Menu

1. General Principles & Basic Science MCQs

Practice Set 650 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 12981

Topic: Biomechanics & Biomaterials

A surgeon is revising a failed internal fixation of a femur. The original construct consisted of a stainless steel plate with several titanium screws used as replacements during a previous reoperation. Severe localized corrosion is noted at the plate-screw interfaces. Which of the following best describes the electrochemical phenomenon occurring in this mixed-metal construct?

. Crevice corrosion due to oxygen depletion
. Fretting corrosion from micromotion
. Galvanic corrosion with titanium acting as the anode
. Galvanic corrosion with stainless steel acting as the anode
. Pitting corrosion due to chloride ion attack

Correct Answer & Explanation

. Galvanic corrosion with stainless steel acting as the anode

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic solution (body fluid). Titanium is more noble (more cathodic) in the body environment due to its highly stable oxide layer, forcing the stainless steel to act as the anode and undergo accelerated corrosion.

Question 12982

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following represents the primary mechanism of action of this agent?
. Reversible blockade of the ADP receptor (P2Y12) on platelets
. Competitive inhibition of plasminogen activation by binding to lysine receptor sites
. Enhancement of antithrombin III binding to factor Xa
. Direct inhibition of tissue plasminogen activator (tPA) synthesis
. Promotion of von Willebrand factor release from Weibel-Palade bodies

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation by binding to lysine receptor sites

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It exerts its antifibrinolytic effect by reversibly and competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin, inhibiting its conversion to plasmin by tPA.

Question 12983

Topic: 1. General Principles & Basic Science

Which of the following modifications to a cortical bone screw design will most significantly increase its pullout strength in diaphyseal bone?

. Increasing the inner core diameter
. Increasing the outer thread diameter
. Increasing the thread pitch
. Decreasing the insertion torque
. Decreasing the thread depth

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

Pullout strength of a screw is most strongly influenced by its outer (major) diameter. Increasing the outer diameter, increasing the thread depth, or decreasing the pitch all enhance a screw's pullout strength.

Question 12984

Topic: 1. General Principles & Basic Science

A researcher is analyzing the biochemical composition of normal articular cartilage. Which of the following accurately describes the superficial zone compared to the deep zone?

. Highest proteoglycan concentration
. Highest concentration of water
. Vertically oriented collagen fibers
. Lowest concentration of chondrocytes
. Highest concentration of type X collagen

Correct Answer & Explanation

. Highest concentration of water

Explanation

The superficial zone of articular cartilage contains the highest concentration of water and horizontally oriented collagen fibers to resist shear stress. The deep zone has the highest proteoglycan concentration and vertically oriented collagen fibers.

Question 12985

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, hearing loss, and anterior bowing of the tibia. A bone biopsy of the affected tibia would most likely show which of the following cellular abnormalities?

. Defective osteoid mineralization
. Absence of ruffled borders on osteoclasts
. Woven bone lacking osteocytes
. Large multinucleated osteoclasts with viral-like inclusion bodies
. A decreased ratio of woven to lamellar bone

Correct Answer & Explanation

. Large multinucleated osteoclasts with viral-like inclusion bodies

Explanation

Paget's disease is driven by intense, unregulated osteoclastic bone resorption followed by disorganized osteoblastic bone formation. The hallmark histological finding is hyper-multinucleated osteoclasts that may contain paramyxovirus-like inclusion bodies.

Question 12986

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is utilized to enhance spinal fusion. Through which of the following intracellular signaling pathways does rhBMP-2 primarily exert its osteoinductive effect?

. Wnt/beta-catenin pathway
. JAK/STAT pathway
. RANK/RANKL pathway
. SMAD 1/5/8 pathway
. MAP kinase pathway

Correct Answer & Explanation

. SMAD 1/5/8 pathway

Explanation

BMPs are members of the TGF-beta superfamily and bind to serine/threonine kinase receptors. This activates the intracellular SMAD 1/5/8 complex, which translocates to the nucleus to upregulate osteogenic genes like Runx2.

Question 12987

Topic: Biomechanics & Biomaterials

A patient undergoes revision surgery for a failed dynamic compression plate. Intraoperatively, black debris is noted at the plate-screw interface with no evidence of infection. Both the plate and screws are made of titanium. What is the most likely mechanism of this wear?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs due to micromotion at the interface between two highly loaded components, such as a screw head and a plate hole, even if they are made of the same metal. Galvanic corrosion requires dissimilar metals.

Question 12988

Topic: 1. General Principles & Basic Science

Which of the following best describes the primary mechanism by which an autologous cancellous bone graft incorporates into a host site?

. Initial osteoclastic resorption followed by osteoblastic bone formation
. Direct membranous ossification without a cartilage intermediate
. Creeping substitution with appositional new bone formation on existing trabeculae
. Chondrocyte hypertrophy and endochondral ossification
. Fibrous tissue interposition followed by progressive mineralization

Correct Answer & Explanation

. Creeping substitution with appositional new bone formation on existing trabeculae

Explanation

Cancellous grafts primarily incorporate via creeping substitution, where host osteoblasts lay down appositional new bone directly on the existing necrotic trabecular framework. In contrast, cortical grafts must first undergo extensive osteoclastic resorption.

Question 12989

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse bone pain and muscle weakness. Radiographs demonstrate bilateral symmetric radiolucent lines perpendicular to the cortex in the femoral necks. Laboratory studies show low serum calcium and elevated alkaline phosphatase. A bone biopsy would most likely reveal:

. Increased woven bone with a mosaic pattern
. Abundant unmineralized osteoid seams
. Empty lacunae with extensive marrow fibrosis
. Subperiosteal bone resorption
. Multinucleated giant cells in a dense fibrous stroma

Correct Answer & Explanation

. Abundant unmineralized osteoid seams

Explanation

The patient's presentation and radiographic Looser zones (pseudofractures) are classic for osteomalacia. The histological hallmark of osteomalacia is an accumulation of abundant, unmineralized osteoid seams due to defective mineralization.

Question 12990

Topic: Biology, Genetics & Bone Healing

A patient with metastatic breast cancer to the spine is started on denosumab. This medication inhibits osteoclastogenesis by directly binding to which target, effectively mimicking the action of which endogenous protein?

. Binds to RANK, mimicking Osteoprotegerin (OPG)
. Binds to RANKL, mimicking Osteoprotegerin (OPG)
. Binds to Osteoprotegerin, mimicking RANKL
. Binds to M-CSF, mimicking RANK
. Binds to alpha-v beta-3 integrin, mimicking Osteopontin

Correct Answer & Explanation

. Binds to RANKL, mimicking Osteoprotegerin (OPG)

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor on osteoclasts. This mimics the normal physiologic function of endogenous Osteoprotegerin (OPG).

Question 12991

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopedic metal implant, the exact point at which the material ceases to exhibit elastic behavior and begins to permanently deform is known as the:

. Ultimate tensile strength
. Proportional limit
. Yield point
. Failure point
. Elastic modulus

Correct Answer & Explanation

. Yield point

Explanation

The yield point represents the transition from elastic deformation (where the material returns to its original shape) to plastic deformation (where permanent structural changes occur). The slope of the elastic region is the Young's elastic modulus.

Question 12992

Topic: 1. General Principles & Basic Science

Intravenous tranexamic acid (TXA) is routinely used to reduce blood loss during total joint arthroplasty. What is the primary mechanism of action of this pharmacological agent?

. Direct irreversible inhibition of Factor Xa
. Reversible binding to the thrombin receptor
. Competitive inhibition of plasminogen activation
. Stimulation of von Willebrand factor release from endothelium
. Irreversible inhibition of platelet cyclooxygenase-1

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is an antifibrinolytic agent that structurally mimics lysine. It binds to plasminogen, competitively inhibiting its activation into plasmin, thereby preventing the degradation of fibrin clots.

Question 12993

Topic: Biomechanics & Biomaterials
Increasing the radiation dose during the cross-linking process of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty has which of the following biomechanical effects?
. Increases both wear resistance and fatigue strength
. Increases wear resistance but decreases fatigue strength
. Decreases wear resistance and decreases fatigue strength
. Decreases wear resistance but increases fatigue strength
. Increases wear resistance without affecting fatigue strength

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Highly cross-linked polyethylene significantly improves adhesive and abrasive wear resistance, reducing osteolysis. However, the cross-linking process reduces the material's mechanical properties, including fatigue strength and fracture toughness.

Question 12994

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents with a secondary radial nerve palsy. An EMG at 4 weeks shows fibrillation potentials, but surgical exploration reveals an intact epineurium, perineurium, and endoneurium. According to the Seddon classification, this nerve injury is best classified as:

. Neuropraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade IV
. Sunderland Grade V

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis involves disruption of the axon and myelin sheath with Wallerian degeneration (causing fibrillation potentials on EMG), but the supporting connective tissue frameworks (endoneurium, perineurium, epineurium) remain completely intact.

Question 12995

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently used in joint arthroplasty. Which of the following statements regarding the mechanical properties and functional characteristics of PMMA is true?

. It is strongest in tension and weakest in compression.
. The addition of barium sulfate increases its ultimate tensile strength.
. The polymerization process is a strongly endothermic reaction.
. It acts as an adhesive that chemically bonds directly to the host bone.
. It functions via mechanical interlock and is strongest in compression.

Correct Answer & Explanation

. It functions via mechanical interlock and is strongest in compression.

Explanation

PMMA acts as a grout, relying on mechanical interlocking with cancellous bone rather than chemical adhesion. It is significantly stronger in compression than in tension or shear, and its polymerization is highly exothermic.

Question 12996

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with back pain and a lytic lesion in the L3 vertebral body. Laboratory studies reveal a monoclonal gammopathy and hypercalcemia. Which of the following cytokines is most responsible for stimulating the osteoclastic bone resorption seen in this condition?

. Interleukin-2 (IL-2)
. Interleukin-6 (IL-6)
. Transforming growth factor-beta (TGF-beta)
. Interferon-gamma (IFN-gamma)
. Bone morphogenetic protein-4 (BMP-4)

Correct Answer & Explanation

. Interleukin-6 (IL-6)

Explanation

In multiple myeloma, malignant plasma cells secrete osteoclast-activating factors. Interleukin-6 (IL-6) and RANKL are primarily responsible for upregulating osteoclast activity, leading to characteristic lytic bone lesions.

Question 12997

Topic: 1. General Principles & Basic Science

Which of the following represents the earliest biochemical change in articular cartilage during the pathogenesis of primary osteoarthritis?

. Decrease in total water content
. Increase in total water content
. Increase in proteoglycan concentration
. Decrease in chondrocyte synthesis of type II collagen
. Increase in the ratio of keratin sulfate to chondroitin sulfate

Correct Answer & Explanation

. Increase in total water content

Explanation

The earliest biochemical change in osteoarthritis is the disruption of the collagen matrix, which leads to an increase in total water content and cartilage swelling. This is accompanied by a decrease in proteoglycan concentration.

Question 12998

Topic: Biology, Genetics & Bone Healing

Which of the following represents the primary receptor on osteoclast precursors required for their differentiation, and what is its competitive decoy receptor?

. RANK and Osteoprotegerin
. RANKL and Osteoprotegerin
. M-CSF and RANK
. Osteoprotegerin and RANKL
. Integrin avb3 and RANK

Correct Answer & Explanation

. RANKL and Osteoprotegerin

Explanation

Receptor Activator of Nuclear factor Kappa-B (RANK) is expressed on osteoclast precursors and is essential for their differentiation and activation. Osteoprotegerin (OPG) is secreted by osteoblasts and acts as a decoy receptor for RANKL, competitively inhibiting it from binding to RANK.

Question 12999

Topic: Biology, Genetics & Bone Healing

A 45-year-old female with short bowel syndrome presents with diffuse bone pain and muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone. A bone biopsy would most likely show which of the following?

. Haphazard woven bone pattern
. Empty lacunae and necrotic bone marrow
. Unmineralized osteoid seams
. Thickened cortical bone with narrowed medullary canals
. Giant cell granulomas

Correct Answer & Explanation

. Unmineralized osteoid seams

Explanation

The clinical and laboratory picture is classic for osteomalacia secondary to malabsorption. Osteomalacia is characterized histologically by wide, unmineralized osteoid seams due to defective mineralization of newly formed osteoid.

Question 13000

Topic: Biomechanics & Biomaterials

Mixing stainless steel and titanium implants in the same surgical site increases the risk of which specific type of material degradation?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within a conductive fluid environment, such as the human body. This leads to accelerated corrosion of the less noble metal.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page