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1. General Principles & Basic Science MCQs

Practice Set 449 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 8961

Topic: Infection, Pharmacology & VTE

A 7-year-old boy from an endemic region develops a large, painless knee effusion without fever. Joint fluid analysis shows 35,000 WBC/mm3. Serology confirms Borrelia burgdorferi infection. What is the recommended initial management?

. Urgent surgical irrigation and debridement
. 28 days of oral antibiotics (e.g., amoxicillin or doxycycline)
. Intra-articular corticosteroid injection
. Arthroscopic synovectomy
. Intravenous vancomycin

Correct Answer & Explanation

. 28 days of oral antibiotics (e.g., amoxicillin or doxycycline)

Explanation

Lyme arthritis classically presents with a large, minimally painful effusion and is treated initially with a 28-day course of oral antibiotics. Surgical drainage is reserved for cases that fail antibiotic therapy or if concomitant bacterial septic arthritis is suspected.

Question 8962

Topic: Biology, Genetics & Bone Healing

Intermittent administration of recombinant human parathyroid hormone (Teriparatide) is used for the treatment of osteoporosis. By which primary mechanism does it achieve its therapeutic effect?

. Inhibiting osteoclast bone resorption
. Stimulating osteoblast-mediated bone formation
. Increasing intestinal calcium absorption directly
. Decreasing renal calcium reabsorption
. Downregulating Wnt/beta-catenin signaling

Correct Answer & Explanation

. Stimulating osteoblast-mediated bone formation

Explanation

While continuous exposure to PTH causes net bone resorption, intermittent administration (e.g., daily Teriparatide injections) provides an anabolic effect. It directly stimulates osteoblast proliferation and action, significantly increasing bone mineral density.

Question 8963

Topic: Infection, Pharmacology & VTE
Rivaroxaban and apixaban are frequently prescribed for venous thromboembolism (VTE) prophylaxis following total joint arthroplasty. What is their specific pharmacologic mechanism of action?
. Direct thrombin (Factor IIa) inhibition
. Vitamin K antagonism
. Direct Factor Xa inhibition
. Antithrombin III activation
. Platelet ADP receptor blockade

Correct Answer & Explanation

. Direct Factor Xa inhibition

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa in the coagulation cascade. Dabigatran, by contrast, is a direct thrombin inhibitor.

Question 8964

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman with a history of gastric bypass presents with severe bone pain and recurrent stress fractures. Labs reveal low serum calcium, low phosphorus, and elevated alkaline phosphatase. A bone biopsy would most likely demonstrate which histological finding?

. Thickened trabeculae with a mosaic pattern of lamellar bone
. Abundant, widened unmineralized osteoid seams
. Osteoclastic tunneling and peritrabecular fibrosis
. Empty lacunae with extensive marrow fat necrosis
. Monoclonal plasma cell infiltration

Correct Answer & Explanation

. Abundant, widened unmineralized osteoid seams

Explanation

This patient has osteomalacia due to malabsorption and Vitamin D deficiency. Osteomalacia is characterized histologically by defective mineralization of the newly formed bone matrix, resulting in thick, unmineralized osteoid seams.

Question 8965

Topic: Biomechanics & Biomaterials

Which of the following implant combinations poses the highest risk for galvanic corrosion in orthopedic surgery?

. A titanium alloy screw used with a titanium alloy plate
. A stainless steel screw used with a titanium alloy plate
. A cobalt-chromium head on a titanium stem
. A ceramic head on a cobalt-chromium stem
. A PMMA mantle surrounding a cobalt-chromium stem

Correct Answer & Explanation

. A stainless steel screw used with a titanium alloy plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct contact within an electrolytic environment, such as bodily fluids. Combining stainless steel and titanium implants creates a strong galvanic cell that accelerates corrosion.

Question 8966

Topic: Biology, Genetics & Bone Healing

Romosozumab is an advanced pharmacological agent used in the treatment of severe osteoporosis. What is its primary mechanism of action?

. Binds RANKL to prevent osteoclast activation
. Inhibits sclerostin to upregulate Wnt signaling
. Acts as a selective estrogen receptor modulator (SERM)
. Provides a recombinant form of parathyroid hormone
. Directly inhibits cathepsin K

Correct Answer & Explanation

. Inhibits sclerostin to upregulate Wnt signaling

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin. Since sclerostin normally downregulates bone formation, its inhibition leads to increased Wnt signaling and enhanced osteoblastic bone formation.

Question 8967

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with persistent right knee pain. Radiographs reveal an eccentric, lytic lesion in the proximal tibial epiphysis extending to the subchondral bone without a sclerotic rim.

Histology shows mononuclear cells and multinucleated giant cells. Which of the following targeted therapies acts directly on the primary pathogenic mechanism of this tumor?

. Imatinib
. Denosumab
. Infliximab
. Rituximab
. Bisphosphonates

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumor of bone is driven by neoplastic mononuclear cells that overexpress RANKL, which recruits reactive osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, directly inhibits this recruitment and is used for advanced or unresectable cases.

Question 8968

Topic: 1. General Principles & Basic Science

Articular cartilage exhibits depth-dependent variations in its structural composition. Which zone of articular cartilage has the highest water content and contains collagen fibrils oriented parallel to the articular surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone of articular cartilage contains the highest concentration of water and predominantly Type II collagen. The collagen fibers are oriented parallel to the joint surface to effectively resist shear forces during motion.

Question 8969

Topic: Biomechanics & Biomaterials
To decrease the rate of adhesive and abrasive wear in total joint arthroplasty, ultra-high-molecular-weight polyethylene (UHMWPE) can be highly cross-linked via irradiation. Which of the following processes is required to eliminate the resulting free radicals and prevent subsequent oxidative degradation?
. Gamma irradiation in air
. Ethylene oxide sterilization
. Remelting or annealing
. Cold working
. Addition of barium sulfate

Correct Answer & Explanation

. Remelting or annealing

Explanation

Irradiating polyethylene creates cross-links but also generates free radicals that can lead to oxidation and structural degradation over time. Thermal processing, either by remelting or annealing, extinguishes these free radicals and improves long-term oxidation resistance.

Question 8970

Topic: Biology, Genetics & Bone Healing

A 24-year-old man undergoes open reduction and internal fixation of a transverse radial shaft fracture with absolute stability using a dynamic compression plate. This construct promotes primary bone healing. Which of the following is an essential characteristic of this healing process?

. Formation of a robust cartilaginous callus
. Healing mediated by cutting cones directly crossing the fracture site
. Endochondral ossification
. High interfragmentary strain at the fracture gap
. Healing driven by the periosteal blood supply forming a soft callus

Correct Answer & Explanation

. Healing mediated by cutting cones directly crossing the fracture site

Explanation

Primary bone healing occurs under conditions of absolute stability and minimal interfragmentary strain. It bypasses callus formation entirely, healing via direct Haversian remodeling where osteoclastic cutting cones cross the fracture site followed by osteoblastic bone deposition.

Question 8971

Topic: Infection, Pharmacology & VTE

An 18-year-old male complains of dull, aching pain in his right tibia that is worse at night and completely relieved by ibuprofen. A CT scan reveals a 1 cm cortical radiolucent nidus surrounded by dense reactive sclerosis.

The profound pain relief from NSAIDs is due to the inhibition of which molecule highly expressed by the nidus?

. Interleukin-1 (IL-1)
. Tumor necrosis factor-alpha (TNF-a)
. Cyclooxygenase-2 (COX-2)
. Matrix metalloproteinase-9 (MMP-9)
. Fibroblast growth factor (FGF)

Correct Answer & Explanation

. Cyclooxygenase-2 (COX-2)

Explanation

The nidus of an osteoid osteoma produces excessively high levels of prostaglandins due to the upregulation of COX-2. NSAIDs inhibit COX-2, reducing prostaglandin E2 levels and providing rapid, characteristic pain relief.

Question 8972

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) plays a critical role in calcium homeostasis by ultimately promoting bone resorption. Which of the following describes the primary cellular mechanism by which PTH stimulates osteoclast activity?

. Direct binding to osteoclast surface receptors
. Binding to osteoblasts to stimulate RANKL expression
. Inhibition of osteoprotegerin (OPG) synthesis by osteoclasts
. Direct stimulation of macrophage colony-stimulating factor (M-CSF) from osteocytes
. Conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D within the bone marrow

Correct Answer & Explanation

. Binding to osteoblasts to stimulate RANKL expression

Explanation

Osteoclasts do not possess PTH receptors. PTH binds to its receptors on osteoblasts, which subsequently upregulate the expression of RANK ligand (RANKL) to stimulate osteoclast differentiation and activation.

Question 8973

Topic: Biology, Genetics & Bone Healing

A 55-year-old woman with metastatic breast cancer is treated with a monoclonal antibody to prevent skeletal-related events. This medication primarily binds to which of the following targets to inhibit osteoclastogenesis?

. RANK receptor
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. RANK ligand
. Transforming growth factor-beta (TGF-b)

Correct Answer & Explanation

. RANK ligand

Explanation

Denosumab is a human monoclonal antibody that directly binds to RANK ligand (RANKL). This prevents RANKL from interacting with the RANK receptor on osteoclasts, profoundly inhibiting osteoclast formation, function, and survival.

Question 8974

Topic: 1. General Principles & Basic Science

Which of the following modifications to a standard cortical screw design will most significantly increase its pullout strength when utilized in osteoporotic bone?

. Increasing the outer thread diameter
. Decreasing the outer thread diameter
. Increasing the inner root diameter
. Increasing the thread pitch
. Decreasing the length of engagement

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

Screw pullout strength is most significantly influenced by the outer thread diameter. Pullout strength can also be improved by decreasing the inner root diameter (increasing thread depth), decreasing thread pitch (increasing threads engaged), and maximizing engagement length.

Question 8975

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, the addition of Vitamin E (alpha-tocopherol) primarily serves to:
. Increase the degree of polymer cross-linking
. Scavenge free radicals to prevent oxidative degradation
. Enhance the elastic modulus of the bearing surface
. Decrease the melting temperature of the polymer
. Promote osteointegration at the bone-implant interface

Correct Answer & Explanation

. Scavenge free radicals to prevent oxidative degradation

Explanation

Vitamin E is blended into highly cross-linked UHMWPE to act as a potent antioxidant. It actively scavenges residual free radicals produced during gamma irradiation, thereby preventing long-term oxidative degradation without the mechanical compromises of post-irradiation melting.

Question 8976

Topic: 1. General Principles & Basic Science

Within normal articular cartilage, which zone possesses the highest concentration of water and the lowest concentration of proteoglycans?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone of articular cartilage contains the highest concentration of water and the lowest concentration of proteoglycans. It is characterized by densely packed collagen fibers oriented parallel to the joint surface to effectively resist shear forces.

Question 8977

Topic: Infection, Pharmacology & VTE

Following total knee arthroplasty, a patient develops a periprosthetic joint infection caused by Staphylococcus epidermidis. The resistance of these bacteria to systemic antibiotics is primarily mediated by their ability to form a biofilm. What is the principal structural component of this biofilm matrix?

. Lipopolysaccharide
. Peptidoglycan
. Teichoic acid
. Extracellular polymeric substances (glycocalyx)
. Hyaluronic acid

Correct Answer & Explanation

. Extracellular polymeric substances (glycocalyx)

Explanation

The biofilm matrix is primarily composed of extracellular polymeric substances (EPS), specifically a highly hydrated polysaccharide glycocalyx. This dense slime layer protects sessile bacteria from both the host immune system and systemic antimicrobial agents.

Question 8978

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the management of severe, high-risk osteoporosis. Its profound anabolic effect on bone is primarily mediated through which of the following mechanisms?

. Inhibition of osteoclast proton pumps
. Intermittent activation of the PTH receptor stimulating osteoblast activity
. Competitive binding of RANK ligand
. Inhibition of sclerostin production by osteocytes
. Downregulation of macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. Intermittent activation of the PTH receptor stimulating osteoblast activity

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered via intermittent daily injections, it acts as an anabolic agent by directly stimulating osteoblast activity and extending their lifespan, leading to net bone formation.

Question 8979

Topic: Biomechanics & Biomaterials

According to fundamental biomechanical principles, if the diameter of a solid titanium intramedullary nail is doubled, its overall torsional rigidity will theoretically increase by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The torsional rigidity of a solid cylindrical implant is directly proportional to its polar moment of inertia. Because the polar moment of inertia scales with the radius to the fourth power (r^4), doubling the diameter increases the rigidity by a factor of 16.

Question 8980

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with generalized bone pain, hypercalcemia, and renal insufficiency. Radiographs show multiple "punched-out" lytic lesions in the skull. Which of the following cytokines plays a central role as an osteoclast-activating factor in this condition?

. Interleukin-1 (IL-1)
. Interleukin-6 (IL-6)
. Tumor necrosis factor-alpha (TNF-a)
. Interferon-gamma
. Transforming growth factor-beta (TGF-b)

Correct Answer & Explanation

. Interleukin-6 (IL-6)

Explanation

Interleukin-6 (IL-6) acts as a potent osteoclast-activating factor in multiple myeloma, driving extensive localized bone resorption. Myeloma cells also secrete factors like MIP-1alpha that further upregulate RANKL expression while actively inhibiting OPG.

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