Effects of Nerve Root Lesion

In a nerve root lesion, the patient will have parasthesiae localised to the dermatome of the involved nerve root and will have altered sensation in the same dermatome. There will be muscle weakness in the corresponding myotome. This is known as a radiculopathy.

L4/5 disc prolapse

An L4/5 disc prolapse will tend to cause pressure on the L5 nerve root (Fig 1).

L5/S1 disc prolapse

An L5/S1 Prolapse will cause pressure on the S1 nerve root (Fig 2).

Serious signs indicating involvement of the spinal cord rather than a nerve root will be present where there is:
• Muscle weakness on one side
• Sensory changes on the other side, or
• Dissociated sensory changes (e.g. loss of light touch on one side and pain sensation on the other side)

Learning bite

A knowledge of the nerve supply to the lower limb is essential for the assessment of patients with spinal problems.