Lumbosacral radiculopathy

[masterofnone101]

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So I am reviewing MSK and i have a question in general to help understand and get down these radiuculopathys - when it says for example common peroneal nerve is L4-S2 and a herniation at disc L3-L4 affects the L4 spinal nerve thus affecting the peroneal nerve so shouldnt i see a foot drop for findings? Why are the only findings for a L3-L4 herniation weakness of knee extension , and decrease in patellar reflex? Am I not understanding this?

How would one know what exatly know what a L3-L4 herniation corresponds to findings wise besides memorizing?

 

[tasar1898]

this may be completely unscientific but it helped me remember the radiculopathy deficits: First of all , its always the higher number , i.e l3-l4 herniation = L4 root , c6-c7 herniation = C7 root etc.. and the deficits are always near the dermotome , i.e in l4 root pathology , you get l4 dermotome pain/numbness + weakness in knee extension since l4 dermotome involves the patella ( that obviously has a role in knee extension )

 

[dfib slim]

You just have to put the puzzle together with the physical findings they give you in the question. The only things you need to memorize are the roots involved with 1. Muscle stretch reflexes, 2. Dermatomes, and 3. Common muscle strength tests for each root like L3/L4 for quads, L5 for EHL, and S1 for gastroc.

Since the common peroneal nerve is comprised of L4-S2, maybe impinging on the L4 root may not be enough to appreciate clinical symptoms such as foot drop due to L5, S1, and S2 still functioning.

 

[masterofnone101]

Thank you , where can i find the common strength tests? I could not find it in FA..

 

[dfib slim]

Thank you , where can i find the common strength tests? I could not find it in FA..

http://www.fpnotebook.com/neuro/exam/MtrExm.htm
Here is a simple one but it may not be worth it to memorize everything. Usually questions will either ask you if this is in fact a radiculopathy or to differentiate between L3-L4, L4-L5, or L5-S1 herniation.

If it's a radiculopathy they may give the classic pain radiating down one leg with muscle weakness, numbness in a dermatomal pattern, decreased reflexes, and a positive straight leg test.

Generally,
For L3-L4: Weakness with knee extension, numbness to the front of the thigh, and decreased patellar reflexes.
For L4-L5: Weakness with dorsiflexion with numbness to the dorsum of the foot. <--- this would be the one with foot drop.
For L5-S1: Weakness with plantarflexion, numbness to the back of the leg, and decreased Achilles reflex