USMLE Anatomy 2 — Questions and Answers
Question 1: A patient sustains a fibular neck fracture and subsequently develops foot drop with loss of sensation over the dorsum of the foot. Which nerve was most likely injured?
- Tibial nerve
- Common fibular (peroneal) nerve (Correct answer)
- Sural nerve
- Saphenous nerve
Correct answer: Common fibular (peroneal) nerve
The common fibular nerve winds superficially around the fibular neck, making it highly susceptible to injury; it innervates dorsiflexors and evertors of the foot, and its injury produces foot drop.
Question 2: Which of the following structures correctly passes through the inguinal canal in males?
- Round ligament of the uterus
- Ilioinguinal nerve and spermatic cord (Correct answer)
- Femoral nerve
- Obturator nerve
Correct answer: Ilioinguinal nerve and spermatic cord
In males, the inguinal canal transmits the spermatic cord along with the ilioinguinal nerve; in females, the round ligament of the uterus passes through instead of the spermatic cord.
Question 3: When performing a lumbar puncture at L4-L5, which sequence of structures does the needle correctly traverse from superficial to deep?
- Skin → supraspinous ligament → interspinous ligament → ligamentum flavum → epidural space → dura mater → subdural space → arachnoid mater → subarachnoid space (Correct answer)
- Skin → interspinous ligament → supraspinous ligament → epidural space → dura mater → arachnoid mater → subarachnoid space
- Skin → ligamentum flavum → interspinous ligament → supraspinous ligament → epidural space → dura mater → subarachnoid space
- Skin → supraspinous ligament → ligamentum flavum → interspinous ligament → epidural space → dura mater → subarachnoid space
Correct answer: Skin → supraspinous ligament → interspinous ligament → ligamentum flavum → epidural space → dura mater → subdural space → arachnoid mater → subarachnoid space
A lumbar puncture needle traverses in order: skin, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura mater, subdural space, and arachnoid mater before entering the subarachnoid space.
Question 4: A patient develops a 'winged scapula' following a radical mastectomy with axillary dissection. Which nerve was most likely damaged during the procedure?
- Accessory nerve (CN XI)
- Long thoracic nerve (Correct answer)
- Thoracodorsal nerve
- Medial pectoral nerve
Correct answer: Long thoracic nerve
The long thoracic nerve innervates the serratus anterior; its injury during mastectomy or axillary dissection causes winging of the scapula as the medial border protrudes from the thoracic wall.
Question 5: The sinoatrial (SA) node receives its arterial supply from the SA nodal artery, which arises from which vessel in approximately 60% of individuals?
- Left anterior descending artery
- Right coronary artery (Correct answer)
- Left circumflex artery
- Posterior descending artery
Correct answer: Right coronary artery
In approximately 60% of individuals, the SA nodal artery arises from the right coronary artery; in the remaining ~40%, it arises from the left circumflex artery.
Question 6: A patient presents with inability to initiate arm abduction—unable to abduct beyond 15 degrees—after an anterior shoulder dislocation. Which muscle was most likely injured?
- Supraspinatus (Correct answer)
- Infraspinatus
- Teres minor
- Subscapularis
Correct answer: Supraspinatus
The supraspinatus initiates the first 15 degrees of arm abduction by stabilizing the glenohumeral joint; injury prevents initiation of abduction even though the deltoid remains intact.
Question 7: A patient develops a Pancoast tumor at the apex of the right lung and presents with ptosis, miosis, and anhidrosis on the right side of the face. Which structure is most likely being compressed?
- Right vagus nerve
- Right phrenic nerve
- Cervical sympathetic chain (Correct answer)
- Brachial plexus upper trunk (C5-C6)
Correct answer: Cervical sympathetic chain
Pancoast tumors compress the cervical sympathetic chain, interrupting the sympathetic pathway and causing ipsilateral Horner's syndrome (ptosis, miosis, anhidrosis).
USMLE Anatomy 2
A patient sustains a fibular neck fracture and subsequently develops foot drop with loss of sensation over the dorsum of the foot.
Which nerve was most likely injured?