Musculoskeletal anatomy Practice Questions
20 free Musculoskeletal anatomy practice questions for the USMLE Step 1. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
A patient presents with difficulty initiating shoulder abduction. Which muscle is primarily responsible for initiating the first 15 degrees of abduction?
- A Deltoid
- B Supraspinatus
- C Infraspinatus
- D Teres minor
Correct answer: Supraspinatus
The supraspinatus initiates the first 15 degrees of shoulder abduction before the deltoid takes over. It is frequently injured in rotator cuff tears.
A fracture of the surgical neck of the humerus damages the axillary nerve. Which muscle will show the greatest functional loss?
- A Latissimus dorsi
- B Pectoralis major
- C Deltoid
- D Subscapularis
Correct answer: Deltoid
The axillary nerve innervates the deltoid, essential for shoulder abduction beyond 15 degrees. Injury results in loss of shoulder contour and abduction weakness.
A patient has weakness in wrist extension after a midshaft humeral fracture. Which nerve is most likely affected?
- A Median nerve
- B Ulnar nerve
- C Radial nerve
- D Musculocutaneous nerve
Correct answer: Radial nerve
The radial nerve runs in the radial groove of the humerus and supplies wrist extensors. Injury causes wrist drop.
A medical student palpates a muscle that flexes the hip and originates from the anterior inferior iliac spine. Which muscle is being palpated?
- A Rectus femoris
- B Iliacus
- C Sartorius
- D Tensor fasciae latae
Correct answer: Rectus femoris
Rectus femoris originates at the anterior inferior iliac spine and contributes to hip flexion and knee extension. It is unique among quadriceps muscles for crossing the hip joint.
Damage to the superior gluteal nerve results in a Trendelenburg gait. Which muscle is primarily impaired?
- A Gluteus maximus
- B Gluteus medius
- C Gluteus minimus
- D Piriformis
Correct answer: Gluteus medius
The gluteus medius stabilizes the pelvis during single-leg stance. Superior gluteal nerve injury leads to pelvic drop on the contralateral side.
A patient is unable to stand on tiptoes due to weakness in plantarflexion. Which muscle is most directly involved?
- A Tibialis anterior
- B Gastrocnemius
- C Fibularis longus
- D Popliteus
Correct answer: Gastrocnemius
The gastrocnemius, along with soleus, is the primary plantarflexor of the ankle. It is essential for activities like tiptoe standing and jumping.
A boxer presents with a winged scapula. Which muscle is most likely paralyzed?
- A Trapezius
- B Rhomboid major
- C Serratus anterior
- D Levator scapulae
Correct answer: Serratus anterior
Serratus anterior, innervated by the long thoracic nerve, anchors the scapula to the thoracic wall. Injury results in scapular winging.
A patient cannot flex the distal interphalangeal joint of the index finger. Which muscle is impaired?
- A Flexor digitorum superficialis
- B Flexor digitorum profundus
- C Lumbrical muscle
- D Flexor pollicis longus
Correct answer: Flexor digitorum profundus
Flexor digitorum profundus is the only muscle that flexes the distal interphalangeal joints of the fingers; flexor digitorum superficialis flexes the PIP joints. The portion serving the index finger is innervated by the anterior interosseous nerve.
A patient with ulnar nerve injury has difficulty abducting the fingers. Which muscle is primarily affected?
- A Dorsal interossei
- B Lumbricals
- C Flexor digitorum profundus
- D Opponens digiti minimi
Correct answer: Dorsal interossei
Dorsal interossei abduct the fingers and are innervated by the ulnar nerve. Loss leads to impaired finger spreading.
A patient presents with difficulty extending the knee. All of the following muscles contribute to this action EXCEPT:
- A Vastus lateralis
- B Vastus medialis
- C Rectus femoris
- D Biceps femoris
Correct answer: Biceps femoris
Biceps femoris is a knee flexor, not an extensor. The quadriceps group is responsible for knee extension.
An athlete experiences pain during forearm supination and elbow flexion. Which muscle is most likely strained?
- A Brachialis
- B Biceps brachii
- C Pronator teres
- D Triceps brachii
Correct answer: Biceps brachii
Biceps brachii is a powerful supinator and elbow flexor. Overuse can cause tendon irritation.
A patient with difficulty internally rotating the humerus likely has injury to which muscle?
- A Teres minor
- B Infraspinatus
- C Subscapularis
- D Supraspinatus
Correct answer: Subscapularis
Subscapularis is the main internal rotator among the rotator cuff muscles. Its injury compromises internal rotation strength.
During a lung biopsy, a needle passes through the intercostal muscles. Which muscle layer is penetrated first?
- A Innermost intercostal muscles
- B Internal intercostal muscles
- C External intercostal muscles
- D Transversus thoracis
Correct answer: External intercostal muscles
The external intercostal muscles form the superficial layer of the intercostal space. They assist with inspiration.
A clinician tests the Achilles tendon reflex. Which spinal nerve roots primarily mediate this reflex?
- A L2–L3
- B L3–L4
- C L4–L5
- D S1–S2
Correct answer: S1–S2
The Achilles reflex tests S1–S2 nerve roots, which innervate the gastrocnemius and soleus. A diminished reflex suggests S1 pathology.
A patient has loss of thumb opposition. Which muscle is most directly responsible for this action?
- A Abductor pollicis longus
- B Flexor pollicis brevis
- C Opponens pollicis
- D Adductor pollicis
Correct answer: Opponens pollicis
Opponens pollicis allows the thumb to oppose the fingers. It is innervated by the median nerve via the recurrent branch.
A motorcyclist suffers a fracture of the fibular neck, injuring the common fibular nerve. Which function is most impaired?
- A Foot inversion
- B Foot eversion
- C Plantarflexion
- D Toe flexion
Correct answer: Foot eversion
The common fibular nerve innervates muscles responsible for foot eversion via the superficial fibular nerve. Injury also causes foot drop.
A patient has difficulty rising from a seated position due to weakness in hip extension. Which muscle is most likely affected?
- A Gluteus maximus
- B Gluteus medius
- C Quadratus lumborum
- D Sartorius
Correct answer: Gluteus maximus
Gluteus maximus is the primary hip extensor used in powerful movements like rising from a chair. Its weakness significantly affects hip extension.
A rock climber injures the muscle that flexes the elbow when the forearm is pronated. Which muscle is most affected?
- A Biceps brachii
- B Brachialis
- C Brachioradialis
- D Pronator quadratus
Correct answer: Brachioradialis
Brachioradialis flexes the elbow most effectively when the forearm is in a mid-pronated position. It is a key stabilizer during grip activities.
A patient has difficulty with lateral rotation of the hip. Which muscle is least likely to be involved?
- A Piriformis
- B Obturator internus
- C Quadratus femoris
- D Gluteus minimus
Correct answer: Gluteus minimus
Gluteus minimus primarily assists with hip abduction and internal rotation. The other listed muscles are lateral rotators of the hip.
A patient with carpal tunnel syndrome experiences weakness in thumb flexion. Which muscle is likely affected?
- A Flexor pollicis longus (flexes thumb IP joint)
- B Flexor pollicis brevis (superficial head)
- C Adductor pollicis (thumb adduction)
- D Abductor pollicis longus (thumb abduction)
Correct answer: Flexor pollicis brevis (superficial head)
The superficial head of flexor pollicis brevis is innervated by the median nerve, which is compressed in carpal tunnel syndrome. This results in weakened thumb flexion.