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Abnormal postural control Learning objectives • Following the completion of this chapter, the student must be able to 1. Summarize fall rates and risk factors for falls among persons with neurologic pathology 2. Give examples of sequencing and timing problems that affect the coordination of postural motor responses. 3. Discuss two deficits affecting the ability to modify postural motor responses to changing task and environmental conditions Learning objectives continued 4. Describe the effect of impaired anticipatory postural control on voluntary movement – which neural pathologies are likely to result in these types of problems Introduction • Balance is critical to independence in daily living activities. • Impairments in postural control producing loss of stability have a profound impact on the daily life of individuals with neurologic pathology. • The consequences of impaired stability include loss of functional independence, increased prevalence of disability and falls. Falls following neurologic pathology • Falls are a major problem among persons with neurologic pathology. • Among individuals who had a stroke, falls are four times more likely to result in a hip fracture, because of increased rates of osteoporosis in their paretic side. • Falls are also a significant problem in Parkinson’s disease (PD), with falls rates ranging from 40% – 68% • Falls were one of the most common reasons for emergency hospital admissions among people with PD. Falls following neurological pathology continued... • Fall rates are high among people with multiple sclerosis • As was true for older adults, the majority of falls in persons with neurologic pathology are associated with mobility, occuring during walking, transfers, and stair climbing. Risk factors for falls in neurologic population • • • • Lower balance score (< 30 on Berg balance test) Presence of apraxia Cognitive deficits Lower Functional Independence Measure (FIM) score Factors predicting falls in persons with Parkinson’s disease • • • • • • • • • Multiple medications Increased physical disability Dementia Depression Increased severity Marked response to levadopa Dyskinesia Impaired balance and gait Reduced stability when performing concurrent tasks 3 Variables predicting falls in persons with multiple sclerosis • Balance • Walking ability • Use of cane Problems in the motor components of postural control • Motor components include neuromuscular (coordinating multiple muscles into postural muscle synergies) systems and musculoskeletal systems Motor coordination problems • Sequencing problems – delayed recruitment of synergistic muscles, co activation of antagonist muscles resulting in stiffness • Problems with the timely activation of postural responses. • Problems adapting postural activity to changing task and environment demands. Musculoskeletal contributions to coordination problems • In a person with a central nervous system lesion, musculoskeletal disorders develop most often secondary to immobility and restricted movement. • Alignment – refers to the relationship of body segments to one another as well as to the position of the body with reference to gravity and the base of support. Alignment determines movement strategies that will be effective in controlling posture. Musculoskeletal contributions to coordination problems continued Alignment continued • Children with CP – restricted ROM, contractures, atypical postures • Unilateral neural lesion – change in the position of the body with reference to gravity and the base of support. Weight displaced to non involved side, wide base of support. • Neurological deficit – center of mass displaced either forwards or backwards Musculoskeletal contributions to coordination problems continued • Changes in alignment can be viewed as either a musculoskeletal impairment or as a strategy compensating for other impairments. Musculoskeletal contributions to coordination problems continued • Constraining movement at a joint • Example: AFO’s (ankle foot orthoses) • The type of device we use to contol position and motion at the ankles can have a significant impact on the sequencing and timing of muscles used to recover balance. • AFOs that restrict motion at the ankle will reduce the participation of ankle joint muscles in the control of stability. This will result in an increase in the use of hip and trunk muscles for balance control. Loss of anticipatory postural control • The inability to adapt how we move in response to changing task and environmental conditions can be a source of instability in many persons with instability. • Another source of postural dyscontrol is, is the loss of anticipatory processes that activate postural adjustments in advance of potentially destabilizing voluntary movements. • Anticipatory postural activity is heavily dependent on previous experience and learning Sensory disorders • Normal postural control requires (1) the organisation of sensory information from visual, somatosensory and vestibular systems that provide information about the body’s position and movement with respect to the environment, and (2) the coordination of sensory information with motor actions. • Sensory problems can disrupt postural control by (1) affecting a person’s ability to adapt sensory inputs to change in task and environmental demands, and (2) preventing the development of accurate internal models of the body for postural control Impaired postural stability under dual task conditions • Inability to maintain balance while performing multiple tasks have been found in persons with various types of neurologic pathology. Postural control in persons with Dementia • The relationship between impairments in cognitive function and postural control are being studied by many researchers, in part because of the high fall rates of falls reported in persons with various types of dementia, including Alzheimer’s disease Impaired seated postural control • Postural control underlying the ability to sit independently is a critical part of functional independence in ADL. Impaired sitting balance is a frequent occurence in both children and adults with neurologic pathology. • Acquisition of sitting balance in both children with neurologic pathology has been shown to be a good predictor of functional outcomes • Sitting balance has been shown to be a good prognostic indicator of outcome for persons who have had a stroke and traumatic brain injury. Summary • An enormous range of problems can contribute to postural dyscontrol in individuals with a neurologic deficit. • Coordination problems that manifest within postural movement strategies include: (a) sequencing problems; (b) problems with the timely activation of muscle response synergies; (c) disorders related to the scaling of postural muscle activity and (d) problems adapting motor responses to changing task conditions • Musculoskeletal disorders present in individuals with neurologic deficits develop most often secondary to the neurologic lesion. Yet, musculoskeletal problems can be a major limitation to normal postural function in the neurologically impaired patient.