You just saw your fifth back pain patient of the shift. As you present your patient and their 4 years of chronic sciatica, your attending, desperate to find a teachable moment, asks you what you would expect to find in terms of motor, sensory, and reflex deficit in a patient with sciatic nerve compression.
Spinal levels and their associated motor, sensory and reflex function are very popular pimp topics, and popular exam topics as well. They are also important to know in real life in evaluating your patients with back pain, weakness, neurologic complaints, or spinal cord injury. So get to know them well.
Here are the common lower extremity nerve roots and their associated (simplified) motor, sensory, and reflex functions if applicable:
L2: Hip flexion, Upper thigh sensation
L3: Knee extension, Lower thigh sensation
L4: Knee and foot extension, Medial leg sensation, Patellar reflex
L5: Foot dorsiflexion, Dorsum of the foot sensation
S1-2: Foot plantar flexion, Lateral foot sensation, Ankle jerk
S3-5: Sphincter tone, Saddle distribution sensation, Bulbocavernosus and anal reflexes
Also remember when checking reflexes that a diminished reflex means a peripheral nerve compromise, while hyperreflexia indicates a CNS issue.