Biomechanics of Posture

posture analysis and alignment in different views,
deformities of different parts of the body segments

1. POSTURE T. YASWANTHI (MPT)

2. DEFINITION Posture can be defined as the relative arrangement of different parts of the body with line of gravity. Each structure contributes to equilibrium and stability of body in optimal standing position.

3. TYPES OF POSTURE Humans have the ability to arrange and rearrange body segments to form a large variety of postures. ( Erect bipedal stance ) STATIC POSTURE : The body and its segments are aligned and maintained in certain positions. Examples : standing, sitting, lying, and kneeling. DYNAMIC POSTURE : postures in which the body or its segments are moving Examples : walking, running, jumping, throwing, and lifting.

4. POSTURAL CONTROL It is the persons ability to maintain-stability of body and body segments in response to forces that disturb the body’s structural equilibrium Postural control depends on integrity of CNS, visual, vestibular, and musculoskeletal system. It also depends on information from receptors located in and around joints and from sole of foot. Reactive responses –reactions to external that displaces body COM Proactive response—internally generated destabilizing forces Example :rising arms to catch a ball

5. MAJOR GOAL AND BASIC ELEMENTS OF CONTROL Major goals : Control body’s orientation in space Maintain body’s COG and BOS Stabilize the head vertically –eye gaze is appropriately oriented Elements of control : CNS is able to detect instability and respond to the input with appropriate output to maintain equilibrium of body. Musculoskeletal system have ROM for responding to specific tasks Muscles able to respond with appropriate speed and forces.

6. ABSENT OR ALTERED INPUTS : When inputs are altered , control system respond to incomplete data and posture may be altered . Example : foot “FALLEN ASLEEP”. ALTERED OUT PUTS : Inability of muscles to respond to appropriately to signals from CNS. Example : sedentary elderly persons .

7. MUSCLE SYNERGIES “PERTURBATION” is any sudden change in conditions that displaces the body posture away from equilibrium . perturbation SENSORY MECHANICAL (Altering of visual (displacements-movements input) of body segment or entire body [COM to BOS ]) Postural response to perturbations caused by either platform or by pushes or pulls are called REACTIVE or COMPENSATORY response.

8. SYNERGIES Fixed support synergies Change in support synergies Head supporting strategies The postural responses are called SYNERGIES or STRATEGIES

9. FIXED SUPPORT SYNERGIES: Pattern of muscle activity in which the BOS remains fixed during the perturbation and recovery of equilibrium. Stability is regained through movements of parts of the body but ,the feet remains fixed on BOS. EXAMPLES: Ankle synergy ,Hip synergy ANKLE SYNERGY: It consists of discrete bursts of muscle activity on either the anterior or posterior aspects of the body that occur in response to forward and backward movements of the supporting platform . Muscle activity from distal to proximal pattern.

10. ANKLE SYNERGY Anterior (forward) movement of platform Posterior (backward) movement of body---displacement of body’s LOG posterior to BOS. Activation of dorsiflexors, hip flexors, abdominal muscles, neck flexors LOG back over BOS STABILITY

11. ANTERIOR PERTURBATION Posterior movement of platform Anterior movement of body----displacement of body’s LOG anterior over BOS Activation of plantar flexors ,hip extensors , back and neck extensors LOG back over BOS -----STABILITY

12. HIP SYNERGY It consists discrete bursts of muscle activity in a proximal-to-distal pattern of activation. Fixed-support hip synergy may be used primarily in situations in which change-in-support strategies ( stepping or grasping synergies ) are not possible

13. CHANGE-IN-SUPPORT SYNERGIES Strategies include stepping (forward, backward, or sidewise) and grasping (using one’s hands to grab a bar or other fixed support) in response to movements of the platform. Maintains stability in instance of large perturbations. Tether-release system. Backward movement of platform, person uses steeping strategy to keep from falling forward .it brings body’s COM over a new BOS.

14. HEAD STABILIZING STRATEGIES Proactive strategy occur in anticipation of initiation of internally generated forces caused by change in position from sitting to standing. Used in dynamic equilibrium situation. Example : maintain head during walking. Vertical stability of head is maintained by two types of strategies HEAD STABILIZATION IN SPACE (HSS): Modification of head position in anticipation of displacements of body COG. HEAD STABILIZATION ON TRUNK (HST): Head and trunk move as a single unit.

15. KINETICS AND KINEMATICS OF POSTURE In response to perturbations , active internal forces employed to counteract the external forces that affect the equilibrium and stability of the body in the erect standing posture. External forces : Inertia, Gravity and ground reaction forces (GRF’S) Internal forces : Muscle activity, passive tension in ligaments, tendons, joint capsules and other soft tissue structures . INERTIA : In erect standing posture body undergoes a constant swaying motion called postural sway or way envelop (4inches b/w feet—12 in sagittal plane ,16 in frontal plane) GRAVITY : Forces acts downward from body’s COG (LOG falls within BOS)

16. GROUND REACTION FORCES : When ever body contacts the ground , the ground pushes back on body (GRF ) Vector representing it is called GRFV. GRF have 3 component forces 1 vertical component force 2 horizontal component forces - Medial and lateral direction - Anterior and posterior direction GRFV is equal in magnitude but opposite in direction to GF in erect standing posture The point of application of GRFV is at body’s centre of pressure (COP) COP is located in foot in unilateral stance and b/w feet in bilateral stance.

17. COINCIDENT ACTION LINES : GRFV and LOG have coincident action lines in static erect posture. It help to analysis of effect of these forces on body segments. External and Internal movements: LOG passes at a distance from axis, an external gravitational moment is created and it causes rotation of superimposed body segments around that joint axis unless it opposed by counterbalancing internal moment (muscle contraction).

18. OPTIMAL POSTURE An ideal posture is one in which the body segments are aligned vertically and LOG passes through all the joint axes Normal body structures makes it impossible to achieve, but is possible to attain a posture, close to ideal one In normal standing posture ,the LOG falls close to, but not through most jt. axes -Compressive forces are distributed over the weight bearing surfaces of joints; no excessive tension exerted on ligamentous or required muscles Analysis of Posture from side view: Analysis of posture involves identification of the location of body segments relative to the LOG Body segments-either side of LOG- symmetrical A plumb line is used to represent the LOG Postural analysis may be performed using; Radiography, photography, EMG, electro goniometry, force plates, 3- dimensional computer analysis

19. ALIGNMENT AND ANALYSIS: LATERAL VIEW ANKLE: LOG passes slightly anterior to lateral malleolus

20. ANALYSIS OF KNEE IN SIDE VIEW KNEE : LOG passes anterior to midline of knee and posterior to patella.

21. HIP AND PELVIS ANALYSIS IN SIDE VIEW LOG passes slightly posterior to axis of hip joint, through greater trochanter leads to posterior pelvic tilt on femoral head.

22. SWAYBACK POSTURE LOG falls farther behind the hip joint axis than optimal posture

23. Analysis of lumbosacral and sacroiliac joint

24. ANALYSIS OF VERTEBRAL COLUMN Optimal position of plum line through midline of trunk. At cervical- LOG posterior, extension At thoracic- LOG anterior, flexion At lumbar- LOG posterior, extension

25. ANALYSIS OF HEAD

26. Deviations from optimal alignment view from side Foot and Toes:- Claw toes Hammer toes Knee:- Flexed Knee Posture -Genu Recurvatum Pelvis:- Excessive Anterior Pelvic Tilt Excessive posterior pelvic tilt Vertebral column:- Lordosis Kyphosis Head:- Forward Head Posture

27. CLAW TOES : Hyperextension of MTP joint, flexion of PIP and DIP joints. Callus (thickening of epidermis )Formation on dorsal aspect of flexed phalanges. Affects all toes (2nd through 5th) Hammer Toe : Deformity-hyperextension of MTP and DIP joints - flexion of PIP joint. Callus on superior surface of PIP joints

28. FLEXED KNEE POSTURE This stance is maintained by increased activity by quadriceps, gastrocnemius, soleus, and hip extensors

29. GENU RECURVATUM The hyper extended knee posture, LOG locates anteriorly, puts the posterior joint capsule under tension stress and lengthening of posterior capsule, cruciate ligament. Anterior compression leads to degenerative changes of cartilaginous joint surface.

30. PELVIS Excessive Anterior Pelvic Tilt Excessive Posterior Pelvic Tilt Straightening of lumbar spine and loss of flexibility and also loss its ability to withstand high load.

31. VERTEBRAL COLUMN Kyphosis : It refers to an abnormal increase in the normal posterior convexity of the thoracic vertebral column. Two types : Gibbus Hump Back is a deformity that may occur as result of TB. It forms a sharp posterior angulation in the upper thoracic region of vertebral column Dowager’s Hump is found in post-menopausal women with osteoporosis. Anterior aspect of bodies of series of vertebra collapse due to osteoporotic weakening and therefore, increase in posterior convexity of thoracic area Lordosis : It refers to an abnormal increase in the normal anterior convexities of either the cervical or lumbar regions of the vertebral column

32. HEAD Forward head posture : Anterior location LOG ,increases flexion movement this leads to increase constant isometric muscle tension to support forward head posture Compression of posterior zygapophyseal joints and posterior intervertebral disc and narrowing of intervertebral foramen in lordotic areas of cervical region.

33. ANTERIOR AND POSTERIOR VIEW OF LOG

34. OPTIMAL ALIGNMENT AND ANALYSIS IN ANTERIOR AND POSTERIOR VIEW

35. PES PLANUS (FLAT FOOT ) Reduced or absent MEDIAL LONGITUDINAL ARCH, which may be either rigid or flexible Talar head-displaced-anterior, medial, inferior and causes depression of navicular bone and plantar calcaneonavicular (spring) ligament, and lengthening of tibialis posterior muscle Navicular lies below the Feiss line and may even rest on the floor in severe conditions

36. RIGID FLAT FOOT It is a structural deformity where the medial longitudinal arch of foot is absent in NWB,WB and toe standing The arch is reduced during normal weight bearing, but reappears during toe standing and non weight bearing FLEXIBLE FLAT FOOT

37. PES CAVUS The medial longitudinal arch of foot may be unusually high A high arch is called pes cavus It is a more stable position of foot than pes planus Weight borne on lateral borders of foot Lateral ligament and peroneus longus muscle stretched

38. KNEES GENU VALGUM (Knock knees) Mechanical axes of lower extremities are displaced laterally and patella may be displaced laterally If genu valgum exceeds 30° (5 to 7 ) persists beyond 8yrs of age – structural changes occur Medial knee joint structures – abnormal tensile or distraction stress Lateral knee joint Structures – abnormal compressive stress

39. GENU VARUM (Bow legs ) Knees are widely separated when the feet are together and malleoli touches. Cortical thickening on medial concavity – on femur and tibia due to increased compressive force Patella may be displaced medially Causes—vit D deficiency, renal rickets , osteochondritis.

40. VERTEBRAL COLUMN

41. Idiopathic scoliosis are categorized by age infantile (0 to 3yrs ), juvenile (4 to 10yrs), adolescent (older than 10yrs)

42. ANALYSIS OF SITTING POSTURES Sitting postures are more complex than standing postures. The same gravitational moments as in standing posture must be considered, The contact forces that are created when various portions of the body interface with various parts of chairs, such as head, back, and foot rests, and seats.

43. TYPES OF SITTING POSTURES Active erect sitting posture Relaxed erect sitting posture Slumped posture Slouched posture

44. MUSCLE ACTIVITY IN SITTING POSTURES Static erect posture: LOG close to joint axis in head and spine Slumped posture : LOG passes anterior to joint axis Slouched posture : LOG passes posterior to joint axis Flexion relaxation phenomenon helps to less muscle activity in slouched posture than active erect sitting. Muscles activity help in sitting posture-superficial lumbar multifidus, thoracic erector spinae, internal oblique abdominal muscles

45. Intervertebral disc pressure and compressive loads on spine IVD pressure is measured by creep phenomenon Compressive force by calculating muscle activity with electromyography Flexed sitting posture is more harmful than extend sitting posture Because in kyphosis sitting increased intervertebral disc shear force Posterior annulus tensile force and anterior anulus load, hydrostatic force in nucleus and load on posterior ligaments

46. Seat interface pressures Contact forces between persons body and seat are called seat interface pressure Measured by sensory-containing mats Force per unit are measured by pascals Individuals with physical disabilities (paraplegia), thin elderly persons have higher pressure Wheel-chair users have high tension, compression, shear forces in gluteus muscles Less muscle thickness under ischial tuberosity in elders These measurements help to prevent pressure sores To reduce seat interface pressure Change the posture of body-forward and lateral trunk flexion Alteration in angulation of chairs back rest Using cushions (synthetic material, water, air, gel)reduces stress Cushion thickness should be up to 8cm is useful

47. ANALYSIS OF LYING POSTURE Interdiscal pressures are less in lying posture than in standing and sitting postures. Interdiscal pressures in supine lying (0.10 mpA ) were less than in either lying prone (0.11 mpA ) or lying on the side (0.12 mpA ). Some pressure-reducing mattress surfaces include foam, air, gas, water and gel. Other pressure-relieving surfaces include movable surfaces, usually powered by a motor or pump, which can alternatively inflate and deflate.

48. Factors affecting posture alignment

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