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1. General Principles & Basic Science MCQs

Practice Set 672 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 13421

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, organisms often form a biofilm. Which phase of biofilm formation is characterized by the production of an extracellular polymeric substance (EPS) matrix that confers profound antibiotic resistance?

. Reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic shedding

Correct Answer & Explanation

. Maturation

Explanation

During the maturation phase, bacteria secrete an abundant extracellular polymeric substance (EPS) matrix. This matrix shields the community from host immune responses and dramatically increases resistance to antimicrobial agents.

Question 13422

Topic: 1. General Principles & Basic Science

An orthopedic surgeon wishes to minimize radiation exposure to the surgical team during fluoroscopy. According to the inverse square law, doubling the distance from the radiation source reduces the exposure by what factor?

. 1/2
. 1/4
. 1/8
. 1/16
. There is no reduction

Correct Answer & Explanation

. 1/4

Explanation

The inverse square law states that radiation intensity is inversely proportional to the square of the distance from the source. Therefore, doubling the distance reduces the exposure to one-fourth (1/4) of the original amount.

Question 13423

Topic: 1. General Principles & Basic Science

When using a cortical structural allograft, the process of creeping substitution occurs. Which of the following accurately describes the initial sequence of this process?

. Osteoblastic bone formation followed by osteoclastic resorption
. Osteoclastic resorption followed by osteoblastic bone formation
. Simultaneous fibrous encapsulation and chondrogenesis
. Vascular ingrowth without cellular remodeling
. Direct mineralization of the necrotic graft matrix

Correct Answer & Explanation

. Osteoclastic resorption followed by osteoblastic bone formation

Explanation

Creeping substitution in cortical grafts begins with osteoclastic resorption of the necrotic host bone via cutting cones, followed immediately by osteoblastic deposition of new bone. This initial resorption weakens the graft before it strengthens.

Question 13424

Topic: Biomechanics & Biomaterials

A 45-year-old male undergoes revision internal fixation for a femoral shaft nonunion. The surgeon plans to use a stainless steel plate with the retained titanium screws from the index procedure. Which of the following best describes the primary type of corrosion that is likely to occur?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Uniform corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., titanium and stainless steel) are placed in contact within a conductive fluid environment (body fluid). The less noble metal undergoes accelerated corrosion due to electrochemical differences.

Question 13425

Topic: Biomechanics & Biomaterials

Which of the following factors is most strongly associated with increased volumetric wear of highly cross-linked polyethylene in total hip arthroplasty?

. Decreased femoral head size
. Increased femoral head size
. Increased polyethylene thickness
. Use of a ceramic femoral head
. Sterilization in an inert gas environment

Correct Answer & Explanation

. Increased femoral head size

Explanation

Increased femoral head size increases the sliding distance per step, which inherently increases volumetric wear of the polyethylene liner, although it decreases the risk of dislocation. While highly cross-linked polyethylene mitigates wear compared to conventional polyethylene, the physical relationship with head size remains.

Question 13426

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal lesion in the distal femur extending to the subchondral bone without a sclerotic rim. Biopsy shows multinucleated giant cells in a background of mononuclear stromal cells. Which of the following is the most appropriate targeted medical therapy?

. Imatinib
. Denosumab
. Methotrexate
. Doxorubicin
. Bisphosphonates

Correct Answer & Explanation

. Denosumab

Explanation

The clinical and histologic description is classic for a Giant Cell Tumor (GCT) of bone. Denosumab, a monoclonal antibody against RANKL, is specifically used to treat locally advanced or unresectable GCTs by inhibiting the RANK-RANKL interaction, thereby halting the osteoclast-like giant cells.

Question 13427

Topic: 1. General Principles & Basic Science
A 55-year-old diabetic male presents with severe right leg pain, swelling, and erythema out of proportion to physical exam findings. Which of the following laboratory parameters is included in the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score?
. Serum potassium
. Serum sodium
. Platelet count
. Lactate dehydrogenase
. Erythrocyte sedimentation rate

Correct Answer & Explanation

. Serum sodium

Explanation

The LRINEC score uses six routine laboratory parameters to risk-stratify for necrotizing fasciitis: C-reactive protein (CRP), total White Blood Cell (WBC) count, Hemoglobin, Serum sodium, Serum creatinine, and Serum glucose. Hyponatremia (< 135 mmol/L) scores 2 points.

Question 13428

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing, what is the predominant collagen type synthesized during the soft callus (cartilaginous) phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Secondary fracture healing relies heavily on endochondral ossification. During the soft callus phase, chondrocytes proliferate and predominantly produce Type II collagen (cartilage). This is later replaced by Type I collagen as the soft callus mineralizes into a hard callus (woven bone).

Question 13429

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers arranged perpendicular to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage provides the greatest resistance to compressive loads. It has the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented perpendicular to the joint line. The superficial zone has the highest water content and parallel collagen fibers.

Question 13430

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with frequent fractures and cranial nerve palsies. Radiographs demonstrate diffusely dense bones with a 'bone-within-bone' appearance. A mutation affecting which of the following is most likely responsible for this condition?

. Type I collagen
. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II
. Runx2 (Cbfa1)
. Type X collagen

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

This patient has osteopetrosis, a condition caused by osteoclast dysfunction leading to impaired bone resorption. A common autosomal recessive form is caused by a mutation in carbonic anhydrase II (CA II), resulting in an inability to secrete protons and acidify Howship's lacunae, which is required to dissolve bone mineral.

Question 13431

Topic: Biomechanics & Biomaterials

During the application of a halo vest, the pins are initially torqued to 8 in-lbs. After 48 hours, the torque on the pins is measured and found to have decreased, despite the pins not visibly moving. Which of the following viscoelastic properties best explains this phenomenon?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property defined as a decrease in stress (or torque) over time when a material is held at a constant strain (or deformation). Creep, conversely, is the progressive deformation (strain) of a material over time under a constant load.

Question 13432

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing. Which of the following intracellular signaling molecules is directly phosphorylated following the binding of a BMP to its cell surface serine/threonine kinase receptor?

. JAK/STAT
. cAMP
. Smad 1/5/8
. Beta-catenin
. NF-kappa B

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs belong to the TGF-beta superfamily. When they bind to their specific membrane receptors, the receptors phosphorylate intracellular proteins known as receptor-regulated Smads (specifically Smad 1, 5, and 8). These then form a complex with the co-Smad (Smad 4) and translocate to the nucleus to induce transcription of osteogenic genes.

Question 13433

Topic: 1. General Principles & Basic Science

A new rapid diagnostic test for periprosthetic joint infection is implemented in a clinic. If the prevalence of periprosthetic joint infection in the clinic's patient population suddenly doubles while the sensitivity and specificity of the test remain unchanged, which of the following statistical values will increase?

. Positive predictive value
. Negative predictive value
. Positive likelihood ratio
. Negative likelihood ratio
. Reliability

Correct Answer & Explanation

. Positive predictive value

Explanation

Positive predictive value (PPV) is highly dependent on disease prevalence. As the prevalence of a disease increases in a population, the PPV increases, while the negative predictive value (NPV) decreases. Sensitivity, specificity, and likelihood ratios are intrinsic properties of the test itself and do not fluctuate with disease prevalence.

Question 13434

Topic: Biology, Genetics & Bone Healing

A 45-year-old man with a history of severe alcohol use disorder presents with swollen bleeding gums, petechiae, and joint pain. Radiographs of his knees show osteopenia and a dense provisional zone of calcification. The underlying nutritional deficiency in this patient primarily impairs which of the following steps of collagen synthesis?

. Cleavage of procollagen C- and N-terminals
. Hydroxylation of proline and lysine residues
. Glycosylation of hydroxylysine residues
. Formation of the triple helix
. Cross-linking by lysyl oxidase

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has scurvy caused by Vitamin C (ascorbic acid) deficiency. Vitamin C is a required cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes are responsible for the hydroxylation of proline and lysine residues in procollagen, a critical step that allows for stable hydrogen bonding and subsequent triple helix formation.

Question 13435

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with a dense radial nerve palsy. After 3 weeks of observation, an electromyography (EMG) study is performed. Which of the following EMG findings is most indicative of active axonal denervation?

. Polyphasic motor unit potentials
. Fibrillation potentials and positive sharp waves
. Decreased insertional activity
. Normal motor nerve conduction velocity
. High-amplitude, long-duration potentials

Correct Answer & Explanation

. Fibrillation potentials and positive sharp waves

Explanation

Fibrillation potentials and positive sharp waves appearing roughly 2 to 4 weeks after an injury are the classic EMG signs of active denervation, indicating that muscle fibers have lost their nerve supply and are firing spontaneously. Polyphasic potentials indicate early reinnervation, while high-amplitude, long-duration potentials represent chronic reinnervation (giant motor units).

Question 13436

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the highest concentration of proteoglycans and the thickest collagen fibrils oriented perpendicular to the joint surface are found in which of the following zones?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest concentration of water. The thick Type II collagen fibrils in this zone are oriented strictly perpendicular to the joint surface to effectively resist compressive loads.

Question 13437

Topic: 1. General Principles & Basic Science

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

. Directly inhibits thrombin activation
. Competitively inhibits the activation of plasminogen to plasmin
. Promotes the release of von Willebrand factor from endothelial cells
. Inhibits cyclooxygenase-1 to prevent platelet aggregation
. Acts as a direct factor Xa inhibitor

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen 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 receptor sites on plasminogen, which prevents plasminogen from binding to fibrin and activating into plasmin. This stabilizes existing blood clots.

Question 13438

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials possesses a modulus of elasticity that most closely matches that of normal human cortical bone, thereby minimizing stress shielding?

. Cobalt-chromium alloy
. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Polymethylmethacrylate (PMMA)
. Tantalum

Correct Answer & Explanation

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

Explanation

The modulus of elasticity (stiffness) of cortical bone is roughly 15-20 GPa. Titanium alloys (approx. 110 GPa) are closer to this value than 316L stainless steel (~200 GPa) or Cobalt-chromium (~220 GPa). This relative flexibility helps reduce stress shielding of the adjacent bone compared to stiffer metals. PMMA has a much lower modulus (~3 GPa).

Question 13439

Topic: 1. General Principles & Basic Science
Which of the following laboratory parameters is assigned the highest point value (4 points) in the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score if its value exceeds a specific threshold?
. White blood cell count
. C-reactive protein (CRP)
. Serum sodium
. Serum creatinine
. Hemoglobin

Correct Answer & Explanation

. C-reactive protein (CRP)

Explanation

The LRINEC score is a clinical tool used to distinguish necrotizing fasciitis from other soft tissue infections. The variables are CRP, WBC count, hemoglobin, serum sodium, creatinine, and glucose. A CRP level >= 150 mg/L is assigned the highest individual weight (4 points).

Question 13440

Topic: Biology, Genetics & Bone Healing
During active bone resorption, osteoclasts attach to the bone matrix to create an isolated microenvironment known as the sealing zone. Which of the following integrin receptors mediates this firm attachment to osteopontin and bone sialoprotein?
. Alpha-5 beta-1
. Alpha-v beta-3
. Alpha-2 beta-1
. Alpha-L beta-2
. Alpha-M beta-2

Correct Answer & Explanation

. Alpha-v beta-3

Explanation

The alpha-v beta-3 (αvβ3) integrin is highly expressed on the ruffled border and sealing zone of osteoclasts. It is the primary receptor responsible for binding to the RGD (Arg-Gly-Asp) amino acid sequences found in bone matrix proteins like osteopontin and bone sialoprotein, anchoring the osteoclast to the bone surface.

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