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1. General Principles & Basic Science MCQs

Practice Set 646 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 12901

Topic: 1. General Principles & Basic Science

Administration of non-steroidal anti-inflammatory drugs (NSAIDs) shortly after a fracture can impair bone healing primarily by inhibiting cyclooxygenase-2 (COX-2). Which specific stage of fracture repair is most adversely affected by this COX-2 inhibition?

. Immediate hematoma formation and initial coagulation
. Early differentiation of mesenchymal stem cells into osteoblasts and chondrocytes
. Late maturation of woven bone into lamellar bone
. Angiogenesis strictly during the hard callus remodeling phase
. Osteoclastic resorption of the devitalized primary fracture ends

Correct Answer & Explanation

. Early differentiation of mesenchymal stem cells into osteoblasts and chondrocytes

Explanation

COX-2 is crucial for the early inflammatory phase; its inhibition impairs the differentiation of mesenchymal stem cells into the osteogenic and chondrogenic lineages required for soft callus formation.

Question 12902

Topic: Biomechanics & Biomaterials

Stress shielding around a stiff orthopedic implant can lead to localized osteopenia. Which of the following solid metallic implant materials possesses an elastic modulus most closely approximating that of human cortical bone?

. Cobalt-chromium alloy
. Stainless steel (316L)
. Titanium alloy (Ti-6Al-4V)
. Solid tantalum
. Zirconium alloy

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

Titanium alloy has an elastic modulus (approx. 110 GPa) closer to cortical bone (15-20 GPa) than stainless steel (200 GPa) or cobalt-chromium (240 GPa), thereby reducing stress shielding.

Question 12903

Topic: Infection, Pharmacology & VTE
A 65-year-old patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a primary total knee arthroplasty. What is the precise mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III
. Direct, competitive inhibition of Factor Xa
. Antagonism of Vitamin K-dependent clotting factors
. Irreversible inhibition of ADP-induced platelet aggregation

Correct Answer & Explanation

. Direct, competitive inhibition of Factor Xa

Explanation

Rivaroxaban is an oral anticoagulant that works by directly and reversibly binding to and inhibiting Factor Xa, interrupting both the intrinsic and extrinsic coagulation pathways.

Question 12904

Topic: 1. General Principles & Basic Science

During a minor orthopedic procedure under local anesthesia, a 70 kg patient inadvertently receives an intravascular injection of bupivacaine. To avoid severe cardiotoxicity, what is the generally accepted maximum safe dose of bupivacaine with epinephrine for this patient?

. 140 mg
. 210 mg
. 350 mg
. 490 mg
. 700 mg

Correct Answer & Explanation

. 210 mg

Explanation

The maximum safe dose of bupivacaine with epinephrine is 3 mg/kg. For a 70 kg patient, this equates to a maximum dose of 210 mg.

Question 12905

Topic: 1. General Principles & Basic Science

In the destructive joint changes characteristic of osteoarthritis, which of the following matrix metalloproteinases (MMPs) is primarily recognized as the major collagenase responsible for the cleavage of Type II collagen?

. MMP-1
. MMP-2
. MMP-3
. MMP-9
. MMP-13

Correct Answer & Explanation

. MMP-13

Explanation

MMP-13 (Collagenase-3) is highly overexpressed in osteoarthritic cartilage and is the principal enzyme responsible for the irreversible degradation of the Type II collagen network.

Question 12906

Topic: Biology, Genetics & Bone Healing

Which of the following accurately describes the primary mechanism by which Denosumab affects bone remodeling in the treatment of osteoporosis or giant cell tumor of bone?

. Binds directly to the RANK receptor on osteoclasts
. Binds to RANKL, preventing its interaction with the RANK receptor
. Directly inhibits osteoblast apoptosis via the Wnt pathway
. Stimulates the production of endogenous Osteoprotegerin (OPG)
. Inhibits the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with the RANK receptor

Explanation

Denosumab is a monoclonal antibody that functionally mimics osteoprotegerin (OPG) by binding to RANKL. This prevents RANKL from interacting with the RANK receptor on osteoclast precursors, thereby inhibiting osteoclast differentiation, activation, and bone resorption.

Question 12907

Topic: Biomechanics & Biomaterials
What is the primary mechanical trade-off associated with the use of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) compared to conventional UHMWPE in total hip arthroplasty?
. Decreased wear resistance with increased fracture toughness
. Increased wear resistance with decreased fracture toughness
. Increased oxidative degradation with decreased elasticity
. Decreased oxidative degradation with increased fatigue crack propagation
. Improved elasticity with decreased ultimate tensile strength

Correct Answer & Explanation

. Increased wear resistance with decreased fracture toughness

Explanation

Highly cross-linked UHMWPE provides excellent wear resistance, significantly reducing particulate debris and subsequent osteolysis. However, the radiation and thermal processes used to cross-link the material decrease its mechanical properties, particularly fracture toughness and resistance to fatigue crack propagation.

Question 12908

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with a dense radial nerve palsy. Electromyography at 4 weeks shows fibrillation potentials but no motor unit action potentials. If the nerve injury is classified as a Sunderland Grade II (axonotmesis), what key histological structure remains intact to allow for predictable axonal regeneration?

. Epineurium only
. Epineurium and perineurium only
. Endoneurium, perineurium, and epineurium
. Myelin sheath only
. Axolemma

Correct Answer & Explanation

. Endoneurium, perineurium, and epineurium

Explanation

In a Sunderland Grade II injury (axonotmesis), the axon is disrupted, leading to Wallerian degeneration distal to the injury site. However, the entire connective tissue framework (endoneurium, perineurium, and epineurium) remains completely intact, guiding the regenerating axon to its appropriate target at roughly 1 mm per day.

Question 12909

Topic: 1. General Principles & Basic Science

In normal adult articular cartilage, which zone is characterized by the highest concentration of proteoglycans, the largest diameter collagen fibrils oriented perpendicularly to the joint surface, and chondrocytes arranged in vertical columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the joint surface to resist compressive loads. This zone also possesses the highest concentration of proteoglycans and the lowest water content.

Question 12910

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, the surgeon pre-tensions the soft-tissue graft by securing it on a board and holding it at a constant length for 10 minutes. The surgeon notes that the tension required to maintain this specific length gradually decreases over time. This biomechanical phenomenon is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Strain rate dependency

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (internal tension) within a material gradually decreases when it is held at a constant strain (length). In contrast, creep is the gradual increase in length (strain) when a material is subjected to a constant load (stress).

Question 12911

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is frequently used in orthopedic surgery to reduce perioperative blood loss. Which of the following accurately describes the specific molecular mechanism of action of TXA?

. Inhibits the conversion of prothrombin to thrombin in the common pathway
. Irreversibly binds to COX-1 to prevent platelet aggregation
. Competitively inhibits plasminogen activation to plasmin
. Directly inhibits factor Xa
. Acts as a direct thrombin inhibitor

Correct Answer & Explanation

. Competitively inhibits plasminogen activation to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It exerts its antifibrinolytic effect by competitively binding to the lysine-binding sites on plasminogen, preventing its activation to plasmin and subsequent degradation of fibrin clots.

Question 12912

Topic: Infection, Pharmacology & VTE

During the pathogenesis of a periprosthetic joint infection, Staphylococcus aureus utilizes surface proteins to adhere to host proteins that have coated an orthopedic implant. What is the initial, prerequisite step in biofilm formation before irreversible attachment occurs?

. Quorum sensing to coordinate gene expression
. Planktonic cell dispersal from mature matrix
. Exopolysaccharide (glycocalyx) matrix production
. Reversible attachment to the conditioned surface via van der Waals forces
. Irreversible attachment via MSCRAMMs

Correct Answer & Explanation

. Reversible attachment to the conditioned surface via van der Waals forces

Explanation

The primary initial step of biofilm formation is the reversible, non-specific attachment of planktonic bacteria to the host-conditioned surface of the implant, mediated by electrostatic and van der Waals forces. This is rapidly followed by irreversible attachment mediated by specific bacterial adhesins known as MSCRAMMs.

Question 12913

Topic: Infection, Pharmacology & VTE
A 5-year-old boy is evaluated for an acute onset of right hip pain and a limp. He is afebrile but refuses to bear any weight on the right leg. Laboratory tests show a WBC count of 11,000/mm³, an ESR of 25 mm/hr, and a CRP of 0.8 mg/dL. Radiographs of the pelvis are unremarkable. According to the Kocher criteria, what is the approximate statistical probability that this patient has septic arthritis of the hip?
. < 5% (approximately 3%)
. ~ 40%
. ~ 71%
. ~ 93%
. 100%

Correct Answer & Explanation

. < 5% (approximately 3%)

Explanation

The Kocher criteria differentiate septic arthritis from transient synovitis in children. The four criteria are: non-weight-bearing on the affected side, fever > 38.5°C (101.3°F), ESR > 40 mm/hr, and WBC > 12,000/mm³. This patient meets only one criterion (non-weight-bearing). The probability of septic arthritis based on the number of criteria met is: 0 criteria = <1%, 1 criterion = 3%, 2 criteria = 40%, 3 criteria = 71%, and 4 criteria = 93%.

Question 12914

Topic: 1. General Principles & Basic Science

A 7-year-old boy is evaluated for a painless, audible 'clunking' in his lateral knee during walking. Physical examination reveals a palpable snapping over the lateral joint line during active knee extension. MRI confirms a thick, block-like lateral meniscus. Which specific ligamentous attachments are uniquely deficient in the Wrisberg variant of this condition?

. Anterior meniscofemoral ligament (Humphrey)
. Posterior meniscofemoral ligament (Wrisberg)
. Meniscotibial (coronary) ligaments
. Transverse intermeniscal ligament
. Fibular collateral ligament

Correct Answer & Explanation

. Posterior meniscofemoral ligament (Wrisberg)

Explanation

The patient has a snapping discoid lateral meniscus. The Wrisberg variant is a specific type of discoid meniscus characterized by a lack of normal posterior meniscotibial (coronary) ligament attachments. Its only posterior attachment is to the posterior meniscofemoral ligament of Wrisberg. This lack of peripheral fixation causes hypermobility, leading the meniscus to subluxate anteriorly into the joint during extension, causing the classic 'snap' or 'clunk'.

Question 12915

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy is referred for progressive lower extremity bowing and short stature. He has a waddling gait. Laboratory analysis reveals normal serum calcium, significantly low serum phosphate, normal parathyroid hormone (PTH) levels, and elevated alkaline phosphatase. Which of the following is the most likely underlying genetic mechanism for his disorder?

. Mutation in the COL1A1 gene
. Mutation in the FGFR3 gene
. Inactivating mutation in the vitamin D receptor
. Defect in the 1-alpha-hydroxylase enzyme
. Mutation in the PHEX gene

Correct Answer & Explanation

. Mutation in the PHEX gene

Explanation

The clinical and laboratory picture (normal calcium, normal PTH, low phosphate) is classic for X-linked hypophosphatemic rickets (XLHR), the most common form of heritable rickets. It is caused by a mutation in the PHEX gene, which leads to overactivity of FGF23, resulting in profound renal phosphate wasting and impaired bone mineralization. Nutritional rickets would typically present with low/normal calcium and elevated PTH.

Question 12916

Topic: 1. General Principles & Basic Science

A 2-year-old girl is brought in by her parents for significant bowing of both legs.

You are trying to differentiate between physiologic genu varum and infantile Blount disease. Which of the following radiographic parameters is most diagnostic of infantile Blount disease?

. Metaphyseal-diaphyseal angle (Drennan's angle) of 18 degrees
. Mechanical axis passing through zone 3
. Tibiofemoral angle of 15 degrees varus
. Symmetrical flaring of the distal femoral and proximal tibial metaphyses
. Medial compartmental joint space narrowing

Correct Answer & Explanation

. Metaphyseal-diaphyseal angle (Drennan's angle) of 18 degrees

Explanation

Drennan's metaphyseal-diaphyseal angle (MDA) is critical in differentiating physiologic bowing from infantile Blount disease. An angle >16 degrees has a very high positive predictive value for Blount disease. An angle <10 degrees strongly suggests physiologic bowing.

Question 12917

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with an acute onset limp, severe right hip pain, and a temperature of 38.6°C. He refuses to bear weight on the right leg. Laboratory evaluation reveals an ESR of 45 mm/hr and a WBC count of 13,500/mm³. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 73%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis include non-weight-bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. This patient meets all four criteria, which yields a 93% predicted probability of septic arthritis.

Question 12918

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with a 3-day history of right hip pain and refusal to bear weight. His temperature is 38.6°C (101.5°F). Labs reveal a WBC count of 14,000/mm³, ESR of 45 mm/hr, and a CRP of 3.5 mg/dL. According to the Kocher criteria, what is the probability that this child has septic arthritis?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The child has 3 of the 4 classic Kocher criteria (fever, inability to bear weight, ESR >40). The probability of septic arthritis with 3 criteria is approximately 93%.

Question 12919

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents to the emergency department with a 2-day history of right hip pain, a severe limp, and a temperature of 38.9°C. He refuses to bear weight on the right leg. Laboratory evaluation reveals a WBC count of 14,000/mm³ and an ESR of 55 mm/hr. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 3% - 5%
. 25% - 35%
. 50% - 60%
. 93% - 99%
. 100%

Correct Answer & Explanation

. 93% - 99%

Explanation

The patient meets all 4 Kocher criteria (non-weight-bearing, temperature > 38.5°C, WBC > 12,000/mm³, ESR > 40 mm/hr). The presence of all four criteria carries a 93% to 99% predictive probability for septic arthritis.

Question 12920

Topic: Biology, Genetics & Bone Healing

What is the primary mediator of the initial inflammatory phase of secondary bone healing, which peaks at 24 hours post-fracture?

. Bone Morphogenetic Protein-2 (BMP-2)
. Interleukin-1 (IL-1) and Interleukin-6 (IL-6)
. Transforming Growth Factor-beta (TGF-beta)
. Platelet-Derived Growth Factor (PDGF)
. Fibroblast Growth Factor (FGF)

Correct Answer & Explanation

. Interleukin-1 (IL-1) and Interleukin-6 (IL-6)

Explanation

Pro-inflammatory cytokines, specifically IL-1, IL-6, and TNF-alpha, are the primary mediators of the initial inflammatory phase of secondary bone healing. They recruit inflammatory cells and promote angiogenesis. BMPs are involved later in the cascade to promote osteogenesis.

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