Basic Science in Orthopaedics Practice Questions

Q: "Marble Bone" appearance is seen in:

Osteopetrosis. **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).

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

Down's syndrome. 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

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

Long bones. **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.

Q: What are the musculoskeletal abnormalities seen in neurofibromatosis?

All of the above. 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).

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

RANK-L inhibits osteoclasts and inhibits osteoporosis.. ### 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.

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

Renal osteodystrophy. **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 1

"Marble Bone" appearance is seen in:

Accepted Answer

Osteopetrosis

Answer

Osteomalacia

Answer

Rickets

Answer

Osteoporosis

Question 2

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

Accepted Answer

Down's syndrome

Answer

Turner's syndrome

Answer

Pseudohypoparathyroidism

Answer

Post-trauma

Question 3

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

Accepted Answer

Long bones

Answer

Skull bones

Answer

Carpals

Answer

Metacarpals

Question 4

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

Accepted Answer

Osteophyte formation

Answer

Osteoporosis

Answer

Osteopenia

Answer

Osteochondritis

Question 5

What are the musculoskeletal abnormalities seen in neurofibromatosis?

Accepted Answer

All of the above

Answer

Hypertrophy of limb

Answer

Scoliosis

Answer

Pseudoarthrosis

Question 6

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

Accepted Answer

RANK-L inhibits osteoclasts and inhibits osteoporosis.

Answer

It is secreted from osteoblasts.

Answer

It acts on the RANK receptor present on osteoclasts.

Answer

Denosumab is a monoclonal antibody that inhibits RANK-Ligand.

Question 7

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?

Accepted Answer

Periosteum

Answer

Cancellous bone

Answer

Cartilage

Answer

Compact bone

Question 8

Which one of the following definitions best fits the term enthesitis?

Accepted Answer

Inflammation at the site of tendinous or ligamentous insertion into bone

Answer

Inflammation of the periarticular membrane lining the joint capsule

Answer

Inflammation of a sac-like cavity near a joint that decreases friction

Answer

All of the above

Question 9

Wormian bones are seen in all the following conditions except?

Accepted Answer

Renal osteodystrophy

Answer

Osteogenesis imperfecta

Answer

Pyknodysostosis

Answer

Cretinism

Question 10

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

Accepted Answer

Alkaline phosphatase

Answer

Serum calcium

Answer

Serum potassium

Answer

Serum acid phosphatase

Basic Science in Orthopaedics — MCQs

Basic Science in Orthopaedics — MCQs

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