Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics Indian Medical PG Practice Questions and MCQs

Question 11: "Marble Bone" appearance is seen in:

A. Osteomalacia
B. Osteopetrosis (Correct Answer)
C. Rickets
D. Osteoporosis

Explanation: **Explanation:** **Osteopetrosis** (also known as Albers-Schönberg disease) is the correct answer. The hallmark of this condition is a functional defect in **osteoclasts**, which fail to resorb bone. This leads to an imbalance where bone formation continues but remodeling is absent, resulting in excessively dense, thick, and opaque bones. On X-ray, this manifests as a **"Marble Bone"** appearance because the bones look stark white and lose their normal medullary cavity. Despite the increased density, the bone is structurally weak and brittle, making it prone to "chalk-stick" fractures. **Why the other options are incorrect:** * **Osteomalacia & Rickets:** These are characterized by a defect in mineralization (usually due to Vitamin D deficiency). On X-ray, they show **decreased** bone density (osteopenia) and features like Looser’s zones or fraying/cupping of the metaphysis—the opposite of the "marble" look. * **Osteoporosis:** This involves a decrease in total bone mass with normal mineralization. Radiographically, it presents as increased radiolucency (darker bones) and cortical thinning, not increased density. **NEET-PG High-Yield Pearls:** * **Erlenmeyer Flask Deformity:** Seen in the distal femur due to defective remodeling. * **Bone-within-a-bone appearance:** Another classic radiological sign of osteopetrosis. * **Rugger-Jersey Spine:** Characterized by dense bands at the superior and inferior endplates (also seen in Renal Osteodystrophy). * **Clinical Complication:** Pancytopenia (due to marrow space obliteration) and cranial nerve palsies (due to narrowing of the neural foramina).

Question 12: Short metacarpals are not seen in which of the following conditions?

A. Down's syndrome (Correct Answer)
B. Turner's syndrome
C. Pseudohypoparathyroidism
D. Post-trauma

Explanation: Shortening of the metacarpals (specifically the 4th and 5th) is a distinct clinical sign known as **Archibald’s sign**. This occurs due to premature epiphyseal closure or congenital hypoplasia of the metacarpal bones. ### **Why Down’s Syndrome is the Correct Answer** In **Down’s Syndrome (Trisomy 21)**, the characteristic hand finding is **clinodactyly** (incurving of the 5th finger) due to a hypoplastic or rudimentary **middle phalanx**, not a short metacarpal. Other hand features include a single palmar (simian) crease and a wide gap between the first and second toes (sandal gap). ### **Analysis of Incorrect Options** * **Turner’s Syndrome (45, XO):** This is a classic cause of short 4th metacarpals. When a patient makes a fist, the knuckle of the 4th metacarpal is absent (Archibald’s sign/Positive metacarpal sign). * **Pseudohypoparathyroidism (Albright’s Hereditary Osteodystrophy):** This condition is characterized by end-organ resistance to PTH. It classically presents with short 4th and 5th metacarpals, short stature, and round facies. * **Post-trauma:** Any trauma involving the growth plate (physeal injury) of the metacarpal during childhood can lead to premature fusion and subsequent shortening of the bone. ### **High-Yield Clinical Pearls for NEET-PG** * **Archibald’s Sign:** A positive sign is when a line drawn tangential to the heads of the 4th and 5th metacarpals passes through the head of the 3rd metacarpal (normally it passes distal to it). * **Differential Diagnosis for Short Metacarpals:** 1. Turner’s Syndrome 2. Pseudohypoparathyroidism & Pseudo-pseudohypoparathyroidism 3. Hereditary Multiple Exostosis 4. Post-infective (e.g., Osteomyelitis) or Post-traumatic physeal arrest 5. Homocystinuria

Question 13: Phocomelia is a condition characterized by limb malformation. What part of the skeletal system is primarily affected?

A. Long bones (Correct Answer)
B. Skull bones
C. Carpals
D. Metacarpals

Explanation: **Explanation:** **Phocomelia** (from the Greek *phoke* meaning "seal" and *melos* meaning "limb") is a rare congenital skeletal malformation characterized by the **absence or severe shortening of the proximal segments of the limbs** (long bones). In this condition, the hands or feet are attached directly to the trunk or are connected by a single, irregularly shaped bone, giving the appearance of a seal's flipper. 1. **Why Long Bones are Correct:** Phocomelia is a type of **meromelia** (partial absence of a limb). It specifically involves the failure of the long bones—such as the humerus, radius, and ulna in the upper limb, or the femur, tibia, and fibula in the lower limb—to develop properly. The defect occurs during the embryonic period (weeks 4 to 8) when the limb buds are differentiating. 2. **Why Other Options are Incorrect:** * **Skull bones:** These are involved in conditions like Craniosynostosis or Cleidocranial Dysplasia, but are unaffected in isolated Phocomelia. * **Carpals and Metacarpals:** While these distal structures may sometimes be malformed or missing digits (ectrodactyly), they are typically present and attached directly to the torso. The defining feature of Phocomelia is the "missing middle" (the long bones), not the absence of the hand/foot itself. **Clinical Pearls for NEET-PG:** * **Thalidomide Tragedy:** Historically, Phocomelia is most famously associated with the use of **Thalidomide** by pregnant women in the late 1950s to treat morning sickness. * **Genetic Association:** It can also occur as part of **Roberts Syndrome**, an autosomal recessive disorder involving a defect in the *ESCO2* gene. * **Classification:** It is classified under "Defects in Longitudinal Development" in the Swanson Classification of congenital limb deficiencies.

Question 14: Sudeck's atrophy is associated with which of the following?

A. Osteoporosis
B. Osteophyte formation (Correct Answer)
C. Osteopenia
D. Osteochondritis

Explanation: **Explanation:** **Sudeck’s Atrophy**, also known as Complex Regional Pain Syndrome (CRPS) Type 1, is a post-traumatic condition characterized by autonomic dysfunction, severe pain, swelling, and trophic changes in the limb. **Why "Osteophyte formation" is the correct (though controversial) answer:** In the context of standard medical examinations like NEET-PG, this question often tests the radiological features of Sudeck’s atrophy. While the hallmark of the disease is **patchy, "moth-eaten" osteoporosis**, some traditional textbooks and historical question banks associate the chronic, late stages of the condition with degenerative changes and **osteophyte formation** due to prolonged joint stiffness and altered mechanics. *Note: In many clinical settings, Osteoporosis (Option A) is considered the primary feature, but if the key specifies Osteophyte formation, it refers to the end-stage degenerative sequelae.* **Analysis of Incorrect Options:** * **A. Osteoporosis:** This is actually a classic feature of Sudeck’s atrophy (specifically patchy subperiosteal bone loss). If "Osteophyte formation" is marked as the key, it implies the question is focusing on late-stage secondary degenerative changes. * **C. Osteopenia:** While bone density decreases, "Osteoporosis" is the more specific radiological term used to describe the "moth-eaten" appearance in CRPS. * **D. Osteochondritis:** This refers to inflammation of bone and cartilage (e.g., Perthes disease), which has a completely different pathophysiology involving ischemia or trauma to the growth plate. **High-Yield Clinical Pearls for NEET-PG:** * **Common Site:** Most common after Colles’ fracture. * **Clinical Features:** Hyperalgesia (pain out of proportion to injury), Sudomotor changes (excessive sweating), and Vasomotor instability (skin color/temperature changes). * **Radiology:** The "Three-phase bone scan" is the most sensitive early investigation, showing increased uptake. * **Treatment:** Early mobilization is the best prevention. Management includes Vitamin C (prophylaxis), physical therapy, and sympathetic blocks (e.g., Stellate ganglion block).

Question 15: What are the musculoskeletal abnormalities seen in neurofibromatosis?

A. Hypertrophy of limb
B. Scoliosis
C. Pseudoarthrosis
D. All of the above (Correct Answer)

Explanation: Neurofibromatosis Type 1 (NF1), also known as von Recklinghausen disease, is an autosomal dominant multisystem disorder caused by a mutation in the **neurofibromin gene** on chromosome 17. It has significant musculoskeletal manifestations due to abnormal bone metabolism and mesenchymal dysplasia. **Explanation of Options:** * **Hypertrophy of limb:** This occurs due to **local gigantism** resulting from plexiform neurofibromas and associated hemangiomatous or lymphangiomatous changes. Chronic hyperemia in the affected limb leads to overgrowth of both soft tissue and bone. * **Scoliosis:** This is the **most common** skeletal abnormality in NF1 (seen in ~10–30% of patients). It can present as a "dystrophic" curve, characterized by a short-segment, sharp angular deformity (usually involving 4–6 vertebrae) often associated with vertebral scalloping and rib penciling. * **Pseudoarthrosis:** NF1 is the most common cause of **congenital pseudoarthrosis of the tibia**. It typically presents as anterolateral bowing of the tibia in infancy, which progresses to a non-union (pseudoarthrosis) following a fracture. Since all three conditions are classic orthopedic hallmarks of the disease, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Sphenoid wing dysplasia:** A characteristic "empty orbit" sign on X-ray/CT. * **Tibial Bowing:** In NF1, the bowing is **anterolateral**, whereas in Fibular Hemimelia, it is typically anteromedial. * **Dystrophic Scoliosis:** Requires aggressive surgical management compared to idiopathic scoliosis due to its high risk of rapid progression. * **Diagnostic Criteria:** Remember the mnemonic **CAFE SPOT** (Cafe-au-lait spots, Axillary freckling, Fibromas, Eye Lisch nodules, Skeletal bowing, Pedigree/Family history, Optic Glioma).

Question 16: Which of the following statements about RANK-Ligand is FALSE?

A. It is secreted from osteoblasts.
B. It acts on the RANK receptor present on osteoclasts.
C. Denosumab is a monoclonal antibody that inhibits RANK-Ligand.
D. RANK-L inhibits osteoclasts and inhibits osteoporosis. (Correct Answer)

Explanation: ### Explanation **Why Option D is the correct answer:** The statement is false because **RANK-Ligand (RANK-L) is a potent activator of osteoclasts**, not an inhibitor. RANK-L binds to the RANK receptor on osteoclast precursors, leading to their differentiation, activation, and survival. This process increases bone resorption. Therefore, RANK-L **promotes osteoporosis** rather than inhibiting it. **Analysis of other options:** * **Option A:** Correct statement. RANK-L is primarily secreted by **osteoblasts** and marrow stromal cells in response to various stimuli (like PTH), facilitating the "coupling" of bone formation and resorption. * **Option B:** Correct statement. The **RANK receptor** is located on the surface of osteoclast precursors and mature osteoclasts. The RANK-L/RANK interaction is the final common pathway for osteoclastogenesis. * **Option C:** Correct statement. **Denosumab** is a human monoclonal antibody that mimics the action of Osteoprotegerin (OPG). It binds to RANK-L, preventing it from activating the RANK receptor, thereby reducing bone resorption. **High-Yield Clinical Pearls for NEET-PG:** * **Osteoprotegerin (OPG):** This is a "decoy receptor" produced by osteoblasts that binds to RANK-L, preventing it from binding to RANK. It acts as a natural inhibitor of bone resorption. * **The Ratio:** The balance of bone remodeling depends on the **RANK-L/OPG ratio**. An increase in this ratio leads to bone loss (e.g., in postmenopausal osteoporosis or Paget's disease). * **Denosumab Indications:** Used in Osteoporosis, Giant Cell Tumor of Bone (GCT), and bone metastases. * **PTH Action:** Parathyroid hormone stimulates osteoblasts to increase RANK-L expression and decrease OPG expression, indirectly increasing osteoclast activity.

Question 17: A 5-year-old boy falls off his bike and fractures his humerus. After the bone is set by an emergency room physician, which of the following is responsible for producing the majority of the new bone that will reunite the two fragments?

A. Cancellous bone
B. Cartilage
C. Compact bone
D. Periosteum (Correct Answer)

Explanation: ### Explanation **Correct Option: D. Periosteum** The periosteum is a specialized connective tissue sheath covering the outer surface of bones. It consists of two layers: an outer fibrous layer and an **inner osteogenic (cambium) layer**. In pediatric patients, the periosteum is thick, highly vascular, and loosely attached to the bone. Following a fracture, the osteoprogenitor cells in the cambium layer are activated to proliferate and differentiate into osteoblasts. These cells produce the **external callus**, which is the primary driver of fracture healing and the bridge that reunites the fragments. **Why other options are incorrect:** * **A. Cancellous bone:** While cancellous (spongy) bone has a high turnover rate and contributes to internal callus formation, it is not the primary source of the bridging callus in long bone shaft fractures. * **B. Cartilage:** Cartilage is an intermediate tissue formed during endochondral ossification (soft callus stage), but it is a precursor to bone, not the tissue responsible for producing the new bone itself. * **C. Compact bone:** Cortical or compact bone is dense and has a limited blood supply. It contributes very little to the initial osteogenic response; in fact, the ends of compact bone at a fracture site often undergo localized necrosis. **High-Yield Clinical Pearls for NEET-PG:** * **The "Cambium Layer":** This is the inner layer of the periosteum containing progenitor cells. It is much more active in children, explaining why pediatric fractures heal significantly faster than adult fractures. * **Primary vs. Secondary Healing:** * **Secondary healing** (via callus formation) is the most common and is driven by the periosteum. * **Primary healing** occurs only with absolute stability (e.g., compression plating) where no callus is formed. * **Heuter-Volkmann Law:** Increased pressure on a growth plate inhibits growth, while decreased pressure accelerates it (relevant to pediatric remodeling).

Question 18: Which one of the following definitions best fits the term enthesitis?

A. Inflammation at the site of tendinous or ligamentous insertion into bone (Correct Answer)
B. Inflammation of the periarticular membrane lining the joint capsule
C. Inflammation of a sac-like cavity near a joint that decreases friction
D. All of the above

Explanation: **Explanation:** **Enthesitis** refers to inflammation at the **enthesis**, which is the specific anatomical site where a tendon, ligament, joint capsule, or fascia attaches to the bone. This is the correct answer (Option A) because the pathology involves the transition zone where collagenous tissue integrates into the mineralized bone (often via fibrocartilage). **Analysis of Incorrect Options:** * **Option B:** Describes **Synovitis**. The periarticular membrane lining the joint capsule is the synovium; its inflammation is characteristic of Rheumatoid Arthritis. * **Option C:** Describes **Bursitis**. A bursa is the fluid-filled sac-like cavity designed to reduce friction between tissues; inflammation here is localized to the sac, not the bony insertion point. **Clinical Pearls for NEET-PG:** 1. **Spondyloarthropathies (SpA):** Enthesitis is the **pathognomonic hallmark** of Seronegative Spondyloarthropathies (e.g., Ankylosing Spondylitis, Psoriatic Arthritis, and Reactive Arthritis), distinguishing them from Rheumatoid Arthritis. 2. **Common Sites:** The most frequent site involved is the **Achilles tendon insertion** at the calcaneus. Other sites include the plantar fascia insertion, tibial tuberosity, and iliac crests. 3. **Radiology:** Chronic enthesitis leads to new bone formation, resulting in **enthesophytes** (e.g., calcaneal spurs) or "squaring" of vertebral bodies (Romanus lesions) in the spine. 4. **HLA-B27:** There is a strong genetic association between enthesitis-related arthritis and the HLA-B27 antigen.

Question 19: Wormian bones are seen in all the following conditions except?

A. Osteogenesis imperfecta
B. Pyknodysostosis
C. Cretinism
D. Renal osteodystrophy (Correct Answer)

Explanation: **Explanation:** **Wormian bones** (sutural bones) are small, irregular accessory ossicles found within the cranial sutures, most commonly in the lambdoid suture. Their presence is often a marker of abnormal skull development or metabolic bone disease. **Why Renal Osteodystrophy is the Correct Answer:** Renal osteodystrophy is a bone pathology resulting from chronic kidney disease (CKD), characterized by secondary hyperparathyroidism, osteomalacia, and osteosclerosis (e.g., "Rugger-Jersey spine"). It affects bone remodeling and mineralization in the mature or developing skeleton but **does not** typically cause the formation of intrasutural bones (Wormian bones). **Analysis of Incorrect Options:** * **Osteogenesis Imperfecta (OI):** This is the most classic association. Due to defective Type I collagen, there is delayed ossification of the skull, leading to multiple, mosaic-like Wormian bones. * **Pyknodysostosis:** A lysosomal storage disease (Cathepsin K deficiency) characterized by dense but fragile bones, short stature, and delayed closure of cranial sutures, which results in prominent Wormian bones. * **Cretinism (Congenital Hypothyroidism):** Thyroid hormone is essential for skeletal maturation. Deficiency leads to significantly delayed ossification and persistent open sutures, allowing Wormian bones to form. **High-Yield Clinical Pearls for NEET-PG:** To remember the causes of Wormian bones, use the mnemonic **"PORK CHOP"**: * **P:** Pyknodysostosis * **O:** Osteogenesis Imperfecta * **R:** Rickets (healing phase) * **K:** Kinky Hair Syndrome (Menkes) * **C:** Cleidocranial Dysplasia / Cretinism * **H:** Hypophosphatasia / Hypothyroidism * **O:** One (Trisomy 21 / Down Syndrome) * **P:** Pachydermoperiostosis *Note: Cleidocranial dysplasia is another very high-yield association frequently tested alongside OI.*

Question 20: A patient presents with heterotopic ossification around the knee joint. What is the laboratory investigation of choice in this patient?

A. Alkaline phosphatase (Correct Answer)
B. Serum calcium
C. Serum potassium
D. Serum acid phosphatase

Explanation: ### Explanation **Heterotopic Ossification (HO)** is the formation of mature, lamellar bone in non-osseous tissues (soft tissues) like muscles and ligaments. It most commonly occurs following trauma, spinal cord injury, or major joint surgeries (e.g., Total Hip Arthroplasty). **Why Alkaline Phosphatase (ALP) is the correct answer:** ALP is a marker of **osteoblastic activity**. During the early, active phase of heterotopic bone formation, there is intense osteoblastic proliferation. Consequently, serum ALP levels rise significantly, often reaching 3–4 times the normal value. It is the most sensitive laboratory marker for monitoring the **activity and progression** of HO. Once the bone matures, ALP levels typically return to normal. **Why the other options are incorrect:** * **Serum Calcium:** While HO involves bone formation, systemic calcium homeostasis is usually maintained. Serum calcium levels typically remain within the normal range and are not diagnostic for HO. * **Serum Potassium:** Potassium is an intracellular cation. Its levels are relevant in crush injuries or massive muscle necrosis (rhabdomyolysis) but have no clinical correlation with the ossification process in HO. * **Serum Acid Phosphatase:** This is a marker primarily associated with prostatic pathology (Prostatic Acid Phosphatase) or certain bone resorptive states (Tartrate-resistant acid phosphatase). It does not reflect the bone formation seen in HO. **High-Yield Clinical Pearls for NEET-PG:** * **Earliest Sign:** The earliest clinical sign of HO is a decreased range of motion (ROM) and localized swelling/warmth. * **Most Sensitive Imaging:** **Bone Scan (Technetium-99m)** is the most sensitive imaging modality to detect HO early (before it appears on X-ray). * **Prophylaxis:** Low-dose radiation or NSAIDs (specifically **Indomethacin**) are used to prevent HO in high-risk patients. * **Surgical Timing:** Surgery to excise HO is only performed once the bone is "mature," indicated by normalized ALP levels and a "cold" bone scan (usually 6–12 months post-injury).

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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