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1. General Principles & Basic Science MCQs

Practice Set 657 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 13121

Topic: Biomechanics & Biomaterials

If the diameter of a solid circular intramedullary nail is doubled, its torsional rigidity increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia, which scales with the radius (or diameter) to the fourth power (r^4). Therefore, doubling the diameter increases torsional rigidity by 2^4, or 16 times.

Question 13122

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used to reduce blood loss in major orthopedic surgeries. What is the specific mechanism of action of this pharmacological agent?
. Directly inhibits Factor Xa in the coagulation cascade
. Competitively inhibits the activation of plasminogen to plasmin
. Promotes the cross-linking of fibrin via Factor XIII
. Directly inhibits thrombin formation
. Prevents platelet aggregation by blocking ADP receptors

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively inhibits the activation of plasminogen to plasmin, thereby preventing the degradation of fibrin clots (fibrinolysis).

Question 13123

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Following the binding of a BMP to its cell surface receptor, which intracellular signaling proteins are directly phosphorylated to translocate to the nucleus and regulate gene expression?

. Janus kinases (JAK)
. Signal Transducers and Activators of Transcription (STAT)
. Smad proteins
. Wnt/beta-catenin
. Nuclear factor kappa B (NF-kB)

Correct Answer & Explanation

. Smad proteins

Explanation

BMPs belong to the TGF-beta superfamily and signal through serine/threonine kinase receptors. Upon binding, they induce phosphorylation of intracellular Smad proteins (primarily Smad 1, 5, and 8), which then translocate to the nucleus.

Question 13124

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a third-degree injury is best characterized by:

. Demyelination with intact axons
. Disruption of the axon and myelin sheath with an intact endoneurium
. Disruption of the axon and endoneurium with an intact perineurium
. Disruption of the perineurium with an intact epineurium
. Complete nerve transection

Correct Answer & Explanation

. Disruption of the axon and endoneurium with an intact perineurium

Explanation

A Sunderland third-degree nerve injury involves disruption of the axon, myelin sheath, and the endoneurium, while the perineurium and epineurium remain intact. Wallerian degeneration occurs, and recovery is often incomplete due to intrafascicular scarring.

Question 13125

Topic: Biology, Genetics & Bone Healing

Perren's strain theory dictates the type of tissue that can form in a fracture gap based on the mechanical environment. What is the maximum tissue strain tolerated by the formation of lamellar bone?

. Less than 2%
. Up to 10%
. Up to 20%
. Up to 50%
. Up to 100%

Correct Answer & Explanation

. Less than 2%

Explanation

According to Perren's strain theory, lamellar bone can only form under very low strain conditions (less than 2%). Granulation tissue can tolerate up to 100% strain, and cartilage can tolerate up to 10% strain.

Question 13126

Topic: Biomechanics & Biomaterials

Which type of corrosion is most likely to occur at the modular junction of a titanium femoral stem and a cobalt-chrome femoral head in a total hip arthroplasty?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion is the primary and most common corrosive process at modular interfaces (tapers) of total joint implants. It involves mechanically induced micromotion that repeatedly disrupts the oxide passivation layer, accelerating corrosion.

Question 13127

Topic: Infection, Pharmacology & VTE

A patient develops a surgical site infection with Methicillin-resistant Staphylococcus aureus (MRSA) following internal fixation. Vancomycin is initiated. What is the precise mechanism of action of this antibiotic?

. Inhibition of DNA gyrase
. Binding to the 50S ribosomal subunit to prevent protein synthesis
. Binding to the D-ala-D-ala terminus of peptidoglycan precursors
. Inhibition of folate synthesis via dihydrofolate reductase
. Irreversible binding to penicillin-binding proteins (PBPs)

Correct Answer & Explanation

. Binding to the D-ala-D-ala terminus of peptidoglycan precursors

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis. It achieves this by binding to the D-alanyl-D-alanine terminus of cell wall precursor units, preventing the cross-linking of the peptidoglycan layer.

Question 13128

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient with untreated celiac disease presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal low normal serum calcium, low phosphorus, high alkaline phosphatase, and elevated parathyroid hormone. What is the most likely diagnosis?

. Paget's disease of bone
. Primary hyperparathyroidism
. Osteomalacia
. Osteoporosis
. Renal osteodystrophy

Correct Answer & Explanation

. Osteomalacia

Explanation

Osteomalacia is characterized by impaired mineralization of osteoid, frequently due to vitamin D deficiency secondary to malabsorption. This leads to secondary hyperparathyroidism, resulting in low or normal calcium, low phosphorus, and elevated alkaline phosphatase.

Question 13129

Topic: 1. General Principles & Basic Science

A new diagnostic test for periprosthetic joint infection is evaluated in a clinical trial. As the prevalence of the infection in the tested population increases, which of the following statistical measures of the test will concurrently increase?

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

Correct Answer & Explanation

. Positive predictive value

Explanation

The Positive Predictive Value (PPV) is heavily dependent on the prevalence of the disease in the population. As disease prevalence increases, the proportion of true positive results among all positive test results increases, thereby raising the PPV.

Question 13130

Topic: Physiology & Rehabilitation

Type I (slow-twitch) skeletal muscle fibers are specialized for endurance activities. Compared to Type IIb fibers, Type I fibers possess which of the following characteristics?

. Lower myoglobin content
. Dependence on anaerobic metabolism
. Higher mitochondrial density
. Faster contraction speed
. Larger fiber cross-sectional diameter

Correct Answer & Explanation

. Higher mitochondrial density

Explanation

Type I muscle fibers are optimized for aerobic metabolism and fatigue resistance. They have a higher mitochondrial density, higher myoglobin content, greater capillary density, and rely primarily on oxidative phosphorylation.

Question 13131

Topic: Physiology & Rehabilitation

During the normal human gait cycle, the peak joint reaction force at the hip occurs during which specific phase?

. Initial contact (heel strike)
. Loading response
. Terminal stance
. Pre-swing
. Mid-swing

Correct Answer & Explanation

. Terminal stance

Explanation

The peak joint reaction force at the hip reaches approximately 2.5 to 3 times body weight and occurs during the terminal stance phase. This peak is driven primarily by the contraction of the hip abductor muscles to stabilize the pelvis prior to toe-off.

Question 13132

Topic: 1. General Principles & Basic Science

When comparing a standard cortical bone screw to a cancellous bone screw of the identical outer thread diameter, the cortical screw is mechanically characterized by:

. A smaller core diameter and larger thread pitch
. A larger core diameter and smaller thread pitch
. A larger core diameter and larger thread pitch
. A smaller core diameter and smaller thread pitch
. An identical core diameter but significantly deeper threads

Correct Answer & Explanation

. A larger core diameter and smaller thread pitch

Explanation

Cortical screws are designed for dense cortical bone and feature a larger core diameter (providing greater bending strength) and a smaller thread pitch (more threads per inch). Cancellous screws possess deeper threads and a larger pitch for better purchase in spongy metaphyseal bone.

Question 13133

Topic: Biology, Genetics & Bone Healing

A 35-year-old male undergoes locked intramedullary nailing for a transverse midshaft femur fracture. During the initial 4 weeks of healing, the construct allows for a specific amount of interfragmentary strain that promotes cartilaginous callus formation. According to Perren's strain theory, what range of strain best promotes secondary bone healing via endochondral ossification?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. 2% to 10%

Explanation

According to Perren's strain theory, the type of tissue that forms at a fracture site is dependent on the strain it can tolerate. Woven bone can tolerate up to 2% strain (promoting primary bone healing without callus), cartilage can tolerate up to 10% strain (promoting secondary bone healing via endochondral ossification), and granulation tissue can tolerate up to 100% strain. A strain of 2-10% favors cartilaginous callus formation.

Question 13134

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four distinct zones. Which zone is characterized by having the highest concentration of collagen, the lowest concentration of proteoglycans, and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone makes up 10-20% of articular cartilage thickness. It has the highest concentration of collagen (primarily Type II) and the lowest concentration of proteoglycans. The collagen fibers in this zone are oriented parallel to the articular surface to resist shear forces.

Question 13135

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with a progressive bowing deformity of his tibia and increasing local warmth over the bone. Radiographs reveal cortical thickening and coarsened trabeculae. A biopsy is obtained. Which histologic finding is considered pathognomonic for the mixed phase of this disease?

. Extensive osteoid seams with a lack of mineralization
. Granulomas containing multinucleated giant cells
. Woven bone completely lacking osteocytes
. Empty lacunae with surrounding necrotic marrow
. Mosaic pattern of lamellar bone with prominent cement lines

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

The patient has Paget's disease of bone (osteitis deformans). The disease has three phases: lytic, mixed, and sclerotic. In the mixed phase, there is rapid, chaotic bone turnover characterized histologically by a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with prominent cement lines due to irregular periods of bone resorption and formation.

Question 13136

Topic: Biology, Genetics & Bone Healing
A 7-year-old child presents with gingival bleeding, petechiae, and progressively worsening joint pain. Radiographs show a distinct radiolucent line proximal to the metaphysis (Trรผmmerfeld zone) and a dense zone of provisional calcification. This condition impairs bone formation primarily due to a defect in which of the following cellular processes?
. Cleavage of procollagen into tropocollagen
. Cross-linking of collagen fibers by lysyl oxidase
. Hydroxylation of proline and lysine residues
. Intracellular triple helix formation
. Mineralization of the osteoid matrix

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The child is exhibiting signs of scurvy, caused by Vitamin C deficiency. Vitamin C (ascorbic acid) is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Without it, the hydroxylation of proline and lysine residues on procollagen alpha chains cannot occur, leading to defective triple helix formation and structurally unstable collagen.

Question 13137

Topic: Biomechanics & Biomaterials

A surgeon plans to use a plate and screw construct to stabilize a peri-prosthetic femur fracture around a well-fixed cobalt-chromium total hip stem. To minimize the risk of severe galvanic corrosion, which of the following combinations of metals should be strictly avoided in direct contact?

. 316L Stainless Steel and Titanium alloy
. Titanium alloy and Cobalt-Chromium alloy
. Tantalum and Titanium alloy
. Titanium plate with Titanium screws
. Cobalt-Chromium stem and Cobalt-Chromium cable

Correct Answer & Explanation

. 316L Stainless Steel and Titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different electrochemical potentials are placed in contact within a conducting medium (e.g., bodily fluids). Stainless steel and titanium have highly disparate potentials and should not be mixed in vivo. Titanium and Cobalt-Chromium have similar passivation layers and electrochemical potentials, making their combination (e.g., in total joint arthroplasty) relatively safe.

Question 13138

Topic: Infection, Pharmacology & VTE
A 65-year-old woman is prescribed rivaroxaban for venous thromboembolism (VTE) prophylaxis following a total knee arthroplasty. What is the primary mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibitor
. Vitamin K epoxide reductase inhibitor
. Antithrombin III activator
. Cyclooxygenase-1 inhibitor
. Direct Factor Xa inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban (along with apixaban and edoxaban) is a direct, reversible inhibitor of Factor Xa. It interrupts the intrinsic and extrinsic pathway of the blood coagulation cascade, inhibiting both thrombin formation and the development of thrombi. Dabigatran is a direct thrombin (IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase.

Question 13139

Topic: 1. General Principles & Basic Science

During a wide local excision of a soft tissue mass under local anesthesia, the surgeon injects a solution of 1% lidocaine with 1:100,000 epinephrine. What is the generally accepted maximum safe dose of lidocaine when combined with epinephrine for a healthy adult patient?

. 3 mg/kg
. 4.5 mg/kg
. 5 mg/kg
. 7 mg/kg
. 10 mg/kg

Correct Answer & Explanation

. 4.5 mg/kg

Explanation

The maximum safe dose of lidocaine in a healthy adult is approximately 4.5 to 5 mg/kg without epinephrine. When epinephrine is added (which causes local vasoconstriction and delays systemic absorption), the maximum safe dose increases to 7 mg/kg. For bupivacaine, the toxic limits are generally 2.5 mg/kg without epinephrine and 3 mg/kg with epinephrine.

Question 13140

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is started on denosumab therapy. Which of the following best describes the molecular mechanism of action of this drug?

. Binds to RANKL, preventing its interaction with RANK
. Binds to RANK, preventing its interaction with RANKL
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Stimulates osteoblast differentiation via the Wnt/beta-catenin pathway
. Acts as a recombinant parathyroid hormone analog

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with RANK

Explanation

Denosumab is a fully human monoclonal antibody that directly targets and binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding RANKL, it prevents it from interacting with the RANK receptor on osteoclasts and their precursors, thereby profoundly inhibiting osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

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