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1. General Principles & Basic Science MCQs

Practice Set 713 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 14241

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with severe bowing of the lower extremities. Laboratory evaluation reveals X-linked hypophosphatemic rickets. Which of the following serum laboratory profiles is most characteristic of this specific condition prior to treatment?

. Low calcium, low phosphorus, high PTH
. Normal calcium, low phosphorus, normal PTH
. Normal calcium, high phosphorus, low PTH
. Low calcium, normal phosphorus, high PTH
. High calcium, low phosphorus, normal PTH

Correct Answer & Explanation

. Normal calcium, low phosphorus, normal PTH

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX gene mutation leading to excess FGF23 and subsequent renal phosphate wasting. Typical labs show low phosphorus, normal calcium, and normal parathyroid hormone (PTH) levels.

Question 14242

Topic: 1. General Principles & Basic Science
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is used to distinguish necrotizing fasciitis from other soft tissue infections. Which of the following laboratory values is NOT a variable utilized in calculating the LRINEC score?
. C-reactive protein (CRP)
. White blood cell count
. Serum sodium
. Serum calcium
. Hemoglobin

Correct Answer & Explanation

. Serum calcium

Explanation

The LRINEC score comprises six parameters: CRP, WBC count, Hemoglobin, Serum Sodium, Creatinine, and Serum Glucose. Serum calcium is not part of the scoring system.

Question 14243

Topic: Biology, Genetics & Bone Healing

When a massive structural cortical bone allograft is utilized in reconstruction, it incorporates via a process known as creeping substitution. Which of the following best describes the initial cellular sequence of this process in dense cortical bone?

. Rapid vascular ingrowth followed by enchondral ossification
. Osteoclast cutting cones followed by osteoblast bone deposition
. Woven bone formation followed by lamellar remodeling
. Hematoma organization followed by direct intramembranous ossification
. Direct appositional bone growth from host periosteum

Correct Answer & Explanation

. Osteoclast cutting cones followed by osteoblast bone deposition

Explanation

In dense cortical bone grafts, creeping substitution is initiated by osteoclastic resorption via cutting cones, followed by osteoblastic new bone deposition. This sequential remodeling temporarily weakens the structural allograft before it fully incorporates.

Question 14244

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits complex biomechanical behavior under load. Which of the following statements provides the best definition of the viscoelastic property known as 'stress relaxation'?

. Increasing deformation over time under a constant applied load
. Decreasing internal stress required to maintain a constant tissue deformation
. Loss of energy (hysteresis) during a complete loading-unloading cycle
. Fluid exudation leading to irreversible breakdown of the collagen matrix
. Decreasing coefficient of friction as the sliding velocity of the joint increases

Correct Answer & Explanation

. Decreasing internal stress required to maintain a constant tissue deformation

Explanation

Stress relaxation is the time-dependent decrease in the internal stress of a viscoelastic material when it is held at a constant strain (deformation). Creep, by contrast, is increasing deformation under a constant load.

Question 14245

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum allowable interfragmentary strain necessary to achieve primary bone healing via cutting cones?

. Less than 2%
. 2% to 10%
. 10% to 15%
. 15% to 30%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which is defined as an interfragmentary strain of less than 2%. This environment allows for direct osteonal remodeling via cutting cones without the formation of an intermediate fracture callus.

Question 14246

Topic: 1. General Principles & Basic Science

In articular cartilage, which collagen type primarily provides the tensile strength, and what is the primary proteoglycan responsible for compressive strength?

. Type I collagen; Aggrecan
. Type II collagen; Aggrecan
. Type II collagen; Decorin
. Type X collagen; Biglycan
. Type I collagen; Versican

Correct Answer & Explanation

. Type II collagen; Aggrecan

Explanation

Articular cartilage is primarily composed of water. Its solid matrix consists mainly of Type II collagen, which is distributed to resist shear and provide tensile strength, and proteoglycans. Aggrecan is the primary proteoglycan; it binds to hyaluronic acid and traps water, providing compressive strength through osmotic swelling pressure.

Question 14247

Topic: 1. General Principles & Basic Science

During anterior cruciate ligament (ACL) reconstruction using a hamstring autograft, graft healing within the osseous tunnel primarily occurs via which of the following mechanisms?

. Primary bone healing
. Endochondral ossification
. Sharpey-like fiber formation
. Intramembranous ossification
. Creeping substitution

Correct Answer & Explanation

. Sharpey-like fiber formation

Explanation

Soft tissue grafts (such as hamstring or quadriceps tendons) heal in bone tunnels via indirect insertion, which is characterized by the formation of Sharpey-like penetrating collagen fibers extending from the surrounding bone into the graft. This typically takes 8-12 weeks and differs from the direct bone-to-bone healing seen with bone-patellar tendon-bone (BPTB) grafts.

Question 14248

Topic: Biology, Genetics & Bone Healing
A patient with a history of multiple low-energy fractures and a 'rugger-jersey' spine appearance on plain radiographs is diagnosed with a metabolic bone disorder. This condition is primarily characterized by a defect in which of the following cellular mechanisms?
. Osteoblast differentiation via Runx2 mutation
. Type I collagen alpha chain synthesis
. Osteoclast ruffled border formation and acidification
. Fibroblast growth factor receptor 3 (FGFR3) hyperactivity
. Excessive production of unmineralized osteoid

Correct Answer & Explanation

. Osteoclast ruffled border formation and acidification

Explanation

The patient has Osteopetrosis (Albers-Schönberg disease), characterized by dense, brittle bones and a 'rugger-jersey' spine. It is caused by impaired osteoclast function. Mutations affecting the proton pump (TCIRG1), chloride channel (CLCN7), or carbonic anhydrase II impair the formation of the acidic microenvironment needed at the osteoclast ruffled border for bone resorption.

Question 14249

Topic: Surgical Anatomy & Approaches

A 35-year-old male sustains a closed mid-shaft humerus fracture and is noted to have a radial nerve palsy on initial presentation. He is managed non-operatively in a functional brace. At 12 weeks, there is no clinical or electromyographic (EMG) evidence of nerve recovery. What is the most appropriate next step in management?

. Continue observation for an additional 12 weeks
. Ultrasound-guided corticosteroid injection at the spiral groove
. Surgical exploration of the radial nerve
. Tendon transfer surgery for wrist and finger extension
. Magnetic resonance neurography without further intervention

Correct Answer & Explanation

. Surgical exploration of the radial nerve

Explanation

Radial nerve palsy associated with a closed humeral shaft fracture is initially managed expectantly, as up to 90% recover spontaneously. However, if there is no clinical or EMG evidence of reinnervation by 12 weeks (3 months), surgical exploration of the radial nerve is indicated to evaluate for entrapment, severe laceration, or neuroma formation.

Question 14250

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is an FDA-approved osteoinductive agent commonly used in anterior lumbar interbody fusion (ALIF), and which cell surface receptor type does it primarily bind to?

. BMP-2; Serine/threonine kinase receptor
. BMP-7; Tyrosine kinase receptor
. BMP-2; G-protein coupled receptor
. BMP-7; Ion channel receptor
. BMP-4; Tyrosine kinase receptor

Correct Answer & Explanation

. BMP-2; Serine/threonine kinase receptor

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for ALIF procedures (delivered via an absorbable collagen sponge). BMPs are part of the TGF-beta superfamily and exert their cellular effects by binding to transmembrane serine/threonine kinase receptors (Types I and II), which subsequently phosphorylate intracellular Smad proteins to alter gene transcription.

Question 14251

Topic: Biology, Genetics & Bone Healing

During the endochondral ossification phase of secondary fracture healing, which factor secreted by hypertrophic chondrocytes is most responsible for triggering vascular invasion into the cartilaginous callus?

. Vascular Endothelial Growth Factor (VEGF)
. Transforming Growth Factor Beta (TGF-beta)
. Fibroblast Growth Factor 2 (FGF-2)
. Insulin-like Growth Factor 1 (IGF-1)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Vascular Endothelial Growth Factor (VEGF)

Explanation

During endochondral ossification, hypertrophic chondrocytes secrete Vascular Endothelial Growth Factor (VEGF), which is essential for angiogenesis. The invasion of blood vessels brings osteoprogenitor cells and osteoclasts into the cartilaginous callus, triggering chondrocyte apoptosis and the replacement of cartilage with woven bone.

Question 14252

Topic: Biomechanics & Biomaterials

Viscoelastic materials exhibit time-dependent deformation. A surgeon applies a dynamic splint to a contracted joint, keeping the force constant while the tissue slowly lengthens. What viscoelastic property does this demonstrate?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a material under a constant load over time. Stress relaxation, in contrast, is the decrease in stress over time when the material is held at a constant strain (deformation).

Question 14253

Topic: 1. General Principles & Basic Science

In normal adult articular cartilage, which zone is characterized by the highest concentration of proteoglycans and the lowest concentration of water?

. 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 has the highest proteoglycan content and the lowest water concentration. The superficial zone has the highest water and lowest proteoglycan concentration, with collagen fibers oriented parallel to the joint surface to resist shear forces.

Question 14254

Topic: Biomechanics & Biomaterials

Mixing dissimilar metals in an orthopedic implant construct, such as utilizing a stainless steel screw through a titanium plate, primarily increases the risk of which type of corrosion?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Fatigue corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within an electrolytic medium (like body fluid), leading to accelerated corrosion of the less noble metal.

Question 14255

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently used in major orthopedic surgeries to reduce blood loss. What is its exact mechanism of action?
. Directly inhibits thrombin generation
. Competitively inhibits the activation of plasminogen to plasmin
. Promotes the release of von Willebrand factor from endothelial cells
. Inactivates factors Va and VIIIa
. Inhibits cyclooxygenase-1 (COX-1) mediated thromboxane A2 production

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

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

Question 14256

Topic: Infection, Pharmacology & VTE
Low-molecular-weight heparin (LMWH) is commonly prescribed for deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty. LMWH exerts its primary anticoagulant effect by binding to antithrombin III, which predominantly inactivates which of the following?
. Factor IIa (Thrombin)
. Factor VIIa
. Factor IXa
. Factor Xa
. Factor XIIa

Correct Answer & Explanation

. Factor Xa

Explanation

LMWH binds to antithrombin III and primarily accelerates the inactivation of Factor Xa. Due to its shorter chain length compared to unfractionated heparin, it has much less inhibitory effect on Factor IIa (thrombin).

Question 14257

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Which of the following is a key intracellular signaling molecule directly activated by BMP receptors?

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

Correct Answer & Explanation

. Smad

Explanation

BMPs bind to serine/threonine kinase cell surface receptors, which phosphorylate intracellular Smad proteins (specifically R-Smads 1, 5, and 8). These then form a complex with Smad4, translocate to the nucleus, and regulate the transcription of osteogenic genes such as Runx2.

Question 14258

Topic: 1. General Principles & Basic Science

In the classical phases of wound healing, which cell type becomes the predominant cell in the wound bed 48 to 72 hours post-injury?

. Platelets
. Neutrophils
. Macrophages
. Fibroblasts
. Lymphocytes

Correct Answer & Explanation

. Macrophages

Explanation

Neutrophils are the first inflammatory cells to arrive (within 24 hours). Macrophages migrate into the wound after 48-72 hours, becoming the predominant cell type and orchestrating the transition to the proliferative phase by releasing cytokines (e.g., TGF-beta, PDGF). Fibroblasts predominate later (days 3-5).

Question 14259

Topic: Physiology & Rehabilitation
A patient suffers a penetrating trauma to the spinal cord resulting in Brown-Séquard syndrome. Clinical examination below the level of the lesion will typically demonstrate:
. Ipsilateral loss of pain and temperature, contralateral loss of motor function
. Ipsilateral loss of motor function and proprioception, contralateral loss of pain and temperature
. Bilateral loss of motor function, preservation of dorsal columns
. Contralateral loss of proprioception, ipsilateral loss of pain and temperature
. Bilateral loss of pain and temperature, preservation of motor function

Correct Answer & Explanation

. Ipsilateral loss of motor function and proprioception, contralateral loss of pain and temperature

Explanation

Brown-Séquard syndrome (hemisection of the spinal cord) causes ipsilateral loss of motor function (corticospinal tract) and proprioception/vibration (dorsal columns), and contralateral loss of pain and temperature sensation (spinothalamic tract, which decussates 1-2 levels above entry).

Question 14260

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of Rheumatoid Arthritis, the interaction between RANKL and RANK leads to characteristic periarticular bone erosions. Which cell type is the primary source of RANKL in the inflamed rheumatoid synovium?

. Osteoblasts
. Osteoclasts
. Synovial fibroblasts and T cells
. Chondrocytes
. Neutrophils

Correct Answer & Explanation

. Synovial fibroblasts and T cells

Explanation

In Rheumatoid Arthritis, the inflamed synovium (pannus) is rich in synovial fibroblasts and activated T-lymphocytes, both of which secrete copious amounts of RANKL. This drives massive local osteoclastogenesis and the characteristic marginal bone erosions.

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