Lower Limb Anatomy
| Nerve | Motor | Sensory | Typical mechanism of injury & notes |
|---|---|---|---|
| Femoral nerve | Knee extension, thigh flexion | Anterior and medial aspect of the thigh and lower leg | Hip and pelvic fractures |
| Stab/gunshot wounds | |||
| Obturator nerve | Thigh adduction | Medial thigh | Anterior hip dislocation |
| Lateral cutaneous nerve of the thigh | None | Lateral and posterior surfaces of the thigh | Compression of the nerve near the ASIS → meralgia paraesthetica, a condition characterised by pain, tingling and numbness in the distribution of the lateral cutaneous nerve |
| Tibial nerve | Foot plantarflexion and inversion | Sole of foot | Not commonly injured as deep and well protected. |
| Popliteral lacerations, posterior knee dislocation | |||
| Common peroneal nerve | Foot dorsiflexion and eversion | ||
| Extensor hallucis longus | Dorsum of the foot and the lower lateral part of the leg | Injury often occurs at the neck of the fibula | |
| Tightly applied lower limb plaster cast | |||
| Injury causes foot drop | |||
| Superior gluteal nerve | Hip abduction | None | Misplaced intramuscular injection |
| Hip surgery | |||
| Pelvic fracture | |||
| Posterior hip dislocation |
Injury results in a positive Trendelenburg sign | | Inferior gluteal nerve | Hip extension and lateral rotation | None | Generally injured in association with the sciatic nerve Injury results in difficulty rising from seated position. Can't jump, can't climb stairs |
A prolapsed lumbar disc usually produces clear dermatomal leg pain associated with neurological deficits.
Features
The table below demonstrates the expected features according to the level of compression:
| Site of compression | Features |
|---|---|
| L3 nerve root compression | Sensory loss over anterior thigh |
| Weak hip flexion, knee extension and hip adduction | |
| Reduced knee reflex | |
| Positive femoral stretch test | |
| L4 nerve root compression | Sensory loss anterior aspect of knee and medial malleolus |
| Weak knee extension and hip adduction | |
| Reduced knee reflex | |
| Positive femoral stretch test | |
| L5 nerve root compression | Sensory loss dorsum of foot |
| Weakness in foot and big toe dorsiflexion | |
| Reflexes intact | |
| Positive sciatic nerve stretch test | |
| S1 nerve root compression | Sensory loss posterolateral aspect of leg and lateral aspect of foot |
| Weakness in plantar flexion of foot | |
| Reduced ankle reflex | |
| Positive sciatic nerve stretch test |
Management