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motor examination muscle power grading neurological
Here is a comprehensive overview of the Motor Examination as part of the neurological assessment:
Motor Examination — Neurological Assessment
The motor exam systematically evaluates: Inspection → Tone → Power/Strength → Reflexes → Coordination → Gait
1. Inspection
Before touching the patient, observe:
- Muscle bulk/atrophy — look for wasting, particularly distal muscles
- Fasciculations — spontaneous muscle twitching at rest (sign of LMN disease)
- Abnormal posture or movements — tremors, dystonia, chorea, myoclonus
- In an UMN lesion, the arm rests in a flexed posture; the leg may be externally rotated at the hip
2. Muscle Tone
Test by passively flexing and extending joints while the patient is relaxed. Ask: "Let your arm go floppy — don't help me."
| Finding | Description | Significance |
|---|---|---|
| Normal | Consistent resistance throughout range, unchanged with speed | — |
| Spasticity | Increased resistance to rapid passive stretch; clasp-knife phenomenon (resistance then sudden release) | UMN (corticospinal) lesion |
| Rigidity | Constant "lead-pipe" resistance; may be cogwheel (ratchety, with tremor) | Extrapyramidal (Parkinson disease, basal ganglia) |
| Flaccidity / Hypotonia | Loss of tone, floppy limbs, joints may be hyperextended | LMN lesion, acute spinal cord/cerebral lesion, cerebellar disease |
Tip for legs: With the patient supine, grasp behind the knee and lift briskly. In spasticity, the heel lifts off the table; normally it stays in contact.
3. Muscle Power (Strength)
MRC Grading Scale (Medical Research Council)
| Grade | Description |
|---|---|
| 0 | No contraction |
| 1 | Flicker or trace of contraction (visible/palpable but no movement) |
| 2 | Active movement with gravity eliminated |
| 3 | Active movement against gravity, but not against added resistance |
| 4 | Active movement against gravity and resistance (can sub-divide as 4−, 4, 4+) |
| 5 | Normal power |
Grade 4 covers a wide range; subdivisions (4−/4/4+) help track subtle changes.
Key Tests for Subtle Weakness
- Pronator drift — arms outstretched, supinated, eyes closed → weak arm pronates/sags (corticospinal lesion)
- Orbiting sign — ask the patient to rotate fists around each other; the weaker side "orbits" asymmetrically
- Hip flexors/quadriceps — note these are normally stronger than the examiner's arm, so be cautious not to undergrade
Muscle Groups to Test (Standard Survey)
- Upper limb: Shoulder abduction, elbow flexion/extension, wrist flexion/extension, finger abduction/adduction, grip
- Lower limb: Hip flexion/extension, knee flexion/extension, ankle dorsiflexion/plantar flexion, great toe extension
4. Reflexes
Deep Tendon Reflexes (DTRs)
| Reflex | Root | Test |
|---|---|---|
| Biceps | C5–C6 | Tap biceps tendon at elbow |
| Brachioradialis (supinator) | C5–C6 | Tap radial styloid |
| Triceps | C7 | Tap triceps tendon |
| Patellar (knee jerk) | L3–L4 | Tap patellar tendon |
| Achilles (ankle jerk) | S1 | Tap Achilles tendon |
Grading DTRs:
- 0 = absent, 1+ = diminished, 2+ = normal, 3+ = brisk (hyperreflexia), 4+ = clonus
Reinforcement (Jendrassik maneuver): When reflexes are hypoactive, have the patient interlock hands and pull them apart — this facilitates elicitation of lower limb reflexes.
Plantar Response (Babinski Sign)
Stroke the lateral sole from heel to toe.
- Normal (flexor): Toes curl downward
- Babinski positive (extensor): Great toe dorsiflexes + fanning of other toes → sign of corticospinal (UMN) lesion
- Also: "triple flexion" (knee + hip flexion + toe dorsiflexion) = equivalent pathological significance
Alternative stimuli if withdrawal interferes: squeeze the calf (Schaefer), stroke the dorsum of the foot, or flick the 4th toe.
Superficial Cutaneous Reflexes
- Abdominal reflexes (T8–T12) and cremasteric reflex (L1–L2) — absent in corticospinal lesions (useful ancillary sign, especially when unilateral)
5. UMN vs. LMN Patterns
| Feature | Upper Motor Neuron (UMN) | Lower Motor Neuron (LMN) |
|---|---|---|
| Tone | Increased (spasticity) | Decreased (flaccidity) |
| Power | Weakness (often pyramidal pattern) | Weakness (often distal/segmental) |
| Reflexes | Hyperreflexia | Hypo- or areflexia |
| Babinski | Extensor (positive) | Flexor (normal) |
| Bulk | Minimal atrophy (disuse only) | Wasting + fasciculations |
Other causes of weakness: neuromuscular junction (fatigable weakness, normal tone/reflexes — test with repetitive use) and myopathy (proximal weakness, decreased reflexes in proportion to weakness).
6. Coordination (Cerebellar Function)
- Finger-nose-finger test: Arm outstretched → touch nose → touch examiner's moving finger (repeat); look for dysmetria, intention tremor
- Heel-knee-shin test: Supine patient slides heel down the contralateral shin; look for incoordination
- Dysdiadochokinesia: Rapidly alternating hand movements (pronation/supination), finger tapping
- Cerebellar lesion → ipsilateral incoordination, past-pointing, increased amplitude of movements, slow initiation
7. Gait Assessment
| Gait Pattern | Cause |
|---|---|
| Hemiplegic (circumduction) | Unilateral UMN lesion |
| Spastic/scissor gait | Bilateral UMN lesion (both legs stiff) |
| Steppage gait | Footdrop (LMN, common peroneal nerve) |
| Waddling gait | Proximal weakness (myopathy, pelvic girdle) |
| Parkinsonian | Stooped, short steps, reduced arm swing, festination |
| Cerebellar/ataxic | Wide-based, staggering, irregular |
Romberg test: Stand with feet together, eyes open → then close. Falling with eyes closed = positive (proprioceptive/posterior column loss). If unsteady with eyes open, suggests cerebellar dysfunction.
Summary: Order of Motor Exam
- Inspect — bulk, fasciculations, posture, involuntary movements
- Tone — passive joint movement (upper + lower limbs)
- Power — MRC grade each muscle group; check for drift
- Reflexes — DTRs + Babinski + superficial reflexes
- Coordination — finger-nose-finger, heel-shin, diadochokinesis
- Gait — observe freely; assess Romberg
Sources: Adams and Victor's Principles of Neurology 12th Ed. · Bradley and Daroff's Neurology in Clinical Practice · Textbook of Family Medicine 9th Ed.
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