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1. General Principles & Basic Science MCQs

Practice Set 220 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 4381

Topic: 1. General Principles & Basic Science

Which of the following best describes the predominant collagen type found in normal articular cartilage and its primary biomechanical function?

. Type I collagen; provides compressive stiffness
. Type II collagen; provides compressive stiffness
. Type II collagen; provides tensile strength
. Type IX collagen; regulates fluid permeability
. Type X collagen; provides shear strength

Correct Answer & Explanation

. Type II collagen; provides compressive stiffness

Explanation

Type II collagen comprises 90-95% of the collagen in normal articular cartilage. The highly cross-linked Type II collagen fibril network functions primarily to resist tensile forces and constrain the swelling pressure generated by proteoglycans (aggrecan). Proteoglycans and water are responsible for providing compressive stiffness, not the collagen itself.

Question 4382

Topic: 1. General Principles & Basic Science
Biochemical changes in articular cartilage differ significantly between normal physiologic aging and the onset of early osteoarthritis (OA). Which of the following biochemical alterations is characteristic of early osteoarthritis, distinguishing it from normal aging cartilage?
. Decreased total water content
. Increased total water content
. Increased proportion of keratin sulfate relative to chondroitin sulfate
. Decreased matrix metalloproteinase (MMP) activity
. Increased concentration of aggregated proteoglycans

Correct Answer & Explanation

. Increased total water content

Explanation

In early osteoarthritis, there is a disruption of the Type II collagen fibril network. This breakdown reduces the constraint on the hydrophilic proteoglycan aggregates, allowing them to swell, resulting in an increased total water content. In contrast, normal aging cartilage is characterized by a decreased total water content, smaller proteoglycan size, and an increased ratio of keratin sulfate to chondroitin sulfate.

Question 4383

Topic: 1. General Principles & Basic Science

During the surgical repair of a Zone II flexor tendon laceration, the surgeon must carefully preserve the intrinsic vascular supply to the tendon. Which of the following structures provides the primary intrinsic blood supply to the flexor tendons within the digital fibro-osseous sheath?

. Vincula brevia and vincula longa
. Direct branches from the common digital arteries
. Synovial fluid diffusion
. Branches from the superficial palmar arch
. Musculotendinous junction vessels

Correct Answer & Explanation

. Vincula brevia and vincula longa

Explanation

Within the digital sheath, flexor tendons receive their intrinsic blood supply through the vincula (brevia and longa), which carry vessels from the digital arteries to the dorsal aspect of the tendons. Synovial diffusion provides nutrition but is not the structural vascular supply.

Question 4384

Topic: 1. General Principles & Basic Science

In the pathogenesis of osteoarthritis, the articular cartilage undergoes progressive biochemical and structural degradation. Which of the following represents the earliest detectable biochemical alteration in osteoarthritic articular cartilage?

. Decrease in water content
. Increase in water content
. Increase in proteoglycan concentration
. Decrease in chondrocyte size
. Increase in Type II collagen production

Correct Answer & Explanation

. Increase in water content

Explanation

The earliest biochemical change in osteoarthritis is an increase in water content due to the disruption of the collagen network. This leads to swelling of the cartilage matrix and a subsequent decrease in proteoglycan concentration.

Question 4385

Topic: Biology, Genetics & Bone Healing

A partial-thickness articular cartilage laceration that does not penetrate the tidemark into the subchondral bone is observed incidentally during arthroscopy. Which of the following best describes the expected physiological healing response of this specific lesion?

. Robust regeneration via hyaline cartilage synthesis
. Complete filling with fibrocartilage via subchondral bleeding
. Little to no healing response due to lack of vascular access
. Extensive woven bone formation within the defect
. Rapid chondrocyte proliferation from the deep zone

Correct Answer & Explanation

. Little to no healing response due to lack of vascular access

Explanation

Partial-thickness cartilage injuries do not violate the subchondral bone and therefore do not access the marrow elements necessary for a hematoma or stem cell response. Consequently, they elicit little to no healing response due to the avascular nature of articular cartilage.

Question 4386

Topic: 1. General Principles & Basic Science

In the ultrastructural organization of articular hyaline cartilage, specific zones exhibit distinct cellular and matrix architectures. Which zone is characterized by the largest diameter collagen fibers oriented perpendicular to the joint surface and chondrocytes arranged in vertical columns?

. Superficial (Tangential) zone
. Middle (Transitional) zone
. Deep (Radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (Radial) zone

Explanation

The deep (radial) zone of articular cartilage contains chondrocytes arranged in vertical columns parallel to the collagen fibers, which are oriented perpendicularly to the subchondral bone. This zone possesses the largest diameter collagen fibers and the highest concentration of proteoglycans.

Question 4387

Topic: Surgical Anatomy & Approaches

During a primary THA using the direct anterior (Smith-Petersen) approach, the surgeon develops the internervous plane between the sartorius and the tensor fasciae latae. Which of the following nerves is at greatest risk of injury during this superficial dissection?

. Femoral nerve
. Superior gluteal nerve
. Lateral femoral cutaneous nerve
. Sciatic nerve
. Obturator nerve

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

The lateral femoral cutaneous nerve (LFCN) crosses the anterior thigh and is at significant risk of injury during the superficial dissection of the direct anterior approach. The internervous plane is between the sartorius (femoral n.) and the tensor fasciae latae (superior gluteal n.).

Question 4388

Topic: Infection, Pharmacology & VTE

A 72-year-old female undergoes a debridement, antibiotics, and implant retention (DAIR) procedure for an acute hematogenous periprosthetic joint infection of her total knee arthroplasty. Cultures yield methicillin-susceptible Staphylococcus aureus (MSSA). According to current infectious disease guidelines, what is the optimal timing for the initiation of adjunctive Rifampin therapy?

. Pre-operatively, as soon as the diagnosis is suspected
. Intra-operatively, administered intravenously prior to tourniquet inflation
. Immediately post-operatively along with the primary intravenous antibiotic
. Delayed for 3 to 5 days after initiation of appropriate intravenous therapy and surgical debridement
. Only after the patient transitions completely to an oral antibiotic regimen

Correct Answer & Explanation

. Delayed for 3 to 5 days after initiation of appropriate intravenous therapy and surgical debridement

Explanation

Rifampin is highly efficacious against staphylococcal biofilms. However, staphylococci can rapidly develop resistance to Rifampin if it is used as monotherapy or if it is initiated when the bacterial burden is very high (such as during active bacteremia or immediately pre/post-op before source control is achieved). Current guidelines recommend delaying the initiation of Rifampin for 3 to 5 days after the start of active intravenous therapy and surgical debridement. This reduces the bacterial burden and minimizes the risk of rapid resistance development.

Question 4389

Topic: Biomechanics & Biomaterials

A surgeon is preparing antibiotic-loaded bone cement (ALBC) to create a temporary articulating spacer for a two-stage exchange of an infected total knee arthroplasty. To maximize the elution profile of the antibiotics, which of the following preparation techniques is most appropriate?

. Vacuum-mixing the cement to decrease porosity
. Decreasing the ratio of antibiotic powder to cement powder to < 5% by weight
. Hand-mixing the cement and using high-dose antibiotics (>10% by weight)
. Increasing the liquid monomer-to-powder ratio significantly
. Pre-heating the monomer to accelerate the exothermic reaction

Correct Answer & Explanation

. Hand-mixing the cement and using high-dose antibiotics (>10% by weight)

Explanation

To maximize antibiotic elution from a PMMA spacer, the cement should be highly porous. This is best achieved by hand-mixing (non-vacuum mixing) the cement and adding high doses of antibiotics (typically >10% of the cement weight, e.g., 4 to 8 grams of antibiotic per 40-gram bag of PMMA). Vacuum mixing decreases porosity and improves mechanical strength, which is desired for definitive fixation but counterproductive for a temporary spacer where maximum antibiotic elution is the primary goal.

Question 4390

Topic: Infection, Pharmacology & VTE

Which of the following is considered an absolute contraindication for attempting a debridement, antibiotics, and implant retention (DAIR) procedure in a patient presenting with an acute periprosthetic joint infection?

. Symptom duration of 2 weeks
. Infection with Staphylococcus aureus
. Well-fixed, uncemented porous components
. Evidence of radiographic loosening of the prosthetic components
. Patient age greater than 85 years

Correct Answer & Explanation

. Evidence of radiographic loosening of the prosthetic components

Explanation

A loose prosthesis is an absolute contraindication for a DAIR procedure. Successful eradication of infection with implant retention requires components that are stably fixed to the bone. If a component is loose, the interface between the implant and bone is compromised, allowing biofilm and purulence to harbor in areas inaccessible to debridement, necessitating implant removal (1-stage or 2-stage exchange). Symptom duration < 3-4 weeks is an indication for DAIR, not a contraindication.

Question 4391

Topic: Infection, Pharmacology & VTE

Staphylococcal species are the most common pathogens in periprosthetic joint infections, largely due to their ability to form resilient biofilms. Which phase of biofilm formation is critically mediated by the synthesis of polysaccharide intercellular adhesin (PIA) via the icaADBC operon?

. Initial reversible attachment
. Irreversible adherence via microbial surface components recognizing adhesive matrix molecules (MSCRAMMs)
. Accumulation and maturation phase
. Quorum sensing activation
. Detachment and planktonic dispersion

Correct Answer & Explanation

. Accumulation and maturation phase

Explanation

Biofilm formation occurs in multiple stages: 1) Initial attachment, 2) Irreversible adherence (mediated by MSCRAMMs), 3) Accumulation and maturation, and 4) Detachment. The accumulation and maturation phase is characterized by cellular proliferation and the production of an extracellular polymeric substance (EPS) matrix. In staphylococci, a major component of this matrix is polysaccharide intercellular adhesin (PIA), which is synthesized by the products of the icaADBC operon.

Question 4392

Topic: Infection, Pharmacology & VTE

A patient is identified as a nasal carrier of methicillin-resistant Staphylococcus aureus (MRSA) during routine preoperative screening for a total hip arthroplasty. According to evidence-based protocols, which of the following is the most effective decolonization regimen to reduce the risk of surgical site infection?

. Oral Vancomycin for 5 days pre-operatively
. Intranasal mupirocin 2% ointment twice daily and daily chlorhexidine bathing for 5 days pre-operatively
. Intravenous Linezolid administered 24 hours prior to surgery
. A single preoperative dose of intranasal povidone-iodine alone
. Oral Rifampin and Doxycycline for 7 days pre-operatively

Correct Answer & Explanation

. Intranasal mupirocin 2% ointment twice daily and daily chlorhexidine bathing for 5 days pre-operatively

Explanation

The gold standard for MRSA decolonization prior to elective total joint arthroplasty is a 5-day regimen consisting of intranasal 2% mupirocin ointment applied twice daily coupled with daily bathing using chlorhexidine gluconate. This protocol has been shown in numerous studies to significantly decrease the MRSA carrier burden and reduce the incidence of postoperative periprosthetic joint infections.

Question 4393

Topic: 1. General Principles & Basic Science

When evaluating a patient with a suspected periprosthetic joint infection, an implant sonication protocol is utilized on the explanted prosthesis. What is the primary mechanism by which sonication improves microbiological yield compared to standard periprosthetic tissue cultures?

. It selectively lyses human macrophages to release intracellular bacteria
. It utilizes low-frequency ultrasound to physically dislodge and disperse bacteria embedded in the biofilm
. It neutralizes residual systemic antibiotics present in the synovial fluid
. It accelerates the reproductive cycle of slow-growing organisms like Cutibacterium acnes
. It provides immediate identification of antibiotic susceptibility patterns via acoustic resonance

Correct Answer & Explanation

. It utilizes low-frequency ultrasound to physically dislodge and disperse bacteria embedded in the biofilm

Explanation

Implant sonication involves placing the explanted prosthesis in a sterile fluid and applying low-frequency ultrasound. The acoustic cavitation physically disrupts and dislodges the bacterial biofilm from the surface of the implant, releasing the bacteria into a planktonic state in the fluid. This fluid is then cultured, significantly increasing the sensitivity and microbiological yield compared to standard tissue cultures, especially in patients who have received prior antibiotic therapy.

Question 4394

Topic: Biomechanics & Biomaterials

During a two-stage exchange for a periprosthetic joint infection, the surgeon prepares an articulating antibiotic-loaded polymethylmethacrylate (PMMA) spacer. To maximize the local elution of antibiotics, which of the following preparation techniques should be employed?

. Mixing the cement under a strong vacuum
. Increasing the ratio of liquid monomer to powder
. Hand-mixing the cement to increase porosity
. Using entirely pre-mixed commercial antibiotic bone cement
. Adding more than 10 grams of antibiotics per 40-gram bag of PMMA

Correct Answer & Explanation

. Hand-mixing the cement to increase porosity

Explanation

Hand-mixing cement increases its porosity, which significantly enhances the surface area and subsequent elution profile of the incorporated antibiotics. Vacuum mixing decreases porosity and therefore decreases antibiotic elution.

Question 4395

Topic: Infection, Pharmacology & VTE

Based on the results of the Oral Versus Intravenous Antibiotics for Bone and Joint Infection (OVIVA) trial, how does early transition to oral antibiotics compare to standard 6-week intravenous therapy in the management of periprosthetic joint infection?

. Oral therapy has a significantly higher failure rate for MRSA infections
. Intravenous therapy is superior for polymicrobial infections
. Oral therapy is non-inferior to intravenous therapy regarding treatment failure at 1 year
. Oral therapy leads to a higher rate of catheter-related complications
. Intravenous therapy provides superior eradication of biofilms on retained hardware

Correct Answer & Explanation

. Oral therapy is non-inferior to intravenous therapy regarding treatment failure at 1 year

Explanation

The OVIVA trial demonstrated that a highly bioavailable oral antibiotic regimen is non-inferior to intravenous antibiotics for the treatment of bone and joint infections when evaluating treatment failure at 1 year. This paradigm shift supports early transition to oral therapy in appropriately selected patients.

Question 4396

Topic: Biomechanics & Biomaterials

A 70-year-old diabetic male undergoes an aspiration of a painful TKA. Cultures grow Candida albicans. A two-stage exchange is planned. Which of the following is the most appropriate local antibiotic spacer strategy for this patient?

. Vancomycin and Tobramycin loaded PMMA
. Voriconazole or Amphotericin B loaded PMMA
. Caspofungin loaded PMMA
. Micafungin loaded calcium sulfate beads
. Fluconazole administered intravenously only with standard antibiotic PMMA

Correct Answer & Explanation

. Voriconazole or Amphotericin B loaded PMMA

Explanation

Fungal periprosthetic joint infections require local antifungal delivery to effectively clear the joint space. Voriconazole and Amphotericin B maintain their stability and elute effectively from polymethylmethacrylate (PMMA) cement, unlike echinocandins.

Question 4397

Topic: Infection, Pharmacology & VTE

Bacteria residing within a mature biofilm on a prosthetic joint surface exhibit high tolerance to systemic antibiotics. Which of the following mechanisms best explains this phenotypic antibiotic resistance?

. Rapid cell division rates within the deeper layers of the biofilm
. Acquisition of plasmid-mediated efflux pumps specific to the biofilm structure
. Transition of bacteria into a dormant, metabolically inactive stationary phase
. Increased permeability of the bacterial cell wall induced by the glycocalyx
. Spontaneous mutation of the ribosomal binding sites targeted by beta-lactams

Correct Answer & Explanation

. Transition of bacteria into a dormant, metabolically inactive stationary phase

Explanation

Within a mature biofilm, deep-layer bacteria transition into a metabolically dormant, stationary phase. Since many antibiotics (like beta-lactams) rely on active cell wall synthesis and metabolic activity, these dormant 'persister' cells become highly tolerant to antimicrobial therapy.

Question 4398

Topic: Infection, Pharmacology & VTE

A 70-year-old female undergoes a 2-stage revision for a Staphylococcus epidermidis periprosthetic joint infection. Her antibiotic regimen includes Rifampin, which is highly effective against biofilm-associated staphylococci. What is the mechanism of action of Rifampin?

. Inhibition of bacterial cell wall synthesis by binding penicillin-binding proteins
. Inhibition of DNA gyrase and topoisomerase IV
. Binding to the 50S ribosomal subunit to inhibit protein synthesis
. Inhibition of DNA-dependent RNA polymerase
. Disruption of bacterial cell membrane permeability

Correct Answer & Explanation

. Inhibition of DNA-dependent RNA polymerase

Explanation

Rifampin is a potent bactericidal agent against staphylococci in biofilms because it easily penetrates the biofilm matrix. It exerts its effect by inhibiting bacterial DNA-dependent RNA polymerase, thereby suppressing RNA synthesis.

Question 4399

Topic: Biomechanics & Biomaterials

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) for a structural articulating spacer in a two-stage revision, what is the maximum recommended weight of antibiotic powder per 40-gram bag of cement to avoid catastrophic mechanical failure?

. 1 gram
. 4 grams
. 8 grams
. 12 grams
. 20 grams

Correct Answer & Explanation

. 4 grams

Explanation

For structural PMMA spacers, adding more than 4 grams (approx 10%) of antibiotics per 40-gram bag significantly compromises the mechanical compressive strength of the cement. Non-structural beads can accommodate higher ratios up to 20% without clinical consequence.

Question 4400

Topic: Biomechanics & Biomaterials

When formulating an antibiotic-loaded polymethylmethacrylate (PMMA) spacer for a two-stage exchange arthroplasty, which of the following mixing techniques is recommended to maximize antibiotic elution?

. Vacuum mixing to reduce cement porosity
. Adding liquid antibiotics to the monomer phase prior to mixing
. Hand-mixing the cement in an open bowl at atmospheric pressure
. Increasing the ratio of liquid monomer to polymer powder
. Cooling the monomer to 4 degrees Celsius prior to vacuum mixing

Correct Answer & Explanation

. Hand-mixing the cement in an open bowl at atmospheric pressure

Explanation

Hand-mixing PMMA cement in an open bowl at atmospheric pressure increases the porosity of the cement mantle. This high porosity is undesirable for structural long-term fixation but is necessary to maximize the elution of antibiotics in a temporary spacer.

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