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1. General Principles & Basic Science MCQs

Practice Set 664 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 13261

Topic: Surgical Anatomy & Approaches
A patient sustains a closed midshaft humerus fracture with an associated radial nerve palsy. An EMG at 3 weeks shows fibrillation potentials. Based on the Sunderland classification, an injury involving disruption of axons and endoneurium, but with an intact perineurium and epineurium, is classified as:
. Grade I
. Grade II
. Grade III
. Grade IV
. Grade V

Correct Answer & Explanation

. Grade III

Explanation

A Sunderland Grade III nerve injury involves disruption of the axon and endoneurium while preserving the perineurium and epineurium. Recovery is unpredictable and may result in intrafascicular scarring.

Question 13262

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a leading cause of prosthetic joint infections due to its ability to form a robust biofilm. Which of the following components is primarily responsible for facilitating intercellular adhesion within this biofilm?

. Protein A
. Polysaccharide intercellular adhesin (PIA)
. Alpha-toxin
. Panton-Valentine leukocidin (PVL)
. Teichoic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis produces polysaccharide intercellular adhesin (PIA), which is crucial for cell-to-cell adhesion and structural integrity of the biofilm matrix, allowing evasion of host immune defenses.

Question 13263

Topic: 1. General Principles & Basic Science

When utilizing a cortical structural allograft for large bone defects, the graft incorporates via a process known as creeping substitution. Which statement best describes the biomechanical behavior of cortical allografts during this process?

. Rapid vascularization leading to immediate mechanical weakening
. Slow vascularization with initial preservation of mechanical strength
. Rapid osteoinduction driven exclusively by innate bone morphogenetic proteins
. Delayed osteogenesis secondary to acute immune rejection
. Immediate osteoconduction leading to an initial increase in stiffness

Correct Answer & Explanation

. Slow vascularization with initial preservation of mechanical strength

Explanation

Cortical allografts incorporate slowly, initially maintaining their structural integrity and mechanical strength. Over time, they undergo creeping substitution, during which they may actually become temporarily weaker as osteoclasts resorb the graft before new bone formation.

Question 13264

Topic: Biomechanics & Biomaterials

Mixing stainless steel and titanium implants within the same surgical site increases the risk of galvanic corrosion. Which of the following factors is the primary driving force for this specific type of corrosion?

. Differences in the elastic modulus between the two metals
. Friction at the metal-to-metal interface
. Differences in the electrochemical potential of the metals
. Release of reactive oxygen species from local macrophages
. Fatigue failure of the passivation layer on the implants

Correct Answer & Explanation

. Differences in the electrochemical potential of the metals

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are connected in a conductive fluid (body fluids). The metal with the lower electrochemical potential acts as an anode and undergoes accelerated corrosion.

Question 13265

Topic: Infection, Pharmacology & VTE
According to AAOS clinical practice guidelines, rivaroxaban is frequently used for DVT prophylaxis following total joint arthroplasty. What is the primary pharmacological mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Factor Xa inhibitor
. Antithrombin III activator
. Platelet ADP receptor antagonist

Correct Answer & Explanation

. Factor Xa inhibitor

Explanation

Rivaroxaban is an oral, direct and highly selective Factor Xa inhibitor. By blocking Factor Xa, it interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade.

Question 13266

Topic: Biology, Genetics & Bone Healing
The annulus fibrosus of the intervertebral disc is engineered to resist immense multidirectional tensile forces. Which type of collagen predominantly constitutes the outer concentric lamellae of the annulus fibrosus?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type IX collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The outer annulus fibrosus consists predominantly of Type I collagen, which is optimized to withstand high tensile forces. Conversely, the nucleus pulposus is rich in Type II collagen to resist compressive loads.

Question 13267

Topic: Biology, Genetics & Bone Healing

In advanced rheumatoid arthritis, hyperplastic synovial pannus progressively destroys articular cartilage. Which specific cell type within the pannus is the primary source of matrix metalloproteinases (MMPs) responsible for this degradation?

. CD4+ T lymphocytes
. Fibroblast-like synoviocytes
. B lymphocytes
. Neutrophils
. Osteoclasts

Correct Answer & Explanation

. Fibroblast-like synoviocytes

Explanation

Fibroblast-like synoviocytes are key effector cells in the rheumatoid pannus. Under inflammatory stimulation, they produce massive amounts of MMPs and cathepsins that actively degrade the articular cartilage matrix.

Question 13268

Topic: Infection, Pharmacology & VTE

A 60-year-old diabetic male presents with rapidly spreading erythema, severe pain out of proportion to exam, and crepitus in his lower leg. Surgical exploration reveals dishwater-like fluid. Type I necrotizing fasciitis, the most common variant, is typically caused by:

. Monomicrobial Group A Streptococcus
. Monomicrobial Clostridium perfringens
. Polymicrobial mixture of aerobes and anaerobes
. Methicillin-resistant Staphylococcus aureus (MRSA)
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Polymicrobial mixture of aerobes and anaerobes

Explanation

Type I necrotizing fasciitis is a synergistic polymicrobial infection involving both aerobic and anaerobic bacteria. It most commonly affects older adults with multiple comorbidities, such as diabetes mellitus.

Question 13269

Topic: Biology, Genetics & Bone Healing

Teriparatide is administered for the treatment of severe osteoporosis in select patients. What is the precise mechanism of action by which this drug improves bone mineral density?

. Inhibition of osteoclast action via RANKL blockade
. Direct stimulation of osteoblast activity via PTH receptor agonism
. Inhibition of cathepsin K enzymatic activity
. Selective estrogen receptor modulation
. Binding to hydroxyapatite and inducing osteoclast apoptosis

Correct Answer & Explanation

. Direct stimulation of osteoblast activity via PTH receptor agonism

Explanation

Teriparatide is a recombinant fragment of parathyroid hormone (PTH 1-34). When administered intermittently, it possesses an anabolic effect by directly stimulating osteoblast activity and bone formation.

Question 13270

Topic: 1. General Principles & Basic Science
During the reparative phase of tendon healing, fibroblasts rapidly synthesize new extracellular matrix to bridge the defect. Which type of collagen is laid down initially in the highest concentration before remodeling occurs?
. Type I
. Type II
. Type III
. Type V
. Type X

Correct Answer & Explanation

. Type III

Explanation

During the initial repair phase of tendon healing, Type III collagen is produced in large quantities by fibroblasts. It forms a disorganized, mechanically weak matrix that is eventually replaced by the stronger, longitudinally oriented Type I collagen during the remodeling phase.

Question 13271

Topic: Infection, Pharmacology & VTE

During the administration of a regional nerve block, a patient inadvertently receives an intravascular injection of bupivacaine and subsequently goes into cardiac arrest. Alongside standard ACLS protocols, what is the most appropriate specific antidote for this local anesthetic systemic toxicity (LAST)?

. Intravenous flumazenil
. High-dose epinephrine boluses
. Intravenous lipid emulsion therapy
. Calcium gluconate infusion
. Sodium bicarbonate bolus

Correct Answer & Explanation

. Intravenous lipid emulsion therapy

Explanation

Intravenous lipid emulsion therapy (Intralipid) is the primary specific rescue treatment for bupivacaine-induced cardiac toxicity. The lipid emulsion creates a "lipid sink" that sequesters the highly lipophilic local anesthetic molecules away from cardiac tissue.

Question 13272

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum tissue strain tolerated by lamellar bone formation during fracture healing?

. 2%
. 10%
. 15%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory postulates that specific tissues tolerate specific maximum strain levels before failing. For lamellar bone to form, the strain must be less than 2%. This is the principle behind primary bone healing, which requires absolute stability. Woven bone can tolerate up to 10% strain, cartilage up to 30%, and granulation tissue can tolerate up to 100% strain.

Question 13273

Topic: Biomechanics & Biomaterials

What specific element is added to 316L stainless steel orthopedic implants to increase resistance to pitting corrosion and crevice corrosion in the chloride-rich environment of the human body?

. Carbon
. Molybdenum
. Nickel
. Chromium
. Vanadium

Correct Answer & Explanation

. Molybdenum

Explanation

Molybdenum (usually 2-3%) is added to 316L stainless steel specifically to enhance resistance to pitting and crevice corrosion. Chromium is added to provide a passivating surface oxide layer. Nickel is used to stabilize the austenitic crystal structure at room temperature.

Question 13274

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials has a Young's modulus most closely matching that of cortical bone?

. Titanium alloy (Ti-6Al-4V)
. Cobalt-chromium alloy
. 316L Stainless steel
. Polyetheretherketone (PEEK)
. Alumina ceramic

Correct Answer & Explanation

. Polyetheretherketone (PEEK)

Explanation

Cortical bone has a Young's modulus of approximately 15-20 GPa. Polyetheretherketone (PEEK) has a modulus of around 3-4 GPa, and carbon-fiber-reinforced PEEK can be tailored to ~18 GPa, making it nearly isoelastic with cortical bone. This minimizes stress shielding compared to Titanium (~110 GPa), Stainless steel (~200 GPa), and CoCr (~240 GPa).

Question 13275

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach for an acetabular fracture, significant arterial hemorrhage occurs near the superior pubic ramus. This is most likely due to an iatrogenic injury of an anastomosis between which two vascular systems?

. Internal iliac and internal pudendal
. External iliac and obturator
. Superior gluteal and inferior gluteal
. Femoral and deep circumflex iliac
. Inferior epigastric and superficial epigastric

Correct Answer & Explanation

. External iliac and obturator

Explanation

The 'corona mortis' is a critical vascular anastomosis between the obturator vessels (internal iliac system) and external iliac (or inferior epigastric) vessels. It traverses the posterior aspect of the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis and is at high risk of iatrogenic injury during anterior pelvic approaches.

Question 13276

Topic: Infection, Pharmacology & VTE

A 2-year-old child presents with a limp, low-grade fever, and refusal to bear weight. Laboratory studies show mild elevation of ESR and CRP. Blood cultures are negative at 48 hours. Joint aspiration yields synovial fluid with 45,000 WBCs/mm3. If special culture techniques or PCR were utilized, what is the most likely pathogen to be identified?

. Staphylococcus aureus
. Haemophilus influenzae type B
. Kingella kingae
. Streptococcus pneumoniae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is now recognized as the most common cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. It often presents with milder systemic symptoms compared to S. aureus. It is a fastidious Gram-negative organism that is notoriously difficult to culture on standard solid media, often requiring inoculation into liquid blood culture vials or molecular detection via PCR.

Question 13277

Topic: Biomechanics & Biomaterials

A 45-year-old patient undergoes open reduction and internal fixation of a distal radius fracture using a titanium plate and stainless steel screws. Which of the following forms of corrosion is most likely to occur at the implant interface?

. 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 contact within a conductive fluid (such as serum or interstitial fluid), creating an electrochemical cell. This leads to the accelerated corrosion of the less noble metal (in this case, stainless steel). Mixing metals like titanium and stainless steel should generally be avoided in orthopedics to prevent this phenomenon.

Question 13278

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone possesses the highest concentration of proteoglycans and the largest diameter collagen fibrils oriented perpendicular to the joint surface?

. 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 is characterized by the highest concentration of proteoglycans and the largest diameter type II collagen fibrils, which are oriented radially (perpendicular) to the joint surface. This structure provides maximal resistance to compressive forces.

Question 13279

Topic: Biology, Genetics & Bone Healing

A 52-year-old woman presents with diffuse bone pain and muscle weakness. Radiographs demonstrate bilateral symmetric radiolucent lines perpendicular to the cortex in her femoral necks. Laboratory evaluation reveals low serum calcium, low phosphorus, elevated alkaline phosphatase, and low 25-hydroxyvitamin D. What is the primary underlying defect in this condition?

. Failure of osteoclast-mediated bone resorption
. Defective mineralization of newly formed osteoid
. Abnormal cross-linking of type I collagen
. Gain-of-function mutation in the FGFR3 gene
. Excessive disorganized bone remodeling

Correct Answer & Explanation

. Defective mineralization of newly formed osteoid

Explanation

The clinical picture, lab profile, and radiographic findings (Looser zones/pseudofractures) are classic for osteomalacia. Osteomalacia is defined by defective mineralization of newly formed osteoid, most commonly due to severe vitamin D deficiency in adults.

Question 13280

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently used in total joint arthroplasty to reduce perioperative blood loss. Which of the following best describes its primary mechanism of action?
. Direct inhibition of Factor Xa
. Competitive inhibition of plasminogen activation
. Irreversible inhibition of cyclooxygenase
. Direct activation of antithrombin III
. Stimulation of von Willebrand factor release

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is an antifibrinolytic agent that acts by competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin and being activated into plasmin, thereby inhibiting fibrinolysis and stabilizing clots.

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