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1. General Principles & Basic Science MCQs

Practice Set 686 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 13701

Topic: 1. General Principles & Basic Science

A patient sustained a closed crush injury to the forearm 6 weeks ago. Electromyography (EMG) is performed to assess nerve recovery. Which of the following EMG findings indicates active denervation and a poor prognosis for spontaneous recovery if persistent?

. Polyphasic action potentials
. Fibrillation potentials at rest
. Large amplitude, long duration motor unit action potentials (MUAPs)
. Decreased insertional activity
. Triphasic motor unit potentials during voluntary contraction

Correct Answer & Explanation

. Fibrillation potentials at rest

Explanation

Fibrillation potentials and positive sharp waves at rest on an EMG indicate active denervation of the muscle (individual muscle fibers firing spontaneously without central nerve input). Polyphasic potentials and large amplitude MUAPs indicate reinnervation and collateral sprouting.

Question 13702

Topic: 1. General Principles & Basic Science

Compared to normal walking, what is the approximate increase in energy expenditure required for a patient ambulating with a unilateral traumatic transfemoral (above-knee) amputation?

. 10-15%
. 25-30%
. 60-65%
. 100-110%
. 150-160%

Correct Answer & Explanation

. 25-30%

Explanation

Energy expenditure during gait increases as the level of amputation moves proximally. The approximate increases in energy expenditure are: unilateral Syme's (15%), unilateral transtibial (25-30%), unilateral transfemoral (60-65%), and bilateral transfemoral (>200%).

Question 13703

Topic: Biology, Genetics & Bone Healing
A midshaft tibia fracture is treated with a cast. Callus formation is noted on radiographs at 4 weeks. Which type of collagen is the predominant structural component of the soft callus prior to its replacement by woven bone?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

Secondary bone healing occurs via endochondral ossification. During the soft callus phase, chondrocytes produce a cartilaginous matrix predominantly composed of Type II collagen. This is subsequently replaced by woven bone (Type I collagen) during the hard callus phase.

Question 13704

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femur extending to the subchondral bone without a sclerotic margin. Biopsy reveals multinucleated giant cells interspersed among mononuclear stromal cells. Denosumab is considered for treatment. What is the molecular target of this medication in this specific tumor?

. RANK receptor on the giant cells
. RANKL produced by the mononuclear stromal cells
. Osteoprotegerin (OPG) in the surrounding matrix
. Vascular endothelial growth factor (VEGF)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. RANKL produced by the mononuclear stromal cells

Explanation

In Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear stromal cells, which produce copious amounts of RANK Ligand (RANKL). This RANKL recruits normal macrophages and induces their fusion into osteoclast-like multinucleated giant cells. Denosumab binds and inhibits RANKL produced by the stromal cells.

Question 13705

Topic: Biomechanics & Biomaterials

A 65-year-old male presents with acute swelling and severe pain in his right knee. Aspiration yields cloudy synovial fluid with a WBC count of 45,000 cells/mm3. Polarized light microscopy reveals rhomboid-shaped crystals with weak positive birefringence. What is the composition of these crystals?

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

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

The clinical and microscopic findings are diagnostic of pseudogout (CPPD). The crystals are made of Calcium Pyrophosphate Dihydrate, which are classically rhomboid-shaped and exhibit weak positive birefringence under polarized light. Monosodium urate (gout) crystals are needle-shaped and strongly negatively birefringent.

Question 13706

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the organization of collagen fibers and chondrocytes varies by depth. Which zone is characterized by collagen fibers oriented perpendicular to the joint surface and chondrocytes arranged in columnar profiles?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

In the deep (radial) zone of articular cartilage, collagen fibers are oriented perpendicular to the articular surface, and chondrocytes are arranged in vertical columns. This structural arrangement provides maximal resistance to compressive forces. The superficial zone has collagen parallel to the surface to resist shear forces.

Question 13707

Topic: Biology, Genetics & Bone Healing

The ruffled border of osteoclasts represents the highly folded cell membrane where active bone resorption takes place. Which of the following is primarily responsible for the active acidification of the resorption lacuna at this site?

. Na+/K+ ATPase pump
. Voltage-gated calcium channels
. Carbonic anhydrase II
. Vacuolar-type H+ ATPase (V-ATPase)
. Cathepsin K

Correct Answer & Explanation

. Vacuolar-type H+ ATPase (V-ATPase)

Explanation

Acidification of the resorption pit (Howship's lacuna) is essential for bone resorption. This is primarily achieved by the vacuolar-type H+ ATPase (V-ATPase) proton pump located heavily on the ruffled border. Carbonic anhydrase II generates the protons intracellularly, but the V-ATPase actively pumps them into the lacuna. Cathepsin K is a lysosomal enzyme that degrades the organic matrix (type I collagen) once the mineral is dissolved by the acidic environment.

Question 13708

Topic: Biomechanics & Biomaterials

When analyzing the biomechanical properties of an orthopedic implant material using a standard stress-strain curve, the 'yield point' specifically represents:

. The point at which the material fractures completely.
. The transition from reversible elastic deformation to irreversible plastic deformation.
. The maximum stress a material can withstand before necking.
. The area under the curve representing overall material toughness.
. The slope of the linear elastic region representing stiffness.

Correct Answer & Explanation

. The transition from reversible elastic deformation to irreversible plastic deformation.

Explanation

The yield point on a stress-strain curve defines the exact point at which a material transitions from elastic deformation (where it will return to its original shape when the load is removed) to plastic deformation (irreversible, permanent structural change). The ultimate tensile strength is the maximum stress on the curve. The slope of the elastic region is Young's modulus (stiffness). The total area under the curve represents toughness.

Question 13709

Topic: Infection, Pharmacology & VTE

Biofilm formation is a critical factor in the pathogenesis of prosthetic joint infections. Which of the following phases of biofilm development or bacterial state is targeted most effectively by the adjunctive use of Rifampin?

. Initial reversible bacterial adherence to the implant
. Irreversible attachment via cell-surface adhesins
. Maturation and production of the exopolysaccharide matrix
. Stationary phase planktonic bacteria
. Sessile bacteria embedded within the established biofilm

Correct Answer & Explanation

. Sessile bacteria embedded within the established biofilm

Explanation

Rifampin has a unique molecular ability to penetrate the exopolysaccharide matrix (glycocalyx) of established biofilms and kill sessile (dormant or slow-growing) staphylococcal organisms. It is highly effective against these biofilm-embedded bacteria, which is why it is utilized as an adjunctive treatment in prosthetic joint infections, provided the implant is retained and the bacterial burden has been surgically minimized. Standard IV antibiotics primarily target planktonic (free-floating) bacteria.

Question 13710

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., Alendronate, Zoledronate) are commonly prescribed for osteoporosis and Paget's disease. What is their primary molecular mechanism of action?

. Inhibition of RANKL binding to the RANK receptor
. Inhibition of farnesyl pyrophosphate (FPP) synthase
. Activation of the Wnt/beta-catenin signaling pathway
. Binding to the calcium-sensing receptor (CaSR)
. Direct inhibition of Cathepsin K secretion

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates inhibit the enzyme farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway inside osteoclasts. This prevents the essential prenylation (attachment of lipid tails) of small GTP-binding proteins (such as Ras, Rho, and Rac) that are critical for osteoclast ruffled border formation, function, and survival, ultimately leading to osteoclast apoptosis. Denosumab, a monoclonal antibody, works by inhibiting RANKL.

Question 13711

Topic: 1. General Principles & Basic Science

According to Sunderland's classification of peripheral nerve injuries, a second-degree injury (Axonotmesis) is characterized by:

. Focal conduction block with intact axons and connective tissue
. Disruption of axons with completely intact endoneurium
. Disruption of axons and endoneurium with an intact perineurium
. Disruption of axons, endoneurium, and perineurium with an intact epineurium
. Complete nerve transection including the epineurium

Correct Answer & Explanation

. Disruption of axons with completely intact endoneurium

Explanation

Sunderland's classification: 1st degree (Neuropraxia) = local conduction block; 2nd degree (Axonotmesis) = axonal disruption with an intact endoneurium; 3rd degree = axonal and endoneurial disruption with an intact perineurium; 4th degree = disruption of everything inside the epineurium (perineurium torn, epineurium intact); 5th degree (Neurotmesis) = complete nerve transection. Second-degree injuries undergo Wallerian degeneration but have excellent recovery potential because the intact endoneurial tubes effectively guide regenerating axons.

Question 13712

Topic: Infection, Pharmacology & VTE

Aspiration of a 3 cm central, radiolucent bone lesion in the proximal humerus of an 8-year-old child yields clear, serosanguinous fluid. Laboratory analysis of this specific aspirate fluid is most likely to demonstrate markedly elevated levels of:

. Alkaline phosphatase
. Prostaglandins
. Matrix metalloproteinases
. Lactic acid
. Beta-2 microglobulin

Correct Answer & Explanation

. Prostaglandins

Explanation

The clinical presentation (central lucent lesion in proximal humerus in a child) and aspiration findings describe a Unicameral Bone Cyst (UBC). Fluid analysis of a UBC classically reveals high levels of prostaglandins (particularly PGE2), interleukins, and other inflammatory mediators. These factors stimulate osteoclastic bone resorption and prevent bone healing, leading to cyst expansion. This pathophysiology forms the rationale behind treating UBCs with intralesional corticosteroid injections, which inhibit prostaglandin synthesis.

Question 13713

Topic: Biology, Genetics & Bone Healing

A 55-year-old female undergoes a total thyroidectomy for carcinoma. Postoperatively, she develops severe muscle cramping and perioral numbness, and her intact PTH is notably undetectable. Which specific step in Vitamin D metabolism will be directly and severely impaired by this complication?

. Conversion of 7-dehydrocholesterol to cholecalciferol in the skin
. Hepatic conversion of cholecalciferol to 25-hydroxyvitamin D
. Renal conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D
. Inactivation of 1,25-dihydroxyvitamin D via 24-hydroxylase
. Intestinal absorption of dietary Vitamin D3

Correct Answer & Explanation

. Renal conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

Explanation

Inadvertent removal of the parathyroid glands causes hypoparathyroidism and low Parathyroid Hormone (PTH). PTH is essential for upregulating the enzyme 1-alpha-hydroxylase in the proximal tubules of the kidney. This enzyme catalyzes the conversion of 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D (calcitriol). Without PTH, this critical final activation step is impaired, severely exacerbating her hypocalcemia.

Question 13714

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue designed to resist both compressive and shear forces. In which histologic zone of articular cartilage are the type II collagen fibers strictly oriented parallel to the joint surface to specifically resist shear forces?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

In the superficial (tangential) zone of articular cartilage, the chondrocytes are flattened, and the Type II collagen fibers are aligned parallel to the articular surface. This specific orientation provides the cartilage with its primary resistance to shear stress and acts as a gliding surface. In the deep (radial) zone, the thick collagen fibers are perpendicular to the surface to anchor the cartilage and resist compressive forces. The middle zone features a more random, oblique collagen network.

Question 13715

Topic: Biomechanics & Biomaterials

Regarding the inherent mechanical properties of orthopedic implant materials and bone, which of the following materials possesses the lowest Young's modulus (thereby exhibiting the greatest relative elasticity/least stiffness)?

. Cobalt-chromium-molybdenum alloy
. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Cortical bone
. Cancellous bone

Correct Answer & Explanation

. Cancellous bone

Explanation

Young's modulus is a measure of the stiffness of a solid material. A lower Young's modulus indicates less stiffness (greater elasticity). Cancellous bone has a significantly lower Young's modulus (approx. 0.1 - 2 GPa) compared to cortical bone (15 - 20 GPa). Among the common metals, Titanium alloy has the lowest modulus (~110 GPa), followed by Stainless steel (~200 GPa) and Cobalt-chromium (~210-250 GPa). Therefore, cancellous bone is the least stiff of the options provided.

Question 13716

Topic: 1. General Principles & Basic Science

Which of the following best describes the normal physiologic direction of arterial blood flow within the diaphyseal cortex of a mature, uninjured long bone?

. Centripetal (from periosteum to endosteum)
. Centrifugal (from endosteum to periosteum)
. Bidirectional depending on systemic blood pressure
. Strictly longitudinal (parallel to Haversian canals only)
. Randomized through the capillary network

Correct Answer & Explanation

. Centrifugal (from endosteum to periosteum)

Explanation

In a normal, mature long bone, the diaphyseal cortex receives its primary blood supply from the high-pressure nutrient artery system within the medullary canal. The physiologic flow is centrifugal, moving from the higher-pressure medullary canal (endosteum) outward toward the lower-pressure periosteum. In the setting of trauma or disruption of the medullary supply (e.g., reamed intramedullary nailing), the flow can temporarily reverse, becoming centripetal as the intact periosteal blood supply compensates.

Question 13717

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with deep, aching pain in his right thigh and complains that his hats no longer fit. Radiographs of the femur show cortical thickening and coarse trabeculae. Baseline laboratory evaluation is most likely to show which of the following profiles for serum Calcium, Phosphorus, and Alkaline Phosphatase (ALP)?

. Elevated Calcium, Decreased Phosphorus, Elevated ALP
. Normal Calcium, Normal Phosphorus, Elevated ALP
. Decreased Calcium, Normal Phosphorus, Elevated ALP
. Normal Calcium, Normal Phosphorus, Normal ALP
. Normal Calcium, Elevated Phosphorus, Normal ALP

Correct Answer & Explanation

. Normal Calcium, Normal Phosphorus, Elevated ALP

Explanation

The clinical presentation (thigh pain, increased hat size) and radiographic appearance (cortical thickening, coarse trabeculae) are classic for Paget's disease of bone (osteitis deformans). In Paget's disease, there is massive, disorganized bone remodeling driven by overactive osteoclasts followed by chaotic osteoblast activity. Despite this intense turnover, serum calcium and phosphorus levels typically remain remarkably normal in untreated patients. The robust bone formation leads to an isolated, significantly elevated serum alkaline phosphatase (ALP).

Question 13718

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is widely used in total joint arthroplasty to minimize wear debris. However, which critical mechanical property is significantly decreased as a direct result of the high-dose irradiation process used to cross-link the polyethylene?
. Abrasive wear resistance
. Oxidation resistance (if remelted appropriately)
. Ultimate tensile strength and fatigue crack propagation resistance
. Young's modulus
. Compressive yield strength

Correct Answer & Explanation

. Ultimate tensile strength and fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured by subjecting UHMWPE to high-dose gamma or electron-beam irradiation, which severs molecular chains and induces dense cross-linking. While this process vastly improves adhesive and abrasive wear resistance, the trade-off is a measurable decrease in mechanical properties, specifically ultimate tensile strength, fatigue crack propagation resistance, and ductility. For this reason, HXLPE is used with caution in high-stress, non-conforming joints or in very thin acetabular liners where fatigue failure could occur.

Question 13719

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing, the soft callus phase is primarily characterized by the formation of:

. Woven bone directly via intramembranous ossification
. Cartilage via migrating chondrocytes
. Lamellar bone via osteoclastic cutting cones
. Fibrous scar tissue via fibroblasts exclusively
. Hematoma organization featuring only inflammatory cells

Correct Answer & Explanation

. Cartilage via migrating chondrocytes

Explanation

Secondary fracture healing progresses sequentially through inflammation, soft callus formation, hard callus formation, and remodeling. The soft callus phase is primarily characterized by endochondral ossification, where chondrocytes produce a cartilaginous matrix that bridges the fracture site, providing initial semi-rigid stability. Woven bone formation subsequently characterizes the hard callus phase as it replaces the cartilage. Cutting cones are a feature of primary (direct) bone healing and late remodeling.

Question 13720

Topic: Infection, Pharmacology & VTE
Rivaroxaban is frequently prescribed for deep vein thrombosis (DVT) prophylaxis following lower extremity total joint arthroplasty. What is its specific mechanism of action in the coagulation cascade?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via binding to antithrombin III
. Direct, competitive inhibition of Factor Xa
. Vitamin K antagonism via inhibition of epoxide reductase
. Irreversible inhibition of the P2Y12 ADP receptor on platelets

Correct Answer & Explanation

. Direct, competitive inhibition of Factor Xa

Explanation

Rivaroxaban (as well as Apixaban) is a direct oral anticoagulant (DOAC) that specifically and directly inhibits Factor Xa in the coagulation cascade, preventing the conversion of prothrombin to thrombin. Dabigatran directly inhibits thrombin (Factor IIa). Low molecular weight heparins (like enoxaparin) and fondaparinux indirectly inhibit Factor Xa by binding to antithrombin III. Warfarin is a vitamin K antagonist. Clopidogrel inhibits the ADP receptor on platelets.

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