Back Muscles and Fasciae — MCQs
Which muscle is affected in winging of the scapula?
Which of the following is NOT a hybrid muscle?
Winging of scapula is due to paralysis of
During a knife fight, a person is injured in the neck region and presents with weakness in raising the right arm above the head. On further examination, winging of the right scapula is noted. The injury has damaged:
Which of the following is not a branch of the cervical plexus?
Which of the following structures is NOT pierced by the parotid duct?
Which of the following statements about Sibson's fascia is correct?
What is the nerve supply of the shown muscle?
Posterior wall of the inguinal canal is formed by all of the following structures, except which of the following?
Stage III "Pressure sore" is full thickness skin loss extending:
Back Muscles and Fasciae Indian Medical PG Practice Questions and MCQs
Question 1: Which muscle is affected in winging of the scapula?
- A. Latissimus dorsi
- B. Subscapularis
- C. Serratus anterior (Correct Answer)
- D. Teres minor
Explanation: ***Serratus anterior*** - Damage to the **long thoracic nerve**, which innervates the serratus anterior muscle, leads to paralysis of this muscle. - The **serratus anterior** is crucial for holding the scapula against the thoracic wall and for **scapular protraction**, so its weakness results in a prominent medial border of the scapula, known as **winging**. *Latissimus dorsi* - The **latissimus dorsi** is an important muscle for **adduction**, **extension**, and **internal rotation** of the shoulder. - Injury to this muscle or its innervation (thoracodorsal nerve) primarily affects these movements, not causing scapular winging. *Subscapularis* - The **subscapularis** is part of the rotator cuff and is primarily involved in **internal rotation** of the humerus. - Dysfunction of the subscapularis would manifest as weakness in internal rotation and possibly shoulder instability, but not scapular winging. *Teres minor* - The **teres minor** is another rotator cuff muscle responsible for **external rotation** and stabilization of the humeral head. - Weakness of the teres minor would impair external rotation and contribute to rotator cuff dysfunction, but it is not associated with scapular winging.
Question 2: Which of the following is NOT a hybrid muscle?
- A. Sternocleidomastoid
- B. Flexor pollicis brevis
- C. Brachialis
- D. Adductor pollicis (Correct Answer)
Explanation: ***Adductor pollicis*** - The adductor pollicis is solely innervated by the **deep branch of the ulnar nerve (C8, T1)**, making it a non-hybrid muscle. - Its primary actions are **adduction, opposition, and flexion of the thumb**. *Sternocleidomastoid* - This muscle is considered hybrid because it is innervated by two different nerves: the **spinal accessory nerve (CN XI)** and branches from the **cervical plexus (C2-C3)**. - The spinal accessory nerve innervates primarily the motor function, while the cervical plexus provides proprioceptive fibers. *Flexor pollicis brevis* - This muscle often has a dual innervation, with its superficial head supplied by the **median nerve** and its deep head by the **ulnar nerve** [1]. - This dual innervation pattern qualifies it as a hybrid muscle [1]. *Brachialis* - The brachialis muscle is typically innervated by the **musculocutaneous nerve (C5, C6)**, but it also receives a small contribution from the **radial nerve (C7)**. - This additional supply from the radial nerve makes it a hybrid muscle.
Question 3: Winging of scapula is due to paralysis of
- A. Serratus anterior (Correct Answer)
- B. Rhomboid major
- C. Trapezius
- D. Levator scapulae
Explanation: ***Serratus anterior*** - The **serratus anterior muscle** is responsible for **protraction and rotation of the scapula**, holding it close to the thoracic wall. - Paralysis of this muscle, often due to injury to the **long thoracic nerve**, causes the **medial border of the scapula** to protrude posteriorly, a condition known as **medial scapular winging**. - This is the **classic and most common cause** of scapular winging. *Rhomboid major* - The rhomboid major muscle primarily performs **retraction and downward rotation of the scapula**. - Paralysis of this muscle would lead to the scapula being displaced laterally and superiorly, not winging. *Trapezius* - The trapezius muscle has multiple actions, including **elevating, depressing, retracting, and rotating the scapula**. - Paralysis of the trapezius (e.g., due to **accessory nerve damage**) can cause **lateral scapular winging** where the inferior angle protrudes, along with shoulder drooping and difficulty shrugging. - However, **serratus anterior paralysis** is the classic answer for scapular winging in exam contexts. *Levator scapulae* - The levator scapulae muscle is primarily involved in **elevating and downwardly rotating the scapula**. - Dysfunction of this muscle would impair shoulder elevation but would not be the direct cause of scapular winging.
Question 4: During a knife fight, a person is injured in the neck region and presents with weakness in raising the right arm above the head. On further examination, winging of the right scapula is noted. The injury has damaged:
- A. Long thoracic nerve of Bell
- B. Dorsal scapular nerve
- C. Suprascapular nerve
- D. Spinal accessory nerve (Correct Answer)
Explanation: ***Spinal accessory nerve*** - **Weakness in raising the arm above the head** and **winging of the scapula** are characteristic signs of **trapezius muscle dysfunction**, which is supplied by the **spinal accessory nerve (CN XI)**. - The trapezius is essential for **upward rotation of the scapula** during overhead arm abduction (>90°). - Injury to the spinal accessory nerve in the posterior triangle of the neck causes **lateral winging** of the scapula (inferior angle moves laterally), which is most prominent when attempting to raise the arm overhead. - The combination of **scapular winging** + **inability to abduct the arm above horizontal** is pathognomonic for trapezius paralysis. *Long thoracic nerve of Bell* - Damage to the long thoracic nerve causes paralysis of the **serratus anterior muscle**, leading to **medial winging** of the scapula (medial border lifts away from chest wall). - While scapular winging occurs, it is most prominent during **forward flexion** or **pushing movements** (e.g., push-ups, pushing against a wall), not specifically when raising the arm overhead. - Patients can usually still abduct the arm overhead, though with altered scapular mechanics. *Dorsal scapular nerve* - The dorsal scapular nerve innervates the **rhomboid major and minor muscles** and the **levator scapulae**. - Injury primarily causes difficulty **retracting the scapula** (pulling shoulders back) and weakness in shoulder elevation. - Does **not** cause scapular winging or significant weakness in overhead arm movement. *Suprascapular nerve* - The suprascapular nerve innervates the **supraspinatus** and **infraspinatus muscles**. - Damage causes weakness of shoulder **initiation of abduction** (first 15° by supraspinatus) and **external rotation** (infraspinatus). - Does **not** cause scapular winging, as these are rotator cuff muscles, not scapular stabilizers.
Question 5: Which of the following is not a branch of the cervical plexus?
- A. Suprascapular nerve (Correct Answer)
- B. Supraclavicular nerve
- C. Lesser occipital nerve
- D. Greater auricular nerve
Explanation: ***Suprascapular nerve*** - The **suprascapular nerve** originates from the **brachial plexus** (specifically the upper trunk), not the cervical plexus. - It primarily innervates the **supraspinatus** and **infraspinatus muscles**. *Lesser occipital nerve* - The **lesser occipital nerve** is a cutaneous branch of the **cervical plexus** (C2) that supplies the skin behind the ear. - It provides sensory innervation to the **scalp posterior to the auricle**. *Greater auricular nerve* - The **greater auricular nerve** is a branch of the **cervical plexus** (C2, C3) and provides sensory innervation to the skin over the parotid gland, mastoid process, and auricle. - It supplies sensation to the **external ear** and the **angle of the mandible**. *Supraclavicular nerve* - The **supraclavicular nerves** (C3, C4) are cutaneous branches of the **cervical plexus** that provide sensory innervation to the skin over the shoulder and upper chest. - They provide sensory innervation to the skin overlying the **clavicle** and the **pectoral region**.
Question 6: Which of the following structures is NOT pierced by the parotid duct?
- A. Buccopharyngeal fascia
- B. Buccinator muscle
- C. Buccal fat pad
- D. Investing layer of deep cervical fascia (Correct Answer)
Explanation: ***Investing layer of deep cervical fascia*** - The parotid duct (Stensen's duct) **does not pierce** the investing layer of the deep cervical fascia. - The investing layer **forms the capsule** of the parotid gland itself, and the duct **emerges from within** this fascial investment at the anterior border of the gland. - Since the duct originates from within the parotid gland (which is enclosed by the investing fascia), it does not pierce through this layer. *Buccopharyngeal fascia* - This is **also NOT pierced** by the parotid duct in its typical course. - The buccopharyngeal fascia covers the outer surface of the buccinator muscle and pharyngeal constrictors. - The parotid duct runs **superficial** to this fascial layer before piercing the buccinator muscle itself. - However, for exam purposes, the **investing layer of deep cervical fascia** is the most clearly established structure that is NOT pierced. *Buccinator muscle* - The parotid duct **definitively pierces** the buccinator muscle to reach the oral cavity. - It enters the oral vestibule **opposite the upper second molar tooth**. - This is a consistent anatomical landmark. *Buccal fat pad* - The parotid duct runs **lateral and superficial** to the buccal fat pad (Bichat's fat pad). - The duct does **not typically pierce through** the buccal fat pad; rather, it courses along its superficial surface. - The buccal fat pad lies deep to the buccinator muscle and provides cushioning in the cheek.
Question 7: Which of the following statements about Sibson's fascia is correct?
- A. Part of scalenus anterior muscle
- B. Vessel pass above the fascia
- C. Covers apical part of lung (Correct Answer)
- D. Attached to the inner border of 2nd rib
Explanation: ***Covers apical part of lung*** - **Sibson's fascia**, also known as the **suprapleural membrane**, is a dense fascial layer that covers and reinforces the **apex of the lung** and pleura. - It protects the lung apex and helps to support structures in the **root of the neck**. *Part of scalenus anterior muscle* - Sibson's fascia is a **separate fascial structure** extending from the first rib to the C7 transverse process, and is not a part of the scalenus anterior muscle. - The **scalenus anterior muscle** is one of the muscles of the neck, and while anatomically related by proximity to the fascia, it is not structurally part of it. *Vessel pass above the fascia* - Key neurovascular structures like the **subclavian artery** and the **brachial plexus** pass *below* Sibson's fascia, as the fascia protects the lung apex. - The fascia acts as a barrier, separating the lung apex from the more superficial structures of the neck. *Attached to the inner border of 2nd rib* - Sibson's fascia is primarily attached to the **inner border of the first rib** and the transverse process of the seventh cervical vertebra. - Its attachment to the first rib is crucial for its supportive role over the lung apex.
Question 8: What is the nerve supply of the shown muscle?
- A. Suprascapular
- B. Dorsal scapular (Correct Answer)
- C. Dorsal rami of C1
- D. Subscapular
Explanation: ***Dorsal scapular*** - The image points to the **levator scapulae muscle**, which elevates and rotates the scapula. - The **dorsal scapular nerve** (C5 root, with contributions from C3-C4) innervates the levator scapulae, as well as the rhomboid major and minor muscles. - This nerve arises from the C5 root of the brachial plexus and pierces through the middle scalene muscle. - Clinically, injury to the dorsal scapular nerve can cause **medial scapular winging** and difficulty elevating the shoulder. *Suprascapular* - The suprascapular nerve (C5-C6) primarily innervates the **supraspinatus and infraspinatus muscles**, which are involved in rotator cuff function. - It does not supply the levator scapulae muscle. - This nerve passes through the suprascapular notch beneath the superior transverse scapular ligament. *Dorsal rami of C1* - The **dorsal ramus of C1** (suboccipital nerve) primarily innervates the muscles of the suboccipital triangle: rectus capitis posterior major and minor, obliquus capitis superior and inferior. - These nerves are involved in fine head and neck movements but do not innervate the levator scapulae. - The levator scapulae receives segmental innervation from C3-C4 cervical nerves directly, in addition to the dorsal scapular nerve. *Subscapular* - The subscapular nerves (upper and lower, from C5-C6) innervate the **subscapularis muscle**, which is part of the rotator cuff. - They also innervate the **teres major muscle**, but not the levator scapulae. - These are branches from the posterior cord of the brachial plexus.
Question 9: Posterior wall of the inguinal canal is formed by all of the following structures, except which of the following?
- A. Parietal peritoneum
- B. Interfoveolar ligament
- C. Internal oblique muscle (Correct Answer)
- D. Fascia transversalis
Explanation: ***Internal oblique muscle*** - The **internal oblique muscle** forms part of the **anterior wall** and the **roof** of the inguinal canal, not the posterior wall [1], [3]. - Its fibers arch over the spermatic cord and contribute to the conjoint tendon (inguinal falx) medially, which does contribute to the posterior wall, but the muscle itself does not [3]. *Interfoveolar ligament* - The **interfoveolar ligament** is a fibrous band lateral to the deep inguinal ring that contributes to the **posterior wall** of the inguinal canal. - It arises from the fascia transversalis and helps reinforce the lateral portion of the posterior wall. *Parietal peritoneum* - The **parietal peritoneum** forms the deepest (most posterior) layer of the **posterior wall** of the inguinal canal, lying posterior to the fascia transversalis with extraperitoneal fat in between [2]. - Although not a strong structural component, it is the innermost layer forming the posterior boundary. *Fascia transversalis* - The **fascia transversalis** is the primary and strongest component forming the majority of the **posterior wall** of the inguinal canal throughout its entire length. - It is a dense fibrous sheet that forms the deep boundary of the canal [4].
Question 10: Stage III "Pressure sore" is full thickness skin loss extending:
- A. through subcutaneous tissue into fascia, muscles and bone
- B. into subcutaneous tissue but not through fascia (Correct Answer)
- C. through subcutaneous tissue into fascia
- D. through subcutaneous tissue into fascia and muscles
Explanation: ***into subcutaneous tissue but not through fascia*** - A **Stage III pressure ulcer** involves **full-thickness skin loss** with damage or necrosis of **subcutaneous tissue** that may extend down to, but **NOT through**, the underlying fascia. - The ulcer presents as a **deep crater** with or without undermining of adjacent tissue, slough, or eschar. - **Muscle, tendon, and bone are NOT visible or directly palpable** in Stage III ulcers. *through subcutaneous tissue into fascia* - This description is **too deep** for Stage III; fascia penetration indicates **Stage IV**. - Stage III extends **to** the fascia but does **not penetrate through** it. *through subcutaneous tissue into fascia and muscles* - This is the definition of a **Stage IV pressure ulcer**, not Stage III. - **Muscle exposure** indicates full-thickness tissue loss beyond the subcutaneous layer and signifies Stage IV. *through subcutaneous tissue into fascia, muscles and bone* - This is also **Stage IV** (most severe form with bone, tendon, or muscle exposure). - **Bone exposure** is pathognomonic of Stage IV pressure ulcers and never occurs in Stage III.
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