Basic Science in Orthopaedics Practice Questions

Q: What is the latent period in distraction osteogenesis?

5-7 days. **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. 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).

Q: Bone resorption is enhanced by which of the following?

PGE2. **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.

Q: Which anatomical structure is considered a dynamic stabilizer of the shoulder joint?

Rotator cuff. **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.

Q: Molten-wax appearance is seen in which of the following conditions?

Melorheostosis. **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.

Q: Epiphyseal enlargement is seen in which condition?

All of the above. **Explanation:** Epiphyseal enlargement (widening of the ends of long bones) is a common radiological and clinical finding in several pediatric orthopedic conditions. The underlying mechanism usually involves either **metabolic derangement** of the growth plate or **chronic hyperemia** (increased blood flow) to the epiphysis. * **Rickets:** This is the most classic cause. Failure of mineralization of the osteoid leads to an accumulation of hypertrophic chondrocytes at the growth plate. This results in the characteristic "cupping, splaying, and fraying" of the metaphysis and clinical enlargement of joints (e.g., Rachitic rosary, widened wrists). * **Hemophilia:** Recurrent hemarthrosis (bleeding into the joint) causes chronic synovial inflammation and hyperemia. This increased blood supply stimulates the adjacent epiphysis to overgrow, leading to a "ballooned" appearance of the epiphysis (e.g., Jordan’s sign in the knee). * **Septic Arthritis:** Similar to hemophilia, the intense inflammatory response and associated hyperemia in the joint can stimulate the growth plate, leading to accelerated maturation and enlargement of the epiphysis. **High-Yield Clinical Pearls for NEET-PG:** * **Differential Diagnosis for Enlarged Epiphysis:** Juvenile Rheumatoid Arthritis (JRA), Hemophilia, Rickets, and Tuberculosis of the joint. * **Trevor’s Disease:** Also known as *Dysplasia Epiphysealis Hemimelica*, it is a rare developmental disorder characterized by asymmetric overgrowth of the epiphysis. * **Kohlmann’s Sign:** Radiological widening of the epiphysis specifically seen in Hemophilia. * **Metaphyseal Blanch Sign:** Seen in Slipped Capital Femoral Epiphysis (SCFE), not to be confused with epiphyseal enlargement.

Question 1

What is the latent period in distraction osteogenesis?

Accepted Answer

5-7 days

Answer

4-6 weeks

Answer

6-8 months

Answer

4 months

Question 2

Bone resorption is enhanced by which of the following?

Accepted Answer

PGE2

Answer

PGD2

Answer

PDF2

Answer

PGI2

Question 3

Which anatomical structure is considered a dynamic stabilizer of the shoulder joint?

Accepted Answer

Rotator cuff

Answer

Glenoid labrum

Answer

Coracohumeral ligament

Answer

Glenohumeral ligament

Question 4

Molten-wax appearance is seen in which of the following conditions?

Accepted Answer

Melorheostosis

Answer

Osteoporosis

Answer

Osteopoikilosis

Answer

Osteogenesis imperfecta

Question 5

Epiphyseal enlargement is seen in which condition?

Accepted Answer

All of the above

Answer

Rickets

Answer

Hemophilia

Answer

Septic arthritis

Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics — MCQs

On this page

Practice by Chapter

Want unlimited practice?