (103.2) Lateral heel (92.8) (88.2) (81.8) (88.7) Midfoot (128.1) (59.3) (84.4) (74.6) st Metatarsal region (140.1) (113.9) (86.5) (113.5) nd Metatarsal region (140.5) (141.6) (112.1) (121.2) rd Metatarsal region (83.7) (173.5) (94.2) (138.8) th Metatarsal region (84.5) (127.1) (123.9) (103.8) th Metatarsal region (112.1) (10.7) (118.1) (136.4) st toe (123.9) (96.9) (129.1) (100.1) nd 5th toes (129.1) (85.9) (112.7) (70.3) Discussion This study has shown that patients with chronic gout have important foot related pain and disability. Biomechanical analysis has demonstrated significant alterations in peak plantar pressures and pressure time integrals, and alterations in temporal spatial gait parameters. The self-reported LFIS assesses the burden of foot disease on two scales related to impairments and activity limitation/participation restriction (Turner et al., 2009). Turner et al. (2009) reported that a LFISIF N7 point and LFISAP N10 point as a high-to severe level of foot impairment and disability [12,13]. Based upon these criteria, the current study has demonstrated that over 30% of patients with chronic gout have moderate foot related impairment and over 30% of patients have severe disability. This degree of foot related impairment and disability is similar to that observed in patients with early and established RA [Turner and Woodburn, 2008; Turner et al., 2006). We found that the patients with chronic gout experienced greater foot pain compared to controls. These findings are also similar to studies of other rheumatic diseases such as RA (Turner et al., 2006, 2009; Woodburn et al., 2002). Foot pain may affect everyday activities such as walking. Consistent with this, we identified slow walking velocity with associated step and stride length reductions in patients with chronic gout. Reducing walking speed is a well-recognised compensatory mechanism for pain in the foot [Turner and Woodburn, Fig. 1. Comparison between a gout case and a control illustrating the late phase of stance. The dotted line illustrates the centre of pressure of the foot. 2008; Magalhaes et al., 2006). The difference in gait speed between cases and controls may be related to our key finding of reduced peak plantar pressure under the hallux. The underlying cause for the reduced peak plantar pressure under the hallux is uncertain. The 1st MTPJ is the most affected joint in chronic gout (Grahame and Scott, 1970). We postulate that people with chronic gout alter their gait pattern in an attempt to reduce pain by off-loading at the 1st MTPJ, and thus avoid weight-bearing at the toe-off phase of gait. Other researchers have reported that patients with established RA and chronic diabetes have lower plantar-flexor ankle moments and power compared to the age-matched controls and this has been related to a reduction in gait velocity (van der Leeden et al., 2006; Kelly et al., 2000; Bacarin et al., 2009; Otter et al., 2004; Eppeland et al., 2009). Furthermore, clinical and radiographic studies have both shown osteoarthritis of the 1st MTPJ joint and midtarsal joints to be associated with gout, and hallux valgus has also shown to be frequent in subjects with gout than controls (Roddy et al., 2007, 2008). While speculative, the strategy of gout patients in decreasing load at toe off will involve reduced plantar flexor muscle activity, and such disuse may contribute to weakness in these muscles. Although the current study did not undertake kinematic or kinetic analysis of the lower limb and ankle, future studies using three-dimensional instrumented gait analysis combined with strength testing would provide a better understanding of the mechanisms associated dysfunction in these regions. We also found that midfoot pressure time integrals in the gout cases were higher compared to the controls. The pressure time integral is calculated from the impulse of peak pressure over the stance phase. As peak pressures were not different across cases and controls during this phase of gait, when the midfoot is in contact with the ground, the increase in the integral is likely to be due to an increase in the duration of mid stance phase. In support of this conjecture, there was a trend for overall stance phase time to be increased. In both the cases and controls, we found high mean BMIs indicative of obesity. The findings in the patients with gout are consistent other gout studies (Kushner and Roth, 2003; Choi et al., 2008). The feet are exposed to high ground reaction forces (1 5 body weights) during gait activities (Hills et al., 2002; Wearing et al., 2006). The sustained repetition of such loading in these activities make significant demands on the feet in normal-weight individuals, and these demands are likely to be magnified in those with obesity (Hills et al., 2002). It is possible that the increased demand related to obesity, coupled with the structural changes associated with chronic gout, contributes to foot disability in patients with gout. The study is not without limitations. Although the sample sizes were relatively small, clear differences between cases and controls were identified. The case-control nature of the analysis limits our ability to determine causality between foot pain and foot function. Patients with diabetes were excluded from the study in order to ensure that the foot characteristics of gout could be specifically assessed. The additional co-morbidity of type 2 diabetes, a disease strongly

4 K. Rome et al. / Clinical Biomechanics 26 (2011) Table 4 Comparison of pressure time integral measures between cases and controls (KPa s). Medial heel 42.1 (13.9) 53.8 (23.9) (14.6) 46.7 (16.9) Lateral heel 39.9 (13.3) 50.8 (19.1) (12.5) 47.6 (15.5) Midfoot 23.1 (9.7) 29.9 (10.3) (10.9) 39.1 (21.9) st Metatarsal region 43.8 (22.6) 43.9 (18.5) (17.6) 41.2 (21.8) nd Metatarsal region 56.4 (22.9) 57.0 (22.2) (19.1) 51.1 (21.2) rd Metatarsal region 60.2 (19.0) 65.3 (36.9) (23.8) 59.2 (29.0) th Metatarsal region 49.1 (19.5) 53.8 (25.2) (16.5) 59.5 (27.2) th Metatarsal region 42.5 (21.0) 41.1 (22.8) (23.4) 60.1 (46.8) st toe 33.4 (19.7) 17.5 (13.0) (19.4) 19.5 (17.0) nd 5th toes 22.7 (9.6) 17.5 (13.6) (16.8) 23.7 (16.4) Table 5 Comparison of gait measures between cases and controls. Step length (m) 0.66 (0.1) 0.57 (0.1) (0.1) 0.57 (0.1) Stride length (m) 1.32 (0.2) 1.14 (0.2) (0.2) 1.13 (0.3) Single leg support (s) 0.42 (0.1) 0.41 (0.1) (0.1) 0.57 (0.8) Double leg support (s) 0.19 (0.1) 0.19 (0.1) (0.1) 0.20 (0.1) Stance phase (s) 0.75 (0.1) 0.99 (0.8) (0.1) 1.1 (1.2) Swing phase (s) 0.41 (0.1) 0.48 (0.3) (0.1) 0.41 (0.1) Velocity (m/s) 0.90 (0.3) 1.10 (0.3) Cadence (steps/min) (36.9) 93.7 (16.9) associated with gout, may further contribute to foot disability in many patients with gout (Choi et al., 2008; Suppiah et al., 2008). The Foot Function Index was used to provide a measure of pain over a time period of one week rather than current pain. The current findings of finding foot pain greater in gout cases could have been influenced by a recent resolved attack of gout. The relationship between pain and function was not determined in the current study but quantifying the relationship between pain and foot function in chronic gout will give a better understanding of the issues of foot pain, function and impairment in chronic gout. This study specifically excluded patients with an acute gout flare at the time of the assessment, thus the changes observed in the current study are likely to be conservative and cannot be extrapolated to acute gout. Future research will address the effects of acute gout on foot function. 6. Conclusion The aim of the current study was to provide insights into the foot function and gait characteristics of individuals with chronic gout and compare the results to age and gender matched controls. Changes in gait parameters within the gout cases were focused upon the midfoot and the hallux and were indicative of a pain avoidance strategy. It seems likely that these changes contribute to altered loading patterns and impaired foot function in chronic gout. Such information has not been previously available. This knowledge may allow clinicians to make informed decisions when considering management programmes that require a non-surgical approach such as the prescription of foot orthoses to re-distribute pressure or footwear advice. Acknowledgements DS was supported by a research grant from AUT University. Disclosure statement: All authors have declared no conflicts of interest. KR, PMCN and ND were involved in the study design, analysis and discussion. AS and DS were involved in the data collection. DS was involved in the data analysis. ML and FMcQ were involved in recruitment and data collection. All authors were involved in the draft and final versions of the manuscript. 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