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1. General Principles & Basic Science MCQs

Practice Set 512 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 10221

Topic: Surgical Anatomy & Approaches

A 30-year-old male sustains a midshaft humerus fracture resulting in a complete radial nerve palsy. Closed reduction is performed. Based on the expected rate of axonal regeneration following Wallerian degeneration, what is the approximate rate of nerve recovery once the distal segment is prepared?

. 0.1 mm per day
. 1 mm per day
. 5 mm per day
. 1 cm per day
. 5 cm per day

Correct Answer & Explanation

. 1 mm per day

Explanation

Following a nerve injury (axonotmesis) and subsequent Wallerian degeneration of the distal segment, axonal regeneration occurs at a relatively constant rate of approximately 1 mm per day (or 1 inch per month) after an initial delay period.

Question 10222

Topic: Biomechanics & Biomaterials

A patient undergoes revision total hip arthroplasty. The surgeon uses a stainless steel cerclage wire around the proximal femur in contact with a titanium femoral stem. What specific type of corrosion is most likely to occur at the interface of these two metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within an electrolytic solution (such as bodily fluids). The less noble metal acts as an anode and corrodes.

Question 10223

Topic: Biomechanics & Biomaterials

The observation that bone architecture remodels in response to the mechanical stresses placed upon it is mathematically and mechanistically explained by which of the following principles?

. Heuter-Volkmann principle
. Wolff's Law
. Hooke's Law
. Young's modulus
. Poisson's ratio

Correct Answer & Explanation

. Wolff's Law

Explanation

Wolff's Law states that bone grows and remodels in response to the forces that are placed upon it ('form follows function'). The Heuter-Volkmann principle applies to physeal growth, stating that compressive forces inhibit growth while tensile forces stimulate it.

Question 10224

Topic: 1. General Principles & Basic Science
Following an acute grade III medial collateral ligament (MCL) tear of the knee, the ligament undergoes a predictable multi-phase healing process. During the remodeling phase, which of the following cellular and biochemical changes predominantly occurs?
. Accumulation of neutrophils and macrophages
. Rapid synthesis of Type III collagen
. Conversion of Type I collagen to Type III collagen
. Conversion of Type III collagen to Type I collagen with realignment along lines of stress
. Chondrocyte proliferation and endochondral ossification

Correct Answer & Explanation

. Conversion of Type III collagen to Type I collagen with realignment along lines of stress

Explanation

Ligament healing consists of three phases: inflammatory, proliferative, and remodeling. During the proliferative phase, fibroblasts synthesize a disorganized Type III collagen scar. During remodeling (months to years later), the weaker Type III collagen is gradually replaced by stronger Type I collagen, and the fibers realign along the longitudinal axis of mechanical stress.

Question 10225

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman with severe osteoporosis and a history of a vertebral compression fracture is started on teriparatide. Which of the following best describes the physiological basis for its efficacy in increasing bone mass?

. Continuous activation of osteoblasts
. Inhibition of the RANKL pathway
. Intermittent administration preferentially stimulates osteoblastic bone formation over osteoclastic resorption
. Irreversible binding to farnesyl pyrophosphate synthase in osteoclasts
. Direct binding to osteoid inhibiting osteoclastic attachment

Correct Answer & Explanation

. Intermittent administration preferentially stimulates osteoblastic bone formation over osteoclastic resorption

Explanation

Teriparatide is a recombinant parathyroid hormone (PTH 1-34) analog. While continuous high levels of PTH lead to net bone resorption (hyperparathyroidism), intermittent daily subcutaneous injection of PTH paradoxically stimulates osteoblastic bone formation more than bone resorption, resulting in a net increase in bone mass.

Question 10226

Topic: 1. General Principles & Basic Science

Articular cartilage relies on specific lubrication mechanisms depending on the load and speed of the joint movement. During periods of heavy, sustained loading (e.g., prolonged standing), fluid is exuded from the cartilage into the joint space to separate the articular surfaces. What is this specific mechanism of lubrication called?

. Boundary lubrication
. Elastohydrodynamic lubrication
. Weeping lubrication
. Squeeze-film lubrication
. Hydrodynamic lubrication

Correct Answer & Explanation

. Weeping lubrication

Explanation

'Weeping lubrication' occurs under high, sustained loads when fluid is squeezed out (exuded) of the cartilage matrix to form a fluid film layer separating the joint surfaces. Boundary lubrication, dependent on molecules like lubricin, dominates under low loads.

Question 10227

Topic: 1. General Principles & Basic Science

Parathyroid hormone (PTH) regulates serum calcium by acting on multiple target organs. What is its direct physiological effect on the kidney?

. Decreases calcium reabsorption in the distal convoluted tubule
. Increases phosphate reabsorption in the proximal tubule
. Inhibits the 1-alpha-hydroxylase enzyme
. Increases calcium reabsorption and decreases phosphate reabsorption
. Decreases both calcium and phosphate reabsorption

Correct Answer & Explanation

. Increases calcium reabsorption and decreases phosphate reabsorption

Explanation

PTH acts on the kidneys to increase calcium reabsorption (in the distal tubule) and decrease phosphate reabsorption (in the proximal tubule, causing phosphaturia). It also stimulates the enzyme 1-alpha-hydroxylase, which converts 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D.

Question 10228

Topic: 1. General Principles & Basic Science

During the incorporation of a non-vascularized cortical bone autograft, which of the following biological processes must occur first at the host-graft interface?

. Osteoblastic deposition of woven bone
. Osteoclastic bone resorption via cutting cones
. Direct endochondral ossification
. Hypertrophy of pre-existing chondrocytes
. Formation of a fibrous tissue barrier

Correct Answer & Explanation

. Osteoclastic bone resorption via cutting cones

Explanation

Cortical bone graft incorporation relies on creeping substitution, which begins with osteoclastic resorption via cutting cones. In contrast, cancellous grafts incorporate first via osteoblastic apposition on dead trabeculae.

Question 10229

Topic: Biology, Genetics & Bone Healing

Intermittent administration of recombinant human parathyroid hormone (teriparatide) exerts an anabolic effect on bone mass. This effect is primarily mediated by the activation of which of the following intracellular signaling pathways in osteoblasts?

. Inhibition of the Wnt/beta-catenin pathway
. Direct inhibition of osteoclast ruffled border formation
. Activation of the adenylate cyclase/cAMP/PKA pathway
. Upregulation of the Smad 1/5/8 transcription factors
. Downregulation of the Runx2 transcription factor

Correct Answer & Explanation

. Activation of the adenylate cyclase/cAMP/PKA pathway

Explanation

Teriparatide binds to the PTH1 receptor, a G-protein coupled receptor on osteoblasts. This binding primarily activates the adenylate cyclase/cAMP/Protein Kinase A (PKA) pathway, promoting osteoblast survival and bone formation.

Question 10230

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe postmenopausal osteoporosis is treated with denosumab. What is the precise molecular target of this pharmacological agent?

. Farnesyl pyrophosphate synthase
. Cathepsin K
. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Sclerostin

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to and inhibits RANKL. This prevents RANKL from binding to its receptor (RANK) on osteoclasts, thereby inhibiting osteoclast maturation and survival.

Question 10231

Topic: Biomechanics & Biomaterials

Which of the following clinical scenarios is most likely to result in galvanic corrosion of an orthopedic implant?

. Fretting at the head-neck junction of a modular titanium hip prosthesis
. Using a stainless steel screw to secure a titanium alloy plate
. Scratching the passivation layer of a cobalt-chrome femoral stem
. High-cycle fatigue loading of a stainless steel intramedullary nail
. Contact between ultra-high-molecular-weight polyethylene and a roughened metallic surface

Correct Answer & Explanation

. Using a stainless steel screw to secure a titanium alloy plate

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in contact within an electrolytic environment, such as the human body. This leads to an electrochemical potential difference and accelerated corrosion of the less noble metal.

Question 10232

Topic: Biomechanics & Biomaterials

On a standard load-elongation (stress-strain) curve for a healthy ligament, what structural phenomenon is primarily responsible for the initial 'toe region'?

. Microscopic failure of individual collagen fibers
. Macroscopic plastic deformation
. Uncrimping of type I collagen fibrils
. Breaking of enzymatic cross-links between proteoglycans
. Elastic deformation of the bone-ligament interface

Correct Answer & Explanation

. Uncrimping of type I collagen fibrils

Explanation

The non-linear 'toe region' of the stress-strain curve represents the straightening out, or 'uncrimping,' of the wavy collagen fibrils in tendons and ligaments. Once uncrimped, the structure enters the linear elastic region.

Question 10233

Topic: Biomechanics & Biomaterials

According to the mechanical principles of intramedullary nailing, how is the torsional rigidity of a solid cylindrical titanium rod affected if its radius is doubled?

. It increases by a factor of 2
. It increases by a factor of 4
. It increases by a factor of 8
. It increases by a factor of 16
. It remains unchanged

Correct Answer & Explanation

. It increases by a factor of 16

Explanation

The torsional rigidity of a solid cylinder is proportional to the polar moment of inertia, which is directly proportional to the fourth power of the radius (r^4). Therefore, doubling the radius increases the torsional rigidity by a factor of 16.

Question 10234

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMP-2) are utilized to promote spinal fusion and fracture healing. Upon binding to their respective cell surface receptors, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus?

. Beta-catenin
. STAT3
. Smad 1/5/8
. NF-kappa B
. JAK2

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface. This induces the phosphorylation of receptor-regulated Smads (Smad 1, 5, and 8), which then complex with Smad 4 and translocate to the nucleus to regulate target gene transcription.

Question 10235

Topic: 1. General Principles & Basic Science

During a regional nerve block with bupivacaine, a patient inadvertently receives an intravascular injection resulting in cardiac arrest. Alongside standard cardiopulmonary resuscitation, which of the following is the most critical targeted pharmacological intervention?

. Intravenous flumazenil
. Intravenous 20% lipid emulsion
. High-dose intravenous naloxone
. Intravenous calcium gluconate
. Intravenous dantrolene

Correct Answer & Explanation

. Intravenous 20% lipid emulsion

Explanation

Local anesthetic systemic toxicity (LAST), particularly severe cardiotoxicity from bupivacaine, is treated with an intravenous 20% lipid emulsion. The lipid emulsion creates a 'lipid sink' that sequesters the lipophilic local anesthetic molecules away from myocardial tissue.

Question 10236

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total hip arthroplasty. This medication primarily exerts its anticoagulant effect by directly inhibiting which of the following components of the coagulation cascade?
. Thrombin (Factor IIa)
. Factor Xa
. Plasminogen
. Vitamin K epoxide reductase
. Antithrombin III

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that competitively and reversibly inhibit Factor Xa. This prevents the conversion of prothrombin to thrombin in the common pathway of the coagulation cascade.

Question 10237

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture with an associated radial nerve palsy. According to Seddon's classification, if the nerve injury is characterized by axonal disruption with an intact endoneurium, what is the specific classification of this injury?

. Neurapraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade IV
. Sunderland Grade V

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis involves disruption of the axon and myelin sheath, but preservation of the supporting connective tissue framework (endoneurium, perineurium, and epineurium). This allows for potential spontaneous nerve regeneration along the intact endoneurial tubes at a rate of 1 mm/day.

Question 10238

Topic: 1. General Principles & Basic Science
Which of the following types of collagen is the predominant structural component of normal hyaline articular cartilage, responsible for providing tensile strength to the extracellular matrix?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

Type II collagen makes up 90-95% of the collagen in articular cartilage. It forms a fibrillar network that restrains the swelling pressure of proteoglycans, thereby providing tensile strength and load-bearing capabilities.

Question 10239

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, the release of calcium ions from the sarcoplasmic reticulum initiates cross-bridge cycling by directly binding to which of the following regulatory proteins?

. Tropomyosin
. Troponin I
. Troponin C
. Myosin heavy chain
. Actin

Correct Answer & Explanation

. Troponin C

Explanation

Calcium ions bind directly to Troponin C on the actin thin filament. This binding induces a conformational change that moves tropomyosin away from the myosin-binding sites on actin, allowing cross-bridge formation to occur.

Question 10240

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely swollen knee. Joint aspiration yields cloudy fluid with a white blood cell count of 45,000 cells/mcL (60% polymorphonuclear leukocytes). Polarized light microscopy reveals negatively birefringent, needle-shaped crystals. What is the most likely diagnosis?

. Septic arthritis
. Rheumatoid arthritis
. Gouty arthritis
. Pseudogout (CPPD)
. Osteoarthritis

Correct Answer & Explanation

. Gouty arthritis

Explanation

Gout is characterized by the presence of monosodium urate crystals, which appear needle-shaped and are strongly negatively birefringent under polarized light. The cell count (often 10,000 to 50,000 WBCs/mcL) is consistent with an acute inflammatory monoarthritis.

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