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1. General Principles & Basic Science MCQs

Practice Set 513 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 10241

Topic: 1. General Principles & Basic Science
In the cellular pathogenesis of osteoarthritis, which of the following classes of enzymes, upregulated by IL-1 and TNF-alpha, is primarily responsible for the early degradation of aggrecan in the articular cartilage?
. ADAMTS-4 and ADAMTS-5
. Cathepsin K and Cathepsin D
. Alkaline phosphatase
. Lysyl oxidase
. Matrix metalloproteinase-13 (MMP-13)

Correct Answer & Explanation

. ADAMTS-4 and ADAMTS-5

Explanation

ADAMTS-4 and ADAMTS-5 (aggrecanases) are primarily responsible for the cleavage and degradation of aggrecan, a crucial early event in osteoarthritis. MMP-13 is a collagenase that subsequently degrades the Type II collagen network.

Question 10242

Topic: Biomechanics & Biomaterials
Which of the following processing methods for ultra-high-molecular-weight polyethylene (UHMWPE) in total joint arthroplasty provides the greatest reduction in long-term oxidative degradation while maintaining wear resistance?
. Gamma irradiation in air followed by terminal sterilization
. Gamma irradiation in an inert gas environment followed by remelting
. Ethylene oxide sterilization without irradiation
. Gamma irradiation followed by cold sterilization
. Cross-linking with electron beam irradiation without thermal treatment

Correct Answer & Explanation

. Gamma irradiation in an inert gas environment followed by remelting

Explanation

Irradiation of UHMWPE creates cross-links that improve wear resistance but also creates free radicals that lead to oxidative degradation and embrittlement. Processing the polyethylene in an inert (oxygen-free) environment and subsequently thermally treating it (remelting or annealing) extinguishes the free radicals, significantly reducing long-term oxidative degradation while maintaining the wear properties of highly cross-linked polyethylene.

Question 10243

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with osteoporosis is started on Denosumab. This medication exerts its primary biological effect by directly interacting with which of the following molecular targets?

. RANK receptor on osteoclast precursors
. RANK ligand (RANKL) secreted by osteoblasts
. Osteoprotegerin (OPG) secreted by stromal cells
. Sclerostin secreted by osteocytes
. Carbonic anhydrase II within the osteoclast ruffled border

Correct Answer & Explanation

. RANK ligand (RANKL) secreted by osteoblasts

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). RANKL is produced by osteoblasts and stromal cells. By binding to RANKL, denosumab prevents RANKL from activating its receptor, RANK, on the surface of osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival, thereby decreasing bone resorption.

Question 10244

Topic: Biology, Genetics & Bone Healing

In evaluating bone graft substitutes for a posterolateral lumbar fusion, a surgeon selects Demineralized Bone Matrix (DBM). Which of the following accurately describes the bone-forming properties of DBM?

. Osteogenic, osteoconductive, and osteoinductive
. Osteoconductive and osteoinductive, but not osteogenic
. Osteoconductive only
. Osteoinductive only
. Osteogenic and osteoconductive, but not osteoinductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive, but not osteogenic

Explanation

Demineralized bone matrix (DBM) is an allograft derivative. It provides a scaffold for bone growth (osteoconductive) and contains bone morphogenetic proteins (BMPs) and other growth factors that stimulate mesenchymal stem cells to differentiate into osteoblasts (osteoinductive). However, because it is decellularized during processing, it lacks live bone-forming cells and is therefore NOT osteogenic.

Question 10245

Topic: Infection, Pharmacology & VTE

A 72-year-old patient requires emergent orthopedic surgery for a displaced femoral neck fracture. The patient is on Warfarin for atrial fibrillation, and the current INR is 3.5. Which of the following is the most rapid and effective method to reverse the coagulopathy prior to surgical intervention?

. Intravenous Vitamin K alone
. Fresh Frozen Plasma (FFP) and Intravenous Vitamin K
. Prothrombin Complex Concentrate (PCC) and Intravenous Vitamin K
. Cryoprecipitate and Subcutaneous Vitamin K
. Recombinant Factor VIIa

Correct Answer & Explanation

. Prothrombin Complex Concentrate (PCC) and Intravenous Vitamin K

Explanation

Prothrombin Complex Concentrate (PCC) is the most rapid and effective agent for reversing Warfarin-induced coagulopathy in an emergent setting. It contains concentrated Vitamin K-dependent factors (II, VII, IX, X). Intravenous Vitamin K is given simultaneously to provide sustained reversal once the half-life of the administered PCC factors expires. FFP requires thawing, necessitates large volumes (risk of fluid overload), and reverses INR more slowly than PCC.

Question 10246

Topic: 1. General Principles & Basic Science
In the peripheral nerve injury classification described by Sunderland, a third-degree injury (Sunderland III) is characterized by loss of continuity of the axon and which other neural structures?
. Myelin sheath only
. Endoneurium only
. Endoneurium and Perineurium
. Endoneurium, Perineurium, and Epineurium
. Myelin sheath and Epineurium

Correct Answer & Explanation

. Endoneurium and Perineurium

Explanation

Sunderland classification: Type I is neuropraxia (myelin injury, intact axon). Type II is axonotmesis (axon disrupted, all connective tissues intact). Type III is disruption of the axon and the endoneurium, but the perineurium and epineurium remain intact. Type IV is disruption of the axon, endoneurium, and perineurium (only epineurium intact). Type V is neurotmesis (complete transection).

Question 10247

Topic: Physiology & Rehabilitation

During normal human gait, the center of mass reaches its highest vertical displacement at which phase of the gait cycle?

. Heel strike
. Mid-stance
. Toe-off
. Mid-swing
. Deceleration

Correct Answer & Explanation

. Mid-stance

Explanation

During the gait cycle, the body's center of mass undergoes a sinusoidal vertical displacement. It reaches its highest point during mid-stance (when the body passes directly over the supporting limb) and its lowest point during double limb support (which occurs around heel strike of the leading limb and toe-off of the trailing limb).

Question 10248

Topic: Infection, Pharmacology & VTE
A 55-year-old patient undergoing a total knee arthroplasty is prescribed Enoxaparin for deep vein thrombosis (DVT) prophylaxis. What is the primary molecular mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Binding to antithrombin III to preferentially inhibit Factor Xa
. Vitamin K antagonism through inhibition of epoxide reductase
. Direct inhibition of Factor Xa without antithrombin interaction

Correct Answer & Explanation

. Binding to antithrombin III to preferentially inhibit Factor Xa

Explanation

Enoxaparin is a Low Molecular Weight Heparin (LMWH). Unlike unfractionated heparin, which has roughly equal activity against Factor Xa and Factor IIa (thrombin), LMWH primarily binds to Antithrombin III, causing a conformational change that vastly accelerates its inhibition of Factor Xa, with much less effect on Factor IIa. Rivaroxaban and Apixaban are direct Factor Xa inhibitors (do not require ATIII).

Question 10249

Topic: Biology, Genetics & Bone Healing

A 40-year-old male sustains a transverse midshaft humerus fracture, which is treated with open reduction and rigid internal fixation utilizing absolute stability principles (lag screw and compression plate).

Which of the following processes is the primary mechanism of bone healing expected in this scenario?

. Endochondral ossification
. Intramembranous ossification via cutting cones
. Callus formation followed by remodeling
. Primary bone healing via Haversian remodeling
. Fibrous union followed by creeping substitution

Correct Answer & Explanation

. Primary bone healing via Haversian remodeling

Explanation

Rigid internal fixation with absolute stability (e.g., compression plating) eliminates interfragmentary motion, bypassing the intermediate stage of callus formation. This leads to primary bone healing, characterized by osteoclastic 'cutting cones' directly crossing the fracture line, followed immediately by osteoblast-mediated deposition of new Haversian systems. Endochondral ossification/callus formation happens with relative stability (secondary bone healing).

Question 10250

Topic: Biology, Genetics & Bone Healing

Which of the following cellular markers is most specific for identifying osteoclasts in histological preparations of bone?

. Alkaline phosphatase
. Type I collagen
. Osteocalcin
. Tartrate-resistant acid phosphatase (TRAP)
. Bone sialoprotein

Correct Answer & Explanation

. Tartrate-resistant acid phosphatase (TRAP)

Explanation

Tartrate-resistant acid phosphatase (TRAP) is an enzyme highly expressed by osteoclasts and is commonly used as a histological marker to identify them in bone tissue sections. Alkaline phosphatase, Type I collagen, and osteocalcin are markers associated with osteoblasts and bone formation.

Question 10251

Topic: Infection, Pharmacology & VTE

A 9-year-old boy with sickle cell disease presents with an acute onset of fever, severe left femur pain, and an elevated C-reactive protein. Blood cultures are drawn. Statistically, what is the most common causative organism for hematogenous osteomyelitis in this specific patient population?

. Salmonella typhimurium
. Staphylococcus aureus
. Streptococcus pneumoniae
. Haemophilus influenzae
. Pseudomonas aeruginosa

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

While Salmonella is classically associated with sickle cell disease and is highly unique to this population (due to hyposplenism and gastrointestinal microinfarctions), Staphylococcus aureus remains the most common overall cause of osteomyelitis in sickle cell patients worldwide in most large epidemiological studies. (Note: Many board questions test Salmonella as the 'classic' association, but careful wording regarding 'most common overall' leads to S. aureus; if asked for the 'classic unique organism', it is Salmonella).

Question 10252

Topic: 1. General Principles & Basic Science

In healthy adult articular cartilage, what structural landmark separates the deep uncalcified zone from the calcified cartilage zone?

. The lamina splendens
. The superficial tangential zone
. The tidemark
. The subchondral bone plate
. The cement line

Correct Answer & Explanation

. The tidemark

Explanation

The tidemark is a distinct histological line that separates the uncalcified deep zone of articular cartilage from the calcified cartilage zone. The lamina splendens is the acellular layer at the very surface of the superficial zone. The cement line separates the calcified cartilage from the subchondral bone.

Question 10253

Topic: 1. General Principles & Basic Science

During a routine anterior cruciate ligament reconstruction, a pneumatic tourniquet is inflated to 250 mmHg. After 90 minutes of continuous inflation, which of the following systemic metabolic changes is most likely to be observed immediately upon deflation?

. Transient decrease in end-tidal CO2
. Transient increase in systemic pH
. Transient increase in serum potassium
. Sustained hypertension
. Decrease in systemic core temperature

Correct Answer & Explanation

. Transient increase in serum potassium

Explanation

Tourniquet deflation after a prolonged period of ischemia results in the release of metabolic byproducts into the systemic circulation. This includes a washout of carbon dioxide (leading to an increase in end-tidal CO2), lactic acid (leading to a transient drop in systemic pH/metabolic acidosis), and intracellular contents from ischemic muscle (transient increase in serum potassium). Core temperature usually drops slightly due to reperfusion of the cooled limb.

Question 10254

Topic: 1. General Principles & Basic Science

A new diagnostic test for periprosthetic joint infection is evaluated. The study reports that the test has a High Positive Predictive Value (PPV). How is the Positive Predictive Value mathematically defined?

. True Positives / (True Positives + False Negatives)
. True Negatives / (True Negatives + False Positives)
. True Positives / (True Positives + False Positives)
. True Negatives / (True Negatives + False Negatives)
. (True Positives + True Negatives) / Total Population

Correct Answer & Explanation

. True Positives / (True Positives + False Positives)

Explanation

Positive Predictive Value (PPV) is the probability that subjects with a positive screening test truly have the disease. It is calculated as True Positives divided by the sum of True Positives and False Positives (all positive tests). Unlike sensitivity and specificity, PPV is dependent on the prevalence of the disease in the studied population.

Question 10255

Topic: Biology, Genetics & Bone Healing

Which of the following nutritional deficiencies directly impairs the hydroxylation of proline and lysine residues during collagen synthesis, leading to weakened bone matrix and poor wound healing?

. Vitamin A deficiency
. Vitamin B12 deficiency
. Vitamin C deficiency
. Vitamin D deficiency
. Calcium deficiency

Correct Answer & Explanation

. Vitamin C deficiency

Explanation

Vitamin C (ascorbic acid) is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes are required for the hydroxylation of proline and lysine residues in procollagen. This hydroxylation is critical for the cross-linking and stabilization of the collagen triple helix. Deficiency leads to Scurvy, characterized by fragile blood vessels, poor wound healing, and weakened bone matrix.

Question 10256

Topic: Biology, Genetics & Bone Healing

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is utilized in spine surgery and fracture repair for its potent osteoinductive properties. Binding of BMP-2 to its cell-surface serine/threonine kinase receptors directly initiates which of the following intracellular signaling cascades?

. Wnt/beta-catenin pathway
. MAPK/ERK pathway
. Smad 1/5/8 pathway
. JAK-STAT pathway
. Notch/Hes pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily. When BMP-2 binds to its cell surface receptors, it causes phosphorylation of the intracellular receptor-regulated Smads, specifically Smad 1, 5, and 8. These then form a complex with Smad 4, translocate to the nucleus, and upregulate osteogenic genes like Runx2.

Question 10257

Topic: 1. General Principles & Basic Science

Within normal human articular cartilage, the extracellular matrix exhibits distinct structural variations by depth. Which zone contains the highest concentration of water and is characterized by collagen fibers oriented strictly parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains the highest water content (approx. 80%), the lowest proteoglycan content, and collagen fibers (primarily Type II) arranged parallel to the articular surface to effectively resist shear forces. The deep zone has the lowest water content and collagen fibers arranged perpendicular to the surface.

Question 10258

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a lytic, eccentrically located epiphyseal lesion in the proximal tibia.

Biopsy confirms a Giant Cell Tumor (GCT) of bone. Denosumab, a monoclonal antibody, may be used as neoadjuvant therapy. Denosumab exerts its effect by targeting RANKL. In the pathophysiology of GCT, which cells primarily express RANKL?

. The multinucleated giant cells
. The neoplastic mononuclear stromal cells
. Surrounding reactive osteoblasts
. Infiltrating T-lymphocytes
. Osteocytes within the adjacent trabeculae

Correct Answer & Explanation

. The neoplastic mononuclear stromal cells

Explanation

Giant cell tumor of bone consists of two main cell populations: the reactive, osteoclast-like multinucleated giant cells and the true neoplastic mononuclear stromal cells. The mononuclear cells inappropriately express high levels of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which recruits and activates the multinucleated giant cells to cause massive bone destruction. Denosumab binds to RANKL, preventing this activation.

Question 10259

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, as visually contextualized in the following radiograph

, what specific interfragmentary strain environment is required to promote secondary bone healing with robust callus formation?

. Strain less than 2%
. Strain between 2% and 10%
. Strain between 10% and 30%
. Strain greater than 30%
. Complete absence of strain (0%)

Correct Answer & Explanation

. Strain between 2% and 10%

Explanation

According to Perren's strain theory, an interfragmentary strain of 2% to 10% stimulates secondary bone healing via endochondral ossification, leading to callus formation. A strain less than 2% promotes primary bone healing (cutting cones without callus). Strain greater than 10% results in fibrous tissue formation, and strain over 30% typically leads to a nonunion.

Question 10260

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is widely used in modern total joint arthroplasty to reduce wear. While cross-linking successfully decreases adhesive and abrasive wear, it significantly diminishes which of the following mechanical properties?
. Hardness
. Fatigue resistance
. Oxidation resistance
. Elastic modulus
. Melting temperature

Correct Answer & Explanation

. Fatigue resistance

Explanation

The irradiation process used to highly cross-link UHMWPE improves wear resistance but decreases its fatigue resistance, ductility, ultimate tensile strength, and yield strength. To mitigate free radicals generated during this process and prevent oxidation, manufacturers utilize techniques such as remelting, annealing, or adding an antioxidant like Vitamin E.

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