To the best of our knowledge, this is the first study to analyze the foot problem prevalence, the association between foot problems and walking, and toe-grip strength in older people attending day service and day care centers in Japan. Our target participants were frailer older people who use services under long-term care insurance but are not in a bedridden condition.
The strength of the study is that we obtained the data based on clinical assessment instead of self-reporting. In addition, the current foot problems were identified by data collection using multiple items so that the whole picture of the foot was captured. Three research questions were answered.
The prevalence of foot condition in older people
Our study target was frail older people in the community who use long-term care insurance. As frailty advances, various factors of the body may negatively affect the foot health of older people. Our investigation on foot items indicated that the rate of incidence of floating toes, toe deformities, nail color change, arch deformities, nail length, thickened nail, skin dryness, edema, skin color change, suspected or existing nail fungal infection was relatively high, whereas the rate of corn and callus were pretty low. Various factors including aging may trigger these foot problems. Physical condition varies among community-dwelling older people; hence, foot conditions also differ among them. The high prevalence of hypertension, diabetes, and brain diseases may be associated with foot conditions, leading to lower immune system, circulation impediment, and increase of muscle generation with aging.
The reason of lower incidence of corn and callus may indicate that walking time is less for the frail older population; therefore, the repeated pressure on the sole is minimum. The rate of incidence of palpable tibial arteries may indicate the changes in the circulatory system based on aging. The change in the condition of peripheral blood vessels with aging is related to nail color and nail growth [31, 32]. However, as we did not use Doppler, the pressure level of the examiner may be associated with the detection of palpating the pulse. The temperature of the lower extremities indicated the condition of foot circulation because of aging, sedentary behavior, and lack of foot movement. This indicates that temperature is associated with the coldness of the feet of many older people using the service, which is observed when the examiners touch the skin and palpate the pulse of the posterior tibial artery.
The other study indicated that awake temperature of 30·6 °C (SD 2·6) at awake time and 34·0 °C (SD1.8) at sleep time also varies from 15·9 °C to 37·5 °C depending on seasons . For our future study, the consistency of the targeted site of temperature measurement and time with larger number of participants, a larger number of samples, and a comparison of the data with that from younger people would provide more accurate data.
The author’s previous research demonstrated that foot skin dryness was found in 89·5–100% of frail older people who used homecare service . A few studies reported that 44–45% of older people in-home care  and 52·6% in residents of nursing home had dry skin . Both the caregiver and older people should understand the mechanism of skin barrier and apply the appropriate skin-protecting ointment.
This study assessed for possible nail fungal infection based on observation and the clinical hallmarks of onychomycosis were followed for some participants by a dermatologist. The nail with fungal infection becomes friable and appears yellowish . The nail condition can be detected through mycological test, but the false-negative culture rate of this test is at least 30% . Fungal infection of the foot is an indicator of lower limb cellulitis development . Additionally, it may lead to psychological disorders due to its appearance .
Toe and arch deformity are interlinked with muscle degeneration, weakening of tendons and ligament with aging, lifestyle, walking, or the selection of shoes, or less walking. These deformities cause floating toes, leading to balance instability.
As we expected, walking speed was slower and width of opening toes was narrow and toe-grip strength was weak for people with more care. Previous studies indicated that toe-grip strength has declined with aging [40, 41].
Uritani et al  classified the data of toe-grip strength into six age groups and reported that women in their 70 s (men: 10·4, women: 7·3) had a significantly weaker toe-grip strength than those in their 20s–60 s. The mean age of our study participants was 83 years, which was lower than their report (70 years, [mean: 4·026, median: 3·3]). Thus, building strategies to maintain or enhance toe-grip strength in this frail population is essential.
The foot item variables correlate with toe-grip strength and walking speed
The right toe-grip strength had a statistically significant association with the arch deformity, suspected or existing nail fungal infection, and nail thickness of the right sided foot although no independent variables were selected on left foot. The corn, callus, and toe deformity of the right sided foot was significantly associated with walking test (p-value, 0·026, 0·033 respectively). The finding may be associated with a higher rate of participants represented by right distribution to the floor. However, more studies are needed to explore the finding. Although the adjusted R2/ was 0.099 for right toe grip force and 0.067 for walking speed were week, significant P values indicated that relationship between predictors and response variables. The individual variability of foot may associate with the lower of R2 scores. Further study will be needed to explore the generation of combination of higher adjusted R2 and lower P value.
Several reasons can be considered for the association between toe-grip strength and nail problems. The association between nail problems and toe force was previously reported [42–44]; however, the number of studies was limited in Japan and overseas. Nail abnormality including thickened, deformed or friable nails caused by fungal infection may trigger the decline of toe-grip strength because nail has the power to firmly step on the floor. Thus, nail care significantly affects the toe-grip strength. In the present study, abnormalities of the right foot arch led to a decrease in the right toe-grip strength. A few studies investigated the changes in foot shape with aging [45–47]. Deformity of arches may lead to the decline of range of motion, change in plantar loading pattern, and postural stability [48, 49], causing instability of balance.
The foot arch is known to be associated with the plantar fascia, which is also known as plantar aponeurosis . In one study, Erdemir et al described the role of plantar fascia during walking . The study, which evaluated the association between plantar fascia and toe force, was conducted in 20 people and found that there was no relationship between the progression of the first metatarsophalangeal (MTP) joint and the presence of plantar fascia. This study concluded that further investigation on this matter would be required .
Since the bar of the device measuring toe-grip strength is gripped at the MTP joint part of the foot, it is considered that an abnormality in the foot arch may lead to a decrease in the toe-grip strength. However, more data needs to be accumulated on the relationship between toe-grip strength and arch correction.
In a study, Digiovanni et al stated that adequate rehabilitation affects the stretching of the plantar fascia . In another study, Mickel et al suggested “plantar fascia stretching, perception, and balance training, along with pain management and weight control” as components of rehabilitation program in order to prevent falling . However, we suggest that the contents of an adequate rehabilitation program should further be assessed. For example, instead of just an exercise that moves the muscles, stretching of the foot before the exercise may prevent the generation of pain and could make the exercise more effective. Additionally, there are various auxiliary tools and pads for arch correction, and thus, further data to verify the substantial effects on the strength of toe force should be gathered.
Interestingly, the walking speed was significantly associated with the existence of corn and callus as well as toe deformities. The formation of corn and callus itself and pain caused by them may be associated with plantar pressure, leading to decline of walking speed. The association between walking speed and plantar pressure has been widely studied [55–58].
Another study reported the effect of treatment to solve the pain due to the keratosis, such as corns and callus [59, 60]. However, the association between corn and callus with plantar pressure remains unclear [61, 62]. Another study revealed that plantar pressure is higher in older people with callused regions and an intervention study indicated the removal of callus reduces planter foot pressure . The lower rate of having callus and corns indicated that the walking time of study participants was less due to frailty. Simply concluding the association between corn, callus, and toe-grip strength should be avoided because the generation of corn and callus are limited for this targeted population and rate of having corn and callus are low.
Toe deformities include the hallux valgus and lower-toe deformities. Interestingly, some patients have no toe deformity, whereas others have multiple toe deformities.
Mickle et al suggest that toe deformation of the lower toes changes the load distribution during walking because such a toe condition results in the toes being pulled back into extension, thus reducing the contact areas of the toes .
As the presence of corn and callus trigger pain, both toe deformities, including the hallux valgus and lower-toe deformities, may generate pain . Therefore, pain may greatly affect the walking speed.
Hughes concluded that toes roles as the contact portion of three-quarter of the walking cycle and weight bearing function . The balance transition from the medial to the lateral side of a patient with hallux valgus is significantly delayed . The toe plays an important role in maintaining the body’s balance and reflects the lower limb function. Therefore, appropriate efforts to strengthen the toe function, such as washing, nail care, stretching, and exercise are required. In the present study, no significant relationship was observed between the toe-grip strength or walking speed and the hallux valgus and floating toes.
In the present study, no significant relationship was observed between toe-grip strength or walking speed and hallux valgus and floating toes.
When the foot arch deforms, occurrence of a bunion may be inevitable. When the foot spreads laterally due to muscle degeneration or other reasons such as arch deformation, it causes the adductor muscle of the toes to be pulled outward; thus leading to the formation of the hallux valgus. Many studies have majorly focused on hallux valgus among other toe deformities [66, 67]. Further, a report also indicated an association between the degree of hallux valgus and toe-grip strength .
In this study, the analysis was conducted by dividing the degree of hallux valgus into three stages. Our study revealed that prevalence of hallux valgus (> 15°) in women was 29·9%–35·9%, which was higher than that in men; however, it did not reveal the angles of hallux valgus and walking speed. The small sample size may be associated with the results of undifferentiation of angles of hallux valgus.
Future studies with more samples may explore the association between the angles of hallux valgus and walking speeds. Arch deformity may prevent the toes from firmly attaching to the floor, resulting in floating toe complication, which has recently gained attention of the researchers [69, 70]. However, the number of studies remain limited both in Japan as well as overseas. Uritani et al. concluded from their study that the floating toe is associated with walking ; however, further studies are required to confirm this.
The study showed that negative and significant correlation between walking speed and toe-grip strength. A previous study reported the association between the decreased strength of toe flexor and slow walking . However, correlation was not so strong. There is a great deal of individual variability, therefore, we were not able to conclude that individual with lower strength of toe flexor have longer walking time. Further studies will explore this association in the stratified aging group.
The foot data obtained by assessing and measuring the foot from various angles revealed the prevalence of foot disorder in frail old-aged people. Future strategies can be considered based on the foot deformities that have higher prevalence. For example, awareness regarding skin care should be spread among older people as well as care givers, which may lead to a higher usage of skin ointments and appropriate methods of skin care, leading to prevention of cracks in the skin.
The results of multiple regression analysis implicated the presence of an impaired area of foot condition, which may trigger lower walking speed and toe-grip force.
It provided insights into future strategies to prevent the foot condition from worsening as well as the possibility of effective nail care and prevention of skin lesion in maintaining the toe-grip strength or walking speed, which are key indicators of foot health. There are high chances of frail old-aged people falling and becoming bedridden in the future. According to the Ministry of Health, Labor and Welfare, fractures and falls are the third most common cause of need for long-term care for people who are certified as requiring care level 4 or 5 by long-term care insurance that requires severe long-term care . Therefore, new approaches which incorporate appropriate foot care into daily practice among day service or day care would be desirable. Information on how to prevent the occurrence of nail thickness, nail fungal infection, toe and foot deformity, corn, and callus as well as information on how to appropriately provide foot care and promote the stretching of plantar fascia and exercise of foot would be key components for future strategies of preserving foot health for this age group as well as other age groups living in the community. In addition, the delivery of knowledge information and practice of foot care among the caregivers who provide care for people of this age group would be significantly helpful for preserving their foot health.
Our study has limitations with regard to the data collected. Because of the physical condition of older people, some of the participants were unable step on to the table of the Foot Look machine. Therefore, it was impossible to obtain data from all the participants. Although there are very few studies that describe the factors causing deformation of the arch and toes, there are various possible factors that need to be considered. This study, however, does not mention to them. In addition, the increased association between the decrease in skeletal muscle mass with arch and toe deformity because of aging was not evaluated in this study, although this is something that has gained much attention in the recent years.