In a 26-year-old woman with traumatic low back pain, bilateral thigh numbness, right-leg weakness and foot drop, how should I assess lower-extremity deep-tendon reflexes and interpret abnormal findings?

Assessment of Lower-Extremity Deep Tendon Reflexes in Traumatic Radiculopathy

In this 26-year-old woman with traumatic low back pain, bilateral thigh numbness, right-leg weakness and foot drop, you should immediately assess patellar and Achilles reflexes bilaterally, looking specifically for diminished or absent reflexes in a nerve root distribution pattern—findings that indicate radiculopathy and warrant urgent MRI lumbar spine without contrast to evaluate for cauda equina syndrome or severe nerve root compression 1.

Clinical Context and Urgency

This presentation is concerning for cauda equina syndrome (CES) or severe radiculopathy given the combination of bilateral symptoms, unilateral weakness, and foot drop following trauma. The most common physical finding in CES is low back pain, with absent lower limb reflexes being a key diagnostic feature 2. Bilateral motor weakness of the lower extremities is specifically mentioned as part of the CES constellation 1.

Specific DTR Assessment Technique

Which Reflexes to Test

• Patellar tendon reflex (PTR): Tests L2-L4 nerve roots, primarily L4
• Achilles tendon reflex (ATR): Tests S1-S2 nerve roots
• Both reflexes must be assessed bilaterally for comparison 3

How to Elicit Reflexes

For the patellar reflex, use the standard method first, then if unclear, employ the "superior patellar supine" method, which is the single best alternative technique (best or equal best in 42% of difficult cases) 4.

For the Achilles reflex, begin with the "plantar strike method" and if necessary use the "Achilles strike elevated" method (best or equal best in 71% of cases) 4.

Apply standardized force: 21-50 Newtons for expected normal reflexes, 0-20 Newtons when testing for hyperreflexia 5.

Interpretation of Abnormal Findings

Diminished or Absent Reflexes

Radiculopathy is defined as nerve root dysfunction associated with pain, sensory impairment, weakness, or diminished deep tendon reflexes in a nerve root distribution 1. In this patient:

• Absent or diminished patellar reflex (especially on the right with foot drop) suggests L4 radiculopathy
• Absent or diminished Achilles reflex suggests S1 radiculopathy
• Bilateral absent reflexes in lower extremities is specifically described in CES 2, 1

The combination of right foot drop (L5 distribution) with bilateral thigh numbness and weakness creates a pattern suggesting multilevel or cauda equina involvement.

Critical Assessment Points

To determine pathological changes, you must assess 3:

1. Left-right differences: Asymmetry indicates lateralized nerve root pathology
2. Upper versus lower extremity comparison: Normal upper extremity reflexes with absent lower extremity reflexes localizes to lumbosacral pathology
3. Overall limb balance: The pattern across multiple nerve root levels

In this case, the right-sided foot drop with bilateral symptoms suggests either multilevel radiculopathy or cauda equina compression affecting multiple nerve roots asymmetrically.

Immediate Management Algorithm

1. Document baseline reflexes bilaterally (patellar and Achilles)
2. Assess for urinary retention (90% sensitive for CES) 2
3. Check for saddle anesthesia and rectal tone
4. If any CES features present: Obtain urgent MRI lumbar spine without IV contrast 2—this is the imaging study of choice because of its ability to accurately depict soft-tissue pathology and assess spinal canal patency
5. If isolated radiculopathy without CES features: The patient still requires imaging given the traumatic mechanism and progressive neurologic deficit 2, 6

Common Pitfalls to Avoid

• Do not rely solely on reflexes if technically difficult to elicit—the absence of a reflex may be due to examiner technique rather than true pathology. Use alternative elicitation methods 4.
• Do not dismiss bilateral symptoms as "nonspecific"—bilateral thigh numbness with unilateral weakness and foot drop in trauma is CES until proven otherwise 2, 1.
• Do not wait for complete CES syndrome (urinary retention, saddle anesthesia) before imaging—back pain with radiculopathy, weakness, and absent reflexes warrants urgent evaluation 2.
• Consider lumbosacral transitional vertebrae or nerve root malformations if imaging and clinical findings are discordant 3.

Prognostic Value

The entry neurological grade, including reflex status, predicts neurological outcome in thoracolumbar fractures 7. Absent reflexes indicate more severe nerve root dysfunction and potentially worse prognosis for recovery, particularly when combined with motor weakness 8.

The presence of areflexia with isolated proximal weakness (as opposed to the typical distal pattern) can represent atypical presentations of acute polyradiculopathy, though this is less likely given the traumatic mechanism 9.