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1. General Principles & Basic Science MCQs

Practice Set 406 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 8101

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, purely lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a giant cell tumor of bone. Denosumab is considered for medical management to facilitate surgery. What is the primary cellular target of this medication?

. RANK receptor on the multinucleated giant cells
. RANKL produced by the neoplastic mononuclear stromal cells
. Osteoprotegerin (OPG) produced by osteoblasts
. Vascular Endothelial Growth Factor (VEGF)
. Tumor Necrosis Factor-alpha (TNF-alpha)

Correct Answer & Explanation

. RANKL produced by the neoplastic mononuclear stromal cells

Explanation

Giant cell tumor of bone is composed of neoplastic mononuclear stromal cells and reactive multinucleated giant cells. The mononuclear cells express high levels of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which recruits and activates the osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds to RANKL, inhibiting this process.

Question 8102

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is FDA-approved specifically for use in acute, open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for the treatment of acute, open tibial shaft fractures when used in conjunction with an intramedullary nail. RhBMP-7 (osteogenic protein-1) was previously approved under a Humanitarian Device Exemption for recalcitrant long bone nonunions but not specifically for acute open tibial fractures.

Question 8103

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman presents with persistent knee pain. Radiographs reveal an eccentric, purely lytic lesion in the proximal tibial epiphysis that extends to the subchondral bone. A core needle biopsy demonstrates a proliferation of mononuclear stromal cells interspersed with numerous multinucleated giant cells. For cases of this disease that are deemed unresectable or recurrent, medical therapy is often employed. What is the primary mechanism of action of the most commonly used targeted biologic agent for this condition?

. Inhibits vascular endothelial growth factor (VEGF)
. Inhibits the mammalian target of rapamycin (mTOR) pathway
. Induces apoptosis via stabilization of p53
. Binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Acts as a broad-spectrum tyrosine kinase inhibitor

Correct Answer & Explanation

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

Explanation

The patient has a Giant Cell Tumor (GCT) of bone, which typically presents as an eccentric, lytic epiphyseal lesion in a skeletally mature patient. The neoplastic cells in GCT are the mononuclear stromal cells, which express high levels of RANKL. This recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) that cause the characteristic osteolysis. Denosumab, a fully human monoclonal antibody, specifically binds to RANKL, preventing RANK activation. This halts osteoclastogenesis and bone destruction, and is highly effective in treating recurrent or unresectable GCT of bone.

Question 8104

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a lytic, eccentrically located lesion in the distal radius extending into the subchondral bone. Biopsy demonstrates mononuclear cells intermixed with numerous large, multinucleated osteoclast-like giant cells. The patient is prescribed a targeted medical therapy for her condition. Which of the following best describes the mechanism of action of this drug?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct binding to the RANK receptor on osteoclasts
. Binding to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)
. Inhibition of matrix metalloproteinases
. Activation of the Wnt/beta-catenin pathway

Correct Answer & Explanation

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

Explanation

The clinical and histologic description is classic for a giant cell tumor of bone (GCT). The neoplastic cells are the mononuclear cells, which express high levels of RANKL. This recruits and activates reactive osteoclast-like giant cells, leading to bone destruction. Denosumab is a monoclonal antibody that targets and binds to RANKL, preventing it from binding to the RANK receptor on the surface of osteoclast precursors, thereby profoundly inhibiting osteoclast formation and function.

Question 8105

Topic: Biology, Genetics & Bone Healing

A 65-year-old man is incidentally found to have a substantially elevated serum alkaline phosphatase level on routine laboratory work. His serum calcium, phosphorus, and parathyroid hormone levels are strictly normal. Radiographs of his pelvis show thickened trabeculae, cortical thickening, and overall bone enlargement. A defect in which of the following cell types is considered the primary initiating event in the pathogenesis of this condition?

. Osteoblast
. Osteocyte
. Osteoclast
. Chondrocyte
. Fibroblast

Correct Answer & Explanation

. Osteoclast

Explanation

The patient's clinical and radiographic profile is classic for Paget's disease of bone. The disease is characterized by an isolated elevation of alkaline phosphatase with normal calcium and phosphate profiles. The primary pathologic cellular defect in Paget's disease lies in the osteoclasts, which are greatly increased in number, abnormally large, and possess numerous nuclei. This leads to a primary intense osteolytic phase, which is subsequently followed by chaotic, excessive, and structurally unsound osteoblastic bone formation.

Question 8106

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with progressive pain and swelling in her left knee. Radiographs reveal an eccentric, completely lytic lesion in the proximal tibia extending to the subchondral bone without a sclerotic margin. Biopsy shows multinucleated giant cells in a background of mononuclear stromal cells. If targeted pharmacological therapy is considered to reduce tumor burden, what is the mechanism of action of the most appropriate agent?

. Inhibition of vascular endothelial growth factor (VEGF)
. Binding to the RANK receptor on osteoclast precursors
. Binding to RANK ligand (RANKL) expressed by neoplastic stromal cells
. Inhibition of cyclooxygenase-2 (COX-2) enzyme activity
. Selective estrogen receptor modulation

Correct Answer & Explanation

. Binding to RANK ligand (RANKL) expressed by neoplastic stromal cells

Explanation

The clinical and histologic picture describes a Giant Cell Tumor (GCT) of bone. In GCT, the mononuclear stromal cells are the true neoplastic cells, and they express high levels of RANKL. Denosumab is a monoclonal antibody that targets and binds to RANKL, preventing it from interacting with RANK on the surface of osteoclast precursors. This inhibits osteoclast-mediated bone resorption and effectively reduces tumor size and progression.

Question 8107

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a lytic lesion in the distal femur that extends to the subchondral bone. Biopsy reveals multinucleated giant cells in a background of mononuclear stromal cells. She is treated with denosumab preoperatively. What is the mechanism of action of this medication?

. Direct induction of apoptosis in the multinucleated giant cells
. Inhibition of the RANK ligand (RANKL) secreted by the mononuclear stromal cells
. Binding to the osteoprotegerin (OPG) receptor on osteoclasts
. Inhibition of farnesyl pyrophosphate synthase
. Direct cross-linking of DNA leading to cell death

Correct Answer & Explanation

. Inhibition of the RANK ligand (RANKL) secreted by the mononuclear stromal cells

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express RANKL, which recruits and activates normal multinucleated giant cells (osteoclast-like cells) expressing RANK. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to RANK, thus inhibiting osteoclast-mediated bone destruction and inducing ossification of the tumor.

Question 8108

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced the rate of wear. What is the primary trade-off or disadvantage associated with increasing the cross-linking dose in ultra-high-molecular-weight polyethylene (UHMWPE)?
. Increased adhesive wear
. Decreased ultimate tensile strength and fatigue resistance
. Decreased oxidative stability
. Increased third-body wear
. Increased generation of submicron particles per volume of wear

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue resistance

Explanation

Increasing the radiation dose to cross-link UHMWPE decreases its ultimate tensile strength, yield strength, and fatigue resistance (fracture toughness). To mitigate oxidative degradation, it is often remelted or annealed, or doped with Vitamin E. However, the primary mechanical trade-off of high cross-linking is reduced fatigue strength, making it more susceptible to fracture under high-stress conditions or when used in thin liners.

Question 8109

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Following the binding of BMP to its cell surface receptor, which intracellular signaling molecules are primarily phosphorylated to translocate to the nucleus and regulate gene expression?

. Wnt and beta-catenin
. JAK and STAT
. Smad 1, 5, and 8
. MAP kinase
. Runx2 and Osterix

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs (part of the TGF-beta superfamily) bind to serine/threonine kinase receptors. Upon activation, they primarily phosphorylate receptor-regulated Smads (Smad 1, 5, and 8). These phosphorylated Smads then form a complex with the common-partner Smad (Smad 4) and translocate to the nucleus to regulate the transcription of osteogenic genes like Runx2.

Question 8110

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy is evaluated for multiple fractures with minimal trauma. Radiographs demonstrate diffusely increased bone density, a 'bone-within-bone' appearance in the spine, and Erlenmeyer flask deformities of the distal femora. Which of the following best describes the underlying cellular defect in this condition?

. Defective synthesis of type I collagen by osteoblasts
. Absence of a ruffled border on osteoclasts due to a defect in carbonic anhydrase II
. Increased osteoclast apoptosis due to bisphosphonate exposure
. Overexpression of fibroblast growth factor receptor 3 (FGFR3)
. Mutation in the COMP gene

Correct Answer & Explanation

. Absence of a ruffled border on osteoclasts due to a defect in carbonic anhydrase II

Explanation

The patient has osteopetrosis, characterized by dense, brittle bones due to defective osteoclastic bone resorption. A common form involves a mutation in the carbonic anhydrase II gene or the TCIRG1 gene (encoding a vacuolar proton pump), which prevents the creation of an acidic environment in the Howship lacuna, leading to the absence of the osteoclast's ruffled border and failure to resorb bone.

Question 8111

Topic: Infection, Pharmacology & VTE

In periprosthetic joint infections, Staphylococcus epidermidis is a frequent pathogen due to its ability to form a biofilm. Which of the following components is primarily responsible for the structural integrity of the biofilm matrix, shielding the bacteria from host immunity and antibiotics?

. Teichoic acid
. Peptidoglycan
. Polysaccharide intercellular adhesin (PIA)
. Protein A
. Lipopolysaccharide

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Polysaccharide intercellular adhesin (PIA), synthesized by products of the icaADBC operon, is the primary component of the extracellular polymeric substance (EPS) or slime layer in Staphylococcus epidermidis biofilms. This matrix allows the bacteria to adhere to the implant and provides a formidable barrier against antibiotics and host immune cells.

Question 8112

Topic: Biomechanics & Biomaterials

When a continuous, constant load is applied to a ligament over time, the ligament will gradually elongate. This viscoelastic property is best described as:

. Stress relaxation
. Creep
. Hysteresis
. Isotropic behavior
. Fatigue failure

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent increase in strain (deformation or elongation) of a viscoelastic material when subjected to a constant stress (load). Stress relaxation is the time-dependent decrease in stress when the material is held at a constant strain. Hysteresis refers to the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 8113

Topic: 1. General Principles & Basic Science

A 55-year-old woman with chronic kidney disease presents with diffuse bone pain and muscle weakness. Radiographs reveal Looser zones in the femoral neck and pubic rami. Bone biopsy is performed for histomorphometry. Which of the following parameters is most likely to be increased in this patient?

. Mineralization lag time
. Cortical thickness
. Trabecular bone volume
. Osteoclast number
. Bone mineral density

Correct Answer & Explanation

. Mineralization lag time

Explanation

The patient has osteomalacia secondary to chronic kidney disease (renal osteodystrophy), characterized by defective mineralization of the osteoid matrix. Histomorphometric analysis of osteomalacia classically shows increased osteoid thickness, increased osteoid volume, and a prolonged mineralization lag time due to the failure of hydroxyapatite crystals to deposit properly into the osteoid.

Question 8114

Topic: Surgical Anatomy & Approaches

During an extensile anterior approach to the humerus for fracture fixation, the surgeon must be cautious to identify and protect a nerve that pierces the lateral intermuscular septum to enter the anterior compartment of the arm. This nerve innervates which of the following muscles?

. Brachioradialis
. Biceps brachii
. Coracobrachialis
. Triceps brachii
. Deltoid

Correct Answer & Explanation

. Brachioradialis

Explanation

The radial nerve pierces the lateral intermuscular septum approximately 10 cm proximal to the lateral epicondyle, passing from the posterior to the anterior compartment of the arm. In the anterior compartment, it innervates the brachioradialis and the extensor carpi radialis longus before crossing the elbow joint into the forearm.

Question 8115

Topic: Biomechanics & Biomaterials

The compressive stiffness of normal articular cartilage is primarily dependent on which of the following structural interactions?

. Covalent cross-linking of type II collagen fibrils
. Repulsive forces between negatively charged glycosaminoglycan chains and restricted water flow
. Lubricin binding to superficial zone chondrocytes
. Hyaluronic acid degradation by matrix metalloproteinases
. Interaction between type I collagen and decorin

Correct Answer & Explanation

. Repulsive forces between negatively charged glycosaminoglycan chains and restricted water flow

Explanation

The compressive stiffness of articular cartilage is mainly due to the swelling pressure exerted by the highly negatively charged glycosaminoglycan (GAG) chains (part of the aggrecan molecule). These fixed negative charges repel each other and attract cations (and water via osmosis). The collagen network restricts the swelling, and the resistance to fluid flow through this matrix provides the viscoelastic compressive strength.

Question 8116

Topic: 1. General Principles & Basic Science
A 45-year-old diabetic patient is undergoing treatment for a chronic lower extremity ulcer. Which of the following phases of wound healing is primarily characterized by the proliferation of fibroblasts and the synthesis of type III collagen?
. Hemostasis phase
. Inflammatory phase
. Proliferative phase
. Remodeling phase
. Maturation phase

Correct Answer & Explanation

. Proliferative phase

Explanation

The proliferative phase of wound healing occurs days to weeks after injury and is characterized by angiogenesis, fibroplasia, and epithelialization. Fibroblasts migrate into the wound and secrete a provisional matrix composed largely of type III collagen and fibronectin. Later, during the remodeling and maturation phase, type III collagen is gradually replaced by the stronger type I collagen.

Question 8117

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a giant cell tumor of bone. She is treated with denosumab to downstage the tumor prior to curettage. What is the primary mechanism of action of denosumab in the treatment of this lesion?

. Direct induction of apoptosis in neoplastic stromal cells
. Inhibition of the RANKL-RANK interaction, decreasing osteoclast-like giant cell formation
. Activation of osteoprotegerin (OPG) secretion
. Inhibition of vascular endothelial growth factor (VEGF)
. Direct alkylation of DNA in rapidly dividing cells

Correct Answer & Explanation

. Inhibition of the RANKL-RANK interaction, decreasing osteoclast-like giant cell formation

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that overexpress RANKL. This RANKL recruits and stimulates the formation of reactive osteoclast-like giant cells, which cause bone destruction. Denosumab is a monoclonal antibody that binds directly to RANKL, preventing its interaction with RANK on the osteoclast precursors, thereby halting osteolysis and allowing bone to ossify.

Question 8118

Topic: Biology, Genetics & Bone Healing

A 15-year-old boy presents with knee pain. Radiographs reveal a well-circumscribed, eccentrically located lytic lesion in the proximal tibial epiphysis with a thin sclerotic rim. Which of the following histological findings is most characteristic of this lesion?

. Mononuclear cells with scattered multinucleated giant cells and a 'chicken wire' pattern of calcification
. Spindle cells arranged in a 'herringbone' pattern
. Small blue cells forming Homer-Wright rosettes
. Woven bone trabeculae rimmed by prominent osteoblasts
. Anaplastic cells producing delicate lace-like osteoid

Correct Answer & Explanation

. Mononuclear cells with scattered multinucleated giant cells and a 'chicken wire' pattern of calcification

Explanation

The patient's presentation (epiphyseal lesion in a skeletally immature individual) points to a chondroblastoma. Histologically, it is characterized by sheets of mononuclear cells (chondroblasts), scattered osteoclast-like giant cells, and fine, pericellular 'chicken wire' calcifications. Herringbone pattern denotes fibrosarcoma. Prominent osteoblasts rimming woven bone describes an osteoblastoma. Lace-like osteoid is diagnostic of osteosarcoma.

Question 8119

Topic: Biology, Genetics & Bone Healing

A 28-year-old woman presents with persistent, aching knee pain. Radiographs reveal an eccentric, lytic epiphyseal-metaphyseal lesion of the distal femur. Biopsy reveals uniform mononuclear cells interspersed with numerous multinucleated giant cells. Which of the following describes the mechanism of action of the targeted medical therapy most commonly used for this condition?

. Inhibition of vascular endothelial growth factor (VEGF)
. Monoclonal antibody against receptor activator of nuclear factor kappa-B ligand (RANKL)
. Tyrosine kinase inhibition of c-KIT
. Selective estrogen receptor modulation
. Inhibition of matrix metalloproteinases

Correct Answer & Explanation

. Monoclonal antibody against receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Giant cell tumor (GCT) of bone is a locally aggressive benign tumor. The neoplastic mononuclear cells express RANKL, which recruits and activates osteoclast-like multinucleated giant cells, leading to bone destruction. Denosumab, a monoclonal antibody against RANKL, is utilized in advanced, recurrent, or unresectable GCTs to inhibit giant cell formation and function, resulting in tumor consolidation and ossification.

Question 8120

Topic: Biology, Genetics & Bone Healing
A 65-year-old man presents with diffuse bone pain and fatigue. Laboratory investigations reveal normocytic anemia, hypercalcemia, and an elevated serum creatinine. Serum protein electrophoresis shows a monoclonal IgG spike. A plain radiograph skeletal survey demonstrates multiple 'punched-out' lytic lesions in the skull and pelvis. Which of the following advanced imaging modalities is considered the most sensitive for assessing the true extent of skeletal involvement in this condition?
. Technetium-99m methylene diphosphonate (Tc-99m MDP) bone scan
. Whole-body low-dose computed tomography (WBLDCT) or MRI
. Gallium-67 citrate scan
. Dual-energy X-ray absorptiometry (DEXA)
. Indium-111 labeled white blood cell scan

Correct Answer & Explanation

. Whole-body low-dose computed tomography (WBLDCT) or MRI

Explanation

Multiple myeloma lesions are purely osteolytic and inhibit osteoblast function. Thus, a traditional Tc-99m MDP bone scan (which relies on osteoblastic activity) is frequently falsely negative. Whole-body low-dose CT (WBLDCT), whole-body MRI, or PET-CT are the modalities of choice for accurately staging and assessing skeletal involvement in multiple myeloma.

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