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1. General Principles & Basic Science MCQs

Practice Set 673 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 13441

Topic: Infection, Pharmacology & VTE

A 65-year-old man is scheduled for a total hip arthroplasty. He has a documented severe, IgE-mediated anaphylactic allergy to penicillin. Which of the following is the most appropriate preoperative prophylactic antibiotic regimen?

. Cefazolin
. Cefuroxime
. Vancomycin
. Clindamycin and gentamycin
. Ampicillin-sulbactam

Correct Answer & Explanation

. Vancomycin

Explanation

In patients with a severe, IgE-mediated allergy (e.g., anaphylaxis, bronchospasm, hives) to penicillins, first- and second-generation cephalosporins (like cefazolin and cefuroxime) are generally contraindicated due to the risk of cross-reactivity. Vancomycin or Clindamycin are the standard evidence-based alternative prophylactic agents for joint arthroplasty in this scenario.

Question 13442

Topic: Biomechanics & Biomaterials

When a stainless steel plate is fixed with titanium screws in an orthopedic construct, accelerated localized corrosion may occur at the screw-plate interface over time. Which specific type of corrosion is primarily responsible for this degradation?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within a conductive fluid environment (body fluids). An electrochemical cell is created where the less noble metal acts as the anode and undergoes accelerated corrosion.

Question 13443

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is FDA-approved and primarily used as an adjunct for the treatment of acute, open tibial shaft fractures treated with an intramedullary nail?

. 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 acute, open tibial shaft fractures treated with an intramedullary nail. BMP-7 (rhBMP-7) is typically utilized as an alternative to autograft for recalcitrant long bone nonunions.

Question 13444

Topic: Biology, Genetics & Bone Healing

Secondary bone healing (callus formation) after a fracture is driven predominantly by which physiologic process?

. Intramembranous ossification
. Endochondral ossification
. Appositional ossification
. Creeping substitution
. Haversian remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary bone healing involves the formation of a cartilaginous callus that is subsequently mineralized and replaced by bone, a process known as endochondral ossification. Intramembranous ossification bypasses the cartilage phase and occurs in primary bone healing.

Question 13445

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a giant cell tumor extending into the metaphysis of the proximal tibia. Which targeted pharmacotherapy acts as an effective adjuvant treatment for aggressive or unresectable disease?

. Imatinib
. Denosumab
. Bisphosphonates
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab, a monoclonal antibody against RANKL, is highly effective in treating Giant Cell Tumor of Bone (GCTB). It inhibits the RANK-RANKL interaction, effectively suppressing the activation of the osteoclast-like giant cells.

Question 13446

Topic: 1. General Principles & Basic Science
Ultra-high-molecular-weight polyethylene (UHMWPE) wear debris in total joint arthroplasty primarily leads to osteolysis through the initial activation of which cell type?
. Osteoblasts
. T-lymphocytes
. Macrophages
. Fibroblasts
. Chondrocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose particulate UHMWPE wear debris, triggering an inflammatory cascade. They release cytokines (such as TNF-alpha, IL-1, and IL-6) that subsequently recruit and activate osteoclasts, leading to periprosthetic osteolysis.

Question 13447

Topic: 1. General Principles & Basic Science

A 70-year-old male undergoes a lumbar decompressive laminectomy. During the procedure, the dura is inadvertently torn, resulting in a cerebrospinal fluid (CSF) leak which is primarily repaired. What is the best immediate postoperative management?

. Immediate revision surgery with fascial grafting
. Placement of a subarachnoid lumbar drain
. Strict bed rest with the head of the bed flat for 24-48 hours
. High-dose intravenous corticosteroids
. Early aggressive mobilization and standing

Correct Answer & Explanation

. Strict bed rest with the head of the bed flat for 24-48 hours

Explanation

Following a primary repair of an incidental durotomy, keeping the patient flat for 24-48 hours decreases hydrostatic pressure on the dural repair, minimizing the risk of a persistent CSF leak. Lumbar drains are typically reserved for refractory or unrepairable leaks.

Question 13448

Topic: Biology, Genetics & Bone Healing

A 40-year-old male undergoes open reduction and internal fixation of a radius fracture with a dynamic compression plate. Which type of bone healing is expected to primarily occur at the fracture site?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with callus formation
. Chondroid metaplasia

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Rigid internal fixation with absolute stability, such as dynamic compression plating, suppresses callus formation and promotes primary (Haversian) bone healing. This process relies on osteoclast cutting cones crossing the fracture site followed by osteoblast bone deposition.

Question 13449

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with an enlarging hat size and progressively worsening right thigh pain. Radiographs of the femur show cortical thickening, coarse trabeculae, and bowing. Laboratory tests reveal an isolated, significantly elevated alkaline phosphatase. Which of the following is the primary cellular defect in this condition?

. Defective osteoid mineralization by osteoblasts
. Excessive osteoclastic bone resorption followed by disorganized osteoblastic bone formation
. Mutations in the type I collagen gene
. Autoimmune destruction of articular cartilage
. Overproduction of parathyroid hormone

Correct Answer & Explanation

. Excessive osteoclastic bone resorption followed by disorganized osteoblastic bone formation

Explanation

The patient has Paget disease of bone, characterized by an initial phase of excessive osteoclast activity followed by a compensatory, but disorganized, osteoblast response. This results in structurally weak woven bone that is prone to deformity and fracture.

Question 13450

Topic: Surgical Anatomy & Approaches

A 35-year-old male sustains a midshaft humeral fracture and immediately presents with an inability to extend his wrist or fingers. He undergoes closed management in a Sarmiento brace. At 12 weeks, there is no clinical or electromyographic (EMG) evidence of nerve recovery. What is the most appropriate next step?

. Continue bracing and re-evaluate at 6 months
. Order a high-resolution MRI of the brachial plexus
. Surgical exploration of the radial nerve
. Tendon transfers for wrist and finger extension
. Switch to operative fixation of the humerus

Correct Answer & Explanation

. Surgical exploration of the radial nerve

Explanation

Most radial nerve palsies associated with closed humeral shaft fractures resolve spontaneously. However, if there is no clinical or EMG evidence of recovery by 3 to 4 months, surgical exploration of the nerve is indicated.

Question 13451

Topic: Biology, Genetics & Bone Healing

A 60-year-old woman presents with severe back pain. Radiographs reveal a compression fracture of L2 and multiple punched-out lytic lesions in her skull. Serum protein electrophoresis shows a monoclonal spike. Which of the following is the most likely mechanism of osteolysis in this patient?

. Production of PTH-related peptide (PTHrP) by tumor cells
. Direct enzymatic degradation of bone by plasma cells
. Tumor secretion of RANK ligand (RANKL) and IL-6 stimulating osteoclasts
. Deposition of amyloid fibrils in the osteoid matrix
. Mutation in the FGFR3 gene

Correct Answer & Explanation

. Tumor secretion of RANK ligand (RANKL) and IL-6 stimulating osteoclasts

Explanation

Multiple myeloma causes osteolytic lesions primarily through the secretion of factors like RANKL, IL-6, and MIP-1 alpha by myeloma cells. These factors potently stimulate osteoclastogenesis while inhibiting osteoblast function.

Question 13452

Topic: 1. General Principles & Basic Science

Articular cartilage has a limited capacity for repair following injury. Which of the following zones of articular cartilage contains the highest concentration of proteoglycans and the lowest concentration of water?

. 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 has the highest proteoglycan content and the lowest water content. Conversely, the superficial zone has the highest water content and collagen concentration but the lowest proteoglycan content.

Question 13453

Topic: Infection, Pharmacology & VTE

A 45-year-old farmer sustains an open tibia fracture highly contaminated with soil. He is given broad-spectrum antibiotics and undergoes emergent irrigation and debridement. Which specific antibiotic should be added to his regimen to cover the most likely atypical pathogen associated with this environment?

. Vancomycin
. Ceftriaxone
. High-dose Penicillin
. Gentamicin
. Clindamycin

Correct Answer & Explanation

. High-dose Penicillin

Explanation

Farm injuries or fractures heavily contaminated with soil are at high risk for Clostridium perfringens infection. High-dose penicillin is added to the standard broad-spectrum regimen to provide specific coverage against these anaerobic, spore-forming bacteria.

Question 13454

Topic: Surgical Anatomy & Approaches

A 35-year-old male sustains a spiral fracture of the distal third of the humerus. On presentation, he lacks active wrist and thumb extension. He undergoes closed reduction and splinting. At 12 weeks, there is no clinical or electromyographic (EMG) evidence of radial nerve recovery. What is the most appropriate next step in management?

. Continue observation for an additional 12 weeks
. Nerve conduction studies at 6 months
. Tendon transfer surgery
. Surgical exploration of the radial nerve
. Ultrasound-guided perineural steroid injection

Correct Answer & Explanation

. Surgical exploration of the radial nerve

Explanation

A radial nerve palsy associated with a closed humeral shaft fracture typically warrants observation for 3 months. If there is no clinical or EMG evidence of recovery by 12 weeks, surgical exploration of the nerve is definitively indicated.

Question 13455

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, which growth factor is most directly responsible for the induction of angiogenesis during the transition from a soft cartilaginous callus to a hard bony callus?

. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-beta (TGF-beta)
. Vascular Endothelial Growth Factor (VEGF)
. Fibroblast Growth Factor (FGF)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Vascular Endothelial Growth Factor (VEGF)

Explanation

Vascular Endothelial Growth Factor (VEGF) is critical for angiogenesis during the transition from a hypoxic cartilaginous soft callus to an ossified hard callus. Inhibition of VEGF halts endochondral ossification and impairs fracture healing.

Question 13456

Topic: Biomechanics & Biomaterials

A 45-year-old male undergoes revision ORIF for a nonunion of the femur. The surgeon uses a stainless steel plate and titanium screws. Which of the following best describes the likely consequence of mixing these metals in vivo?

. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Pitting corrosion
. No adverse effect

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Mixing dissimilar metals with different anodic/cathodic potentials in an electrolytic environment (body fluid) leads to galvanic corrosion. Stainless steel and titanium have different potentials, making the stainless steel more susceptible to anodic dissolution when coupled with titanium.

Question 13457

Topic: 1. General Principles & Basic Science

What is the primary function of the superficial (tangential) zone of articular cartilage?

. Resisting compressive forces
. Resisting shear forces
. Anchoring cartilage to subchondral bone
. Providing a scaffold for chondrocyte hypertrophy
. Maximizing proteoglycan concentration

Correct Answer & Explanation

. Resisting shear forces

Explanation

The superficial (tangential) zone of articular cartilage consists of flattened chondrocytes and collagen fibers oriented parallel to the joint surface. Its primary biomechanical role is to resist shear forces. Compressive forces are primarily resisted by the middle and deep zones, where proteoglycan concentration is higher and collagen fibers are arranged vertically.

Question 13458

Topic: Biology, Genetics & Bone Healing

A 65-year-old female presents with generalized bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). A bone biopsy would most likely show which of the following?

. Decreased osteoclast activity
. Decreased osteoblast activity
. Increased unmineralized osteoid
. Normal bone mineralization with decreased bone mass
. Mosaic pattern of lamellar bone

Correct Answer & Explanation

. Increased unmineralized osteoid

Explanation

The clinical and laboratory picture (low Ca, low PO4, high Alk Phos, high PTH) is classic for osteomalacia, often due to Vitamin D deficiency. Bone biopsy in osteomalacia typically shows increased unmineralized osteoid (wide osteoid seams) due to a defect in bone mineralization. 'Normal bone mineralization with decreased bone mass' describes osteoporosis, and a 'mosaic pattern' is indicative of Paget's disease.

Question 13459

Topic: 1. General Principles & Basic Science

Which modification to a cortical screw design will most significantly increase its pullout strength?

. Decreasing the outer diameter
. Increasing the inner root diameter
. Decreasing the thread pitch
. Increasing the core diameter
. Decreasing the thread depth

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength of a screw is directly related to the outer diameter, thread depth, and thread density (number of threads per inch), and the shear strength of the host material. Decreasing the thread pitch increases the number of threads per unit length (higher thread density), thereby increasing the pullout strength.

Question 13460

Topic: Infection, Pharmacology & VTE

A 68-year-old male is scheduled for a total hip arthroplasty. He has a history of atrial fibrillation and is currently taking Rivaroxaban. According to current perioperative guidelines, when should the Rivaroxaban be discontinued prior to surgery?

. 12 hours prior
. 24 hours prior
. 3 days prior
. 5 days prior
. 7 days prior

Correct Answer & Explanation

. 3 days prior

Explanation

Rivaroxaban is a direct Factor Xa inhibitor. For major orthopedic surgery with a high bleeding risk, current guidelines generally recommend discontinuing Rivaroxaban 3 days (approx. 72 hours) prior to surgery in patients with normal renal function to allow for adequate drug clearance.

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