Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics Indian Medical PG Practice Questions and MCQs

Question 21: Which of the following statements about the menisci is not true?

A. The medial meniscus is more mobile than the lateral meniscus. (Correct Answer)
B. The lateral meniscus covers more tibial articular surface than the medial meniscus.
C. The medial meniscus is more commonly injured than the lateral meniscus.
D. Menisci are predominantly made up of Type I collagen.

Explanation: ### Explanation The correct answer is **A**. This statement is false because the **lateral meniscus is significantly more mobile than the medial meniscus.** #### 1. Why Option A is the Correct Answer (The False Statement) The mobility of the menisci is determined by their attachments. The **medial meniscus** is firmly attached to the joint capsule and the **Medial Collateral Ligament (MCL)**, making it relatively fixed. In contrast, the **lateral meniscus** is smaller, more circular, and is not attached to the Lateral Collateral Ligament (LCL). It is also separated from the capsule by the popliteus tendon. This increased mobility allows the lateral meniscus to "get out of the way" during trauma, making it less prone to injury compared to the medial meniscus. #### 2. Analysis of Other Options * **Option B:** True. The lateral meniscus is nearly circular and covers approximately **70-80%** of the lateral tibial condyle, whereas the C-shaped medial meniscus covers only about **50-60%** of the medial condyle. * **Option C:** True. Because the medial meniscus is fixed and less mobile, it cannot easily adapt to sudden rotational forces, leading to a higher frequency of tears (roughly 3:1 ratio compared to lateral). * **Option D:** True. Menisci are composed of **fibrocartilage**. The dry weight of the meniscus consists of approximately 60-70% collagen, of which **Type I collagen** is the predominant type (90%). #### 3. Clinical Pearls for NEET-PG * **Shape:** Medial = 'C' shaped; Lateral = 'O' shaped (Circular). * **Blood Supply:** Only the peripheral **10-30% (Red-Red zone)** is vascularized. Central tears (White-White zone) do not heal well and often require meniscectomy. * **Function:** They act as shock absorbers and increase the congruency of the knee joint. * **McMurray Test:** Used clinically to diagnose meniscal tears (Internal rotation for lateral meniscus, External rotation for medial meniscus).

Question 22: Which of the following is NOT a characteristic of osteogenesis imperfecta?

A. Impaired healing of fractures (Correct Answer)
B. Deafness
C. Laxity of joints
D. Frequent fractures

Explanation: **Explanation:** **Osteogenesis Imperfecta (OI)**, also known as "Brittle Bone Disease," is a genetic disorder primarily caused by mutations in the **COL1A1 and COL1A2 genes**, leading to a quantitative or qualitative defect in **Type 1 Collagen**. 1. **Why "Impaired healing of fractures" is the correct answer:** Despite the bones being fragile and prone to multiple fractures, the **healing process (callus formation) in OI is generally normal**. In fact, some patients may even exhibit "Hyperplastic Callus" formation (especially in Type V). The defect lies in the structural integrity of the bone matrix, not in the biological capacity of the bone to repair itself. 2. **Analysis of Incorrect Options:** * **Deafness:** This is a classic feature caused by otosclerosis (fixation of stapes) or compression of the auditory nerve due to deformities in the skull bones. * **Laxity of joints:** Since Type 1 collagen is a major component of ligaments and tendons, its deficiency leads to significant ligamentous laxity and joint hypermobility. * **Frequent fractures:** This is the hallmark of the disease. The defective collagen leads to thin, porous cortices and sparse trabeculae, making bones extremely brittle. **High-Yield Clinical Pearls for NEET-PG:** * **Blue Sclera:** The most famous sign; occurs because the thinness of the scleral collagen allows the underlying choroidal veins to show through. * **Sillence Classification:** Used to grade severity (Type I is mildest/most common; Type II is perinatal lethal). * **Wormian Bones:** Multiple small intrasutural bones seen on skull X-rays. * **Treatment:** Bisphosphonates (e.g., Pamidronate) are the medical mainstay to increase bone density; **Sillence (telescoping) nails** are used surgically to manage long bone fractures.

Question 23: Which part of the bone is the most metabolically active?

A. Cortical bone
B. Cancellous bone
C. Periosteal surface
D. Endosteal surface (Correct Answer)

Explanation: **Explanation:** The **Endosteal surface** (Endosteum) is the most metabolically active part of the bone. This is primarily because the endosteum lines the inner cavities of the bone (medullary canal and trabeculae), where it remains in direct contact with the highly vascular bone marrow. It contains a high concentration of osteoprogenitor cells, osteoblasts, and osteoclasts, making it the primary site for **bone remodeling** and mineral exchange. **Analysis of Options:** * **Endosteal surface (Correct):** It has the highest rate of turnover. In conditions like hyperparathyroidism, the endosteal surface shows the earliest signs of resorption (subendosteal resorption). * **Cancellous bone (Incorrect):** While cancellous (trabecular) bone is significantly more metabolically active than cortical bone due to its high surface-area-to-volume ratio, the *surface* where the cellular activity actually occurs is the endosteum. * **Cortical bone (Incorrect):** This is the dense, outer shell of the bone. It is primarily structural and has a much slower turnover rate compared to cancellous bone. * **Periosteal surface (Incorrect):** The periosteum is essential for appositional growth and fracture healing (callus formation), but its baseline metabolic turnover is lower than that of the endosteal surface. **NEET-PG High-Yield Pearls:** 1. **Bone Remodeling Units (BRUs):** Remodeling occurs 5–10 times faster in cancellous bone than in cortical bone. 2. **Blood Supply:** The inner 2/3rd of the cortex is supplied by the nutrient artery (centrifugal flow), while the outer 1/3rd is supplied by periosteal vessels. 3. **Endosteal Scalloping:** This is a classic radiological sign seen in intramedullary tumors (like Chondromas) or metabolic bone diseases, reflecting high endosteal activity.

Question 24: Wormian bones are seen in which of the following conditions?

A. Osteogenesis imperfecta (Correct Answer)
B. Scheuermann's disease
C. Paget's disease
D. Osteoclastoma

Explanation: **Explanation:** **Wormian bones** (also known as intrasutural bones) are small, accessory bone ossicles found within the sutures of the skull, most commonly in the lambdoid suture. Their presence is a hallmark radiographic sign of certain skeletal dysplasias and metabolic bone diseases. 1. **Why Osteogenesis Imperfecta (OI) is correct:** OI is a genetic disorder of Type I collagen synthesis. The defective collagen leads to delayed ossification of the skull. As a result, multiple small, irregular centers of ossification form within the sutures to fill the gaps, appearing as a "mosaic" or "jigsaw puzzle" pattern on X-rays. In OI, these are often numerous (more than 10) and are a diagnostic criteria. 2. **Why the other options are incorrect:** * **Scheuermann's disease:** This is a condition of juvenile kyphosis caused by wedge-shaped vertebrae and Schmorl’s nodes; it does not involve skull ossification defects. * **Paget's disease:** Characterized by disordered bone remodeling, it shows "Cotton wool spots" on the skull and thickening of the vault, but not Wormian bones. * **Osteoclastoma (Giant Cell Tumor):** A benign but locally aggressive bone tumor typically found in the epiphysis of long bones (e.g., distal femur); it has no association with sutural bones. **High-Yield Clinical Pearls for NEET-PG:** To remember the causes of Wormian bones, use the mnemonic **"PORK CHOP"**: * **P:** Pyknodysostosis (associated with "doll-like" face and osteosclerosis) * **O:** Osteogenesis Imperfecta * **R:** Rickets (healing phase) * **K:** Kinky Hair Syndrome (Menkes disease) * **C:** Cleidocranial Dysplasia (associated with absent clavicles) * **H:** Hypothyroidism / Hypophosphatasia * **O:** One (Trisomy 21 / Down Syndrome) * **P:** Pachydermoperiostosis

Question 25: Which of the following is NOT TRUE regarding the effect of aging on articular cartilage?

A. Increased production of glycosaminoglycans (Correct Answer)
B. Decreased production of glycosaminoglycans
C. Increased degradation of glycosaminoglycans
D. Decreased water content

Explanation: **Explanation:** Articular cartilage undergoes specific biochemical and structural changes as a result of physiological aging (senescence), which are distinct from the pathological changes seen in osteoarthritis. **Why Option A is the Correct Answer (The "Not True" Statement):** With aging, the synthetic activity of chondrocytes decreases. There is a **decreased production of glycosaminoglycans (GAGs)** and proteoglycans. Furthermore, the GAG chains produced are shorter in length (specifically a decrease in Chondroitin-6-Sulfate). Therefore, an *increased* production of GAGs is incorrect. **Analysis of Other Options:** * **B & C (Decreased production/Increased degradation):** Aging is characterized by a shift in the metabolic balance where the rate of degradation of the extracellular matrix (ECM) exceeds the rate of synthesis. This leads to a net loss of proteoglycan content. * **D (Decreased water content):** This is a high-yield distinction. In **normal aging**, the water content of articular cartilage **decreases**, leading to reduced elasticity. (Contrast this with **Osteoarthritis**, where water content initially **increases** due to the breakdown of the collagen network). **High-Yield Clinical Pearls for NEET-PG:** * **Chondroitin Sulfate Ratio:** Aging leads to a decrease in the Chondroitin-4-Sulfate to Chondroitin-6-Sulfate ratio (C4S decreases more than C6S). * **Keratan Sulfate:** Unlike GAGs, the concentration of Keratan Sulfate actually **increases** with age. * **Modulus of Elasticity:** Due to decreased water and proteoglycans, the modulus of elasticity decreases, making the cartilage more brittle and prone to fatigue failure. * **Advanced Glycation End-products (AGEs):** Aging increases the non-enzymatic cross-linking of collagen, which turns the cartilage yellowish and increases stiffness.

Question 26: In achondroplasia, a mutation occurs in which of the following genes?

A. FGFR3 (Correct Answer)
B. FGFR2
C. FGFR1
D. FGFR6

Explanation: **Explanation:** **Achondroplasia** is the most common form of disproportionate short-limbed dwarfism. It is an autosomal dominant condition caused by a **gain-of-function mutation** in the **FGFR3 (Fibroblast Growth Factor Receptor 3)** gene located on chromosome 4p16.3. 1. **Why FGFR3 is correct:** Normally, the FGFR3 protein acts as a negative regulator (inhibitor) of endochondral bone growth. In achondroplasia, a point mutation (most commonly G1138A) causes the receptor to be constitutively active (always "on"). This overactivity leads to excessive inhibition of chondrocyte proliferation and maturation at the epiphyseal growth plate, resulting in shortened long bones. 2. **Why other options are incorrect:** * **FGFR1 & FGFR2:** Mutations in these genes are primarily associated with **Craniosynostosis syndromes** (e.g., Pfeiffer, Apert, and Crouzon syndromes), where there is premature fusion of skull sutures. * **FGFR6:** This is not a standard human fibroblast growth factor receptor associated with known skeletal dysplasias. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** 80% of cases are due to **de novo mutations** (sporadic), often associated with **advanced paternal age**. * **Clinical Features:** Rhizomelic shortening (proximal limb segments), "Trident hand," frontal bossing, and lumbar lordosis. * **Radiology:** Narrowing of the interpedicular distance in the lumbar spine and "Champagne glass" pelvis. * **Most Common Cause of Death:** Foramen magnum stenosis leading to brainstem compression (in infancy).

Question 27: All of the following are properties of synovial fluid EXCEPT?

A. It is a pale yellow, clear, and sufficiently viscous fluid such that droplets expelled from a needle tip fall in a long string.
B. It is a non-Newtonian fluid.
C. It does not clot because it lacks fibrinogen.
D. Normal WBC count in synovial fluid is 350 - 3500 / mm³. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because the normal White Blood Cell (WBC) count in synovial fluid is significantly lower than the range provided. In a healthy joint, the WBC count is typically **less than 200 cells/mm³**, with less than 25% being polymorphonuclear (PMN) leukocytes. A count of 350–3,500/mm³ would be indicative of a non-inflammatory or mildly inflammatory condition (like osteoarthritis), rather than a normal physiological state. **Analysis of other options:** * **Option A:** Synovial fluid is normally clear, straw-colored (pale yellow), and highly viscous due to high concentrations of **Hyaluronic acid**. The "string sign" (forming a 3–5 cm string when dropped) is a classic test for normal viscosity. * **Option B:** It is a **non-Newtonian fluid**. Its viscosity is not constant; it exhibits "thixotropy," meaning it becomes less viscous as the shear rate increases (e.g., during rapid joint movement) to reduce friction. * **Option C:** Normal synovial fluid **does not clot** because it lacks fibrinogen and other clotting factors. If a sample clots, it suggests an inflammatory process or a traumatic tap where blood has entered the space. **NEET-PG High-Yield Pearls:** * **Mucin Clot Test:** Adding acetic acid to normal synovial fluid forms a tight, ropy clot (indicates good quality hyaluronic acid). * **Septic Arthritis:** WBC count is typically **>50,000/mm³** with >75% neutrophils. * **Inflammatory (e.g., RA):** WBC count is usually 2,000–50,000/mm³. * **Glucose levels:** Normally mirror serum levels; a significant drop (>20–40 mg/dL lower than serum) suggests infection.

Question 28: The tensile strength of a bone is due to which component?

A. Strands of collagen (Correct Answer)
B. Hydroxyapatite crystals
C. Periosteum
D. Metaphysis

Explanation: **Explanation:** Bone is a composite material consisting of an organic matrix and an inorganic mineral phase. Its mechanical properties are determined by the synergy between these two components. **1. Why Option A is Correct:** The organic matrix of bone is primarily composed of **Type I Collagen** (90%). Collagen fibers provide **tensile strength**, which is the ability of the bone to resist being pulled apart or stretched. Think of collagen as the "reinforcing steel bars" (rebar) in concrete; it allows for flexibility and prevents the bone from being brittle. **2. Why the other options are incorrect:** * **Option B (Hydroxyapatite crystals):** These represent the inorganic component (Calcium phosphate). Hydroxyapatite provides **compressive strength** and hardness. Without minerals, bone would be overly flexible (like a rubber bone); without collagen, it would shatter easily. * **Option C (Periosteum):** This is the fibrous membrane covering the outer surface of the bone. While it is essential for appositional growth and fracture healing (due to its osteogenic potential), it is not the primary structural component responsible for tensile strength. * **Option D (Metaphysis):** This is an anatomical region of a long bone located between the epiphysis and diaphysis. It is a site of high metabolic activity and growth but is a structural location, not a biochemical component. **High-Yield Clinical Pearls for NEET-PG:** * **Type I Collagen:** Found in **B**one, Skin, and Tendons (Mnemonic: "Type **One** is in B**one**"). * **Osteogenesis Imperfecta:** A genetic defect in Type I collagen synthesis, leading to decreased tensile strength and multiple pathological fractures. * **Scurvy:** Vitamin C deficiency leads to defective collagen cross-linking, weakening the bone matrix. * **Young’s Modulus:** This measures the "stiffness" of bone. Bone is **anisotropic**, meaning its strength varies depending on the direction of the applied load (it is strongest in compression and weakest in shear).

Question 29: What is the major protein of bone?

A. Osteocalcin
B. Osteopontin
C. Collagen type 1 (Correct Answer)
D. Collagen type 4

Explanation: **Explanation:** Bone is a specialized connective tissue composed of an organic matrix (30%) and an inorganic mineral phase (70%). The organic matrix, also known as **osteoid**, is primarily responsible for the tensile strength of the bone. **Why Collagen Type 1 is Correct:** Approximately **90% of the organic matrix of bone** is composed of **Collagen Type 1**. It forms a triple-helical structure that provides the structural framework for the deposition of hydroxyapatite crystals (mineralization). In the context of NEET-PG, remember the mnemonic: *"Type **1** is for B**one**."* **Analysis of Incorrect Options:** * **A. Osteocalcin:** This is the most abundant **non-collagenous** protein in bone. It is produced by osteoblasts and is a marker of bone formation/turnover, but it constitutes only a small fraction of the total protein mass compared to collagen. * **B. Osteopontin:** Another non-collagenous protein involved in cell adhesion and anchoring osteoclasts to the bone surface (mineralized matrix). * **C. Collagen Type 4:** This type is primarily found in the **basal lamina** (basement membranes) and is not a structural component of the bone matrix. **High-Yield Clinical Pearls for NEET-PG:** * **Osteogenesis Imperfecta:** Caused by a genetic defect in the synthesis of **Type 1 Collagen**, leading to "brittle bones." * **Collagen Type 2:** Found in **Cartilage** (Mnemonic: *"Type **2** is for Car-two-lage"*). * **Inorganic Component:** Primarily **Calcium Hydroxyapatite** $[Ca_{10}(PO_4)_6(OH)_2]$, which provides compressive strength. * **Vitamin K:** Necessary for the gamma-carboxylation of Osteocalcin, allowing it to bind calcium.

Question 30: Which subtype of Osteogenesis imperfecta is not associated with blue sclera?

A. Type I
B. Type II
C. Type III
D. Type IV (Correct Answer)

Explanation: **Explanation:** Osteogenesis Imperfecta (OI) is a heterogeneous group of connective tissue disorders primarily caused by mutations in the **COL1A1** and **COL1A2** genes, leading to defective Type I collagen synthesis. **Why Type IV is the correct answer:** The presence of blue sclera is caused by the thinning of the scleral collagen, which allows the underlying choroidal veins to show through. In **Type IV OI**, the sclera is characteristically **normal (white)**. This subtype is classified as "mild to moderate" in severity, featuring osteoporosis and bone fragility, but it is clinically distinguished from Type I by the absence of blue sclera after infancy. **Analysis of Incorrect Options:** * **Type I:** This is the most common and mildest form. It is classically associated with **persistent blue sclera**, premature deafness, and mild bone fragility. * **Type II:** This is the **perinatal lethal** form. It presents with severe skeletal deformities, multiple in-utero fractures, and **deep blue/gray sclera**. * **Type III:** Known as the **progressive deforming** type. It is the most severe non-lethal form. Patients have significant limb deformities, short stature, and **blue sclera that often fades to white** as the patient reaches adulthood (but is present during development). **NEET-PG High-Yield Pearls:** * **Sillence Classification:** The standard system used to categorize OI (Types I-IV). * **Type I Collagen:** The primary defect in OI (found in bone, skin, and sclera). * **Dentinogenesis Imperfecta:** Often associated with Type IV (specifically Subtype IVB). * **Wormian Bones:** Multiple small intrasutural bones in the skull, a classic radiographic sign of OI. * **Treatment:** Bisphosphonates (e.g., Pamidronate) are the medical mainstay to increase bone mineral density.

Practice by Chapter

Bone Structure and Function

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Cartilage Biology and Physiology

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Muscle and Tendon Physiology

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Joint Biomechanics

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Fracture Healing Process

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Bone Metabolism and Turnover

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Orthopaedic Biomaterials

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Tribology in Orthopaedics

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Gait Analysis

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Biomechanics of Spine

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Applied Surgical Anatomy

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Bone Banking and Grafting

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