Background
Falls represent an important burden to healthcare resources worldwide and treatment of fall related injuries accounts for a significant proportion of healthcare spending [
1,
2]. For individuals, loss of confidence and independence as a consequence of falling can significantly reduce quality of life. Education regarding fall risk and prevention is fundamental to health and well-being in older adults [
3].
People with rheumatoid arthritis (RA) are at greater risk of falling than healthy older adults [
4]. RA is a chronic, inflammatory, autoimmune disease characterised by systemic inflammation, persistent synovitis and progressive articular destruction [
5]. Most synovial joints can be affected, however, the peripheral joints are predominantly involved, most often the small joints of the hands and feet, and usually in a symmetrical distribution [
6]. Previous studies in people with RA have reported falls incidence ranging from 10 to 54 % [
4,
7‐
12]. Fall risk factors common to older people have been identified in people with RA [
4,
9‐
11,
13]. These include history of a previous fall [
4,
11], fear of falling [
4], impaired general health [
13], number of co-morbid conditions [
10], fatigue and dizziness [
4] and antihypertensive medication [
9]. Fall risk factors which may be RA disease-specific have also been reported including activity limitation as measured by the Health Assessment Questionnaire (HAQ) [
4,
13], tender joint count [
4,
13], swollen joint count [
9], 28 joint Disease Activity Score (DAS28) [
4], pain intensity [
4,
11], number of medications [
4,
7], use of corticosteroids, psychotropic medications [
4] and antidepressants [
7]. Decreased lower extremity muscle strength [
4] and impaired standing balance [
4,
9] have also been associated with falls in people with RA.
The foot is a common site of pathology in RA, with many patients reporting foot symptoms at initial diagnosis, and as many as 90 % of people with established RA report current foot problems [
6]. Postural stability is also decreased in people with RA compared to the non-RA population. As a result, people with RA have difficulty maintaining postural control when undertaking everyday activities [
14]. Several studies in healthy older adult populations have identified foot and ankle characteristics which may impair balance and increase the risk of falling [
15‐
21]. The foot and ankle characteristics related to fall risk factors in older adults include lesser toe deformity [
16], reduced ankle range of motion [
21], severe bunion deformity [
21], pes planovalgus foot-type [
15], reduced plantar sensitivity [
15,
21], decreased toe strength [
16,
21], disabling foot pain [
15,
17,
21], slower gait speed [
22] and increased peak plantar pressures and pressure–time integrals [
17].
There is a dearth of evidence regarding foot and ankle characteristics and falls in people with RA. The aim of this study was therefore to determine the foot and ankle characteristics associated with falls in people with RA. This paper reports the findings of a cross-sectional study in adults with established disease. We compared fallers and non-fallers, according to falls experienced in the preceding 12 months, on a range of foot and ankle measures and common falls risk factors.
Discussion
In this study, 59 % of participants reported at least one fall during the preceding 12-months. This is much higher than the 30 % reported for community dwelling older adults [
40] and is consistent with reports that adults with RA are at increased risk of falling compared to the non-RA population [
4,
9,
11]. Previous studies in RA populations have identified fall risk factors common to older adults generally, as well as disease-specific fall risk factors. The current study sought to extend our understanding of fall risk in this group through the inclusion of foot and ankle measures known to be associated with falls in healthy older adults.
We found fallers to have higher peak plantar pressures in the midfoot region compared to non-fallers. Midfoot peak plantar pressure was also found to be independently associated with falls in the previous year, with the odds of falling increasing by 12 % for each 20kPa increase in pressure. Increased midfoot plantar pressures have been reported in RA patients with pes planovalgus (flatfoot) deformity, leading to adaptive changes which may compromise stability and increase falls risk compared to healthy controls [
41]. Increased pressure at the midfoot is also associated with a pronated foot posture, which has previously been shown to impair postural stability in healthy younger adults [
42]. This is the first study to assess plantar pressures as a potential fall risk factor in people with RA. Our results suggest that measurement of plantar pressures, at the midfoot, may be useful in identifying people with RA at increased fall risk. Plantar pressure systems are commonly used in clinical practice to identify areas of high pressure which may compromise tissue viability in patients with high risk foot conditions [
43]. Such equipment could also be utilised to identify increased pressures at the midfoot, as part of a fall risk assessment in patients with RA. In clinical settings where pressure analysis equipment is unavailable, the identification of a pes planovalgus foot-type may suffice as an indicator of increased midfoot pressures, particularly in the presence of callosities at the talonavicular joint [
41].
In agreement with previous studies [
4,
11,
22], self-reported disability and impairment (HAQ-II score) and fear of falling (short FES-I score) were significantly associated with increased risk of falling. Foot-related disability and impairment were also found to be independently associated with a history of falls. Specifically, the odds of falling increased by 17 % for each three point increase on the FIS
AP subscale. The FIS was designed specifically to assess the impact of RA disease-related foot involvement in terms of impairment, disability and quality of life [
27]. The current findings suggest that the FIS, particularly the activities/participation subscale, may also be useful in identifying and monitoring people with RA with increased risk of falling. Clinical guidelines recommend the use of patient-reported outcome measures (PROMs) in the management of foot health in people with RA [
44]. Our findings suggest that PROMs, including the HAQ-II, the Short FES-I, and in particular, the FIS may be also useful in identifying people with RA with increased risk of falling and could be incorporated as part of a regular fall risk assessment.
In the current study, lower limb tender joint count was significantly higher for fallers compared to non-fallers. Lower limb joint count included the knees, ankles and sixteen joints in each foot. Several previous falls studies in RA populations have assessed tender joints as a risk factor for falls, with conflicting results [
4,
9,
10,
13]. However, only one study reported findings related to the lower extremities [
4]. In this study, Stanmore et al. [
4] found that the presence of tender or swollen lower extremity joints was an independent predictor of falls (OR 1.7). However, lower extremity joints included the hips, knees and ankles only [
4]. Joint tenderness in RA is usually an indicator of synovitis associated with active disease [
45]. Although we found no difference in swollen joint count between fallers and non-fallers in the current study, synovitis in the small joints of the feet can be difficult to detect clinically [
46]. The feet are often overlooked during consultations and it is possible that active foot disease may go unnoticed [
47]. Our findings suggest that assessment of tenderness and swelling in the lower limb joints, including the feet, may be important in identifying people with RA at increased fall risk.
We found fallers to have longer RA disease duration than non-fallers. As falls are generally associated with older adults, clinicians may not identify younger people with established RA, who are at increased fall risk. Number of co-morbid conditions was also associated with increased falls risk, as observed in previous studies in RA [
10,
11]. In addition, vascular disease (including stroke, ischemic heart disease, arrhythmia and peripheral vascular disease) was independently associated with a history of falling in the current study, with the odds of falling more than tripling (OR 3.2) compared to those without vascular disease. Co-morbid conditions, including cardiovascular diseases, cancer, osteoporosis and depression, are common complications of RA [
5]. Therefore, an association between falls risk and co-morbid conditions, in particular vascular disease, is an important finding.
In this study, falls were not associated with older age or female sex which is in agreement with several other studies in people with RA [
4,
7,
9‐
11,
22]. In the general population, older adults (over 65 years) and women experience significantly more falls than younger adults and men, and falls rate increases with increasing age [
48]. It is possible that age related fall risk factors, such as impaired general health, co-morbid conditions, fatigue and history of prior falls, may occur in adults of all ages with RA, thus mitigating age-related differences.
Strengths of the study are the large sample size and the inclusion of a comprehensive range of validated foot and ankle measures. The study has some limitations. Firstly, the recruitment strategy involved inviting clinic patients to participate in a study of fall risk, so the frequency of falls may have been over-estimated and may not be a true representation of people with RA. Secondly, the retrospective recording of falls may be subject to recall bias [
49]. There was no adjustment applied for multiple comparisons in the univariate analysis. Finally, the cross-sectional design prohibits determination of causality and it is not possible to determine the temporal nature of observed associations. Prospective analysis of this cohort is ongoing to provide more definitive conclusions regarding causes of falls in people with RA.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
ABR participated in the design of the study, collected the data, performed the statistical analysis and drafted the manuscript. ND participated in the study design and helped to draft the manuscript. HBM participated in the study design and helped to draft the manuscript. SB participated in the study design and helped to analyse the data. KR conceived of the study, participated in the study design and helped to draft the manuscript. All authors read and approved the final manuscript.