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1. General Principles & Basic Science MCQs

Practice Set 692 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 13821

Topic: 1. General Principles & Basic Science
In a patient presenting with aseptic loosening of a total hip arthroplasty, particulate ultra-high-molecular-weight polyethylene (UHMWPE) wear debris primarily stimulates osteolysis through the initial activation of which of the following cell types?
. Osteoblasts
. Fibroblasts
. Macrophages
. T-lymphocytes
. Neutrophils

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose UHMWPE wear debris, triggering the release of inflammatory cytokines such as TNF-alpha and IL-1. This local inflammatory cascade ultimately increases RANKL expression, driving osteoclast activation and subsequent periprosthetic bone resorption.

Question 13822

Topic: Biology, Genetics & Bone Healing

A patient with recurrent fractures and widespread diffuse osteosclerosis on radiographs is diagnosed with autosomal recessive osteopetrosis. The pathogenesis of this condition is most commonly due to a deficiency in which of the following enzymes?

. Alkaline phosphatase
. Type I collagenase
. Carbonic anhydrase II
. Cathepsin K
. Tartrate-resistant acid phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Autosomal recessive osteopetrosis is frequently caused by a genetic mutation resulting in a deficiency of Carbonic Anhydrase II. This prevents osteoclasts from generating the acidic environment necessary to dissolve bone mineral, leading to dense but mechanically weak bones.

Question 13823

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is commonly used to reduce perioperative blood loss in total joint arthroplasty. What is the primary mechanism of action of this medication?

. Inhibits factor Xa
. Directly activates thrombin
. Competitively inhibits plasminogen activation
. Promotes platelet aggregation
. Inhibits cyclooxygenase-1

Correct Answer & Explanation

. Competitively inhibits plasminogen activation

Explanation

Tranexamic acid is a synthetic antifibrinolytic agent that reversibly and competitively binds to the lysine receptor sites on plasminogen. This prevents the conversion of plasminogen to active plasmin, effectively stabilizing the fibrin clot.

Question 13824

Topic: Biomechanics & Biomaterials

During the clinical management of a clubfoot, a serial casting technique is utilized. The progressive deformation of the contracted soft tissues under a constant applied load over time demonstrates which of the following viscoelastic properties?

. Hysteresis
. Stress relaxation
. Creep
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material when it is subjected to a constant load over time. This principle is applied in serial casting to gradually lengthen contracted ligaments and tendons.

Question 13825

Topic: Infection, Pharmacology & VTE

During the pathogenesis of a periprosthetic joint infection, which of the following organisms relies primarily on the production of a polysaccharide glycocalyx slime layer to facilitate initial adherence and biofilm formation on the implant surface?

. Staphylococcus aureus
. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Cutibacterium acnes
. Streptococcus pyogenes

Correct Answer & Explanation

. Staphylococcus epidermidis

Explanation

Staphylococcus epidermidis is a ubiquitous skin commensal and a major pathogen in implant-related infections. It produces an exopolysaccharide glycocalyx slime layer that facilitates adherence to hardware and protects the bacteria from both host immunity and systemic antibiotics.

Question 13826

Topic: Surgical Anatomy & Approaches

The anterior (Smith-Petersen) approach to the hip utilizes a true internervous plane. This approach develops the interval between muscles innervated by which of the following pairs of nerves?

. Femoral and Superior Gluteal
. Femoral and Obturator
. Superior Gluteal and Inferior Gluteal
. Sciatic and Femoral
. Obturator and Sciatic

Correct Answer & Explanation

. Femoral and Superior Gluteal

Explanation

The Smith-Petersen approach exploits the true internervous plane between the femoral nerve and the superior gluteal nerve. Superficially, the plane is between the sartorius (femoral) and tensor fasciae latae (superior gluteal), and deeply between the rectus femoris (femoral) and gluteus medius (superior gluteal).

Question 13827

Topic: Biomechanics & Biomaterials

Which of the following material properties best explains why a titanium alloy implant exhibits a lower modulus of elasticity compared to a stainless steel implant, thereby reducing stress shielding in orthopaedic fixation?

. Increased yield strength
. Lower density
. Different atomic bonding and crystalline structure
. Increased fatigue strength
. Higher ultimate tensile strength

Correct Answer & Explanation

. Different atomic bonding and crystalline structure

Explanation

The modulus of elasticity (Young's modulus) is an intrinsic material property that dictates the stiffness of an implant. It is fundamentally determined by the atomic bonding and crystalline lattice structure of the metal. Titanium alloys have a modulus of elasticity closer to that of cortical bone compared to stainless steel or cobalt-chrome, reducing the stress-shielding effect. Yield strength, density, and fatigue strength are separate properties that do not dictate the intrinsic stiffness of the material.

Question 13828

Topic: Biology, Genetics & Bone Healing

During the healing of a diaphyseal fracture treated with rigid internal fixation providing absolute stability, bone healing occurs primarily via which of the following mechanisms?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing (Haversian remodeling)
. Creeping substitution
. Callus distraction

Correct Answer & Explanation

. Primary bone healing (Haversian remodeling)

Explanation

Rigid internal fixation that provides absolute stability (e.g., compression plating) bypasses callus formation and results in primary bone healing. This occurs via direct Haversian remodeling, where cutting cones of osteoclasts cross the fracture site, followed immediately by osteoblasts laying down new bone. Endochondral ossification (callus formation) is seen in secondary bone healing (relative stability). Creeping substitution refers to the incorporation of bone grafts.

Question 13829

Topic: 1. General Principles & Basic Science

Articular cartilage relies on multiple mechanisms to maintain extremely low friction coefficients. At the exact initiation of joint movement from a stationary position (under high load and low speed), which type of lubrication mechanism is predominantly responsible for reducing friction?

. Elastohydrodynamic lubrication
. Boundary lubrication
. Weeping lubrication
. Squeeze-film lubrication
. Boosted lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication is the primary mechanism operating at the initiation of movement, under high loads, and at low speeds. It is mediated by superficial molecules, primarily lubricin (PRG4), which attach to the articular surface and prevent direct surface-to-surface contact. Fluid-film lubrication mechanisms (like elastohydrodynamic and squeeze-film) dominate during sustained dynamic joint motion at higher speeds.

Question 13830

Topic: Biomechanics & Biomaterials
The introduction of highly cross-linked polyethylene (HXLPE) in total hip arthroplasty has significantly reduced volumetric wear rates compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE). However, the cross-linking and subsequent thermal stabilization processes alter the material's bulk mechanical properties. Which of the following represents a known mechanical tradeoff of HXLPE?
. Increased ultimate tensile strength
. Increased fatigue crack propagation resistance
. Decreased yield strength and ductility
. Increased oxidative degradation rate in vivo
. Generation of substantially larger wear particles

Correct Answer & Explanation

. Decreased yield strength and ductility

Explanation

Irradiation to create cross-links improves wear resistance but decreases the mechanical robustness of the polyethylene. Specifically, highly cross-linked polyethylene (HXLPE) exhibits decreased yield strength, ultimate tensile strength, ductility, and resistance to fatigue crack propagation compared to conventional UHMWPE. Thermal processing (e.g., remelting) removes free radicals to prevent oxidation but further reduces these mechanical properties.

Question 13831

Topic: 1. General Principles & Basic Science

Articular cartilage is highly resilient and capable of withstanding massive compressive loads during normal joint kinematics. This remarkable compressive stiffness and resilience is primarily mediated by which of the following extracellular matrix components?

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

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, the major proteoglycan in articular cartilage, possesses a high concentration of negatively charged glycosaminoglycans (chondroitin sulfate and keratan sulfate). These negative charges repel each other and draw water into the matrix via Donnan osmotic pressure, creating a swelling pressure that resists compressive loads. While Type II collagen provides the tensile framework, it is the aggrecan-water interaction that provides compressive stiffness.

Question 13832

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis and a recent vertebral compression fracture is prescribed a bone-modifying agent.

She is initiated on teriparatide. What is the primary mechanism of action of this medication when administered as a daily subcutaneous injection?

. Inhibition of osteoclast activation via direct binding to RANK ligand
. Intermittent stimulation of parathyroid hormone (PTH) receptors, leading to a net anabolic effect on bone
. Direct inhibition of farnesyl pyrophosphate synthase within osteoclasts
. Binding and neutralizing the Wnt signaling pathway antagonist sclerostin
. Stimulation of calcium-sensing receptors on the parathyroid gland to suppress endogenous PTH

Correct Answer & Explanation

. Intermittent stimulation of parathyroid hormone (PTH) receptors, leading to a net anabolic effect on bone

Explanation

Teriparatide is a recombinant human parathyroid hormone analog (PTH 1-34). While continuous exposure to high levels of PTH (as in hyperparathyroidism) leads to bone resorption, intermittent administration (such as daily subcutaneous injection) preferentially stimulates osteoblast activity over osteoclast activity. This results in a net anabolic (bone-building) effect, differentiating it from antiresorptive agents like bisphosphonates (farnesyl pyrophosphate synthase inhibitors) or denosumab (RANKL inhibitor).

Question 13833

Topic: Infection, Pharmacology & VTE
A 4-year-old child presents with a 2-day history of refusal to bear weight on the right leg. Clinical evaluation reveals a temperature of 38.6°C (101.5°F). Laboratory workup shows a WBC count of 14,000/mm³, an ESR of 50 mm/hr, and a CRP of 3.5 mg/dL. According to the classic Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?
. 10%
. 40%
. 71%
. 99%
. 100%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria are used to differentiate septic arthritis from transient synovitis in children. The four classic criteria are: history of fever (>38.5°C), non-weight bearing, ESR >40 mm/hr, and serum WBC >12,000/mm³. The probability of septic arthritis based on the number of criteria present is approximately: 1 predictor = 3%, 2 predictors = 40%, 3 predictors = 93%, and 4 predictors = 99%. This patient meets all 4 criteria.

Question 13834

Topic: Biomechanics & Biomaterials

A patient with a previously implanted stainless steel plate for a femur fracture undergoes revision surgery. The surgeon inadvertently uses a titanium screw to secure an adjunctive piece of hardware in direct physical contact with the stainless steel plate. Over time, rapid corrosion and eventual failure of the less noble metal occurs.

This process is best described as:

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct contact with each other within an electrolytic solution (like human bodily fluids). An electrochemical cell is created, and the less noble metal (the anode) undergoes accelerated corrosive degradation. Fretting corrosion is mechanically induced by micromotion between components, whereas crevice corrosion occurs in restricted spaces with oxygen depletion. Using titanium and stainless steel in direct contact is a classic setup for galvanic corrosion.

Question 13835

Topic: Biology, Genetics & Bone Healing

What is the primary cellular abnormality that drives the initial phase of Paget disease of bone (osteitis deformans)?

. Osteoblast apoptosis and failure of bone formation
. Excessive number of nuclei and increased activity per osteoclast
. Defective mineralization of newly formed osteoid
. Defective collagen cross-linking by lysyl oxidase
. Malignant transformation of mesenchymal stem cells

Correct Answer & Explanation

. Excessive number of nuclei and increased activity per osteoclast

Explanation

Paget disease occurs in three phases: an initial lytic (osteoclastic) phase, a mixed osteoclastic-osteoblastic phase, and a late sclerotic (osteoblastic) phase. The primary defect lies in the osteoclast. Pagetic osteoclasts are larger and contain an excessive number of nuclei (up to 100 per cell, compared to the normal 3-5). This leads to massive localized bone resorption.

Question 13836

Topic: Biomechanics & Biomaterials

What is the predominant mechanism of corrosion seen at the modular head-neck taper junction (trunnionosis) in modern total hip arthroplasty?

. Uniform attack corrosion
. Mechanically assisted crevice corrosion
. Pitting corrosion
. Galvanic corrosion exclusively
. Intergranular corrosion

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

The primary mechanism of corrosion at modular junctions (like the head-neck trunnion) is Mechanically Assisted Crevice Corrosion (MACC). Micromotion (fretting) at the taper junction mechanically disrupts the protective passivation layer (titanium or chromium oxide). The fluid-filled gap (crevice) between the components becomes depleted of oxygen, leading to an acidic microenvironment that prevents repassivation and accelerates active metal dissolution.

Question 13837

Topic: Biomechanics & Biomaterials

A 65-year-old man presents with an acutely swollen and painful knee. Synovial fluid aspiration yields a yellow fluid with a WBC count of 45,000 cells/uL (predominantly PMNs). Polarized light microscopy reveals weakly positively birefringent rhomboid-shaped crystals. What is the composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

The classic presentation of pseudogout (calcium pyrophosphate deposition disease, CPPD) includes an acutely inflamed joint with synovial fluid showing rhomboid-shaped crystals that exhibit weak positive birefringence under polarized light. Monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 13838

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy suffers a subtrochanteric femur fracture. Radiographs show a diffusely dense, 'bone-in-bone' appearance and loss of the medullary canal. The underlying cause of this condition is most commonly due to a defect in:

. Osteoblast differentiation and maturation
. Carbonic anhydrase II leading to absent ruffled borders in osteoclasts
. Type I collagen triple helix formation
. Core binding factor alpha-1 (Cbfa1/RUNX2) expression
. RANK ligand secretion by osteoblasts

Correct Answer & Explanation

. Carbonic anhydrase II leading to absent ruffled borders in osteoclasts

Explanation

The clinical picture describes osteopetrosis (marble bone disease). It results from defective osteoclast function, preventing normal bone resorption and remodeling. The most well-known functional defect is a mutation in Carbonic Anhydrase II (or the TCIRG1 gene affecting the vacuolar proton pump), which prevents the osteoclast from creating the acidic environment necessary for bone resorption, often resulting in osteoclasts that lack a functional ruffled border.

Question 13839

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently used in arthroplasty for implant fixation. Which of the following additives is responsible for making PMMA radiopaque on standard plain radiographs?

. Benzoyl peroxide
. N,N-dimethyl-p-toluidine
. Hydroquinone
. Barium sulfate
. Polystyrene

Correct Answer & Explanation

. Barium sulfate

Explanation

In standard PMMA formulations, barium sulfate (BaSO4) or zirconium dioxide (ZrO2) is added as a radiopacifier so the cement mantle can be evaluated radiographically. Benzoyl peroxide is the initiator in the powder, N,N-dimethyl-p-toluidine is the accelerator in the liquid, and hydroquinone is added to the liquid as a stabilizer to prevent premature polymerization.

Question 13840

Topic: 1. General Principles & Basic Science

According to Sunderland's classification of peripheral nerve injuries, a third-degree nerve injury is characterized by the disruption of the axon and which of the following connective tissue structures?

. Endoneurium only
. Endoneurium and perineurium
. Epineurium only
. Myelin sheath only
. Epineurium and perineurium

Correct Answer & Explanation

. Endoneurium and perineurium

Explanation

Sunderland classified nerve injuries into five degrees: 1st degree (Neurapraxia) involves focal demyelination; 2nd degree (Axonotmesis) involves axonal disruption with an intact endoneurium; 3rd degree involves disruption of the axon and endoneurium (but perineurium and epineurium remain intact); 4th degree involves disruption of the axon, endoneurium, and perineurium (only epineurium is intact); 5th degree (Neurotmesis) is complete transection of the nerve.

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