Foot and ankle characteristics associated with fear of falling and mobility in community-dwelling older people: a cross-sectional study

Ethical approval was granted by the Isfahan University of Medical Sciences (IR.MUI.RESEARCH.REC.1398.451) and informed consent was obtained from all persons before their participation.

Sample size (n) was calculated using the sample size formula:

…where z is the confidence level (1.96 standard deviations; 95%), α is the alpha level (0.05), \(p\) is the estimated probability of having a foot problem (0.45) and \(d\) is the precision (0.06). This calculation identified that 264 participants would need to be recruited. However, due to the impact of the coronavirus pandemic, recruitment had to cease at 225 participants (94% of the eligible sample), and of these, 38 cases were excluded due to errors in the plantar pressure data. Therefore, the final study sample comprised 187 community dwelling older people (106 females) aged 62–90 years (mean 70.5 ± 5.2, body mass index 27.7 ± 4.1).

Structural and functional characteristics of the foot and ankle were tested across the domains of foot posture, muscle strength, range of motion, tactile sensitivity, deformity, foot pain, and plantar pressure.

Foot posture was assessed using foot posture index (FPI), arch index (AI), and normalised navicular height truncated (NNHt). The FPI involved the rating of 6 criteria, the sum of which provided a single index of the pronated/supinated foot posture. The AI was calculated by the ratio of midfoot area to the foot (excluding toes) using the EMED pressure plate (novelGmbH, Munich, Germany, 2 sensor/cm², 50Hz). NNHt represents the navicular height divided by truncated foot length (i.e. foot length excluding the toes) in bipedal standing.

Isometric muscle strength of the ankle (dorsiflexion, plantar flexion, inversion, and eversion) was measured with a hand-held dynamometer (Digital Force Gauge 5kg; accuracy 0.001 kg) mounted on an apparatus to ensure isometric contraction via the make-test. Hallux and lesser toe muscle strength were quantified using a previously developed protocol. Participants were instructed to push down as hard as possible on an EMED pressure platform. The test protocols have been described in detail elsewhere [5].

Two measures of foot and ankle passive range of motion, passive ankle dorsiflexion and hallux first metatarsophalangeal (MTP) joint extension, were performed via a single standard video camera (50 Hz, 25 fps) which was placed perpendicular to the plane of motion and three skin markers (based on the same goniometry protocol) employed to capture the range of motion. Frame by frame advance was used to identify the instance of the maximum range of motion. Kinovea software (https://​www.​kinovea.​org/​) was used to measure these angles. Tactile sensitivity at the ankle was assessed using a single Semmes–Weinstein-type pressure monofilament. The monofilament was applied three times to the lateral malleolus of the ankle while the participant kept their eyes closed.

Hallux valgus was documented using the Manchester scale, a reliable and valid clinical tool based on four photographs of the foot [9]. The presence of foot pain was determined with the Manchester Foot Pain and Disability Index (MFPDI) [10].

Foot function was assessed using barefoot plantar pressure analysis using the EMED-le pressure plate. Three trials were recorded for each participant’s dominant limb with a two-step gait initiation protocol at a comfortable walking speed. Following data collection, the novel scientific software v23 was used to calculate the pressure-time integral in the total foot, centre of pressure (COP) velocity of the total foot, and the centre of pressure excursion index (CPEI), a measure of the mediolateral shift in COP throughout the gait cycle.

The Falls Efficacy Scale International (FESI) was used to assess the level of concern of falling during 16 activities of daily living, including social activities that may contribute to the quality of life [11]. The level of concern for each item was scored using a four-point scale (1 = not at all concerned, 4 = very concerned) within a total score range of 16–64. Mobility was assessed using the Timed Up and Go (TUGT) test by measuring the time taken for the participant to stand up from a chair, walk 3m, turn around, walk back, and sit down. Three trials were recorded for each participant and averaged. The TUGT has good validity and reliability as a measure of mobility [12].

Statistical analyses were carried out using IBM Statistical Package for the Social Sciences (SPSS) (IBM Corporation, Armonk, NY) with a 5% level of significance. Descriptive statistics were used to provide an overview of the demographic variables. The Kolmogorov–Smirnov test was used to check the normality of the data. Pearson’s r linear correlation was used where the relationship between normally distributed parameters was assessed. Otherwise, Spearman’s rho correlation test was used. Independent samples t-tests were performed to evaluate differences in FESI and TUGT according to dichotomous variables. All variables significantly associated with the dependent variable were entered in two stepwise multiple linear regression models to determine their relative importance in explaining variance in FESI and TUGT. Variables were selected based on the results of the correlation results (r > 0.3) or t-test (p < 0.2) for dichotomous variables. Preliminary analyses were conducted to ensure no violation of the assumption of normality, linearity, multicollinearity, and homoscedasticity. The overall fit of linear regression models was quantified by R².

Of the 187 participants recruited into the study, 109 (58.6%) had poor visual acuity (using a 10% low-contrast letter chart), 40 (21.5%) used psychoactive medications, and 95 (51.1%) reported taking > 4 medications per day (Table 1).

Descriptive statistics for each of the foot and ankle characteristics are shown in Table 2.

Tables 3 and 4 show the associations between the foot and ankle characteristics with fear of falling and mobility performance on continuous (Pearson’s r) and dichotomous variables (independent sample t-tests), respectively. Independent sample t-tests revealed that participants who failed the ankle tactile sensation and vision test and use > 4 medications per day scored worse on FESI and TUGT (p < 0.001). FESI scores were worse in older adults who used psychoactive medications (p = 0.06).

Multivariate linear regression examined the associations of foot and ankle characteristics with fear of falling and mobility in two linear regression models (Table 5). The first model examined foot and ankle structural and functional characteristics (using a stepwise method) with fear of falling. Eleven continuous (r > 0.3) and dichotomous variables (p < 0.2) were considered in the first regression model, including plantar flexor and invertor muscle strength, first MTP joint ROM, PTI, COP velocity, MFPDI, ankle tactile sensitivity, hallux valgus, vision, use of psychoactive medications and using four or more medications. To avoid multicollinearity, dorsiflexor muscle strength was excluded from the model as it was highly correlated with plantarflexor muscle strength (r = 0.7). Plantarflexor muscle strength, PTI, ankle tactile sensitivity in addition to foot pain were independently associated with fear of falling. The total variance explained by the model was 59% (F _{5, 158}= 46.19, p < 0.001).

For the second linear regression model, the same procedure was performed with the TUGT score as the dependent variable. In addition to the previous independent variables, the FESI score was entered in the model, and the use of psychoactive medications was excluded. Plantarflexor muscle strength, PTI, and COP velocity were independently associated with the TUGT score. Total variance explained by the model was 48% (F _{6, 157}= 24.86, p < 0.001).