ESTUDYR
USMLE STEP 1 ANATOMY MASTERY EXAM HIGH-YIELD CLINICAL
SCENARIOS, BOARD-STYLE QUESTIONS, AND DETAILED RATIONALES
Question 1
A 27-year-old male construction worker falls from a ladder and lands directly on his shoulder.
Radiographic imaging reveals a fracture at the surgical neck of the humerus. Several weeks later,
the patient presents with difficulty abducting his arm between 15° and 90°, as well as flattening
of the shoulder contour due to muscle atrophy.
Which nerve was most likely injured in this patient?
A. Radial nerve
B. Musculocutaneous nerve
C. Axillary nerve
D. Median nerve
E. Ulnar nerve
Correct Answer: C. Axillary nerve
Rationale:
The axillary nerve innervates the deltoid and teres minor muscles. The deltoid muscle is
responsible for arm abduction from 15° to 90°. Injury to this nerve results in:
Loss of arm abduction
Flattened shoulder contour
Sensory loss over lateral shoulder ("regimental badge area")
The surgical neck of the humerus is a classic injury site affecting the axillary nerve.
Incorrect answers:
Radial nerve: wrist extension
Musculocutaneous nerve: elbow flexion
Median nerve: forearm flexors, thumb opposition
Ulnar nerve: intrinsic hand muscles
Question 2
,ESTUDYR
A 32-year-old female presents with numbness and tingling over the palmar surface of the thumb,
index finger, middle finger, and lateral half of the ring finger. She also reports weakness when
attempting to oppose her thumb.
Compression of which anatomical structure is the most likely cause?
A. Guyon's canal
B. Cubital tunnel
C. Carpal tunnel
D. Anatomical snuffbox
E. Radial groove
Correct Answer: C. Carpal tunnel
Rationale:
The carpal tunnel contains the median nerve, which provides sensation to:
Thumb
Index finger
Middle finger
Lateral half of ring finger
Median nerve injury also causes loss of thumb opposition.
Incorrect answers:
Guyon's canal affects ulnar nerve
Cubital tunnel affects ulnar nerve
Anatomical snuffbox contains radial artery
Radial groove contains radial nerve
Question 3
A 45-year-old man suffers a penetrating injury to the posterior arm affecting the radial groove of
the humerus. Following recovery, he is unable to extend his wrist and fingers.
What clinical condition results from this injury?
A. Ape hand
B. Claw hand
C. Wrist drop
D. Dupuytren contracture
E. Trigger finger
, ESTUDYR
Correct Answer: C. Wrist drop
Rationale:
The radial nerve controls:
Wrist extension
Finger extension
Damage results in wrist drop due to unopposed flexor muscles.
Incorrect answers:
Ape hand: median nerve injury
Claw hand: ulnar nerve injury
Dupuytren contracture: fascia fibrosis
Trigger finger: tendon inflammation
Question 4
A surgeon accidentally damages the long thoracic nerve during axillary lymph node dissection.
The patient subsequently develops difficulty raising her arm above shoulder level and
demonstrates scapular winging.
Which muscle is paralyzed?
A. Trapezius
B. Rhomboid major
C. Levator scapulae
D. Serratus anterior
E. Teres minor
Correct Answer: D. Serratus anterior
Rationale:
The serratus anterior:
Holds scapula against rib cage
Enables upward rotation
Injury causes:
USMLE STEP 1 ANATOMY MASTERY EXAM HIGH-YIELD CLINICAL
SCENARIOS, BOARD-STYLE QUESTIONS, AND DETAILED RATIONALES
Question 1
A 27-year-old male construction worker falls from a ladder and lands directly on his shoulder.
Radiographic imaging reveals a fracture at the surgical neck of the humerus. Several weeks later,
the patient presents with difficulty abducting his arm between 15° and 90°, as well as flattening
of the shoulder contour due to muscle atrophy.
Which nerve was most likely injured in this patient?
A. Radial nerve
B. Musculocutaneous nerve
C. Axillary nerve
D. Median nerve
E. Ulnar nerve
Correct Answer: C. Axillary nerve
Rationale:
The axillary nerve innervates the deltoid and teres minor muscles. The deltoid muscle is
responsible for arm abduction from 15° to 90°. Injury to this nerve results in:
Loss of arm abduction
Flattened shoulder contour
Sensory loss over lateral shoulder ("regimental badge area")
The surgical neck of the humerus is a classic injury site affecting the axillary nerve.
Incorrect answers:
Radial nerve: wrist extension
Musculocutaneous nerve: elbow flexion
Median nerve: forearm flexors, thumb opposition
Ulnar nerve: intrinsic hand muscles
Question 2
,ESTUDYR
A 32-year-old female presents with numbness and tingling over the palmar surface of the thumb,
index finger, middle finger, and lateral half of the ring finger. She also reports weakness when
attempting to oppose her thumb.
Compression of which anatomical structure is the most likely cause?
A. Guyon's canal
B. Cubital tunnel
C. Carpal tunnel
D. Anatomical snuffbox
E. Radial groove
Correct Answer: C. Carpal tunnel
Rationale:
The carpal tunnel contains the median nerve, which provides sensation to:
Thumb
Index finger
Middle finger
Lateral half of ring finger
Median nerve injury also causes loss of thumb opposition.
Incorrect answers:
Guyon's canal affects ulnar nerve
Cubital tunnel affects ulnar nerve
Anatomical snuffbox contains radial artery
Radial groove contains radial nerve
Question 3
A 45-year-old man suffers a penetrating injury to the posterior arm affecting the radial groove of
the humerus. Following recovery, he is unable to extend his wrist and fingers.
What clinical condition results from this injury?
A. Ape hand
B. Claw hand
C. Wrist drop
D. Dupuytren contracture
E. Trigger finger
, ESTUDYR
Correct Answer: C. Wrist drop
Rationale:
The radial nerve controls:
Wrist extension
Finger extension
Damage results in wrist drop due to unopposed flexor muscles.
Incorrect answers:
Ape hand: median nerve injury
Claw hand: ulnar nerve injury
Dupuytren contracture: fascia fibrosis
Trigger finger: tendon inflammation
Question 4
A surgeon accidentally damages the long thoracic nerve during axillary lymph node dissection.
The patient subsequently develops difficulty raising her arm above shoulder level and
demonstrates scapular winging.
Which muscle is paralyzed?
A. Trapezius
B. Rhomboid major
C. Levator scapulae
D. Serratus anterior
E. Teres minor
Correct Answer: D. Serratus anterior
Rationale:
The serratus anterior:
Holds scapula against rib cage
Enables upward rotation
Injury causes:
