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1. General Principles & Basic Science MCQs

Practice Set 668 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 13341

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia. Biopsy shows mononuclear cells interspersed with multinucleated giant cells. If pharmacological treatment is indicated, which of the following medications directly targets the pathophysiology of this lesion?

. Bisphosphonates
. Denosumab
. Methotrexate
. Imatinib
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Giant Cell Tumor of Bone is characterized by neoplastic mononuclear stromal cells that express high levels of RANKL, driving the recruitment of reactive osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, directly inhibits this essential pathway.

Question 13342

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with a secondary radial nerve palsy. According to the Seddon classification, if this is an axonotmesis, which of the following histologic structures remains intact?

. Myelin sheath only
. Axon and myelin sheath
. Endoneurium, perineurium, and epineurium
. Axon only
. No structures remain intact

Correct Answer & Explanation

. Endoneurium, perineurium, and epineurium

Explanation

In an axonotmesis, the axon and its myelin sheath are disrupted, leading to Wallerian degeneration distally. However, the surrounding connective tissue framework (endoneurium, perineurium, and epineurium) remains completely intact, allowing for potential spontaneous axonal regeneration.

Question 13343

Topic: 1. General Principles & Basic Science

Which glycosaminoglycan is the most abundant in the extracellular matrix of adult articular cartilage?

. Chondroitin sulfate
. Keratan sulfate
. Dermatan sulfate
. Hyaluronic acid
. Heparan sulfate

Correct Answer & Explanation

. Chondroitin sulfate

Explanation

Chondroitin sulfate is the most abundant glycosaminoglycan in articular cartilage, followed by keratan sulfate. Its concentration decreases with age, whereas keratan sulfate concentration increases over time.

Question 13344

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with hearing loss and increasing hat size. Radiographs show a "cotton wool" appearance of the skull. Which of the following is the primary cellular abnormality initiating this disease process?

. Overactive osteoblasts with disorganized woven bone formation
. Increased number and size of multinucleated osteoclasts
. Defective mineralization of osteoid by osteoblasts
. Deficient type I collagen synthesis
. Autonomous hypersecretion of parathyroid hormone

Correct Answer & Explanation

. Increased number and size of multinucleated osteoclasts

Explanation

Paget's disease is primarily a disorder of osteoclast function, characterized by large, multinucleated osteoclasts leading to massive bone resorption. This is followed by a secondary, disorganized osteoblastic response.

Question 13345

Topic: Biomechanics & Biomaterials

When two dissimilar metals, such as a titanium plate and stainless steel screws, are placed in contact within the body's electrolyte-rich environment, which type of corrosion is most likely to occur?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct contact within an electrolyte solution, leading to an electrochemical gradient and material breakdown.

Question 13346

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, at which specific stage does the peak expression of Type II collagen occur?

. Hematoma formation
. Soft callus formation
. Hard callus formation
. Remodeling phase
. Inflammation phase

Correct Answer & Explanation

. Soft callus formation

Explanation

Type II collagen is the primary collagen type found in cartilage and reaches peak expression during the soft callus (chondrogenic) phase of secondary fracture healing. Type I collagen peaks later during hard callus formation.

Question 13347

Topic: 1. General Principles & Basic Science

Which of the following bone graft substitutes possesses osteoinductive properties but definitively lacks osteoconductive and osteogenic properties?

. Cancellous autograft
. Demineralized bone matrix (DBM)
. Calcium phosphate cement
. Cancellous allograft
. Synthetic hydroxyapatite

Correct Answer & Explanation

. Demineralized bone matrix (DBM)

Explanation

Demineralized bone matrix (DBM) provides osteoinductive proteins, such as BMPs, but lacks a structural scaffolding for osteoconduction and contains no live cells for osteogenesis.

Question 13348

Topic: 1. General Principles & Basic Science

Which specific modification to a standard cortical screw design will most effectively increase its pullout strength in dense bone?

. Increasing the inner core diameter
. Decreasing the outer thread diameter
. Decreasing the thread pitch
. Increasing the screw head diameter
. Increasing the length of the unthreaded shaft

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the volume of bone caught between the screw threads. Decreasing the thread pitch (creating more threads per unit length) effectively increases pullout strength.

Question 13349

Topic: Infection, Pharmacology & VTE
A patient is scheduled for a total hip arthroplasty and will receive rivaroxaban for postoperative venous thromboembolism prophylaxis. What is the specific mechanism of action of this drug?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K antagonist
. Enhances antithrombin III activity
. Irreversible cyclooxygenase inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that works by directly inhibiting Factor Xa, interrupting the common pathway of the coagulation cascade. Dabigatran, in contrast, is a direct thrombin (Factor IIa) inhibitor.

Question 13350

Topic: Physiology & Rehabilitation

During an eccentric muscle contraction, how does the force-velocity relationship primarily differ from that of a concentric muscle contraction?

. Force decreases as the velocity of lengthening increases
. Force increases as the velocity of lengthening increases
. Force remains constant regardless of lengthening velocity
. Force generated is strictly lower than maximum isometric force
. Force decreases linearly with overall muscle length

Correct Answer & Explanation

. Force increases as the velocity of lengthening increases

Explanation

In an eccentric contraction, the muscle lengthens while contracting against a load. The force generated increases as the velocity of lengthening increases until a plateau is reached, generating forces greater than maximum isometric force.

Question 13351

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with progressive bowing of his lower extremities. Laboratory evaluation reveals profound hypophosphatemia, normal serum calcium, normal PTH, and elevated alkaline phosphatase. Which of the following is the most likely diagnosis?

. Vitamin D-dependent rickets type I
. Nutritional rickets
. X-linked hypophosphatemic rickets
. Osteogenesis imperfecta
. Renal osteodystrophy

Correct Answer & Explanation

. X-linked hypophosphatemic rickets

Explanation

X-linked hypophosphatemic rickets is driven by an excess of FGF-23, leading to severe renal phosphate wasting. This results in isolated hypophosphatemia with classically normal calcium and parathyroid hormone levels.

Question 13352

Topic: Biomechanics & Biomaterials

Stress shielding around an orthopedic implant occurs because the metallic implant is significantly stiffer than the surrounding bone. Among the following orthopedic biomaterials, which has a modulus of elasticity closest to that of human cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Alumina
. Zirconia

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity of approximately 110 GPa, which is lower than stainless steel (~200 GPa) and cobalt-chromium (~240 GPa), making it the closest metal to human cortical bone (~15-20 GPa).

Question 13353

Topic: Infection, Pharmacology & VTE

A 3-year-old girl is brought to the emergency department with an acute limp and refuses to bear weight on her right leg. Joint aspiration of the hip reveals a synovial fluid white blood cell count of 85,000 cells/mm3 with 90% polymorphonuclear leukocytes. What is the most common causative organism of septic arthritis in this age group?

. Streptococcus pyogenes
. Staphylococcus aureus
. Kingella kingae
. Haemophilus influenzae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Staphylococcus aureus remains the single most common organism causing septic arthritis in children overall. While Kingella kingae is increasingly recognized in children under 4 years old, S. aureus represents the classic and most frequent isolate.

Question 13354

Topic: 1. General Principles & Basic Science

In a healthy native diarthrodial joint during high-load and low-speed activities (e.g., initiating standing from a chair), which type of cartilage lubrication mechanism is predominantly active to minimize friction?

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

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication depends on a distinct molecular layer of lubricin adhering directly to the articular surfaces. It is the primary mechanism preventing surface wear and reducing friction during conditions of extreme load and low speed.

Question 13355

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman is treated for severe osteoporosis with a targeted medication that directly stimulates osteoblastic bone formation by acting as a recombinant fragment of human parathyroid hormone. Which medication was prescribed?

. Alendronate
. Denosumab
. Teriparatide
. Raloxifene
. Romosozumab

Correct Answer & Explanation

. Teriparatide

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34) that acts as a powerful anabolic agent to directly stimulate new bone formation. Unlike bisphosphonates or denosumab, it builds bone rather than primarily inhibiting resorption.

Question 13356

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft substitutes possesses osteoinductive, osteoconductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous autograft
. Cortical allograft
. Calcium sulfate
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Cancellous autograft

Explanation

Cancellous autograft is the gold standard because it is the only option that possesses all three properties: osteogenesis (live cells), osteoinduction (growth factors like BMPs), and osteoconduction (trabecular scaffold). Demineralized bone matrix (DBM) is osteoconductive and osteoinductive but lacks live cells, meaning it is not osteogenic.

Question 13357

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive bowing of his right tibia and an increasing hat size. Radiographs show cortical thickening and altered trabecular patterns. What is the primary cellular defect initiating this condition?

. Decreased osteoblast function
. Increased osteoblast function
. Defective mineralization of osteoid
. Increased osteoclast activity with abnormal morphology
. Deficiency of Type I collagen synthesis

Correct Answer & Explanation

. Increased osteoclast activity with abnormal morphology

Explanation

Paget's disease of bone is primarily driven by abnormal, hyperactive osteoclasts that are larger and multinucleated (often containing viral inclusion bodies like paramyxovirus). This triggers a chaotic secondary osteoblastic response resulting in disorganized woven bone.

Question 13358

Topic: 1. General Principles & Basic Science
In evaluating a patient with suspected necrotizing fasciitis, the LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score is calculated. Which of the following laboratory parameters is most heavily weighted in this scoring system?
. Erythrocyte sedimentation rate (ESR)
. C-reactive protein (CRP)
. Serum lactate
. Procalcitonin
. Serum creatinine

Correct Answer & Explanation

. C-reactive protein (CRP)

Explanation

The LRINEC score utilizes CRP, WBC count, Hemoglobin, Serum sodium, Serum creatinine, and Serum glucose. CRP > 150 mg/L contributes 4 points, making it the most heavily weighted single parameter in the scoring system. ESR, lactate, and procalcitonin are not part of the standard LRINEC score.

Question 13359

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone has the highest concentration of water and the lowest concentration of proteoglycans?

. 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 has the highest water content (approx. 80%) and the lowest concentration of proteoglycans. Collagen fibers (primarily Type II) are aligned parallel to the joint surface to resist shear forces.

Question 13360

Topic: Biomechanics & Biomaterials

Galvanic corrosion of orthopedic implants is most likely to occur under which of the following conditions?

. Cyclic loading of a single metal implant
. Fretting between the screw head and the plate
. Contact between two dissimilar metals in an electrolytic environment
. Lack of oxygen at the interface of the implant and bone
. Excessive release of metal ions due to high wear rates

Correct Answer & Explanation

. Contact between two dissimilar metals in an electrolytic environment

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in electrical contact within an electrolytic medium (like body fluids). This leads to an electrochemical potential difference, causing the less noble metal to corrode.

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