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1. General Principles & Basic Science MCQs

Practice Set 250 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 4981

Topic: Biomechanics & Biomaterials

Which of the following viscoelastic principles describes the phenomenon where articular cartilage experiences a progressive decrease in internal stress over time when subjected to a constant, maintained displacement?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is subjected to a constant deformation (strain or displacement), resulting in a gradual decrease in internal stress over time. Conversely, 'creep' refers to the progressive deformation (strain) of a material over time when subjected to a constant load (stress). Hysteresis represents energy lost as heat during the loading and unloading cycles. Articular cartilage exhibits both creep and stress relaxation due to fluid exudation and macromolecular rearrangement.

Question 4982

Topic: 1. General Principles & Basic Science
The oxidation of ultra-high molecular weight polyethylene (UHMWPE) components in total joint arthroplasty significantly increases wear rates and leads to catastrophic failure. Which of the following sterilization methods carries the highest risk for in vivo oxidation?
. Gamma irradiation in an inert argon gas environment
. Gamma irradiation in air
. Ethylene oxide sterilization
. Gas plasma sterilization
. Gamma irradiation followed by remelting

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation of UHMWPE in air generates free radicals that react with oxygen to form hydroperoxides, leading to chain scission, decreased molecular weight, and severe oxidative degradation (shelf oxidation and in vivo oxidation). This dramatically reduces the mechanical properties and wear resistance of the plastic. To combat this, modern PE is sterilized in inert environments (like argon or vacuum), treated with ethylene oxide/gas plasma (which do not create free radicals), or irradiated and then thermally treated (remelted or annealed) to quench free radicals.

Question 4983

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct histological and functional zones. Which zone contains the highest concentration of proteoglycans, the lowest concentration of water, and chondrocytes that are arranged in columns parallel to the direction of applied load?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is characterized by the highest proteoglycan content, the lowest water content, and large collagen fibrils that are oriented vertically (perpendicular to the joint surface). The chondrocytes in this zone are arranged in vertical columns parallel to the collagen fibers and the axis of mechanical loading. The superficial zone has the highest water content and collagen parallel to the joint surface.

Question 4984

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction by binding to serine/threonine kinase transmembrane receptors. This binding directly phosphorylates and activates which of the following intracellular signaling molecules to translocate into the nucleus and initiate transcription of osteogenic genes?

. Beta-catenin
. Smad 1/5/8
. JAK-STAT
. NF-kappa B
. RANKL

Correct Answer & Explanation

. Smad 1/5/8

Explanation

The canonical BMP signaling pathway involves BMP ligands binding to type I and type II serine/threonine kinase receptors. This causes phosphorylation and activation of the receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These phosphorylated Smads then form a complex with the common-mediator Smad 4 (Co-Smad), which translocates to the nucleus to regulate transcription of osteogenic target genes like RUNX2. Beta-catenin is involved in the Wnt pathway.

Question 4985

Topic: 1. General Principles & Basic Science

In the rehabilitation of a Zone II flexor tendon repair, which of the following biomechanical effects is most directly associated with early active motion compared to passive motion protocols?

. Decreased ultimate tensile strength of the repair at 3 weeks
. Increased excursion of the repaired tendon relative to the surrounding sheath
. Decreased gap formation at the repair site
. Delayed intrinsic healing of the tendon
. Increased reliance on extrinsic healing mechanisms

Correct Answer & Explanation

. Increased excursion of the repaired tendon relative to the surrounding sheath

Explanation

Early active motion protocols increase tendon excursion relative to the sheath, which decreases adhesion formation and relies more on intrinsic healing. It actually increases the ultimate tensile strength of the repair during the remodeling phase compared to passive protocols.

Question 4986

Topic: Biology, Genetics & Bone Healing

The process of 'creeping substitution' in the incorporation of a cortical bone allograft is characterized by which of the following sequences?

. Immediate osteoblastic bone formation followed by osteoclastic resorption
. Simultaneous osteoclastic resorption and osteoblastic bone formation along the surface
. Osteoclastic resorption via cutting cones followed by osteoblastic bone deposition
. Endochondral ossification transforming cartilage into bone
. Intramembranous ossification mediated solely by mesenchymal stem cells

Correct Answer & Explanation

. Osteoclastic resorption via cutting cones followed by osteoblastic bone deposition

Explanation

Creeping substitution refers to the process by which a graft is slowly resorbed and replaced by host bone. In cortical grafts, this occurs via osteoclasts creating cutting cones that resorb the dead graft bone, closely followed by osteoblasts depositing new lamellar host bone within these channels.

Question 4987

Topic: Biology, Genetics & Bone Healing

Denosumab is frequently used in the neoadjuvant management of locally advanced Giant Cell Tumor of Bone. Its primary mechanism of action involves binding to and inhibiting which of the following?

. RANK receptor on osteoclasts
. RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (produced by the neoplastic mononuclear cells in Giant Cell Tumor of Bone). By inhibiting RANKL, it prevents the activation of the RANK receptor on osteoclast precursors, thereby halting the formation and function of the osteoclast-like giant cells that cause bone destruction.

Question 4988

Topic: Biology, Genetics & Bone Healing

During the incorporation of a cortical bone allograft, what process relies on the 'cutting cone' phenomenon orchestrated by osteoclasts and subsequent osteoblast activity?

. Creeping substitution
. Osteoconduction
. Osteoinduction
. Endochondral ossification
. Intramembranous ossification

Correct Answer & Explanation

. Creeping substitution

Explanation

Creeping substitution is the process by which a bone graft is resorbed and simultaneously replaced by new host bone. In cortical grafts, this occurs via the cutting cone mechanism, where osteoclasts bore through the dense bone, followed by osteoblasts laying down new osteoid.

Question 4989

Topic: Biology, Genetics & Bone Healing

Denosumab is frequently used in the treatment of unresectable or recurrent giant cell tumor (GCT) of bone. What is its mechanism of action?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of the neoplastic stromal cells
. Inhibition of the mammalian target of rapamycin (mTOR) pathway
. Monoclonal antibody binding to RANK Ligand (RANKL)
. Stimulation of osteoblast differentiation via Wnt signaling

Correct Answer & Explanation

. Monoclonal antibody binding to RANK Ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANK Ligand (RANKL), preventing it from activating RANK on the surface of osteoclasts and their precursors. In GCT, the neoplastic stromal cells express high levels of RANKL, which recruits reactive osteoclast-like giant cells that cause massive bone destruction.

Question 4990

Topic: 1. General Principles & Basic Science

Articular cartilage is highly specialized to withstand compressive and shear forces. In which zone of the articular cartilage are the collagen fibers oriented parallel to the articular surface to primarily resist shear stress?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone has the highest water content and contains Type II collagen fibers that are oriented strictly parallel to the joint surface. This structural arrangement is uniquely designed to resist high levels of shear stress. Deep zone fibers are oriented perpendicularly to resist compressive forces.

Question 4991

Topic: 1. General Principles & Basic Science

Biomechanical studies evaluating medial meniscus posterior root tears have demonstrated that an untreated complete root tear results in knee joint contact pressures that are most similar to which of the following conditions?

. A normal, intact meniscus
. A peripheral longitudinal (bucket-handle) tear
. A total meniscectomy
. A partial meniscectomy removing 20% of the posterior horn
. A horizontal cleavage tear

Correct Answer & Explanation

. A total meniscectomy

Explanation

Complete radial tears or posterior root tears of the medial meniscus disrupt the circumferential hoop fibers. This complete loss of hoop tension biomechanically equates to a total meniscectomy, leading to significantly increased peak contact pressures and rapid cartilage degeneration if left unrepaired.

Question 4992

Topic: Biology, Genetics & Bone Healing

Which of the following intracellular signaling molecules is directly phosphorylated by the Type I bone morphogenetic protein (BMP) receptor kinase upon ligand binding?

. STAT3
. Smad 1/5/8
. Smad 2/3
. beta-catenin
. NF-kappaB

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs signal primarily through the canonical Smad pathway. Upon ligand binding, Type II receptors phosphorylate Type I receptors, which then phosphorylate receptor-regulated Smads (Smad 1, 5, and 8). These form a complex with Smad 4 to enter the nucleus. Smad 2 and 3 are primarily involved in the TGF-beta signaling pathway.

Question 4993

Topic: Biomechanics & Biomaterials

Which of the following combinations of annular pulleys is absolutely essential to preserve or reconstruct during flexor tendon repair to prevent bowstringing and ensure nearly normal finger kinematics?

. A1 and A3
. A2 and A4
. A1, A3, and A5
. A2 and A5
. A3 and A4

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the major biomechanical components of the flexor tendon sheath. They arise directly from the periosteum of the proximal and middle phalanges, respectively. Their preservation or reconstruction is critical to prevent tendon bowstringing and preserve mechanical advantage.

Question 4994

Topic: Surgical Anatomy & Approaches

During an anterior (ilioinguinal) approach for fixing a right anterior column acetabular fracture, significant hemorrhage occurs while dissecting near the superior pubic ramus. Which vascular structures are most likely involved in this 'corona mortis' anastomosis?

. Internal iliac artery and superior gluteal artery
. External iliac artery/vein and obturator artery/vein
. Inferior epigastric artery and internal pudendal artery
. Femoral artery and lateral circumflex femoral artery
. Internal iliac vein and external pudendal vein

Correct Answer & Explanation

. External iliac artery/vein and obturator artery/vein

Explanation

The corona mortis is a critical anastomotic vascular connection (arterial, venous, or both) between the external iliac (or inferior epigastric) system and the obturator system. It crosses the superior pubic ramus approximately 4-6 cm from the pubic symphysis.

Question 4995

Topic: Infection, Pharmacology & VTE
Apixaban is frequently used for venous thromboembolism (VTE) prophylaxis following total joint arthroplasty. What is its specific mechanism of action?
. Direct inhibition of thrombin (Factor IIa)
. Competitive inhibition of Vitamin K epoxide reductase
. Direct, reversible inhibition of Factor Xa
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase-1

Correct Answer & Explanation

. Direct, reversible inhibition of Factor Xa

Explanation

Apixaban and rivaroxaban are direct, reversible inhibitors of Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. Heparins activate antithrombin III.

Question 4996

Topic: Physiology & Rehabilitation

During the normal human gait cycle, at what specific phase does the gluteus maximus exhibit its peak electromyographic (EMG) activity?

. Mid-swing
. Terminal swing and initial contact (heel strike)
. Mid-stance
. Terminal stance (heel off)
. Pre-swing (toe off)

Correct Answer & Explanation

. Terminal swing and initial contact (heel strike)

Explanation

The gluteus maximus works eccentrically at terminal swing to decelerate the forward momentum of the swinging leg, and then achieves peak concentric activity immediately after initial contact (heel strike) to extend the hip and stabilize the trunk from pitching forward.

Question 4997

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that allows for primary bone healing (direct osteonal reconstruction without callus formation)?

. < 2%
. 2% to 10%
. 10% to 15%
. 15% to 20%
. > 20%

Correct Answer & Explanation

. < 2%

Explanation

According to Perren's strain theory, primary bone healing (intramembranous/osteonal without callus) occurs only when interfragmentary strain is less than 2%. Strain between 2% and 10% promotes secondary bone healing via endochondral ossification (callus formation). Strain above 10-15% leads to fibrous tissue formation and nonunion.

Question 4998

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman is diagnosed with an unresectable giant cell tumor of the sacrum. She is started on denosumab therapy. What is the precise mechanism of action of this medication?

. Inhibits matrix metalloproteinases to prevent tumor invasion
. Directly induces apoptosis of the neoplastic stromal cells
. Binds to the RANK receptor on osteoclasts
. Monoclonal antibody that binds to RANKL, preventing osteoclast activation
. Inhibits vascular endothelial growth factor (VEGF) to reduce tumor vascularity

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL, preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANK Ligand (RANKL), preventing it from interacting with the RANK receptor on the surface of osteoclasts and their precursors. This inhibits osteoclast-mediated bone resorption. Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express RANKL, which recruits the multinucleated osteoclast-like giant cells.

Question 4999

Topic: 1. General Principles & Basic Science

Which of the following components of articular cartilage is primarily responsible for providing tensile strength to the extracellular matrix?

. Aggrecan
. Hyaluronic acid
. Type II collagen
. Type X collagen
. Chondroitin sulfate

Correct Answer & Explanation

. Type II collagen

Explanation

In articular cartilage, Type II collagen forms a cross-linked fibrillar network that primarily provides the tissue with tensile strength and restrains the swelling pressure of the proteoglycans. Proteoglycans (such as aggrecan) draw water into the matrix via osmotic pressure, providing compressive stiffness and resistance.

Question 5000

Topic: 1. General Principles & Basic Science

In the flexor tendon pulley system of the fingers, which two annular pulleys are considered the most critical to prevent bowstringing of the flexor tendons and must be preserved or reconstructed during surgery?

. A1 and A3
. A2 and A4
. A3 and A5
. A1 and A5
. A2 and A3

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the major biomechanical pulleys in the digital flexor sheath. They arise directly from the periosteum of the proximal and middle phalanges, respectively. They are critical to prevent bowstringing of the flexor tendons, which would cause a significant loss of active flexion and mechanical disadvantage.

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