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1. General Principles & Basic Science MCQs

Practice Set 674 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 13461

Topic: Biology, Genetics & Bone Healing

Which Bone Morphogenetic Protein (BMP) is FDA-approved for use in acute open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-6
. BMP-7

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for use in acute, open tibial shaft fractures when applied via an absorbable collagen sponge. BMP-7 (Osteogenic Protein-1) historically had a Humanitarian Device Exemption for recalcitrant tibial nonunions.

Question 13462

Topic: Infection, Pharmacology & VTE

In evaluating synovial fluid from a painful knee, which of the following profiles is most characteristic of an inflammatory arthropathy such as Rheumatoid Arthritis?

. Clear, highly viscous fluid with 1,500 WBC/mm3 and <25% PMNs
. Yellow, translucent fluid with 4,000 WBC/mm3 and 30% PMNs
. Opaque, yellow-green fluid with 45,000 WBC/mm3 and 80% PMNs
. Opaque, purulent fluid with 120,000 WBC/mm3 and 95% PMNs
. Bloody fluid with lipid droplets

Correct Answer & Explanation

. Opaque, yellow-green fluid with 45,000 WBC/mm3 and 80% PMNs

Explanation

Inflammatory synovial fluid (Group II) is typically translucent to opaque, yellow/green, with decreased viscosity and a WBC count ranging from 2,000 to 50,000 cells/mm3, containing >50% PMNs. Non-inflammatory (OA) fluid has <2,000 WBCs. Septic arthritis fluid typically has >50,000 WBCs with >90% PMNs.

Question 13463

Topic: Biomechanics & Biomaterials
What is the primary purpose of highly cross-linking ultra-high molecular weight polyethylene (UHMWPE) used in total joint arthroplasty?
. To increase the ultimate tensile strength
. To improve resistance to adhesive and abrasive wear
. To increase the ductility of the material
. To reduce the risk of implant fracture
. To enhance the oxidation resistance without additives

Correct Answer & Explanation

. To improve resistance to adhesive and abrasive wear

Explanation

Cross-linking UHMWPE using gamma irradiation significantly improves its resistance to adhesive and abrasive wear, thereby minimizing wear debris and reducing the incidence of periprosthetic osteolysis. However, this process sacrifices mechanical properties, decreasing ultimate tensile strength, fatigue strength, and ductility.

Question 13464

Topic: Biology, Genetics & Bone Healing
During the remodeling phase of tendon healing, which type of collagen is primarily synthesized to replace the initial provisional matrix?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

During the initial proliferative phase of tendon healing, fibroblasts rapidly deposit Type III collagen, forming a disorganized provisional matrix. In the remodeling phase, this is gradually replaced by thicker, highly organized Type I collagen, which restores the tensile strength of the mature tendon.

Question 13465

Topic: Biology, Genetics & Bone Healing

What is the primary cellular mechanism by which nitrogen-containing bisphosphonates (e.g., Alendronate) inhibit osteoclast function?

. Inhibition of RANKL binding to RANK
. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway
. Direct activation of osteoblast apoptosis
. Incorporation into ATP to form a non-hydrolyzable ATP analogue
. Binding to the estrogen receptor to modulate gene transcription

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (like alendronate and zoledronate) inhibit bone resorption by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins (such as Ras, Rho, and Rac) that are essential for osteoclast survival and ruffled border formation. Non-nitrogenous bisphosphonates form toxic ATP analogues.

Question 13466

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated by lamellar bone during fracture healing?

. 2%
. 10%
. 30%
. 50%
. 100%

Correct Answer & Explanation

. 2%

Explanation

According to Perren's strain theory, lamellar bone can only tolerate up to 2% strain before failing. In contrast, cartilage tolerates up to 10% strain, and granulation tissue can withstand up to 100% strain.

Question 13467

Topic: 1. General Principles & Basic Science

Which of the following is the earliest biochemical change seen in the articular cartilage of a patient developing osteoarthritis?

. Increased collagen content
. Decreased water content
. Increased water content
. Decreased chondroitin sulfate
. Increased keratin sulfate

Correct Answer & Explanation

. Increased water content

Explanation

The earliest biochemical change in osteoarthritis is an increase in the water content of the articular cartilage. This is accompanied by a decrease in proteoglycan concentration and an alteration in the structural collagen network.

Question 13468

Topic: Biology, Genetics & Bone Healing

A 70-year-old female is treated with denosumab for severe osteoporosis. Which of the following best describes the molecular mechanism of this medication?

. Bisphosphonate analogue that induces osteoclast apoptosis
. Monoclonal antibody against RANK ligand (RANKL)
. Recombinant parathyroid hormone that stimulates osteoblasts
. Monoclonal antibody against sclerostin
. Selective estrogen receptor modulator

Correct Answer & Explanation

. Monoclonal antibody against RANK ligand (RANKL)

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL, preventing it from interacting with the RANK receptor on osteoclasts. This effectively inhibits osteoclast formation, function, and survival, thereby decreasing bone resorption.

Question 13469

Topic: 1. General Principles & Basic Science

A new diagnostic test for periprosthetic joint infection is evaluated at a tertiary referral center. If the prevalence of the infection in the study population increases, which of the following statistical parameters will also increase?

. Sensitivity
. Specificity
. Positive predictive value
. Negative predictive value
. Likelihood ratio

Correct Answer & Explanation

. Positive predictive value

Explanation

Positive predictive value (PPV) is highly dependent on the prevalence of the disease in the test population. As disease prevalence increases, the PPV of a given test increases, while the negative predictive value (NPV) decreases.

Question 13470

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used in orthopedic surgery to augment fracture healing. Which of the following best describes its primary biologic properties?

. Osteoconductive only
. Osteoinductive only
. Osteogenic only
. Osteoconductive and osteoinductive
. Osteoinductive and osteogenic

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM provides a structural scaffold for new bone growth (osteoconductive) and contains bone morphogenetic proteins (BMPs) that stimulate local cells to form bone (osteoinductive). It lacks viable bone-forming cells, so it is not osteogenic.

Question 13471

Topic: 1. General Principles & Basic Science

Which of the following modifications to a cortical screw design would most significantly increase its pullout strength from bone?

. Increasing the inner core diameter
. Decreasing the outer thread diameter
. Decreasing the thread pitch
. Decreasing the thread depth
. Increasing the screw head diameter

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the outer diameter, thread depth, and length of engagement, and inversely proportional to thread pitch. Decreasing the thread pitch increases the number of threads engaged in the bone, increasing pullout strength.

Question 13472

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of nerve injuries, a third-degree injury is characterized by the disruption of which of the following microanatomical structures?

. Myelin sheath only
. Axon only
. Axon and endoneurium
. Axon, endoneurium, and perineurium
. Entire nerve trunk including epineurium

Correct Answer & Explanation

. Axon and endoneurium

Explanation

A Sunderland third-degree nerve injury involves disruption of the axon and the endoneurium, while the perineurium remains intact. Recovery is often unpredictable and variable due to the development of endoneurial scarring.

Question 13473

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is frequently used in major orthopedic surgeries to reduce intraoperative and postoperative blood loss. What is the primary mechanism of action of TXA?

. Inhibition of cyclooxygenase
. Activation of the extrinsic coagulation cascade
. Competitive inhibition of plasminogen activation
. Direct inhibition of factor Xa
. Cross-linking of fibrin monomers

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively inhibits the activation of plasminogen to plasmin, thereby acting as an antifibrinolytic agent that prevents the degradation of fibrin clots.

Question 13474

Topic: Infection, Pharmacology & VTE

During the pathogenesis of prosthetic joint infections, Staphylococcus epidermidis utilizes which of the following components to facilitate initial adherence and biofilm formation on the metal implant surface?

. Exotoxins
. Polysaccharide intercellular adhesin (PIA)
. Peptidoglycan
. Lipopolysaccharide
. Protein A

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Staphylococcus epidermidis establishes infections on implants by forming a biofilm, which begins with adherence followed by the production of a protective slime layer. This process is heavily mediated by the production of polysaccharide intercellular adhesin (PIA).

Question 13475

Topic: Physiology & Rehabilitation

A patient walks with a compensatory Trendelenburg gait, shifting their trunk laterally over the stance leg. This gait adaptation is primarily designed to reduce the mechanical demand on which of the following muscles?

. Contralateral gluteus medius
. Ipsilateral gluteus medius
. Ipsilateral quadriceps
. Contralateral hamstrings
. Ipsilateral gluteus maximus

Correct Answer & Explanation

. Ipsilateral gluteus medius

Explanation

Shifting the trunk laterally over the stance leg (abductor lurch) decreases the lever arm of the body's center of gravity relative to the hip joint. This reduces the joint reactive force and the force required by the ipsilateral gluteus medius to maintain a level pelvis.

Question 13476

Topic: Physiology & Rehabilitation

During the descent phase of a deep squat, the quadriceps muscle actively lengthens to control the downward movement. Which type of muscle contraction is taking place?

. Isometric
. Concentric
. Eccentric
. Isokinetic
. Auxotonic

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when a muscle generates tension while it actively lengthens. This type of contraction is highly energy-absorbent and is commonly used for deceleration, such as controlling the descent of a squat.

Question 13477

Topic: 1. General Principles & Basic Science

Which of the following factors is the primary driver of galvanic corrosion when two different orthopaedic metals are placed in direct contact within the human body?

. Difference in their elastic moduli
. Difference in their electrochemical potentials
. Mechanical fretting between the surfaces
. Differences in their yield strengths
. Presence of a proteinaceous biofilm

Correct Answer & Explanation

. Difference in their electrochemical potentials

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in electrical contact within an electrolytic solution like bodily fluids. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 13478

Topic: Biology, Genetics & Bone Healing

A 12-year-old child with a history of recurrent fractures, delayed dentition, and anemia is diagnosed with osteopetrosis. The pathogenesis of this condition is primarily related to a defect in which of the following?

. Type I collagen synthesis
. Carbonic anhydrase II
. Fibroblast growth factor receptor 3 (FGFR3)
. Runx2 transcription factor
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclast function, frequently due to a mutation in carbonic anhydrase II. This enzyme is crucial for generating the acidic environment required by osteoclasts to dissolve the bone mineral matrix.

Question 13479

Topic: 1. General Principles & Basic Science

Following a flexor tendon repair in zone II, the surgeon initiates an early passive mobilization protocol. What is the primary biological rationale for this early motion?

. To accelerate the inflammatory phase of healing
. To favor intrinsic tendon healing and minimize peritendinous adhesions
. To promote scar tissue formation from the tendon sheath
. To increase the cross-sectional area of the repair
. To stimulate angiogenesis from the vincular system

Correct Answer & Explanation

. To favor intrinsic tendon healing and minimize peritendinous adhesions

Explanation

Early mobilization of repaired flexor tendons promotes intrinsic healing, which is driven by tenocytes residing within the tendon itself. This limits extrinsic healing, thereby preventing the formation of restrictive peritendinous adhesions.

Question 13480

Topic: Biology, Genetics & Bone Healing

Which of the following ultrastructural components allows for direct communication and the exchange of nutrients between adjacent osteocytes within dense cortical bone?

. Haversian canals
. Volkmann canals
. Canaliculi
. Howship lacunae
. Sharpey fibers

Correct Answer & Explanation

. Canaliculi

Explanation

Osteocytes reside within lacunae and extend long cytoplasmic processes through microscopic channels called canaliculi. These networks connect via gap junctions, facilitating essential intercellular communication and nutrient transport.

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