Assessment and treatment of biomechanical properties of foot and mobility disorder in elderly with type 2 diabetes

Abstract

The prevalence of people suffering from diabetes mellitus is rising. This disease causes impairment in the blood glucose regulation and peripheral circulation, which may lead to complications that begin at the most distal part of the lower limbs. Subsequently, the disease may end up in diabetic peripheral neuropathy or foot ulceration. Concerning diabetic foot ulceration, there are various predisposing factors. Apart from the decrease in the sensation over the sole of foot, an increase in plantar pressure is one of the factors contributing to the development of foot ulcer. People with diabetes are prone to have increased plantar pressure due to the non-enzymatic glycosylation of collagen which increases the stiffness of the soft tissue of the sole. With such an increase in stiffness, the shock absorption ability is reduced during weight bearing activities and wear and tear of the soft tissue due to microtrauma might occur in this group of people. Besides, dehydration of soft tissue due to aging would reduce the thickness of plantar soft tissue and increases the likelihood of skin breakdown. This explains why foot ulceration is more commonly observed in elderly with diabetes. As the thickness and stiffness of plantar soft tissue are found to be related to plantar pressure, various devices have been recently developed to assess the thickness and stiffness of the plantar soft tissue. Such device can be useful in predicting the risk of foot ulcer. However, there is a lack of a reliable and standardized assessment on this aspect. Apart from the change in biomechanical properties of foot, elderly with diabetes were found to have higher chance to fall and present in deteriorated mobility performance as compared with healthy age-matched control. Some studies suggested that the higher risk of fall might be contributed by the impairment over the ankles, including a decrease in ankle joint proprioception and muscles strength, and an increase in the stiffness in ankle dorsiflexion. However, no previous study has examined the influence of the abovementioned ankle characteristics on the risk of fall and mobility deterioration in diabetic population. Besides, no previous studies have examined the effects of targeted exercise training to improve the balance performance specifically to people with diabetes. In order to fill up the above research gaps, three inter-related studies with specific objectives for each study were carried out. The objectives of the three studies are: (I) To investigate the test-retest reliability of the innovative Ultrasound Foot Scanner System in measuring the thickness and stiffness of plantar soft tissue of healthy subjects in sitting and standing positions; (II) To investigate the correlation between the ankle muscle strength, range of motion of ankle dorsiflexion, ankle joint proprioception and the mobility performance as measured by Timed Up and Go test in elderly with type 2 diabetes; (III) To investigate the effectiveness of a 10-week exercise program with specific regimen designed, based on findings obtained in study II, that aims at improving the balance and mobility performance in elderly with type 2 diabetes. The summary of the methodology and the results of the three studies are shown as below. Study I: Method and results: Fifteen healthy subjects were recruited in this study. Thickness and stiffness of the plantar soft tissue over the pulp of big toes, 1st metatarsal head, 2nd metatarsal heads, and 5th metatarsal heads and heel pads were measured by an innovative Ultrasound Foot Scanner System. The measurements were performed in both sitting and standing positions respectively. Same procedures were repeated again after one week-time for the retest assessment. The results obtained in sitting and standing in the first assessment day was compared. Our results showed a significant and excellent test-retest reliability (all Intraclass Correlation Coefficient (3,2) >0.90) (all p<0.001); paired t-test showed that the plantar soft tissue became significantly thinner (with percentage decrease ranged from 10% to 14% at various sties) and stiffer (with percentage increase ranged from 123% to 164% at various sites) when changed from a sitting to standing position (all p<0.05). Study II: Method and results: Eighty-five community dwelling elderly who had been diagnosed with type 2 diabetes were recruited. Timed Up and Go test was used to assess their mobility performance; active ankle joint repositioning test was used to assess for ankle joint proprioception sense; weight-bearing lunge test was used for assessing the stiffness of ankle dorsiflexion and Cybex Norm dynamometer was used to assess the ankle muscle strength (peak dorsiflexors and plantar flexors torque). Pearson correlation coefficient was used to analyze the relationship between Timed Up and Go test and the following independent variables: gender, age, history of diabetes, body mass index (BMI), glycated hemoglobin (HbA1c), normalized peak torque of ankle dorsiflexors, normalized peak torque of ankle plantar flexors, weight-bearing lunge test distance and active ankle joint repositioning error. Multiple regressions were used to examine the degree of association between the aforementioned independent variables and Timed Up and Go test. Our results showed that age, body mass index, normalized peak torque of plantar flexors and dorsiflexors, active ankle joint repositioning test errors and the weight-bearing lunge test distance were significantly associated with the Timed Up and Go test (all p<0.05). These physical characteristics, together with the demographic data of the subjects contributed to 59.9% of the variance in the findings of the Timed Up and Go test. Study III: Method and results: Ninety-eight community dwelling elderly diagnosed with type 2 diabetes were recruited in community centers and divided into exercise group and control group. A 10-week exercise program was implemented in order to improve the mobility performance, postural control and reduction in the stiffness of plantar soft tissue. Based on the findings obtained in study II, a specially designed exercise program was adopted targeting on the ankle characteristics that we identified in this group of client. In addition, home exercise was emphasized in the training period. Subjects in the control group did not receive any exercise training during the study period. Outcome measures included Timed Up and Go test for mobility performance; Sensory Organization Test for postural stability; single leg stance test for unipedal balance. Two-way repeated measures ANCOVA with HbA1c entered as co-variate was used for interaction analysis. Our results showed that there were time x group interaction in the Sensory Organization Test composite score, visual ratio and vestibular ratio. Pair t-test showed significant within-group differences in the abovementioned variables in the exercise group. Trends of improvement were found in Timed Up and Go test and single leg stance test in exercise group.