Reflex HammerTraditionally in medical school, it is taught that lower extremity deep tendon reflexes for L4 and S1 nerve root levels can be elicited by tapping on the patella and Achilles tendons. It was just taught that L5 didn’t have a reflex to check. Knowing if an L5 radiculopathy existed would be especially helpful when assessing a patient for a potential lumbar disc herniation where a careful lower extremity neurologic exam is important. It turns out one can actually check for a L5 reflex.

Trick of the Trade

L5 Medial Hamstring Reflex 

The authors of a 2012 study [1], which enrolled 100 consecutive patients with documented lumbar disc herniations, studied the accuracy rate of the patellar, medial hamstring, and Achilles reflexes to identify the correct disc level:

  • Patella (L4): 86%
  • Medial Hamstring (L5): 79%
  • Achilles (S1): 67%

How do you check the L5 medial hamstring reflex?

  1. For optimal visualization, place the patient in a prone position [2].
  2. Place your finger over the medial hamstring (semitendinosus and semimembranosus muscles).
  3. Tap over your finger and watch for medial hamstring contractions.
  4. Alternative but less ideal position: Supine position with the hip slightly externally rotated.

 

 

Thanks to Dr. Juan Carlos Montoy for teaching me about this.

References

  1. Esene IN, Meher A, Elzoghby MA, El-Bahy K, Kotb A, El-Hakim A. Diagnostic performance of the medial hamstring reflex in L5 radiculopathy. Surg Neurol Int. 2012;3:104. PMID: 23087820
  2. Perloff MD, Leroy AM, Ensrud ER. Teaching video neuroimages: the elusive L5 reflex. Neurology. 2010 Sep 14;75(11):e50. PMID: 20837959 [Free full text with 2 downloadable videos]

 

Michelle Lin, MD
ALiEM Founder and CEO
Professor and Digital Innovation Lab Director
Department of Emergency Medicine
University of California, San Francisco
Michelle Lin, MD

@M_Lin

Professor of Emerg Med at UCSF-Zuckerberg San Francisco General. Founder of ALiEM @aliemteam #PostitPearls https://t.co/7v7cgJqNEn
Michelle Lin, MD