Question
A middle aged lady presents with complaints of lower back pain. ON examination there is weakness of extension of right great toe with no sensory impairment. An MRI of the lumbosacral spine would most probably reveal a prolapsed intervertebral disc at what level?
| A. |
L3 – L4
|
| B. |
L4-L5
|
| C. |
L5-S1
|
| D. |
S1-S2
|
Show Answer
|
Correct Answer » B
Explanation
|
|
- Weakness of great toe extension indicates involvement of the extensor hallucis longus muscle.
- Extensor hallucis longus is mainly supplied by the L5 nerve root.
- The most common disc prolapse compressing the L5 root is an L4–L5 disc prolapse.
Clinical Correlation
L5 Root Compression Features
- Weakness of great toe dorsiflexion/extension
- Difficulty heel walking
- Usually minimal or no reflex changes
- Sensory symptoms may involve dorsum of foot, but may be absent early
Why Other Options Are Incorrect
- A. L3–L4:
- Typically affects L4 root
- Causes quadriceps weakness and reduced knee jerk
- C. L5–S1:
- Usually affects S1 root
- Causes loss of ankle jerk and plantar flexion weakness
- D. S1–S2:
- Rare level for typical lumbar disc prolapse
