Lower Limb Neurological OSCE Examination

Power is tested by asking the patient to move against your resistance, comparing the two sides and working through the muscle groups systematically. Each movement is supplied predominantly by a particular myotome (the group of muscles supplied by one spinal nerve root), so a pattern of weakness helps localise a lesion to a root, a peripheral nerve, or a more diffuse process.

Grade power using the Medical Research Council (MRC) scale:

• 0: no movement
• 1: a flicker of contraction
• 2: movement with gravity eliminated
• 3: movement against gravity but not resistance
• 4: movement against some resistance
• 5: normal power

Test each of the following movements in turn. The main nerve roots are shown so that you can match a pattern of weakness to a root level:

• Hip flexion: L1/L2
• Hip extension: L5/S1/S2
• Knee extension: L3/L4
• Knee flexion: S1
• Ankle dorsiflexion: L4/L5
• Ankle plantarflexion: S1/S2
• Big toe extension: L5

The pattern of weakness is more important than its severity. A pyramidal pattern of weakness (the pattern seen when the corticospinal tract is damaged), in which the flexors are weaker than the extensors in the leg, is characteristic of a UMN lesion. Weakness confined to muscles supplied by a single nerve root (for example weak big toe and ankle dorsiflexion in an L5 radiculopathy, a disorder of the L5 nerve root) or a single peripheral nerve suggests an LMN lesion at that level. Symmetrical proximal weakness suggests a myopathy, whereas distal weakness is more typical of a peripheral neuropathy.

Deep tendon reflexes test a simple reflex arc: a tap on the tendon stretches the muscle, triggering a sensory signal to the spinal cord that produces a motor contraction. The response is normally modulated (dampened) by descending UMN pathways, which is why reflex changes are so useful for localising lesions.

• Knee-jerk reflex: L3/L4. Support the knee in slight flexion and strike the patellar tendon; the leg should extend.
• Ankle-jerk reflex: S1. With the ankle relaxed and slightly everted (turned outwards), strike the Achilles tendon; the foot should plantarflex.
• Plantar reflex: run a blunt object along the lateral border of the sole and then across the ball of the foot. Unlike the knee and ankle jerks this is not a simple tendon reflex but a test of the corticospinal tract (the main pathway carrying movement signals from the brain to the spinal cord), so it is interpreted differently (see the Babinski sign below).

If a reflex appears absent, ask the patient to perform a reinforcement manoeuvre (such as clenching the teeth or interlocking and pulling the fingers apart) and test again before concluding it is truly absent.

Reflexes are graded from 0 to 4 (the scale proposed by the US National Institute of Neurological Disorders and Stroke): 0 is absent, 1 is small or present only with reinforcement, 2 and 3 are within the normal range (lower and upper half), and 4 is enhanced (brisk), including clonus if present. A plus sign after a grade does not change its meaning. Always compare like with like on the two sides, since asymmetry is often more telling than the absolute briskness.

• Brisk (exaggerated) reflexes indicate a UMN lesion, because loss of the normal descending inhibition leaves the reflex arc over-active.
• Reduced or absent reflexes indicate an LMN lesion (interruption of the reflex arc itself), as seen in radiculopathy or peripheral neuropathy. They can also be lost temporarily in the acute phase of a UMN lesion (spinal shock).

The plantar reflex deserves particular attention. The normal adult response is flexion (downward movement) of the big toe. An abnormal response is extension (upward movement) of the big toe with fanning of the other toes. This is a positive Babinski sign and points to a UMN lesion, although examiners do not always agree on whether it is present, so interpret it alongside the other findings. (An extensor plantar response is normal in young infants and usually disappears by around 6 to 12 months of age, as the nervous system matures.)

Image - The plantar reflex. Extension of the big toe with fanning of the other toes (a positive Babinski sign) indicates an upper motor neurone lesion

Creative commons source [Public domain]

Coordination in the lower limb is assessed primarily with the heel-to-shin test. Ask the patient to place one heel on the opposite knee and then slide it smoothly down the front of the shin to the ankle, lift it off, and repeat. Demonstrate the movement first.

A smooth, accurate movement is normal. In a cerebellar lesion, the movement becomes clumsy and erratic, with the heel wobbling off the line of the shin. Two terms describe this incoordination: intention tremor (a tremor that worsens as the heel nears its target) and dysmetria (misjudging the distance, so the movement overshoots or falls short). This is part of the wider picture of cerebellar dysfunction, which classically also includes ataxic gait, nystagmus (involuntary, rhythmic eye movements) and slurred speech.

Interpret incoordination in the context of power. A patient who is simply weak may perform the test poorly without any cerebellar problem, so always assess coordination alongside the rest of the examination.

Image - The cerebellum. Damage to it produces the incoordination (dysmetria and intention tremor) seen on heel-to-shin testing, classically on the same side as the lesion

SimpleMed original

Sensory testing maps any deficit onto either a dermatome (a strip of skin supplied by a single nerve root) or the territory of a peripheral nerve, which again helps localise the lesion. Always demonstrate each type of sensation on the sternum or another normal area first, so the patient knows what to expect. Then test with their eyes closed, comparing left with right at each level.

Different modalities travel in different spinal pathways, which is why testing several is informative:

• Light touch: tested with a wisp of cotton wool. Carried by both the dorsal columns (which carry fine touch, vibration and joint position sense) and the spinothalamic tracts (which carry pain, temperature and crude touch).
• Pin-prick (pain): tested with a disposable neuro-pin. Carried by the spinothalamic tract (which crosses to the opposite side within the spinal cord). If sensation is reduced distally, work proximally up the limb until normal sensation returns, which maps out a ‘stocking’ loss (loss over the feet and lower legs, like a sock).
• Temperature: also carried by the spinothalamic tract and tested with a cold object (the flat of a tuning fork feels suitably cold, or a dedicated cold tube). It is often omitted in practice if pin-prick is normal, since the two share a pathway.
• Vibration: tested with a 128 Hz tuning fork placed on a bony prominence, starting at the big toe and moving proximally if reduced. Carried by the dorsal columns.
• Proprioception (joint position sense): tested by holding the sides of the big toe and moving it up or down with the patient’s eyes closed. Also carried by the dorsal columns.

The distribution of any loss is the key to interpretation. A dermatomal pattern suggests a nerve root lesion (radiculopathy). A peripheral nerve pattern suggests mononeuropathy (damage to a single nerve). A ‘stocking’ distribution (worst distally and improving proximally) suggests a peripheral polyneuropathy (damage to many peripheral nerves), classically caused by diabetes or alcohol excess. A clear sensory level on the trunk (a line below which sensation is lost) suggests a spinal cord lesion. Loss of proprioception and vibration on the same side as the lesion, with loss of pain and temperature on the opposite side, suggests cord hemisection (damage to one half of the spinal cord, or Brown-Séquard syndrome), usually with weakness on the same side, reflecting the different routes the pathways take.

Clinical note - Map the distribution of sensory loss and compare it with weakness and reflex changes when localising a lesion. See How To Assess Sensation.

Thank the patient, help them to re-dress, and wash your hands.

Summarise your findings, ideally framing them as a pattern, for example ‘an upper motor neurone pattern of weakness in the right leg’ or ‘a length-dependent sensory neuropathy’ (damage to the sensory nerves that affects the longest nerves first, so the feet before the hands).

To complete the examination, suggest performing a full upper limb neurological examination and a cranial nerve examination to define the extent of any deficit. Also examine the patient’s gait if not already done, and assess the back and spine. Relevant bedside tests and investigations include a blood glucose and HbA1c (a blood test of average blood sugar over the previous few months, for diabetic neuropathy) and vitamin B12 and folate levels (deficiency, especially of B12, can damage nerves). Depending on the suspected lesion, you may also suggest imaging of the brain or spine (MRI) and nerve conduction studies (tests of how well electrical signals travel along nerves).