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1. General Principles & Basic Science MCQs

Practice Set 236 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 4701

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a painful lytic epiphyseal lesion of the distal femur. Biopsy confirms the diagnosis of Giant Cell Tumor of bone. Due to the proximity to the joint space and the large size of the defect, the multidisciplinary tumor board recommends neoadjuvant treatment with Denosumab to downstage the tumor prior to intralesional curettage. What is the precise mechanism of action of Denosumab?

. Inhibition of osteoclast proton pumps
. Monoclonal antibody against RANK Ligand
. Monoclonal antibody against the RANK receptor
. Inhibition of vascular endothelial growth factor (VEGF)
. Cross-linking of intracellular DNA

Correct Answer & Explanation

. Monoclonal antibody against RANK Ligand

Explanation

Giant cell tumor of bone (GCTB) is characterized by neoplastic mononuclear stromal cells that express RANKL, which recruits and activates the multinucleated giant cells (osteoclasts) responsible for the osteolysis. Denosumab is a fully human monoclonal antibody that binds directly to RANK Ligand (RANKL), preventing it from interacting with the RANK receptor on osteoclasts and their precursors, thereby inhibiting osteoclast-mediated bone destruction.

Question 4702

Topic: 1. General Principles & Basic Science

Articular cartilage depends on a highly organized extracellular matrix to resist compressive loads. Which of the following is the most abundant proteoglycan found in articular cartilage, functioning to provide compressive stiffness through its massive water-binding capacity when complexed with hyaluronic acid?

. Decorin
. Biglycan
. Aggrecan
. Fibromodulin
. Lumican

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the predominant proteoglycan in articular cartilage, constituting up to 90% of the proteoglycan mass. It possesses highly negatively charged glycosaminoglycan (GAG) side chains (chondroitin sulfate and keratan sulfate) that attract water (Donnan osmotic effect). When bound to hyaluronic acid via link proteins, aggrecan forms massive aggregates that become trapped within the Type II collagen meshwork, conferring the cartilage's ability to resist compressive loads.

Question 4703

Topic: Biology, Genetics & Bone Healing

Which Bone Morphogenetic Protein (BMP) is most closely associated with the FDA-approved indication for use in acute, open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for the treatment of acute open tibial shaft fractures, typically administered via an absorbable collagen sponge. rhBMP-7 (also known as Osteogenic Protein-1 or OP-1) was previously approved under a humanitarian device exemption for recalcitrant tibial nonunions.

Question 4704

Topic: Biomechanics & Biomaterials

A 45-year-old female presents with sudden onset medial knee pain while squatting. MRI shows a medial meniscus posterior root tear. Biomechanically, what is the consequence of this specific injury on the knee joint?

. Increased contact area in the medial compartment
. Decreased peak contact pressure during weight-bearing
. Kinematics equivalent to a total medial meniscectomy
. Increased anterior tibial translation during the Lachman test
. Decreased varus laxity in full extension

Correct Answer & Explanation

. Kinematics equivalent to a total medial meniscectomy

Explanation

A complete posterior root tear of the medial meniscus leads to a complete loss of hoop stresses, resulting in radial extrusion of the meniscus during axial loading. Biomechanically, this is equivalent to a total medial meniscectomy, significantly decreasing the contact area and markedly increasing peak contact pressures, leading to accelerated osteoarthritis.

Question 4705

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion of the proximal tibia.

Biopsy reveals multinucleated giant cells in a background of mononuclear stromal cells. What is the primary molecular target of the systemic therapy commonly used to treat unresectable cases of this tumor?

. Vascular Endothelial Growth Factor (VEGF)
. Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL)
. Platelet-Derived Growth Factor (PDGF)
. Mammalian Target of Rapamycin (mTOR)
. Human Epidermal Growth Factor Receptor 2 (HER2)

Correct Answer & Explanation

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

Explanation

The diagnosis is Giant Cell Tumor of Bone (GCTB). The neoplastic cells are the mononuclear stromal cells, which express high levels of RANKL. This recruits and activates osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is used for unresectable GCTB or to downstage tumors prior to surgery.

Question 4706

Topic: Biomechanics & Biomaterials

Which of the following best defines 'stress relaxation' in the context of orthopedic biomechanics and viscoelastic materials?

. Increasing deformation over time under a constant load
. Decreasing force over time under a constant deformation
. Energy lost as heat during a loading-unloading cycle
. Increased stiffness with an increased rate of loading
. The point at which a material transitions from elastic to plastic deformation

Correct Answer & Explanation

. Decreasing force over time under a constant deformation

Explanation

Viscoelastic materials exhibit time-dependent properties. 'Stress relaxation' is the decrease in stress (force) over time when the material is held at a constant strain (deformation). 'Creep' is the progressive deformation (strain) over time under a constant load (stress).

Question 4707

Topic: 1. General Principles & Basic Science

Articular cartilage has specialized zones with varying structure and function. Which of the following best describes the collagen fiber orientation and primary collagen type in the superficial zone of articular cartilage?

. Perpendicular to the joint surface, Type I
. Parallel to the joint surface, Type II
. Randomly oriented, Type II
. Perpendicular to the joint surface, Type II
. Parallel to the joint surface, Type I

Correct Answer & Explanation

. Parallel to the joint surface, Type I

Explanation

The superficial (tangential) zone of articular cartilage makes up 10-20% of the thickness. The collagen fibers (primarily Type II, like the rest of hyaline cartilage) are oriented parallel to the joint surface to resist shear forces. The deep zone fibers are oriented perpendicularly to anchor the cartilage to the subchondral bone.

Question 4708

Topic: Biology, Genetics & Bone Healing

An adult tibia shaft fracture is treated with a statically locked intramedullary nail, creating a biomechanical environment that allows for micromotion at the fracture site. This environment promotes secondary bone healing. What is the correct physiological sequence of secondary bone healing?

. Inflammation, soft callus, hard callus, remodeling
. Soft callus, hard callus, inflammation, remodeling
. Inflammation, hard callus, soft callus, remodeling
. Inflammation, remodeling, soft callus, hard callus
. Hard callus, soft callus, remodeling, inflammation

Correct Answer & Explanation

. Inflammation, soft callus, hard callus, remodeling

Explanation

Secondary bone healing occurs when there is relative stability (micromotion) at the fracture site, promoting callus formation. The classic sequential phases are: 1) Inflammation (hematoma formation and cytokine release), 2) Soft callus (fibrocartilage generation via chondrogenesis), 3) Hard callus (conversion of cartilage to woven bone via endochondral ossification), and 4) Remodeling (replacement of woven bone with lamellar bone via osteoclast and osteoblast activity).

Question 4709

Topic: Biology, Genetics & Bone Healing

A 65-year-old male complains of severe mechanical back pain and profound fatigue. Laboratory tests show anemia, hypercalcemia, and an elevated M-spike on serum protein electrophoresis. Plain radiographs demonstrate multiple 'punched-out' lytic lesions in the skull and spine. What is the current imaging modality of choice to accurately assess the extent of skeletal burden in this disease?

. Technetium-99m bone scintigraphy
. Whole-body low-dose CT or MRI
. Gallium-67 scan
. Dual-energy x-ray absorptiometry (DEXA)
. Positron emission tomography without CT

Correct Answer & Explanation

. Whole-body low-dose CT or MRI

Explanation

The diagnosis is Multiple Myeloma. The characteristic bone lesions are purely osteolytic, caused by myeloma cells stimulating osteoclasts (via RANKL) while inhibiting osteoblast activity (via DKK1 and sFRP-2). Because there is little to no reactive osteoblastic bone formation, traditional Technetium-99m bone scans frequently yield false negatives. Therefore, whole-body low-dose CT, whole-body MRI, or PET-CT are the modalities of choice to identify myeloma bone lesions.

Question 4710

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) plays a central role in maintaining systemic calcium homeostasis by acting on bone, kidneys, and the intestines. What is the direct mechanism by which continuously elevated PTH levels stimulate bone resorption?

. Directly binding to receptors on mature osteoclasts to increase their resorptive activity
. Binding to receptors on osteoblasts, causing upregulation of RANKL, which subsequently activates osteoclasts
. Downregulating the expression of RANKL and upregulating osteoprotegerin (OPG)
. Stimulating the release of calcitonin from the thyroid gland
. Inducing rapid apoptosis of osteoblasts

Correct Answer & Explanation

. Binding to receptors on osteoblasts, causing upregulation of RANKL, which subsequently activates osteoclasts

Explanation

Osteoclasts do not possess receptors for PTH. Instead, continuous PTH binds to PTH receptors (PTH1R) on the surface of osteoblasts. This binding stimulates osteoblasts to upregulate the expression of RANKL (and downregulate OPG). RANKL then binds to the RANK receptor on osteoclast precursors, promoting their differentiation, fusion, and activation into mature bone-resorbing osteoclasts.

Question 4711

Topic: 1. General Principles & Basic Science
A 65-year-old female presents with severe base of thumb pain. Radiographs reveal advanced thumb carpometacarpal (CMC) joint arthritis with complete loss of joint space, significant subluxation, and cystic changes. Additionally, there is complete loss of joint space and osteophyte formation at the scaphotrapezial trapezoid (STT) joint. According to the Eaton-Littler classification, what stage is this disease?
. Stage I
. Stage II
. Stage III
. Stage IV
. Stage V

Correct Answer & Explanation

. Stage II

Explanation

The Eaton-Littler classification for thumb CMC arthritis: Stage I (subtle widening, no subluxation), Stage II (slight narrowing, <1/3 subluxation, osteophytes <2mm), Stage III (marked narrowing, >1/3 subluxation, osteophytes >2mm), Stage IV (pantrapezial arthritis, which involves the STT joint in addition to the CMC joint).

Question 4712

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) are used as osteoinductive agents in spine fusions and nonunion surgery. Which of the following BMPs is an FDA-approved recombinant protein utilized in anterior lumbar interbody fusion (ALIF) within a specific carrier?

. rhBMP-2
. rhBMP-3
. rhBMP-4
. rhBMP-6
. rhBMP-9

Correct Answer & Explanation

. rhBMP-2

Explanation

rhBMP-2 (recombinant human bone morphogenetic protein-2) is FDA approved for use in single-level anterior lumbar interbody fusions (ALIF) with an absorbable collagen sponge carrier and a specific interbody cage. It acts as an osteoinductive agent by stimulating mesenchymal stem cells to differentiate into osteoblasts.

Question 4713

Topic: Surgical Anatomy & Approaches

A 42-year-old male sustains a high-energy distal tibia pilon fracture.

An anterolateral surgical approach is planned for open reduction and internal fixation. During this approach, which nerve is at greatest risk of iatrogenic injury as it crosses the operative field?

. Sural nerve
. Deep peroneal nerve
. Superficial peroneal nerve
. Saphenous nerve
. Tibial nerve

Correct Answer & Explanation

. Superficial peroneal nerve

Explanation

The anterolateral approach to the distal tibia uses the internervous plane between the superficial peroneal nerve (lateral compartment) and deep peroneal nerve (anterior compartment). The superficial peroneal nerve crosses the surgical field from medial to lateral as it travels distally over the ankle, placing it at high risk of iatrogenic injury.

Question 4714

Topic: 1. General Principles & Basic Science

Articular cartilage is highly specialized to withstand compressive and shear forces. Within the deep (basal) zone of articular cartilage, how is the type II collagen network primarily oriented relative to the articular surface?

. Parallel
. Randomly oriented
. Perpendicular
. Tangential
. Oblique at 45 degrees

Correct Answer & Explanation

. Parallel

Explanation

The structural arrangement of articular cartilage varies by depth. In the superficial zone, collagen fibers are oriented parallel to the joint surface to resist shear forces. In the transitional (middle) zone, they are randomly oriented. In the deep (basal) zone, collagen fibers run strictly perpendicular to the articular surface, firmly anchoring the cartilage to the underlying calcified zone.

Question 4715

Topic: Biology, Genetics & Bone Healing

A 29-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the distal femoral epiphysis extending into the metaphysis.

Biopsy confirms a Giant Cell Tumor of bone. Neoadjuvant therapy with denosumab is considered. What is the mechanism of action of this medication?

. Monoclonal antibody against Vascular Endothelial Growth Factor (VEGF).
. Bisphosphonate that inhibits osteoclast farnesyl pyrophosphate synthase.
. Monoclonal antibody against Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL).
. Tyrosine kinase inhibitor targeting c-kit.
. Selective estrogen receptor modulator.

Correct Answer & Explanation

. Monoclonal antibody against Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL).

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL. In Giant Cell Tumor of Bone (GCTB), neoplastic mononuclear stromal cells secrete massive amounts of RANKL, recruiting and activating the reactive osteoclast-like multinucleated giant cells that cause bone destruction. Denosumab blocks this interaction, inhibiting osteoclast activity.

Question 4716

Topic: Biology, Genetics & Bone Healing

Which phase of fracture healing is most dependent on the inflammatory cascade initiated by macrophages and platelets?

. Hard callus formation
. Soft callus formation
. Hematoma formation and inflammation
. Remodeling
. Woven bone deposition

Correct Answer & Explanation

. Hematoma formation and inflammation

Explanation

The initial phase of fracture healing is the hematoma formation and inflammatory phase. Platelets and macrophages release cytokines (e.g., PDGF, TGF-beta) that recruit mesenchymal stem cells and initiate the healing process.

Question 4717

Topic: Biomechanics & Biomaterials
Which of the following sterilization methods for ultra-high molecular weight polyethylene (UHMWPE) components in total joint arthroplasty promotes cross-linking but also generates free radicals that can lead to oxidation and degradation if not properly treated?
. Ethylene oxide gas
. Gamma irradiation in air
. Autoclaving
. Gas plasma
. Dry heat

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation induces cross-linking, which improves wear resistance. However, if performed in air, it generates free radicals that react with oxygen, leading to oxidation, chain scission, and subsequent degradation of the polyethylene. Modern techniques involve irradiation in an inert environment (e.g., argon or vacuum) and subsequent melting or annealing to quench free radicals.

Question 4718

Topic: Surgical Anatomy & Approaches

A 35-year-old male sustains an anteroposterior compression (APC) type II pelvic ring injury.

During anterior ring fixation via an ilioinguinal approach, massive hemorrhage is encountered posterior to the superior pubic ramus. Which anomalous anatomical connection represents the classic 'corona mortis'?

. External iliac artery to internal pudendal artery
. External iliac artery or inferior epigastric artery to the obturator artery
. Internal iliac artery to superior gluteal artery
. Internal pudendal artery to inferior epigastric artery
. Internal pudendal artery to obturator artery

Correct Answer & Explanation

. External iliac artery or inferior epigastric artery to the obturator artery

Explanation

The 'corona mortis' (crown of death) refers to a vascular anastomosis between the obturator and external iliac (or inferior epigastric) vascular systems. It is located posterior to the superior pubic ramus at a variable distance (average 5-6 cm) from the symphysis pubis and can cause life-threatening hemorrhage if inadvertently disrupted during anterior pelvic ring surgery (ilioinguinal or Stoppa approaches).

Question 4719

Topic: 1. General Principles & Basic Science

A 30-year-old sustains a laceration to the volar aspect of his index finger in Zone II, requiring primary FDP repair.

To safely allow an early active motion protocol without gap formation or rupture, biomechanical studies suggest a minimum of how many core strands crossing the repair site?

. 2 strands
. 4 strands
. 6 strands
. 8 strands
. Epitendinous repair alone is sufficient

Correct Answer & Explanation

. 4 strands

Explanation

Early active motion protocols after flexor tendon repair reduce adhesions and improve outcomes but place higher stresses on the repair. Biomechanical studies have demonstrated that a 2-strand repair is generally insufficient to withstand the forces of active flexion without gap formation. A minimum of a 4-strand core repair, ideally augmented with an epitendinous repair, is recommended for early active mobilization.

Question 4720

Topic: Biology, Genetics & Bone Healing

A 32-year-old female is diagnosed with a Giant Cell Tumor (GCT) of the proximal tibia. She is prescribed Denosumab as neoadjuvant therapy.

What is the precise mechanism of action of Denosumab in treating GCT?

. Binds to RANK receptor on osteoclasts, directly inhibiting their activation
. Binds to RANK Ligand (RANKL) expressed by the mononuclear stromal cells
. Inhibits vascular endothelial growth factor (VEGF), leading to tumor necrosis
. Binds directly to the multinucleated giant cells and induces apoptosis
. Inhibits farnesyl pyrophosphate synthase within osteoclasts

Correct Answer & Explanation

. Binds to RANK Ligand (RANKL) expressed by the mononuclear stromal cells

Explanation

In Giant Cell Tumor of bone, the neoplastic cells are actually the mononuclear stromal cells, not the giant cells themselves. These stromal cells overexpress RANK Ligand (RANKL), which recruits and activates the reactive osteoclast-like multinucleated giant cells that cause bone destruction. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from interacting with the RANK receptor on osteoclast precursors, thereby halting osteolysis.

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