Applied Anatomy of the Back — MCQs

10 questions

Which of the following is not a typical symptom of a lumbar disc herniation?

When a lumbar puncture is performed to sample cerebrospinal fluid, which of the following external landmarks is the most reliable to determine the position of the L4 vertebral spine?

A patient while lifting a heavy weight presents with sudden onset pain in the lower back radiating along the postero-lateral thigh and lateral leg to the big toe with numbness. The most likely diagnosis is:

Regarding the epidural space, all are true except:

Which of the following is not a boundary of the triangle of auscultation?

A radiograph is obtained from a child with scoliosis. What is the name of the angle used to measure spinal curvature?

Which of the following does not require a lumbar puncture in children?

Prolapsed intervertebral Disc (PID) is most common at -

While performing a lumbar puncture, a snap is felt just before entering into the epidural space. This is due to piercing of which structure?

Q10

In a diving accident that severed the spinal cord below the sixth cervical vertebra, which of the following muscles would be affected?

Applied Anatomy of the Back Indian Medical PG Practice Questions and MCQs

Question 1: Which of the following is not a typical symptom of a lumbar disc herniation?

A. Positive straight leg raise test
B. Saddle anesthesia (Correct Answer)
C. Radicular leg pain
D. Weakness in foot dorsiflexion

Explanation: ***Saddle anesthesia*** - While a severe complication, **saddle anesthesia** is indicative of **cauda equina syndrome**, a medical emergency, and not a typical, isolated symptom of a simple lumbar disc herniation. - It suggests **compression of multiple nerve roots** in the lumbosacral region, beyond what is usually seen with a single disc herniation. *Positive straight leg raise test* - This is a common and reliable physical exam finding in patients with **lumbar disc herniation**, indicating nerve root irritation. - It elicits radiating pain down the leg when the affected leg is raised between 30 and 70 degrees. *Radicular leg pain* - **Radicular pain**, often described as sharp, shooting pain down the leg, is the hallmark symptom of a lumbar disc herniation as it signifies **nerve root compression**. - The pain typically follows a **dermatomal pattern**, corresponding to the specific nerve root involved. *Weakness in foot dorsiflexion* - Weakness in **foot dorsiflexion** (commonly affecting the **L4 or L5 nerve roots**) is a frequently observed neurological deficit in lumber disc herniation. - This can be assessed through manual muscle testing and is a sign of **motor nerve root compression**.

Question 2: When a lumbar puncture is performed to sample cerebrospinal fluid, which of the following external landmarks is the most reliable to determine the position of the L4 vertebral spine?

A. The iliac crests (Correct Answer)
B. The lowest pair of ribs bilaterally
C. The inferior angles of the scapulae
D. The posterior superior iliac spines

Explanation: ***The iliac crests*** - A line drawn between the **highest points of the iliac crests** on both sides typically intersects the L4 vertebral body or the L4-L5 intervertebral space. - This anatomical landmark provides a **safe entry point** for lumbar puncture, avoiding the spinal cord which usually ends at L1-L2. *The lowest pair of ribs bilaterally* - The lowest pair of ribs (12th ribs) corresponds to the **twelfth thoracic vertebra (T12)**, which is much higher than the desired lumbar puncture site. - Using this landmark would place the needle at a level where the **spinal cord is still present**, posing a significant risk of injury. *The inferior angles of the scapulae* - The inferior angle of the scapula typically corresponds to the **seventh thoracic vertebra (T7)**. - This landmark is also too superior for a safe lumbar puncture and does not accurately localize the lumbar spine. *The posterior superior iliac spines* - The posterior superior iliac spines (PSIS) are located at the level of the **S2 vertebra**, which is too far inferior for a standard lumbar puncture at L4-L5. - While they are important pelvic landmarks, they are not used for determining the L4 vertebral spine in this context.

Question 3: A patient while lifting a heavy weight presents with sudden onset pain in the lower back radiating along the postero-lateral thigh and lateral leg to the big toe with numbness. The most likely diagnosis is:

A. L4 - L5 Disc prolapsed (Correct Answer)
B. L3 - IA Disc prolapsed
C. L5 fracture
D. L5 - SI Disc prolapse

Explanation: ***L4 - L5 Disc prolapsed*** - A disc prolapse at the **L4-L5 level** typically compresses the **L5 nerve root**. - This compression leads to pain radiating along the **postero-lateral thigh** and **lateral leg**, reaching the **big toe**, often accompanied by numbness in the same distribution due to **L5 dermatome** involvement. *L3 - IA Disc prolapsed* - A prolapse at the **L3-L4 level** would compress the **L4 nerve root**, causing pain in the **anterior thigh** and medial leg, with potential numbness over the **medial calf** and ankle. - This presentation does not match the described symptoms of pain radiating to the big toe and lateral leg. *L5 fracture* - An **L5 fracture** would primarily manifest as localized lower back pain, often exacerbated by movement, and might not necessarily cause radiating pain or numbness in a dermatomal pattern to the big toe unless there's associated nerve root compression. - The sudden onset with radiating pain in a specific distribution points more towards nerve impingement from a disc prolapse rather than a fracture. *L5 - SI Disc prolapse* - A disc prolapse at the **L5-S1 level** compresses the **S1 nerve root**. - This typically results in pain radiating down the **posterior thigh**, **calf**, and to the **little toe** and lateral foot, along with numbness in the **S1 dermatome**, which is different from the big toe and lateral leg involvement described.

Question 4: Regarding the epidural space, all are true except:

A. Ends at the sacrococcygeal membrane
B. Is an open space
C. Continues through foramen magnum into the skull (Correct Answer)
D. Lies outside of the dura mater

Explanation: ***Continues through foramen magnum into the skull*** - The **epidural space** in the spinal column ends superiorly at the **foramen magnum** and does **not continue into the skull** as a defined space. - Within the cranial vault, the dura mater is fused with the periosteum of the skull, meaning there is no true epidural space like that found in the spine. *Lies outside of the dura mater* - The epidural space is indeed located **outside the dura mater**, which is the outermost layer of the meninges in the spinal cord. - This space contains **fat**, **loose connective tissue**, and a **venous plexus**. *Is an open space* - The epidural space is considered an **open or potential space**, meaning it is not normally filled with fluid but can be expanded by injections (e.g., epidural anesthesia) or pathology (e.g., hematoma). - Its contents allow for flexibility and cushioning of the spinal cord within the vertebral canal. *Ends at the sacrococcygeal membrane* - Inferiorly, the spinal epidural space terminates at the **sacrococcygeal membrane**, covering the sacral hiatus. - This anatomical landmark is important for procedures like **caudal epidural blocks**.

Question 5: Which of the following is not a boundary of the triangle of auscultation?

A. Trapezius
B. Scapula
C. Rhomboid major (Correct Answer)
D. Latissimus dorsi

Explanation: ***Rhomboid major*** - The **rhomboid major** muscle forms the **floor** of the triangle of auscultation, not one of its boundaries. - Its function is to **retract** and **rotate** the scapula, anchoring it to the thoracic wall. *Trapezius* - The **trapezius** muscle forms the **superior** and **medial** boundary of the triangle of auscultation. - It defines the upper limit of this anatomical space on the back. *Scapula* - The **medial border of the scapula** forms the **lateral** boundary of the triangle of auscultation. - This bony landmark helps to delineate the outer edge of the triangle. *Latissimus dorsi* - The **latissimus dorsi** muscle forms the **inferior** boundary of the triangle of auscultation. - It defines the lower limit of this region, allowing for better sound transmission to the thoracic cavity.

Question 6: A radiograph is obtained from a child with scoliosis. What is the name of the angle used to measure spinal curvature?

A. Bohler's Angle
B. Ferguson's Angle
C. Cobb's Angle (Correct Answer)
D. Pauwels' Angle

Explanation: **Cobb's Angle** - **Cobb's angle** is the primary method for measuring the severity of **scoliosis** on radiographs. - It is measured by drawing lines parallel to the superior endplate of the most tilted superior vertebra and the inferior endplate of the most tilted inferior vertebra of the curve; the angle between these two lines (or their perpendiculars) is the Cobb angle. *Bohler's Angle* - **Bohler's angle** is used in the assessment of **calcaneus fractures** and is measured on a lateral foot radiograph. - A decrease in this angle is indicative of a calcaneal fracture. *Ferguson's Angle* - **Ferguson's angle**, also known as the lumbosacral angle, measures the inclination of the sacrum relative to the horizontal in the standing position. - It is primarily used in the assessment of **spondylolisthesis** and other lumbosacral conditions. *Pauwels' Angle* - **Pauwels' angle** is used to classify **femoral neck fractures** based on the angle of the fracture line relative to the horizontal. - It helps determine the severity and stability of femoral neck fractures, guiding treatment decisions.

Question 7: Which of the following does not require a lumbar puncture in children?

A. HL (Correct Answer)
B. AML
C. NHL
D. ALL

Explanation: ***HL*** - While central nervous system (CNS) involvement is possible in Hodgkin lymphoma (HL), it is **rare** and does not routinely warrant a **lumbar puncture** for initial staging or surveillance in asymptomatic children. - HL primarily affects **lymph nodes** and the **spleen**, with CNS spread being an uncommon complication that typically presents with specific neurological symptoms. *AML* - **Acute myeloid leukemia (AML)** has a significant risk of **CNS involvement**, requiring a **lumbar puncture** for diagnostic staging and administration of intrathecal chemotherapy. - CNS prophylaxis and treatment are crucial in AML to prevent and manage **leptomeningeal disease**. *NHL* - **Non-Hodgkin lymphoma (NHL)**, particularly aggressive subtypes like Burkitt lymphoma or lymphoblastic lymphoma, has a **high propensity for CNS spread**. - A **lumbar puncture** is essential for staging to detect CNS involvement and guide the need for intrathecal chemotherapy or radiation. *ALL* - **Acute lymphoblastic leukemia (ALL)** carries a well-documented **high risk of CNS infiltration**, necessitating routine **lumbar punctures** at diagnosis for CNS staging and throughout treatment for intrathecal chemotherapy. - CNS prophylaxis is a cornerstone of ALL treatment to prevent **leptomeningeal relapse**.

Question 8: Prolapsed intervertebral Disc (PID) is most common at -

A. L2-L4
B. L5-S1 (Correct Answer)
C. C5-C6
D. C2-C3

Explanation: ***L5-S1*** - The **L5-S1** disc is most frequently affected due to its location at the junction of the **lumbar spine** and the relatively immobile **sacrum**, leading to high biomechanical stress. - This level experiences significant forces during bending and lifting, making it vulnerable to **disc herniation**. *L2-L4* - While disc prolapse can occur at these levels, it is **less common** than at the lower lumbar segments like L5-S1. - The L2-L4 discs are under less mechanical stress compared to the lower lumbar and lumbosacral junctions. *C5-C6* - This level is a common site for cervical disc prolapse, but the question generally refers to the **overall most common site** for PID, which is in the lumbar region. - Cervical disc prolapse at C5-C6 typically presents with **neck pain** and **radiculopathy** affecting the upper extremities. *C2-C3* - Disc prolapse at this level is **rare** due to the relatively small range of motion and protective musculature in the upper cervical spine. - When it does occur, it can cause severe symptoms including **myelopathy** due to spinal cord compression.

Question 9: While performing a lumbar puncture, a snap is felt just before entering into the epidural space. This is due to piercing of which structure?

A. Dura mater
B. Posterior longitudinal ligament
C. Ligamentum flavum (Correct Answer)
D. Supraspinous ligament

Explanation: ***Ligamentum flavum*** - The sensation of a "snap" or "pop" during a lumbar puncture just before the epidural space is characteristically felt when the needle penetrates the tough and elastic **ligamentum flavum**. - This ligament connects the laminae of adjacent vertebrae and is the most significant resistance felt by the needle before reaching the epidural space. *Duramater* - The **dura mater** is the outermost meningeal layer, which is pierced after passing through the epidural space. - Penetrating the dura mater provides a second, typically less pronounced, "pop" or "give" sensation as the needle enters the subarachnoid space to access cerebrospinal fluid. *Posterior longitudinal ligament* - The **posterior longitudinal ligament** is located on the posterior surface of the vertebral bodies, within the spinal canal. - It is not typically pierced during a standard posterior approach lumbar puncture and is not associated with the characteristic "snap." *Supraspinous ligament* - The **supraspinous ligament** is the most superficial ligament in the midline posterior to the vertebral column, connecting the tips of the spinous processes. - While it offers initial resistance, the "snap" associated with entering the epidural space comes from the deeper **ligamentum flavum**, not the supraspinous ligament.

Question 10: In a diving accident that severed the spinal cord below the sixth cervical vertebra, which of the following muscles would be affected?

A. Deltoid
B. Infraspinatus
C. Levator Scapulae
D. Latissimus Dorsi (Correct Answer)

Explanation: ***Latissimus Dorsi*** - The **latissimus dorsi muscle** is primarily innervated by the **thoracodorsal nerve**, which arises from the **C6, C7, and C8** nerve roots (with C7 and C8 being the predominant contributors) [1]. - A spinal cord injury below the sixth cervical vertebra would affect the C7 and C8 segments, thereby disrupting the nerve supply to the latissimus dorsi, leading to weakness or paralysis. - This muscle is responsible for adduction, extension, and internal rotation of the shoulder. *Deltoid* - The **deltoid muscle** is innervated by the **axillary nerve**, which arises predominantly from the **C5 and C6** nerve roots. - Since the injury is below the C6 vertebra, the upper cervical segments (C5 and C6) would remain intact above the level of injury. - Therefore, deltoid function would be preserved. *Infraspinatus* - The **infraspinatus muscle** is innervated by the **suprascapular nerve**, which arises from the **C5 and C6** nerve roots. - Similar to the deltoid, its innervation originates above the level of the spinal cord injury and would be spared. *Levator Scapulae* - The **levator scapulae muscle** receives innervation from the **C3, C4, and C5** spinal nerves, as well as contributions from the dorsal scapular nerve (predominantly C5). - All of these nerve roots originate well above the level of injury, so this muscle would not be affected.

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