Differentiating L5 Radiculopathy from Peroneal Nerve Entrapment
A 42-year-old warehouse supervisor reports 3 weeks of intermittent low back pain with radiation to the lateral right calf and dorsum of the foot. Symptoms began after lifting a heavy box. He denies bowel/bladder changes, saddle anesthesia, or bilateral symptoms. On exam: lumbar flexion 40°, extension 15° with right-sided pain; right straight leg raise positive at 35° reproducing leg pain; right ankle dorsiflexion 4/5; sensation decreased over the dorsum of the right foot; right patellar reflex 2+, Achilles 2+. No calf swelling.
1. Interpret the exam findings and identify the most likely nerve root level. Explain the reasoning that links each finding to that level.
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The findings point to an L5 nerve root irritation rather than a peroneal nerve entrapment at the fibular head. Reasoning: (1) The positive straight leg raise at 35° reproduces leg pain, indicating tension on the lower lumbar nerve roots (L4–S1) and supporting a radicular source. (2) Weakness of ankle dorsiflexion (4/5) is supplied primarily by L5 via the deep peroneal nerve. (3) Decreased sensation over the dorsum of the foot follows the L5 dermatome. (4) Patellar (L4) and Achilles (S1) reflexes are preserved, which is consistent with an L5 lesion because L5 has no reliably tested reflex. (5) The distribution of pain into the lateral calf and dorsum of the foot matches the L5 dermatome. A peroneal neuropathy at the fibular head would typically cause foot drop and sensory loss over the lateral calf and dorsum of the foot but would not reproduce leg pain with a straight leg raise, and it would not be associated with lumbar extension pain.
2. List two additional assessment procedures you would perform to confirm the level and screen for red flags. State what findings would concern you.
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Additional procedures: (1) A slump test to assess neural tension and provoke L5 root symptoms; a positive result reproduces the patient's leg pain and is relieved by neck extension. (2) A focused red-flag screen including questions about bowel/bladder function, saddle sensation, bilateral leg symptoms, unexplained weight loss, fever, and night pain, plus a check of great toe extension strength (extensor hallucis longus, L5) and gait. Concerning findings: new urinary retention or incontinence, saddle anesthesia, bilateral sciatica, progressive foot drop, fever, or unexplained weight loss. These would raise suspicion for cauda equina syndrome or a non-musculoskeletal cause and require urgent medical referral rather than continued physiotherapy assessment.
3. Given the positive straight leg raise at 35°, how would you modify the assessment to avoid aggravating symptoms while still gathering needed data?
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Because the straight leg raise is positive at a low angle (35°), repeating it forcefully or frequently will likely aggravate the nerve root. I would modify the exam by: (1) performing the straight leg raise slowly and stopping at the onset of symptoms rather than pushing to end range; (2) using the seated slump test with gentle neck flexion and knee extension only to the point of symptom reproduction; (3) assessing ankle dorsiflexion strength in a non-provocative position, such as seated with the knee flexed; (4) checking sensation and reflexes before any tension tests to minimize repeated nerve irritation; and (5) spacing provocative tests with rest breaks. This approach preserves diagnostic value while reducing the risk of post-exam flare-up.