Foot drop: L4/5 root or peroneal nerve?

Foot drop is a gait abnormality in which the dropping of the forefoot happens due to weakness, damage to the peroneal nerve or paralysis of the muscles in the anterior portion of the lower leg.

Possible lesion sites causing foot drop include (going from peripheral to central):

• Peroneal nerve - common, deep or superficial;
• Sciatic nerve;
• Lumbosacral plexus;
• L5 nerve root - herniated disc;
• Spinal cord - poliomyelitis, tumor;
• Brain (uncommon, but often overlooked) - stroke, tumor;

Other causes of foot drop are diabetes, trauma, motor neuron disease (MND), adverse reaction to a drug or alcohol, neuromuscular disease, and multiple sclerosis.

The challenge for a Physical Therapist is to differentiate between the orthopedic causes; in other words, to find the location of entrapment or trauma. Is it distally or proximally to the spinal cord? The diagnosis of diabetes, MND, and the rest of the systemic causes are the subject of another discussion.

The main question a Physical Therapist should put to himself is the following, as commonly discussed in literature: is this problem a radiculopathy or a neuropathy?

1. Radiculopathy: involves one spinal nerve root distribution following the patterns of a myotome and/or a dermatome.

2. Neuropathy: usually involves one peripheral nerve branch entrapped somewhere along its course.

Here are some general principles you could follow in such case:

1. Radiculopathy

Motor examination

• Remember that one root supplies more than one peripheral nerves innervating many muscles
• Muscle weakness is partial or incomplete
• Atrophy is quite rare
• Fasciculations are very rare
• Reflexes depressed or absent early

Sensory examination

• Sensory distribution of spinal nerve roots overlap
• Total sensory loss virtually never occurs

Pain

• Common history of pain proximally to the spinal cord
• Pain radiates down to the limp
• Traction of the spinal segments relaxes pain
• Compression of the spinal segments reproduces pain

EMG quite sensitive and posterior paraspinal muscles affected

2. Neuropathy

Motor examination

• Muscle weakness usually complete
• Worse with use, better with rest
• Early atrophy
• Fasciculations are common
• Rare reflex changes - depends on location of entrapment

Sensory examination

• Sensory distribution of peripheral nerve branches are discrete

Pain

• Rarely pain around the spinal cord
• Pain may be around the joint
• Compression or stretching of the nerve reproduces pain

EMG usually normal and no posterior paraspinal muscles affected

You can see a very useful video on lower extremity nerve root and peripheral nerve sensory differentiation below:

Furthermore, there is a great presentation by Adam P. Smith, MD, on www.auroramed.com. You can find it here. This presentation is on the cervical spine level, but the logic is the same. Read also the cases presented; they very interesting.

In the case of the dropping foot, treatment for some can be as easy as a foot-up ankle support (ankle-foot orthoses). A cuff is placed around the patient's ankle, and a hook is installed under the shoelaces. The hook connects to the ankle cuff and lifts the shoe up when the patient walks.