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1. General Principles & Basic Science MCQs

Practice Set 644 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 12861

Topic: Biology, Genetics & Bone Healing

In a high-risk patient undergoing posterolateral lumbar fusion, recombinant human bone morphogenetic protein-2 (rhBMP-2) is utilized off-label. Which of the following is a recognized complication specifically associated with the use of rhBMP-2 in the spine?

. Aseptic meningitis
. Radiculitis and ectopic bone formation
. Anaphylaxis to bovine collagen
. Systemic hypocalcemia
. Increased risk of deep vein thrombosis

Correct Answer & Explanation

. Radiculitis and ectopic bone formation

Explanation

The use of rhBMP-2 in spine surgery is associated with several specific complications, including postoperative radiculitis, ectopic bone formation within the canal, and massive osteolysis/subsidence.

Question 12862

Topic: 1. General Principles & Basic Science

A 38-year-old male is scheduled for an anterior lumbar interbody fusion (ALIF) at L5-S1 for severe degenerative disc disease. He is counseled regarding the risk of retrograde ejaculation. Injury to which of the following structures is primarily responsible for this complication?

. Superior hypogastric plexus
. Inferior hypogastric plexus
. Pudendal nerve
. Parasympathetic pelvic splanchnic nerves
. Lumbosacral trunk

Correct Answer & Explanation

. Superior hypogastric plexus

Explanation

The superior hypogastric plexus, which lies anterior to the lower lumbar vertebrae and aortic bifurcation, provides sympathetic innervation to the internal urethral sphincter. Injury during an ALIF approach can lead to sphincter incompetence and retrograde ejaculation.

Question 12863

Topic: Biology, Genetics & Bone Healing

A 78-year-old female with osteoporosis suffers a sudden onset of mid-back pain while lifting groceries. Radiographs show an acute wedge compression fracture at T12 with 20% loss of height. She is neurologically intact. What is the most appropriate initial management?

. Immediate percutaneous kyphoplasty
. Posterior long-segment instrumented fusion
. Conservative management with short rest, analgesics, and mobilization
. Anterior decompression and strut grafting
. Rigid custom clamshell orthosis for 6 months

Correct Answer & Explanation

. Conservative management with short rest, analgesics, and mobilization

Explanation

The initial treatment for osteoporotic vertebral compression fractures without neurologic deficit is conservative, focusing on pain control, a short period of rest, and progressive mobilization. Cement augmentation (kyphoplasty) is typically reserved for those who fail conservative care after 4-6 weeks.

Question 12864

Topic: Biology, Genetics & Bone Healing

Which of the following cellular events most accurately differentiates primary (direct) bone healing from secondary (indirect) bone healing?

. Presence of a robust soft callus
. Intramembranous ossification alone
. Absence of a cartilaginous intermediate phase
. Dependence on mechanical micromotion
. Exclusive utilization of osteoblasts without osteoclasts

Correct Answer & Explanation

. Absence of a cartilaginous intermediate phase

Explanation

Primary (direct) bone healing occurs under conditions of absolute stability (e.g., rigid fixation with compression plates) and is characterized by cutting cones that directly cross the fracture site. Crucially, it skips the cartilaginous intermediate phase (endochondral ossification) that is a hallmark of secondary (indirect) bone healing via callus formation. It still relies on the coupled action of osteoclasts and osteoblasts for Haversian remodeling.

Question 12865

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following describes its primary molecular mechanism of action?
. Direct inhibition of factor Xa in the coagulation cascade
. Synthetic analog of lysine that reversibly binds to plasminogen
. Irreversible antagonist of the platelet ADP receptor (P2Y12)
. Enhancement of antithrombin III activity
. Promotion of von Willebrand factor release from Weibel-Palade bodies

Correct Answer & Explanation

. Synthetic analog of lysine that reversibly binds to plasminogen

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly binding to the lysine-binding sites on plasminogen. This competitive binding prevents plasminogen from adhering to fibrin and subsequently being activated to plasmin, thereby inhibiting fibrin degradation.

Question 12866

Topic: Infection, Pharmacology & VTE
A 4-year-old child presents with a painful limp and refusal to bear weight on the right leg. Vitals show a temperature of 38.6°C (101.5°F). Laboratory analysis reveals a WBC count of 13,000/mm³ and an ESR of 45 mm/hr. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria for septic arthritis of the hip in pediatrics include four parameters: 1) Non-weight-bearing on the affected side, 2) ESR > 40 mm/hr, 3) Fever > 38.5°C, and 4) WBC > 12,000/mm³. This patient meets all 4 criteria. The probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.

Question 12867

Topic: Biology, Genetics & Bone Healing

A 70-year-old man presents with increasing hat size, hearing loss, and deep, aching bone pain in his right tibia. Radiographs reveal cortical thickening and coarsened trabeculae. Which of the following histological findings is a hallmark of the active or mixed phase of this disease?

. Mosaic pattern of woven and lamellar bone with prominent cement lines
. Osteoid seams thicker than 15 micrometers
. Avascular necrosis of the medullary cavity with empty lacunae
. Massive infiltration of plasma cells with Russell bodies
. Subperiosteal bone resorption with brown tumors

Correct Answer & Explanation

. Mosaic pattern of woven and lamellar bone with prominent cement lines

Explanation

The patient's presentation is classic for Paget's disease of bone (osteitis deformans). The histological hallmark in the mixed or later sclerotic phases is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone. This appearance is due to prominent, haphazard cement lines that reflect repeated, disorganized episodes of chaotic osteoclastic bone resorption followed by rapid osteoblastic formation.

Question 12868

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture resulting in a radial nerve palsy. According to Seddon's classification of nerve injuries, a neurapraxia is characterized by which of the following?

. Complete axonal disruption with intact endoneurium
. Complete axonal disruption with disrupted endoneurium
. Focal demyelination with intact axons and no Wallerian degeneration
. Disruption of the epineurium, perineurium, and endoneurium
. Irreversible Wallerian degeneration distal to the injury

Correct Answer & Explanation

. Focal demyelination with intact axons and no Wallerian degeneration

Explanation

Neurapraxia (comparable to Sunderland Grade I) is a temporary physiological conduction block caused by focal demyelination. Because the axons themselves remain physically intact, Wallerian degeneration does not occur distal to the lesion. Recovery is usually spontaneous and complete within days to weeks. Axonal disruption defines axonotmesis, and complete nerve transection defines neurotmesis.

Question 12869

Topic: Biology, Genetics & Bone Healing
Osteoclasts attach tightly to the bone surface via specialized structures called sealing zones, creating an isolated acidic microenvironment for bone resorption. Which integrin is primarily responsible for osteoclast attachment to bone matrix proteins such as osteopontin?
. Integrin alpha-5 beta-1
. Integrin alpha-v beta-3
. Integrin alpha-2 beta-1
. Integrin alpha-L beta-2
. Integrin alpha-4 beta-1

Correct Answer & Explanation

. Integrin alpha-v beta-3

Explanation

Integrin alpha-v beta-3 (αvβ3) is highly expressed on the ruffled border and sealing zone of osteoclasts. It binds specifically to bone matrix proteins that contain the RGD (Arginine-Glycine-Aspartic acid) amino acid sequence, such as osteopontin and bone sialoprotein. This interaction is critical for osteoclast adhesion and function.

Question 12870

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman presents with vague thigh pain for the past 3 weeks. She has been on alendronate for 8 years for osteoporosis. A radiograph of her femur is obtained. Which of the following radiographic findings constitutes an absolute indication for prophylactic intramedullary fixation of an impending atypical femur fracture?

. Endosteal scalloping of the diaphysis
. A transverse radiolucent line across the lateral cortex with localized pain
. Medial cortical spiking without periosteal reaction
. Generalized diaphyseal cortical thickening with an asymptomatic 'beak' sign
. Dorsal cortical comminution

Correct Answer & Explanation

. A transverse radiolucent line across the lateral cortex with localized pain

Explanation

Atypical femur fractures are associated with prolonged bisphosphonate use. Prophylactic fixation is highly indicated if there is a radiolucent line (incomplete fracture) on the lateral cortex accompanied by prodromal thigh pain, as this indicates a high risk for impending complete fracture.

Question 12871

Topic: 1. General Principles & Basic Science

Histologically, normal articular cartilage is divided into four distinct zones. Which zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers arranged perpendicular to the articular surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils, which are oriented perpendicular to the joint surface to resist compressive forces. It has the highest concentration of proteoglycans and the lowest water content of the uncalcified zones.

Question 12872

Topic: Biomechanics & Biomaterials

During a revision open reduction and internal fixation of a nonunion, a surgeon considers supplementing an existing titanium alloy (Ti-6Al-4V) intramedullary nail with stainless steel (316L) cerclage wires. If these two different metals are placed in direct physical contact within the corrosive physiological environment of the human body, which of the following is the most likely biomechanical or biochemical consequence?

. Fretting corrosion of the titanium implant
. Galvanic corrosion of the titanium implant
. Galvanic corrosion of the stainless steel implant
. Crevice corrosion of the titanium implant
. Passivation of both implants preventing any further corrosion

Correct Answer & Explanation

. Galvanic corrosion of the stainless steel implant

Explanation

Mixing dissimilar metals in a conductive fluid environment (like the human body) leads to galvanic corrosion. The metal that is less noble (more anodic) will undergo accelerated corrosion. In the orthopaedic hierarchy of metals, titanium is more noble (cathodic) than 316L stainless steel. Therefore, the stainless steel implants will undergo accelerated galvanic corrosion when in direct contact with a titanium implant.

Question 12873

Topic: Biology, Genetics & Bone Healing

A 45-year-old female with a history of malabsorption secondary to Crohn's disease presents with diffuse, dull bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low phosphorus, and elevated alkaline phosphatase. A bone biopsy reveals thickened, unmineralized osteoid seams. Which of the following represents the primary pathophysiologic defect in this condition?

. Overactivity of osteoclasts leading to increased bone resorption
. A primary genetic defect in Type I collagen synthesis
. Inadequate mineralization of the newly formed organic bone matrix
. A gain-of-function mutation in the FGFR3 gene
. Excessive uncoordinated bone remodeling resulting in woven bone formation

Correct Answer & Explanation

. Inadequate mineralization of the newly formed organic bone matrix

Explanation

The patient's clinical and laboratory profile is characteristic of osteomalacia, commonly caused by severe Vitamin D deficiency (often due to malabsorption). Osteomalacia is defined histologically by a defect in the mineralization of the organic bone matrix (osteoid), leading to widened unmineralized osteoid seams. Overactivity of osteoclasts occurs in Paget's disease or hyperparathyroidism. A defect in Type I collagen is seen in Osteogenesis Imperfecta.

Question 12874

Topic: Infection, Pharmacology & VTE

Periprosthetic joint infections caused by Staphylococcus epidermidis are notoriously difficult to eradicate due to biofilm formation. During the accumulation/proliferation phase of biofilm development, which of the following molecules mediates the critical cell-to-cell adhesion and structural integrity of the extracellular polymeric substance?

. Fibronectin-binding proteins (FnBPs)
. Polysaccharide intercellular adhesin (PIA)
. Protein A
. Panton-Valentine leukocidin (PVL)
. Hyaluronidase

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Biofilm formation occurs in stages: attachment, proliferation/accumulation, maturation, and dispersion. While initial attachment relies on autolysins and surface-binding proteins like fibronectin-binding proteins, the critical component for intercellular adhesion and forming the protective slime layer (extracellular polymeric substance) during the proliferation phase is Polysaccharide Intercellular Adhesin (PIA), mediated by the icaADBC operon in Staphylococcus epidermidis.

Question 12875

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely utilized in total joint arthroplasty to reduce perioperative blood loss. Which of the following best describes the specific mechanism of action of this pharmacological agent?
. Irreversibly inhibits cyclooxygenase to prevent platelet aggregation
. Directly inhibits Factor Xa in the coagulation cascade
. Binds to antithrombin III, accelerating its inhibition of thrombin
. Competitively blocks the lysine-binding sites on plasminogen
. Promotes the release of von Willebrand factor from endothelial cells

Correct Answer & Explanation

. Competitively blocks the lysine-binding sites on plasminogen

Explanation

Tranexamic acid is an antifibrinolytic agent. It works as a synthetic analog of the amino acid lysine. It reversibly and competitively blocks the lysine-binding sites on plasminogen molecules. This prevents plasminogen from binding to fibrin, thereby inhibiting its activation into plasmin and preventing the subsequent enzymatic degradation of fibrin clots.

Question 12876

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue divided into distinct structural zones. Which zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibrils oriented perpendicular to the articular surface?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils, which are oriented perpendicular to the joint surface to resist compressive loads. It also has the highest concentration of proteoglycans and the lowest water content. Conversely, the superficial zone has the highest water content, the lowest proteoglycan concentration, and collagen fibrils parallel to the joint surface.

Question 12877

Topic: Biology, Genetics & Bone Healing
Romosozumab is a monoclonal antibody recently developed for the treatment of severe osteoporosis. It functions by binding to and inhibiting sclerostin, thereby activating the Wnt/β-catenin signaling pathway to stimulate bone formation. Under normal physiologic conditions, sclerostin is primarily synthesized and secreted by which of the following cell types?
. Osteoblasts
. Osteoclasts
. Osteocytes
. Chondrocytes
. Mesenchymal stem cells

Correct Answer & Explanation

. Osteocytes

Explanation

Sclerostin is a glycoprotein encoded by the SOST gene and is primarily produced by mature osteocytes embedded within the mineralized bone matrix. Sclerostin acts as a negative regulator of bone formation by binding to LRP5/6 receptors on osteoblasts, inhibiting the Wnt/β-catenin signaling pathway. Monoclonal antibodies targeting sclerostin release this inhibition, powerfully stimulating osteoblastic bone formation.

Question 12878

Topic: 1. General Principles & Basic Science

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

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

Correct Answer & Explanation

. Increasing the major (outer) diameter

Explanation

The pullout strength of a screw is most significantly dependent on the major (outer) diameter of the thread. Increasing the core diameter or thread pitch can actually decrease pullout strength by reducing the volume of bone engaged between the threads.

Question 12879

Topic: Biology, Genetics & Bone Healing

A 68-year-old osteoporotic woman is prescribed a biologic agent that mimics the body's natural osteoprotegerin (OPG). Which of the following best describes the specific mechanism of action of this medication?

. Inhibition of farnesyl pyrophosphate synthase
. Binding to RANK to stimulate osteoclast apoptosis
. Binding to RANKL to prevent osteoclast activation
. Stimulation of Wnt/beta-catenin signaling in osteoblasts
. Direct inhibition of cathepsin K

Correct Answer & Explanation

. Binding to RANKL to prevent osteoclast activation

Explanation

Denosumab is a monoclonal antibody that mimics OPG by binding to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to RANK on osteoclasts, thereby inhibiting osteoclast formation, function, and survival.

Question 12880

Topic: 1. General Principles & Basic Science

During the evaluation of normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented perpendicular to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicularly, the highest concentration of proteoglycans, and the lowest water content. This structure provides high resistance to compressive forces.

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