Basic Science in Orthopaedics Practice Questions

Q: Insal-Salvati index is used for evaluation of which bone?

Patella. **Explanation:** The **Insall-Salvati index** is a radiographic measurement used to assess the position of the **patella** (Option B) relative to the tibia. It is calculated on a lateral knee X-ray (ideally flexed at 30°) by dividing the length of the **patellar tendon (LT)** by the **greatest diagonal length of the patella (LP)**. * **Normal Index:** 0.8 – 1.2 * **Patella Alta (High-riding patella):** Index **> 1.2**. Associated with patellar tendon rupture or recurrent patellar subluxation. * **Patella Baja (Low-riding patella):** Index **< 0.8**. Associated with quadriceps tendon rupture, neuromuscular disorders, or post-surgical changes. **Analysis of Incorrect Options:** * **Olecranon (A):** Evaluated for fractures or bursitis, but no specific "Insall-Salvati" index applies here. * **Talus (B):** Assessed using angles like the Boehler’s angle or Gissane’s angle (primarily for the calcaneus). * **Scaphoid (D):** Evaluated for fractures or AVN (Preiser’s disease) using specific views like the "Scaphoid view" (Ulnar deviation), but not this index. **High-Yield Clinical Pearls for NEET-PG:** * **Modified Insall-Salvati Index:** Uses the length of the posterior articular surface of the patella instead of the whole bone; it is considered more accurate in cases of an elongated inferior pole (Cyrano patella). * **Other Knee Indices:** Blackburne-Peel and Caton-Deschamps indices are alternative methods to measure patellar height. * **Radiology Fact:** The lateral view at 30° flexion is crucial because it puts the patellar tendon under tension, ensuring an accurate measurement.

Q: What material is used in vertebroplasty?

Polymethyl methacrylate. **Explanation:** **Polymethyl methacrylate (PMMA)**, commonly known as "bone cement," is the standard material used in vertebroplasty and kyphoplasty. In these procedures, PMMA is injected into a fractured vertebral body (typically due to osteoporosis or malignancy) to provide immediate internal stabilization and pain relief. * **Why PMMA is correct:** PMMA is a biocompatible polymer that acts as a grout rather than a glue. It undergoes an **exothermic reaction** during polymerization, reaching high temperatures which may contribute to pain relief by destroying local nerve endings (thermal neurolysis). It provides high compressive strength, making it ideal for weight-bearing bones like the vertebrae. * **Why other options are incorrect:** Options A, B, and C (Isomethyl, Isoethyl, and Polyethyl methacrylate) are chemically distinct variants that do not possess the specific mechanical properties, handling characteristics, or long-standing clinical track record required for orthopedic bone augmentation. PMMA remains the gold standard in both arthroplasty (joint replacement) and spinal augmentation. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** Bone cement is supplied as a powder (polymer) and a liquid (monomer). The liquid contains **Methyl methacrylate** and an inhibitor (Hydroquinone). * **Radiopacity:** To make the cement visible under fluoroscopy during injection, a radio-opaque agent like **Barium sulphate** or **Zirconium dioxide** is added. * **Complications:** The most feared complication of vertebroplasty is **cement leakage**, which can lead to pulmonary embolism or spinal cord compression. * **BCIS (Bone Cement Implantation Syndrome):** Characterized by hypoxia and hypotension during cementation, often due to fat embolism or monomer toxicity.

Q: All of the following cause osteonecrosis except?

None of the above. **Explanation:** Osteonecrosis, also known as **Avascular Necrosis (AVN)**, is a condition resulting from the temporary or permanent loss of blood supply to the bone, leading to cell death and eventual collapse of the bone structure. The correct answer is **"None of the above"** because all three listed conditions (A, B, and C) are well-established causes of osteonecrosis. * **Sickle Cell Anemia:** This is a classic cause of AVN. The sickled red blood cells cause "sludging" and vaso-occlusion in the microvasculature of the bone (especially the femoral head), leading to ischemia. * **Corticosteroid Use:** Steroids are the most common non-traumatic cause of AVN. They are thought to cause hypertrophy of fat cells in the bone marrow, increasing intraosseous pressure and reducing sinusoidal blood flow. * **Disseminated Intravascular Coagulation (DIC):** DIC leads to the formation of widespread microthrombi within the systemic circulation. When these thrombi occur in the terminal vessels supplying bone, they cause infarction and subsequent necrosis. **Clinical Pearls for NEET-PG:** * **Most Common Site:** The **Femoral Head** is the most common site for AVN due to its retrograde blood supply (primarily the medial circumflex femoral artery). * **Most Sensitive Investigation:** **MRI** is the gold standard for early diagnosis (shows the "double line sign"). * **X-ray Finding:** The **"Crescent Sign"** (subchondral lucency) indicates impending articular collapse. * **Mnemonic for Causes (PLASTIC RAGS):** **P**ancreatitis/Pregnancy, **L**upus (SLE), **A**lcohol, **S**teroids, **T**rauma, **I**diopathic/Infection, **C**aisson disease, **R**adiation, **A**myloidosis, **G**aucher disease, **S**ickle cell anemia.

Q: What is true about neuropraxia?

Both. ### Explanation **Neuropraxia** is the mildest form of nerve injury according to Seddon’s classification. It involves a temporary physiological block of nerve conduction without any structural damage to the axon or the connective tissue sheath (epineurium, perineurium, or endoneurium). **Why Option C (Both) is Correct:** 1. **Prolongation of Conduction Velocity:** The primary pathology in neuropraxia is focal **demyelination**. Since myelin is essential for saltatory conduction, its focal loss leads to a significant slowing or complete block of the action potential across the injured segment. [1] 2. **Good Prognosis:** Because the axon remains intact and there is no Wallerian degeneration, recovery does not depend on axonal regrowth (which is slow). Once the myelin sheath is repaired (remyelination), function returns completely, usually within days to a few weeks (typically 3–6 weeks). [2] **Why other options are incorrect:** * **Option A & B** are both true statements; therefore, they are incomplete on their own. In the context of a "Both" option in NEET-PG, selecting only one would be technically incorrect. --- ### High-Yield Clinical Pearls for NEET-PG * **Seddon’s Classification:** * **Neuropraxia:** Conduction block; intact axon; fastest recovery. * **Axonotmesis:** Axon divided but sheath intact; Wallerian degeneration occurs; recovery is slow (1mm/day). * **Neurotmesis:** Complete nerve transection; requires surgical intervention; poorest prognosis. * **Clinical Example:** "Saturday Night Palsy" (radial nerve compression) is a classic example of neuropraxia. * **EMG/NCV Findings:** In neuropraxia, Nerve Conduction Velocity (NCV) shows a block at the site of injury, but stimulation *distal* to the lesion remains normal (as the distal axon is still healthy) [2]. This distinguishes it from higher grades of injury [1].

Q: Identify the clinical examination test being performed in the given image.

Thomas test. ***Thomas test*** - This image illustrates the **Thomas test**, which assesses for **hip flexion contracture** or tightness of the **iliopsoas muscle**. - The patient lies supine, and one knee is fully flexed to the chest; if the contralateral hip flexes off the table, it indicates a positive test. *Patrick test* - The **Patrick test**, also known as the **FABER (Flexion, Abduction, External Rotation) test**, is performed to evaluate for hip or sacroiliac joint pathology. - It involves flexing, abducting, and externally rotating the hip, then applying downward pressure on the flexed knee and contralateral anterior superior iliac spine (ASIS). *Hoover test* - The **Hoover test** is used to detect **malingering** or non-organic weakness in a patient's lower extremity. - The examiner places hands under both heels while the patient is supine and asks them to raise one leg; if no downward pressure is felt on the contralateral heel, the test is positive for malingering. *McMurray test* - The **McMurray test** is a diagnostic test for **meniscal tears** in the knee. - It involves flexing and extending the knee with applied varus/valgus stress and rotation to elicit a click or pain indicating a tear.

Q: In a fracture of shaft of longbone, the component which contributes least in fracture healing is:

Endosteum. ***Endosteum*** - The **endosteum** is a thin vascular membrane that lines the inner surface of the bony tissue forming the medullary cavity of long bones. - While it has osteogenic potential, its contribution to callus formation and overall fracture healing is **less significant** compared to the richly vascularized periosteum and the surrounding musculature. *Blood vessels* - **Blood vessels** are crucial for delivering essential nutrients, oxygen, and cells (like **osteoblasts** and **osteoclasts**) to the fracture site, which are fundamental for callus formation and bone remodeling. - Their disruption can significantly impair healing, making them a **major contributor** to the process. *Periosteum* - The **periosteum** is a dense, fibrous membrane covering the outer surface of bones, except at articular surfaces, and is rich in **osteogenic cells** and blood vessels. - It plays a **dominant role** in forming the external callus, especially in long bone fractures, due to its **cambial layer** containing progenitor cells. *Matrix* - The **bone matrix** (both organic and inorganic components) is the framework upon which new bone is laid down during fracture healing. - While it provides structural support, the matrix itself does not actively *contribute* to the cellular processes of healing; rather, it is the **product of these processes** involving cells like osteoblasts.

Q: The X-ray shows plating done for a fracture. How does this fracture heal?

Primary healing. **Primary healing** - **Plating of a fracture** aims to achieve **absolute stability** at the fracture site, which facilitates primary bone healing. - In primary healing, there is **direct bone formation** across the fracture gap without the formation of a significant callus. *Secondary healing* - Secondary healing involves the formation of a **callus** (fibrous tissue, cartilage, and immature bone) to bridge the fracture gap. - This type of healing occurs in situations with **relative stability** and some micromotion at the fracture site, such as with casting or intramedullary nailing. *Tertiary healing* - **Tertiary healing** is not a recognized term in the context of fracture healing. - Bone healing typically involves either primary or secondary mechanisms depending on the stability achieved. *Distraction histiogenesis* - **Distraction histiogenesis** is the process by which new bone is formed between bone surfaces that are gradually pulled apart using an external fixator (**distraction osteogenesis**). - This is used in procedures like **limb lengthening** and is distinct from the direct healing of a fracture fixed with a plate.

Q: If the outer sheath and nerve fibres are intact and the inner axon is damaged, it is known as

Axonotmesis. ***Axonotmesis*** - This type of nerve injury involves damage to the **axon** itself, while the connective tissue layers (**endoneurium, perineurium, epineurium**) remain intact. - While the axon is disrupted, the preservation of the nerve's outer sheath allows for potential, albeit slow, **regeneration** of the axon. *Axonapraxia* - This term is not a standard classification of nerve injury. The correct term for a transient block in nerve conduction is **neurapraxia**. *Neurotmesis* - **Neurotmesis** is the most severe type of nerve injury, involving complete severance of the **axon** and all supporting **connective tissue sheaths**. - This type of injury requires **surgical repair** for any chance of functional recovery. *Neurapraxia* - **Neurapraxia** is the mildest form of nerve injury, characterized by a temporary **conduction block** without axonal damage. - Recovery is typically complete within days to weeks, as the **myelin sheath** may be temporarily dysfunctional but the axon remains intact.

Question 1

Which nerve injury has the best prognosis?

Accepted Answer

Radial nerve

Answer

Ulnar nerve

Answer

Median nerve

Answer

Axillary nerve

Question 2

Which of the following signs is used to assess nerve regeneration?

Accepted Answer

Nerve regeneration

Answer

Severity of nerve damage

Answer

Type of nerve injury

Answer

Location of nerve injury

Question 3

Insal-Salvati index is used for evaluation of which bone?

Accepted Answer

Patella

Answer

Olecranon

Answer

Talus

Answer

Scaphoid

Question 4

What material is used in vertebroplasty?

Accepted Answer

Polymethyl methacrylate

Answer

Isomethyl methacrylate

Answer

Isoethyl methacrylate

Answer

Polyethyl methacrylate

Question 5

All of the following cause osteonecrosis except?

Accepted Answer

None of the above

Answer

Sickle cell anemia

Answer

Corticosteroid use

Answer

Disseminated intravascular coagulation (DIC)

Question 6

What is true about neuropraxia?

Accepted Answer

Both

Answer

Prolongation of conduction velocity

Answer

Good prognosis

Answer

None

Question 7

Identify the clinical examination test being performed in the given image.

Accepted Answer

Thomas test

Answer

Patrick test

Answer

Hoover test

Answer

McMurray test

Question 8

In a fracture of shaft of longbone, the component which contributes least in fracture healing is:

Accepted Answer

Endosteum

Answer

Blood vessels

Answer

Periosteum

Answer

Matrix

Question 9

The X-ray shows plating done for a fracture. How does this fracture heal?

Accepted Answer

Primary healing

Answer

Secondary healing

Answer

Tertiary healing

Answer

Distraction histiogenesis

Question 10

If the outer sheath and nerve fibres are intact and the inner axon is damaged, it is known as

Accepted Answer

Axonotmesis

Answer

Axonapraxia

Answer

Neurotmesis

Answer

Neurapraxia

Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics — MCQs

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