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Autonomic nervous system disorders

Horner syndrome

Orthostatic hypotension




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High Yield Notes

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USMLE® Step 1 style questions USMLE

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A 52-year-old man presents to the emergency department to evaluate low back pain. The patient was using the rowing machine at the gym when he felt a “pop” in his back followed by pain. He is otherwise healthy and does not take any medications daily. Vital signs are within normal limits. On physical examination, the patient has tenderness to palpation over the lumbar spine and diminished sensation over the anterior aspect of the left leg. The patient has 4/5 strength with hip flexion on the left compared to 5/5 strength on the right. Which of the following physical examination maneuvers is most likely to demonstrate a positive finding given this patient’s clinical presentation? 


Sciatica is a condition where there’s pain that starts in the lower back which then travels down the leg. Since the pain is associated with injury or compression of the sciatic nerve and follows the path of the sciatic nerve, it makes sense to name it sciatica.

The sciatic nerve is the longest and widest nerve in the body. It’s formed by the spinal nerves L4, L5, and S1-3, which leave the spinal canal through intervertebral foramen, an opening located between the vertebrae and behind the intervertebral discs. These nerves travel to the area in front of the sacrum, and join to make the sacral plexus.

All the nerves in the plexus, except S3 are split into two divisions: anterior and posterior. Anterior divisions of the L4, L5, S1, S2 and the entire S3 nerve create the tibial nerve, while posterior divisions of the L4, L5, S1 and S2 form the common fibular nerve. These two nerves are bound together by connective tissue and make up the sciatic nerve.

The sciatic nerve then passes beneath the piriformis muscle and through the greater sciatic foramen which is an opening formed by the pelvic bone, sacrospinous, and sacrotuberous ligaments.

It then travels down the back of the thigh to the back of the knee where it splits into the tibial and common fibular nerves. The sciatic nerve innervates the muscles in the back of the thigh. The Tibial nerve innervates the muscles of the posterior compartment of the leg and intrinsic flexors of the foot.

The Common fibular nerve is in charge of the muscles in the anterior and lateral compartments of the leg and intrinsic extensors of the foot. Now, each spinal nerve is in charge of the sensation of a specific area of the skin, called a dermatome.


Sciatica is a term used to describe symptoms of lower back pain, numbness, or tingling that originate in the lower back and travel down the sciatic nerve. It is often due to a spinal disc herniation pressing on one of the lumbar or sacral nerve roots. Other common causes are spinal stenosis, degenerative disc diseases. Treatment options include physical therapy, pain medication, exercise, and in some cases, surgery.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Sciatica" British Journal of Hospital Medicine (2016)
  6. "Late sciatic nerve entrapment following pelvic plate reconstruction in total hip arthroplasty" The Journal of Arthroplasty (1998)

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