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1. General Principles & Basic Science MCQs

Practice Set 665 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 13281

Topic: Infection, Pharmacology & VTE

Prosthetic joint infections are characterized by bacterial formation of a protective biofilm. The extracellular polymeric substance (EPS) that comprises the bulk of this biofilm and shields bacteria from both the host immune system and antimicrobial agents is primarily composed of:

. Peptidoglycan
. Teichoic acid
. Hyaluronic acid
. Polysaccharides
. Lipopolysaccharides

Correct Answer & Explanation

. Polysaccharides

Explanation

The biofilm extracellular polymeric substance (EPS) is primarily composed of polysaccharides, along with proteins, extracellular DNA, and lipids. This complex matrix physically shields the bacteria embedded within it, requiring significantly higher minimum inhibitory concentrations of antibiotics to eradicate.

Question 13282

Topic: 1. General Principles & Basic Science

When modifying the design of a cortical bone screw to maximize its pullout strength, which of the following geometric alterations would be most effective?

. Decreasing the outer diameter
. Increasing the inner (root) diameter
. Decreasing the thread pitch
. Decreasing the thread depth
. Increasing the cannulation diameter

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength of a screw is proportional to the outer diameter, the length of thread engagement, and inversely proportional to the thread pitch. Decreasing the thread pitch (meaning more threads per inch) increases the amount of thread contact with bone, thereby increasing pullout strength. Increasing the inner diameter or decreasing the outer diameter would decrease pullout strength.

Question 13283

Topic: Biology, Genetics & Bone Healing

Which of the following fixation constructs is most heavily reliant on cutting cone remodeling (primary bone healing) for the resolution of the fracture?

. Casting
. Intramedullary nailing
. Bridge plating
. Dynamic compression plating
. Circular external fixation

Correct Answer & Explanation

. Dynamic compression plating

Explanation

Primary (direct) bone healing occurs under conditions of absolute stability without callus formation and relies on cutting cones of osteoclasts followed by osteoblasts bridging the fracture gap. Dynamic compression plating provides the absolute stability required for primary bone healing. The other options provide relative stability and heal via secondary bone healing (callus formation).

Question 13284

Topic: 1. General Principles & Basic Science

In evaluating a diagnostic test for periprosthetic joint infection, which of the following statistical parameters will universally increase if the test is applied to a tertiary referral population with a significantly higher disease prevalence compared to the general population?

. Sensitivity
. Specificity
. Positive predictive value
. Positive likelihood ratio
. Negative likelihood ratio

Correct Answer & Explanation

. Positive predictive value

Explanation

Positive Predictive Value (PPV) is inherently dependent on the prevalence of the disease in the population being tested. As prevalence increases, PPV increases, and Negative Predictive Value (NPV) decreases. Sensitivity, specificity, and likelihood ratios are intrinsic properties of the test and do not change with disease prevalence.

Question 13285

Topic: 1. General Principles & Basic Science

During prolonged standing, normal human articular cartilage relies primarily on which form of lubrication to prevent surface-to-surface wear under high-load, low-speed conditions?

. Elastohydrodynamic lubrication
. Boundary lubrication
. Weeping lubrication
. Hydrodynamic lubrication
. Boosted lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication is driven by lubricin (PRG4) adhering to the articular surfaces, preventing direct contact. It is the primary lubrication mechanism under high-load and low-velocity conditions (such as standing). Elastohydrodynamic and weeping lubrication predominate during dynamic joint motion.

Question 13286

Topic: 1. General Principles & Basic Science

Following a clean transection and meticulous microsurgical epineural repair of a peripheral nerve, axonal sprouting occurs. Once these regenerating sprouts cross the repair site and enter the distal endoneurial tubes, what is their approximate rate of growth?

. 0.2 mm/day
. 1 mm/day
. 3 mm/day
. 5 mm/day
. 10 mm/day

Correct Answer & Explanation

. 1 mm/day

Explanation

After Wallerian degeneration clears the distal nerve segment, regenerating axons grow down the endoneurial tubes at a rate of approximately 1 mm per day (or about 1 inch per month) under optimal conditions.

Question 13287

Topic: 1. General Principles & Basic Science

A 35-year-old carpenter sustains a zone II flexor tendon laceration and undergoes primary repair. At what time point post-operatively does the repaired tendon normally reach its lowest ultimate tensile strength?

. 1 to 2 days
. 5 to 7 days
. 14 to 21 days
. 4 weeks
. 6 weeks

Correct Answer & Explanation

. 5 to 7 days

Explanation

Following primary tendon repair, the strength of the repair decreases during the inflammatory phase due to collagenase activity and reaches its lowest point around 5 to 7 days (the transition from the inflammatory to the fibroblastic phase). Controlled passive motion protocols must carefully navigate this period of mechanical vulnerability.

Question 13288

Topic: Biomechanics & Biomaterials
In modern total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is routinely utilized. Increasing the radiation dose during the manufacturing of the polyethylene achieves which of the following biomechanical tradeoffs?
. Increases wear resistance but decreases fatigue strength
. Increases both wear resistance and fatigue strength
. Decreases wear resistance but increases fracture toughness
. Increases wear resistance but increases ultimate tensile strength
. Decreases oxidation resistance and increases fatigue strength

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Irradiating ultra-high molecular weight polyethylene (UHMWPE) creates free radicals that recombine to form cross-links between polymer chains. This drastically increases wear resistance (reducing osteolysis) but simultaneously decreases mechanical properties such as fatigue strength, ultimate tensile strength, and fracture toughness.

Question 13289

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this medication?
. Directly inhibits thrombin (Factor IIa)
. Competitively inhibits vitamin K epoxide reductase
. Directly inhibits Factor Xa
. Binds antithrombin III to accelerate its action
. Inhibits platelet aggregation via ADP receptor blockade

Correct Answer & Explanation

. Directly inhibits Factor Xa

Explanation

Rivaroxaban and apixaban are oral direct Factor Xa inhibitors. They act independently of antithrombin III to block the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin inhibitor. Warfarin inhibits vitamin K epoxide reductase. Heparins function via antithrombin III.

Question 13290

Topic: 1. General Principles & Basic Science

Which of the following best describes the classical sequence of incorporation for a structural cortical bone graft compared to a cancellous bone graft?

. It immediately provides osteoinductive growth factors to stimulate rapid bone formation.
. It undergoes rapid revascularization via creeping substitution without losing structural integrity.
. It primarily heals via endochondral ossification with a cartilaginous intermediate.
. It undergoes initial osteoclastic resorption, leading to transient mechanical weakening before osteoblastic deposition.
. It becomes fully incorporated and mechanically stronger within 4 weeks of implantation.

Correct Answer & Explanation

. It undergoes initial osteoclastic resorption, leading to transient mechanical weakening before osteoblastic deposition.

Explanation

Cortical bone grafts incorporate via creeping substitution, but unlike cancellous grafts (which undergo early osteoblastic bone apposition on existing trabeculae), cortical grafts first undergo osteoclastic resorption to widen Haversian canals. This makes cortical grafts transiently weaker than their initial state before osteoblasts deposit new bone.

Question 13291

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is utilized in spine and trauma surgery for its osteoinductive properties. Once rhBMP-2 binds to its target cell surface receptor, which intracellular signaling pathway is primarily activated to upregulate osteoblast differentiation?

. Wnt/beta-catenin pathway
. Hedgehog (Ihh) pathway
. SMAD 1/5/8 pathway
. SMAD 2/3 pathway
. Notch signaling pathway

Correct Answer & Explanation

. SMAD 1/5/8 pathway

Explanation

BMPs belong to the TGF-beta superfamily. When osteoinductive BMPs (like BMP-2 and BMP-7) bind to their serine/threonine kinase receptors, they trigger the phosphorylation of receptor-regulated SMADs 1, 5, and 8. These complex with SMAD 4, enter the nucleus, and upregulate the transcription factor Runx2, driving osteoblast differentiation. SMAD 2/3 is associated with the TGF-beta/Activin pathway.

Question 13292

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a highly organized extracellular matrix to withstand various mechanical loads. Which zone of articular cartilage is characterized by collagen fibrils oriented parallel to the joint surface, providing the highest resistance to shear forces?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains densely packed, fine collagen fibrils (primarily Type II) oriented parallel to the articular surface. This specialized structure provides high tensile stiffness and represents the primary defense against shear stresses applied to the joint.

Question 13293

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal lesion of the distal femur without sclerotic margins. A biopsy confirms Giant Cell Tumor (GCT). If treated with Denosumab prior to surgical intervention, what is its primary mechanism of action?

. Inhibits RANKL, decreasing osteoclast-like giant cell activity
. Binds RANK receptor on stromal cells, inducing apoptosis
. Inhibits VEGF, decreasing tumor angiogenesis
. Cross-links DNA strands, preventing tumor cell replication
. Stimulates osteoprotegerin (OPG) production directly

Correct Answer & Explanation

. Inhibits RANKL, decreasing osteoclast-like giant cell activity

Explanation

Denosumab is a monoclonal antibody that binds to RANKL. In GCT, the neoplastic stromal cells overexpress RANKL, which recruits and activates the reactive, bone-resorbing multinucleated giant cells. By inhibiting RANKL, denosumab reduces the giant cell population, decreasing tumor-associated osteolysis and facilitating intralesional curettage.

Question 13294

Topic: Biology, Genetics & Bone Healing

During anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone (BTB) autograft, the bone plugs heal to the host bone tunnels via which of the following primary biologic mechanisms?

. Creeping substitution
. Direct Sharpey fiber formation
. Endochondral ossification
. Membranous ossification
. Fibrocartilaginous zone formation

Correct Answer & Explanation

. Creeping substitution

Explanation

Bone-to-bone healing in a BTB graft occurs via creeping substitution, a process where osteoclasts resorb the graft bone and osteoblasts lay down new woven bone. This leads to earlier rigid fixation at approximately 6 weeks, compared to soft tissue grafts (e.g., hamstrings) which heal to the bone tunnel via a slower fibrovascular interface (Sharpey fibers) taking 8-12 weeks.

Question 13295

Topic: 1. General Principles & Basic Science

In normal adult articular cartilage, which zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and chondrocytes arranged in distinct vertical columns?

. 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 provides the greatest resistance to compressive forces. It has the highest proteoglycan content, the lowest water content, and features chondrocytes arranged in vertical columns (perpendicular to the joint surface). The superficial zone has the highest water content and collagen fibers oriented parallel to the joint surface to resist shear forces.

Question 13296

Topic: Biology, Genetics & Bone Healing

Following a diaphyseal femur fracture treated with a relatively stable but not absolutely rigid construct (e.g., intramedullary nail), secondary fracture healing occurs. Which phase of this healing process is fundamentally characterized by the conversion of woven bone to lamellar bone according to Wolff's law?

. Inflammatory phase
. Soft callus formation
. Hard callus formation
. Remodeling phase
. Hematoma organization

Correct Answer & Explanation

. Remodeling phase

Explanation

Secondary fracture healing consists of inflammation, soft callus (cartilage) formation, hard callus (woven bone) formation, and remodeling. The remodeling phase takes months to years and is driven by coupled osteoclast and osteoblast activity acting according to Wolff's law, where mechanically inferior woven bone is gradually replaced by mechanically robust lamellar bone along lines of stress.

Question 13297

Topic: 1. General Principles & Basic Science

A 45-year-old male sustains a severe crush injury to his lower extremity. The vascular surgeon restores perfusion after 7 hours of ischemia. To utilize the Mangled Extremity Severity Score (MESS) effectively for amputation decision-making, which of the following accurately describes how the ischemia scoring component is calculated in this patient?

. Ischemia time does not impact the score if a palpable pulse is restored
. Points for ischemia are doubled if the ischemic time exceeds 6 hours
. A strict cutoff of 4 hours mandates automatic amputation regardless of the score
. Ischemia scoring only applies to patients over the age of 50
. Points are assigned based solely on the mechanism of injury, not time

Correct Answer & Explanation

. Points for ischemia are doubled if the ischemic time exceeds 6 hours

Explanation

In the Mangled Extremity Severity Score (MESS), the variables include skeletal/soft-tissue injury, limb ischemia, shock, and age. For the limb ischemia component, the points are doubled if the ischemic time exceeds 6 hours. A total MESS score of 7 or higher historically correlates with a high likelihood of eventual amputation.

Question 13298

Topic: 1. General Principles & Basic Science

During a primary repair of a Zone II flexor digitorum profundus (FDP) laceration, an epitenon (epitendinous) suture is placed circumferentially around the repair site in addition to a multistrand core suture. What is the primary biomechanical advantage of adding the epitenon suture?

. It provides the primary resistance to gap formation during the first 3 days
. It increases the strength of the repair by 10-30% and smooths the repair site
. It promotes intrinsic healing by carrying vascularized tissue into the repair
. It reduces the risk of triggering by acting as a pulley
. It shifts the weakest point of the tendon repair from the knot to the tendon substance

Correct Answer & Explanation

. It increases the strength of the repair by 10-30% and smooths the repair site

Explanation

The addition of a running epitenon suture over a core suture provides two major benefits in flexor tendon repair: it smooths the surface to reduce gliding resistance (preventing snagging on the pulleys) and it significantly increases the overall tensile strength of the repair, often by 10% to 30%, which helps prevent gap formation during early active rehabilitation protocols.

Question 13299

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones. Which of the following characteristics accurately describes the superficial (tangential) zone of normal adult articular cartilage?

. It contains the highest concentration of proteoglycans
. Collagen fibrils are oriented perpendicular to the joint surface
. It has the lowest water content of all the zones
. Collagen fibrils are oriented parallel to the joint surface to resist shear forces
. Chondrocytes are large, spherical, and arranged in distinct vertical columns

Correct Answer & Explanation

. Collagen fibrils are oriented parallel to the joint surface to resist shear forces

Explanation

The superficial (tangential) zone of articular cartilage is the thinnest layer but is critical for resisting shear stress. It is characterized by having the highest water content, the lowest concentration of proteoglycans, and flattened chondrocytes. Most importantly, its Type II collagen fibrils are oriented parallel to the joint surface to withstand sheer forces. The deep zone features perpendicular collagen, highest proteoglycan content, and columnar chondrocytes.

Question 13300

Topic: Infection, Pharmacology & VTE

A 4-year-old child is brought to the ED refusing to walk on her right leg. She has a temperature of 38.8°C (101.8°F). Laboratory tests show an ESR of 45 mm/h, a WBC count of 13,000/mm^3, and a CRP of 3.5 mg/dL. According to the classic Kocher criteria and subsequent validated models (e.g., Caird), what is the approximate probability that this child has septic arthritis of the hip rather than transient synovitis?

. Less than 10%
. 25 - 35%
. 50 - 60%
. 70 - 80%
. Greater than 90%

Correct Answer & Explanation

. Greater than 90%

Explanation

The classic Kocher criteria for differentiating septic arthritis from transient synovitis include: 1) Non-weight bearing, 2) ESR > 40 mm/hr, 3) Fever > 38.5°C, and 4) WBC > 12,000. Having 4 of 4 predictors yields a 99% probability of septic arthritis. Additionally, Caird et al. added CRP > 2.0 mg/dL as an independent predictor. Since this patient meets all 4 classic criteria plus the CRP criterion, the probability is > 90% (specifically, historically quoted as 99%).

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