Basic Science in Orthopaedics Practice Questions

Q: What type of primary healing is described?

Both contact and gap healing. **Explanation:** Bone healing is broadly classified into **Primary (Direct)** and **Secondary (Indirect)** healing. Primary healing occurs when there is absolute stability (no motion at the fracture site), typically achieved through rigid internal fixation like compression plating. **Primary healing consists of two distinct mechanisms:** 1. **Contact Healing:** Occurs when the gap between bone ends is **less than 0.01 mm** and interfragmentary strain is less than 2%. Under these conditions, "cutting cones" (osteoclasts followed by osteoblasts) can cross the fracture line directly to create new haversian systems without any precursor callus. 2. **Gap Healing:** Occurs when the gap is **between 0.01 mm and 1 mm**. Here, the space is first filled by lamellar bone oriented perpendicular to the long axis, which is later remodeled into longitudinal haversian systems. Since both mechanisms occur under conditions of absolute stability and result in bone union without the formation of an external callus, the correct answer is **Both contact and gap healing.** **Why other options are incorrect:** * **Options A & B:** These are components of primary healing, but neither occurs in isolation during a clinical fracture repair; they often coexist depending on the precision of the reduction. * **Option D:** This describes secondary healing, which involves callus formation and occurs under conditions of relative stability (e.g., casting, intramedullary nailing). **High-Yield NEET-PG Pearls:** * **Absolute Stability:** Leads to Primary Healing (No Callus). * **Relative Stability:** Leads to Secondary Healing (Callus formation). * **Cutting Cones:** The functional unit of primary bone remodeling. * **Strain Theory (Perren):** Bone formation requires <2% strain; Primary healing requires absolute stability.

Q: What is the last step in fracture healing?

Remodeling. **Explanation:** Fracture healing is a continuous biological process typically divided into four distinct histological stages. The correct answer is **Remodeling**, which represents the final and longest phase of bone repair. **1. Why Remodeling is correct:** Remodeling (Phase of Modeling) begins once the fracture has been bridged by firm bone. In this stage, the bulky clinical callus is reshaped. Osteoclasts resorb unnecessary bone (external callus), while osteoblasts lay down lamellar bone along the lines of mechanical stress (**Wolff’s Law**). This process restores the bone to its original shape and restores the medullary canal. It can take months to years to complete. **2. Why other options are incorrect:** * **A. Hematoma:** This is the **first stage** (Inflammation). It occurs within hours of injury, providing a fibrin scaffold for signaling molecules and progenitor cells. * **B. Callus formation:** This occurs in the middle stages. **Soft callus** (cartilage/fibrous tissue) is formed first, followed by **Hard callus** (woven bone), which provides initial structural stability. * **C. Consolidation:** This is the stage where the woven bone of the hard callus is transformed into mature lamellar bone. While it signifies clinical union, it precedes the final structural "fine-tuning" of remodeling. **NEET-PG High-Yield Pearls:** * **Sequence of Healing:** Hematoma → Inflammation → Soft Callus → Hard Callus → Consolidation → Remodeling. * **Primary Bone Healing:** Occurs via absolute stability (e.g., compression plating). There is **no callus formation**; healing happens via "cutting cones." * **Secondary Bone Healing:** Occurs via relative stability (e.g., intramedullary nailing or casts). It involves **callus formation**. * **Wolff’s Law:** Bone grows or remodels in response to the forces or demands placed upon it.

Q: Marie and Sainton's disease is also known as:

Cleidocranial dysostosis.. **Explanation:** **Marie and Sainton’s disease** is the eponym for **Cleidocranial Dysostosis (CCD)**. It is an autosomal dominant skeletal dysplasia caused by a mutation in the **RUNX2 gene** (located on chromosome 6), which is essential for osteoblast differentiation and intramembranous ossification. **Why Cleidocranial Dysostosis is correct:** The disease primarily affects bones formed via intramembranous ossification (skull and clavicles). Key clinical features include: * **Aplasia or hypoplasia of clavicles:** Patients can often approximate their shoulders in the midline. * **Skull abnormalities:** Delayed closure of fontanelles, presence of multiple **Wormian bones**, and frontal bossing. * **Dental anomalies:** Failure of eruption of permanent teeth and the presence of multiple **supernumerary teeth**. **Why other options are incorrect:** * **Dentinogenesis imperfecta:** A genetic disorder of tooth development resulting in discolored (opalescent) and weak teeth; it is often associated with Osteogenesis Imperfecta but is not Marie and Sainton’s disease. * **Turner’s hypoplasia:** An enamel defect in permanent teeth caused by periapical infection or trauma to the preceding deciduous tooth. * **Amelogenesis imperfecta:** A group of hereditary disorders affecting enamel formation in the absence of systemic features. **High-Yield Clinical Pearls for NEET-PG:** * **Gene:** RUNX2 (CBFA1). * **Radiology:** "Hot cross bun" appearance of the skull (due to prominent sutures) and widened symphysis pubis. * **Classic Sign:** Ability to touch shoulders together anteriorly. * **Inheritance:** Autosomal Dominant (though 1/3rd are spontaneous mutations).

Q: The Trendelenburg test is primarily performed to assess the integrity of which muscle group?

Gluteus medius. ### Explanation The **Trendelenburg test** is a clinical examination used to assess the integrity of the **hip abductor mechanism**. **Why Gluteus Medius is the Correct Answer:** The primary muscle responsible for stabilizing the pelvis during the stance phase of the gait cycle is the **Gluteus medius** (assisted by the gluteus minimus and tensor fasciae latae). When a person stands on one leg, the gluteus medius on the weight-bearing side contracts to prevent the opposite (unsupported) side of the pelvis from sagging. A positive Trendelenburg sign occurs when the pelvis drops on the unsupported side, indicating weakness or paralysis of the gluteus medius on the **standing (weight-bearing) side**. **Analysis of Incorrect Options:** * **Gluteus maximus (A):** This is the primary extensor of the hip. While crucial for climbing stairs and rising from a seated position, it does not play a primary role in lateral pelvic stabilization. * **Gluteus minimus (C):** Although it is an abductor, it is significantly weaker than the gluteus medius. While it contributes to the mechanism, the test is clinically defined by the failure of the gluteus medius. * **All of the above (D):** Incorrect because the test specifically targets the abductor group, excluding the maximus. **NEET-PG High-Yield Pearls:** 1. **Nerve Supply:** The gluteus medius and minimus are supplied by the **Superior Gluteal Nerve (L4, L5, S1)**. Injury to this nerve results in a positive Trendelenburg sign. 2. **Trendelenburg Gait:** Also known as a "lurching gait." To compensate for the pelvic drop, the patient tilts their trunk *toward* the affected side to shift the center of gravity. 3. **Causes of Positive Sign:** Polio, Superior Gluteal Nerve injury, L5 radiculopathy, Congenital Dislocation of the Hip (CDH/DDH), and ununited fractures of the femoral neck.

Q: After bone fracture, primary healing will show which of these features?

The fracture line disappears very soon radiographically.. ### Explanation **Primary Bone Healing (Direct Healing)** occurs when there is absolute stability (no movement at the fracture site) and anatomical reduction. This is typically achieved through internal fixation using compression plates and screws. **Why the correct answer is right:** In primary healing, there is no formation of an external callus. Instead, "contact healing" or "gap healing" occurs via **Haversian remodeling**. Osteoclasts form "cutting cones" that cross the fracture line, followed by osteoblasts laying down new bone. Because the bone ends are compressed and the gap is bridged directly by new bone without a precursor callus, the **fracture line disappears very soon radiographically** as it is replaced by new lamellar bone. **Analysis of Incorrect Options:** * **Option A & B:** Callus molding is a feature of **Secondary Bone Healing** (indirect healing), which occurs in the presence of micromotion (e.g., casts, intramedullary nails). In primary healing, there is **no callus formation**, so there is nothing to mold or evaluate on a radiograph. * **Option D:** The fracture line *must* disappear for union to be considered complete. If the fracture line persists indefinitely, it suggests a non-union or failure of fixation. **Clinical Pearls for NEET-PG:** * **Primary Healing:** Requires **Absolute Stability**. No callus formation. Mechanism: Cutting cones/Haversian remodeling. * **Secondary Healing:** Requires **Relative Stability**. Characterized by four stages: Inflammation, Soft Callus, Hard Callus, and Remodeling. * **Gold Standard for Primary Healing:** Compression plating. * **Radiographic Sign of Primary Union:** Gradual disappearance of the fracture line without external callus.

Q: Following nerve injury, at what rate does the injured nerve regenerate?

0.1 cm/day. **Explanation:** The correct answer is **0.1 cm/day (Option B)**. Following a peripheral nerve injury (specifically Seddon’s Axonotmesis or Sunderland’s Grade II-IV), the distal segment undergoes **Wallerian degeneration**. Once the debris is cleared, the proximal axon begins to sprout and regenerate along the preserved endoneurial tubes. In clinical practice, the standard accepted rate of axonal regeneration is approximately **1 mm per day**. Converting this to centimeters: * 1 mm = 0.1 cm * Therefore, the rate is **0.1 cm/day**. **Analysis of Incorrect Options:** * **Option A (0.001 cm/day):** This equals 0.01 mm/day, which is far too slow to be clinically significant. * **Option C (1 cm/day):** This equals 10 mm/day. This is an overestimation; while regeneration can occasionally reach 2-3 mm/day in proximal segments, 10 mm/day is physiologically impossible for human nerves. * **Option D (0.0001 cm/day):** This is an infinitesimal rate (0.001 mm/day) and does not represent biological growth. **High-Yield Clinical Pearls for NEET-PG:** 1. **Tinel’s Sign:** This is used to track regeneration. A positive Tinel’s sign (tingling on percussion) at a site distal to the injury indicates the presence of regenerating axonal sprouts. 2. **Order of Recovery:** Nerve recovery typically follows a specific sequence: **Sympathetic function → Pain → Temperature → Touch → Proprioception → Motor function.** 3. **Hoffmann-Tinel Sign:** If the distal point of tingling advances by roughly 1 mm/day, it indicates successful progression of regeneration. 4. **Factors:** Regeneration is faster in children and in proximal injuries compared to distal ones.

Q: All are true regarding bone remodeling, EXCEPT:

It involves the replacement of lamellar bone by woven bone.. **Explanation:** Bone remodeling is a lifelong physiological process where mature bone tissue is removed (resorption) and new bone tissue is formed (ossification). **1. Why Option A is the Correct Answer (The Exception):** In bone remodeling, the goal is to maintain structural integrity. Therefore, **woven bone (immature, disorganized bone) is replaced by lamellar bone (mature, organized bone)**, not the other way around. Woven bone is typically seen during rapid growth, initial fracture healing (callus), or pathological states (e.g., Paget’s disease). Remodeling converts this weak woven bone into strong, load-bearing lamellar bone. **2. Analysis of Other Options:** * **Option B:** Resorption is the first stage of the remodeling cycle (ARF: Activation-Resorption-Formation). This is carried out by **osteoclasts**, which create Howship’s lacunae. * **Option C:** Both cortical and cancellous bones undergo remodeling via **Basic Multicellular Units (BMUs)**, which consist of a coordinated team of osteoclasts (cutting cone in cortical bone) and osteoblasts (closing cone). * **Option D:** Once osteoblasts finish secreting the bone matrix (osteoid), some become trapped within the matrix and differentiate into **osteocytes**, which act as mechanosensors. **High-Yield NEET-PG Pearls:** * **Woven Bone:** Characterized by random collagen arrangement; it is always pathological in adults except during fracture healing. * **Lamellar Bone:** Characterized by parallel collagen layers; it is the hallmark of healthy mature bone. * **Wolff’s Law:** Bone remodels in response to the mechanical stresses placed upon it. * **RANKL/OPG Pathway:** The primary regulator of osteoclast differentiation and activity during remodeling.

Question 1

What is the consequence of weakness of the Vastus Medialis?

Accepted Answer

Lateral dislocation of the patella

Answer

Patellar Clunk Syndrome

Answer

Medial dislocation of the patella

Answer

Weakness in abduction at the hip joint

Question 2

What type of primary healing is described?

Accepted Answer

Both contact and gap healing

Answer

Contact healing

Answer

Gap healing

Answer

Neither contact nor gap healing

Question 3

What is the last step in fracture healing?

Accepted Answer

Remodeling

Answer

Hematoma

Answer

Callus formation

Answer

Consolidation

Question 4

Marie and Sainton's disease is also known as:

Accepted Answer

Cleidocranial dysostosis.

Answer

Dentinogenesis imperfecta.

Answer

Turners hypoplasia.

Answer

Amelogenesia imperfecta.

Question 5

The Trendelenburg test is primarily performed to assess the integrity of which muscle group?

Accepted Answer

Gluteus medius

Answer

Gluteus maximus

Answer

Gluteus minimus

Answer

All of the above

Question 6

Wolff's law states that:

Accepted Answer

If a bone is continuously subjected to a particular stress, it will adapt to become stronger to resist that loading.

Answer

Only the diaphysis allows longitudinal growth in childhood.

Answer

Any infection not showing periosteal reaction within 1 week of symptoms can be ruled out to be osteomyelitis.

Answer

Angular deformities will progress until the closure of the physis.

Question 7

After bone fracture, primary healing will show which of these features?

Accepted Answer

The fracture line disappears very soon radiographically.

Answer

Callus molding can be evaluated on the radiograph.

Answer

Cannot be seen.

Answer

The fracture line does not disappear.

Question 8

What is the difference between neuropraxia and axonotmesis?

Accepted Answer

Electromyography (EMG) finding

Answer

Sensory loss

Answer

Motor loss

Answer

All of the above

Question 9

Following nerve injury, at what rate does the injured nerve regenerate?

Accepted Answer

0.1 cm/day

Answer

0.001 cm/day

Answer

1 cm/day

Answer

0.0001 cm/day

Question 10

All are true regarding bone remodeling, EXCEPT:

Accepted Answer

It involves the replacement of lamellar bone by woven bone.

Answer

Osteoclastic activity at the resorption site.

Answer

Osteoclastic activity and osteoblastic activity are both needed for bone remodeling in cortical and cancellous bones.

Answer

Osteoblasts transform into osteocytes.

Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics — MCQs

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