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1. General Principles & Basic Science MCQs

Practice Set 681 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 13601

Topic: 1. General Principles & Basic Science

Within the ultrastructure of normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans and collagen fibrils oriented perpendicular to the articular surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Normal articular cartilage is divided into four zones. The deep (radial) zone has the highest proteoglycan content, the lowest water content, and its type II collagen fibrils are oriented radially (perpendicular to the joint surface). This structure is optimized to distribute and resist heavy compressive loads. The superficial zone has collagen parallel to the surface to resist shear stress.

Question 13602

Topic: Biomechanics & Biomaterials

Orthopedic materials such as ligaments and tendons exhibit viscoelastic properties. If a tendon is subjected to a constant, sustained elongation (constant strain), the force required to maintain that elongation decreases over time. What is the biomechanical term for this phenomenon?

. Creep
. Hysteresis
. Stress relaxation
. Fatigue failure
. Isotropic degradation

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a primary viscoelastic property defined as the decrease in stress (internal force) over time when a material is held at a constant strain (constant length). Conversely, creep is defined as the progressive deformation (increase in strain) over time when a material is subjected to a constant force (constant stress).

Question 13603

Topic: Biology, Genetics & Bone Healing

A 32-year-old female is diagnosed with an advanced, surgically unresectable giant cell tumor (GCT) of the sacrum. Her oncologist recommends medical therapy with Denosumab to halt disease progression. What is the primary molecular target of this monoclonal antibody?

. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Vascular endothelial growth factor (VEGF)
. Colony-stimulating factor 1 receptor (CSF1R)
. Tumor necrosis factor-alpha (TNF-alpha)

Correct Answer & Explanation

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

Explanation

Denosumab is a fully human monoclonal antibody that binds to and inhibits RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand). In Giant Cell Tumor of bone, the neoplastic mononuclear stromal cells overexpress RANKL, which aggressively recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) responsible for massive bone destruction. Blocking RANKL effectively arrests the osteolysis and tumor progression.

Question 13604

Topic: Infection, Pharmacology & VTE
Following a total hip arthroplasty, a patient is prescribed Rivaroxaban for deep vein thrombosis (DVT) prophylaxis. What is the precise pharmacological mechanism of action of this medication?
. Reversible, competitive inhibition of thrombin (Factor IIa)
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Direct, selective inhibition of Factor Xa
. Vitamin K epoxide reductase inhibition
. Activation of antithrombin III to inhibit both Factor Xa and Thrombin

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are novel oral anticoagulants (NOACs) that work as direct, highly selective inhibitors of Factor Xa. This blocks the convergence point of the intrinsic and extrinsic coagulation pathways, preventing the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. LMWH works via antithrombin III.

Question 13605

Topic: Biomechanics & Biomaterials
What is the primary advantage of highly cross-linking ultra-high molecular weight polyethylene (UHMWPE) via gamma irradiation, followed by remelting, in total joint arthroplasty?
. Increases ultimate tensile strength of the polyethylene
. Significantly reduces adhesive and abrasive wear
. Eliminates the risk of rim cracking in the liner
. Increases fatigue strength and resistance to fracture
. Reduces the melting temperature to improve molding

Correct Answer & Explanation

. Significantly reduces adhesive and abrasive wear

Explanation

Cross-linking UHMWPE significantly reduces abrasive and adhesive wear, which is the primary driver of macrophage-induced osteolysis. However, the process of cross-linking and subsequent remelting (done to eliminate free radicals and prevent oxidation) actually decreases the mechanical properties of the polyethylene, such as fatigue strength, yield strength, and ultimate tensile strength.

Question 13606

Topic: Infection, Pharmacology & VTE

A 65-year-old male presents with acute knee pain. Synovial fluid analysis reveals weakly positively birefringent rhomboid-shaped crystals under polarized light microscopy. Which of the following conditions is most strongly associated with these findings?

. Hemochromatosis
. Psoriatic arthritis
. Chronic renal failure
. Lesch-Nyhan syndrome
. Rheumatoid arthritis

Correct Answer & Explanation

. Hemochromatosis

Explanation

The crystals described are calcium pyrophosphate dihydrate (CPPD), which are characteristic of pseudogout. Pseudogout is strongly associated with the '3 Hs': Hyperparathyroidism, Hemochromatosis, and Hypothyroidism, as well as hypomagnesemia and hypophosphatasia. Lesch-Nyhan and chronic renal failure are more typically associated with gout (negatively birefringent needle-shaped monosodium urate crystals).

Question 13607

Topic: Biology, Genetics & Bone Healing

A 72-year-old man with increasing hat size and bowing of his femurs is diagnosed with Paget's disease. The primary cellular defect in this condition is characterized by:

. A primary defect in osteoblast mineralization
. Excessive proliferation of atypical chondrocytes
. Overactive osteoclasts with an increased number of nuclei
. An absence of functional ruffled borders on osteoclasts
. Deficient production of type I collagen by fibroblasts

Correct Answer & Explanation

. Overactive osteoclasts with an increased number of nuclei

Explanation

Paget's disease of bone is driven by a primary abnormality in osteoclasts. These cells are massively enlarged, overactive, and multinucleated (sometimes containing up to 100 nuclei per cell, often with paramyxovirus-like inclusion bodies). This intense resorptive phase is followed by chaotic, disorganized osteoblastic bone formation.

Question 13608

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent cause of periprosthetic joint infection primarily due to its ability to form a biofilm. Which of the following describes the critical first step in biofilm formation on a metal orthopedic implant?

. Bacterial quorum sensing activation
. Synthesis of bacterial exopolysaccharide glycocalyx
. Adsorption of host proteins (fibronectin/fibrinogen) onto the implant surface
. Shedding of planktonic bacteria into the joint fluid
. Intracellular bacterial invasion into host macrophages

Correct Answer & Explanation

. Adsorption of host proteins (fibronectin/fibrinogen) onto the implant surface

Explanation

The sequence of biofilm formation begins instantly upon implantation with the rapid adsorption of host proteins (such as fibronectin, fibrinogen, and vitronectin) onto the foreign body surface. This forms a conditioning layer that facilitates the subsequent initial adhesion of bacteria, which then proliferate and secrete an exopolysaccharide matrix.

Question 13609

Topic: Biomechanics & Biomaterials
Two solid titanium rods, Rod A and Rod B, have the exact same length, but Rod B has twice the radius of Rod A. By what factor is the torsional stiffness of Rod B greater than that of Rod A?
. 2 times
. 4 times
. 8 times
. 16 times
. 32 times

Correct Answer & Explanation

. 16 times

Explanation

The torsional stiffness of a solid cylinder is directly proportional to its polar moment of inertia (J = πr⁴ / 2). Because the radius is raised to the fourth power, doubling the radius increases the torsional stiffness by a factor of 2⁴, which equals 16.

Question 13610

Topic: 1. General Principles & Basic Science

Which of the following best describes the organization of type II collagen fibers in the superficial (tangential) zone of normal articular cartilage?

. Randomly oriented throughout the matrix
. Oriented parallel to the joint surface
. Oriented perpendicular to the joint surface
. Arranged in an arcade-like honeycomb lattice
. Completely absent from this specific zone

Correct Answer & Explanation

. Oriented parallel to the joint surface

Explanation

In the superficial (tangential) zone of articular cartilage, collagen fibers are oriented parallel to the joint surface to resist shear forces. The deep zone features collagen fibers oriented perpendicular to the surface to resist compressive loads, crossing the tidemark to anchor into subchondral bone.

Question 13611

Topic: Physiology & Rehabilitation

Which of the following physiologic characteristics is true regarding Type I skeletal muscle fibers when compared to Type IIb fibers?

. Higher glycogen content
. Primary reliance on anaerobic glycolysis
. Higher concentration of mitochondria
. Faster speed of contraction
. Larger cross-sectional area

Correct Answer & Explanation

. Higher concentration of mitochondria

Explanation

Type I muscle fibers are 'slow-twitch' endurance fibers. They are rich in myoglobin (appearing red), have a high concentration of mitochondria, and rely primarily on aerobic oxidative phosphorylation. In contrast, Type IIb fibers are 'fast-twitch' fibers that rely on anaerobic glycolysis, fatigue rapidly, and have a higher glycogen content.

Question 13612

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse, dull bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH) levels. What is the most likely diagnosis?

. Osteoporosis
. Osteomalacia
. Paget's disease
. Primary hyperparathyroidism
. Renal osteodystrophy

Correct Answer & Explanation

. Osteomalacia

Explanation

The laboratory profile of low calcium, low phosphorus, high alkaline phosphatase, and high parathyroid hormone (secondary hyperparathyroidism) is the classic hallmark of osteomalacia, most commonly due to severe Vitamin D deficiency. Osteoporosis typically features normal lab values. Primary hyperparathyroidism presents with high calcium.

Question 13613

Topic: 1. General Principles & Basic Science
Low molecular weight heparin (LMWH) provides deep vein thrombosis prophylaxis primarily by binding to antithrombin III, which then preferentially accelerates the inhibition of which of the following coagulation factors?
. Factor IIa (Thrombin)
. Factor VIIa
. Factor VIIIa
. Factor IXa
. Factor Xa

Correct Answer & Explanation

. Factor Xa

Explanation

LMWH binds to antithrombin III and preferentially accelerates its inhibition of Factor Xa. Unfractionated heparin (UFH) inhibits both Factor Xa and Factor IIa (thrombin) equally (1:1 ratio), whereas LMWH has a much higher ratio of anti-Factor Xa to anti-Factor IIa activity (typically 2:1 to 4:1) because the shorter molecular chains cannot easily bridge antithrombin to thrombin.

Question 13614

Topic: Biomechanics & Biomaterials

In the biomechanical assessment of viscoelastic materials such as ligaments and tendons, what is the term for the time-dependent decrease in applied stress when the tissue is held at a constant strain (deformation)?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a hallmark of viscoelasticity defined as the decrease in stress over time when a material is subjected to a constant strain (held at a constant length). Creep is the opposite counterpart: a time-dependent increase in strain (deformation) when the material is subjected to a constant load (stress).

Question 13615

Topic: Biomechanics & Biomaterials

A surgeon implants a 316L stainless steel screw to temporarily secure a titanium alloy plate. This combination creates a risk of galvanic corrosion. In this scenario, which component acts as the anode, and what is the consequence?

. Titanium plate acts as the anode, leading to dissolution of the plate
. Titanium plate acts as the anode, leading to passivation of the metal
. Stainless steel screw acts as the anode, leading to accelerated corrosion of the screw
. Stainless steel screw acts as the anode, leading to deposition of titanium on the screw
. Both metals corrode equally due to identical electronegativity

Correct Answer & Explanation

. Stainless steel screw acts as the anode, leading to accelerated corrosion of the screw

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic solution (like bodily fluids). The less noble (more reactive) metal, which is stainless steel in this pairing, becomes the anode and undergoes accelerated dissolution/corrosion. The more noble metal (titanium) acts as the cathode and is protected.

Question 13616

Topic: Biology, Genetics & Bone Healing
Osteoclasts tightly adhere to the bone surface to form a sealed resorptive microenvironment. This attachment is primarily mediated by the binding of which integrin to the RGD (Arg-Gly-Asp) sequence found in bone matrix proteins like osteopontin?
. Integrin alpha-5 beta-1
. Integrin alpha-v beta-3
. Integrin alpha-2 beta-1
. Integrin alpha-L beta-2
. Integrin alpha-M beta-2

Correct Answer & Explanation

. Integrin alpha-v beta-3

Explanation

The αvβ3 integrin is heavily expressed on the surface of osteoclasts. It binds to RGD (arginine-glycine-aspartic acid) sequences in non-collagenous bone matrix proteins such as osteopontin and bone sialoprotein. This binding is essential for creating the sealing zone required for effective ruffled border function and bone resorption.

Question 13617

Topic: 1. General Principles & Basic Science

Following a primary surgical repair of an acute flexor tendon laceration, during which timeframe is the repair construct mechanically at its weakest due to the overlap of the inflammatory and early proliferative phases of healing?

. Days 1 to 3
. Days 5 to 21
. Days 28 to 42
. Weeks 8 to 10
. Months 3 to 6

Correct Answer & Explanation

. Days 5 to 21

Explanation

A repaired tendon is mechanically at its weakest between roughly days 5 and 21 post-repair. During this transition from the inflammatory phase to the early fibroblastic (proliferative) phase, the rate of collagen degradation by matrix metalloproteinases temporarily exceeds the rate of new collagen synthesis, causing a drop in tensile strength.

Question 13618

Topic: Surgical Anatomy & Approaches

A patient sustains a closed fracture of the humerus resulting in a radial nerve palsy. According to the Sunderland classification, a 2nd-degree nerve injury (equivalent to Seddon's axonotmesis) is strictly characterized by:

. Transient focal conduction block with no Wallerian degeneration
. Disruption of the axon and myelin sheath with an intact endoneurium
. Disruption of the axon and endoneurium with an intact perineurium
. Disruption of the perineurium with an intact epineurium
. Complete nerve transection including the epineurium

Correct Answer & Explanation

. Disruption of the axon and myelin sheath with an intact endoneurium

Explanation

A Sunderland 2nd-degree injury (Seddon's axonotmesis) involves complete disruption of the axon and myelin sheath, causing Wallerian degeneration distal to the injury site. Crucially, the endoneurial tube and all outer connective tissues (perineurium, epineurium) remain completely intact, allowing for excellent predictable spontaneous recovery at approximately 1 mm/day.

Question 13619

Topic: 1. General Principles & Basic Science

A new diagnostic ultrasound protocol for deep vein thrombosis (DVT) is evaluated. Out of 100 patients confirmed to have a DVT by venography, the new protocol correctly identifies 90. Out of 100 patients confirmed not to have a DVT, the protocol correctly identifies 80. What is the sensitivity of this new protocol?

. 80%
. 85%
. 90%
. 95%
. 100%

Correct Answer & Explanation

. 90%

Explanation

Sensitivity is the proportion of actual positives that are correctly identified as such. Formula: True Positives / (True Positives + False Negatives). Out of 100 patients with the disease, 90 are correctly identified (True Positives), making the sensitivity 90/100, or 90%.

Question 13620

Topic: Biomechanics & Biomaterials
Which of the following modifications is utilized in the manufacturing of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) to reduce the concentration of free radicals and improve oxidation resistance, albeit at the expense of mechanical properties such as fatigue strength?
. Ethylene oxide gas sterilization
. Remelting above the melting temperature (approx. 150°C)
. Annealing below the melting temperature (approx. 110°C)
. Gamma irradiation in an oxygen-rich environment
. Addition of polymethylmethacrylate (PMMA) during polymerization

Correct Answer & Explanation

. Remelting above the melting temperature (approx. 150°C)

Explanation

Remelting highly cross-linked UHMWPE above its melting temperature eliminates residual free radicals created during the gamma irradiation cross-linking process. This significantly improves oxidation resistance but reduces the polymer's crystallinity and, consequently, its mechanical and fatigue strength. Annealing reduces but does not completely eliminate free radicals. Ethylene oxide does not create free radicals but does not cross-link the material.

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