Among the total number of individuals evaluated in this study, plantar protective sensitivity was absent in more than 50% of them and decreased by 36.68%. There was a high percentage of individuals with muscular and dermatological changes, being more evident in the right foot. More than half of the patients had balance changes with a moderate and increased risk of falling, with slightly less than half wearing appropriate shoes. Furthermore, it was possible to identify an increase in plantar pressure, above the values considered normal in the healthy population, especially in the individuals' left foot.
These findings are worrisome since the dermatological and muscular alterations cause the displacement of support and pressure areas in a contralateral way during the walk. Thus, in their presence, there may be an increase in the contact of the foot with the ground in some areas and a decrease in this contact in opposite areas of the plantar surface. These changes associated with loss of protective sensitivity compromise the biomechanics of the feet, altering gait and balance and increasing the risk for the development of plantar ulcers in individuals with NDP.
In NDP, the impairment of fine fibers of type Aδ and C[19], cause a decrease in plantar protective sensitivity, especially regarding the tactile, thermal, pressure and proprioception perception, and the absence of the latter leads to the loss of deep tendon reflexes [20]. Thus, neuropathy leads to insensitivity, and subsequently to foot deformity, with the possibility of developing abnormal gait [21]. Still, due to the lack of a painful response, NDP favors the repetition of trauma in the tissue, and dermatological and bone changes such as calluses and bone prominence [22].
In addition, when there is damage to the peripheral nervous system, a significant deficit in muscle strength can be evidenced, which can lead to losses in the strategies necessary to maintain the stability and balance of the human body during gait, leading to serious future losses, such as ulcerations [23].
Maintaining the balance of the human body depends on the intrinsic coordination of the vestibular system, vision and tactile and proprioceptive information. These components work in an integrated and complementary way and any change in one or more of these systems results in postural instability and, consequently, increases the risk of falls, skin lesions, fractures and prolonged immobilizations [24]. In the present study, 57.5% had a serious risk of falling due to changes in balance, showing that sensory deficit is one of the main causes of postural instability in people with diabetic neuropathy.
Thus, it is evident that the patients included in this study have favorable conditions for the development of plantar injuries and that they would benefit from the implementation of systematic assessment strategies and early interventions to prevent complications resulting from the conditions imposed by the underlying disease.
The evaluation of plantar pressure using baropodometry in order to identify the increase in plantar pressure in vulnerable areas in the feet of people with NDP, has been widely used, as demonstrated by Arts et al (2012) [25] and Waaijman et al (2012 ) [26], to enable changes in patients' shoes and insoles to obtain adequate footwear, with reductions in peak plantar pressure and decreased risk of pre-ulcerations and ulcerations in these individuals [16,27].
NDP is a factor that is related to the increase in plantar pressure mainly in the anterior region of the feet (metatarsal head), and these values of peak plantar pressure expressed in kgf /cm2 or kPa, correspond to the average of the pressure values occurred by region of the sole of the foot (hindfoot, midfoot and forefoot) during dynamic baropodometry, showing the influence that foot deformities have on peak plantar pressure values [10]. Therefore, it appears that in our study there was an increase in plantar pressure in the dynamic examination due to the presence of these deformities.
The pressure center (COP) is a parameter that represents a weighted average of the total pressure exerted on the surface in contact with the ground, where its trajectory and displacement parameters can be adopted as indicators of balance and body posture, thus becoming crucial tools in providing information regarding the postural balance of individuals with NDP [28], in addition to formulating an index capable of evaluating the effectiveness of rehabilitation devices, such as orthoses, dynamic study of the function and process of rolling the foot, calculating the degree of twisting the axis of the foot joint and assessing movement, which can show us the reliability of these parameters for such changes [29].
According to Armstrong, Boulton and Bus (2017) [30] it is likely that there is a relationship between these variables, mean peak plantar pressure, pressure center and contact surface, because with the increase in the time of diagnosis of diabetes, there is an increase in plantar pressure and a greater oscillation of these individuals. Therefore, understanding this process would optimize the physiotherapeutic assessment and treatment procedures, as well as providing early action in the prevention of falls and ulceration.
Footwear considered appropriate must have a thick sole, sufficient width and depth to accommodate a sock and the foot comfortably, the inside of the footwear must be soft and seamless, adjustable with laces or velcro, offering total protection to the toes (round or square toe), sole up to three centimeters, and made with soft raw material [7,18,31]. It should be noted that the use of inappropriate shoes has been described in the literature as a relevant factor for the development of the risk of ulceration and peak plantar pressure [17,32–35].
According to Luna et al (2020) [36], the use of inadequate footwear increases the repetitive local mechanical efforts on the foot in patients with DM and NDP, and the accurate measurement of the foot and shoe length is necessary to ensure a correct fit, avoiding the risk of foot ulcer.
According to Collings et al (2019) [37] and Jarls et al (2020) [29], therapeutic / suitable footwear is often used to reduce high tissue pressures associated with the risk of foot ulceration, therefore, guidelines for the care of the feet of people with diabetes recommend the use of therapeutic shoes or personalized insoles in the preventive management of people at risk of foot ulceration, as defined by the National Institute for Health and Care Excellence [38].
Discharge devices such as suitable footwear reduce peak plantar pressure by 14–76% compared to plantar pressure in the bare feet of individuals with NDP [39], which means that adherence to the use of this device is an important contributor to reducing the foot load [40]. Thus, plantar pressure, weight-bearing activity and adherence play a role in the foot load [41].
The findings on plantar pressure and device adherence confirm the importance of providing people with diabetic foot disease with pressure-reducing interventions and ensuring adherence to their use [42]. In addition, the findings emphasize that, to determine foot load, it is important to look beyond a single foot load factor, as single foot load factors are likely to be insufficient to understand treatment progress [43].
In this study, evaluations were performed only in patients with already diagnosed diabetic peripheral neuropathy. Diabetic patients without neuropathy were not evaluated. Thus, it was not possible to carry out measures of association between neuropathy and the presence of changes, with only measures of frequency of changes being presented. Although this is a limitation, the simple description of the occurrence and types of changes in the feet of patients with neuropathy already constitutes an alert factor for physiotherapists and other health professionals who care for individuals with this patholo