Hand Anatomy and Biomechanics — MCQs
Hand deformity presenting as hyperextension at the metacarpophalangeal joint and flexion at the interphalangeal joint occurs due to paralysis of which muscle group?
A patient presents with loss of sensation on the lateral 3½ fingers and thenar atrophy. Which nerve is most likely involved?
The image shows a highlighted region on the dorsal aspect of the hand (anatomical snuffbox). Which of the following anatomical structures form the boundaries or floor of this region?
Which muscle is not part of the superficial anterior compartment of the forearm?
Which carpal bone does not articulate with the radius?
Ulnar nerve injury results in:
Median nerve injury at the wrist is commonly tested by.
A patient came with history of fall and on examination there was tenderness between the extensor pollicis longus and brevis. The likely lesion is
A 50-year-old female presents with wrist drop. Which nerve is most likely involved?
A 54-year-old female marathon runner presents with pain in her right wrist that resulted from a fall onto her outstretched hand. Radiographic studies indicate an anterior dislocation of a carpal bone. Which of the following bones is most likely dislocated?
Hand Anatomy and Biomechanics Indian Medical PG Practice Questions and MCQs
Question 1: Hand deformity presenting as hyperextension at the metacarpophalangeal joint and flexion at the interphalangeal joint occurs due to paralysis of which muscle group?
- A. Extensor digitorum
- B. Lumbricals and interossei (Correct Answer)
- C. Flexor digitorum profundus
- D. Intrinsic hand muscles excluding interossei
Explanation: ***Lumbricals and interossei*** - This deformity, also known as a **claw hand**, results from the paralysis of the **lumbricals** and **interossei** muscles, which are crucial for flexing the **metacarpophalangeal (MCP)** joints and extending the **interphalangeal (IP)** joints [1]. - When these muscles are paralyzed, the unopposed action of the **extensor digitorum** causes **MCP joint hyperextension**, and the unopposed action of the **flexor digitorum superficialis** and **profundus** causes **IP joint flexion**. *Extensor digitorum* - The **extensor digitorum** primarily extends the **MCP** and **IP** joints; its paralysis would lead to **flexion deformities**, not hyperextension at the MCP joint. - Paralysis of the intrinsic muscles removes the counteracting force that limits **extensor digitorum** action at the **MCP joints**, leading to their hyperextension. *Flexor digitorum profundus* - The **flexor digitorum profundus** primarily flexes the **distal interphalangeal (DIP)** joints [1]. Its paralysis would result in an inability to flex these joints, not the described deformity. - This muscle contributes to the IP flexion seen in claw hand when unbalanced by weak intrinsic muscles, but its paralysis alone would not cause this specific pattern. *Intrinsic hand muscles excluding interossei* - This option is too broad and vague. While some intrinsic muscles (e.g., thenar or hypothenar muscles) contribute to hand function, the specific combination of **lumbricals** and **interossei** is responsible for the classic claw hand deformity. - The **lumbricals** and **interossei** are the key intrinsic muscles for the balance of forces at the MCP and IP joints; excluding interossei would leave out a critical component of the deformity's cause [1].
Question 2: A patient presents with loss of sensation on the lateral 3½ fingers and thenar atrophy. Which nerve is most likely involved?
- A. Median (Correct Answer)
- B. Ulnar
- C. Radial
- D. Anterior interosseous nerve
Explanation: ***Median*** - The **median nerve** provides sensation to the **lateral 3½ fingers** (thumb, index, middle, and radial half of the ring finger) and innervates the **thenar muscles**, making its involvement consistent with the described symptoms [1]. - **Thenar atrophy** points directly to motor innervation loss of the thenar eminence, which is a key function of the median nerve. *Ulnar* - The **ulnar nerve** supplies sensation to the **medial 1½ fingers** (little finger and ulnar half of the ring finger) and innervates most of the **intrinsic hand muscles**, but not the thenar muscles [1]. - Damage typically causes **hypothenar atrophy** and **clawing** of the 4th and 5th digits, which are not described here. *Radial* - The **radial nerve** primarily provides sensation to the **dorsal aspect of the hand** and innervates the **extensor muscles of the forearm and hand**. - Its injury would typically lead to **wrist drop** and sensory loss in the dorsal hand, not thenar atrophy or lateral finger sensory loss. *Anterior interosseous nerve* - The **anterior interosseous nerve** is a **purely motor branch of the median nerve** that innervates muscles involved in **flexion of the thumb IP joint** and **index finger DIP joint**. - It does not have any sensory innervation, so loss of sensation in the lateral 3½ fingers would not be a symptom.
Question 3: The image shows a highlighted region on the dorsal aspect of the hand (anatomical snuffbox). Which of the following anatomical structures form the boundaries or floor of this region?
- A. Abductor pollicis longus muscle.
- B. Styloid process of the radius.
- C. Extensor pollicis longus muscle.
- D. All of the above anatomical structures. (Correct Answer)
Explanation: ***All of the above anatomical structures.*** - The image highlights the **anatomical snuffbox**, a triangular depression on the radial dorsal aspect of the hand. Its boundaries are formed by the tendons of the **extensor pollicis longus muscle** (ulnar side), and the **abductor pollicis longus** and **extensor pollicis brevis muscles** (radial side). - The **styloid process of the radius** forms the floor of the anatomical snuffbox along with the scaphoid and trapezium bones. All the options listed are key anatomical features associated with this region. *Extensor pollicis longus muscle.* - This muscle forms the **ulnar (medial) border** of the anatomical snuffbox. - Its tendon can be palpated during **thumb extension** and contributes to the overall structure of the highlighted area. *Abductor pollicis longus muscle.* - This muscle, along with the extensor pollicis brevis, forms the **radial (lateral) border** of the anatomical snuffbox. - Its tendon is visible and palpable on the radial side of the highlighted region when the thumb is abducted. *Styloid process of the radius.* - This bony prominence is located at the **distal end of the radius** on the radial side of the wrist. - It forms part of the **proximal floor** of the anatomical snuffbox, contributing to its definition.
Question 4: Which muscle is not part of the superficial anterior compartment of the forearm?
- A. FDS
- B. FCR
- C. Palmaris longus
- D. Flexor pollicis longus (FPL) (Correct Answer)
Explanation: **Flexor pollicis longus (FPL)** - The **FPL** is located in the **deep anterior compartment** of the forearm, differentiating it from the superficial muscles [1]. - Its primary function is **flexion of the thumb's interphalangeal joint**, requiring a deeper anatomical position for mechanical advantage [1]. *FDS* - The **Flexor digitorum superficialis (FDS)** is a key muscle of the superficial anterior compartment, visible just beneath the skin and fascia. - It is responsible for **flexing the middle phalanges** of the medial four digits. *FCR* - The **Flexor carpi radialis (FCR)** is situated in the superficial anterior compartment, running obliquely across the forearm. - It functions in **flexion and abduction of the wrist**. *Palmaris longus* - The **Palmaris longus** is a superficial anterior compartment muscle, though it is absent in a significant portion of the population. - When present, its main action is **flexion of the wrist** and tightening of the palmar aponeurosis.
Question 5: Which carpal bone does not articulate with the radius?
- A. Pisiform (Correct Answer)
- B. Scaphoid
- C. Lunate
- D. Triquetrum
Explanation: ***Pisiform*** - The **pisiform** is a sesamoid bone located within the tendon of the **flexor carpi ulnaris** muscle. - It articulates only with the **triquetrum**, not directly with the radius. *Scaphoid* - The **scaphoid** is one of the carpal bones that directly articulates with the radius, forming part of the **radiocarpal joint**. - It is located in the **proximal row** of carpal bones on the lateral side. *Lunate* - The **lunate** is another bone in the proximal carpal row that articulates directly with the **radius**, alongside the scaphoid. - It plays a crucial role in wrist movement and stability. *Triquetrum* - The **triquetrum** is a carpal bone in the proximal row, located medially. - Although it is in the proximal row, it primarily articulates with the **ulnar articular disc** (triangular fibrocartilage complex), which separates it from the distal ulna, and does not directly articulate with the radius.
Question 6: Ulnar nerve injury results in:
- A. Pointing index
- B. Ape thumb deformity
- C. Clawing of fingers (Correct Answer)
- D. Wrist drop
Explanation: ***Clawing of fingers*** - An ulnar nerve injury, particularly at the elbow, often leads to **paralysis of the interossei muscles** and the **medial two lumbricals**. [1] - This results in **hyperextension at the metacarpophalangeal joints** and **flexion at the interphalangeal joints** of the 4th and 5th fingers (and sometimes 3rd), creating the characteristic claw hand deformity. [1] *Pointing index* - **Pointing index**, also known as the **sign of benediction** or **preacher's hand**, occurs with **high median nerve lesions** affecting the lateral lumbricals and flexor digitorum superficialis. - The patient is unable to flex the index and middle fingers, especially when attempting to make a fist. *Ape thumb deformity* - **Ape thumb deformity** is caused by a **median nerve injury**, specifically affecting the **thenar muscles** (abductor pollicis brevis, opponens pollicis, and superficial head of flexor pollicis brevis). - This paralysis leads to the thumb being pulled laterally and into the same plane as the other fingers, losing its ability to oppose. *Wrist drop* - **Wrist drop** is a classic sign of **radial nerve injury**, which paralyzes the **extensor muscles of the wrist and fingers**. - This prevents the patient from extending their wrist and metacarpophalangeal joints.
Question 7: Median nerve injury at the wrist is commonly tested by.
- A. Contraction of abductor pollicis brevis (Correct Answer)
- B. Loss of sensation on palm
- C. Loss of sensation on ring finger
- D. Contraction of flexor pollicis brevis
Explanation: ***Contraction of abductor pollicis brevis*** - The **abductor pollicis brevis (APB)** is primarily innervated by the **median nerve**, and its motor function is often the **first to be affected** and is a reliable test for median nerve integrity at the wrist. - Testing the **abduction of the thumb** against resistance (often called the "OK" sign or simply checking for strength) directly assesses the function of the APB and therefore the median nerve. *Contraction of flexor pollicis brevis* - The **flexor pollicis brevis (FPB)** has a **dual innervation**; its superficial head is supplied by the median nerve, but its deep head is often supplied by the ulnar nerve. - This dual innervation makes its contraction an unreliable isolated test for median nerve injury, as ulnar nerve compensation might mask a median nerve deficit. *Loss of sensation on palm* - While the median nerve supplies sensation to the radial side of the palm, an injury at the wrist, specifically within the **carpal tunnel**, typically spares the palmar cutaneous branch. - The **palmar cutaneous branch** of the median nerve arises proximal to the carpal tunnel and provides sensation to the thenar eminence and central palm, so its sensation is often preserved even with significant carpal tunnel syndrome. *Loss of sensation on ring finger* - The **ring finger** receives sensory innervation from both the **median nerve** (radial half) and the **ulnar nerve** (ulnar half). - Therefore, isolated loss of sensation on the ring finger would not be a definitive test for median nerve injury alone, as it requires assessment of both nerve distributions.
Question 8: A patient came with history of fall and on examination there was tenderness between the extensor pollicis longus and brevis. The likely lesion is
- A. 1st metacarpal fracture
- B. Scaphoid fracture (Correct Answer)
- C. Trapezoid fracture
- D. Lower end of radius fracture
Explanation: ***Scaphoid fracture*** - Tenderness in the **anatomical snuffbox**, which is the area between the **extensor pollicis longus** and **extensor pollicis brevis** tendons, is a classic sign of a scaphoid fracture. - A fall on an **outstretched hand** is a common mechanism of injury for scaphoid fractures. *1st metacarpal fracture* - This type of fracture would typically present with tenderness and swelling over the **base of the thumb** or the body of the first metacarpal bone, not specifically the anatomical snuffbox. - While a fall can cause it, the precise location of tenderness points away from the first metacarpal. *Trapezoid fracture* - Fractures of the trapezoid bone are **rare** and often occur in conjunction with other carpal injuries. - Tenderness would be located more proximally and centrally in the wrist, not primarily in the anatomical snuffbox. *Lower end of radius fracture* - This injury, often a **Colles' fracture**, presents with pain, swelling, and deformity (dinner fork deformity) near the **wrist joint**, proximal to the carpal bones. - The tenderness would be more widespread and not confined to the anatomical snuffbox.
Question 9: A 50-year-old female presents with wrist drop. Which nerve is most likely involved?
- A. Ulnar Nerve
- B. Radial Nerve (Correct Answer)
- C. Median Nerve
- D. Musculocutaneous Nerve
Explanation: ***Radial Nerve*** - **Wrist drop** is a classic symptom of **radial nerve** injury, which compromises the innervation of the **extensor muscles** of the wrist and fingers. - The radial nerve supplies motor function to the **triceps brahii**, brachioradialis, supinator, and the wrist and finger extensors. *Ulnar Nerve* - Injury to the ulnar nerve typically causes a **claw hand deformity** due to paralysis of the **interossei** and **lumbricals 3 and 4**, with sparing of the finger extensors. - Patients experience weakness in **finger adduction and abduction**, as well as sensory loss over the medial 1.5 digits and hypothenar eminence. *Median Nerve* - Median nerve injury often results in an **ape hand deformity** or **hand of benediction** (when attempting to make a fist), affecting muscles responsible for **thumb opposition** and **flexion of digits 2 and 3**. - It would not cause wrist drop, as the wrist extensors are innervated by the radial nerve. *Musculocutaneous Nerve* - Injury to the musculocutaneous nerve primarily affects the **biceps brachii** and **brachialis muscles**, leading to weakness in **elbow flexion** and **supination of the forearm**. - It does not innervate any muscles responsible for wrist extension or flexion, therefore it would not cause wrist drop.
Question 10: A 54-year-old female marathon runner presents with pain in her right wrist that resulted from a fall onto her outstretched hand. Radiographic studies indicate an anterior dislocation of a carpal bone. Which of the following bones is most likely dislocated?
- A. Capitate
- B. Lunate (Correct Answer)
- C. Trapezoid
- D. Triquetrum
Explanation: ***Lunate*** - The **lunate bone** is the most commonly dislocated carpal bone, especially with a fall onto an **outstretched hand**. - Its central position in the proximal carpal row and its articulation with the radius make it vulnerable to **anterior dislocation** with forced dorsiflexion. *Capitate* - The **capitate** is the largest carpal bone but is more stable due to its central position and strong ligamentous attachments. - Isolated dislocation of the capitate is **rare** and usually accompanies other carpal injuries. *Trapezoid* - The **trapezoid** is a small, irregularly shaped carpal bone in the distal row, which is very stable. - Its strong articulations with the trapezium, capitate, and second metacarpal make its dislocation **extremely uncommon**. *Triquetrum* - The **triquetrum** is the second most commonly fractured carpal bone but is less prone to dislocation than the lunate. - While it can dislocate, it typically occurs with **ulnar impaction** or other complex carpal instabilities rather than an isolated anterior dislocation from a fall onto an outstretched hand.
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