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1. General Principles & Basic Science MCQs

Practice Set 548 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 10941

Topic: Physiology & Rehabilitation

Which of the following characteristics best describes Type I skeletal muscle fibers?

. Fast twitch, high glycolytic capacity, fatigue resistant
. Slow twitch, high oxidative capacity, fatigue resistant
. Fast twitch, high oxidative capacity, easily fatigable
. Slow twitch, high glycolytic capacity, easily fatigable
. Fast twitch, low oxidative capacity, high force production

Correct Answer & Explanation

. Fast twitch, high glycolytic capacity, fatigue resistant

Explanation

Type I muscle fibers are "slow-twitch" fibers that have a high oxidative capacity, dense capillary network, high myoglobin content, and are highly fatigue resistant. They are primarily used for endurance and posture. Type II fibers are "fast-twitch" and rely more on glycolytic metabolism, generating high force but fatiguing quickly.

Question 10942

Topic: Biology, Genetics & Bone Healing

During collagen synthesis, the hydroxylation of proline and lysine residues is a critical intracellular step that provides structural stability to the collagen triple helix. Which of the following is required as an essential cofactor for this process?

. Vitamin D
. Vitamin K
. Calcium
. Ascorbic acid (Vitamin C)
. Copper

Correct Answer & Explanation

. Vitamin D

Explanation

Ascorbic acid (Vitamin C) is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase, which catalyze the hydroxylation of proline and lysine residues in procollagen. This hydroxylation is critical for the cross-linking and stability of the collagen triple helix. Deficiency results in scurvy.

Question 10943

Topic: 1. General Principles & Basic Science

The large aggregating proteoglycan found predominantly in articular cartilage is aggrecan. Which of the following glycosaminoglycans (GAGs) are the primary components of aggrecan?

. Chondroitin sulfate and keratan sulfate
. Dermatan sulfate and heparan sulfate
. Hyaluronic acid and dermatan sulfate
. Heparan sulfate and keratan sulfate
. Chondroitin sulfate and dermatan sulfate

Correct Answer & Explanation

. Chondroitin sulfate and keratan sulfate

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage. Its core protein has numerous covalently attached glycosaminoglycan (GAG) side chains, which are primarily chondroitin sulfate and keratan sulfate. These aggrecan monomers then non-covalently bind to a central hyaluronic acid backbone via link proteins.

Question 10944

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is often loaded with antibiotics for the treatment or prophylaxis of infection. To be effective and not compromise the cement's mechanical properties, the ideal antibiotic should possess which of the following characteristics?

. Liquid formulation
. High thermal stability
. Bacteriostatic action
. Lipophilic nature
. Low water solubility

Correct Answer & Explanation

. Liquid formulation

Explanation

Antibiotics added to PMMA must be available in a powder form (to avoid compromising the mechanical properties of the cement), possess high thermal stability (to withstand the exothermic polymerization reaction of PMMA, which can reach 80-100°C), have high water solubility (to allow elution from the cement into the surrounding tissue), and ideally be bactericidal. Examples include tobramycin, gentamicin, and vancomycin.

Question 10945

Topic: 1. General Principles & Basic Science
A 45-year-old male presents with an acute, swollen, and painful knee. Synovial fluid analysis reveals a white blood cell count of 65,000 cells/mm³ with 90% polymorphonuclear leukocytes. Under polarized light microscopy, negatively birefringent needle-shaped crystals are observed. What is the composition of these crystals?
. Calcium pyrophosphate dihydrate
. Monosodium urate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Monosodium urate

Explanation

The clinical picture and synovial fluid findings are pathognomonic for gout. Gout crystals are composed of monosodium urate and appear as needle-shaped, strongly negatively birefringent under polarized light microscopy. Calcium pyrophosphate dihydrate (CPPD) crystals are seen in pseudogout and are rhomboid-shaped with weak positive birefringence.

Question 10946

Topic: Biomechanics & Biomaterials

Galvanic corrosion is a concern when mixing different metals in orthopedic implants. If a stainless steel screw is placed through a titanium alloy plate, which metal acts as the anode and is subject to accelerated corrosion?

. Titanium alloy
. Stainless steel
. Both will corrode equally
. Neither will corrode due to passivation
. The surrounding bone acts as the anode

Correct Answer & Explanation

. Titanium alloy

Explanation

In a galvanic cell composed of stainless steel and titanium, titanium is more noble (cathodic), and stainless steel is more active (anodic). Therefore, the stainless steel screw will act as the anode and undergo accelerated corrosion. This is why mixing these specific metals in permanent implants is generally avoided.

Question 10947

Topic: Biology, Genetics & Bone Healing

Which of the following cells is considered the primary mechanosensor in bone, responsible for translating mechanical strain into biochemical signals to regulate bone remodeling?

. Osteoprogenitor cells
. Osteoblasts
. Osteoclasts
. Osteocytes
. Lining cells

Correct Answer & Explanation

. Osteoprogenitor cells

Explanation

Osteocytes are the most abundant cells in bone and form an extensive dendritic network within the lacunocanalicular system. They sense fluid shear stress induced by mechanical loading and respond by secreting signaling molecules (such as sclerostin, RANKL, and nitric oxide) that orchestrate the activity of osteoblasts and osteoclasts to remodel bone according to Wolff's law.

Question 10948

Topic: 1. General Principles & Basic Science

Creeping substitution is the process by which cortical bone grafts are incorporated. What is the correct sequence of events in creeping substitution of a cortical bone graft?

. Osteoclastic resorption followed by osteoblastic bone formation
. Osteoblastic bone formation followed by osteoclastic resorption
. Simultaneous osteoclastic resorption and osteoblastic formation
. Revascularization followed directly by osteocyte survival
. Chondrogenesis followed by endochondral ossification

Correct Answer & Explanation

. Osteoclastic resorption followed by osteoblastic bone formation

Explanation

Cortical bone grafts are incorporated via creeping substitution, a process that begins with osteoclastic resorption of the necrotic graft bone, followed by the deposition of new host bone by osteoblasts. In contrast, cancellous grafts incorporate more rapidly and initially undergo osteoblastic bone formation on the dead trabeculae before later remodeling. Cortical grafts are temporarily weakened during the resorptive phase.

Question 10949

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of nerve injuries, a third-degree nerve injury involves disruption of which of the following structures?

. Myelin sheath only
. Axon and myelin sheath, but endoneurium remains intact
. Axon, myelin sheath, and endoneurium, but perineurium remains intact
. Axon, myelin sheath, endoneurium, and perineurium, but epineurium remains intact
. Complete transection of the nerve including the epineurium

Correct Answer & Explanation

. Myelin sheath only

Explanation

In Sunderland's classification: 1st degree (Neuropraxia) = local myelin damage; 2nd degree (Axonotmesis) = axon severed, endoneurium intact; 3rd degree = axon and endoneurium severed, perineurium intact; 4th degree = axon, endoneurium, and perineurium severed, epineurium intact; 5th degree (Neurotmesis) = complete nerve transection.

Question 10950

Topic: Infection, Pharmacology & VTE
Rivaroxaban is an oral anticoagulant frequently used for DVT prophylaxis following total joint arthroplasty. What is its mechanism of action?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K antagonist
. Potentiates antithrombin III to inhibit Factor Xa and IIa
. Inhibits ADP-induced platelet aggregation

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban (Xarelto) and apixaban (Eliquis) are oral, direct inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin is a vitamin K antagonist. Heparin and low molecular weight heparins (LMWH) potentiate antithrombin III. Clopidogrel inhibits ADP-induced platelet aggregation.

Question 10951

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) was developed to reduce wear rates in total hip arthroplasty. What is the primary trade-off or mechanical disadvantage of increasing the cross-linking of ultra-high molecular weight polyethylene (UHMWPE)?
. Increased oxidation potential
. Decreased fatigue strength and fracture toughness
. Increased elastic modulus
. Decreased biocompatibility
. Increased risk of third-body wear

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Cross-linking of polyethylene by gamma or electron beam irradiation significantly improves its wear resistance. However, it also reduces its mechanical properties, specifically fatigue strength, fracture toughness, and ultimate tensile strength. To mitigate oxidation, the material must be melted or annealed to extinguish free radicals, or doped with an antioxidant like Vitamin E.

Question 10952

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, fracture healing pathways are dictated by the mechanical strain environment at the fracture gap. What is the maximum interfragmentary strain tolerance of normal lamellar bone before mechanical failure occurs?

. Less than 2%
. Up to 10%
. Up to 30%
. Up to 50%
. Up to 100%

Correct Answer & Explanation

. Less than 2%

Explanation

Lamellar bone can only tolerate up to 2% strain before failing or preventing direct bone healing. Cartilage can tolerate up to 10% strain, and granulation tissue can tolerate up to 100% strain.

Question 10953

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament reconstruction, the graft is tensioned to a specific length and fixed. Over the next several hours, the tension required to maintain this constant length gradually decreases. This viscoelastic property is best described by which of the following terms?

. Creep
. Stress relaxation
. Hysteresis
. Isotropy
. Fatigue failure

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the decrease in stress (tension) over time when a viscoelastic material is held at a constant strain (length). Creep is the progressive deformation of a material when subjected to a constant load.

Question 10954

Topic: 1. General Principles & Basic Science

Osteoclasts utilize a highly specialized mechanism to dissolve inorganic hydroxyapatite and degrade the organic bone matrix. Which of the following enzymes is primarily secreted by osteoclasts into the sealed zone to degrade type I collagen in an acidic environment?

. Alkaline phosphatase
. Cathepsin K
. Matrix metalloproteinase-3 (MMP-3)
. Stromelysin
. Tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. Alkaline phosphatase

Explanation

Cathepsin K is a crucial lysosomal protease secreted by osteoclasts that degrades type I collagen and other non-collagenous proteins in the acidic environment of the resorption pit. While TRAP is an osteoclast marker, Cathepsin K is the primary collagen-degrading enzyme.

Question 10955

Topic: Biology, Genetics & Bone Healing

The synovial membrane plays a critical role in joint homeostasis and nutrition. Which of the following cell types in the synovial lining is primarily responsible for the production of hyaluronic acid?

. Type A synoviocytes
. Type B synoviocytes
. Chondrocytes
. Osteoblasts
. Fibroblasts

Correct Answer & Explanation

. Type A synoviocytes

Explanation

Type B synoviocytes are fibroblast-like cells responsible for synthesizing hyaluronic acid and other components of the synovial fluid. Type A synoviocytes are macrophage-like cells responsible for phagocytosis and immune surveillance.

Question 10956

Topic: Biomechanics & Biomaterials

Titanium alloys (e.g., Ti-6Al-4V) are widely used in orthopedics due to their excellent biocompatibility and modulus of elasticity that is closer to cortical bone than stainless steel. Which of the following is a primary biomechanical disadvantage of using titanium alloys for internal fixation plates?

. High galvanic corrosion potential
. Poor osteointegration
. High notch sensitivity
. Extreme rigidity leading to severe stress shielding
. Inability to be used safely in MRI machines

Correct Answer & Explanation

. High galvanic corrosion potential

Explanation

Titanium alloys have a high notch sensitivity, meaning any surface scratch or defect significantly concentrates stress and dramatically lowers the material's fatigue strength, predisposing the implant to early mechanical failure.

Question 10957

Topic: Biomechanics & Biomaterials
The process of highly cross-linking ultra-high-molecular-weight polyethylene (UHMWPE) using gamma or electron beam irradiation significantly alters its material properties. Which of the following best describes the effect of increasing the cross-linking in UHMWPE?
. Increased wear resistance and increased ductility
. Increased wear resistance and decreased fatigue crack propagation resistance
. Decreased wear resistance and increased yield strength
. Decreased wear resistance and decreased ultimate tensile strength
. Increased oxidation resistance and increased ductility

Correct Answer & Explanation

. Increased wear resistance and decreased fatigue crack propagation resistance

Explanation

Highly cross-linking UHMWPE significantly improves its abrasive wear resistance. However, this comes at the cost of diminished mechanical properties, including decreased ductility, fracture toughness, and resistance to fatigue crack propagation.

Question 10958

Topic: 1. General Principles & Basic Science

Normal articular cartilage utilizes multiple lubrication mechanisms depending on the load and joint velocity. Under high-load, low-velocity conditions, which of the following molecules acts as the primary agent responsible for boundary lubrication?

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

Correct Answer & Explanation

. Aggrecan

Explanation

Boundary lubrication prevents direct surface-to-surface contact under high loads and low velocities. Lubricin (proteoglycan 4 or PRG4), a glycoprotein secreted by superficial zone chondrocytes and synoviocytes, is the primary molecule responsible for boundary lubrication.

Question 10959

Topic: Physiology & Rehabilitation

A marathon runner sustains a minor muscle tear in the gastrocnemius. The primary skeletal muscle fibers utilized by this athlete during endurance running are characterized by which of the following physiological profiles?

. Fast twitch, glycolytic metabolism, fast fatigue
. Slow twitch, oxidative metabolism, slow fatigue
. Fast twitch, oxidative metabolism, intermediate fatigue
. Slow twitch, glycolytic metabolism, slow fatigue
. Fast twitch, oxidative metabolism, fast fatigue

Correct Answer & Explanation

. Fast twitch, glycolytic metabolism, fast fatigue

Explanation

Endurance athletes rely heavily on Type I muscle fibers. Type I fibers are slow-twitch, utilize oxidative metabolism (rich in mitochondria and myoglobin), and are highly resistant to fatigue.

Question 10960

Topic: Biology, Genetics & Bone Healing

Which of the following pharmacological agents used in the treatment of severe osteoporosis acts primarily as an anabolic agent through the direct inhibition of the Wnt signaling antagonist, sclerostin?

. Denosumab
. Teriparatide
. Romosozumab
. Abaloparatide
. Zoledronic acid

Correct Answer & Explanation

. Denosumab

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin, unblocking the Wnt pathway to strongly stimulate osteoblastic bone formation. Denosumab inhibits RANKL, while Teriparatide and Abaloparatide are PTH analogs.

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