A 57-year-old man presents to the ED complaining of back and left leg pain. He was lifting heavy furniture while helping his daughter move into college when all of sudden he felt a sharp pain at his back. The pain is described as severe, worse with movement, and shoots down his lateral thigh. The patient denies any bowel/urinary incontinence, saddle anesthesia, weight loss, or weakness. He denies any past medical history but endorses a family history of osteoporosis. He has been smoking 1 pack per day for the past 20 years. Physical examination demonstrated decreased sensation at the left knee, decreased patellar reflex, and a positive straight leg test. There is diffuse tenderness to palpation at the lower back but no vertebral step-offs were detected. What is the most likely etiology for this patient’s pain?

Disc herniation at the L3/L4 vertebra

Disc herniation at the L4/L5 vertebra

Spinal metastasis from lung cancer

A 28-year-old woman, gravida 2, para 1, at 24 weeks gestation comes to the physician for a prenatal visit. She reports dull aching pain and paresthesia over her left hand during the last few weeks. The pain radiates to her shoulder and is worse at night. Her hand feels numb upon waking up in the morning. She has a sister who has multiple sclerosis. Her current medications include iron supplements and a multivitamin. Vital signs are within normal limits. When the wrist is passively held in full flexion, aggravation of paresthesia is perceived immediately. Which of the following is the most likely explanation for this patient's symptoms?

Demyelinating disease of peripheral nerves

A 23-year-old woman presents to the emergency department with an acute exacerbation of her 3-month history of low back and right leg pain. She says she has had similar symptoms in the past, but this time the pain was so excruciating, it took her breath away. She describes the pain as severe, shock-like, and localized to her lower back and radiating straight down the back of her right thigh and to her calf, stopping at the ankle. Her pain is worse in the morning, and, sometimes, the pain wakes her up at night with severe buttock and posterior thigh pain but walking actually makes the pain subside somewhat. The patient reports no smoking history or alcohol or drug use. She has been working casually as a waitress and does find bending over tables a strain. She is afebrile, and her vital signs are within normal limits. On physical examination, her left straight leg raise test is severely limited and reproduces her buttock pain at 20° of hip flexion. Pain is worsened by the addition of ankle dorsiflexion. The sensation is intact. Her L4 and L5 reflexes are normal, but her S1 reflex is absent on the right side. A CT of the lumbar spine shows an L5–S1 disc protrusion with right S1 nerve root compression. Which of the following muscle-nerve complexes is involved in producing an S1 reflex?

Gastrocnemius/soleus-tibial nerve

Tibialis posterior-tibial nerve

Quadriceps femoris-femoral nerve

Radiculopathy patterns by level for USMLE Step 3: High-Yield Anatomy Lessons

Radiculopathy 101 - The Nerve Squeeze

Definition: A condition where a compressed or irritated nerve root in the spinal column causes pain, numbness, tingling, or weakness along the course of the nerve.
Etiology: Most commonly caused by mechanical compression.
- Herniated Nucleus Pulposus (HNP): Acute, often in younger patients (<50 yrs).
- Spondylosis: Chronic degeneration (osteophytes, facet hypertrophy), typically in older patients.
Clinical Presentation: Symptoms radiate in a specific dermatomal or myotomal pattern.

Spinal nerve root compression by herniated disc

⭐ Exam Favorite: The most common sites for lumbar disc herniation are L4-L5 and L5-S1, affecting the traversing L5 and S1 nerve roots, respectively.

Cervical Radiculopathy - Neck's Nerve Network

Myotome Chart: Spinal Nerve Roots and Muscle Movements

Nerve Root	Motor Function (Myotome)	Sensory Distribution (Dermatome)	Reflex Affected
C5	Deltoid, Biceps (shoulder abduction, elbow flexion)	Lateral arm (deltoid patch)	Biceps
C6	Biceps, Wrist Extensors	Lateral forearm, thumb, index finger	Brachioradialis
C7	Triceps, Wrist Flexors, Finger Extensors	Middle finger	Triceps
C8	Finger Flexors (grip)	Medial forearm, ring and little finger	None

C5: Arms up high (abduction).
C6: "Pick-up sticks" (wrist extension).
C7: "Push away" (triceps extension).

⭐ Spurling's Test: Neck extension, rotation, and lateral bending toward the affected side reproduces symptoms by narrowing the neural foramen.

Lumbosacral Radiculopathy - Back's Nerve Bind

Pathophysiology: Compression or inflammation of a lumbosacral spinal nerve root, most often from disc herniation or spondylosis.

Dermatome Map with Radiculopathy and Shingles Info

Nerve Root	Motor Weakness (Myotome)	Sensory Loss (Dermatome)	Reflex Affected
L4	Foot Dorsiflexion/Inversion (Tibialis anterior)	Medial malleolus	Patellar (Knee)
L5	Great Toe Extension (Extensor hallucis longus)	Dorsum of foot, first web space	None reliable
S1	Plantar Flexion (Gastrocnemius, soleus)	Lateral malleolus, sole of foot	Achilles

⭐ Exam Favorite: The L5 nerve root is the most commonly affected in lumbosacral radiculopathy, followed by S1. Herniated discs are the primary cause in younger patients (< 50 years).

High‑Yield Points - ⚡ Biggest Takeaways

C5 radiculopathy presents with deltoid and biceps weakness and sensory loss over the lateral arm.

C6 radiculopathy involves biceps and wrist extensor weakness, with sensory loss to the thumb and index finger.

C7 radiculopathy is most common, causing triceps weakness, a diminished triceps reflex, and middle finger paresthesia.

L4 radiculopathy affects the quadriceps, leading to a diminished patellar reflex.

L5 radiculopathy causes foot drop from tibialis anterior weakness and difficulty with heel walking.

S1 radiculopathy results in plantarflexion weakness, a diminished Achilles reflex, and difficulty toe walking.

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Radiculopathy patterns by level