A 49-year-old man comes to the physician because of severe, shooting pain in his lower back for the past 2 weeks. The pain radiates down the back of both legs and started after he lifted a concrete manhole cover from the ground. Physical examination shows decreased sensation to light touch bilaterally over the lateral thigh area and lateral calf bilaterally. Patellar reflex is decreased on both sides. The passive raising of either the right or left leg beyond 30 degrees triggers a shooting pain down the leg past the knee. Which of the following is the most likely underlying cause of this patient's current condition?

Herniation of nucleus pulposus into vertebral canal

Inflammatory reaction in the epidural space

Involuntary contraction of the paraspinal muscles

Compromised integrity of the vertebral body

Inflammatory degeneration of the spine

A 38-year-old man is brought to the emergency department after suffering a motor vehicle accident as the passenger. He had no obvious injuries, but he complains of excruciating right hip pain. His right leg is externally rotated, abducted, and extended at the hip and the femoral head can be palpated anterior to the pelvis. Plain radiographs of the pelvis reveal a right anterior hip dislocation and femoral head fracture. Which sensory and motor deficits are most likely in this patient's right lower extremity?

Numbness of the medial side of the thigh and inability to adduct the thigh

Loss of sensation laterally below the knee, weak thigh extension and knee flexion

Numbness of the ipsilateral scrotum and upper medial thigh

Sensory loss to the dorsal surface of the foot and part of the anterior lower and lateral leg and foot drop

Paresis and numbness of the medial thigh and medial side of the calf, weak hip flexion and knee extension

A 48-year-old male presents to his primary care provider with a two-week history of low back pain and left leg pain. He reports that his symptoms started while he was working at his job as a construction worker. He has since experienced intermittent achy pain over his lumbar spine. He has also noticed pain radiating into his left leg and weakness in left ankle dorsiflexion. On exam, he demonstrates the following findings on strength testing of the left leg: 5/5 in knee extension, 4/5 in ankle dorsiflexion, 4/5 in great toe extension, 5/5 in ankle plantarflexion, and 5/5 in great toe flexion. The patellar reflexes are 5/5 bilaterally. He is able to toe walk but has difficulty with heel walking. Weakness in which of the following compartments of the leg is most likely causing this patient’s foot drop?

Superficial posterior compartment

A 25-year-old woman presents with shooting pain along the lateral aspect of her right thigh. The pain is exacerbated by standing or walking for long periods. Physical examination reveals tenderness at the anterior superior iliac spine. Which of the following nerves is most likely affected?

Lateral femoral cutaneous nerve

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

Lumbar dermatomes and myotomes for USMLE Step 2 CK: High-Yield Anatomy Lessons

Lumbar Plexus - Anatomy Blueprint

Lumbosacral Plexus Anatomy Diagram

Roots: Formed from the anterior rami of L1, L2, L3, and the superior part of L4.
Location: Originates within the psoas major muscle.
Key Nerves & Roots:
- Iliohypogastric & Ilioinguinal (L1)
- Genitofemoral (L1, L2)
- Lateral Femoral Cutaneous (L2, L3)
- Femoral (L2, L3, L4 - posterior divisions)
- Obturator (L2, L3, L4 - anterior divisions)

⭐ The entire lumbar plexus is embedded within the psoas major muscle. This makes it highly vulnerable to injury from a psoas abscess or retroperitoneal hematoma.

📌 Mnemonic: Invariably I Get Lazy On Fridays.

Lumbar Dermatomes - The Sensation Map

Lumbar and Sacral Dermatomes of the Lower Limb

Nerve Root	Key Sensory Area
L1	Inguinal ligament region
L2	Upper anterior thigh
L3	Lower anterior thigh & medial knee
L4	Medial malleolus (shin)
L5	Dorsum of the foot & big toe

📌 L4 hits the floor (medial malleolus).

Lumbar Myotomes - The Power Players

Lumbar and Sacral Plexus with Clinical Significance

Nerve Root	Primary Action(s)	Key Muscles	Clinical Test
L1, L2	Hip Flexion	Iliopsoas	Resisted hip flexion
L3	Knee Extension	Quadriceps	Resisted knee extension
L4	Ankle Dorsiflexion	Tibialis Anterior	Heel walking
L5	Great Toe Extension	Extensor Hallucis Longus	Resisted big toe extension
S1	Ankle Plantarflexion	Gastrocnemius, Soleus	Toe walking

📌 Mnemonic: "1, 2 buckle my shoe (hip flexion), 3, 4 kick the door (knee extension), 5 to the sky (dorsiflexion), S1 on the gas (plantarflexion)."

Clinical Testing - Reflexes & Radiculopathy

Reflex Testing:
- Patellar Reflex: Tests the L4 nerve root (femoral nerve).
- Achilles Reflex: Tests the S1 nerve root (tibial nerve).
Radiculopathy Signs:
- Straight Leg Raise (SLR) Test: Positive if radicular pain is reproduced at < 70 degrees of hip flexion, suggesting L5/S1 nerve root compression.

⭐ Exam Favourite: A posterolateral disc herniation at a specific lumbar level (e.g., L4-L5) typically compresses the descending nerve root of the next level down (i.e., the L5 nerve root), not the exiting root (L4).

Straight Leg Raise Test for Lumbar Radiculopathy

High‑Yield Points - ⚡ Biggest Takeaways

L1-L2 lesions primarily cause hip flexion weakness and sensory loss over the anterior thigh.

L3 damage weakens knee extension (quadriceps) and sensation at the medial knee.

L4 is crucial for ankle dorsiflexion (tibialis anterior); sensory loss at the medial malleolus.

The patellar reflex tests both L3 and L4 nerve roots.

L5 controls great toe extension; sensation is on the dorsum of the foot.

A weak "heel walk" points to an L5 lesion, while a weak "toe walk" suggests an S1 issue.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play