Lower Limb Neuro
 
 

Power Assessment

 
 
 
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Overview

  • Power assessment is a key part of the motor examination, and can be used to identify focal or global weakness.

    • How to Perform

    • Ask the patient to move their hips, knees and ankles through each movement.
  • Start by asking the patient to move against resistance (5 / 4). If the patient cannot move against resistance, ask them to move the joint against gravity (3). If they still cannot move the joint, eliminate gravity (2). In the absence of signficant movement of the joint look for flicker movement (1 / 0). Grade as appropriate, comparing both sides.

    • Grading of Power

    • 0: no movement
    • 1: flicker of movement
    • 2 : movement without gravity
    • 3: movement against gravity
    • 4: against weak resistance
    • 5: normal power

    • Causes of Weakness

    • Upper Motor Neuron

    • Brain lesion - ischaemia, haemorrhage, tumour, trauma, encephalitis, vasculitis, demyelination
    • Spinal cord lesion - infarct, haemorrhage, abscess, transverse myelitis

    • Lower Motor Neuron

    • Nerve root pathology - trauma, radiculopathy, neoplasm
    • Brachial plexopathy - 
    • Focal peripheral nerve pathology - trauma, entrapment, focal ischaemia, sarcoidosis, tumour
    • Peripheral polyneuropathy - diabetic neuropathy, hypothyroidism, B12 deficiency, alcohol, paraneoplastic, Guillain-Barre, CIDP, Charcot-Marie-Tooth

    • Other

    • Neuromuscular pathology - myasthenia gravis, Lambert Eaton myaesthenic syndrome
    • Muscular pathology - muscular dystrophy, inflammatory myositis, paraneoplastic, thyroid disease, Cushing’s, statins, sarcoidosis
    • Poor compliance with examination

    • Interpretation

    • Weakness affecting an entire limb or entire side - likely due to central pathology
    • Weakness affecting a single myotome  - likely due to spinal nerve root pathology
    • Weakness affecting a single peripheral nerve distribution - likely due to a focal peripheral nerve palsy
    • Weakness affecting multiple peripheral nerve distributions - potentially due to a brachial plexus lesion
    • Generalised weakness - suggests a polyneuropathy, neuromuscular pathology or myopathy

Myotomes

  • Hip flexion: femoral nerve (L2-L4)Iliopsoas
  • Hip extension: sciatic nerve (L5/S1/S2)Biceps femoris, semitendinosus, semimembranosus
  • Hip adduction: obturator nerve (L2-L4)Adductor muscles, pectineus
  • Hip abduction: superior gluteal nerve (L4/L5/S1)Gluteus muscles
  • Knee flexion: sciatic nerve (L5/S1/S2)Bieps femoris, semitendinosus, semimembranosus
  • Knee extension: femoral nerve (L2-L4)Rectus femoris, vastus lateralis, intermedius & medialis
  • Ankle plantar flexion: tibial nerve (L5/S1)Gastrocnemius, soleus, peroneus muscles
  • Ankle dorsiflexion: deep peroneal nerve (L4)Tibialis anterior
  • Foot inversion: tibial nerve (L4/L5)Tibialis anterior & posterior
  • Foot eversion: peroneal nerve (L5/S1)Peroneus longus & brevis
  • Great toe extension: deep peroneal nerve (L5)Extensor hallucis longus, extensor digitorum longus

The Motor Pathway

  • Upper Motor Nucleus
    Primary motor cortex (precentral gyrus)
     
    Central Pathway
    Corticobulbar tract
    (via cerebral peduncle)
    Decussation
    Medullary Pyramids
    Spinal Pathway
    Lateral corticospinal tract
     
    Lower Motor Nucleus
    Ventral horn at the level of entry into the spinal cord
     
    Neuromuscular Junction
     
     
    Muscle
 
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