Basic Science in Orthopaedics Practice Questions

Q: A 50-year-old male presented to the orthopedic OPD for regular follow-up, being treated for a forearm injury marked in a specimen. During examination, the doctor elicited a specific sign by tapping distal to the injury site, causing the patient to feel a tingling sensation. What is the rate of growth of the injured structure's stump?

1-3 mm/day. ***1-3 mm/day*** - The **Tinel's sign** (tingling sensation when tapping distal to injury site) indicates **peripheral nerve regeneration** at a rate of **1-3 mm/day**. - This rate is crucial for predicting **recovery timeline** and determining when functional improvement might be expected after nerve injury. *10-15 mm/day* - This rate is **significantly higher** than physiological nerve regeneration capacity and would be unrealistic for biological tissue repair. - Such rapid growth would exceed the metabolic capacity of **Schwann cells** and axonal transport mechanisms. *25-30 mm/day* - This rate is **extremely excessive** and incompatible with normal cellular regeneration processes in peripheral nerves. - **Axonal sprouting** and **remyelination** require precise coordination that cannot occur at such accelerated rates. *None of the above* - This option is incorrect as **1-3 mm/day** is the well-established rate for **peripheral nerve regeneration**. - The presence of **Tinel's sign** specifically indicates ongoing nerve repair at this documented physiological rate.

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

FGFR3. **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).

Q: Which of the following is not a good prognostic indicator?

Proximal lesion. In nerve injuries, the prognosis depends on the type of injury, the distance the nerve must regenerate, and the nature of the fibers involved. **Why "Proximal Lesion" is the correct answer:** The prognosis of a nerve injury is inversely proportional to its distance from the target organ (muscle or sensory receptor). Nerve fibers regenerate at a rate of approximately **1 mm per day**. In a **proximal lesion** (e.g., a brachial plexus injury), the regenerating axons must travel a much longer distance to reach the distal effectors. During this prolonged period, the target muscles often undergo irreversible fatty degeneration and fibrosis, and motor end-plates disappear, leading to poor functional recovery. **Analysis of Incorrect Options:** * **Only sensory involvement:** Sensory fibers generally have a better regenerative capacity than motor fibers, and sensory receptors remain viable longer than motor end-plates, making this a good prognostic sign. * **Only motor involvement:** While pure motor involvement is serious, it is generally more favorable than a "mixed" nerve injury where regenerating motor axons might "get lost" and enter sensory sheaths (synkinesis). * **Neuropraxia:** This is the mildest form of nerve injury (Seddon’s classification) involving temporary conduction block without axonal damage. Recovery is typically complete and rapid (weeks), making it the best prognostic indicator among all nerve injuries. **High-Yield Clinical Pearls for NEET-PG:** * **Order of recovery:** Usually, autonomic function returns first, followed by pain, touch, and finally motor function. * **Tinel’s Sign:** A distal tingling sensation on percussion over a nerve; a "marching" Tinel’s sign indicates active axonal regeneration. * **Sunderland Classification:** Grade I (Neuropraxia) has the best prognosis; Grade V (Neurotmesis/Complete transection) has the worst.

Q: Osteonecrosis is not seen in which of the following conditions?

Ollier disease. **Explanation:** The core concept of this question lies in distinguishing between **Osteonecrosis (Avascular Necrosis)** and **Enchondromatosis**. **1. Why Ollier Disease is the Correct Answer:** Ollier disease is a non-hereditary skeletal disorder characterized by multiple **enchondromas** (benign cartilaginous tumors) within the metaphyseal regions of long bones. It is a disorder of bone development and growth, not a vascular or necrotic process. Therefore, it does not involve osteonecrosis. **2. Analysis of Incorrect Options (Conditions involving Osteonecrosis):** The other options are classic examples of **Eponymous Osteochondroses**, where the primary pathology is avascular necrosis (AVN) of the ossification centers: * **Kienböck disease:** Osteonecrosis of the **Lunate** bone in the wrist. * **Köhler disease:** Osteonecrosis of the **Tarsal Navicular** bone in children. * **Perthes disease (Legg-Calvé-Perthes):** Idiopathic osteonecrosis of the **Femoral Head** epiphysis in children. **3. Clinical Pearls for NEET-PG:** * **Ollier Disease + Hemangiomas:** This combination is known as **Maffucci Syndrome**. Both carry a high risk of malignant transformation to Chondrosarcoma. * **Radiological sign in Ollier:** "Vertical streaks" or "Fan-like" radiolucencies extending from the growth plate into the metaphysis. * **Common Osteochondroses Table:** * *Freiberg’s:* 2nd Metatarsal head. * *Panner’s:* Capitellum of the humerus. * *Scheuermann’s:* Vertebral bodies (Ring epiphysis). * *Sever’s:* Calcaneal apophysis (though technically a traction apophysitis).

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

Type IV. **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.

Q: The basic pathology in Myositis Ossificans Progressiva is located in which of the following?

Muscle fibres. **Explanation:** **Myositis Ossificans Progressiva (MOP)**, also known as Fibrodysplasia Ossificans Progressiva (FOP), is a rare genetic disorder characterized by the progressive replacement of soft tissues—specifically skeletal muscles, tendons, and ligaments—with mature heterotopic bone. **Why Option A is Correct:** The primary pathology lies within the **muscle fibers** and their surrounding connective tissue. The condition is caused by a mutation in the **ACVR1 gene**, which leads to over-activation of the Bone Morphogenetic Protein (BMP) signaling pathway. This triggers an inflammatory response in the muscle (myositis), followed by fibroblastic proliferation and eventual endochondral ossification, turning muscle into bone. **Why Other Options are Incorrect:** * **Option B (Serum Chemistry):** In MOP, serum levels of calcium, phosphorus, and alkaline phosphatase are typically **normal**. The pathology is a localized cellular transformation rather than a systemic metabolic or biochemical imbalance. * **Option C (Body Collagen):** While collagenous tissues (tendons/ligaments) are eventually involved, the hallmark and initiating site of the "ossificans" process is the skeletal muscle tissue. It is not a generalized collagen vascular disease. **High-Yield Clinical Pearls for NEET-PG:** * **Inheritance:** Autosomal Dominant (though most cases are sporadic). * **Classic Presentation:** Characterized by the "Great Toe Sign"—congenital **shortening and hallux valgus** of the big toe. * **Progression:** Ossification usually starts in the neck and shoulders, moving cranio-caudally and proximo-distally. * **Management Warning:** Avoid biopsies or intramuscular injections, as **trauma triggers** new flare-ups and rapid ossification.

Q: Which of the following factors does NOT facilitate non-union of a fracture?

Hematoma formation. **Explanation:** The correct answer is **A. Hematoma formation.** Fracture healing is a complex biological process, and the **fracture hematoma** is the essential first stage (Stage of Hematoma). It acts as a scaffold for fibrin and provides a source of signaling molecules (cytokines and growth factors like TGF-beta and BMPs) that trigger the inflammatory cascade and recruit osteoprogenitor cells. Far from causing non-union, a healthy hematoma is a **prerequisite for normal bone healing.** **Analysis of other options:** * **B. Periosteal injuries:** The periosteum is the primary source of blood supply and osteoblasts for the external callus. Extensive stripping or injury to the periosteum severely impairs the healing potential, leading to non-union. * **C. Absence of nerve supply:** While bone can heal in denervated limbs, clinical evidence (especially in spinal cord injuries or leprosy) suggests that intact neurotrophic factors and neuropeptides play a role in regulating bone remodeling. However, in the context of this question, it is a recognized factor that can delay or complicate the biological environment of healing compared to a healthy hematoma. * **D. Chronic infection:** Infection (Osteomyelitis) causes tissue necrosis, persistent inflammation, and bone resorption. It is one of the most common causes of "infected non-union." **NEET-PG High-Yield Pearls:** * **Most common site of non-union:** Scaphoid, Neck of Femur, and Lower 1/3rd of Tibia (due to poor blood supply). * **Hypertrophic Non-union:** Caused by **inadequate fixation** (mechanical failure); characterized by "Elephant foot" appearance on X-ray. * **Atrophic Non-union:** Caused by **poor biology/blood supply**; characterized by tapered bone ends. * **Smoking** is a significant systemic risk factor for non-union due to peripheral vasoconstriction.

Q: What is the major mineral component of bone?

Hydroxyapatite. **Explanation:** Bone is a specialized connective tissue composed of an organic matrix (osteoid) and an inorganic mineral phase. The **inorganic component** accounts for approximately 65-70% of the dry weight of bone and provides its characteristic compressive strength. **Why Hydroxyapatite is correct:** The primary mineral constituent of bone is **Hydroxyapatite**, a crystalline form of calcium phosphate with the chemical formula **$Ca_{10}(PO_4)_6(OH)_2$**. These crystals are deposited within the gaps of the collagen fibrils (Type I collagen) during mineralization. This structural arrangement allows bone to act as a reservoir for 99% of the body’s calcium and 85% of its phosphorus. **Why other options are incorrect:** * **Calcite & Calcium Carbonate:** While calcium carbonate is a major component of the shells of marine organisms and is found in trace amounts in bone, it is not the primary structural mineral. * **Calcium Oxide:** This is a caustic chemical compound (quicklime) not found naturally in human biological tissues. **High-Yield Clinical Pearls for NEET-PG:** * **Organic Matrix:** Composed 90% of **Type I Collagen** (mnemonic: "Bone is One"). * **Non-collagenous proteins:** **Osteocalcin** is the most abundant non-collagenous protein and is a marker of bone formation. * **Mineralization:** Regulated by alkaline phosphatase, which increases local concentrations of inorganic phosphate. * **Stiffness:** The stiffness of bone is directly proportional to its mineral content, whereas its toughness (resistance to fracture) is derived from the collagen fibers.

Question 1

A 50-year-old male presented to the orthopedic OPD for regular follow-up, being treated for a forearm injury marked in a specimen. During examination, the doctor elicited a specific sign by tapping distal to the injury site, causing the patient to feel a tingling sensation. What is the rate of growth of the injured structure's stump?

Accepted Answer

1-3 mm/day

Answer

10-15 mm/day

Answer

25-30 mm/day

Answer

None of the above

Question 2

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

Accepted Answer

FGFR3

Answer

FGFR2

Answer

FGFR1

Answer

FGFR6

Question 3

Which of the following is not a good prognostic indicator?

Accepted Answer

Proximal lesion

Answer

Only motor involvement

Answer

Only sensory involvement

Answer

Neuropraxia

Question 4

Osteonecrosis is not seen in which of the following conditions?

Accepted Answer

Ollier disease

Answer

Kienböck disease

Answer

Köhler disease

Answer

Perthes disease

Question 5

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

Accepted Answer

Strands of collagen

Answer

Hydroxyapatite crystals

Answer

Periosteum

Answer

Metaphysis

Question 6

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

Accepted Answer

Type IV

Answer

Type I

Answer

Type II

Answer

Type III

Question 7

The basic pathology in Myositis Ossificans Progressiva is located in which of the following?

Accepted Answer

Muscle fibres

Answer

Serum chemistry

Answer

Body collagen

Answer

None of the above

Question 8

A patient develops Saturday Night Palsy after consuming alcohol and sleeping overnight with an arm in a dependent position. Which of the following best describes the clinical manifestations of this condition?

Accepted Answer

Neuropraxia

Answer

Axonotmesis

Answer

Neurotmesis

Answer

Necroptosis

Question 9

Which of the following factors does NOT facilitate non-union of a fracture?

Accepted Answer

Hematoma formation

Answer

Periosteal injuries

Answer

Absence of nerve supply

Answer

Chronic infection

Question 10

What is the major mineral component of bone?

Accepted Answer

Hydroxyapatite

Answer

Calcite

Answer

Calcium oxide

Answer

Calcium carbonate

Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics — MCQs

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