Nerve Damage

Sciatic nerve

Nerve roots: L4–S3
→ Divides into tibial + common peroneal nerves

Motor function:

Innervates hamstrings for flexion and everything below the knee

• Paralysis of knee flexion (hamstrings)

• Paralysis of all movements below the knee

Sensory function:

Everything below the knee

• Loss of sensation below the knee

Reflexes:

• ↓/absent ankle jerk

• ↓/absent plantar reflex

• Knee jerk preserved ✅

Causes:

• Neck of femur fracture

• Posterior hip dislocation

• Trauma

💡 Key memory point: Sciatic lesion = everything below the knee is affected, but the knee jerk is spared.