Menu

1. General Principles & Basic Science MCQs

Practice Set 411 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 8201

Topic: Biology, Genetics & Bone Healing

A 35-year-old patient sustained a closed tibia fracture treated with closed reduction and casting. Which of the following best describes the primary source of cells responsible for the formation of the external soft callus during secondary bone healing?

. Endosteum
. Periosteum
. Bone marrow
. Circulating mesenchymal stem cells
. Hematoma

Correct Answer & Explanation

. Periosteum

Explanation

Secondary bone healing relies heavily on the formation of a callus. The external soft callus is primarily formed by chondrocytes and osteoblasts derived from the inner cambium layer of the periosteum. The periosteum is critical for robust callus formation, especially in long bone shaft fractures. The endosteum contributes primarily to the internal callus and remodeling phase, while the hematoma acts as a scaffold and source of signaling molecules but is not the primary source of the structural cells.

Question 8202

Topic: Infection, Pharmacology & VTE
Rivaroxaban is an oral anticoagulant commonly used for venous thromboembolism prophylaxis following total joint arthroplasty. By which of the following mechanisms does it primarily exert its antithrombotic effect?
. Direct inhibition of Thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Direct inhibition of Factor IXa
. Inhibition of Vitamin K epoxide reductase
. Activation of Antithrombin III

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that exert their antithrombotic effects by directly inhibiting Factor Xa, the first step in the common pathway of the coagulation cascade. Dabigatran directly inhibits Thrombin (Factor IIa). Warfarin inhibits Vitamin K epoxide reductase. Heparin and low molecular weight heparins (like enoxaparin) work by binding to and activating Antithrombin III, which in turn inactivates Thrombin and Factor Xa.

Question 8203

Topic: Infection, Pharmacology & VTE

A 60-year-old man with chronic osteomyelitis of the femur requires targeted antibiotic therapy. Intraoperative cultures grow methicillin-resistant Staphylococcus aureus (MRSA). Which of the following antibiotics is a bactericidal agent that disrupts the bacterial cell membrane by causing rapid depolarization, and requires monitoring for creatine kinase (CK) elevation due to the risk of myopathy?

. Vancomycin
. Linezolid
. Daptomycin
. Tigecycline
. Ceftaroline

Correct Answer & Explanation

. Daptomycin

Explanation

Daptomycin is a cyclic lipopeptide antibiotic that is bactericidal against gram-positive organisms, including MRSA. Its unique mechanism of action involves binding to the bacterial cell membrane and causing rapid depolarization, which leads to cell death. A known adverse effect of daptomycin is skeletal muscle toxicity (myopathy), and patients taking this medication must have their creatine kinase (CK) levels monitored weekly. Vancomycin inhibits cell wall synthesis, Linezolid is bacteriostatic and inhibits protein synthesis (50S subunit), and Ceftaroline is a 5th-generation cephalosporin that binds to PBP2a.

Question 8204

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, expansile lytic lesion in the proximal tibia that extends to the subchondral bone. A biopsy is performed, revealing multinucleated giant cells interspersed within a background of mononuclear stromal cells. If pharmacological treatment is considered to downstage the tumor prior to surgery, what is the primary molecular target of the indicated medication?

. Vascular endothelial growth factor (VEGF)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Tyrosine kinase
. Interleukin-6 (IL-6)
. Mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

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

Explanation

The clinical and histological findings are classic for a Giant Cell Tumor (GCT) of bone. The neoplastic cells in GCT are the mononuclear stromal cells, which express high levels of RANKL. This RANKL expression recruits and activates osteoclast-like multinucleated giant cells, leading to extensive bone resorption. Denosumab, a monoclonal antibody that binds and inhibits RANKL, is utilized in advanced or difficult-to-resect GCTs to inhibit bone resorption, resulting in tumor consolidation and downstaging.

Question 8205

Topic: 1. General Principles & Basic Science

Which of the following zones of articular cartilage contains the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the articular surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Articular cartilage is divided into distinct zones. The deep (radial) zone is characterized by having the highest concentration of proteoglycans, the lowest concentration of water, and thick type II collagen fibers oriented perpendicular to the joint surface to resist compressive forces. The superficial zone has the highest water content, the lowest proteoglycan concentration, and collagen fibers oriented parallel to the surface to resist shear forces.

Question 8206

Topic: Biology, Genetics & Bone Healing

A 45-year-old man undergoes closed reduction and intramedullary nailing for a closed, transverse midshaft tibial fracture. Which of the following accurately describes the predominant mechanism of bone healing expected in this scenario?

. Primary bone healing via Haversian remodeling and cutting cones
. Intramembranous ossification with direct woven bone formation without a cartilage intermediate
. Secondary bone healing primarily through endochondral ossification
. Creeping substitution characterized by osteoclastic resorption and osteoblastic deposition
. Distraction osteogenesis relying on continuous tension forces

Correct Answer & Explanation

. Secondary bone healing primarily through endochondral ossification

Explanation

Intramedullary nailing of a diaphyseal long bone fracture provides relative stability (as opposed to absolute stability achieved with rigid plate fixation). Relative stability promotes secondary bone healing, which involves callus formation. This process predominantly occurs via endochondral ossification, where a cartilaginous intermediate is formed and subsequently replaced by bone. Primary bone healing (via cutting cones) occurs only under conditions of absolute stability and anatomic reduction without gap formation.

Question 8207

Topic: Biomechanics & Biomaterials
A 65-year-old active man is undergoing total hip arthroplasty. The surgeon opts to use a highly cross-linked polyethylene (HXLPE) liner. Which of the following best describes the mechanical trade-off when comparing HXLPE to conventional ultra-high-molecular-weight polyethylene (UHMWPE)?
. Decreased volumetric wear but reduced fracture toughness and ultimate tensile strength
. Increased volumetric wear but enhanced fatigue strength and modulus of elasticity
. Decreased oxidation potential with a concurrent increase in yield strength
. Increased resistance to adhesive wear with improved elongation at break
. Decreased abrasive wear but increased risk of catastrophic delamination due to higher crystallinity

Correct Answer & Explanation

. Decreased volumetric wear but reduced fracture toughness and ultimate tensile strength

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured by exposing conventional UHMWPE to radiation, which breaks polymer chains and allows them to recombine (cross-link). This process significantly decreases volumetric wear, thereby drastically reducing the incidence of particle-induced osteolysis. However, the cross-linking process alters the mechanical properties of the material, resulting in decreased fracture toughness, reduced ultimate tensile strength, and reduced ductility (elongation to failure).

Question 8208

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with worsening right knee pain. Radiographs reveal a large, eccentric, purely lytic, epiphyseal-metaphyseal lesion in the proximal tibia extending to the subchondral bone. Histology shows numerous multinucleated giant cells in a background of mononuclear spindle cells. The patient is deemed an unresectable surgical candidate and denosumab therapy is initiated. What is the precise mechanism of action of this medication?

. Inhibits VEGF to decrease tumor angiogenesis
. Inhibits the tyrosine kinase domain of c-kit
. Cross-links DNA, leading to cellular apoptosis
. Binds to RANKL, preventing osteoclast and giant cell activation
. Antagonizes estrogen receptors on the neoplastic stromal cells

Correct Answer & Explanation

. Binds to RANKL, preventing osteoclast and giant cell activation

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express high levels of RANKL. This recruits and activates reactive multinucleated giant cells (osteoclast-like cells) responsible for extensive bone resorption. Denosumab is a fully human monoclonal antibody that binds directly to RANKL, interrupting this pathway, leading to a dramatic reduction in giant cells, tumor necrosis, and subsequent ossification.

Question 8209

Topic: Infection, Pharmacology & VTE

A 9-year-old boy presents with mild shoulder pain after throwing a baseball. Radiographs reveal a centrally located, completely lytic, expansile lesion in the proximal humerus metaphysis that does not breach the cortex. A subtle 'fallen leaf' sign is noted. What biochemical substance is typically found in high concentrations within the fluid of this lesion?

. Lactic acid
. Prostaglandins
. Histamine
. Vasoactive intestinal peptide
. Alkaline phosphatase

Correct Answer & Explanation

. Prostaglandins

Explanation

The classic presentation of a central, purely lytic lesion in the proximal humerus of a child with a 'fallen leaf' or 'fallen fragment' sign (representing a piece of fractured cortex resting at the bottom of the cyst) is highly characteristic of a unicameral (simple) bone cyst. The cyst fluid is clear and serous, and it has been shown to contain high concentrations of prostaglandins (specifically PGE2), interleukins, and other bone-resorbing factors.

Question 8210

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty to reduce the incidence of wear and subsequent osteolysis. What is the primary negative biomechanical consequence of increasing the radiation dose used for cross-linking the ultra-high-molecular-weight polyethylene (UHMWPE)?
. Decreased yield strength
. Decreased fatigue resistance and fracture toughness
. Increased adhesive wear
. Increased volumetric wear
. Increased oxidation potential

Correct Answer & Explanation

. Decreased fatigue resistance and fracture toughness

Explanation

While high levels of radiation used to cross-link polyethylene dramatically decrease wear rates, they negatively impact the material's mechanical properties. Specifically, high radiation doses lead to decreased ultimate tensile strength, decreased fatigue resistance, and decreased fracture toughness. This makes the material more susceptible to fracture, which is why highly cross-linked polyethylene use in total knee arthroplasty (which has higher contact stresses and varied kinematics) required careful optimization.

Question 8211

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with severe osteoporosis is started on denosumab therapy. This medication primarily exerts its mechanism of action by directly inhibiting which of the following cellular interactions?

. Binding of RANKL to RANK on osteoblast precursors
. Binding of RANKL to RANK on osteoclast precursors
. Binding of OPG to RANKL
. Binding of PTH to osteoblasts
. Secretion of cathepsin K by mature osteoclasts

Correct Answer & Explanation

. Binding of RANKL to RANK on osteoclast precursors

Explanation

Denosumab is a human monoclonal antibody that specifically targets and binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, denosumab prevents it from interacting with RANK on the surface of osteoclasts and osteoclast precursors. This inhibits osteoclastogenesis, osteoclast function, and survival, ultimately reducing bone resorption.

Question 8212

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with worsening knee pain. Radiographs display an eccentric, lytic epiphyseal-metaphyseal lesion of the distal femur extending to the subchondral bone. A biopsy demonstrates numerous multinucleated giant cells uniformly distributed in a background of mononuclear stromal cells. Which of the following statements is true regarding the cellular biology and treatment of this lesion?

. The giant cells are the true neoplastic component of the tumor
. The neoplastic mononuclear cells express high levels of RANK
. Treatment with denosumab targets the multinucleated giant cells directly
. The neoplastic mononuclear cells express high levels of RANKL
. The tumor typically exhibits a t(11;22) translocation

Correct Answer & Explanation

. The neoplastic mononuclear cells express high levels of RANKL

Explanation

In Giant Cell Tumor (GCT) of bone, the true neoplastic cells are the spindle-shaped mononuclear stromal cells. These neoplastic cells express high levels of RANKL, which recruits and stimulates the formation of reactive, non-neoplastic multinucleated giant cells (which express the RANK receptor). Denosumab targets the RANKL produced by the neoplastic mononuclear cells, thereby indirectly halting the action of the osteoclast-like giant cells.

Question 8213

Topic: 1. General Principles & Basic Science

Which of the following represents the earliest biochemical change observed in articular cartilage during the pathogenesis of osteoarthritis?

. Decreased water content
. Increased proteoglycan concentration
. Increased water content
. Decreased type II collagen synthesis
. Increased chondroitin sulfate to keratin sulfate ratio

Correct Answer & Explanation

. Increased water content

Explanation

The earliest biochemical change in osteoarthritis is damage and disruption to the superficial collagen network. This disruption allows the hydrophilic proteoglycan molecules to swell, leading to an overall increase in the water content of the cartilage. Subsequently, as the disease progresses, proteoglycan concentration decreases, and the water content eventually decreases in late-stage disease.

Question 8214

Topic: Surgical Anatomy & Approaches

A 28-year-old man sustains a closed midshaft humerus fracture and immediately develops a complete radial nerve palsy. At 12 weeks post-injury, he has zero motor recovery. An electromyogram (EMG) shows prominent fibrillation potentials but no motor unit action potentials. What pathophysiologic process best describes what is occurring in the nerve segment distal to the fracture site?

. Axonotmesis with intact endoneurium preventing Wallerian degeneration
. Myelin degradation by Schwann cells and macrophages with axonal preservation
. Wallerian degeneration characterized by axonal and myelin breakdown distal to the injury
. Neuropraxia with localized conduction block only
. Retrograde chromatolysis extending to the motor endplate

Correct Answer & Explanation

. Wallerian degeneration characterized by axonal and myelin breakdown distal to the injury

Explanation

Fibrillation potentials at 12 weeks signify active denervation of the muscle fibers, effectively ruling out a simple neuropraxia. In axonotmesis and neurotmesis, the axon is disrupted. Distal to the injury site, Wallerian degeneration occurs, which involves the physical breakdown and clearance of both the axon and its surrounding myelin sheath by macrophages and proliferating Schwann cells. Intact endoneurium in axonotmesis guides regeneration but does not prevent distal Wallerian degeneration.

Question 8215

Topic: Biology, Genetics & Bone Healing

A 35-year-old man undergoes open reduction and internal fixation of a diaphyseal radius fracture. The surgeon utilizes compression plating to achieve absolute stability. Assuming standard biological conditions, which of the following mechanisms best describes the primary mode of fracture healing expected?

. Endochondral ossification
. Intramembranous ossification with robust callus formation
. Haversian remodeling via cutting cones across the fracture site
. Differentiation of mesenchymal stem cells into chondrocytes
. Intermembranous ossification followed by enchondral ossification

Correct Answer & Explanation

. Haversian remodeling via cutting cones across the fracture site

Explanation

Fixation that achieves absolute stability (strain < 2%) suppresses callus formation and leads to primary (direct) bone healing. Primary bone healing occurs via direct Haversian remodeling, where osteoclasts create cutting cones that cross the fracture line, followed immediately by osteoblasts laying down new osteons. Secondary bone healing (which involves callus formation via endochondral and intramembranous ossification) occurs with relative stability constructs (e.g., intramedullary nails, external fixators).

Question 8216

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with progressive knee pain. Radiographs reveal an eccentric, purely lytic epiphyseal lesion extending to the subchondral bone of the distal femur. Histological analysis confirms the presence of uniform mononuclear cells mixed with numerous multinucleated giant cells. For unresectable or recurrent disease, systemic therapy can be utilized. Which of the following pathways is the primary target for the medication used in this clinical scenario?

. Vascular endothelial growth factor (VEGF) inhibition
. Receptor activator of nuclear factor kappa-B ligand (RANKL) inhibition
. Mammalian target of rapamycin (mTOR) inhibition
. Tyrosine kinase inhibition
. Tumor necrosis factor-alpha (TNF-a) inhibition

Correct Answer & Explanation

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

Explanation

The patient has a Giant Cell Tumor of Bone (GCTB), characterized by an eccentric, lytic epiphyseal lesion in a skeletally mature individual. The neoplastic mononuclear cells in GCTB express high levels of RANKL, which recruits and activates the reactive multinucleated osteoclast-like giant cells that cause the massive bone destruction. Denosumab is a monoclonal antibody that inhibits RANKL and is FDA-approved for the treatment of GCTB that is unresectable or where resection would result in severe morbidity.

Question 8217

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with severe knee pain and a lytic lesion in the proximal tibia extending right to the subchondral bone. Biopsy confirms a giant cell tumor of bone (GCTB). Due to the extensive size and joint proximity precluding immediate joint-salvage surgery, neoadjuvant medical therapy is planned. Which of the following accurately describes the mechanism of the most appropriate pharmacological agent?

. Inhibition of vascular endothelial growth factor (VEGF) receptors to decrease tumor angiogenesis
. Direct induction of apoptosis in the reactive multinucleated giant cells via bisphosphonate-like action
. Monoclonal antibody binding to RANKL, preventing activation of RANK on osteoclast precursors
. Inhibition of matrix metalloproteinases (MMPs) preventing subchondral cartilage degradation
. Binding to the intracellular domain of tyrosine kinase, inhibiting downstream neoplastic proliferation

Correct Answer & Explanation

. Monoclonal antibody binding to RANKL, preventing activation of RANK on osteoclast precursors

Explanation

Denosumab is highly effective as neoadjuvant therapy for large, complex Giant Cell Tumors of Bone (GCTB) to induce ossification, solidify the tumor margins, and reduce surgical morbidity. It is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). The neoplastic mononuclear stromal cells in GCTB secrete large amounts of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) expressing RANK. By neutralizing RANKL, denosumab prevents the differentiation and bone-resorbing function of these giant cells.

Question 8218

Topic: Surgical Anatomy & Approaches

During an anterior surgical approach to the proximal radius (Henry approach), the surgeon must protect the posterior interosseous nerve (PIN). The PIN enters the supinator muscle beneath a fibrous arch. Which muscle's fascial edge forms the Arcade of Frohse?

. Superficial head of the supinator
. Deep head of the supinator
. Brachioradialis
. Extensor carpi radialis brevis
. Pronator teres

Correct Answer & Explanation

. Superficial head of the supinator

Explanation

The Arcade of Frohse is formed by the thickened proximal fascial edge of the superficial head of the supinator muscle. It is the most common site of compression for the posterior interosseous nerve.

Question 8219

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for an acetabular fracture, significant hemorrhage occurs while dissecting near the superior pubic ramus. The injured vessel represents an anastomosis between which two vascular systems?

. Internal iliac and Internal pudendal
. External iliac and Obturator
. Femoral and Profunda femoris
. Inferior epigastric and Internal pudendal
. Superior gluteal and Inferior gluteal

Correct Answer & Explanation

. Inferior epigastric and Internal pudendal

Explanation

The corona mortis is a vascular anastomosis between the obturator vessels (internal iliac system) and the external iliac or inferior epigastric vessels. It crosses the superior pubic ramus and is highly vulnerable during pelvic surgery.

Question 8220

Topic: 1. General Principles & Basic Science

A rock climber feels a pop in his ring finger followed by bowstringing of the flexor tendons. Biomechanically, which two pulleys of the flexor tendon sheath are most critical to prevent bowstringing and must be preserved or reconstructed?

. A1 and A3
. A2 and A4
. A3 and A5
. A1 and A5
. C1 and C2

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are located over the proximal and middle phalanges, respectively. They are biomechanically the most critical pulleys for preventing flexor tendon bowstringing and maintaining functional excursion.

Test Yourself

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

On this Page