Definition And Physiology

• Tone is the degree of tension in a skeletal muscle at rest.
• It is the physiological resistance offered by the muscle to passive stretch or motion.
• Tone is maintained by the spinal reflex arc:
  • Afferent impulses travel from muscle spindle and Golgi tendon endings to the spinal cord.
  • Efferent impulses travel from the anterior horn cell (alpha and gamma motor neurons) to the muscle.
• Tone is modulated supraspinally by the corticospinal (pyramidal) tract and the extrapyramidal tract / basal ganglia.

Pre-requisites & Examination Etiquette

• State of the Child: Ensure the child is awake, calm, and not crying. Testing during deep sleep (Prechtl States I/II) leads to false hypotonia, while crying or resisting (Prechtl State V) causes voluntary guarding and mimics hypertonia.
• Environment: Perform the examination in a warm room (under a radiant warmer for neonates). Warm hands and stethoscope before touching to avoid startle or reflex guarding.
• Alignment: Keep the head and trunk in a neutral midline axis. Head rotation to one side triggers the Asymmetrical Tonic Neck Reflex (ATNR), falsely altering tone symmetry.
• Examiner Technique: Always look at the child’s face while moving joints to monitor for discomfort or distress rather than staring only at your hands.

Assessment From History

Increased Tone (Hypertonia And Spasticity)

• History of persistent stiffness in the child.
• History of difficulty in wearing diapers, napkins, or toilet care due to adductor stiffness.
• History of stiffness while giving a bath, dressing, or changing clothes.
• History of persistent arching of the back (opisthotonus).
• History of keeping thumbs constantly tucked inside clenched fists (cortical thumbs).
• History of toe walking or scissoring of legs on standing.
• History of early hand preference before 12 months of age (indicates weakness/spasticity in contralateral hand).

Decreased Tone (Hypotonia)

• History of flaccidity, floppiness, or limp posture.
• History of the child slipping through the parent's hands when lifted under the axillae (Forester sign).
• History of failure to mold or cuddle to the parent's body contour when held.
• History of weak cry, poor suck, latching difficulties, and feeding/swallowing problems.
• History of delayed motor milestones with preserved or diminished movements.
• History of excessive joint laxity and increased range of movement.

Differentiating Dystonia From Spasticity

• Spasticity: Present throughout the day, even at rest and during sleep. Consistent velocity-dependent resistance; difficulty putting on diapers is persistent.
• Dystonia: Triggered or worsened by stimulation, handling, emotional stress, or crying. Absent during deep sleep. Typically presents as an alternating pattern of hypotonia and hypertonia with twisting postures.

Clinical Examination

Inspection

• Observe spontaneous resting posture and attitude while the child lies undisturbed in the supine position.
• Look for lateral asymmetry in posture or limb alignment.
• Watch for spontaneous movements versus paucity of movement.

Postures In Normal Term Infant

• Symmetrical, universally flexed posture with abduction at the thighs and flexion at the elbows, hips, knees, and ankles.

Postures In Hypotonia

• Pithed Frog Posture: Lies flat on the mattress with limbs abducted, externally rotated, and resting flat.
• Rag Doll Posture: Complete flaccidity with lack of spontaneous antigravity limb lifting.

Postures In Hypertonia

• Persistent Fisting & Cortical Thumb: Thumb tightly adducted and enclosed in a clenched fist beyond 2 to 3 months of age.
• Scissoring Posture: Adductor spasm causes lower extremities to cross over each other when handled or suspended.
• Opisthotonos: Backward arching of the neck and spine due to loss of cortical inhibition over brainstem motor pathways (e.g., kernicterus, tetanus, severe meningitis).
• Decorticate Posture: Lesion above the midbrain/red nucleus (cerebral cortex/internal capsule).
  • Upper limbs flexed, adducted, bent inward over the chest with clenched fists.
  • Lower limbs extended, rigid, and internally rotated with plantarflexion.
• Decerebrate Posture: Lesion at the brainstem level (below the red nucleus).
  • Upper and lower limbs fully extended.
  • Forearms hyperpronated with flexed wrists, clenched fists, and adducted thumbs.
• Hemiplegic Posture: Upper limb flexed at elbow and wrist against chest; affected lower limb extended and externally rotated.

Palpation

• Feel the muscle belly (biceps, triceps, quadriceps, gastrocnemius) by gently squeezing and rolling between the thumb and forefinger.
• Normal Tone: Muscles feel resilient, firm, and elastic.
• Hypotonia: Muscles feel soft, flabby, doughy, and lack substance.
• Hypertonia: Muscles feel excessively stiff, hard, taut, and rigid.
• Additional Palpation Clues:
  • Check for pseudohypertrophy (e.g., Duchenne muscular dystrophy—calves feel bulky and rubbery-firm, but are weak).
  • Check for peripheral nerve thickening (e.g., lateral popliteal, ulnar, or greater auricular nerves in leprosy/neuropathies).

Percussion

• Percussion is not used to evaluate resting tone directly.
• Used to elicit Deep Tendon Reflexes (DTRs):
  • Exaggerated (brisk/hyperreflexic) with clonus in pyramidal/UMN hypertonia.
  • Diminished or absent in LMN hypotonia; may be preserved/brisk in central hypotonia.
• Percussion of the thenar eminence or tongue using a reflex hammer elicits percussion myotonia (delayed relaxation seen in myotonic dystrophy).

Auscultation

• Not applicable for tone assessment.

Assessment Of Passive Movements

• Ensure the child is relaxed, comfortable, and warm.
• Move the limbs passively across each joint to evaluate resistance to stretch and range of motion.
• Examine all four limbs and compare bilateral symmetry.
• Crucial Action: Ensure the rhythm and rate of passive movement are irregular and unpredictable to prevent anticipatory voluntary resistance.

Upper Extremity Passive Tone Maneuvers

• Forearm Pronation and Supination: Hold the child's hand as if shaking it, support the elbow, and rotate the forearm back and forth. This is the most sensitive and reliable maneuver for upper limb passive tone.
• Elbow and Wrist Flexion/Extension: Move through the full range of motion at variable speeds.

Lower Extremity Passive Tone Maneuvers

• Knee and Hip Flexion/Extension: Support the thigh and knee, moving through full ROM.
• Ankle Dorsiflexion (Slow vs. Rapid Angle):
  • Slow Angle: Apply steady, moderate pressure to assess the maximum dorsiflexion range.
  • Rapid Angle: Perform a sudden, quick dorsiflexion movement.
  • Interpretation: Normally equal. A difference >10° (rapid angle is restricted due to a sudden catch) indicates spasticity.

Findings In Hypotonia

• Decreased resistance to passive movement.
• Increased range of passive motion across joints.
• Joint hyperextensibility.
• Excessive joint flappability.

Findings In Spasticity (Pyramidal / UMN Lesion)

• Velocity-Dependent Resistance: Faster passive stretch produces greater resistance.
• Clasp-Knife Phenomenon: Initial high resistance ("catch") followed by sudden give-way release.
• Predominantly affects antigravity muscles (flexors in upper limbs, extensors in lower limbs).
• Associated with hyperactive DTRs, clonus, and extensor plantar response (Babinski sign).

Findings In Rigidity (Extrapyramidal / Basal Ganglia Lesion)

• Non-Velocity-Dependent Resistance: Uniform resistance felt equally throughout the full range of motion.
• Affects both agonists and antagonists equally.
• Lead-Pipe Rigidity: Smooth, continuous resistance throughout flexion and extension.
• Cogwheel Rigidity: Ratchet-like, stepwise jerky resistance produced by superimposed tremor.
• DTRs are typically normal; no clasp-knife phenomenon.

Comparison: Spasticity vs. Rigidity

Modified Ashworth Scale (MAS) Of Spasticity

Standardized clinical scale to grade spasticity during passive joint movements:

• Grade 0: No increase in muscle tone.
• Grade 1: Slight increase in muscle tone, manifested by a catch and release or minimal resistance at the end of range of motion (ROM) in flexion or extension.
• Grade 1+: Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the ROM.
• Grade 2: Marked increase in muscle tone through most of the ROM, but affected part(s) easily moved.
• Grade 3: Considerable increase in muscle tone; passive movement is difficult.
• Grade 4: Affected part is rigid in flexion or extension.

Assessment Of Clonus

Always evaluate for clonus when hypertonia or hyperactive reflexes are present:

• Ankle Clonus:
  • Technique: Support the knee in slight flexion and hip in external rotation. Grasp the foot and briskly dorsiflex the ankle, maintaining constant upward pressure on the sole.
  • Interpretation: Rhythmic, alternating contractions of the calf muscles. Up to 8 to 10 beats of ankle clonus can be normal in neonates (disappears by 2 months). Beyond 2 months, sustained clonus (>6 beats) signifies a pyramidal/UMN lesion.
• Patellar Clonus:
  • Technique: With the child's leg extended and relaxed, grasp the upper border of the patella between index finger and thumb, and deliver a sudden, sharp downward thrust, holding continuous downward pressure.
  • Interpretation: Rhythmic vertical oscillations of the patella indicate UMN hyperexcitability.

Assessment Of Distal Joint Flappability

• Technique: Grasp the forearm or lower leg and rapidly shake the hand or foot to-and-fro. Observe the amplitude and excursion at the wrist and ankle joints.
• Findings:
  • Normal: Symmetrical, moderate joint excursion with rapid dampening.
  • Hypotonia: Excessive flappability (wide, loose joint excursion).
  • Hypertonia: Absent or restricted flappability (stiff, tight joint with minimal movement).

Age-Specific Key Points: Infants

180-Degree Assessment Maneuvers (Active & Postural Tone)

Essential sequence in infants to evaluate antigravity postural tone and distinguish central from peripheral hypotonia:

1. Traction Response (Pull-to-Sit):
   • Technique: Grasp the infant's hands/wrists and gently pull from supine into a sitting position.
   • Normal Term Response: Infant actively flexes elbows, knees, and hips. Head rises with minimal or no lag, aligns with the trunk, and is held upright briefly in the midline.
   • Hypotonic Response: Complete head lag (head drops back entirely); arms and legs hang limply in extension.
   • Hypertonic Response: Infant pulls up stiffly as a single rigid board without elbow or hip flexion.
2. Held Sitting:
   • Technique: Support the infant in a sitting posture.
   • Normal Term Response: Trunk is gently rounded, but the infant holds the head erect intermittently.
   • Hypotonic Response: Head collapses forward or backward completely with no active neck extensor counter-control.
3. Ventral (Horizontal) Suspension:
   • Technique: Suspend the infant prone in horizontal plane, supporting the chest and abdomen over the examiner's palm.
   • Normal Term Response: Maintains a straight back with head held in plane with the trunk, and limbs flexed against gravity.
   • Hypotonic Response: Infant drapes limply over the hand like a rag doll in an inverted "U" posture.
4. Vertical (Axillary) Suspension:
   • Technique: Hold the infant vertically by placing hands securely under the axillae without compressing the chest.
   • Normal Term Response: Maintains head erect, trunk extended, and hips/knees flexed, feeling secure between the examiner's hands.
   • Hypotonic Response (Forester Sign): Infant slips through the examiner's hands due to severe shoulder girdle weakness.
   • Hypertonic Response: Legs stiffen, extend, adduct, and scissor over each other.
5. Held Standing & Righting Reaction:
   • Technique: Hold infant vertically and allow the soles of the feet to touch a flat examination surface.
   • Normal Term Response: Active extension of legs and trunk supporting body weight (positive supporting reaction).

Amiel-Tison Angles (Passive Appendicular Tone in Infants)

Quantifies passive appendicular tone by measuring specific joint angles. Ensure the infant is calm with head in the midline:

• Adductor Angle:
  • Technique: Place fingers on the femoral shafts and simultaneously abduct both extended lower limbs gently as far as possible.
  • Normal Term Range: 40° to 80° (increases to 100°–140° by 9–12 months). Asymmetry >10°–20° suggests unilateral spasticity or weakness. Wide angle (>100° in term newborn) indicates hypotonia.
• Popliteal Angle:
  • Technique: Flex thighs fully onto the abdomen, then gently extend the leg at the knee until resistance is felt. Measure the angle behind the knee.
  • Normal Term Range: 80° to 100° in newborns (reaches 150°–160° by late infancy). Angle >110° in newborn indicates hypotonia; <80° indicates extensor hypertonia.
• Scarf Sign (Shoulder Girdle Passive Tone):
  • Technique: Take the infant's hand and draw the arm horizontally across the chest toward the contralateral shoulder while supporting the elbow. Note the position of the elbow relative to chest midline.
  • Normal Term Range: Shoulder girdle muscles resist adduction; the elbow does not cross the midline.
  • Hypotonia: The elbow easily crosses the contralateral axillary line without resistance (positive scarf sign).
  • Hypertonia: Resistance prevents the elbow from even reaching the ipsilateral nipple line.
• Heel-To-Ear Maneuver:
  • Technique: Keep the pelvis flat on the bed. Hold the foot and gently draw the heel toward the ipsilateral ear without lifting the pelvis.
  • Normal Term Range: Marked resistance prevents the heel from reaching near the ear.
  • Hypotonia: Heel easily touches the ear with no resistance and flat pelvis (positive heel-to-ear).
• Ankle Dorsiflexion Angle:
  • Technique: Keep leg extended and dorsiflex the foot toward the anterior shin.
  • Normal Term Range: 0° to 20° (foot can touch anterior tibia). Difference between slow and rapid stretch >10° indicates spasticity.

How To Write & Present In Exam

Written Case Sheet Format (Model: Spastic Hemiplegia)

• Inspection: Left upper limb flexed at the elbow and wrist with fingers clenched. Left lower limb extended at the knee and internally rotated. Paucity of spontaneous movements on the left side. Right side displays normal resting posture and movements.
• Palpation: Muscles of the left upper and lower limbs feel taut, firm, and stiff compared to the soft, resilient muscles on the right side.
• Passive Movements: Increased resistance to passive stretch in left upper and lower limbs. Resistance is velocity-dependent.
• Clasp-Knife Phenomenon: Elicitable in left elbow flexors/pronators and knee extensors/hamstrings, with an initial catch followed by give-way release.
• Flappability: Decreased/absent flappability at the left wrist and ankle joints.
• Modified Ashworth Scale: Grade 2 spasticity in left upper and lower limb muscle groups.
• Clonus: Sustained ankle clonus (8 beats) on the left side; absent on the right.
• Interpretation: Hypertonia of the clasp-knife type (spasticity) on the left side, suggestive of an Upper Motor Neuron (pyramidal) lesion involving the right corticospinal pathway (Left Spastic Hemiplegia).

Verbal Presentation To Examiner: Hypotonic Infant

Verbal Presentation To Examiner: Spastic Child

← 🩺 Examination Skills · See also 👶 Floppy Infant