**4. Clinical assessment of balance**

other segments are disturbed, producing instability. Thus the precise movement of distal segments can be realized only by stabilizing more proximal segments [66]. Just before a voluntary movement, the stretch reflex response in agonist muscles is enhanced [67], consistent with a stabilizing effect. In healthy subjects, axial tone is modulated sensitively and dynamically, this control originates, at least in part, from tonic lengthening and shortening reactions, and a similar type of control appears to exist for postural tone in the

130 Peripheral Neuropathy - A New Insight into the Mechanism, Evaluation and Management of a Complex Disorder

To preserve balance, postural adjustments are made through flexible synergies, in which the activity of the participating muscles is set to task-specific conditions [5]. The most rapid postural reactions are a class of motor activities mediated primarily by inputs derived from the forces and motions of the feet upon the surface of support [69]; the supporting reactions and placing reactions (tactile, visual and vestibular) adapt the activity of the postural muscles of the limbs to their function of body support. Perturbations to balance imply that the central nervous system select patterns of muscle activation that are appropriate for a variety of perturbations [70], in agreement with biomechanical constraints such as those imposed by inter-segmental dynamics and musculoskeletal geometry [71]. A confluence of proprioceptive and vestibular modulation to the basic centrally initiated template of activity may establish the amplitude pattern of the muscle response synergy [70, 72-73]. The confluence of sensory inputs presumably permits the proprioceptive and vestibular inputs

It has been suggested that postural adjustments can be described as a single feedback control scheme, with scalable heterogenic gains that are adjusted according to biomechanical constraints [74]. In addition, muscle weakness and muscle fatigue have to be considered. Clinical evidence have shown that patients with polyneuropathy who have ankle weak‐ ness are more likely to experience multiple and injurious falls than are those without specific muscle weakness [75]. Also, an altered posture, which is common in patients with muscle weakness, may interfere with the position of the centre of mass, and there by also cause

In healthy subjects, inducing localized muscle fatigue at various musculatures has been shown to adversely affect postural control. Plantar-flexor muscle fatigue may impair the effectiveness of postural control and increase the amount of postural regulatory activity required to control unperturbed bipedal posture when the quality of the postural support surface information is altered (by standing on a foam support surface) to a greater extent than when it is not [77]. In healthy subjects who perform fatiguing exercises, acute effects of fatigue may differ between joints, with the most substantial effects evident at the lower back, followed by the ankle and recovery of postural control [78]. Also, during quiet standing, fatigue of trunk muscles may increase reliance on somatosensory inputs from the foot soles and ankles for controlling posture [79], while lumbar fatigue impairs the ability

proximal muscles of the arm [68].

balance problems [76].

to sense a change in lumbar position [80].

to reinforce each other righting effects, and prevent to fall.

In order to assess instability or walking difficulty, it is essential to identify the affected movements and circumstances in which they occur (i.e. uneven surfaces, environmental light, activity) as well as any other associated clinical manifestation that could be related to balance, postural control, motor control, muscular force, movement limitations or sensory deficiency.

The clinical evaluation should include a detailed assessment of long tracts, cranial nerves, motor control, motor strength, the eyes and the ears. To evaluate the vestibular system and its relationships with other sensory inputs and the oculo-motor system, specific tests have to be performed, including eye movement recordings and vestibular reflexes.

Standardized scales and questionnaires may be helpful to evaluate and to follow-up deficits that may be evident on daily life activities (e.i. Berg's Balance Scale [81]; Tinetti scale [82]; balance symptoms questionnaire by Jáuregui-Renaud et al.[83]), as well as falls [84]. Some clinical test include the "Get up and go test" [85], the five-step test and the Functional Reach [86], the Mobility Fall Chart [87] and the evidence based risk assessment tool [88], among others. However, before choosing a tool the clinician should consider the purpose of its design and the purpose for which the tool is to be applied, as well as its reliability.

To evaluate balance, a neurological examination should be performed, including an examina‐ tion of motor and sensory function; care should be taken to assess static and dynamic postural control and gait, as well as to identify visual and vestibular disorders. During static upright stance, it is important to observe the width of the stance, the symmetry of the stance, the balance at the level of the joints as well as the trunk posture, while changing the sensory conditions (i.e. visual input and the surface of support). The sensory conditions may include at least: standing with the eyes open and closed, on a hard and a compliant surface, standing with the feet together and balancing on the two legs. To clinically asses the response to simple pertur‐ bations, the clinician may observe the reaction to push gently the patient while standing.

To measure balance, different aspects may be analysed: electric potentials due to muscle activation, kinematics that is concerned with movement itself and kinetics, concerned with the forces and the moments of forces that are developed during movements. To record kinetics, force platforms are used. The centre of pressure is recorded over a period of time, while standing on the force platform (wearing a safety harness) under different sensory conditions. Several moving force platforms have been designed in order to create dynamic conditions, while maintaining a constant angle between the foot and lower leg and moving the visual enclosure of the platform, which can be coupled to the body sway. Regardless of the technique of measurement used, to interpret any recording of body sway, several factors have to be considered, including the fact that body sway increase with age, with an increased dependence on vision [53, 89-90], and may be affected by body weight and gender [90-91]. In patients with polyneuropathy, special care should be taken in considering adaptive compensation to changes in biomechanical factors as well as sensory deficits.

To evaluate gait, a sensory-motor evaluation should be performed, as well as a postural and skeletal examination [92]. To asses walking it is necessary to analyse the initiation, the stepping, the termination and the associated movements. During stepping, it is important to evaluate at least the speed of walking, the rhythm and the length of each stride.

physical disability in adulthood may well be explained by decreased reserves and compen‐ satory mechanisms together with progression of skeletal deformations due to muscle weakness [101]. On the other hand, during static conditions, patients with Charcot-Marie-Tooth type 2 may show less postural stability than patients with Charcot-Marie-Tooth type 1A disease, but similar than the postural stability shown by diabetic patients with periph‐ eral neuropathy [99]; while in patients with diabetic peripheral neuropathy, unsteadiness relates to alterations in medium-size myelinated afferent fibres, possibly originating from

Postural Balance and Peripheral Neuropathy http://dx.doi.org/10.5772/55344 133

A frequent source of polyneuropathy is diabetes mellitus. Diabetic peripheral neuropathy is initially characterized by a reduction in somesthesic sensitivity due to the sensitive nerve damage, and with progression motor nerves are damaged. During upright stance, compared to healthy subjects, recordings of the centre of pressure in patients with diabetic neuropathty have shown larger sway [95-96, 102], as well as increased oscillation at 0.5-1 Hz [103]. However, in this group of patients, in addition to postural instability caused by neuropathy, balance deterioration may also result from the bio-mechanical impairment caused by progression of foot complications [104], as well as from the compromise of other sensory inputs such as vision [105-106]. Compared to healthy subjects, diabetic patients may have poorer balance during

Balance and gait difficulties are the most frequently cited cause of falling in all age and gender groups [107] A fall is often defined as inadvertently coming to rest on the ground, floor or other lower level, excluding intentional change in position to rest in furniture, wall or other objects [108]. Cavanagh et al. (1992) [109] have shown that, compared to patients with diabetes but no peripheral neuropathy, patients with diabetic peripheral neuropathy are more likely to report an injury during walking or standing, which may be more frequent when walking on

Epidemiological surveys have established that a reduction of leg proprioception is a risk factor for falls in the elderly [111-112]. Symptoms and signs of peripheral neuropathy are frequently found during physical examination of older subjects. These clinical manifestations may be related to diabetes mellitus, alcoholism, nutritional deficiencies, autoimmune diseases, among other causes. In this group of patients, loss of plantar sensation may be an important contrib‐

Falls occur as a result of complex interactions among demographic, physical and behavioural factors. Risk factors may be intrinsic or extrinsic: intrinsic factors include demographic and biological factors, while extrinsic factors encompass environmental and behavioural factors [108]. Among other risk factors, the occurrence of falls may be significantly associated with lower extremity weakness, which can be measured by knee extension, ankle dorsiflexion, and chair stands [113], visual acuity of less than 6/12 [114], lower extremity impairments [108-109]

Apart from sensorymotor compromise, fear of falling may relate to restriction and avoidance of activities, which results in loss of strength especially in the lower extremities, and may also

standing in diminished light compared to full light and no light conditions [105].

utor to the dynamic balance deficits and increased risk of falls [34, 109].

spindle secondary terminations [40].

irregular surfaces [110].

and poly-pharmacy [115-116].

be predictive for future falls [117-119].

The analysis of gait may include measurements of joint kinematics and kinetics, other meas‐ urements include electromyography, oxygen consumption and foot pressures. Using electro‐ myography, specific muscles or muscle groups during movement can be studied. A kinematic evaluation (e.i. joint angles, stride length, walking velocity) may be performed by optoelectric methods as well as by tracking the position of the body segments using light-emitting markers. Power is a kinetic variable, to assess the rate of work performed at a given joint [93], which allows to identify when the muscle is generating or absorbing mechanical energy (concentric or eccentric contraction).
