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1. General Principles & Basic Science MCQs

Practice Set 617 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 12321

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with generalized bone pain, anemia, hypercalcemia, and renal dysfunction. Skeletal survey reveals multiple 'punched-out' lytic lesions in the skull and pelvis. The severe osteolytic bone destruction seen in this condition is primarily mediated by myeloma cell-induced:

. Upregulation of osteoprotegerin (OPG)
. Downregulation of RANKL
. Direct secretion of parathyroid hormone (PTH)
. Upregulation of RANKL and downregulation of OPG
. Direct destruction of bone matrix by myeloma cells via metalloproteinases

Correct Answer & Explanation

. Upregulation of RANKL and downregulation of OPG

Explanation

Multiple myeloma causes lytic bone lesions via uncoupling of normal bone remodeling. Myeloma cells interact with bone marrow stromal cells to upregulate RANKL and downregulate OPG (a decoy receptor for RANKL). This severely increased RANKL/OPG ratio leads to massive osteoclast activation and bone resorption.

Question 12322

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy presents with chronic knee pain. Radiographs demonstrate a well-demarcated, lytic lesion in the distal femoral epiphysis with a sclerotic margin. Histological examination of the curettage specimen is most likely to reveal which of the following?

. Sheets of small round blue cells with Homer-Wright rosettes
. Mononuclear cells with scattered multinucleated giant cells and 'chicken-wire' pericellular calcification
. Spindle cells arranged in a classic 'herringbone' pattern
. Abundant myxoid stroma with scattered lipoblasts and a prominent capillary network
. Benign fibrous stroma containing woven bone trabeculae that lack osteoblastic rimming

Correct Answer & Explanation

. Mononuclear cells with scattered multinucleated giant cells and 'chicken-wire' pericellular calcification

Explanation

The clinical and radiographic presentation describes a chondroblastoma (an epiphyseal lytic lesion in an open physis). The classic histological findings are mononuclear cells (chondroblasts), scattered osteoclast-like multinucleated giant cells, and distinctive fine, lacy, 'chicken-wire' pericellular calcification. Fibrous dysplasia (woven bone lacking osteoblastic rimming) is diaphyseal/metaphyseal.

Question 12323

Topic: Biology, Genetics & Bone Healing

Zoledronic acid is frequently administered to patients with metastatic bone disease to reduce the incidence of skeletal-related events (SREs). What is the primary intracellular mechanism of action of this medication in inhibiting osteoclast function?

. Directly binding to RANK ligand, preventing interaction with the RANK receptor
. Inhibition of farnesyl pyrophosphate synthase within the mevalonate pathway
. Direct competitive inhibition of the cathepsin K enzyme
. Activation of the Wnt/beta-catenin signaling pathway
. Stimulation of osteoblasts to secrete osteoprotegerin (OPG)

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase within the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (such as zoledronic acid and alendronate) are internalized by osteoclasts and act by inhibiting farnesyl pyrophosphate synthase (FPPS), a key enzyme in the mevalonate pathway. This prevents the prenylation of small GTPase proteins essential for osteoclast survival and cytoskeletal function, leading to osteoclast apoptosis. Denosumab binds RANKL. Cathepsin K inhibitors (like odanacatib) directly inhibit the enzyme.

Question 12324

Topic: Biology, Genetics & Bone Healing

A 45-year-old male presents with generalized bone pain, severe muscle weakness, and multiple insufficiency fractures. Laboratory studies reveal severe hypophosphatemia, hyperphosphaturia, and low 1,25-dihydroxyvitamin D levels. A small soft tissue mass is incidentally found in his plantar fascia. The mass is resected, and his metabolic abnormalities resolve completely. The tumor most likely secreted which of the following substances?

. Parathyroid hormone (PTH)
. Parathyroid hormone-related peptide (PTHrP)
. Fibroblast growth factor 23 (FGF23)
. Calcitonin
. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Correct Answer & Explanation

. Fibroblast growth factor 23 (FGF23)

Explanation

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome typically caused by a phosphaturic mesenchymal tumor. These tumors overproduce FGF23, which acts on the kidneys to decrease phosphate reabsorption and decrease 1-alpha-hydroxylase activity (lowering active Vitamin D), resulting in profound hypophosphatemia and osteomalacia.

Question 12325

Topic: Biology, Genetics & Bone Healing

A 35-year-old male is diagnosed with a giant cell tumor of the proximal tibia that is deemed surgically unresectable. Systemic therapy with denosumab is initiated. What is the specific mechanism of action of this medication in treating this tumor?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of the neoplastic mononuclear stromal cells
. Binding to RANKL to prevent osteoclast-like giant cell formation
. Inhibition of the mTOR pathway
. Cross-linking of DNA in rapidly dividing cells

Correct Answer & Explanation

. Binding to RANKL to prevent osteoclast-like giant cell formation

Explanation

Denosumab is a monoclonal antibody that binds to RANK ligand (RANKL). The neoplastic mononuclear cells in GCT secrete RANKL, which recruits and differentiates reactive osteoclast-like giant cells that cause bone destruction.

Question 12326

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a recurrently swollen, painless knee. Joint aspiration yields dark brown fluid. MRI demonstrates a villous synovial proliferation with blooming artifact on gradient-echo sequences. Which targeted therapy acts on the driving mutation for this condition?

. Imatinib
. Pexidartinib
. Denosumab
. Sorafenib
. Rituximab

Correct Answer & Explanation

. Pexidartinib

Explanation

Pigmented villonodular synovitis (PVNS/TGCT) is driven by a t(1;2) translocation causing overexpression of CSF1. Pexidartinib is a CSF1 receptor inhibitor approved for severe, symptomatic TGCT not amenable to improvement with surgery.

Question 12327

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with osteoporosis is started on Denosumab. This medication exerts its pharmacological effect by directly targeting and inhibiting which of the following molecular interactions?

. RANKL binding to RANK
. Osteoprotegerin (OPG) binding to RANK
. Parathyroid hormone binding to osteoblasts
. Bisphosphonate binding to hydroxyapatite crystals
. Sclerostin inhibition of the Wnt/beta-catenin pathway

Correct Answer & Explanation

. RANKL binding to RANK

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from binding to the RANK receptor on the surface of osteoclast precursors and mature osteoclasts, thereby fundamentally inhibiting osteoclastogenesis and decreasing bone resorption.

Question 12328

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four distinct histological zones. In which zone do chondrocytes exhibit the highest metabolic activity, synthesizing the largest concentration of proteoglycans, and are arranged in vertical columns?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is characterized by chondrocytes arranged in vertical columns perpendicular to the joint surface. It has the highest concentration of proteoglycans, the lowest water content, and the largest collagen fibrils. This zone provides the highest resistance to compressive forces.

Question 12329

Topic: Biology, Genetics & Bone Healing

A 58-year-old male presents with increasing deep aching pain in his right leg and subjective hearing loss. Radiographs demonstrate anterolateral bowing of the tibia with cortical thickening and mixed sclerotic and lytic lesions. Laboratory tests show isolated elevation of serum alkaline phosphatase. The primary cellular defect in this condition is characterized by:

. Defective osteoblast mineralization of osteoid
. Hyperactive, large multinucleated osteoclasts
. A gain-of-function mutation in Fibroblast Growth Factor Receptor 3
. A quantitative defect in Type I collagen synthesis
. Defective vitamin D receptor function

Correct Answer & Explanation

. Hyperactive, large multinucleated osteoclasts

Explanation

The clinical presentation is classic for Paget's disease of bone (osteitis deformans). The primary cellular abnormality is an initial phase of furious bone resorption by hyperactive, giant, multinucleated osteoclasts (often associated with SQSTM1 gene mutations or paramyxovirus inclusion bodies). This is followed by a disorganized, reactive osteoblastic response resulting in woven bone that is mechanically weak.

Question 12330

Topic: Biomechanics & Biomaterials

During material testing of an orthopedic implant, a stress-strain curve is generated. The total area under the stress-strain curve up to the point of material failure represents which of the following biomechanical properties?

. Yield strength
. Ultimate tensile strength
. Toughness
. Ductility
. Stiffness

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures or fails. It is graphically represented by the entire area under the stress-strain curve. Yield strength is the stress at which a material begins to plastically deform, and stiffness is represented by the slope of the elastic portion of the curve (Young's modulus).

Question 12331

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMPs) are utilized in orthopedics for their strong osteoinductive capabilities. Which specific BMP is FDA-approved for use in acute open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. TGF-beta

Correct Answer & Explanation

. BMP-2

Explanation

rhBMP-2 is FDA-approved for use in acute, open tibial shaft fractures (applied via a collagen sponge) and for single-level anterior lumbar interbody fusions (ALIF). rhBMP-7 (also known as Osteogenic Protein-1 or OP-1) was previously approved for recalcitrant tibial nonunions under a humanitarian device exemption. BMP-3 actually inhibits osteogenesis.

Question 12332

Topic: 1. General Principles & Basic Science
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is a clinical tool used to risk-stratify patients presenting with severe soft tissue infections. Which of the following laboratory parameters and its corresponding threshold is a component of the LRINEC score?
. Serum calcium < 8.5 mg/dL
. Serum sodium < 135 mEq/L
. Serum potassium > 5.5 mEq/L
. Serum AST > 40 U/L
. Serum albumin < 2.5 g/dL

Correct Answer & Explanation

. Serum sodium < 135 mEq/L

Explanation

The LRINEC score includes six variables: C-reactive protein (>150 mg/L), Total white cell count (>15, >25 x 10^9/L), Hemoglobin (<13.5, <11 g/dL), Serum sodium (<135 mmol/L), Serum creatinine (>141 umol/L or >1.6 mg/dL), and Serum glucose (>10 mmol/L or >180 mg/dL). Hyponatremia is a key indicator of systemic toxicity in necrotizing fasciitis.

Question 12333

Topic: Biomechanics & Biomaterials
In orthopedic implant surgery, mixing different metals can lead to galvanic corrosion due to differences in electrochemical potential. Which of the following combinations of implant materials poses the highest risk of clinically significant galvanic corrosion when placed in direct contact in vivo?
. Titanium alloy and Commercially pure titanium
. 316L Stainless Steel and Cobalt-Chromium alloy
. Cobalt-Chromium alloy and Titanium alloy
. Tantalum (trabecular metal) and Titanium alloy
. UHMWPE and Cobalt-Chromium alloy

Correct Answer & Explanation

. 316L Stainless Steel and Cobalt-Chromium alloy

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in contact within an electrolyte solution (like body fluid). 316L stainless steel has a significantly different anodic index compared to cobalt-chromium or titanium. Mixing stainless steel with cobalt-chromium leads to rapid galvanic corrosion of the less noble metal (the stainless steel). Titanium and cobalt-chromium can often be used together with minimal risk (e.g., modular total hips).

Question 12334

Topic: Surgical Anatomy & Approaches
A patient suffers a severe stretch injury to the radial nerve. An EMG/NCS performed 4 weeks later confirms axonal loss. If the surgical exploration were to reveal disrupted axons and endoneurium, but an intact perineurium and epineurium, how would this nerve injury be classified according to Sunderland?
. Grade I
. Grade II
. Grade III
. Grade IV
. Grade V

Correct Answer & Explanation

. Grade III

Explanation

Sunderland classification divides nerve injuries into 5 grades. Grade I is neuropraxia (myelin injury). Grade II is axonotmesis (axon disrupted, endoneurium intact). Grade III involves disruption of the axon and endoneurium, with an intact perineurium. Grade IV involves disruption of the axon, endoneurium, and perineurium, with only the epineurium intact. Grade V is a complete nerve transection.

Question 12335

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) has become standard of care in major orthopedic surgery to reduce perioperative blood loss. What is the specific molecular mechanism of action of tranexamic acid?
. Inhibits factor Xa within the common coagulation cascade
. Directly inhibits thrombin formation
. Competitively inhibits the activation of plasminogen to plasmin
. Enhances the activity of antithrombin III
. Irreversibly inhibits cyclooxygenase in platelets

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic derivative of the amino acid lysine. It exerts its antifibrinolytic effect by reversibly blocking the lysine-binding sites on plasminogen molecules. This competitive inhibition prevents the activation of plasminogen into plasmin, thereby preventing the degradation of fibrin clots.

Question 12336

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. When a constant static load is continuously applied to a ligament over an extended period, the ligament will gradually elongate over time. This specific biomechanical phenomenon is known as:

. Stress relaxation
. Creep
. Hysteresis
. Anisotropy
. Fatigue failure

Correct Answer & Explanation

. Creep

Explanation

Creep is the property of a viscoelastic material to progressively deform (elongate) when subjected to a constant load (stress) over time. In contrast, stress relaxation is the phenomenon where the stress within a material decreases over time when it is held at a constant length (strain).

Question 12337

Topic: Physiology & Rehabilitation

A physical therapist is rehabilitating a patient following an Achilles tendon repair. The therapist instructs the patient to slowly lower their heel off the edge of a step. During the lowering phase, the gastrocnemius-soleus complex is generating tension while simultaneously lengthening. What type of muscle contraction is this?

. Concentric
. Eccentric
. Isometric
. Isokinetic
. Plyometric

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when a muscle generates tension but the external force is greater than the generated force, causing the muscle to lengthen. Eccentric contractions generate the highest maximum muscle forces and are the primary cause of delayed onset muscle soreness (DOMS) and muscle strain injuries. Concentric contraction involves muscle shortening, while isometric involves no change in length.

Question 12338

Topic: 1. General Principles & Basic Science

Collagen provides the primary tensile strength in bone, cartilage, and tendons. During collagen synthesis, covalent cross-linking between adjacent tropocollagen molecules is essential for providing structural integrity. This critical cross-linking step is catalyzed by which of the following enzymes?

. Prolyl hydroxylase
. Lysyl oxidase
. Matrix metalloproteinase-13
. Stromelysin
. Type II Collagenase

Correct Answer & Explanation

. Lysyl oxidase

Explanation

Lysyl oxidase is a copper-dependent extracellular enzyme responsible for cross-linking collagen and elastin. It catalyzes the oxidative deamination of lysine and hydroxylysine residues to form reactive aldehydes, which spontaneously react to form the strong covalent cross-links that give collagen fibrils their ultimate tensile strength. Prolyl hydroxylase acts intracellularly to hydroxylate proline, requiring Vitamin C.

Question 12339

Topic: 1. General Principles & Basic Science

Articular cartilage relies on unique lubrication mechanisms depending on the loading condition. Under high-load, low-speed conditions, fluid-film lubrication breaks down, and boundary lubrication becomes the predominant mechanism preventing cartilage wear. Boundary lubrication is primarily mediated by which molecule?

. Hyaluronic acid
. Lubricin (PRG4)
. Type II collagen
. Chondroitin sulfate
. Aggrecan

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Boundary lubrication prevents direct surface-to-surface contact of cartilage during high-load, low-speed scenarios. It is primarily provided by lubricin (Proteoglycan 4 or PRG4), a glycoprotein secreted by superficial zone chondrocytes and synoviocytes. Elastohydrodynamic (fluid-film) lubrication dominates during low-load, high-speed motions and is heavily dependent on interstitial fluid pressurization and hyaluronic acid.

Question 12340

Topic: Biomechanics & Biomaterials
In the manufacturing of joint arthroplasty components, Ultra-High Molecular Weight Polyethylene (UHMWPE) undergoes gamma irradiation to increase cross-linking and decrease wear. However, if this irradiation is performed in an environment containing oxygen, which deleterious effect is most likely to occur over time?
. Increased formation of favorable cross-links
. Oxidation resulting in chain scission and embrittlement
. Increased percentage of crystalline domains leading to higher toughness
. Melting of the amorphous phase resulting in implant deformation
. Conversion of the material to a thermoset plastic

Correct Answer & Explanation

. Oxidation resulting in chain scission and embrittlement

Explanation

Gamma irradiation generates free radicals within the UHMWPE. If oxygen is present during irradiation or storage (shelf aging), these free radicals combine with oxygen to cause oxidation and chain scission (breaking of polymer chains). This severely decreases the mechanical properties (embrittlement) and increases wear debris in vivo. Modern highly cross-linked polyethylene is irradiated in an inert gas or vacuum and subsequently melted or annealed to extinguish residual free radicals.

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