Biomechanics of Spine — MCQs
Which of the following movements is least permitted in the lumbar region of the vertebral column?
All of the following contribute to the intervertebral disc EXCEPT:
Identify the condition shown in the image:
Dennis stability concept is based on which of the following?
What constitutes a spinal motion segment?
False about fracture of vertebrae
What is the latent period in distraction osteogenesis?
Bone resorption is enhanced by which of the following?
Which anatomical structure is considered a dynamic stabilizer of the shoulder joint?
Molten-wax appearance is seen in which of the following conditions?
Biomechanics of Spine Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following movements is least permitted in the lumbar region of the vertebral column?
- A. Flexion
- B. Extension
- C. Lateral flexion
- D. Rotation (Correct Answer)
Explanation: ***Rotation*** - The **lumbar spine permits the LEAST rotation** of all movements (~5° total rotation), making this the correct answer. - The PRIMARY limiting factor is the **sagittal (near-vertical) orientation of the lumbar facet joints**, which are oriented in the coronal plane and face medially/laterally. - This facet orientation creates a **mechanical block to rotational movement**, acting like interlocking barriers. - The thick **intervertebral discs** in the lumbar region also resist torsional forces, further limiting rotation. *Flexion* - The lumbar region permits **excellent flexion** (forward bending), with approximately 50-60° of range. - The **large, wedge-shaped intervertebral discs** allow substantial anterior compression and movement. - This is one of the primary movements of the lumbar spine. *Extension* - **Extension** (backward bending) is moderately permitted in the lumbar spine, with approximately 15-20° of range. - Eventually limited by contact between **spinous processes** and the posterior ligamentous structures. - Still considerably more movement than rotation. *Lateral flexion* - **Lateral flexion** (sideways bending) is well permitted, with approximately 20° of movement to each side. - The structure of the vertebral bodies and **compressible intervertebral discs** allows good range of motion in the coronal plane. - Significantly more mobile than rotation.
Question 2: All of the following contribute to the intervertebral disc EXCEPT:
- A. Fibrocartilage
- B. Elastic cartilage (Correct Answer)
- C. Annulus fibrosus
- D. Nucleus pulposus
Explanation: ***Elastic cartilage*** - **Elastic cartilage** is characterized by the presence of **elastic fibers**, providing flexibility to structures like the ear and epiglottis. - It is **not found** within the intervertebral disc, which requires specific properties for weight-bearing and shock absorption. *Fibrocartilage* - **Fibrocartilage** is a primary component of the **annulus fibrosus** and plays a crucial role in providing tensile strength and resisting compressive forces [1]. - Its presence is essential for the structural integrity and function of the intervertebral disc. *Annulus fibrosus* - The **annulus fibrosus** is the **tough, outer fibrous ring** of the intervertebral disc, composed of concentric layers of fibrocartilage. - It encircles the nucleus pulposus, containing it and providing stability to the disc. *Nucleus pulposus* - The **nucleus pulposus** is the **gel-like core** of the intervertebral disc, rich in proteoglycans and water. - It acts as a shock absorber and allows for flexibility between vertebrae.
Question 3: Identify the condition shown in the image:
- A. Renal osteodystrophy
- B. Spondylolisthesis
- C. Tuberculosis (TB)
- D. Spondylolysis (Correct Answer)
Explanation: ***Spondylolysis*** * The image shows a **break in the pars interarticularis** of a vertebra, indicated by the arrow, which is characteristic of spondylolysis. * This condition is a **stress fracture** or defect in the pars interarticularis, a bony segment connecting the superior and inferior articular facets. *Renal osteodystrophy* * Renal osteodystrophy refers to a spectrum of **bone abnormalities** that occur in chronic kidney disease, not a specific vertebral fracture pattern. * It typically involves features such as **osteomalacia**, **osteitis fibrosa cystica**, or **osteoporosis**, which are not directly depicted as a fracture in this image. *Spondylolisthesis* * Spondylolisthesis is the **anterior slippage** of one vertebral body over another, which can be caused by bilateral spondylolysis but is not directly shown as a slip in this specific image. * The image distinctly highlights the **fracture line** itself, rather than the displacement of the vertebral body. *Tuberculosis (TB)* * Spinal tuberculosis (Pott's disease) typically presents with **destruction of vertebral bodies**, disc space narrowing, and often a **paravertebral abscess**. * The image does not show these features; instead, it demonstrates a clear **bony defect** in the pars interarticularis.
Question 4: Dennis stability concept is based on which of the following?
- A. 4 columns
- B. 3 columns (Correct Answer)
- C. 5 columns
- D. 2 columns
Explanation: ***3 columns*** - The **Denis classification** system for spinal stability divides the vertebra into three conceptual columns: **anterior**, **middle**, and **posterior**. - This three-column model helps in assessing the **stability of spinal fractures** and guiding treatment decisions. *4 columns* - The four-column concept is **not standard** for Denis classification; it would overcomplicate the established three-column model. - Adding a fourth column lacks the **clinical utility** and widespread acceptance of the Denis system. *5 columns* - A five-column system is **not recognized** in the standard Denis classification of spinal stability. - Such a detailed breakdown would be **excessive** and not provide additional practical information for assessing stability. *2 columns* - The two-column concept, often seen in older classifications like **Holdsworth classification**, predates Denis's work and was found to be **less comprehensive** for assessing spinal stability. - It does not account for the critical stabilizing role of the **middle column** in spinal fractures.
Question 5: What constitutes a spinal motion segment?
- A. A disc and the vertebrae above and below, including their interlocking facet joints. (Correct Answer)
- B. A disc and the facet joints at that level.
- C. A vertebral body and the disc above.
- D. A section of the spine involved in a physiological curve with the similar function (i.e. thoracic kyphosis).
Explanation: ***A disc and the vertebrae above and below, including their interlocking facet joints.*** - A **spinal motion segment** or **functional spinal unit** is defined as two adjacent vertebrae and the intervertebral disc between them. - This unit includes all the associated **ligaments**, **capsules**, and especially the **facet joints**, which together allow for complex movements. *A disc and the facet joints at that level.* - This definition is incomplete as it misses the crucial component of the **vertebral bodies** themselves. - The vertebral bodies provide the main structural support and articulation points for the disc and facet joints. *A vertebral body and the disc above.* - This partial definition describes only a fraction of the components required for a functional segment. - It omits the **inferior vertebral body** and the critical **facet joints** that enable motion. *A section of the spine involved in a physiological curve with the similar function (i.e. thoracic kyphosis).* - This option describes a broader **region** of the spine rather than a single, functional motion unit. - A physiological curve involves multiple motion segments working in concert, not a single segment.
Question 6: False about fracture of vertebrae
- A. Fracture dislocation is common in flexion rotation injury
- B. Chance fracture occurs due to flexion distraction injury
- C. Wedge compression causes flexion injury
- D. Anterior longitudinal ligament runs along the posterior surface of vertebral bodies (Correct Answer)
Explanation: ***Anterior longitudinal ligament runs along the posterior surface of vertebral bodies*** - The **anterior longitudinal ligament (ALL)** runs along the **anterior aspect** of the vertebral bodies, preventing hyperextension. - The **posterior longitudinal ligament (PLL)** runs along the posterior surface of the vertebral bodies, within the vertebral canal. *Fracture dislocation is common in flexion rotation injury* - **Flexion-rotation injuries** are highly unstable and frequently lead to **fracture-dislocations** of the vertebral column. - The combined forces cause significant disruption of both bony and ligamentous structures, increasing the likelihood of displacement. *Chance fracture occurs due to flexion distraction injury* - A **Chance fracture** (or seatbelt fracture) is caused by a **flexion-distraction injury**, typically seen in individuals wearing lap belts during deceleration. - This mechanism results in a horizontal splitting of the vertebral body and posterior elements. *Wedge compression causes flexion injury* - A **wedge compression fracture** is the most common type of vertebral fracture and results from a **flexion injury** (hyperflexion). - The anterior portion of the vertebral body collapses, creating a wedge shape, while the posterior column remains intact.
Question 7: What is the latent period in distraction osteogenesis?
- A. 4-6 weeks
- B. 5-7 days (Correct Answer)
- C. 6-8 months
- D. 4 months
Explanation: **Explanation:** **Distraction Osteogenesis** (Ilizarov technique) is a process of growing new bone by mechanically stretching a vascularized callus. The procedure follows a specific chronological sequence: 1. **Latent Period (The Correct Answer):** This is the duration between the corticotomy (surgical bone cut) and the commencement of distraction. It typically lasts **5–7 days**. This period allows for the inflammatory phase of bone healing to occur and for the initial soft tissue/callus bridge to form. Starting distraction too early (before 5 days) can lead to poor callus formation, while starting too late (after 10–14 days) may result in premature consolidation (early fusion). 2. **Distraction Phase:** The bone is stretched at a rate of **1 mm per day**, usually divided into four increments (0.25 mm every 6 hours). 3. **Consolidation Phase:** The period where the newly formed "regenerate" bone mineralizes and hardens. **Analysis of Incorrect Options:** * **A (4-6 weeks):** This is the typical time for clinical union in simple fractures, not the latent period for distraction. * **C & D (6-8 months / 4 months):** These timeframes are more representative of the total duration an Ilizarov fixator might remain on a limb for complex lengthening or non-union treatments. **High-Yield Clinical Pearls for NEET-PG:** * **The Law of Tension-Stress:** Proposed by Ilizarov, stating that gradual traction on living tissues stimulates and maintains the regeneration and growth of those tissues. * **Rate of Distraction:** 1 mm/day is the gold standard. <0.5 mm/day leads to premature fusion; >2 mm/day leads to non-union and nerve damage. * **Most common complication:** Pin tract infection. * **Best site for corticotomy:** Metaphysis (due to superior vascularity and osteogenic potential).
Question 8: Bone resorption is enhanced by which of the following?
- A. PGD2
- B. PDF2
- C. PGE2 (Correct Answer)
- D. PGI2
Explanation: **Explanation:** Bone remodeling is a dynamic process regulated by various systemic hormones and local inflammatory mediators. Prostaglandins, which are derivatives of arachidonic acid, play a significant role in this process. **Why PGE2 is the Correct Answer:** **Prostaglandin E2 (PGE2)** is the most potent stimulator of bone resorption among the prostaglandins. It acts by stimulating the **RANKL (Receptor Activator of Nuclear Factor kappa-B Ligand)** expression in osteoblasts. This RANKL then binds to RANK receptors on osteoclast precursors, leading to their maturation and activation. While PGE2 has a dual role (it can also stimulate bone formation in certain concentrations), its primary clinical significance in inflammatory states (like rheumatoid arthritis or periodontal disease) is the induction of osteoclastogenesis and subsequent bone loss. **Analysis of Incorrect Options:** * **PGD2 (Prostaglandin D2):** Primarily involved in smooth muscle relaxation and allergic responses; it does not have a significant stimulatory effect on bone resorption. * **PGF2α (often mislabeled as PDF2):** While it can influence bone metabolism, it is significantly less potent than PGE2 and is more associated with uterine contraction. * **PGI2 (Prostacyclin):** Mainly acts as a potent vasodilator and inhibitor of platelet aggregation; it has minimal to no role in enhancing bone resorption. **High-Yield Clinical Pearls for NEET-PG:** * **NSAIDs and Bone:** Since NSAIDs inhibit prostaglandin synthesis (COX inhibition), they can theoretically delay fracture healing by reducing PGE2-mediated bone remodeling. * **IL-1 and TNF-α:** These cytokines also enhance bone resorption by stimulating PGE2 production. * **Bisphosphonates:** These are the drugs of choice to *inhibit* bone resorption by inducing osteoclast apoptosis.
Question 9: Which anatomical structure is considered a dynamic stabilizer of the shoulder joint?
- A. Rotator cuff (Correct Answer)
- B. Glenoid labrum
- C. Coracohumeral ligament
- D. Glenohumeral ligament
Explanation: **Explanation:** The stability of the shoulder (glenohumeral) joint is maintained by a complex interplay between static and dynamic stabilizers. **1. Why the Rotator Cuff is correct:** The **Rotator Cuff** (comprising the Supraspinatus, Infraspinatus, Teres minor, and Subscapularis—SITS muscles) is the primary **dynamic stabilizer**. These muscles stabilize the joint through "concavity compression." As they contract, they pull the large humeral head into the shallow glenoid fossa, centering it during movement. Because they require active muscular contraction to provide stability, they are classified as dynamic. **2. Why the other options are incorrect:** * **Glenoid Labrum (B):** This is a fibrocartilaginous rim that deepens the glenoid cavity. It is a **static stabilizer** because it provides structural stability without active contraction. * **Coracohumeral Ligament (C) & Glenohumeral Ligaments (D):** These are capsular thickenings that act as **static stabilizers**. They provide stability only at the end-range of motion when they become taut, preventing excessive translation of the humeral head. **High-Yield Clinical Pearls for NEET-PG:** * **Static Stabilizers:** Include the glenoid labrum, joint capsule, glenohumeral ligaments (Superior, Middle, and Inferior), and negative intra-articular pressure. * **The "Safety Belt" of the Shoulder:** The **Inferior Glenohumeral Ligament (IGHL)** is the most important static stabilizer against anterior dislocation when the shoulder is abducted and externally rotated. * **Long Head of Biceps:** Often considered a secondary dynamic stabilizer, as it depresses the humeral head. * **Rotator Interval:** A triangular space between the Supraspinatus and Subscapularis; it is a common site for pathology in shoulder instability.
Question 10: Molten-wax appearance is seen in which of the following conditions?
- A. Osteoporosis
- B. Osteopoikilosis
- C. Melorheostosis (Correct Answer)
- D. Osteogenesis imperfecta
Explanation: **Explanation:** **Melorheostosis** is a rare, non-hereditary sclerosing bone dysplasia characterized by linear cortical thickening. The term is derived from Greek (*melos* = limb, *rhein* = flow, *ostosis* = bone formation). 1. **Why Melorheostosis is correct:** The hallmark radiological feature is hyperostosis (excessive bone growth) along the cortex of long bones, typically following a **sclerotomal distribution**. This appearance resembles **wax dripping down the side of a candle** (Molten-wax appearance). It usually affects only one side of the bone (monostotic or polyostotic but unilateral). 2. **Why other options are incorrect:** * **Osteoporosis:** Characterized by decreased bone mineral density and "washed-out" appearance on X-ray (osteopenia), not increased density. * **Osteopoikilosis:** Known as "spotted bone disease." It presents as multiple, small, well-defined symmetric radiopaque spots (islands of bone) near joints, not a flowing wax pattern. * **Osteogenesis Imperfecta:** A genetic disorder of Type 1 collagen. Radiologically, it presents with osteopenia, multiple fractures, and "codfish vertebrae," but not cortical thickening. **High-Yield Clinical Pearls for NEET-PG:** * **Melorheostosis:** Associated with the **LEMD3 gene** mutation. Clinically, it may present with joint stiffness, pain, or limb deformities. * **Osteopoikilosis:** Usually asymptomatic and an incidental finding; also associated with the LEMD3 gene. * **Engelmann’s Disease (Diaphyseal Dysplasia):** Another sclerosing condition, but it is typically bilateral and symmetrical, involving the mid-shaft of long bones.
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