GPAtlas🧭 When to suspect foot drop
Foot drop is weakness of dorsiflexion – the action of lifting the front of the foot and toes upward. The patient catches or drags the toes, trips easily, and often compensates with a high-stepping (steppage) gait, lifting the knee higher than usual to clear the floor. It is a clinical sign, not a diagnosis, so the task in primary care is to localise the lesion and identify the cause.
The commonest cause of a spontaneous, painless, unilateral foot drop is compression of the common peroneal (fibular) nerve where it winds superficially around the neck of the fibula at the knee. The single most important differential is an L5 radiculopathy (compression of the fifth lumbar nerve root in the spine). Distinguishing these at the bedside – and excluding the dangerous mimics below – is the core skill. Consider foot drop in any patient presenting with new walking difficulty, unexplained trips, or falls.
| Site / cause | How to recognise it |
|---|---|
| Common peroneal nerve (at the fibular neck) – commonest | Weak dorsiflexion and eversion; inversion preserved; ankle reflex preserved; sensory loss over the dorsum of the foot and outer shin. Triggers: leg crossing, squatting, prolonged kneeling, a below-knee cast, recent knee surgery, or rapid weight loss. |
| L5 radiculopathy (spinal nerve root) | Weak dorsiflexion and eversion plus weak inversion and hip abduction; back, buttock or leg pain is common; ankle reflex may be reduced. Back pain with weak inversion points here, not to the peroneal nerve. |
| Sciatic nerve lesion | A peroneal-type pattern plus weakness beyond the peroneal territory (e.g. knee flexion), with pain in the back of the thigh and calf. Often follows hip surgery, an injection injury, or trauma. |
| Central / upper motor neurone (stroke, multiple sclerosis, cord lesion) | Look for upper motor neurone signs – increased tone, brisk reflexes, an upgoing plantar – usually with other neurological deficits. |
| Peripheral polyneuropathy (diabetes, alcohol, vitamin B12 deficiency) | Often bilateral and distal with glove-and-stocking sensory loss; suspect when there is no compressive trigger. |
Source: BMJ Clinical Review · NICE NG59
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