Menu

1. General Principles & Basic Science MCQs

Practice Set 509 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 10161

Topic: Biomechanics & Biomaterials

A 65-year-old female presents with acute, intense pain, swelling, and warmth in her left knee. Aspiration yields cloudy synovial fluid. Microscopic analysis of the fluid reveals rhomboid-shaped crystals that exhibit weak positive birefringence under polarized light. What is the primary constituent of these crystals?

. Monosodium urate
. Basic calcium phosphate
. Calcium pyrophosphate dihydrate
. Hydroxyapatite
. Cholesterol

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Rhomboid-shaped, weakly positively birefringent crystals are pathognomonic for pseudogout. The crystals are composed of calcium pyrophosphate dihydrate (CPPD).

Question 10162

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs demonstrate an eccentric, lytic, epiphyseal-metaphyseal lesion in the proximal tibia extending to the subchondral bone. Histopathology reveals abundant multinucleated giant cells distributed uniformly among mononuclear stromal cells. The neoplastic mononuclear cells in this tumor typically express high levels of which molecule to drive local bone destruction?

. Osteoprotegerin (OPG)
. Parathyroid hormone-related protein (PTHrP)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

In a Giant Cell Tumor of bone, the neoplastic cells are the mononuclear stromal cells, which express high levels of RANKL. This recruits and stimulates normal host osteoclast precursors to form the characteristic multinucleated giant cells, leading to aggressive bone resorption.

Question 10163

Topic: 1. General Principles & Basic Science

A 16-year-old male with severe Hemophilia A presents with chronic swelling, reduced range of motion, and joint destruction of the right knee. What is the primary pathophysiological mechanism that leads to progressive cartilage destruction in hemophilic arthropathy?

. Autoimmune targeting of Type II collagen by circulating antibodies
. Direct viral infection of chondrocytes secondary to blood transfusions
. Uric acid crystal deposition in the joint space
. Iron-induced synovial proliferation and direct chondrocyte apoptosis
. Bacterial superinfection leading to rapid enzymatic degradation of cartilage

Correct Answer & Explanation

. Iron-induced synovial proliferation and direct chondrocyte apoptosis

Explanation

In hemophilic arthropathy, recurrent hemarthroses lead to the accumulation of hemosiderin (iron) within the synovium. This causes marked synovial hypertrophy, chronic inflammation, and direct toxicity/apoptosis of articular chondrocytes.

Question 10164

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with an unusual ability to appose his shoulders anteriorly across his chest. Examination reveals an open anterior fontanelle, delayed eruption of his secondary dentition, and a somewhat prominent forehead. Radiographs show hypoplasia of the clavicles. Which essential transcription factor for osteoblast differentiation is mutated in this condition?

. SOX9
. RUNX2 (CBFA1)
. NFATc1
. Osterix (Sp7)
. C-fos

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

The patient has Cleidocranial Dysplasia, characterized by hypoplastic/absent clavicles, delayed suture closure, and dental anomalies. It is an autosomal dominant condition caused by a mutation in RUNX2 (CBFA1), a master transcription factor essential for osteoblast differentiation.

Question 10165

Topic: 1. General Principles & Basic Science
A 10-year-old boy with severe Hemophilia A presents to the emergency department with an acute, warm, and severely swollen right knee. What is the absolute most appropriate initial step in management for this acute hemarthrosis?
. Immediate diagnostic and therapeutic arthrocentesis
. Factor VIII replacement to 100% activity followed by rest and ice
. Urgent arthroscopic synovectomy to prevent cartilage damage
. Intra-articular corticosteroid injection
. Factor IX replacement to 50% activity

Correct Answer & Explanation

. Factor VIII replacement to 100% activity followed by rest and ice

Explanation

The priority in treating an acute hemarthrosis in a hemophilic patient is immediate clotting factor replacement (Factor VIII for Hemophilia A). Arthrocentesis is rarely indicated and must never be performed before adequate factor replacement.

Question 10166

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with mechanical knee pain. Imaging reveals an eccentric, purely lytic epiphyseal lesion of the distal femur extending to the subchondral bone. Biopsy confirms numerous multinucleated giant cells. Which of the following targeted systemic therapies is indicated for unresectable forms of this disease?

. Imatinib
. Denosumab
. Rituximab
. Bevacizumab
. Infliximab

Correct Answer & Explanation

. Denosumab

Explanation

Giant Cell Tumor (GCT) of bone is driven by RANKL-secreting stromal cells that recruit osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is highly effective for unresectable or recurrent GCTs.

Question 10167

Topic: 1. General Principles & Basic Science

A 40-year-old male develops suspected Complex Regional Pain Syndrome (CRPS) following a crush injury to the foot.

If a triple-phase technetium-99m bone scan is performed to aid diagnosis, what is the classic imaging finding?

. Decreased uptake evenly across all three phases
. Increased uptake strictly limited to the initial blood-flow phase
. Diffuse, increased periarticular uptake in the delayed phase (Phase 3)
. A distinct focal cold spot in the affected region
. Symmetrical uptake identical to the unaffected, contralateral limb

Correct Answer & Explanation

. Diffuse, increased periarticular uptake in the delayed phase (Phase 3)

Explanation

A classic triple-phase bone scan in CRPS (Algodystrophy) shows diffusely increased periarticular uptake on the delayed images (Phase 3). This finding has high sensitivity and specificity for the condition.

Question 10168

Topic: Biology, Genetics & Bone Healing

A 9-year-old child presents with a waddling gait, bilateral knee pain, and short stature. Radiographs demonstrate small, irregular, fragmented epiphyses and a characteristic "double-layered" patella. A mutation in which of the following genes is most highly associated with this specific classic presentation?

. COL1A1
. COMP
. FGFR3
. RUNX2
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) commonly presents with delayed, irregular ossification of the epiphyses. The finding of a 'double-layered' patella on a lateral radiograph is virtually pathognomonic and is classically associated with mutations in the COMP gene.

Question 10169

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman presents with a lytic lesion in the distal femur. Biopsy reveals a benign, locally aggressive tumor characterized by mononuclear stromal cells and numerous multinucleated giant cells. Which of the following describes the cellular target of denosumab in the medical management of this tumor?

. It binds to RANK on the surface of the multinucleated giant cells
. It binds to RANKL expressed by the neoplastic mononuclear stromal cells
. It inhibits the IDH1 enzyme within the stromal cells
. It blocks the FGFR3 receptor on osteoblasts
. It inhibits the USP6 ubiquitin-specific protease

Correct Answer & Explanation

. It binds to RANKL expressed by the neoplastic mononuclear stromal cells

Explanation

In Giant Cell Tumor of bone, the mononuclear stromal cells are the true neoplastic cells and heavily express RANKL. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK on the osteoclast-like giant cells, thereby reducing bone resorption.

Question 10170

Topic: Biology, Genetics & Bone Healing

A newborn is noted to have a large anterior fontanelle, midface hypoplasia, and excessive mobility of the shoulders, allowing them to be opposed anteriorly. A mutation in the RUNX2 (CBFA1) gene is suspected. What is the primary role of the protein encoded by this gene?

. It is an essential structural component of articular cartilage
. It is a master transcription factor for osteoblast differentiation
. It acts as an inhibitor of osteoclastogenesis
. It is a transmembrane sulfate transporter
. It forms the cross-links in mature type I collagen

Correct Answer & Explanation

. It is a master transcription factor for osteoblast differentiation

Explanation

Cleidocranial dysplasia is caused by a mutation in RUNX2 (also known as CBFA1). RUNX2 is a crucial transcription factor required for the commitment and differentiation of mesenchymal stem cells into the osteoblast lineage.

Question 10171

Topic: 1. General Principles & Basic Science
A 14-year-old male with severe Hemophilia A presents with chronic knee swelling and restricted range of motion. What is the primary pathophysiologic mechanism driving joint destruction in hemophilic arthropathy?
. Direct bacterial invasion of the joint space leading to cartilage lysis
. Autoimmune attack against type II collagen triggered by factor VIII replacement
. Uric acid crystal deposition in the synovium
. Iron accumulation from recurrent hemarthrosis causing synovial hypertrophy and chondrocyte apoptosis
. Ischemic necrosis of the subchondral bone due to microvascular thrombosis

Correct Answer & Explanation

. Iron accumulation from recurrent hemarthrosis causing synovial hypertrophy and chondrocyte apoptosis

Explanation

Recurrent hemarthrosis in hemophilia leads to the accumulation of iron (hemosiderin) in the joint. This triggers severe synovial hypertrophy, inflammation, and direct toxic effects on chondrocytes, culminating in cartilage apoptosis and joint destruction.

Question 10172

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with severe osteoporosis is started on a nitrogen-containing bisphosphonate (alendronate). Which of the following best describes the molecular mechanism of action of this medication in preventing bone resorption?

. Inhibition of osteoclast ruffled border formation by blocking carbonic anhydrase II
. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway
. Direct binding to RANKL, preventing osteoclast activation
. Formation of toxic ATP analogs that induce osteoclast apoptosis
. Inhibition of cathepsin K, preventing collagen matrix degradation

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate, zoledronate) act by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (such as Ras, Rho, and Rac), which are essential for osteoclast function, ruffled border formation, and cell survival. Non-nitrogenous bisphosphonates (e.g., etidronate) work by forming toxic ATP analogs. Denosumab binds to RANKL. Odanacatib inhibits cathepsin K.

Question 10173

Topic: 1. General Principles & Basic Science

Articular cartilage is composed of structurally distinct zones. Which zone is characterized by the highest concentration of proteoglycans and contains collagen fibrils oriented perpendicular to the articular surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. The type II collagen fibers in this zone are oriented perpendicular to the joint surface to resist compressive forces. The superficial zone has the highest water content, parallel collagen fibers to resist shear stress, and the lowest proteoglycan content.

Question 10174

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to minimize perioperative blood loss. Which of the following describes its primary mechanism of action?
. Direct inhibition of factor Xa in the coagulation cascade
. Reversible competitive blockade of lysine-binding sites on plasminogen
. Activation of antithrombin III leading to thrombin inhibition
. Irreversible inhibition of cyclooxygenase in platelets
. Direct inhibition of active plasmin circulating in the plasma

Correct Answer & Explanation

. Reversible competitive blockade of lysine-binding sites on plasminogen

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic by reversibly binding to the lysine-binding sites on plasminogen. This prevents plasminogen from binding to fibrin, thereby inhibiting its activation to plasmin and subsequent fibrinolysis.

Question 10175

Topic: Biology, Genetics & Bone Healing

A 35-year-old male presents with a large lytic lesion in his distal femur extending into the epiphysis. Biopsy confirms a Giant Cell Tumor of bone. He is treated with Denosumab. What is the specific target of this monoclonal antibody?

. RANK receptor on osteoclasts
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Vascular Endothelial Growth Factor (VEGF)
. Colony Stimulating Factor 1 (CSF-1)
. Tumor Necrosis Factor alpha (TNF-alpha)

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding RANKL, it prevents it from interacting with the RANK receptor on the surface of osteoclasts and their precursors, thereby inhibiting osteoclastogenesis and function. It is a highly effective targeted therapy for Giant Cell Tumor of bone, which is driven by neoplastic stromal cells secreting excessive RANKL.

Question 10176

Topic: Biology, Genetics & Bone Healing

A patient with severe malnutrition presents with bleeding gums, petechiae, and poor wound healing. Radiographs show periosteal elevation and a dense zone of provisional calcification. This condition is caused by a deficiency in a cofactor required for which of the following steps in collagen synthesis?

. Gamma-carboxylation of glutamate residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Cleavage of procollagen C-terminal propeptides
. Hydroxylation of proline and lysine residues in procollagen
. Glycosylation of hydroxylysine residues in the Golgi apparatus

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues in procollagen

Explanation

The patient has scurvy (Vitamin C deficiency). Ascorbic acid is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase, which are responsible for the hydroxylation of proline and lysine residues on the preprocollagen chains in the rough endoplasmic reticulum. This step is critical for the stable triple-helix formation of collagen.

Question 10177

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with bowing of the lower extremities, waddling gait, and short stature. Laboratory tests reveal normal calcium, very low serum phosphate, normal PTH, normal 25(OH) vitamin D, and appropriately normal but functionally low 1,25(OH)2 vitamin D. What is the most likely pathophysiological mechanism of his condition?

. Mutation in the PHEX gene leading to elevated FGF-23 levels
. Inactivating mutation in the 1-alpha-hydroxylase enzyme
. Defect in the intestinal Vitamin D receptor (VDR)
. Autoimmune destruction of the parathyroid glands
. Activating mutation of the calcium-sensing receptor (CaSR)

Correct Answer & Explanation

. Mutation in the PHEX gene leading to elevated FGF-23 levels

Explanation

The clinical and laboratory profile is classic for X-linked hypophosphatemic rickets (XLH). This is caused by a mutation in the PHEX gene, which leads to unregulated overproduction of Fibroblast Growth Factor 23 (FGF-23) by osteocytes. FGF-23 inhibits renal phosphate reabsorption in the proximal tubule and inhibits 1-alpha-hydroxylase, preventing the expected rise in 1,25(OH)2 vitamin D in response to hypophosphatemia.

Question 10178

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, using highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) alters its mechanical properties compared to conventional polyethylene. Which of the following represents the most accurate mechanical trade-off of cross-linking?
. Increases ultimate tensile strength and decreases oxidation resistance
. Decreases volumetric wear but reduces fatigue resistance and fracture toughness
. Decreases adhesive wear but significantly increases abrasive wear
. Increases resistance to third-body wear while increasing creep
. Enhances the elastic modulus but decreases yield strength

Correct Answer & Explanation

. Decreases volumetric wear but reduces fatigue resistance and fracture toughness

Explanation

Highly cross-linked polyethylene significantly decreases the volumetric wear rate (both adhesive and abrasive), reducing osteolysis. However, the cross-linking process and subsequent thermal treatments (remelting/annealing) alter its mechanical properties, resulting in decreased ultimate tensile strength, decreased yield strength, decreased fatigue resistance, and reduced fracture toughness compared to conventional UHMWPE.

Question 10179

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, the mechanical environment dictates the type of tissue that forms in a fracture gap. What range of strain promotes secondary bone healing with callus formation?

. Less than 2%
. 2% to 10%
. 10% to 15%
. 15% to 30%
. Greater than 30%

Correct Answer & Explanation

. 2% to 10%

Explanation

Perren's strain theory posits that tissue cannot form if the strain (deformation) exceeds the yield strain of that tissue. Primary bone healing requires absolute stability with strain < 2%. Secondary bone healing (callus formation via endochondral ossification) occurs with relative stability, corresponding to a strain environment between 2% and 10%. Granulation tissue tolerates up to 100% strain, while cartilage tolerates about 10%.

Question 10180

Topic: Biomechanics & Biomaterials

An orthopedic surgeon utilizes a stainless steel screw to secure a titanium alloy plate. This mixing of dissimilar metals can lead to galvanic corrosion. In this specific construct, which of the following best describes the electrochemical process?

. Titanium acts as the anode and undergoes preferential corrosion
. Stainless steel acts as the anode and undergoes preferential corrosion
. Both metals undergo simultaneous anodic degradation due to crevice corrosion
. Titanium acts as the cathode and dissolves into the surrounding tissue
. Stainless steel acts as the cathode and becomes protected from fretting

Correct Answer & Explanation

. Stainless steel acts as the anode and undergoes preferential corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic solution (body fluid). The less noble (more reactive) metal acts as the anode and corrodes, while the more noble metal acts as the cathode and is protected. Titanium is more noble than stainless steel; therefore, stainless steel acts as the anode and undergoes accelerated corrosion.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page