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1. General Principles & Basic Science MCQs

Practice Set 654 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 13061

Topic: Infection, Pharmacology & VTE

In the management of prosthetic joint infections via debridement and implant retention (DAIR), which of the following antibiotics is essential due to its unique ability to penetrate the glycocalyx biofilm produced by Staphylococcus species?

. Cefazolin
. Vancomycin
. Rifampin
. Clindamycin
. Linezolid

Correct Answer & Explanation

. Rifampin

Explanation

Rifampin is highly lipophilic and has excellent penetration into the glycocalyx biofilm of staphylococcal species. It is a critical adjunctive oral agent used in implant retention protocols after surgical debridement.

Question 13062

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, the process of endochondral ossification requires which of the following critical steps to transition from a soft callus to a hard woven bone callus?

. Apoptosis of hypertrophic chondrocytes and subsequent vascular invasion
. Direct osteoblast differentiation from mesenchymal stem cells without a cartilage model
. Formation of cutting cones by highly active osteoclasts
. Suppression of vascular endothelial growth factor (VEGF) expression
. Maintenance of absolute rigid stability at the fracture site

Correct Answer & Explanation

. Apoptosis of hypertrophic chondrocytes and subsequent vascular invasion

Explanation

Endochondral ossification requires a cartilage intermediate. Hypertrophic chondrocytes within the soft callus undergo apoptosis and release VEGF, which prompts vascular invasion and allows osteoprogenitor cells to enter and form the hard callus.

Question 13063

Topic: Surgical Anatomy & Approaches

During a direct lateral (deltoid-splitting) approach to the proximal humerus, the distal extent of the deltoid split must be carefully limited to no more than 5 cm distal to the acromion to prevent injury to which of the following structures?

. Musculocutaneous nerve
. Radial nerve
. Axillary nerve
. Suprascapular nerve
. Thoracodorsal nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

The axillary nerve courses circumferentially around the proximal humerus deep to the deltoid muscle, typically 5 to 7 cm distal to the lateral edge of the acromion. Extending a deltoid split beyond this safe zone risks permanent denervation of the anterior deltoid.

Question 13064

Topic: Biology, Genetics & Bone Healing

An 80-year-old man presents with increasing hat size and unilateral hearing loss. Laboratory studies demonstrate markedly elevated serum alkaline phosphatase, with normal calcium and phosphorus. Which of the following describes the primary cellular defect in this condition?

. Hyperactive osteoblasts lacking RUNX2 expression
. Intracellular accumulation of unmineralized osteoid
. Formation of highly multinucleated, overactive osteoclasts
. Failure of osteoclast ruffled border formation
. Overproduction of parathyroid hormone-related peptide (PTHrP)

Correct Answer & Explanation

. Formation of highly multinucleated, overactive osteoclasts

Explanation

Paget's disease of bone is primarily driven by abnormal, enlarged, and highly multinucleated osteoclasts. This leads to a profound increase in bone resorption, followed by a chaotic, compensatory overactivity of osteoblasts producing weak woven bone.

Question 13065

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its specific mechanism of action?
. Inhibits the conversion of prothrombin to thrombin
. Irreversibly binds to COX-1 receptors on platelets
. Reversibly blocks lysine binding sites on plasminogen
. Promotes the cross-linking of fibrin strands via Factor XIII
. Directly inhibits Factor Xa in the coagulation cascade

Correct Answer & Explanation

. Reversibly blocks lysine binding sites on plasminogen

Explanation

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

Question 13066

Topic: 1. General Principles & Basic Science

Which of the following mechanisms of joint lubrication is most critical in protecting articular hyaline cartilage under conditions of high physiological load and very low speeds (e.g., prolonged standing)?

. Squeeze-film lubrication
. Elastohydrodynamic lubrication
. Weeping lubrication
. Boundary lubrication mediated by lubricin (PRG4)
. Hydrodynamic lubrication mediated by hyaluronic acid

Correct Answer & Explanation

. Boundary lubrication mediated by lubricin (PRG4)

Explanation

Boundary lubrication occurs under high loads and low speeds where joint surfaces are nearly in direct physical contact. It relies on a monomolecular layer of surface-active glycoproteins, primarily lubricin (PRG4), binding directly to the articular surface.

Question 13067

Topic: 1. General Principles & Basic Science

A 50-year-old patient with end-stage renal disease exhibits classic signs of renal osteodystrophy. Laboratory results show hyperphosphatemia, hypocalcemia, and elevated parathyroid hormone (PTH). This secondary hyperparathyroidism is primarily triggered by the kidneys' inability to perform which function?

. Excrete excess parathyroid hormone
. Reabsorb serum calcium in the distal convoluted tubule
. Convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D
. Synthesize adequate levels of endogenous calcitonin
. Produce sufficient erythropoietin to oxygenate bone marrow

Correct Answer & Explanation

. Convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

Explanation

In chronic kidney disease, the failing kidneys lose 1-alpha-hydroxylase activity, halting the conversion of 25(OH)D into active 1,25(OH)2D (calcitriol). The resulting lack of gastrointestinal calcium absorption causes hypocalcemia, which continuously stimulates PTH release.

Question 13068

Topic: 1. General Principles & Basic Science
During the remodeling phase of ligament healing, the tensile strength of the repair tissue gradually increases over months. Which of the following biochemical changes is primarily responsible for this improvement?
. Replacement of mature Type I collagen with highly elastic Type III collagen
. Increased synthesis and aggregation of hydrophilic glycosaminoglycans
. Transition from disorganized Type III collagen to highly cross-linked Type I collagen
. Apoptosis of intrinsic fibroblasts and replacement by fibrochondrocytes
. Rapid angiogenesis and persistent neovascularization of the scar tissue

Correct Answer & Explanation

. Transition from disorganized Type III collagen to highly cross-linked Type I collagen

Explanation

The initial proliferative phase of ligament healing produces a weak, disorganized matrix composed largely of Type III collagen. During remodeling, this is slowly replaced by longitudinally oriented, highly cross-linked Type I collagen, restoring tensile strength.

Question 13069

Topic: Biology, Genetics & Bone Healing

A 65-year-old man with multiple myeloma presents with a solitary "punched-out" lytic lesion in his L4 vertebral body. The extensive focal osteolysis seen in this disease process is primarily mediated by myeloma cells secreting which of the following?

. Osteoprotegerin (OPG)
. RANK Ligand (RANKL) and Macrophage Inflammatory Protein-1 alpha (MIP-1 alpha)
. Bone morphogenetic protein-2 (BMP-2)
. Matrix metalloproteinase-9 (MMP-9)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. RANK Ligand (RANKL) and Macrophage Inflammatory Protein-1 alpha (MIP-1 alpha)

Explanation

Myeloma cells induce uncoupled bone turnover by secreting osteoclast-activating factors such as RANKL, MIP-1 alpha, and IL-6. This directly stimulates aggressive local osteoclastic bone resorption while simultaneously suppressing osteoblast activity.

Question 13070

Topic: Biology, Genetics & Bone Healing

A 55-year-old female undergoes a DEXA scan revealing a T-score of -2.8. She is started on a medication that is a monoclonal antibody against RANKL. Which of the following is the primary cellular effect of this medication?

. Inhibition of osteoblast apoptosis
. Stimulation of Wnt/beta-catenin signaling
. Prevention of osteoclast differentiation and activation
. Direct induction of osteoclast apoptosis
. Inhibition of sclerostin

Correct Answer & Explanation

. Prevention of osteoclast differentiation and activation

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from interacting with RANK on the surface of osteoclast precursors, thereby inhibiting osteoclast differentiation, activation, and survival.

Question 13071

Topic: Biomechanics & Biomaterials

When evaluating the biomechanical properties of a titanium orthopedic implant, the point on the stress-strain curve where the material transitions from elastic deformation to plastic deformation is known as the:

. Ultimate tensile strength
. Yield point
. Young's modulus
. Failure point
. Proportional limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the transition from the elastic region (where deformation is reversible) to the plastic region (where deformation is permanent). Young's modulus represents the stiffness in the elastic region, represented by the slope of the elastic line.

Question 13072

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel plate with titanium screws for fracture fixation. Which of the following best describes the likely outcome of mixing these two metals in vivo?

. Enhanced osteointegration due to micro-currents
. Galvanic corrosion primarily affecting the titanium screws
. Galvanic corrosion primarily affecting the stainless steel plate
. Crevice corrosion strictly isolated to the screw heads
. No significant corrosive reaction will occur

Correct Answer & Explanation

. Galvanic corrosion primarily affecting the stainless steel plate

Explanation

When dissimilar metals are in contact in an electrolytic fluid (body fluid), galvanic corrosion occurs. The less noble metal (anodic) corrodes more rapidly. Stainless steel is less noble than titanium; thus, the stainless steel plate will undergo accelerated corrosion.

Question 13073

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infection, Staphylococcus epidermidis frequently forms a biofilm. Which of the following best characterizes the composition of the extracellular polymeric substance (EPS) matrix in this biofilm?

. Type I collagen and fibronectin
. Polysaccharide intercellular adhesin (PIA) and extracellular DNA
. Hyaluronic acid and proteoglycans
. Fibrinogen and von Willebrand factor
. Chondroitin sulfate and keratin sulfate

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA) and extracellular DNA

Explanation

The extracellular polymeric substance (EPS) of S. epidermidis biofilm is primarily composed of Polysaccharide Intercellular Adhesin (PIA), extracellular DNA (eDNA), and proteins, which protect the bacteria from the host immune system and antibiotics.

Question 13074

Topic: 1. General Principles & Basic Science

A new clinical test for diagnosing anterior cruciate ligament (ACL) tears is evaluated. If the prevalence of ACL tears in the tested population increases, assuming the sensitivity and specificity of the test remain constant, which of the following statistical parameters will also increase?

. Negative predictive value
. Positive predictive value
. Likelihood ratio of a positive test
. Likelihood ratio of a negative test
. Accuracy of the test

Correct Answer & Explanation

. Positive predictive value

Explanation

Positive predictive value (PPV) is heavily dependent on disease prevalence. As prevalence increases, PPV increases and Negative predictive value (NPV) decreases. Sensitivity, specificity, and likelihood ratios are intrinsic test properties and do not change with prevalence.

Question 13075

Topic: Biology, Genetics & Bone Healing

A 45-year-old immigrant presents with generalized bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low phosphorus, high alkaline phosphatase, and elevated parathyroid hormone (PTH). Radiographs show Looser zones. Which of the following is the underlying pathophysiology of this condition?

. Defective mineralization of osteoid
. Overactivity of osteoclasts
. Mutations in type I collagen
. Decreased osteoblast proliferation
. Abnormal endochondral ossification

Correct Answer & Explanation

. Defective mineralization of osteoid

Explanation

The patient has osteomalacia (likely due to severe Vitamin D deficiency), characterized by defective mineralization of newly formed osteoid matrix in adults. In children, the equivalent condition is rickets, which features abnormal endochondral ossification.

Question 13076

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, the type of wear generated when two articulating surfaces come into direct contact and micro-welds form and break off, generating particulate debris, is classified as:

. Abrasive wear
. Adhesive wear
. Third-body wear
. Corrosive wear
. Fretting wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear occurs when two surfaces slide against each other under pressure, causing localized bonding (micro-welds) that are sheared off during motion. Abrasive wear occurs when a harder surface cuts into a softer one.

Question 13077

Topic: 1. General Principles & Basic Science
A 60-year-old diabetic male presents with an erythematous, swollen, and severely painful left lower leg. The pain is out of proportion to physical findings. Crepitus is palpated. Which of the following scoring systems is specifically designed to help distinguish this condition from non-necrotizing soft tissue infections?
. MESS score
. LRINEC score
. SOFA score
. Cierny-Mader classification
. Gallo classification

Correct Answer & Explanation

. LRINEC score

Explanation

The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score utilizes CRP, WBC, hemoglobin, serum sodium, creatinine, and glucose to help distinguish necrotizing fasciitis from other severe soft tissue infections.

Question 13078

Topic: Biology, Genetics & Bone Healing

A midshaft tibial fracture treated with an intramedullary nail heals via secondary bone healing. During the soft callus phase of this process, which specific cell type is primarily responsible for the formation of the cartilaginous template?

. Osteoblasts from the periosteum
. Mesenchymal stem cells differentiating into chondrocytes
. Osteoclasts from the medullary canal
. Fibroblasts producing type I collagen
. Endothelial cells initiating angiogenesis

Correct Answer & Explanation

. Mesenchymal stem cells differentiating into chondrocytes

Explanation

Secondary bone healing (via callus formation) involves a soft callus phase where mesenchymal stem cells from the periosteum and surrounding tissues differentiate into chondrocytes to form a cartilaginous template, which is later replaced by bone via endochondral ossification.

Question 13079

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials has a Young's modulus most closely matching that of cortical bone?

. Cobalt-chromium alloy
. Stainless steel (316L)
. Titanium alloy (Ti-6Al-4V)
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

Cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloys (~110 GPa) are closer to cortical bone than stainless steel (~200 GPa) or Co-Cr (~210-240 GPa), which helps to minimize stress shielding. PMMA is significantly less stiff (~2-3 GPa).

Question 13080

Topic: Infection, Pharmacology & VTE

A patient undergoes a peripheral nerve block with bupivacaine for post-operative analgesia. Shortly after the injection, the patient develops perioral numbness, tinnitus, and metallic taste, followed by a generalized seizure. Which of the following is the most appropriate initial pharmacological treatment for this specific toxicity?

. Intravenous flumazenil
. Intravenous naloxone
. Intravenous 20% lipid emulsion
. Intramuscular epinephrine
. Intravenous calcium gluconate

Correct Answer & Explanation

. Intravenous 20% lipid emulsion

Explanation

The patient is experiencing Local Anesthetic Systemic Toxicity (LAST), a severe complication common with highly lipophilic agents like bupivacaine. The specific antidote is a 20% lipid emulsion (Intralipid), which acts as a 'lipid sink' to draw the drug away from the myocardium and CNS.

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