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1. General Principles & Basic Science MCQs

Practice Set 678 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 13541

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones, each with unique cellular and biochemical properties. Which zone features the highest concentration of proteoglycans and contains 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 the highest concentration of proteoglycans, maximizing its resistance to compressive forces. Its chondrocytes and thick collagen fibrils are uniquely arranged in vertical columns.

Question 13542

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is widely utilized in cemented total joint arthroplasty. By what primary mechanism does PMMA secure the metallic prosthesis to the host bone?

. Direct chemical bonding to hydroxyapatite
. Osteoinduction leading to biologic osseointegration
. Covalent bonding to type I collagen fibrils
. Micro-interlocking as a mechanical grout
. Piezoelectric stimulation of local osteoblasts

Correct Answer & Explanation

. Micro-interlocking as a mechanical grout

Explanation

PMMA bone cement acts strictly as a mechanical grout, not an adhesive. It achieves fixation by physically micro-interlocking with the porous spaces of cancellous bone and the roughened surface of the metallic implant, without any true chemical or biological bonding.

Question 13543

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with a high risk of osteoporotic fractures is initiated on denosumab therapy. Which of the following best describes the specific mechanism of action of this medication?

. Binds to RANKL to prevent osteoclast activation
. Binds directly to the RANK receptor to stimulate osteoblastogenesis
. Inhibits the farnesyl pyrophosphate synthase enzyme
. Stimulates the Wnt signaling pathway via sclerostin inhibition
. Provides a recombinant parathyroid hormone analogue to stimulate bone formation

Correct Answer & Explanation

. Binds to RANKL to prevent osteoclast activation

Explanation

Denosumab is a monoclonal antibody that targets and binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By blocking RANKL from binding to its receptor on osteoclasts, it effectively inhibits osteoclast activation, function, and survival.

Question 13544

Topic: Surgical Anatomy & Approaches

An 8-year-old child sustains a completely displaced posterolateral supracondylar humerus fracture. Upon examination, which of the following nerves is most at risk of injury due to the direction of the displacement of the proximal fragment?

. Anterior interosseous nerve (AIN)
. Radial nerve
. Ulnar nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Anterior interosseous nerve (AIN)

Explanation

In a posterolaterally displaced supracondylar humerus fracture, the proximal fragment is displaced anteromedially. This puts the median nerve (specifically its anterior interosseous nerve branch) and the brachial artery at the highest risk. Posteromedial displacement endangers the radial nerve.

Question 13545

Topic: 1. General Principles & Basic Science

In articular cartilage, which structural layer marks the transition between the uncalcified deep zone and the calcified cartilage zone, and is often duplicated in osteoarthritis?

. Lamina splendens
. Superficial tangential zone
. Transitional zone
. Tidemark
. Cement line

Correct Answer & Explanation

. Tidemark

Explanation

The tidemark is the basophilic line that separates the deep, uncalcified zone of articular cartilage from the calcified cartilage. It is a highly metabolically active area and can duplicate (multiple tidemarks) as a sign of cartilage repair and remodeling in early osteoarthritis.

Question 13546

Topic: Biology, Genetics & Bone Healing

Denosumab has been increasingly used in the treatment of locally aggressive or metastatic Giant Cell Tumors (GCT) of bone. What is the mechanism of action of this monoclonal antibody?

. It binds to RANKL, preventing the activation of osteoclast-like giant cells
. It acts as a decoy receptor similar to Osteoprotegerin (OPG)
. It inhibits vascular endothelial growth factor (VEGF)
. It binds to the RANK receptor on the stromal cells to induce apoptosis
. It inhibits tyrosine kinase activity within the tumor cells

Correct Answer & Explanation

. It binds to RANKL, preventing the activation of osteoclast-like giant cells

Explanation

In GCT of bone, the neoplastic mononuclear stromal cells express high levels of RANKL, which recruits and activates the reactive osteoclast-like giant cells responsible for bone destruction. Denosumab is a monoclonal antibody that binds to RANKL, thereby inhibiting this interaction and halting osteoclastogenesis and bone resorption.

Question 13547

Topic: Biology, Genetics & Bone Healing

A 55-year-old female is started on denosumab for osteoporosis. This medication primarily targets which of the following molecular pathways to inhibit bone resorption?

. Binding to the RANK receptor on osteoclasts
. Inhibiting sclerostin, thus promoting Wnt signaling
. Binding to RANKL, preventing its interaction with RANK
. Inhibiting cathepsin K activity
. Stimulating osteoprotegerin (OPG) production by osteoblasts

Correct Answer & Explanation

. Binding to RANKL, preventing its interaction with RANK

Explanation

Denosumab is a monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), preventing it from interacting with the RANK receptor on osteoclast precursors, thereby inhibiting osteoclastogenesis and bone resorption.

Question 13548

Topic: Biomechanics & Biomaterials

A patient undergoes revision open reduction and internal fixation of a nonunion. The surgeon places a stainless steel screw through a titanium plate. Which of the following best describes the predominant type of corrosion that is most likely to occur at the screw-plate interface?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within an electrolytic environment (human body fluids). The metal with the lower anodic index (less noble, typically stainless steel in this pairing) undergoes accelerated corrosion.

Question 13549

Topic: 1. General Principles & Basic Science

In cortical bone, which of the following modifications to a screw design or insertion technique will most significantly increase its pullout strength?

. Decreasing the outer (thread) diameter
. Increasing the inner (root) diameter
. Decreasing the thread pitch
. Increasing the pilot hole diameter
. Tapping the bone prior to screw insertion

Correct Answer & Explanation

. Decreasing the outer (thread) diameter

Explanation

Screw pullout strength is proportional to the volume of bone caught between the threads. It is increased by increasing the outer diameter, increasing the length of thread engagement, or decreasing the thread pitch (meaning more threads per unit of length). Increasing the inner (root) diameter increases torsional strength but decreases pullout strength if the outer diameter remains constant.

Question 13550

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 represents the primary mechanism of action of TXA?
. Direct inhibition of factor Xa
. Reversible blockade of lysine binding sites on plasminogen
. Inhibition of cyclooxygenase, preventing platelet aggregation
. Activation of antithrombin III
. Stimulation of von Willebrand factor release from endothelial cells

Correct Answer & Explanation

. Reversible blockade of lysine binding sites on plasminogen

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively binds to the lysine receptor sites on plasminogen, preventing its activation to plasmin, thereby inhibiting fibrinolysis and stabilizing clots.

Question 13551

Topic: Infection, Pharmacology & VTE

Biofilm formation is a critical factor in prosthetic joint infections. Which phase of biofilm development involves the downregulation of planktonic genes and the secretion of an extracellular polymeric substance (EPS) matrix?

. Reversible attachment
. Irreversible attachment
. Maturation
. Dispersion
. Planktonic proliferation

Correct Answer & Explanation

. Maturation

Explanation

Biofilm formation occurs in stages: 1) Reversible attachment of planktonic bacteria, 2) Irreversible attachment, 3) Maturation (microcolony formation, robust EPS production, downregulation of planktonic genes, and quorum sensing), and 4) Dispersion/detachment. The EPS matrix is heavily secreted during the maturation phase.

Question 13552

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient with celiac disease presents with generalized bone pain and muscle weakness. Laboratory studies show low calcium, low phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). Radiographs reveal Looser zones in the femoral neck. What is the primary histological defect in this condition?

. Increased osteoclastic bone resorption out of proportion to osteoblastic activity
. Defective mineralization of newly formed osteoid
. Abnormal cross-linking of type I collagen
. Failure of endochondral ossification at the physis
. Replacement of marrow space with woven bone and fibrous tissue

Correct Answer & Explanation

. Defective mineralization of newly formed osteoid

Explanation

The patient has osteomalacia secondary to vitamin D malabsorption (celiac disease). Osteomalacia is characterized histologically by an increase in unmineralized osteoid (defective mineralization of the organic matrix) due to insufficient calcium and phosphate. Looser zones (pseudofractures) are pathognomonic radiographic findings.

Question 13553

Topic: 1. General Principles & Basic Science

Articular cartilage relies on its extracellular matrix for compressive stiffness. Which of the following components is primarily responsible for the osmotic swelling pressure that resists compressive loads?

. Type II collagen
. Aggrecan
. Hyaluronic acid
. Water
. Chondronectin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage. Its glycosaminoglycan (GAG) side chains are highly negatively charged, which attracts water and creates a large osmotic swelling pressure (Donnan osmotic pressure). This swelling is resisted by the Type II collagen network, providing compressive stiffness.

Question 13554

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with a complete radial nerve palsy. EMGs at 4 weeks show fibrillation potentials but no voluntary motor unit action potentials. However, clinically, the patient regains full function at 12 weeks. According to Seddon's classification, what type of nerve injury did the patient most likely sustain?

. Neurapraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade IV
. Sunderland Grade V

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis involves disruption of the axon and myelin sheath, but the supporting connective tissue frameworks remain intact. Wallerian degeneration occurs, leading to fibrillation potentials on EMG at 3-4 weeks. Recovery occurs via axonal regeneration (~1mm/day), matching the 12-week timeline. Neurapraxia is a conduction block without Wallerian degeneration (no fibrillations).

Question 13555

Topic: Infection, Pharmacology & VTE
A 35-year-old farmer sustains a highly contaminated Type IIIA open tibia fracture while working in a barn. In addition to standard broad-spectrum Gram-positive and Gram-negative antibiotic coverage, which of the following organisms must be specifically targeted with additional antibiotic prophylaxis?
. Methicillin-resistant Staphylococcus aureus (MRSA)
. Pseudomonas aeruginosa
. Clostridium perfringens
. Enterococcus faecalis
. Acinetobacter baumannii

Correct Answer & Explanation

. Clostridium perfringens

Explanation

Farm injuries and highly contaminated wounds carry a high risk of anaerobic infection, specifically Clostridium perfringens (gas gangrene). High-dose penicillin (or metronidazole/clindamycin for allergic patients) should be added to the antibiotic regimen.

Question 13556

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, hearing loss, and deep, aching bone pain in his right thigh. Radiographs of the femur show cortical thickening, coarse trabeculae, and a 'blade of grass' lucency. What is the initial event in the pathogenesis of this disease?

. Osteoblast hyperproliferation
. Mutation in the FGFR3 gene
. Intense, localized osteoclastic bone resorption
. Defective synthesis of Type I collagen
. Inadequate mineralization of the osteoid matrix

Correct Answer & Explanation

. Intense, localized osteoclastic bone resorption

Explanation

The patient has Paget's disease of bone (osteitis deformans). The initial event in its pathogenesis is an intense, localized burst of osteoclastic bone resorption (lytic phase, producing the 'blade of grass' sign). This is followed by a mixed phase of osteoblastic and osteoclastic activity, and finally a sclerotic phase.

Question 13557

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the wear of ultra-high molecular weight polyethylene (UHMWPE) can lead to osteolysis. Which process during the manufacturing of UHMWPE is primarily used to increase its wear resistance?
. Ethylene oxide sterilization
. Gamma irradiation in oxygen
. Highly cross-linking the polymer chains via irradiation and subsequent thermal treatment
. Addition of polymethylmethacrylate (PMMA)
. Cold working the polyethylene prior to machining

Correct Answer & Explanation

. Highly cross-linking the polymer chains via irradiation and subsequent thermal treatment

Explanation

Highly cross-linking UHMWPE significantly increases its wear resistance. This is achieved by irradiating the material to create free radicals that bond to form cross-links. Subsequent thermal treatment (melting or annealing) is necessary to extinguish residual free radicals and prevent long-term oxidative degradation.

Question 13558

Topic: 1. General Principles & Basic Science

A surgeon utilizes a massive structural cortical allograft for a segmental defect reconstruction. By which primary mechanism does the host bone incorporate this allograft?

. Osteoinduction
. Osteogenesis
. Creeping substitution
. Distraction osteogenesis
. Endochondral ossification

Correct Answer & Explanation

. Creeping substitution

Explanation

Structural cortical allografts are osteoconductive only. They incorporate via creeping substitution, a process where host osteoclasts slowly resorb the dead allograft bone and host osteoblasts simultaneously lay down new bone on the remaining scaffold.

Question 13559

Topic: Biology, Genetics & Bone Healing

During the repair of a diaphyseal fracture treated with cast immobilization, a large fracture callus forms. Which of the following factors provides the primary molecular signal that initiates the migration and differentiation of mesenchymal stem cells into the fracture hematoma?

. BMP-2
. VEGF
. PDGF
. TNF-alpha
. IGF-1

Correct Answer & Explanation

. BMP-2

Explanation

Bone morphogenetic proteins (BMPs), particularly BMP-2, are potent osteoinductive cytokines of the TGF-beta superfamily. They signal mesenchymal stem cells (MSCs) to migrate to the injury site and differentiate into osteoprogenitor cells.

Question 13560

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, the mechanical environment dictates the type of tissue that forms in the fracture gap. Which of the following tissues can tolerate the highest level of strain before failing?

. Cortical bone
. Cancellous bone
. Fibrocartilage
. Granulation tissue
. Woven bone

Correct Answer & Explanation

. Granulation tissue

Explanation

According to Perren's strain theory, granulation tissue can tolerate up to 100% strain before failing. Fibrocartilage tolerates roughly 10-15% strain, and solid cortical bone only tolerates about 2% strain. Therefore, high strain environments initially prompt granulation tissue formation, which gradually decreases strain to allow stiffer tissues to form.

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