Postural Control, Optimal Posture & Their Deviations in Different Planes

(MPT-Level Comprehensive Answer - 20 Marks)

1. DEFINITION OF POSTURE

2. POSTURAL CONTROL

Definition

Biomechanical Basis

• Center of Gravity (CoG): A theoretical point at which the entire body weight is considered to act. In anatomical standing position, it lies approximately at S2 level (anterior to the sacrum), approximately 55-57% of total body height from the ground.
• Base of Support (BoS): The area encompassed by all the points of contact the body makes with the supporting surface (the area between the two feet in bipedal standing).
• Line of Gravity (LoG): A vertical line passing through the CoG downward to the supporting surface. For stable posture, the LoG must fall within the BoS.
• Postural Sway: Continuous small oscillations of the body's LoG around its mean position, representing active neuromuscular stabilization.

Sensory Systems Contributing to Postural Control

Neural Substrates of Postural Control

1. Spinal cord level: Spinal reflex arcs mediate the myotatic (stretch) reflex and provide the fastest postural correction loop.
2. Brainstem / Vestibular nuclei: Medial and lateral vestibulospinal tracts mediate trunk and limb postural reflexes. The reticulospinal tract maintains antigravity muscle tone.
3. Cerebellum (Vestibulocerebellum / Spinocerebellum): Coordinates timing and amplitude of postural corrections. The vestibulocerebellum functions in association with the brainstem and spinal cord to control equilibrium and postural movements (Guyton & Hall).
4. Basal Ganglia: Contribute to postural tone and automatic postural adjustments (APAs); dysfunction leads to stooped posture with festination (Parkinson's).
5. Cerebral Cortex: Voluntary aspects of postural control and anticipatory postural adjustments (APAs) prior to voluntary movement. Cortical contributions to postural control are significant during novel or challenging balance tasks (Kandel - Principles of Neural Science).

Postural Body Schema

Postural Responses

3. OPTIMAL (IDEAL / GOOD) POSTURE

Definition

Line of Gravity Reference (Plumb Line)

• Slightly posterior to the apex of the coronal suture (skull)
• Through the external auditory meatus (EAM) / mastoid process
• Through the bodies of cervical vertebrae (odontoid process)
• Through the shoulder joint
• Through the thoracic vertebral bodies (slightly posterior to)
• Through the lumbar vertebral bodies
• Through the sacral promontory
• Slightly posterior to the center of the hip joint
• Slightly anterior to the knee joint axis
• Through the calcaneocuboid joint / anterior to the lateral malleolus

• Midway between the two feet
• Through the midline of the body: symphysis pubis, umbilicus, xiphoid, manubrium, chin, and nasal septum
• Bilateral landmarks (ASIS, PSIS, iliac crests, acromia, ear lobes) should be level and symmetrical

Optimal Alignment by Segment (Sagittal Plane)

Resting Muscle Activity in Optimal Posture

4. DEVIATIONS FROM OPTIMAL POSTURE

A. DEVIATIONS IN THE SAGITTAL PLANE (Anterior-Posterior Plane)

i. Forward Head Posture (FHP)

• Description: Head translated anteriorly relative to the shoulders; EAM is anterior to the plumb line.
• Mechanical consequence: For every 2.5 cm (1 inch) of forward head translation, effective head weight on the cervical spine increases by ~4.5 kg. At 45° forward angle, the neck bears ~22 kg.
• Associated changes: Increased upper cervical extension (atlanto-occipital), loss of lower cervical lordosis, protracted scapulae, rounded shoulders.
• Muscle imbalance: Tight: upper trapezius, levator scapulae, suboccipitals, sternocleidomastoid. Weak: deep cervical flexors (longus colli, longus capitis).

ii. Kyphosis (Thoracic Hyperkyphosis)

• Description: Exaggerated posterior convexity of the thoracic spine (>40-45° by Cobb angle).
• Types:
  • Postural kyphosis: non-structural, correctable, common in adolescents; due to habitual slouching.
  • Structural kyphosis (Scheuermann's disease): rigid, >5° of anterior wedging of 3 consecutive vertebrae.
  • Senile kyphosis: osteoporotic compression fractures.
• Associated changes: Compensatory increased lumbar lordosis or flattened lumbar spine, protracted shoulder girdle, restricted chest expansion, impaired respiratory function.
• Muscle imbalance: Tight: thoracic extensors (contracted in short range), pectorals, intercostals anteriorly. Weak: mid/lower trapezius, rhomboids, thoracic erector spinae.

iii. Lordosis (Lumbar Hyperlordosis)

• Description: Exaggerated anterior convexity of the lumbar spine; anterior pelvic tilt.
• Mechanism: Anterior pelvic tilt increases the lumbar angle, compressing posterior facet joints and causing anterior disc bulge.
• Associated features: Protruding abdomen, hyperextended knee (genu recurvatum), anterior displacement of pelvis.
• Muscle imbalance (Lower Crossed Syndrome - Janda):
  • Tight: hip flexors (iliopsoas, rectus femoris), lumbar erector spinae
  • Weak: abdominals (transversus abdominis, rectus abdominis), gluteus maximus
• Pathological relevance: Lumbar spondylolysis, spondylolisthesis, facet joint syndrome.

iv. Flat Back Posture

• Description: Loss of lumbar lordosis (lumbar spine straightened); posterior pelvic tilt.
• Mechanism: Pelvis tilts posteriorly, flattening the lumbar curve; thoracic kyphosis may be compensatorily reduced.
• Muscle imbalance: Tight: hamstrings, abdominals. Weak: hip flexors, lumbar extensors.
• Clinical consequence: Increased compressive and tensile stresses on intervertebral discs.

v. Swayback Posture (Sway-back)

• Description: Pelvis is displaced anteriorly (forward sway of hips) with posterior displacement of the trunk; elongated thoracic kyphosis and flattened lumbar lordosis; head may be forward.
• Muscle imbalance: Tight: hamstrings (one-joint), upper abdominals. Weak: hip flexors, lower abdominals, lumbar extensors.
• Distinguishing feature from hyperlordosis: In swayback, the pelvis is in posterior tilt but displaced forward; in hyperlordosis, the pelvis is in anterior tilt.

B. DEVIATIONS IN THE FRONTAL (CORONAL) PLANE

i. Scoliosis

• Description: Lateral curvature of the spine in the frontal plane, typically accompanied by vertebral rotation in the transverse plane and sagittal plane changes. Defined as a Cobb angle >10°.
• Types:
  • Structural (true) scoliosis: does not correct with bending; includes Adolescent Idiopathic Scoliosis (AIS), congenital, neuromuscular.
  • Functional (non-structural) scoliosis: corrects with bending; due to leg length discrepancy, muscle spasm, or poor postural habits.
• Curve nomenclature: Named by the side of convexity (e.g., right thoracic scoliosis = convexity to the right at T-spine level).
• Classic presentation: Rib hump on the convex side (due to vertebral rotation causing posterior rib displacement), visible in Adam's forward bend test. Shoulder and iliac crest height asymmetry.
• Muscle imbalance: Concave side: shortened/hypertonic muscles; convex side: lengthened/weak muscles.

ii. Pelvic Obliquity

• Description: Asymmetrical height of the iliac crests - one ASIS higher than the other in standing.
• Causes: Leg length discrepancy (LLD), hip adductor/abductor tightness, spinal scoliosis.
• Effect: If right iliac crest is elevated, trunk leans to the right (Trendelenburg-type pattern), and spine develops a compensatory lateral curve.

iii. Leg Length Discrepancy (LLD)

• Types: True LLD (bony) vs. apparent LLD (functional, due to pelvic obliquity or joint contracture).
• Effect on posture: Pelvic drop on the shorter side, compensatory lumbar scoliosis, hip and knee asymmetry, altered LoG.

iv. Genu Valgum / Varum

• Genu Valgum (knock-knee): Lateral deviation of the knee; medial knee stress increased; tibia externally rotates; foot pronates.
• Genu Varum (bow-leg): Medial deviation; lateral compartment stress; foot supination.

v. Shoulder Level Asymmetry

• Description: One acromion higher than the other in the frontal plane. May be postural (dominant arm side lower due to muscle hypertrophy) or structural (scoliosis, muscle imbalance).

C. DEVIATIONS IN THE TRANSVERSE (HORIZONTAL) PLANE

i. Vertebral Rotation (in Scoliosis)

• Description: The hallmark of structural scoliosis. Vertebral bodies rotate toward the convexity of the curve (Nash-Moe grading I-IV).
• Consequence: Produces the rib hump on the convex side (ribs follow the vertebral rotation), creating a 3D deformity.

ii. Femoral Anteversion / Retroversion

• Femoral anteversion (increased): Femoral neck directed excessively anteriorly relative to the femoral condyle axis. Leads to in-toeing gait, hip internal rotation posture, and medial knee stress.
• Femoral retroversion: Reverse; leads to out-toeing gait.
• Normal anteversion: ~10-15° in adults; neonates ~40°.

iii. Tibial Torsion

• Internal tibial torsion: Tibia rotated internally relative to the femur; produces in-toeing; common cause in children (usually self-corrects by 8 years).
• External tibial torsion: Less common; leads to out-toeing.

iv. Foot Malalignment (Transverse Plane)

• Metatarsus adductus: Forefoot adducted relative to hindfoot.
• Pes planus (flat foot): Associated with subtalar pronation and foot abduction in the transverse plane.

v. Pelvic Rotation

• Description: One side of the pelvis rotated anteriorly or posteriorly relative to the opposite side.
• Effect: Apparent leg length discrepancy, asymmetrical hip joint loading, compensatory spinal rotation.

vi. Shoulder Girdle Rotation

• Description: Protraction of one shoulder girdle relative to the other; commonly the dominant side is slightly anterior.
• Clinical significance: In upper crossed syndrome, both shoulders protrude anteriorly (protraction in horizontal plane).

5. UPPER CROSSED AND LOWER CROSSED SYNDROMES (Janda)

Upper Crossed Syndrome

• Tight: upper trapezius, levator scapulae (posterior); pectoralis major/minor, SCM (anterior)
• Weak: deep cervical flexors (anterior); mid/lower trapezius, serratus anterior, rhomboids (posterior)
• Posture: FHP, rounded shoulders, thoracic kyphosis, winging of scapulae

Lower Crossed Syndrome

• Tight: hip flexors, lumbar erector spinae
• Weak: gluteus maximus, abdominals (transversus, rectus)
• Posture: anterior pelvic tilt, hyperlordosis, slightly flexed knees

6. CLINICAL ASSESSMENT OF POSTURAL DEVIATIONS

7. CONSEQUENCES OF POOR POSTURAL CONTROL AND DEVIATIONS

1. Musculoskeletal pain: Cervicogenic headache, LBP, PFPS, shoulder impingement
2. Altered biomechanics: Changed joint loading, accelerated osteoarthritis
3. Reduced respiratory function: Thoracic kyphosis reduces chest wall compliance
4. Falls risk: Reduced postural stability, especially in elderly (loss of proprioception, visual acuity, muscle strength - Medical Physiology)
5. Neurological compromise: Cervical cord compression in severe FHP; radiculopathy in scoliosis
6. Visceral effects: Abdominal organ compression in severe kyphosis/scoliosis

SUMMARY TABLE: Deviations by Plane

• Kendall FP et al. Muscles: Testing and Function - definition of good posture
• Janda V - Upper/Lower Crossed Syndrome patterns
• Guyton & Hall, Textbook of Medical Physiology - vestibulocerebellum and postural control
• Kandel ER, Principles of Neural Science (6th Ed.) - cortical contributions and body schema in postural control
• Syczewska M et al. (PMID: 29516039) - Non-structural misalignments in the sagittal plane, Scoliosis and Spinal Disorders, 2018
• THIEME Atlas of Anatomy - scoliosis rib hump and postural deformity