Posture (Chapter 13) Lecture Notes 2024 PDF

POSTURE (CHAPTER 13) PT 5501 FALL 2024 Dr. Lucie Pelland  Role of Postural Assessment in PT ◦ The INITIAL OBSERVATION of the patient ◦ Take not of posture (standing, sitting, bed, etc...) and how transition from one posture to another ◦ Starting point in formulating a clinical hy...

POSTURE (CHAPTER 13) PT 5501 FALL 2024 Dr. Lucie Pelland  Role of Postural Assessment in PT ◦ The INITIAL OBSERVATION of the patient ◦ Take not of posture (standing, sitting, bed, etc...) and how transition from one posture to another ◦ Starting point in formulating a clinical hypothesis ◦ Identify potential causes for MSK pain and movement dysfunction § What can the individual do? § How does he/she do this? § Why does he/she do it that way? ◦ Provide insight into risk for falls in different populations ◦ Estimate developmental progression (motor and cognitive) in pediatrics Good Posture – An Invented Problem?  Definition of Terms ◦ Posture = the orientation of the body in space (and the associated organization of the segments). Posture can be static or dynamic ◦ Static Posture = distribution of segmental orientation maintains the body in equilibrium (sum of forces and sum of moments of force = 0) ◦ Dynamic Posture = body and/or its segments are moving ◦ Stability = CoM and vertical projection from CoM (line of gravity, LoG) are maintained within base of support (BoS) ◦ Balance = sensory-motor systems that maintain the body in the desired position (e.g., standing) and the CoM within the BoS ◦ Posture Control = transition from one postural set to another - process of achieving, maintaining, or restoring balance Effects of Different Postures on Equilibrium In seated position, the CoM shift superiorly and BoS includes boundaries of the feet and the outline of the chair  System Integration for Postural Control Anticipatory to compensatory postural adjustments – from preparing postural set for an upcoming (planned) movement to compensating for an error in planning or an unexpected perturbation Example: Prior to lifting 1 or 2 arms in front of us, the ankle PFs contract to draw the tibia (and the rest of the body) posteriorly (slight shift of the body CoM within BoS in the posterior direction). As raising the arms forward will draw the body CoM anteriorly, the preparatory posterior shift in CoM ensures that the CoM will remain within the BoM during arm raising motions. APAs (anticipatory postural adjustments) prepare the posture system for an upcoming movement to keep the CoM centered within the BoS at the end of the intended movement. Balance requires the integration of All postural adjustments are 'learned' through 'trial and error' peripheral and central systems  Postural Control Strategies ◦ Postural sway = the small amounts of displacement that maintain the body CoM within BoS ◦ Static posture maintained through resting muscle tone and small magnitude muscle activation triggered by sensory inputs (muscle spindles) Small displacements in posture are controlled by the ankle strategy. Larger displacements (or stance on a small BoS) are controlled by the hip strategy – pendulum The muscles activated dependent on the direction of displacement e.g., anterior displacement Recording of the movement of the controlled by activation of PF. center of pressure recorded with an individual standing on a force plate  Postural Control Strategies ◦ Why is a postural displacement (perturbaion) in the posterior direction (backward sway) more difficult to control (recover from) than a displacement in the anterior direction? Hint? LoG  Postural Control Strategies ◦ During movement (dynamic stance), muscle strategies are needed to correct the position of the CoM within the BoS - avoid a fall ◦ Three different strategies are available = § Anticipatory synergy adjustments (ASA) - motor strategy prior to APAs organized (at a latency of 250-300 ms prior to a planned movement) to: § Maintain the movement that is intended for the task or action § Provide muscle activation that allows for movement disruption (such as preparing for perturbations) § Anticipatory postural adjustments (APA) - specific trunk and limb postural muscle activation that occur prior (latency of about 100 ms) to planned or anticipated movements – preparation of posture to an upcoming motion § Compensatory postural adjustments (CPA) - muscle activations one balance is disturbed to restore balance or to reduce movement errors in the direction of a movement. ◦ CPAs are triggered by feedback inputs (visual and muscle sensory receptors) Simplified schematic of motor control underlying ASAs and APAs Efferent copy sets the 'sensory receptors' for predicted feedback. E.g., setting of muscle spindles for the needed stiffness of a muscle to maintain a postural set during a planned movement This is learned by trial and error – and must be re-educated after an injury or a perior of immobilization Ground Reaction Force / Center of Pressure ◦ GRF = reaction force equal and opposite to the force applied by the body to the ground (supporting surface) ◦ 3D vector ground reaction force vector (GRFV) = vertical, medial-lateral, and anterior- posterior ◦ In quiet standing, the GRFV and the LoG have coincident lines of action – equal and opposite external forces ◦ If GRFV and LoG are misaligned = risk for fall ◦ CoP = the point of application of the force on the ground ◦ Represents the sum of all contact forces = estimate of the position of the ground reaction force vector (GRFV) and position of the CoM ◦ Path of the CoP = time series of the displacement of the CoP during postural sway  Ground Reaction Force / Center of Pressure In quiet standing, the application of GRF under the feet can be recorded CoP = 'sheep dog' around CoM displacement Plots of the CoP for a person in standing. A. Oscillation in the anterior-posterior direction Loadsol (plantar pressure B. Multidirectional control of postural recording system) sway - 'loss of control possible'  Romberg (and Sharpened Romberg) Test Evaluate the effects of different inputs on balance control: Condition 1: quiet standing with feet side by side (integration of proprioception, visual, and vestibular inputs) Condition 2: quiet standing with feet in tandem stance (integration of proprioception, visual, and vestibular inputs within smaller BoS) - sensitivity and accuracy of integration Conditions 3 and 4: As conditions 1 and 2 but with eyes closed (removes visual input) - integration of proprioception and vestibular inputs Conditions 5 and 6: As conditions 1 and 2 but standing on foam (damping of sensory input) - integration of visual and vestibular inputs Conditions 7 and 8: As conditions 5 and 6 but with eyes closed – reliance on vestibular inputs only  External and Internal Moments ◦ External moment determined by the location of the LoG from the segment's CoM, in relation to the joint axis rotation ◦ The moment arm of the external moment is the perpendicular distance from the joint axis of rotation to the force vector ◦ Internal moment, created by passive tissue tensile force and/or muscle contraction opposes the external moment In ideal standing, the LoG GRF = external force passes close to joint axes of Moment arm of external force rotation. = distance from GRFV and If GRFV is concident with axis of rotation LoG, then the position can be External moment = (a) causes maintained with only 'resting' knee extension (b) causes muscle activity and 'safe' knee flexion tensile force from soft tissues Location of GRFV relative to the knee axis GRFV Describe effects of GRFV and CoM location for this situation. What muscle activity would you expect? Why?  ACL Injury Risk: Single Leg Landing What muscle activity would be important as an APA to reduce the risk of injury? QUESTIONS COMMON DEVIATIONS FROM IDEAL SPINAL ALIGNMENT  SCOLIOSIS ◦ Scoliosis: a 3D deviation in the alignment of the spine o Change in alignment dictated by coupled motion available at spinal facets – these lie in different planes resulting in changes in alignment along transverse (rotary), sagittal (flexion/extension), and frontal (lateral bending) planes ◦ Cause – vicious cycle theory o Change in weight-bearing which induces a deviation in vertebral alignment § Continued change in weight-bearing = asymmetric growth § Continued compensation involving additional levels as compensation  SCOLIOSIS ◦ The combined effects of change in spinal alignment measured using the COBB angle – measured between the superior aspect of vertebra and inferior aspect of inferior vertebra ◦ Apical vertebra = point at which curvature is maximum ◦ Major and Minor curves (minor curve generally compensatory) ◦ Curve named according to convexity = e.g., right convexity = right scoliosis Left Right S-shaped scoliosis, with a left lumbar curve and a right thoracic curve Cobb angle of 45° = decompensation (effects of gravity causes progression – curve falls along gravitational vector) SCOLIOSIS Possible Functional Scoliotic Postures ◦ Different types of scoliosis o Structural = bony and soft tissue change that are irreversible § Most often involves T-spine with ipsilateral rib hump (on convex side) o Functional = results from underlying cause, such as leg length discrepancy and is reversible o Idiopathic = no known cause (or limited evidence of a causal effect of an underlying conditions – genetic, neuromuscular, metabolic, etc. Spondylosis, Spondylolisthesis, and Spondylitis Spondylolisthesis Grading  Lumbo-pelvis and Hip Abnormalities Sway back – anterior displacement of pelvis and posterior displacement of upper trunk Posterior rotation of pelvis causes flattening of L-spine T-spine kyphosis Increase hip extension maintains GRF posterior to hip (with anterior hip ligaments for support) Often associated with anterior hip pain and increased compressive Posterior pelvic tilt – reduced forces on the intervertebral discs of Anterior pelvic tilt – reduced the lumbar spine length of hip extensors and/or LDD length of hip flexors Decrease pelvic tilt = lumbar Increased lumbar lordosis and vertebrae stacked more vertically – hip flexion decreased volume of intervertebral Increased compressive forces foramen on lumbar facet joints Can be associated nerve root Often associated with LBP compression QUESTIONS