Dynamic Posturography Sensory Organization Motor Control Testing Posture Evoked Response Computerized Dynamic Posturography • Sensory Organization Test—measurement of sway energy under various visual and support conditions. • Motor Control Test—measurement of sway in response to tilt or translation in the support surface. • Posture Evoked Responses—EMG recordings during the Motor Control Test. Measuring Sway Energy • Pt stands on force plates (pressure transducers) • pick up vertical forces – weight distribution • front-back • left-right • Pick up horizontal sheer forces LIMITS OF STABILITY The furthest distance in any direction a person can lean away from midline (vertical) without altering the original base-of-support (by stepping, reaching, or falling) Dynamic Equilibrium Sensory Organization Motor Coordination Determination of Body Position Choice of Body Movement Compare, Select & Combine Senses Select & Adjust Muscle Contractile Patterns Visual System Vestibular System Environmental Interaction SomatoSensation Ankle Muscles Thigh Muscles Trunk Muscles Generation of Body Movement Equilibrium Score • Maximum sway compared to calculated limits of stability • 1 – (Max sway/LOS) • 100 % = No Sway • 0% = Sway reaches LOS • Normed for age and height Sway-Referenced Surface Eyes Closed Sway-Referenced Vision 1 2 3 4 5 6 SOT Sensory Organization Test Fixed Surface Normal Vision Equilibrium Scores • For each of the 6 conditions • Composite of all 6 • Derived Sensory Analysis Ratio Conds. Functional Relevance Somatosensory (SOM) 2/1 Pt’s ability to use input from the somatosensory system to maintain balance. Visual (VIS) 4/1 Pt’s ability to use input from the visual system to maintain balance. Vestibular (VEST) 5/1 Pt’s ability to use input to the vestibular system to maintain balance. Preference 3+6/2+5 The degree to which pt relies on visual info to maintain balance, even (PREF) when the info is incorrect. Sensory Analysis Strategy Analysis • Hip vs. Ankle Dominant • Hip–high frequency, greater effect in horizontal shearing force • Ankle–low frequency, greater effect in vertical forces. COG Alignment • Average weight distribution • Displayed for each conditions • Offsets may reflect: – – – – peripheral sensory neurogenic musculoskeletal adaptation Motor Control Test • Support Surface Translations – Forward – Backward • Sway amplitude • Latency • Weight symmetry Motor ControlTest (MCT) • Amplitudes - Threshold/Small - Mid-range/Medium - Saturating/Large • Directions - Forward - Backward • Measures - Latency - Strength - Symmetry MCT: Normal Latencies • Latencies Slightly Shorter For Large vs Medium Displacements • Latencies Symmetrical Between Left & Right Sides • Possible Deficits: - Extremity/Spinal Orthopedic Injury - Output Pathways • Problem Conditions: - Minor If Isolated - Major If Combined • Possible Treatments: - Rehabilitation? - Lifestyle Unilaterally MCT: Latencies Prolonged Possible Deficits: - Neuropathy - Multiple Sclerosis - Spinal Orthopedic - Brainstem/Cortical Problem Conditions: - Minor If Isolated - Major If Combined Possible Treatments: - Lifestyle Bilaterally MCT: Latencies Prolonged Adaptation Test (ADT) •Slow Toes Up (Down) Rotations - 8 degrees/sec •Sequences of 5 Trials measure response time ADT: Adaptation Test • Sway Energy Scores Higher During Initial Trials Sway Energy Decreases Progressively With Repeated Rotations ADT: Adaptation Test Possible Deficits - Mal Adaptation - Ankle Weakness - ROM impairments Problem Conditions - Irregular Surfaces Possible Treatments - Rehabilitation Elderly Fallers: Fail Toes-Up Adaptation Whipple & Wolfson, Balance, 1990 Falls On Toes-Up Adaptation • Toes-Up Adaptation Failure Significantly Higher in Faller Group 80 70 Non-Fallers 60 Fallers Percentage • Age-Matched Groups of Fallers & Non-Fallers Compared 50 40 30 20 10 0 Trial 1 Trial 5 Posture Evoked Responses • EMG from: Gastrocnemius Tibialis anterior PERs Short Latency approx 30 ms Monosynaptic stretch reflex Mid Latency approx 73 ms Polysynaptic segmental reflex Long Latency approx 104 ms Postural response – possibly automatic?