Balance Assessment

1. Balance Assessment Dr.MohammadShafique Asghar Au.D, (USA). American Board of Audiology, (Board certified audiologist). M.Sc Audiological Medicine,(UK). MCPS (ENT), M,B.B,S (Pb).

2. Balance and postural control Introduction & Definitions

3. Introduction. • In mid 80’s after work done by Horak, Henry and Shumway-Cook) the stress changed from ear to Equilibrium. • Different tests were evolved to test the balance function and recovery of astronauts after descent.

4. Introduction. (cont).. • CTSIB (clinical test for sensory integration of Balance) • CDP (Computerized Dynamic Posturography) These tests were evolved to differentiate between , vest, visual, and central lesions. Generally: Vest lesions = 66% Visual and CNS = 33%

5. Postural control system • Neural and musculoskeletal components, involved in maintaining orientation in the environment. • Functions • Resist gravity • Background muscle tone

6. Postural equilibrium: • Condition in which all the forces acting on the body are balanced such that the COG is controlled relative to BOS.

7. Balance • An individuals ability to maintain their COG over their BOS in a given sensory environment. • Skill the CNS learns to accomplish using multiple interacting system, including passive biomechanical elements, all available sensory systems and muscles, and many different parts of the brain. Equilibrium control is quite proactive , adaptive and centrally based upon prior experience and intension. (Horak, Henry, and Shumway-Cook).

8. Center of gravity • During erect standing with the arms at the side and folded at the waist COG is located in the area of lower abdomen. • In a normal person standing erect COG is placed accurately above the center of base of support.

9. Base of support • The area contained within the perimeter of contact between surface and the two feet.

10. Limits of stability • This is a two dimensional quantity defining the maximum possible COG sway angle as a function of sway direction from the center position.

11. System Model of Equilibrium. • A systemic approach to functional balance/postural control involving multiple interacting sensory and motor components.

12. A: Peripheral sensory input. • Somatosensory organs. • Vision. • Vestibular.

13. B: Central sensory organization • Process by which sensory information is correlated and synthesized. • Normal sensory organization is necessary for maintenance of balance. • During sensory conflict situation the brain must quickly sensory inputs providing accurate orientation information and ignore the misleading information..

14. C: Central Sensory – Motor integration • ????

15. D: Central Motor response. • Postural strategies or synergies that; • Minimize sway, • Maintain the body’s COG within BOS • Control movement of COM over the BOS. • Reactive / Compensatory • Proactive / Predictive • CNS organized patterns of muscle activity that are flexible, adaptable

16. D: Central motor responses (cont)… • Strategies are limited by internal/external constraints • Responsive to learning and intention • Reflexes • Short latency (40-59 msec) • Stereotyped reflexes regulate muscle force in response to external stimulus.

17. D: Central motor responses (cont)… • Automatic postural responses. • Reactivity/Compensatory • Elicited by external stimulus • Response matched to stimulus • Rapid short latency (70-180 msec). • Ankle strategy (fixed support). • Hip strategy (fixed support) • Stepping or compensatory Grasp strategies (change in support).

18. D: Central motor responses (cont)… • Anticipatory postural responses. • Similar to automatic, but preparatory in nature • Proactive / Predictive responses. • Elicited by an expectation of disturbance of COG. • Onset of postural muscle activation in advance of movement.

19. D: Central motor responses (cont)… • Volitional postural movements. • Movement patterns under volitional control. • Self-initiated or elicited by external stimulus. • No fixed relationship between stimulus and movement pattern • Slower (180-250 msec).

20. E: Peripheral Muscle activation • Generates compensatory movements to maintain equilibrium.

21. Balance disorders can be due to… • The position of COG relative to the BOS is not sensed accurately. ( Sensory function loss) • The automatic movements required to bring the COG to a balanced position are timely or effectively coordinated. ( Motor function loss)

22. Sensory organs contributing to balance • Visual system • Somatosensory system • Vestibular system

23. Visual system. • Vision measures the orientation of eyes and head in relation surrounding objects. • Vision plays a significant role in balance, especially when the support surface is unstable.

24. Somatosensory system • Somatosensory input provides information on the orientation of body parts relative to one another and to support surface. • Somatosensory input is provided by: • Tactile, deep pressure , joint receptors and muscle proprioceptors. • Somatosensory input from the contact forces and motion between the feet and support surface is the dominant sensory input to balance under normal (fixed support) conditions.

25. Vestibular system • It does not provide input in relation to external objects. • It measures gravitational linear and angular acceleration of the head in relation to inertial space.

26. Vestibular system (cont)… • When functionally useful somatosensory and visual inputs are available vestibular inputs plays plays a minor role in controlling COG. This is because somatosensory and visual inputs are more sensitive to body sway than the vestibular system. • Vestibular input becomes more important in cases of misleading visual or somatosensory inputs.

27. Utilization of sense of Balance

28. Motor control of Balance • There are principle joint systems involved between the BOS and COG • Ankle • Knee • And hip

29. Anatomy of physiology of Movements • Generally the motion about a joint is controlled by the combined action of at least one pair of muscles working in opposition. • Many leg muscles act on two different joints.

30. Functional anatomy of Muscles involved in balance movements Extension Flexion

31. Properties of three Movement systems Movement systems

32. Properties of Movement systems (cont)… Movement systems

33. Coordination of postural movements into strategies. • When a persons balance is disturbed by an external perturbation, one or combination of three different strategies can be used to coordinate movement of COG back to balanced position

34. Strategies used are…. • Ankle strategy • Hip strategy • Stepping strategy. A step or stumbling reaction is the only movement strategy effective in preventing a fall when the perturbation displaces the COG beyond the LOS perimeter.

35. Strategies (cont)… • In case the COG remains within the LOS, two strategies (Ankle and Hip) or combination of both is used to move the COG while maintaining the initial placement of the feet on the support surface. • A step or stumbling reaction is the only movement strategy effective in preventing a fall when the perturbation displaces the COG beyond the LOS perimeter.

36. Ankle strategy • The ankle strategy shifts the COG while maintaining the placement of the feet by rotating the body as an approximate rigid mass about the ankle • Latency of the response is 90-100 msec.

37. Hip strategy • The movements are centered at hip joint. • The COG shifts in the direction opposite to the hip because of the inertia of the trunk (moving in one direction), generating an opposite horizontal (shear) reaction force against the support surface. • Latency f the response is 85-95 msec.

38. Appropriate use of Postural movement strategies. • The relative effectiveness of ankle, hip and stepping strategies in repositioning the COG over BOS depends upon: • Configuration of BOS • Cog alignment in relation to LOS • And speed of postural movement.

39. Ankle strategy • Most effective in executing in relatively slow COG movements, when the BOS is firm. • And COG is well within the LOS. It also helps in maintaining static posture with COG offset from center.

40. Ankle strategy: Limitations • The amplitude and speed of the ankle movements are biomechanically limited by the torque that can be exerted about the ankle before the feet lift off from the support surface.

41. Hip strategy • Hip strategy is effective when COG is positioned near the LOS perimeter. • And when LOS boundaries are contracted by narrowed BOS. • Hip strategy rely on the horizontal shear force. And so is not limited by the ankle torque.

42. Hip strategy: Limitations • They can not produce larger shifts in COG. • Because hip strategy rely on inertial reaction forces , they can not be used to maintain balance effectively with the COG offset from the center.

43. Stepping strategy • When COG is displayed beyond the LOS , a step or stumbling reaction is the only movement strategy effective in preventing a fall.

44. Stepping Strategy: Limitations • Stepping strategy has fewer biomechanical limitations, it is inefficient, disruptive and usually inappropriate, when simpler ankle and hip movements are effective.

45. Selecting a Postural strategy • It depends upon the persons past experience • and not the conscious decision.

46. Coordination of Head and Body Movements • During standing position the movement of the head relative to trunk has a minor effect as mass of the head is substantially smaller than the trunk. • But during motion of head during postural sway is important , because they have strong influence on two of the two of the three principle senses of balance: Vision and vestibular system.

47. Coordination of Head and Body Movements • Picture page 273 Jacobson book

48. Coordination of Head and Body Movements These can be classified into. • Trunk fixed • Gravity fixed • Combination of both.

49. Trunk fixed strategy • The head and trunk move as a unit. • Thus the strategy fixes the movements of the head relative to the trunk.

50. Gravity fixed • This strategy rotates the head in opposite to the trunk so that the head remains level relative to the gravitational vertical.