Clinical Biomechanics 29 (2014) 350–353

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Brief report

The effects of sandals on postural stability in patients with rheumatoid arthritis: An exploratory study Angela Brenton-Rule a,⁎, Stacey D’Almeida a, Sandra Bassett a, Matthew Carroll a, Nicola Dalbeth b, Keith Rome a a b

AUT University, Health & Rehabilitation Research Institute, Auckland, New Zealand University of Auckland, Auckland, New Zealand

a r t i c l e

i n f o

Article history: Received 28 July 2013 Accepted 5 December 2013 Keywords: Balance Rheumatoid arthritis Sandals Footwear Postural stability Foot deformity

a b s t r a c t Background: Rheumatoid arthritis results in postural instability, pain and functional limitations. As rheumatoid arthritis progresses, localised forefoot deformities such as hallux valgus and clawing of the lesser toes occur, leading to a high proportion of people with rheumatoid arthritis wearing sandals. Sandals may affect postural stability due to poor motion control. The aim was to assess two different open-toe sandals on postural stability in people with rheumatoid arthritis. Methods: Twenty women with rheumatoid arthritis were assessed in quiet standing under four conditions: (1) open-back sandal; (2) closed-back sandal; (3) own footwear and (4) bare feet. Postural stability was assessed as postural sway in the anterior-posterior and medial-lateral directions, with eyes open and eyes closed, using a pressure mat. Repeated measures analysis of variance tested the interaction effect of the footwear and eye conditions on anterior-posterior and medial-lateral sway. Findings: In eyes-open, there was no significant difference in anterior–posterior sway (P = .169) and mediallateral sway (P = .325) for footwear conditions. In eyes-closed testing, compared with barefoot conditions, increased anterior–posterior sway was observed with participants' footwear (P b .0001), the open-back sandal (P = .005), and the closed-back sandal (P = .017). With eyes closed, increased anterior–posterior sway was also observed with the participants' footwear compared with the closed-back sandal (P = .041). Increased medial-lateral sway was observed with the closed-back sandal compared with bare feet (P = .014). Interpretation: Sandals may be detrimental to older women with well-established rheumatoid arthritis when eyes are closed. Further investigation is needed to evaluate the effect of sandals on dynamic tasks. © 2013 Elsevier Ltd. All rights reserved.

1. Introduction Rheumatoid arthritis (RA) is a chronic, systemic, inflammatory, joint disease affecting 0.5 to 1.0% of the world population (Scott et al., 2010). The foot is a common site of pathology in early RA and forefoot involvement becomes greater with disease progression (Michelson et al., 1994; Wiener-Ogilvie, 1999). Control of balance, or postural stability, is essential in all static and dynamic activities. A previous study reported that static postural stability, in the anterior–posterior centre of pressure excursion during the eyes open task and the eyes closed task is decreased in RA compared to the non-RA population (Rome et al., 2009a). As a result, people with RA may have difficulty maintaining postural control leading to balance problems in everyday activities (Rome et al., 2009a).

⁎ Corresponding author. E-mail addresses: [email protected] (A. Brenton-Rule), [email protected] (S. D’Almeida), [email protected] (S. Bassett), [email protected] (M. Carroll), [email protected] (N. Dalbeth), [email protected] (K. Rome). 0268-0033/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clinbiomech.2013.12.006

Footwear has a role to play in postural stability by facilitating somatosensory feedback to the foot by the proprioceptive system that detects and processes tactile stimulation/information (Brenton-Rule et al., 2011; Hijmans et al., 2007; Perry et al., 2007). Cutaneous mechanoreceptors, located in the plantar surface of the feet, detect tactile stimuli and provides the central nervous system (CNS) with information regarding plantar pressure distribution (Hijmans et al., 2007). This is important, as changes in foot pressure are often related to changes in an upright position (Kavounoudias et al., 1998). Footwear may also control foot motion, thus potentially affecting foot function and balance (Barton et al., 2009; Menz and Lord, 1999). Previous studies in the older adult population have reported that poor footwear type and poor footwear characteristics lead to postural instability (Brenton-Rule et al., 2011; Keegan et al., 2004; Sherrington and Menz, 2003). Sherrington and Menz (2003) reported unsafe features of shoes identified included excessively flexible heel counter and an excessively soft sole. Furthermore, Keegan et al. (2004) found that slip-on shoes and sandals were associated with a greater risk of a foot fracture from a fall. Sandals have been found to be worn by the majority of patients in two recent studies from New Zealand of people with RA (Rome et al.,

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2009b; Silvester et al., 2010). It is possible that people with RA wear open-type sandals in order to better accommodate forefoot deformity associated with the disease such as clawing of the lesser digits and severe bunions. However, sandals may have a detrimental effect on balance due to poor footwear characteristics such as minimal heel counter stiffness and poor motion control. Variation in sandal design includes backless (no back-strap), open-back (back-strap only) and closed-back (full heel counter). Laboratory based research into the effect of heel counter stiffness on postural stability is not evident in the literature. However, heel counter stiffness is thought to be important in rear foot control and a stiff heel counter may provide mechanical support to the foot (Barton et al., 2009). Flimsy or excessively flexible heel counter has also been associated with falls in older adults (Finlay, 1986; Sherrington and Menz, 2003). Therefore, the aim of the current study is to evaluate the effect of open-back and closed-back sandals, in relation to postural stability, in women with established RA. 2. Methods Twenty participants were recruited from a rheumatology outpatient clinic in Auckland, New Zealand. The study was approved by the Auckland University of Technology Ethics Committee and participants provided written informed consent. Inclusion for the study was women older than 18 years with a diagnosis of RA (Aletaha et al., 2010). People were excluded from the study if they had a neurological condition which could impair balance (including history of stroke, multiple sclerosis and Parkinson's disease); lower limb amputation or diabetes with previously diagnosed peripheral neuropathy. Participant general features and clinical characteristics were recorded prior to testing. Current disease activity was determined through the assessment of tender and swollen joints and calculation of the four variable disease activity score (DAS28) (Van Riel, 2004). Foot pain in the past week and current patient global assessment of disease activity were recorded using a 100 mm visual analogue scale (VAS). The Health Assessment Questionnaire-II (HAQ-II) (Fries et al., 1980) and the Leeds Foot Impact Scale (LFIS), that evaluates foot disability and impairment (Helliwell et al., 2005), were also completed by each participant. Participants' own footwear, which was worn to the study visit, was documented using a list of 17 footwear styles adapted from a previous study (Menz and Sherrington, 2000). Postural stability was assessed through the measurement of postural sway (oscillations around the centre-of-mass) in the anterior–posterior (AP) and medial–lateral (ML) directions, during quiet standing. Sway parameters were measured using the excursion (mm) of the centre of pressure (COP) in the AP and ML directions. Postural sway was measured using a pressure mat; TekScan MatScan® model 3150 (TekScan Inc., South Boston, USA). The MatScan® is a low profile floor mat (5 mm thick) consisting of 2288 resistive sensors with a spatial resolution of 1.4 cells per cm2 and a sampling frequency of 40 Hz. This portable pressure system has been shown to be reliable for the measurement of postural sway in older adults with RA (Brenton-Rule et al., 2012). The Sway Analysis Module (SAM™) software was used to analyse the data. Two different types of sandal were used in the study (Fig. 1): an open-toe, open-back sandal (shoe 1) and an open-toe, closed-back sandal (shoe 2). The shoes were constructed of a synthetic, “leather look” upper with a padded insole. Both sandals had Velcro fasteners and were adjustable at the midfoot and forefoot, to accommodate structural foot changes associated with RA, such as hallux valgus (bunion) deformity. Shoe 1 also adjusted at the rear foot and had a semi-rigid midsole. Shoe 2 had a closed-in heel counter and a rigid midsole. Both sandals had a solid 3 cm rubber wedge heel. All sandals were new at the time of testing. Participants were tested on one occasion wearing the two different types of sandal, their own footwear (Table 1) and no footwear (bare feet). Nylon hosiery was worn with the study sandals. Participants

Fig. 1. Shoe 1 (top), Shoe 2 (bottom).

were asked to stand on the pressure mat and adopt their preferred, comfortable, quiet standing position with their arms by their sides whilst looking straight ahead at a circular black target of 10-cm diameter, fixed at a distance of 2 m at eye level. Each participant was asked to

Table 1 Participant demographic and clinical characteristics. Variable

Value

Age, years, mean (SD) range Ethnicity, n (%) European Pacific Island BMI, kg/m2, mean (SD) range Disease duration, years, mean (SD) range Disease type, n (%) Rheumatoid factor positive Anti-cyclic citrullinated peptide antibody positive Seronegative Tender joint count, mean (SD) range Swollen joint count, mean (SD) range Erosive foot disease, n (%) Medications, n (%) Methotrexate Other disease modifying anti-rheumatic drugs Biologics Corticosteroids DAS28-ESR, mean (SD) range DAS28-CRP, mean (SD) range VAS foot pain, mean (SD) range VAS patient global assessment, mean (SD) range HAQ-II, mean (SD) range LFIS total score, mean (SD) range LFIS impairments/footwear, mean (SD) range LFIS activities/participation, mean (SD) range Participants' footwear at study visit, n (%) Sandal Athletic shoe Closed back sandal Jandal Walking shoe Oxford shoe Backless sandal

67.6 (12.3) 44–84 18 (90%) 2 (10%) 27.7 (5.3) 21.9–40 21.5 (11.5) 2–38 13 (65%) 6 (60%) 3 (9%) 14.6 (18.3) 0–61 12.6 (15.9) 2–59 18 (90%) 18 (90%) 13 (65%) 4 (20%) 7 (35%) 3.81 (0.96) 2.78–5.59 4.06 (1.16) 2–5.76 45 (22.8) 8–80 35.7 (20.9) 8–94 1.07 (0.42) 0.2–2 30 (9.5) 12–44 12.7 (3.2) 5–18 17.3 (7.3) 5–28 6 (30%) 6 (30%) 2 (10%) 2 (10%) 2 (10%) 1 (5%) 1 (5%)

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remain in this position for a period of 30 s while data was recorded. Three repetitions were taken for each condition to obtain a mean value. Foot positioning was standardised throughout using individual foot templates to eliminate confounding effects of altered joint kinetics and datum was captured with eyes open (EO) and eyes closed (EC). Each footwear condition and EO/EC was randomised to reduce a learning effect. To reduce fatigue each participant was allowed to sit and rest for five minutes between footwear changes. The testing protocol was in accordance with a previous study which used the TekScan MatScan® system to evaluate postural sway in healthy older adults (BrentonRule et al., 2011). All measurements and fitting of the shoes were undertaken by one of the researchers (SD). Data were analysed using Statistical Package for Social Sciences (IBM Corp., New York, USA) with the alpha set at 0.05. All continuous data were screened for normality using the K-S (Kolmogorov–Smirnov) one-sample test. The mean and standard deviation (SD) was obtained for all continuous data. The interaction effects of the four footwear conditions and the two eye conditions on AP and ML sway were analysed separately using repeated measures analysis of variance (ANOVA). If significant main effects occurred for the footwear conditions, Sidak post-hoc testing was undertaken to establish where these occurred. 3. Results Participant characteristics are presented in Table 1. All participants were female and 90% were European, with mean (SD) age of 68 (12) years. The mean (SD) RA disease duration was 22 (12) years. Ninety percent of participants had radiographic erosions in the feet. On the day of the study visit, participants had moderate disease activity and disability, with mean (SD) scores: DAS28-ESR 3.68 (1.01), DAS28-CRP 3.74 (1.75), HAQ-II 1.01 (0.42). Participants reported high to severe levels of foot impairment and disability, with mean (SD) score of 12.7 (3.2) for impairments/footwear and 17.3 (7.3) for activities/ participation. Thirty percent of participants wore footwear similar to shoe 1 and 10% wore footwear similar to shoe 2 to the study visit. The remaining participants wore closed-in walking, athletic or Oxford type shoes, backless sandals or jandals (also known as flip-flops or thongs). Descriptive statistics and ANOVA for postural sway values are presented in Table 2. The data were normally distributed. There were no differences in AP or ML sway values between the four footwear conditions with eyes open. However, significant differences were observed for the four AP footwear conditions with eyes closed (ANOVA P = .001).

Table 2 Descriptive data and within subjects effects (ANOVA) for AP and ML postural sway (mm). Postural sway

Eye condition

Footwear condition

Mean (SD)

P-value

AP

Eyes open

Bare feet Participants' footwear Shoe 1 Shoe 2 Bare feet Participants' footwear Shoe 1 Shoe 2 Bare feet Participants' footwear Shoe 1 Shoe 2 Bare feet Participants' footwear Shoe 1 Shoe 2

19.69 (5.24) 23.43 (7.97) 22.74 (5.81) 21.49 (7.40) 25.77 (5.66)a 35.43 (8.71) b 33.08 (7.38) 30.21 (5.08) 13.86 (4.91) 13.60 (3.87) 15.86 (5.29) 14.52 (5.86) 15.43 (4.73) c 18.45 (4.64) 18.12 (5.27) 19.50 (6.48)

.169

Eyes closed

ML

Eyes open

Eyes closed

.001

.325

.023

Mean differences significant at the .05 level using Sidak post-hoc tests. a Significant differences between bare feet and all other footwear conditions. b Significant differences between participants' footwear and shoe 2. c Significant differences between bare feet and shoe 2.

Significant differences, identified by the Sidak post-hoc analysis, occurred between bare feet and participants' footwear (P b .0001), bare feet and shoe 1 (P = .005), bare feet and shoe 2 (P = .017) and participants' footwear and shoe 2 (P = .041). Specifically, AP sway was increased for all shoes compared to bare feet and for participants' footwear compared to bare feet and shoe 2. Similarly, there were significant increases for the four footwear conditions in the ML direction with eyes closed (ANOVA P = .023). The post-hoc test demonstrated that significant increases in ML sway occurred in shoe 2 compared to bare feet (P = .014). 4. Discussion The aim of the study was to evaluate the differences between two types of open-toe sandal, participants' own footwear and bare feet, in relation to postural stability in women with established RA. The population tested had longstanding disease, moderate disease activity and disability, and high to severe foot impairment. Forty percent of participants wore open-toe sandals to the study visit. This was higher than previous studies of RA patients, in which 21% (Rome et al., 2010) and 33% (Silvester et al., 2010) wore open-toe sandals, and confirms that this type of footwear is frequently chosen by women with RA. The findings of our study suggest that footwear did not significantly affect balance in quiet standing in eyes-open test conditions. However, in eyes-closed testing, AP sway was significantly increased in all footwear types compared to bare feet. The role of vision in postural control is well documented and of particular importance in older adults (Hytönen et al., 1993). Visual dependency for postural control is even greater in people with RA compared to healthy controls (Rome et al., 2009a; Tjon et al., 2000). Foot and lower limb pathology, including decreased plantar sensation, is common in RA and has been associated with decreased balance during static and dynamic tasks (Rome et al., 2009a). Tjon et al. (2000) reported that a powerful characteristic of the postural control system is its ability to deal with peripheral lesions by the use of compensatory strategies. One of the most prominent sources for compensation is visual information. Shifting to a more visually dominated control strategy can compensate for a decrease in sensory information from the lower limbs. In the current study, the finding of increased sway in eyes-closed test conditions is in agreement with previous studies in patients with RA (Rome et al., 2009a; Tjon et al., 2000) and older adult populations (Brenton-Rule et al., 2011; Menant et al., 2008a; Menz and Lord, 1999). The finding of significantly increased postural sway in both the ML and AP direction in all footwear, compared to bare feet, is in agreement with an earlier study in which older women were found to sway less in barefoot quiet standing, compared to when wearing their own shoes and other footwear conditions (Lord and Bashford, 1996). AP postural sway was also reported to be increased in older adults wearing athletic footwear compared to bare feet (Brenton-Rule et al., 2011). Footwear can potentially alter tactile postural control mechanisms which provide the CNS with updated sensory information required for the maintenance of balance. As an interface between the foot and supporting surface, footwear can potentially redistribute plantar pressures and insulate plantar afferent receptors (Menz and Lord, 1999), which may be detrimental to people with established RA. Increased sway is generally understood to represent a decline in postural control. However, previous studies, in older adult and diabetic populations, have suggested that larger excursions of postural sway are employed to increase sensory feedback required to maintain balance (Brenton-Rule et al., 2011; Mackey and Robinovitch, 2005; van Deursen, 2008). Therefore, the increase in postural sway observed in the current study may be a postural control strategy in response to the effect of the footwear on the somatosensory system. Footwear characteristics such as heel height, motion control and sole hardness can also affect postural stability by altering foot position and shifting the wearer's centre of mass (COM) and hence the COP under the foot (Menant et al., 2008b). Previous studies have reported that

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postural stability is decreased with increased heel height (Lord and Bashford, 1996; Menant et al., 2008a). By moving the COM forwards balance control is affected resulting in postural adaptations (Snow and Williams, 1994). In the current study, a shift in COM position due to a raised heel (compared to no heel in bare feet) may account for the increase in AP postural sway. We acknowledge the study limitations. As this was an exploratory study the small number of participants reduces the generalisability of the results to the wider population of women with RA in New Zealand and worldwide. The results also cannot be generalised due to the age range (50–82 years old) and the exclusion of men. Cutaneous plantar pressure perception was not assessed in the participant group therefore we can only speculate about the effect of the footwear on the somatosensory system. Future work may need to be conducted using more complex dynamic balance tasks, which incorporates substantial foot motion and may provide a better insight into the role of footwear, such as sandals, commonly worn by people with established RA. For example, assessment of spatial and temporal parameters of gait (Rome et al., 2009a), or the use of other dynamic tasks such as the Tinetti test, timed get-up-and-go test, chair-rising test, tandem walk and tandem stand (Böhler et al., 2012). 5. Conclusion The current study found that open-toe sandals did not significantly affect balance in quiet standing, in eyes-open test conditions, in older women with well-established rheumatoid arthritis. In addition, there was no significant difference in postural sway between open-back and closed-back sandals in eyes-open or eyes-closed test conditions. However, in eyes-closed testing, postural sway was significantly increased in all footwear types compared to bare feet. These findings suggest that open-toe sandals may have a detrimental effect on balance in people with established RA in situations where visual information is limited. However, further investigation into the effects of sandals on dynamic tasks, in people with RA, is warranted. Disclosure statement All authors have declared no conflict of interest. Acknowledgements KR, ABR, ND and MC designed the study. SD collected the data. ABR and SB conducted the statistical analysis. All authors were involved in the draft and final version of the manuscript. Dr Michael Corkill, for training SD in assessing joints for tenderness and swelling and reviewing the manuscript. SD was supported through a summer studentship research grant from Arthritis New Zealand. References Aletaha, D., Neogi, T., Silman, A.J., Funovits, J., Felson, D.T., Bingham, C.O., Birnbaum, N.S., et al., 2010. Rheumatoid arthritis classification criteria: An American College of Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis Rheum. 62, 2569–2581.

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