Mary B. Becker

Postural Instability in Patients with Diabetic Sensory Neuropathy

OBJECTIVE Recent survey evidence suggests that sensory ataxia due to diabetic neuropathy may be a more frequent and serious problem than is commonly recognized. This view is further supported by research that confirms the major contribution of the somatosensory system to the control of posture. We therefore sought to determine the effects of significant diabetic distal symmetrical polyneuropathy on the control of posture. RESEARCH DESIGN AND METHODS Fifty-one subjects, divided into three groups, participated in this study. Seventeen had diabetes and significant sensory neuropathy, 17 had diabetes and no neuropathy, and 17 had neither diabetes nor neuropathy. The subjects were matched across groups, and stringent exclusion criteria were applied. Postural stability during quiet standing was measured using a force platform. In addition to electrophysiological and quantitative sensory tests of neuropathy, a number of physical and functional characteristics were measured for all subjects. RESULTS Postural instability was found to be significantly associated with sensory neuropathy, but not with diabetes per se. Patients with sensory neuropathy demonstrated between 66 and 117% more instability than did control subjects (depending on the testing condition). Based on multiple linear regression analyses, the most significant correlates of instability were the quantitative sensory measures of neuropathy and age. CONCLUSIONS The loss of sensory perception secondary to diabetic distal symmetrical sensory neuropathy has a markedly detrimental effect on postural stability. The deficit is greatest when visual or vestibular cues are absent or degraded. Patients with neuropathy need to be informed of the postural consequences of this condition to limit the potential morbidity caused by falls.

The Mechanism of Plantar Unloading in Total Contact Casts: Implications for Design and Clinical Use

Although the total contact cast (TCC) has been shown to be an extremely effective treatment for the healing of plantar ulcers in diabetic patients, little is known about the biomechanics of its action. In this study, plantar pressure and ground reaction force measurements were obtained from over 750 foot contacts as five subjects with known elevated plantar forefoot pressures walked barefoot, in a padded cast shoe, and a TCC. Peak plantar pressures in the forefoot were markedly reduced in the cast compared with both barefoot and shoe walking (reductions of 75% and 86% respectively, P < 0.05). Peak plantar pressures in the heel were not, however, significantly different between the shoe and the TCC, and the longer duration of heel loading resulted in an impulse that was more than twice as great in the cast compared with the shoe (P < 0.05). An analysis of load distribution indicated that the mechanisms by which the TCC achieves forefoot unloading are (1) transfer of approximately 30% of the load from the leg directly to the cast wall, (2) greater proportionate load sharing by the heel, and (3) removal of a load-bearing surface from the metatarsal heads because of the “cavity” created by the soft foam covering the forefoot. These results point out some of the “essential design features” of the TCC (which are different from what had been previously supposed), support the use of the TCC for healing plantar ulcers in the forefoot, but raise questions about its utility in the healing of plantar ulcers on the heel.

Diabetic sensory neuropathy effect on ankle joint movement perception

OBJECTIVE To determine if diabetic subjects with lower extremity cutaneous sensory neuropathy also have a loss of ankle joint movement perception. The strength of association between measurements of ankle joint movement perception and measures of cutaneous sensory function was also investigated. DESIGN Diabetic subjects with and without sensory neuropathy and individuals without diabetes participated in this study. SETTING All subjects were community-living individuals. PARTICIPANTS Fifty-one subjects, ages 40 to 68. Seventeen of the 34 subjects with diabetes had significant distal sensory neuropathy as determined by cutaneous perception of mechanical vibration. All individuals without diabetes were volunteers from the community. Most subjects with diabetes were recruited through direct referral from their physicians. INTERVENTIONS Ankle joint movement perception threshold (JMPT) was assessed using a device designed for this study. Cutaneous sensory function under both halluces was measured for vibration perception using a vibrometer and for touch-pressure perception using Semmes-Weinstein monofilaments. MAIN OUTCOME MEASURES Ankle JMPTs (degrees) were compared to measurements of cutaneous vibration perception (volts) and touch-pressure perception (monofilaments force ratings). RESULTS Diabetic subjects with cutaneous sensory neuropathy demonstrated a significant loss of ankle movement perception (p < .01). Correlation between JMPT and cutaneous sensory tests ranged from Spearmans rank r = .43 to .67. CONCLUSIONS Although individuals with cutaneous sensory loss secondary to diabetic neuropathy also demonstrated loss of movement perception at the ankle, the relatively low explained variance between the two types of assessment (18% to 45%) indicates that the severity of ankle joint movement perception deficits cannot be directly implied from cutaneous sensory tests.

Design criteria for rigid rocker shoes.

In this study nine different rigid rocker shoe designs were tested in 17 symptom-free male subjects and compared with the control condition of a flexible, non-rockered extra-depth shoe with the same flat insole. Effects of both rocker height and axis location were explored. Peak pressure was reduced at most forefoot locations by rocker shoes, but increased in the midfoot and heel. Axis location was found to have an important effect, particularly on hallux pressures. On average the best axis location for reducing metatarsal head (MTH) pressure was in the region of 55-60% of shoe length, while for the toes it was 65%. There was a mean trend towards optimal reduction of pressure in one of the rocker shoe conditions at each anatomical location, but the axis position for this optimal placement was variable across subjects and anatomical locations. While most configurations of the rocker shoes were superior to the control shoe, no single configuration was optimal for all subjects at all sites or even for all subjects at the same site. Therefore, some form of plantar pressure measurement in conjunction with gait training to ensure correct use of the rocker shoes would appear to be essential if the pressure reducing effect of the rigid rocker bottom shoe is to be optimized.

Neuropathic gait shows only trends towards increased variability of sagittal plane kinematics during treadmill locomotion.

Patients with diabetes mellitus (DM) and peripheral neuropathy (PN) are at greater risk of falling and of suffering injuries during falls. It has been hypothesized that PN leads to changes in gait variability that may account for this increased risk. The purpose of this investigation was to analyze the variability of the sagittal plane kinematics of diabetic neuropathic (NP), diabetic non-neuropathic (NNP) and age- and weight-matched control subjects (Control) during motorized treadmill walking at constant speed. While there were distinct trends towards increased variability within the three diagnostic groups (NP > NNP > Control) for several measures of gait variability, most of these trends were not statistically significant. We hypothesize that motorized treadmill walking may be inherently less variable than overground walking and that statistical measures of variability may not be sufficient to fully characterize stride-to-stride variability in human locomotion.

Foot Function in Diabetic Patients after Partial Amputation

The function of partially amputated feet in 10 patients with diabetes mellitus was studied. First-step bilateral barefoot plantar pressure distribution and three-dimensional kinematic data were collected using a Novel EMED platform and three video cameras. Analysis of the plantar pressure data revealed a significantly greater mean peak plantar pressure in the feet with transmetatarsal amputation (TMA) than in the intact feet of the same patients. The heels of the amputated feet had significantly lower mean peak plantar pressures than all the forefoot regions. A significantly greater maximum dynamic dorsiflexion range of motion was seen in the intact compared with the TMA feet. However, no difference was noted in the static dorsiflexion range of motion between the two feet and there was, therefore, a trend for the TMA feet to use less of the available range of motion. Given the altered kinematics and elevated plantar pressures noted in this study, careful postsurgical footwear management of feet with TMA would appear to be essential if ulceration is to be prevented.

Vibration perception threshold testing in patients with diabetic neuropathy: ceiling effects and reliability.

Aims  To test the reliability of a new vibrometer (Maxivibrometer) which was constructed so that vibration perception threshold (VPT) could be determined without the disadvantage of the off‐scale measurements frequently experienced with the Biothesiometer.

The role of cutaneous information in a contact control task of the leg in humans

The aim of this study was to examine the effect of loss of sensation in the plantar surface of the feet on the learning of a contact control task. It has previously been shown that the biarticular thigh muscles control the external force exerted by the feet by finely regulating the net knee and hip moments. Based on literature which demonstrates strong projections of cutaneous afferents on the motoneurones of biarticular muscles, it has been assumed that this regulation is controlled on the basis of information from the plantar mechanoreceptors of the feet. Subjects with diabetic neuropathy often exhibit marked sensory loss in the distal extremities and thus provide a useful model for studies of the role of afferent input in motor control. Twenty subjects with diabetes mellitus were divided equally between those who had significant peripheral neuropathy and those with no apparent signs of neuropathy. By means of quantitative sensory and motor testing it was possible to select two relatively homogeneous groups matched for age, gender, height, medication, leg strength, weight and duration of diabetes. The task was to learn to push on a force platform with the right foot in four given directions. The foot was not moved relative to the force platform. Visual feedback specifying the direction and magnitude of the ground reaction force was provided on a TV screen. Once subjects had learned to apply the correct force, they were required in the second part of the experiment to maintain a given force direction without visual feedback. Force data and position data were collected and EMG activity was recorded for six muscles of the upper leg. The results showed that all subjects from both groups increased the time they stayed on the targets as they repeated the task (p < 0.01). The accuracy of the task was significantly lower for the neuropathic group than the group with normal sensation (p < 0.05). There were no differences between the two groups in the rate of improvement and both groups showed the same amount of drift of the applied force when visual feedback was removed. There were no significant differences between the two groups in the activation patterns of the thigh muscles. The activation of the biarticular muscles was increased as performance of the task improved and the correlation co-efficients between the activation pattern and the net joint moments improved. The results suggest that mechanoreceptors of the plantar surface of the feet play an important role in the accurate coordination of contact control leg tasks, although the role of other afferent inputs, which may also be degraded in diabetic neuropathy, cannot be excluded. However, this study could not demonstrate that the regulation of the net joint moments by the biarticular thigh muscles is based on information from the mechanoreceptors of the feet. The strong projections of cutaneous afferents on the motoneurones of biarticular muscles do not appear to play a role in the organization of the activation of muscles on an ongoing basis and may be primarily used to allow fast adjustments as a response to unexpected disturbances.