Menu

1. General Principles & Basic Science MCQs

Practice Set 263 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 5241

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing. Following the binding of BMPs to their serine/threonine kinase cell surface receptors, which family of intracellular signaling molecules is directly phosphorylated to translocate to the nucleus and regulate gene transcription?

. JAK/STAT
. MAPK
. Smad
. Wnt/beta-catenin
. Notch

Correct Answer & Explanation

. Smad

Explanation

BMPs signal primarily through the canonical Smad pathway. Binding of BMP to its heterodimeric serine/threonine kinase receptor complex leads to the phosphorylation of receptor-regulated Smads (R-Smads, such as Smad1, 5, and 8), which then complex with the common-partner Smad (Smad4) and translocate to the nucleus to regulate transcription of osteogenic genes.

Question 5242

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a large, lytic, eccentrically located epiphyseal lesion in her distal femur. Biopsy reveals multinucleated giant cells in a background of mononuclear stromal cells. She is prescribed denosumab prior to surgical intervention to downstage the tumor. What is the precise mechanism of action of denosumab in treating this tumor?

. It binds directly to the multinucleated giant cells, inducing apoptosis
. It acts as a decoy receptor for RANKL, similar to osteoprotegerin
. It is a monoclonal antibody that binds to RANKL on mononuclear stromal cells, preventing RANK receptor activation on osteoclast precursors
. It inhibits the mammalian target of rapamycin (mTOR) pathway, halting cellular proliferation
. It covalently binds to the IDH1 enzyme, restoring normal cellular metabolism

Correct Answer & Explanation

. It is a monoclonal antibody that binds to RANKL on mononuclear stromal cells, preventing RANK receptor activation on osteoclast precursors

Explanation

In Giant Cell Tumor (GCT) of bone, neoplastic mononuclear stromal cells overexpress Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which recruits and activates the reactive multinucleated giant cells via their RANK receptors. Denosumab is a monoclonal antibody that binds directly to RANKL, preventing its interaction with RANK, thereby inhibiting osteoclast-like giant cell formation and reducing osteolysis.

Question 5243

Topic: Biomechanics & Biomaterials

In the study of orthopaedic biomechanics, viscoelastic materials such as ligaments and tendons display time-dependent behaviors. When a ligament is subjected to a constant, sustained load over a period of time, it will undergo progressive elongation. This phenomenon is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent progressive deformation (elongation) of a viscoelastic material under a constant applied load. Stress relaxation is the decrease in stress over time when the material is held at a constant length/strain. Hysteresis is the energy lost (as heat) during the loading and unloading cycle.

Question 5244

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman is diagnosed with an aggressive giant cell tumor (GCT) of the distal radius. Due to the size and proximity to the joint, she is treated with neoadjuvant denosumab prior to surgical curettage. What is the specific mechanism of action of denosumab in the treatment of GCT of bone?

. It is a bisphosphonate that induces apoptosis of osteoclasts.
. It is a monoclonal antibody that binds to and inhibits RANKL.
. It acts as a decoy receptor for RANK (osteoprotegerin analog).
. It inhibits vascular endothelial growth factor (VEGF) to decrease tumor angiogenesis.
. It is a tyrosine kinase inhibitor blocking the c-kit pathway.

Correct Answer & Explanation

. It is a monoclonal antibody that binds to and inhibits RANKL.

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In Giant Cell Tumor of bone, the neoplastic mononuclear stromal cells express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) responsible for bone destruction. By inhibiting RANKL, denosumab stops the formation and activity of these destructive giant cells.

Question 5245

Topic: 1. General Principles & Basic Science

Articular cartilage is composed of multiple zones, each with unique ultrastructural properties that provide mechanical resilience. Which zone is characterized by having the largest diameter collagen fibrils oriented perpendicular to the articular surface, as well as the highest concentration of proteoglycans?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It contains the highest concentration of proteoglycans and the lowest water content. The collagen fibrils here are the largest in diameter and are oriented strictly perpendicular to the articular surface to anchor the cartilage to the underlying calcified zone.

Question 5246

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of acute Charcot neuroarthropathy, pro-inflammatory cytokines play a critical role in increasing the expression of which of the following, leading to amplified osteoclastogenesis?

. Osteoprotegerin (OPG)
. RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand)
. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-Beta (TGF-B)
. Sclerostin

Correct Answer & Explanation

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

Explanation

In acute Charcot neuroarthropathy, the inflammatory cascade leads to an over-expression of RANKL relative to OPG. This imbalance drives unchecked osteoclastic bone resorption, resulting in the classic osteopenia and bone fragmentation seen in the acute phase.

Question 5247

Topic: 1. General Principles & Basic Science

Which of the following factors is the most critical determinant of the initial tensile strength of a flexor tendon repair in Zone II?

. The caliber of the suture material used
. The number of core suture strands crossing the repair site
. The use of a running epitendinous suture
. The distance of the core suture purchase from the tendon edge
. The specific configuration of the core suture locking loop

Correct Answer & Explanation

. The number of core suture strands crossing the repair site

Explanation

The number of core suture strands crossing the repair site is directly proportional to the initial tensile strength of a flexor tendon repair. While epitendinous sutures and locking configurations add strength, increasing from a 2-strand to a 4-strand or 6-strand repair provides the most significant increase in tensile strength, allowing for early active motion protocols.

Question 5248

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the management of unresectable Giant Cell Tumor (GCT) of bone. What is the specific cellular target of this monoclonal antibody?

. Vascular Endothelial Growth Factor (VEGF)
. CD20 surface antigen
. RANK Ligand (RANKL)
. Tyrosine kinase domains
. Tumor Necrosis Factor-alpha (TNF-alpha)

Correct Answer & Explanation

. RANK Ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts and their precursors. In GCT, the neoplastic mononuclear stromal cells express RANKL, which recruits and activates the reactive multinucleated giant cells responsible for aggressive bone resorption.

Question 5249

Topic: Surgical Anatomy & Approaches

During the extended deltopectoral approach for open reduction and internal fixation of a proximal humerus fracture, the axillary nerve must be protected during plate placement. What is the typical average distance of the axillary nerve from the tip of the greater tuberosity?

. 2 to 3 cm
. 5 to 7 cm
. 9 to 11 cm
. 12 to 14 cm
. 15 to 17 cm

Correct Answer & Explanation

. 5 to 7 cm

Explanation

The axillary nerve courses laterally around the surgical neck of the humerus. Its average distance from the tip of the greater tuberosity is approximately 5 to 7 cm. Placing retractors or plates blindly below this level poses a significant risk of iatrogenic nerve injury.

Question 5250

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct zones, each with a unique structure and function. Which structure delineates the boundary between the deep (radial) zone and the calcified cartilage zone, and plays a biomechanical role in resisting shear stresses?

. Lamina splendens
. Tidemark
. Cement line
. Superficial zone tangential fibers
. Proteoglycan-rich middle zone

Correct Answer & Explanation

. Tidemark

Explanation

The tidemark is a basophilic line visible on histologic sections that demarcates the deep (radial) zone of uncalcified articular cartilage from the underlying calcified cartilage. It provides a structural transition that helps distribute shear stresses. The cement line separates the calcified cartilage from the subchondral bone.

Question 5251

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoblast differentiation and bone formation. Which of the following best describes the intracellular signaling pathway activated immediately upon BMP-2 binding to its serine/threonine kinase cell surface receptor?

. Activation of the Wnt/beta-catenin pathway
. Phosphorylation of Smad 1/5/8 proteins
. Translocation of NF-kappa B to the nucleus
. Upregulation of the RANK ligand
. Inhibition of the MAP kinase pathway

Correct Answer & Explanation

. Phosphorylation of Smad 1/5/8 proteins

Explanation

BMPs bind to dimeric transmembrane serine/threonine kinase receptors. This binding causes phosphorylation and activation of receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These then form a complex with the co-Smad (Smad 4), which translocates into the nucleus to regulate the transcription of osteogenic target genes like Runx2.

Question 5252

Topic: 1. General Principles & Basic Science

Following a zone II flexor tendon repair, an early active mobilization protocol is planned to prevent adhesions. To safely withstand the forces of early active motion without gap formation or rupture, what is the minimum number of core suture strands crossing the repair site recommended?

. 2 strands
. 4 strands
. 6 strands
. 8 strands
. Core strands are less important than the epitendinous suture

Correct Answer & Explanation

. 4 strands

Explanation

A 2-strand repair is generally considered too weak for early active motion protocols. A minimum of a 4-strand core repair (along with a robust epitendinous suture) is required to safely withstand the forces generated during early active mobilization and minimize the risk of gap formation and rupture. 6 or 8 strands provide even more strength but can increase bulk and affect tendon gliding.

Question 5253

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a large, destructive lytic lesion in her distal radius with cortical breakthrough. Biopsy confirms a Giant Cell Tumor (GCT) of bone. Neoadjuvant therapy with denosumab is considered to downstage the tumor prior to curettage. What is the specific mechanism of action of denosumab in treating this lesion?

. It binds to and inhibits RANK, preventing its interaction with RANKL
. It is a monoclonal antibody that binds directly to RANKL, preventing osteoclast activation
. It induces apoptosis of the neoplastic mononuclear stromal cells via the p53 pathway
. It inhibits the MAP kinase pathway directly within the multinucleated giant cells
. It acts as a bisphosphonate, incorporating into bone matrix and poisoning osteoclasts

Correct Answer & Explanation

. It is a monoclonal antibody that binds directly to RANKL, preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). In Giant Cell Tumor of bone, the neoplastic mononuclear stromal cells overexpress RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) responsible for bone destruction. Denosumab inhibits this interaction.

Question 5254

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) was developed to improve the longevity of total hip arthroplasty implants. While increasing the radiation dose during manufacturing increases cross-linking and dramatically reduces volumetric wear, it also has a detrimental effect on which of the following material properties?
. Oxidation resistance
. Melting temperature
. Ultimate tensile strength and fatigue resistance
. Biocompatibility of the wear debris
. Coefficient of friction

Correct Answer & Explanation

. Ultimate tensile strength and fatigue resistance

Explanation

Increasing the cross-linking of UHMWPE (via gamma or electron beam irradiation) significantly decreases its volumetric wear rate. However, high levels of cross-linking alter the polymer chain mobility, which leads to a decrease in mechanical properties, specifically ultimate tensile strength, fatigue resistance, and fracture toughness.

Question 5255

Topic: Biology, Genetics & Bone Healing

A 25-year-old woman is diagnosed with a giant cell tumor (GCT) of the distal femur. Her surgeon considers neoadjuvant treatment with Denosumab prior to curettage to facilitate intralesional resection. What is the exact mechanism of action of Denosumab?

. Monoclonal antibody against RANK receptor
. Monoclonal antibody against RANKL
. Direct inhibition of osteoblast activity
. Bisphosphonate analog that induces osteoclast apoptosis
. Tyrosine kinase inhibitor

Correct Answer & Explanation

. Monoclonal antibody against RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), preventing it from binding to the RANK receptor on osteoclasts and their precursors. This effectively inhibits osteoclast-mediated bone destruction, which is the primary driver of osteolysis in Giant Cell Tumor of bone.

Question 5256

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used in orthopedic procedures as a bone graft extender. Processing allograft bone into DBM preserves which primary biologic property for bone healing?

. Osteogenesis
. Osteoconduction only
. Osteoinduction
. Both osteogenesis and osteoinduction
. Primary structural support

Correct Answer & Explanation

. Osteoinduction

Explanation

Demineralized bone matrix (DBM) undergoes acid extraction of the mineralized phase, which exposes bone morphogenetic proteins (BMPs) and other growth factors. This confers osteoinductive properties to the graft. Because it lacks live cells, it is not osteogenic. While it provides minimal osteoconductive scaffold, its primary therapeutic advantage over cancellous chips is osteoinduction.

Question 5257

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) play a crucial role in osteoinduction and fracture healing. Biologically, BMPs are members of which of the following larger signaling superfamilies?

. Fibroblast Growth Factor (FGF)
. Platelet-Derived Growth Factor (PDGF)
. Transforming Growth Factor-beta (TGF-beta)
. Insulin-like Growth Factor (IGF)
. Vascular Endothelial Growth Factor (VEGF)

Correct Answer & Explanation

. Transforming Growth Factor-beta (TGF-beta)

Explanation

Bone Morphogenetic Proteins (BMPs) are a group of growth factors structurally classified as part of the Transforming Growth Factor-beta (TGF-beta) superfamily. They bind to serine/threonine kinase receptors on the cell surface and mediate downstream signaling via Smad proteins to induce differentiation of mesenchymal stem cells into osteoblasts.

Question 5258

Topic: Biology, Genetics & Bone Healing

During the incorporation of a cortical bone allograft, what is the term used to describe the process where osteoclasts resorb the dead bone and osteoblasts simultaneously lay down new bone in the cutting cone?

. Osteoinduction
. Osteogenesis
. Creeping substitution
. Endochondral ossification
. Intramembranous ossification

Correct Answer & Explanation

. Creeping substitution

Explanation

Creeping substitution is the process by which cortical bone grafts are incorporated. It involves a cutting cone of osteoclasts resorbing the necrotic host bone, closely followed by osteoblasts depositing new viable bone along the pathways.

Question 5259

Topic: 1. General Principles & Basic Science

A 24-year-old football player sustains a valgus blow to the knee. MRI shows a complete tear of the medial collateral ligament (MCL) and a tear of the posterior oblique ligament (POL). What is the primary biomechanical function of the POL?

. Primary restraint to valgus stress at 30 degrees of flexion
. Primary restraint to anterior tibial translation
. Primary restraint to internal rotation at 90 degrees of flexion
. Primary restraint to internal rotation near full extension
. Secondary restraint to posterior tibial translation

Correct Answer & Explanation

. Primary restraint to internal rotation near full extension

Explanation

The posterior oblique ligament (POL) acts as a primary restraint to internal rotation of the tibia, particularly near full extension, and it provides secondary restraint to valgus stress.

Question 5260

Topic: 1. General Principles & Basic Science

Following a Zone II flexor tendon repair, which rehabilitation protocol initially uses dynamic flexion traction via rubber bands and active extension within the limits of a dorsal blocking splint?

. Duran protocol
. Kleinert protocol
. Washington protocol
. Chow protocol
. Strickland protocol

Correct Answer & Explanation

. Kleinert protocol

Explanation

The Kleinert protocol utilizes a dorsal blocking splint with dynamic rubber band traction pulling the digits into flexion, allowing active extension against the resistance of the rubber bands. The Duran protocol, in contrast, involves controlled passive motion (passive flexion and passive extension).

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page