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1. General Principles & Basic Science MCQs

Practice Set 425 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 8481

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with generalized bone pain, fatigue, and a recent pathologic fracture of the proximal humerus. Laboratory testing reveals hypercalcemia, anemia, and renal insufficiency. A skeletal survey demonstrates multiple punched-out lytic lesions in the skull and pelvis. The neoplastic cells primarily responsible for this condition are derived from which of the following cell lineages?

. T-lymphocytes
. B-lymphocytes (Plasma cells)
. Osteoclasts
. Mesenchymal stem cells
. Hematopoietic stem cells of the myeloid lineage

Correct Answer & Explanation

. B-lymphocytes (Plasma cells)

Explanation

The patient's clinical presentation is classic for multiple myeloma, fulfilling the CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lesions). Multiple myeloma is a plasma cell dyscrasia characterized by the neoplastic proliferation of monoclonal plasma cells, which are terminally differentiated B-lymphocytes. These malignant cells secrete monoclonal immunoglobulins and stimulate aggressive osteoclastic bone resorption via upregulation of RANKL and downregulation of osteoprotegerin (OPG).

Question 8482

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely administered to reduce perioperative blood loss and transfusion requirements in total joint arthroplasty. The specific pharmacological mechanism of action of TXA is best described by which of the following?
. Direct inhibition of Factor Xa in the coagulation cascade
. Binding to antithrombin III to inhibit thrombin activity
. Irreversible inhibition of the cyclooxygenase (COX) enzyme
. Competitive inhibition of plasminogen activation
. Promotion of von Willebrand factor release from endothelial cells

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine and functions as an antifibrinolytic agent. It works by competitively binding to the lysine-binding sites on plasminogen, which prevents its activation into plasmin. By inhibiting the formation of plasmin, TXA blocks the degradation of fibrin clots (fibrinolysis), thereby stabilizing clots and reducing surgical bleeding. Direct inhibition of Factor Xa is the mechanism of drugs like rivaroxaban.

Question 8483

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with persistent knee pain. Radiographs reveal an eccentric, purely lytic, epiphyseal-metaphyseal lesion in the distal femur extending to the subchondral bone without a sclerotic margin. Biopsy confirms a giant cell tumor of bone. She is scheduled for curettage but is prescribed a targeted biologic therapy preoperatively to downstage the tumor. What is the precise mechanism of action of this medication?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct binding to the RANK receptor on the surface of multinucleated giant cells
. Monoclonal antibody binding to RANK ligand (RANKL)
. Inhibition of tyrosine kinase receptors on mononuclear stromal cells
. Direct binding to osteoclast integrin receptors

Correct Answer & Explanation

. Monoclonal antibody binding to RANK ligand (RANKL)

Explanation

The patient is describing Denosumab, which is used in the treatment of Giant Cell Tumor (GCT) of bone. The neoplastic cells in GCT are the mononuclear spindle-shaped stromal cells, which express high levels of RANK Ligand (RANKL). This RANKL recruits and activates reactive, non-neoplastic multinucleated giant cells (osteoclast-like cells) that cause the massive bone destruction seen in this disease. Denosumab is a fully humanized monoclonal antibody that binds directly to RANKL, preventing it from interacting with the RANK receptor on the osteoclast-like giant cells. It does not bind to the RANK receptor itself.

Question 8484

Topic: Biology, Genetics & Bone Healing

In the process of creeping substitution during the incorporation of a massive structural cortical bone allograft, what is the primary mechanism of graft failure in the first few years?

. An excessive immune response leading to acute rejection
. Complete resorption of the graft by osteoclasts before osteoblastic bone formation
. Fatigue microdamage leading to fracture due to incomplete revascularization and remodeling
. Transformation into a malignant sarcoma due to chronic inflammation
. Failure of woven bone to convert to lamellar bone

Correct Answer & Explanation

. Fatigue microdamage leading to fracture due to incomplete revascularization and remodeling

Explanation

Structural cortical allografts undergo creeping substitution, which starts at the graft-host junction and slowly progresses. Because only the outer few millimeters typically become revascularized and remodeled, the bulk of the graft remains necrotic and acts primarily as a mechanical spacer. The remodeling process transiently weakens the graft because osteoclastic resorption precedes osteoblastic formation. This leaves the graft highly susceptible to fatigue microdamage, which can accumulate and result in structural failure (fracture) during the first few years.

Question 8485

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with a painful, radiolucent, eccentrically located lesion in the distal femoral epiphysis extending to the subchondral bone. Biopsy reveals multinucleated giant cells interspersed within a stroma of mononuclear cells. Which of the following best describes the mechanism of action of the targeted medical therapy typically used for advanced or unresectable cases of this condition?

. Inhibition of matrix metalloproteinases
. Monoclonal antibody targeting RANK ligand (RANKL)
. Tyrosine kinase inhibition of c-KIT
. Alkylating agent causing DNA cross-linking
. Competitive inhibition of estrogen receptors

Correct Answer & Explanation

. Monoclonal antibody targeting RANK ligand (RANKL)

Explanation

The clinical and histologic presentation is classic for a giant cell tumor of bone (GCT). The mononuclear stromal cells are the true neoplastic cells, and they overexpress RANK ligand (RANKL). This recruits and activates normal multinucleated osteoclast-like giant cells, causing extensive bone resorption. Denosumab, a monoclonal antibody that binds to RANKL, prevents the RANK-RANKL interaction, effectively inhibiting osteoclast formation and reducing osteolysis.

Question 8486

Topic: Biomechanics & Biomaterials

Which of the following alterations in screw design or insertion technique would most significantly increase the pullout strength of a cortical screw in diaphyseal bone?

. Decreasing the outer (thread) diameter of the screw
. Increasing the inner (root) diameter of the screw
. Decreasing the thread pitch
. Inserting the screw at a 45-degree angle to the long axis of the bone
. Using a cannulated screw instead of a solid screw

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the bone, and inversely proportional to the thread pitch. Decreasing the thread pitch (meaning more threads per unit length) increases the volume of bone caught between the threads, thereby increasing the pullout strength. Increasing the inner (root) diameter increases the screw's resistance to bending and fatigue failure but does not increase pullout strength.

Question 8487

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage makes up about 10-20% of articular cartilage thickness. It contains the highest water content, the lowest proteoglycan concentration, and collagen fibers (primarily Type II) oriented parallel to the articular surface. This specific orientation helps the cartilage resist shear forces. Conversely, the deep zone has the highest proteoglycan content and collagen fibers perpendicular to the surface to resist compressive loads.

Question 8488

Topic: 1. General Principles & Basic Science

Osteoclasts resorb bone by sealing off a localized area (Howship's lacuna) and secreting various substances. Which of the following enzymes is directly responsible for generating the intracellular hydrogen ions needed to create the acidic environment that dissolves inorganic bone mineral (hydroxyapatite)?

. Cathepsin K
. Carbonic anhydrase II
. Matrix metalloproteinase-9
. Tartrate-resistant acid phosphatase (TRAP)
. Alkaline phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteoclasts resorb bone by secreting hydrogen ions to dissolve the inorganic matrix (hydroxyapatite) and proteolytic enzymes (like Cathepsin K) to degrade the organic matrix (type I collagen). The acidic environment is generated by hydrogen ions, which are produced intracellularly by the enzyme carbonic anhydrase II. This enzyme catalyzes the hydration of CO2 to form carbonic acid, which dissociates into H+ and HCO3-. The H+ is then actively pumped into the resorption pit via a vacuolar H+-ATPase.

Question 8489

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate and zoledronic acid, inhibit osteoclast-mediated bone resorption primarily by interfering with which of the following intracellular pathways?

. Wnt/beta-catenin signaling
. Mevalonate pathway via inhibition of farnesyl pyrophosphate synthase
. NF-kB pathway via inhibition of RANKL
. Glycolytic pathway via inhibition of hexokinase
. Arachidonic acid cascade via COX-2 inhibition

Correct Answer & Explanation

. Mevalonate pathway via inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate, risedronate, zoledronate) act by inhibiting the enzyme farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of small GTPase proteins (such as Ras, Rho, and Rab), which are essential for normal osteoclast function, ruffled border formation, and cell survival, ultimately leading to osteoclast apoptosis. Non-nitrogen-containing bisphosphonates (e.g., etidronate) act differently, by forming toxic ATP analogues.

Question 8490

Topic: Biology, Genetics & Bone Healing

During the initial inflammatory phase of fracture healing, which of the following cytokines is considered the primary early initiator of the cascade, promoting angiogenesis and the recruitment of mesenchymal stem cells, and peaks within the first 24 hours?

. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-beta (TGF-beta)
. Tumor Necrosis Factor-alpha (TNF-alpha)
. Interleukin-10 (IL-10)
. Fibroblast Growth Factor-2 (FGF-2)

Correct Answer & Explanation

. Tumor Necrosis Factor-alpha (TNF-alpha)

Explanation

Tumor Necrosis Factor-alpha (TNF-alpha) and Interleukin-1 (IL-1) are key pro-inflammatory cytokines that peak within the first 24 hours after a fracture. They are secreted by macrophages and inflammatory cells in the fracture hematoma. TNF-alpha is essential for initiating the repair cascade, recruiting mesenchymal stem cells, and promoting angiogenesis. The absence of TNF-alpha signaling has been shown to significantly delay fracture healing. BMP-2 and TGF-beta are critical later in the process for driving chondrogenesis and osteogenesis.

Question 8491

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs demonstrate an eccentric, lytic epiphyseal lesion in the distal femur extending to the subchondral bone. Biopsy confirms a giant cell tumor of bone. In cases of unresectable disease, medical therapy can be utilized to downstage the tumor. Which of the following describes the mechanism of action of the most commonly used targeted medication for this condition?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of the neoplastic mononuclear cells
. Monoclonal antibody binding to RANK ligand (RANKL)
. Bisphosphonate-mediated inhibition of osteoclast farnesyl pyrophosphate synthase
. Tyrosine kinase inhibition of c-KIT

Correct Answer & Explanation

. Monoclonal antibody binding to RANK ligand (RANKL)

Explanation

Denosumab is the targeted medical therapy for advanced or unresectable giant cell tumors of bone (GCT). It is a monoclonal antibody that binds to RANKL. In GCT, the neoplastic cells are the mononuclear stromal cells, which express high levels of RANKL. This RANKL normally recruits and activates the reactive, multinucleated osteoclast-like giant cells that cause bone destruction. Denosumab disrupts this pathway, halting bone resorption and tumor progression.

Question 8492

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman presents with generalized back pain and fatigue. Radiographs show multiple punched-out lytic lesions in her skull and spine. Laboratory studies reveal hypercalcemia and elevated serum creatinine. A technetium-99m bone scan is ordered but shows no areas of increased radiotracer uptake in the skeleton. What is the most likely explanation for the false-negative bone scan?

. The lesions are primarily composed of calcified cartilage
. The lesions represent areas of pure osteoblastic activity
. The patient has concurrent severe osteoporosis limiting radiotracer uptake
. Technetium-99m primarily binds to tumor-specific antigens not present in this disease
. The tumor cells produce osteoclast activating factors without a significant osteoblastic response

Correct Answer & Explanation

. The tumor cells produce osteoclast activating factors without a significant osteoblastic response

Explanation

This patient has multiple myeloma, characterized by 'punched-out' lytic lesions, hypercalcemia, and renal failure. Technetium-99m bone scans detect areas of active osteoblastic bone formation (woven bone). Multiple myeloma cells secrete factors that potently activate osteoclasts (e.g., RANKL) while simultaneously suppressing osteoblast activity (e.g., DKK1). Because there is little to no reactive bone formation, the lesions are purely osteolytic and often do not 'light up' on a standard bone scan.

Question 8493

Topic: Biology, Genetics & Bone Healing

A 70-year-old man presents with increasing hat size, progressive hearing loss, and thigh pain. Radiographs of his femur show cortical thickening and coarse trabeculae. Laboratory tests show normal serum calcium, normal phosphate, and markedly elevated serum alkaline phosphatase. Which of the following describes the primary pathological event initiating this disease process?

. Decreased osteoblast proliferation
. Malignant transformation of osteoblasts
. Intense, uncoupled osteoclastic bone resorption
. Vitamin D deficiency leading to unmineralized osteoid
. Deposition of beta-2 microglobulin amyloid in bone

Correct Answer & Explanation

. Intense, uncoupled osteoclastic bone resorption

Explanation

Paget's disease of bone (osteitis deformans) is initiated by an intense, overactive osteoclastic resorptive phase. These osteoclasts are abnormally large and have an increased number of nuclei. This initial lytic phase is followed by a mixed phase where chaotic osteoblastic bone formation attempts to compensate, leading to the deposition of structurally weak woven bone. This ultimately results in the sclerotic phase characterized by thickened cortices and a 'mosaic' cement line pattern on histology.

Question 8494

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) signals through serine/threonine kinase receptors. Which of the following intracellular signaling molecules is directly phosphorylated following the binding of rhBMP-2 to its receptor?

. Wnt
. Beta-catenin
. Smad 1/5/8
. Smad 2/3
. Runx2

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs signal primarily through the Smad pathway. BMPs (such as BMP-2 and BMP-7) bind to transmembrane serine/threonine kinase receptors, which then phosphorylate Smad 1, 5, and 8. These phosphorylated molecules complex with Smad 4 and enter the nucleus to upregulate transcription factors such as Runx2. TGF-beta, on the other hand, primarily phosphorylates Smad 2 and 3. The Wnt pathway signals via beta-catenin stabilization.

Question 8495

Topic: 1. General Principles & Basic Science

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

. 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 contains the largest collagen fibrils, which are oriented perpendicular to the joint surface to resist compressive forces. It also possesses the highest concentration of proteoglycans and the lowest concentration of water. The superficial zone has collagen parallel to the surface, the highest water content, and the lowest proteoglycan content.

Question 8496

Topic: Biomechanics & Biomaterials

Which of the following terms best describes a material's property to exhibit a time-dependent increase in strain when subjected to a constant applied stress?

. Creep
. Stress relaxation
. Viscoelasticity
. Fatigue
. Hysteresis

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive, time-dependent deformation (increase in strain) of a material under a constant stress or load. Stress relaxation is the time-dependent decrease in stress under a constant strain. Hysteresis refers to the energy lost (as heat) during cyclic loading and unloading. Viscoelasticity is the overarching term for materials exhibiting both viscous and elastic characteristics.

Question 8497

Topic: Surgical Anatomy & Approaches
During a surgical approach to the humerus, the radial nerve is identified in the spiral groove. A traction injury occurs, resulting in axonal disruption but preservation of the endoneurium, perineurium, and epineurium. According to Seddon's classification, this type of injury is termed:
. Neuropraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade III
. Sunderland Grade IV

Correct Answer & Explanation

. Axonotmesis

Explanation

Seddon classified nerve injuries into three categories. Axonotmesis involves disruption of the axon and myelin sheath, but the surrounding connective tissue frameworks (endoneurium, perineurium, and epineurium) remain intact. This allows for Wallerian degeneration distally followed by potential guided regeneration. This corresponds to a Sunderland Grade II injury. Neuropraxia is a local conduction block without axonal disruption.

Question 8498

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, the cartilaginous soft callus is replaced by a hard bony callus. This specific phase of tissue differentiation and replacement is driven primarily by which of the following mechanisms?

. Intramembranous ossification
. Endochondral ossification
. Creeping substitution
. Appositional growth
. Osteoclastic cutting cones

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing progresses through inflammation, soft callus formation, hard callus formation, and remodeling. The transition from a cartilaginous soft callus to a woven bone hard callus occurs via endochondral ossification. Intramembranous ossification occurs directly from mesenchymal cells without a cartilaginous intermediate, which is seen in flat bone development and the immediate periosteal response at the fracture edges.

Question 8499

Topic: Infection, Pharmacology & VTE
Which of the following pharmacologic agents used for venous thromboembolism (VTE) prophylaxis acts by directly and reversibly inhibiting Factor Xa?
. Warfarin
. Enoxaparin
. Rivaroxaban
. Dabigatran
. Fondaparinux

Correct Answer & Explanation

. Rivaroxaban

Explanation

Rivaroxaban and apixaban are direct Factor Xa inhibitors. Enoxaparin (a low-molecular-weight heparin) binds antithrombin III, which then indirectly inhibits Factor Xa and IIa. Fondaparinux also binds antithrombin III to indirectly but selectively inhibit Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits vitamin K-dependent factors (II, VII, IX, X).

Question 8500

Topic: Physiology & Rehabilitation

Delayed onset muscle soreness (DOMS) typically peaks 24 to 72 hours after unaccustomed or vigorous exercise. Which type of muscle contraction is most strongly associated with the pathogenesis of DOMS?

. Concentric contraction
. Isometric contraction
. Eccentric contraction
. Isokinetic contraction
. Isotonic contraction

Correct Answer & Explanation

. Eccentric contraction

Explanation

Eccentric muscle contractions occur when a muscle lengthens while generating tension. This type of contraction generates the highest forces per cross-sectional area of muscle and causes the greatest microtrauma to muscle fibers and their connective tissue envelopes. This microtrauma triggers an inflammatory cascade, which is the primary mechanism behind delayed onset muscle soreness (DOMS).

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