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1. General Principles & Basic Science MCQs

Practice Set 731 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 14601

Topic: Biology, Genetics & Bone Healing

In Rheumatoid Arthritis, the hypertrophic synovium (pannus) causes juxta-articular bone destruction primarily through the activation of osteoclasts. Which key pro-inflammatory cytokine, secreted by macrophages and T-cells in the joint, is a primary driver of this RANKL-mediated osteoclastogenesis?

. Interleukin-10 (IL-10)
. Interleukin-4 (IL-4)
. Tumor Necrosis Factor alpha (TNF-alpha)
. Transforming Growth Factor beta (TGF-beta)
. Interferon gamma (IFN-gamma)

Correct Answer & Explanation

. Tumor Necrosis Factor alpha (TNF-alpha)

Explanation

TNF-alpha, along with IL-1 and IL-6, is a pivotal pro-inflammatory cytokine in the pathogenesis of rheumatoid arthritis. TNF-alpha directly stimulates synovial fibroblasts to produce RANKL, which binds to RANK on osteoclast precursors, leading to aggressive bone resorption.

Question 14602

Topic: Infection, Pharmacology & VTE

A 35-year-old presents with a large, recurrent knee effusion. Synovial fluid analysis reveals 25,000 WBCs/mm3 with a negative Gram stain. Due to suspected late Lyme arthritis, serology is ordered. According to CDC criteria, what constitutes a positive Western blot for late Lyme disease?

. 2 of 3 specific IgM bands
. 5 of 10 specific IgG bands
. 2 of 3 specific IgG bands
. 5 of 10 specific IgM bands
. Detection of Borrelia burgdorferi DNA by PCR in the serum

Correct Answer & Explanation

. 5 of 10 specific IgG bands

Explanation

The CDC recommends two-tiered testing for Lyme disease. If the initial EIA or IFA is positive, a Western blot is performed. For late Lyme disease (symptoms present for > 1 month, such as arthritis), the criteria require the presence of 5 of 10 specific IgG bands. IgM bands are not used for late disease due to the high rate of false positives over time.

Question 14603

Topic: 1. General Principles & Basic Science

Articular cartilage exhibits remarkable compressive stiffness due to its extracellular matrix composition. What is the most abundant non-collagenous protein in articular cartilage responsible for generating the tissue's swelling pressure?

. Aggrecan
. Decorin
. Fibronectin
. Tenascin
. Lubricin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage. It consists of a protein core with highly negatively charged glycosaminoglycan (GAG) side chains (chondroitin sulfate and keratan sulfate). These negative charges attract water, creating a massive swelling pressure that is restrained by the Type II collagen network, giving cartilage its compressive stiffness.

Question 14604

Topic: Biology, Genetics & Bone Healing

Denosumab has emerged as a highly effective neoadjuvant and definitive treatment for advanced Giant Cell Tumor of Bone (GCTB). It exerts its therapeutic effect by acting as a monoclonal antibody directly targeting which of the following?

. RANK receptor on osteoclast precursors
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

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

Explanation

Denosumab is a fully human monoclonal antibody that binds to and neutralizes RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In GCTB, the neoplastic stromal cells express high levels of RANKL, which recruits and activates the reactive osteoclast-like giant cells. Denosumab stops this recruitment, leading to rapid clinical and radiographic improvement.

Question 14605

Topic: Biology, Genetics & Bone Healing

Following open reduction and internal fixation of a transverse radius fracture with a dynamic compression plate, the fracture heals via primary bone healing. Which of the following mechanical and biological conditions is essential for this type of healing to occur?

. Callus formation mediated by chondrocytes
. Absolute stability resulting in strain less than 2 percent
. Interfragmentary strain between 2 and 10 percent
. Micromotion to stimulate osteoblast proliferation
. Predominant endochondral ossification

Correct Answer & Explanation

. Absolute stability resulting in strain less than 2 percent

Explanation

Primary (direct) bone healing occurs without callus formation via intramembranous ossification (contact healing or gap healing with cutting cones). It strictly requires absolute stability, defined as interfragmentary strain less than 2%. Strain between 2-10% promotes secondary healing with callus (endochondral ossification).

Question 14606

Topic: Biomechanics & Biomaterials
To reduce wear rates in total joint arthroplasty, ultra-high-molecular-weight polyethylene (UHMWPE) undergoes irradiation to become highly cross-linked. While cross-linking successfully decreases volumetric wear, what is the primary mechanical disadvantage of this process?
. Increased rate of in vivo oxidation over time
. Decreased ultimate tensile strength and reduced fatigue crack propagation resistance
. Increased generation of biologically active wear debris leading to severe osteolysis
. Decreased biocompatibility leading to metal hypersensitivity
. Increased cold flow (creep) deformation under static loads

Correct Answer & Explanation

. Decreased ultimate tensile strength and reduced fatigue crack propagation resistance

Explanation

Highly cross-linking UHMWPE (via gamma or electron beam irradiation) dramatically reduces its wear rate. However, the trade-off is a reduction in mechanical properties, specifically decreased ultimate tensile strength, yield strength, ductility, and resistance to fatigue crack propagation. Oxidation is mitigated by remelting or adding antioxidants like Vitamin E.

Question 14607

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is primarily responsible for resisting shear stress and contains the highest concentration of collagen with fibers aligned parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone is responsible for resisting shear stress. It has the highest collagen content, with fibers aligned parallel to the articular surface.

Question 14608

Topic: Biology, Genetics & Bone Healing

A 25-year-old sustains a midshaft humerus fracture treated with a compression plate. What type of bone healing is expected, and what is the primary biomechanical prerequisite for this type of healing?

. Primary healing requiring absolute stability
. Secondary healing requiring absolute stability
. Primary healing requiring relative stability
. Secondary healing requiring relative stability
. Endochondral ossification requiring absolute stability

Correct Answer & Explanation

. Primary healing requiring absolute stability

Explanation

Compression plating provides absolute stability, which bypasses callus formation and leads to primary bone healing via cutting cones. Secondary healing occurs with relative stability and involves callus formation.

Question 14609

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a lytic epiphyseal lesion of the proximal tibia extending to the subchondral bone. Biopsy confirms Giant Cell Tumor. What is the mechanism of action of the targeted medical therapy for this condition?

. Inhibition of RANKL
. Inhibition of VEGF
. Tyrosine kinase inhibitor
. Bisphosphonate analog
. Estrogen receptor modulation

Correct Answer & Explanation

. Inhibition of RANKL

Explanation

Denosumab is a monoclonal antibody that inhibits RANKL. It is used in giant cell tumors of bone to prevent RANK-mediated osteoclast-like giant cell formation and subsequent bone destruction.

Question 14610

Topic: Biomechanics & Biomaterials

During ACL reconstruction rehabilitation, what biomechanical property is responsible for the gradual elongation of a tendon graft over time when subjected to a constant continuous load?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Viscoelasticity

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. Stress relaxation is the decrease in stress over time under a constant deformation.

Question 14611

Topic: Biomechanics & Biomaterials

A patient with a stainless steel dynamic compression plate subsequently has a titanium screw inserted into the plate. What type of corrosion is most likely to occur at the screw-plate interface?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in physical contact within a conductive fluid (body fluid). The less noble metal acts as an anode and corrodes.

Question 14612

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct zones. Which zone features collagen fibers oriented parallel to the joint surface to resist shear forces, and contains the highest concentration of water?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has collagen fibers oriented parallel to the joint surface to withstand shear forces. It also contains the highest water content and lowest proteoglycan content compared to the deeper zones.

Question 14613

Topic: 1. General Principles & Basic Science

Which of the following bone graft types relies primarily on creeping substitution for incorporation and provides the greatest initial structural support?

. Autogenous cancellous bone
. Autogenous cortical bone
. Demineralized bone matrix
. Calcium phosphate cement
. Cancellous allograft

Correct Answer & Explanation

. Autogenous cortical bone

Explanation

Cortical autografts provide excellent structural support and heal via creeping substitution over a prolonged period. Cancellous autografts heal rapidly via osteogenesis and osteoinduction but lack initial mechanical strength.

Question 14614

Topic: Biomechanics & Biomaterials

Which of the following modifications to a cortical screw will most significantly increase its pullout strength in diaphyseal bone?

. Increasing the outer diameter
. Increasing the inner (core) diameter
. Increasing the thread pitch
. Decreasing the thread density
. Decreasing the outer diameter

Correct Answer & Explanation

. Increasing the outer diameter

Explanation

Screw pullout strength is most significantly increased by increasing the outer diameter. Decreasing the inner core diameter also increases pullout strength but severely reduces the screw's resistance to fatigue failure.

Question 14615

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans and collagen fibers oriented perpendicular to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone contains the largest diameter collagen fibrils oriented perpendicular to the joint surface and possesses the highest concentration of proteoglycans. The superficial zone has collagen oriented parallel to the joint surface to resist shear forces.

Question 14616

Topic: Biology, Genetics & Bone Healing

A 65-year-old female presents with a distal radius fracture. Laboratory results show normal calcium, normal phosphorus, normal alkaline phosphatase, and normal parathyroid hormone levels. What is the most likely underlying metabolic diagnosis?

. Osteomalacia
. Paget disease
. Primary hyperparathyroidism
. Osteoporosis
. Renal osteodystrophy

Correct Answer & Explanation

. Osteoporosis

Explanation

Osteoporosis typically presents with completely normal serum calcium, phosphorus, alkaline phosphatase, and PTH levels. Osteomalacia, Paget disease, and hyperparathyroidism all demonstrate abnormalities in one or more of these laboratory values.

Question 14617

Topic: Biomechanics & Biomaterials

Which type of corrosion occurs primarily when a stainless steel screw is used in direct mechanical combination with a titanium plate in an orthopedic construct?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within an electrolytic fluid medium, creating an electrochemical potential difference. Mixing titanium and stainless steel implants should generally be avoided to prevent this.

Question 14618

Topic: Biology, Genetics & Bone Healing

A 30-year-old female is diagnosed with a giant cell tumor of the distal femur. She is treated with denosumab preoperatively. What is the precise mechanism of action of this medication?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of osteoblasts
. Monoclonal antibody binding to RANK ligand (RANKL)
. Inhibition of matrix metalloproteinases
. Binding to the PTH receptor to inhibit calcium release

Correct Answer & Explanation

. Monoclonal antibody binding to RANK ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that binds directly to RANKL, preventing it from activating the RANK receptor on osteoclasts. This effectively halts osteoclast-mediated bone resorption, which is the primary driver of osteolysis in giant cell tumors.

Question 14619

Topic: Biology, Genetics & Bone Healing

Which type of bone healing is primarily driven by cutting cones and requires absolute stability with no interfragmentary gap?

. Primary (contact) bone healing
. Secondary bone healing
. Endochondral ossification
. Intramembranous ossification
. Callus formation

Correct Answer & Explanation

. Primary (contact) bone healing

Explanation

Primary (contact) bone healing occurs under conditions of absolute stability without callus formation. It relies entirely on Haversian remodeling driven by osteoclastic cutting cones that cross the fracture site.

Question 14620

Topic: Infection, Pharmacology & VTE

A 9-year-old African American boy with homozygous hemoglobin SS disease presents with a 4-day history of fever, localized distal femoral pain, and an inability to bear weight. Blood cultures and a bone aspirate are obtained. While Staphylococcus aureus remains a common pathogen, this patient is at uniquely high risk for osteomyelitis caused by which of the following encapsulated, gram-negative bacilli?

. Pseudomonas aeruginosa
. Haemophilus influenzae
. Salmonella typhimurium
. Escherichia coli
. Klebsiella pneumoniae

Correct Answer & Explanation

. Salmonella typhimurium

Explanation

Correct Answer: C. Salmonella typhimuriumPatients with sickle cell disease are functionally asplenic and have a uniquely high risk of osteomyelitis caused bySalmonellaspecies, an encapsulated, gram-negative bacillus. WhileStaphylococcus aureusis still the most common overall cause of osteomyelitis in this population, the incidence ofSalmonellais disproportionately high compared to the general population. Microinfarctions in the bowel wall are thought to allowSalmonellato translocate into the bloodstream and seed infarcted bone.

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