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1. General Principles & Basic Science MCQs

Practice Set 446 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 8901

Topic: Biology, Genetics & Bone Healing

A midshaft tibia fracture is treated with a reamed, statically locked intramedullary nail. Which type of bone healing predominates in this biomechanical environment?

. Primary bone healing via cutting cones
. Secondary bone healing via endochondral ossification
. Intramembranous ossification exclusively
. Appositional bone growth
. Creeping substitution

Correct Answer & Explanation

. Secondary bone healing via endochondral ossification

Explanation

Intramedullary nailing provides relative stability, which promotes secondary bone healing through callus formation. This process predominantly relies on endochondral ossification, where a cartilage intermediate is formed and subsequently replaced by bone.

Question 8902

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with an immediate complete radial nerve palsy. If an electromyogram (EMG) is obtained, at what time point after injury are fibrillation potentials most likely to first appear?

. Immediately post-injury
. 1 to 3 days post-injury
. 2 to 3 weeks post-injury
. 6 to 8 weeks post-injury
. 3 to 6 months post-injury

Correct Answer & Explanation

. 2 to 3 weeks post-injury

Explanation

Fibrillation potentials and positive sharp waves are hallmark EMG signs of muscle denervation. They typically take 2 to 3 weeks to appear following the nerve injury as Wallerian degeneration progresses.

Question 8903

Topic: 1. General Principles & Basic Science

When evaluating a new diagnostic test for periprosthetic joint infection, the positive predictive value (PPV) of the test is most heavily influenced by which of the following statistical parameters?

. Sensitivity of the test
. Specificity of the test
. Prevalence of the disease in the study population
. P-value of the validation study
. Type II error rate

Correct Answer & Explanation

. Prevalence of the disease in the study population

Explanation

The positive predictive value (PPV) is highly dependent on the prevalence of the disease in the tested population. Even a test with high sensitivity and specificity will have a low PPV if the disease prevalence is very low.

Question 8904

Topic: Biomechanics & Biomaterials

A patient undergoes revision total hip arthroplasty for unexplained pain and a pseudo-tumor associated with a modular neck prosthesis. Black particulate debris is noted at the head-neck junction. What type of corrosion primarily initiates this specific failure cascade?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at modular interfaces (like the trunnion-head junction) due to micromotion under cyclical loading. This mechanical disruption destroys the passivating oxide layer, leading to mechanically assisted crevice corrosion (trunnionosis).

Question 8905

Topic: Biology, Genetics & Bone Healing

A 30-year-old female is diagnosed with an advanced giant cell tumor of bone in the distal femur. Denosumab is recommended for neoadjuvant treatment. What is the exact mechanism of action of this medication?

. Inhibits VEGF to prevent tumor angiogenesis
. Directly induces apoptosis of the neoplastic mononuclear cells
. Binds to RANKL to prevent osteoclastogenesis
. Binds to the RANK receptor directly on giant cells
. Inhibits matrix metalloproteinases

Correct Answer & Explanation

. Binds to RANKL to prevent osteoclastogenesis

Explanation

Denosumab is a human monoclonal antibody that binds to RANK Ligand (RANKL). By preventing RANKL from binding to the RANK receptor on osteoclast precursors, it severely inhibits the formation and function of the reactive osteoclast-like giant cells that destroy bone.

Question 8906

Topic: Biology, Genetics & Bone Healing

During the evaluation of a patient with suspected osteomalacia, vitamin D metabolism is reviewed. Which enzyme is directly responsible for the conversion of 25-hydroxyvitamin D to its most active hormonal form, 1,25-dihydroxyvitamin D?

. 25-hydroxylase
. 1-alpha-hydroxylase
. 24-hydroxylase
. Alkaline phosphatase
. Carbonic anhydrase

Correct Answer & Explanation

. 1-alpha-hydroxylase

Explanation

1-alpha-hydroxylase, located primarily in the proximal tubules of the kidney, converts 25(OH)D to 1,25(OH)2D, the fully active form of vitamin D. This enzyme is stimulated by parathyroid hormone (PTH) and hypophosphatemia.

Question 8907

Topic: Biology, Genetics & Bone Healing

A surgeon plans to use demineralized bone matrix (DBM) to augment a tibial nonunion repair. Compared to an autologous iliac crest bone graft, DBM inherently possesses which of the following biologic properties for bone healing?

. Osteoinduction only
. Osteoconduction only
. Osteogenesis and osteoinduction
. Osteoconduction and osteoinduction
. Osteogenesis only

Correct Answer & Explanation

. Osteoconduction and osteoinduction

Explanation

Demineralized bone matrix (DBM) provides a structural collagen scaffold (osteoconduction) and retains exposed growth factors such as BMPs (osteoinduction). Unlike fresh autograft, it lacks viable cells and is therefore not osteogenic.

Question 8908

Topic: 1. General Principles & Basic Science

In the basic science of skeletal muscle contraction, which of the following events directly initiates the release of calcium ions from the sarcoplasmic reticulum?

. Binding of ATP to the myosin head
. Action potential propagation down the T-tubule
. Binding of acetylcholine to muscarinic receptors
. Detachment of the troponin-tropomyosin complex
. Hydrolysis of ATP by the sarcoplasmic reticulum pump

Correct Answer & Explanation

. Action potential propagation down the T-tubule

Explanation

Skeletal muscle contraction is initiated when an action potential travels down the T-tubules, activating dihydropyridine receptors. These receptors interact with ryanodine receptors on the sarcoplasmic reticulum, triggering massive calcium release.

Question 8909

Topic: Biology, Genetics & Bone Healing

A 40-year-old man sustains a fracture of the tibial shaft and undergoes reamed intramedullary nailing. Which of the following phases of fracture healing is most directly enhanced by the mechanical stability provided by the nail while still allowing controlled micromotion?

. Primary bone healing via cutting cones
. Formation of a hard callus via intramembranous ossification
. Endochondral ossification of the soft callus
. Inflammation and hematoma organization
. Direct lamellar bone deposition

Correct Answer & Explanation

. Endochondral ossification of the soft callus

Explanation

Intramedullary nailing provides relative stability, which promotes secondary bone healing through callus formation. Controlled micromotion specifically stimulates endochondral ossification, where cartilage is progressively replaced by bone.

Question 8910

Topic: Biomechanics & Biomaterials

A researcher is evaluating the mechanical properties of a newly developed orthopaedic alloy. On the generated stress-strain curve, the point at which the material ceases to deform elastically and begins to deform permanently is known as the:

. Ultimate tensile strength
. Proportional limit (Yield point)
. Modulus of elasticity
. Failure point
. Endurance limit

Correct Answer & Explanation

. Proportional limit (Yield point)

Explanation

The yield point, or proportional limit, represents the transition from elastic (reversible) deformation to plastic (permanent) deformation on a stress-strain curve. The modulus of elasticity represents the slope of the elastic region.

Question 8911

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a lytic lesion in the distal femur. Biopsy confirms a giant cell tumor of bone. She is treated with denosumab to downstage the tumor prior to surgery. What is the mechanism of action of this medication?

. Binds to the RANK receptor on osteoclasts
. Binds to RANKL, preventing interaction with RANK
. Inhibits farnesyl pyrophosphate synthase
. Inhibits cathepsin K
. Binds to osteoprotegerin

Correct Answer & Explanation

. Binds to RANKL, preventing interaction with RANK

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL. This prevents RANKL from interacting with the RANK receptor on osteoclasts, thereby inhibiting osteoclast formation, function, and survival.

Question 8912

Topic: Biomechanics & Biomaterials

Which of the following best describes the viscoelastic property of "creep" in orthopedic tissues?

. Progressive deformation over time under a constant load
. Decreasing stress over time under a constant deformation
. Increased stiffness with higher rates of loading
. Energy lost during a loading and unloading cycle
. Failure of a material after repeated cyclic loading

Correct Answer & Explanation

. Progressive deformation over time under a constant load

Explanation

Creep is the gradual, time-dependent deformation of a viscoelastic material when subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when held at a constant deformation.

Question 8913

Topic: 1. General Principles & Basic Science

Which of the following biochemical changes occurs in articular cartilage during the early stages of osteoarthritis but NOT in normal aging?

. Increased water content
. Decreased chondroitin sulfate concentration
. Increased keratin sulfate concentration
. Decreased total proteoglycan content
. Decreased collagen cross-linking

Correct Answer & Explanation

. Increased water content

Explanation

In the early stages of osteoarthritis, the collagen network is disrupted, allowing proteoglycans to swell and leading to an increase in water content. In normal aging, the water content of articular cartilage decreases.

Question 8914

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants due to its biocompatibility. Compared to cobalt-chromium alloys, titanium alloy exhibits which of the following mechanical properties?

. Higher modulus of elasticity
. Higher density
. Lower notch sensitivity
. Lower modulus of elasticity
. Greater galvanic potential

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloys have a lower modulus of elasticity than cobalt-chromium alloys or stainless steel, making them closer to the elasticity of cortical bone. This helps reduce stress shielding around implants.

Question 8915

Topic: Biology, Genetics & Bone Healing

Following a diaphyseal fracture, rigid fixation with compression plating is performed, resulting in absolute stability. By which of the following primary mechanisms will the fracture heal?

. Intramembranous ossification without a cartilaginous intermediate
. Endochondral ossification with a cartilaginous intermediate
. Creeping substitution
. Haversian remodeling across the fracture site
. Osteoconduction via a hematoma scaffold

Correct Answer & Explanation

. Haversian remodeling across the fracture site

Explanation

Rigid fixation providing absolute stability prevents fracture callus formation. The fracture heals via primary bone healing, which involves direct Haversian remodeling (cutting cones) across the fracture site.

Question 8916

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is commonly used in total joint arthroplasty. Which of the following occurs during the polymerization process of PMMA?

. Endothermic reaction resulting in localized cooling
. Release of nitrogen gas to create porosity
. Exothermic reaction that can cause thermal necrosis
. Expansion of the cement volume upon curing
. Cross-linking initiated by exposure to ultraviolet light

Correct Answer & Explanation

. Exothermic reaction that can cause thermal necrosis

Explanation

The polymerization of PMMA is a highly exothermic reaction. Temperatures can exceed 80-100°C, which poses a risk of thermal necrosis to the surrounding bone.

Question 8917

Topic: 1. General Principles & Basic Science
During the remodeling phase of tendon healing, the newly synthesized extracellular matrix undergoes maturation. This phase is characterized primarily by an increase in which of the following?
. Type III collagen relative to Type I collagen
. Cellularity and angiogenesis
. Proportion of Type I collagen and longitudinal fiber alignment
. Glycosaminoglycan content
. Inflammatory macrophage infiltration

Correct Answer & Explanation

. Proportion of Type I collagen and longitudinal fiber alignment

Explanation

The remodeling phase of tendon healing is marked by decreasing cellularity and an increasing synthesis of Type I collagen. The newly formed collagen fibers align longitudinally along lines of mechanical stress.

Question 8918

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman receives intravenous zoledronic acid for the treatment of severe osteoporosis. At the cellular level, this medication inhibits osteoclast-mediated bone resorption primarily by inhibiting which of the following enzymes?

. Matrix metalloproteinase-9
. Farnesyl pyrophosphate synthase
. Carbonic anhydrase II
. Tartrate-resistant acid phosphatase
. Cathepsin K

Correct Answer & Explanation

. Farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates, such as zoledronic acid and alendronate, inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis.

Question 8919

Topic: Biomechanics & Biomaterials
A patient presents with acute knee swelling. Aspiration yields cloudy synovial fluid with a white blood cell count of 65,000 cells/mm³, predominantly polymorphonuclear leukocytes. Polarized light microscopy shows negatively birefringent, needle-shaped crystals. What is the composition of these crystals?
. Calcium pyrophosphate dihydrate
. Monosodium urate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Monosodium urate

Explanation

The clinical picture and fluid analysis are diagnostic of acute gout. Monosodium urate crystals are classically needle-shaped and exhibit strong negative birefringence under polarized light.

Question 8920

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the highest concentration of water and lowest concentration of proteoglycans are found in which structural zone?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (approx. 80%) and the lowest proteoglycan content. The collagen fibers are aligned parallel to the joint surface to resist shear forces.

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