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1. General Principles & Basic Science MCQs

Practice Set 684 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 13661

Topic: Biology, Genetics & Bone Healing

Which of the following cytokines is most strongly implicated as an osteoclast activating factor in the pathogenesis of lytic bone lesions in multiple myeloma?

. Interleukin-1 (IL-1)
. Interleukin-6 (IL-6)
. Tumor necrosis factor-alpha (TNF-a)
. Transforming growth factor-beta (TGF-b)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Interleukin-6 (IL-6)

Explanation

Interleukin-6 (IL-6) is a critical cytokine in multiple myeloma. It acts as a potent osteoclast-activating factor and also promotes the growth and survival of myeloma cells, leading to characteristic lytic bone lesions.

Question 13662

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, hearing loss, and anterior bowing of the tibiae. Laboratory evaluation is most likely to show which of the following?

. Elevated serum calcium, decreased phosphorus, elevated alkaline phosphatase
. Normal serum calcium, normal phosphorus, elevated alkaline phosphatase
. Decreased serum calcium, decreased phosphorus, elevated alkaline phosphatase
. Normal serum calcium, elevated phosphorus, elevated acid phosphatase
. Elevated serum calcium, elevated phosphorus, normal alkaline phosphatase

Correct Answer & Explanation

. Normal serum calcium, normal phosphorus, elevated alkaline phosphatase

Explanation

The patient has Paget's disease of bone (osteitis deformans). In Paget's disease, there is disorganized bone remodeling, leading to markedly elevated alkaline phosphatase, but serum calcium and phosphorus levels typically remain normal.

Question 13663

Topic: Infection, Pharmacology & VTE

Cefazolin is widely used as a prophylactic antibiotic in orthopedic surgery. What is its primary mechanism of action?

. Inhibition of bacterial protein synthesis via the 30S ribosomal subunit
. Inhibition of DNA gyrase
. Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins
. Inhibition of folic acid synthesis
. Disruption of bacterial cell membrane permeability

Correct Answer & Explanation

. Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins

Explanation

Cefazolin is a first-generation cephalosporin (a beta-lactam). Beta-lactams exert their bactericidal effect by binding to penicillin-binding proteins (PBPs), thereby inhibiting the cross-linking of peptidoglycan during bacterial cell wall synthesis.

Question 13664

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) initiate intracellular signaling primarily through which of the following pathways?

. cAMP/PKA pathway
. JAK/STAT pathway
. Smad pathway
. MAPK/ERK pathway
. Wnt/beta-catenin pathway

Correct Answer & Explanation

. Smad pathway

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase cell surface receptors, which phosphorylate intracellular Smad proteins (typically Smad 1, 5, and 8). The phosphorylated Smads complex with Smad 4 and translocate to the nucleus to regulate gene transcription.

Question 13665

Topic: 1. General Principles & Basic Science

When evaluating the pullout strength of a cortical screw, which of the following design alterations will yield the greatest increase in pullout strength?

. Decreasing the outer diameter of the screw thread
. Increasing the inner (core) diameter of the screw
. Decreasing the pitch of the screw threads
. Decreasing the length of screw engagement
. Changing from a self-tapping to a non-self-tapping screw tip

Correct Answer & Explanation

. Decreasing the pitch of the screw threads

Explanation

Pullout strength is directly proportional to the outer diameter of the thread, the length of engagement, and inversely proportional to the thread pitch (distance between threads). Decreasing the pitch means more threads engage the bone per unit length, thus increasing pullout strength.

Question 13666

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with multiple fractures and a 'rugger-jersey' spine appearance on radiographs. Labs show normal calcium, normal phosphorus, and elevated acid phosphatase. Which of the following is the underlying molecular defect most commonly associated with this condition?

. Defect in type I collagen synthesis
. Mutation in the PHEX gene
. Deficiency of carbonic anhydrase II
. Overactivity of fibroblast growth factor receptor 3 (FGFR3)
. Mutation in the COMP gene

Correct Answer & Explanation

. Deficiency of carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclast function, leading to dense, brittle bones and a 'rugger-jersey' spine. A common mutation is a deficiency in carbonic anhydrase II, which normally produces the acidic environment required for osteoclasts to resorb bone.

Question 13667

Topic: 1. General Principles & Basic Science

During the early stages of primary osteoarthritis, which of the following biochemical changes occurs first in the articular cartilage matrix?

. Decrease in water content
. Increase in water content
. Increase in proteoglycan content
. Decrease in collagen synthesis
. Increase in type II collagen content

Correct Answer & Explanation

. Increase in water content

Explanation

In early osteoarthritis, the initial change in articular cartilage is an increase in water content and a decrease in proteoglycan concentration. This leads to a less stiff matrix and increased permeability. In later stages, the water content eventually decreases.

Question 13668

Topic: 1. General Principles & Basic Science

A new point-of-care test for periprosthetic joint infection is implemented in an orthopedic clinic where the prevalence of the disease is very high, compared to a primary care setting where the prevalence is low. Assuming the sensitivity and specificity of the test remain constant, how will the predictive values change in the orthopedic clinic compared to the primary care setting?

. Positive predictive value will increase, negative predictive value will decrease
. Positive predictive value will decrease, negative predictive value will increase
. Both positive and negative predictive values will increase
. Both positive and negative predictive values will decrease
. Predictive values will remain unchanged

Correct Answer & Explanation

. Positive predictive value will increase, negative predictive value will decrease

Explanation

Predictive values are dependent on the prevalence of the disease in the tested population. A higher prevalence increases the positive predictive value (PPV) and decreases the negative predictive value (NPV), while sensitivity and specificity are intrinsic to the test and remain constant.

Question 13669

Topic: 1. General Principles & Basic Science

A 12-year-old boy with severe Hemophilia A presents with chronic knee swelling and restricted range of motion. Radiographs show epiphyseal overgrowth and joint space narrowing. Which of the following is the primary mechanism of cartilage destruction in hemophilic arthropathy?

. Direct immune-complex deposition in the synovial membrane
. Uric acid crystal deposition in the joint space
. Iron-induced chondrocyte apoptosis and synovial hypertrophy
. Mechanical wear due to ligamentous laxity
. Recurrent bacterial infections of the joint

Correct Answer & Explanation

. Iron-induced chondrocyte apoptosis and synovial hypertrophy

Explanation

Hemophilic arthropathy is driven by recurrent hemarthroses. Blood in the joint leads to the accumulation of iron/hemosiderin in the synovium and cartilage, which directly stimulates synovial hypertrophy, inflammatory cytokine release, and iron-mediated chondrocyte apoptosis.

Question 13670

Topic: Biology, Genetics & Bone Healing

A 4-year-old girl is evaluated for bowing of the legs. Laboratory evaluation reveals normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following is the most appropriate medical treatment for this patient?

. High-dose Vitamin D supplementation only
. Calcitonin and bisphosphonates
. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)
. Recombinant human growth hormone
. Dietary calcium supplementation

Correct Answer & Explanation

. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)

Explanation

The patient has X-linked hypophosphatemic rickets (XLHR), caused by a PHEX mutation leading to elevated FGF-23, which wastes phosphate in the kidneys. The classic treatment requires oral phosphate repletion combined with active Vitamin D (calcitriol) to prevent secondary hyperparathyroidism. Burosumab is a newer specific therapy, but among standard options, phosphate plus calcitriol is correct.

Question 13671

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute in spine fusion surgery. Which of the following best describes the biological properties of DBM?

. Osteoconductive only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteogenic and osteoconductive
. Osteogenic, osteoinductive, and osteoconductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM provides a structural scaffold (osteoconductive) and contains retained bone morphogenetic proteins (BMPs) that stimulate bone formation (osteoinductive). Because it is sterilized and processed, it lacks live cells, so it is not osteogenic. Autograft is the only graft type that possesses all three properties.

Question 13672

Topic: Infection, Pharmacology & VTE
An orthopedic surgeon prescribes rivaroxaban for venous thromboembolism prophylaxis following a total hip arthroplasty. What is the mechanism of action of this medication?
. Inhibition of vitamin K epoxide reductase
. Direct inhibition of thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase-1

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by specifically inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits vitamin K epoxide reductase. Heparin/LMWH acts via antithrombin III.

Question 13673

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture resulting in a radial nerve palsy. Electromyography (EMG) at 4 weeks shows fibrillation potentials. According to the Sunderland classification, a third-degree peripheral nerve injury is characterized by the disruption of which structures?

. Axon only (myelin sheath intact)
. Axon and endoneurium (perineurium intact)
. Axon, endoneurium, and perineurium (epineurium intact)
. Complete transection of the nerve including the epineurium
. Transient focal conduction block with no axonal disruption

Correct Answer & Explanation

. Axon, endoneurium, and perineurium (epineurium intact)

Explanation

In the Sunderland classification: 1st degree is Neuropraxia (focal block). 2nd degree is Axonotmesis (axon disrupted, endoneurium intact). 3rd degree involves disruption of the axon and endoneurium, but the perineurium remains intact. 4th degree adds perineurium disruption. 5th degree is complete transection (Neurotmesis).

Question 13674

Topic: Infection, Pharmacology & VTE

A 6-year-old child presents to the emergency department with hip pain and a limp. He refuses to bear weight. His temperature is 38.6°C (101.5°F). Labs show WBC 13,000/mm3, ESR 45 mm/hr, and CRP 2.5 mg/dL. According to the Kocher criteria, what is the probability that this child has septic arthritis rather than transient synovitis?

. Less than 5%
. Approximately 40%
. Approximately 71%
. Approximately 93%
. Approximately 99%

Correct Answer & Explanation

. Approximately 99%

Explanation

The Kocher criteria for pediatric septic arthritis of the hip are: 1) Non-weight bearing, 2) Temperature > 38.5°C, 3) ESR > 40 mm/hr, 4) WBC > 12,000/mm3. This patient meets all 4 criteria. The probability of septic arthritis is approximately 99% when all 4 criteria are present. (3 criteria = 93%, 2 criteria = 40%, 1 criterion = 3%).

Question 13675

Topic: Biomechanics & Biomaterials

A 65-year-old man presents with an acutely swollen, red, and painful knee. Aspiration yields cloudy yellow fluid with a WBC count of 45,000 cells/mm3. Polarized light microscopy reveals rhomboid-shaped crystals that are weakly positively birefringent. What is the composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Rhomboid-shaped, weakly positively birefringent crystals are characteristic of pseudogout, which is caused by the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in the joint. Monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 13676

Topic: Physiology & Rehabilitation

During a physical therapy session, a patient is performing a quadriceps strengthening exercise on a specialized machine that provides accommodating resistance to maintain a constant angular velocity of the knee joint throughout the entire range of motion. What type of muscle contraction is this?

. Isometric contraction
. Isotonic concentric contraction
. Isotonic eccentric contraction
. Isokinetic contraction
. Plyometric contraction

Correct Answer & Explanation

. Isokinetic contraction

Explanation

Isokinetic contractions occur when a muscle contracts at a constant velocity throughout the range of motion. Because mechanical advantage changes with joint angle, maintaining a constant velocity requires specialized equipment (like a Cybex machine) that provides accommodating resistance. Isometric equals constant length; Isotonic equals constant tension.

Question 13677

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, the phenomenon of 'stress shielding' occurs when an implant carries a disproportionate share of the mechanical load, leading to resorption of the surrounding bone. Comparing common orthopedic implant materials, which of the following characteristics makes Titanium alloys less prone to causing stress shielding than Cobalt-Chromium alloys?

. Higher ultimate tensile strength
. Higher resistance to galvanic corrosion
. Modulus of elasticity closer to that of cortical bone
. Higher density and radiopacity
. Greater resistance to abrasive wear

Correct Answer & Explanation

. Modulus of elasticity closer to that of cortical bone

Explanation

Titanium alloys have a lower modulus of elasticity compared to Cobalt-Chromium (CoCr) or stainless steel, making Titanium more flexible and mechanically closer to the stiffness of cortical bone. This similarity allows for better load sharing with the host bone, thereby reducing stress shielding and subsequent osteopenia.

Question 13678

Topic: Biomechanics & Biomaterials
To improve the longevity of ultra-high-molecular-weight polyethylene (UHMWPE) bearings in total joint arthroplasty, cross-linking is performed followed by either remelting, annealing, or Vitamin E doping. What is the primary biomechanical advantage of incorporating Vitamin E (alpha-tocopherol) compared to the remelting process?
. It prevents oxidation without compromising fatigue strength
. It increases the coefficient of friction to improve stability
. It eliminates the need for initial gamma irradiation
. It decreases the ultimate tensile strength to increase elasticity
. It enhances the osteoinductive properties of wear debris

Correct Answer & Explanation

. It prevents oxidation without compromising fatigue strength

Explanation

Remelting eliminates free radicals created during irradiation but alters the crystalline structure, which reduces fatigue strength and crack propagation resistance. Vitamin E scavenges free radicals without the need for thermal remelting, thereby preventing oxidation while preserving the polymer's fatigue strength and mechanical properties.

Question 13679

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach for an acetabular fracture, the surgeon must identify and protect the 'corona mortis' to prevent catastrophic hemorrhage. This vascular structure typically represents an anastomosis between which two vessel systems?

. Internal pudendal and superior gluteal
. External iliac (or inferior epigastric) and obturator
. Internal iliac and inferior gluteal
. Femoral and deep circumflex iliac
. Median sacral and lateral sacral

Correct Answer & Explanation

. External iliac (or inferior epigastric) and obturator

Explanation

The corona mortis (crown of death) is a vascular anastomosis between the external iliac or inferior epigastric vessels and the obturator vessels. It is located over the superior pubic ramus, typically 4 to 9 cm from the pubic symphysis, and is at high risk of iatrogenic injury during anterior pelvic surgical approaches.

Question 13680

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction and fracture healing. They act by binding to specific cell-surface receptors. Which of the following describes the primary intracellular signaling pathway activated directly by BMPs?

. Tyrosine kinase auto-phosphorylation leading to MAP kinase activation
. G-protein coupled receptor activation leading to cAMP production
. Serine/threonine kinase receptor activation leading to Smad 1, 5, and 8 phosphorylation
. Wnt binding to Frizzled receptors causing beta-catenin accumulation
. JAK/STAT pathway activation via cytokine receptors

Correct Answer & Explanation

. Serine/threonine kinase receptor activation leading to Smad 1, 5, and 8 phosphorylation

Explanation

BMPs belong to the TGF-beta superfamily. They bind to Type I and Type II serine/threonine kinase receptors. Upon binding, these receptors phosphorylate receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These subsequently complex with Co-Smad (Smad 4) and translocate to the nucleus to initiate osteogenic gene transcription.

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