Upper limb anatomy questions on USMLE Step 1 usually test which nerve is injured, which muscle does what at the shoulder and which test or sign confirms the diagnosis. Learn the nerve table below, then try the 9 questions.
Upper limb nerve injuries at a glance
Nerve (roots)
Common injury
What you see
Median (C5–T1)
Carpal tunnel syndrome, supracondylar fracture
Numb thumb, index, middle and half of ring finger; weak thumb opposition; thenar wasting
Mid-shaft humerus fracture, “Saturday night palsy”
Wrist drop; numb back of the hand
Axillary (C5–C6)
Surgical neck fracture, shoulder dislocation
Weak abduction past 15°; flat deltoid; numb “regimental badge” area
Long thoracic (C5–C7)
Mastectomy, axillary surgery
Winged scapula; cannot raise arm above the horizontal
Upper plexus (C5–C6)
Erb palsy: shoulder pulled from neck at birth
“Waiter’s tip” position
Lower plexus (C8–T1)
Klumpke palsy: arm pulled up; Pancoast tumor
Claw hand; may have Horner syndrome
Question 1: Numb fingers in a secretary
A 45-year-old woman who works as a secretary has tingling and numbness in her hands. On examination, sensation is decreased in all of her fingers except the little finger. Which muscle is usually weak in this condition?
A. Adductor pollicis B. Dorsal interossei C. Abductor digiti minimi D. Opponens pollicis
Correct answer: D. Opponens pollicis
This is carpal tunnel syndrome: compression of the median nerve under the flexor retinaculum, often from repetitive wrist use, pregnancy, hypothyroidism, diabetes or rheumatoid arthritis. The median nerve supplies the thenar muscles: opponens pollicis, abductor pollicis brevis and flexor pollicis brevis (remember “OAF”), plus the first two lumbricals. Weak opposition and thenar wasting appear in advanced cases.
Why the other options are wrong:
Adductor pollicis, the dorsal interossei and abductor digiti minimi are all supplied by the ulnar nerve.
Question 2: Wrist pain at night
A patient has wrist pain at night that affects his palm, thumb, index finger, middle finger and the thumb side of his ring finger. Holding the wrist fully flexed for one minute brings on the symptoms. Which sign is positive?
A. Froment sign B. Phalen sign C. Tinel sign D. Finkelstein test
Correct answer: B. Phalen sign
The Phalen sign is positive when holding the wrist in full flexion brings on numbness in the median nerve area. It is a test for carpal tunnel syndrome. Nerve conduction studies confirm the diagnosis.
Why the other options are wrong:
Tinel sign is tingling when the examiner taps over the nerve (it is also positive in carpal tunnel, but the test described here is wrist flexion).
Froment sign shows weak adductor pollicis in ulnar nerve palsy.
Finkelstein test is for de Quervain tenosynovitis (thumb tendons).
Question 3: Loss of sensation on the thumb side of the palm
Injury to which nerve causes loss of sensation on the palm side of the lateral three and a half fingers and the lateral part of the palm?
A. Axillary nerve B. Median nerve C. Radial nerve D. Ulnar nerve
Correct answer: B. Median nerve
The median nerve supplies sensation to the palm side of the thumb, index, middle and the lateral half of the ring finger, and the lateral palm. It also supplies most forearm flexors and pronators and the thenar muscles. Note: the palmar cutaneous branch runs above the carpal tunnel, so sensation over the palm itself is usually normal in carpal tunnel syndrome.
Why the other options are wrong:
Ulnar nerve: the little finger and the medial half of the ring finger.
Radial nerve: the back of the hand on the thumb side.
Axillary nerve: the skin over the deltoid.
Question 4: Lower brachial plexus injury
Injury to the C8 and T1 roots (lower brachial plexus) most likely affects which nerve?
A. Axillary nerve B. Median nerve C. Radial nerve D. Ulnar nerve
Correct answer: D. Ulnar nerve
The ulnar nerve comes entirely from C8 and T1, so it is the nerve most affected in a lower plexus injury (Klumpke palsy). Causes include pulling the arm upward (grabbing a branch while falling, or during birth), a cervical rib and a Pancoast tumor. Patients get a claw hand and weak small hand muscles, and may have Horner syndrome if T1 is damaged.
Why the other options are wrong:
Axillary (C5–C6) is affected in upper plexus injury.
Median and radial nerves have roots from C5 to T1, so they are only partly affected.
Question 5: Numb little finger and weak grip
A young man has numbness of his little finger and difficulty gripping things. Which nerve root is most likely affected?
A. C5 B. C6 C. C7 D. C8
Correct answer: D. C8
The C8 dermatome covers the little finger and the medial side of the hand, and C8 supplies the finger flexors and small hand muscles used for grip.
Hand dermatomes to remember: C6 = thumb, C7 = middle finger, C8 = little finger.
Why the other options are wrong:
C5 supplies the lateral arm (the shoulder area).
C6 supplies the thumb; C7 supplies the middle finger.
Question 6: Lifting the arm out to the side
Which muscles are the main abductors of the arm at the shoulder?
A. Deltoid and biceps B. Deltoid and coracobrachialis C. Deltoid and infraspinatus D. Deltoid and supraspinatus
Correct answer: D. Deltoid and supraspinatus
The supraspinatus starts abduction (the first 0 to 15°), then the deltoid takes over up to about 90°. Above 90°, the trapezius and serratus anterior rotate the scapula. Supraspinatus is the most commonly injured rotator cuff muscle (positive “empty can” test).
Why the other options are wrong:
Biceps and coracobrachialis mainly flex the arm.
Infraspinatus rotates the arm outward (external rotation).
Question 7: Rotating the arm inward
Which rotator cuff muscle rotates the arm inward (internal rotation) at the shoulder?
A. Infraspinatus B. Teres minor C. Subscapularis D. Supraspinatus
Correct answer: C. Subscapularis
The subscapularis is the only rotator cuff muscle that rotates the arm inward. It is supplied by the upper and lower subscapular nerves.
Rotator cuff (SITS): Supraspinatus = abduction; Infraspinatus = external rotation; Teres minor = external rotation; Subscapularis = internal rotation. (Outside the rotator cuff, pectoralis major, latissimus dorsi and teres major also rotate the arm inward.)
Why the other options are wrong:
Infraspinatus and teres minor rotate the arm outward.
Supraspinatus starts abduction.
Question 8: What holds the shoulder joint in place
Which of the following is a dynamic stabilizer of the glenohumeral (shoulder) joint?
A. Coracohumeral ligament B. Glenoid fossa C. Inferior glenohumeral ligament D. Subscapularis muscle
Correct answer: D. Subscapularis muscle
Dynamic stabilizers are muscles that actively hold the humeral head in the socket: the rotator cuff (including subscapularis) and the long head of the biceps. Static stabilizers are bones, the labrum, the joint capsule and ligaments. The shoulder is the most commonly dislocated large joint, usually anteriorly, which can injure the axillary nerve.
Why the other options are wrong: The ligaments and the glenoid fossa are static (passive) stabilizers.
Question 9: The only joint between the arm and the trunk
Which joint is the only bony joint between the upper limb and the trunk?
A. Acromioclavicular joint B. Coracoclavicular joint C. Glenohumeral joint D. Sternoclavicular joint
Correct answer: D. Sternoclavicular joint
The sternoclavicular joint connects the clavicle to the sternum and is the only bony joint between the upper limb and the axial skeleton. Everything else holds the shoulder girdle to the trunk with muscles. This is why a fractured clavicle (most often in the middle third) makes the shoulder drop forward and down.
Why the other options are wrong:
The acromioclavicular and glenohumeral joints are between bones of the upper limb itself.
The coracoclavicular connection is a ligament, not a true joint, and it also lies within the shoulder girdle.
Key takeaways
Carpal tunnel: median nerve; numb lateral three and a half fingers; weak opponens pollicis; Phalen (flexion) and Tinel (tapping) signs.
As an Amazon Associate, I earn from qualifying purchases.
Written and reviewed by Dr. Ray Makar, MD, dermatologist with 20 years of clinical practice. Last reviewed: November 2026. For exam preparation only, not medical advice.
FREE USMLE PDFs
Get 80 free practice questions
Four free sampler PDFs by Dr. Ray Makar: Step 1 (Pathology & Pharmacology) and Step 2 CK (Medicine, Surgery & Pediatrics), in both Review style and USMLE style, with answers and explanations. Also useful for NEET-PG, INI-CET and FMGE.
