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1. General Principles & Basic Science MCQs

Practice Set 710 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 14181

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, primary (contact) bone healing via cutting cones requires which of the following mechanical environments?

. Absolute stability with local tissue strain less than 2%
. Relative stability with local tissue strain between 2% and 10%
. Absolute stability with local tissue strain between 2% and 10%
. Relative stability with local tissue strain less than 2%
. High strain environment greater than 10% promoting initial callus formation

Correct Answer & Explanation

. Absolute stability with local tissue strain less than 2%

Explanation

Primary bone healing occurs without callus formation and relies on direct Haversian remodeling (cutting cones). This biologic process can only occur under conditions of absolute stability, requiring an interfragmentary strain of less than 2%.

Question 14182

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a highly organized structure for its biomechanical properties. Which zone of articular cartilage is characterized by collagen fibrils oriented perpendicular to the joint surface and contains the highest concentration of proteoglycans?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It is characterized by perpendicularly oriented collagen fibers and the highest concentration of proteoglycans (and lowest water content) of any uncalcified zone.

Question 14183

Topic: Biomechanics & Biomaterials

An orthopedic surgeon utilizes a stainless steel screw to secure a titanium plate during open reduction internal fixation of a diaphyseal fracture. Postoperatively, the patient develops localized failure and rapid degradation at the screw-plate interface. This failure is primarily due to which phenomenon?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic/cathodic indices (e.g., stainless steel and titanium) are placed in direct physical contact within a conductive fluid environment like the human body. This accelerates the electrochemical breakdown of the less noble metal.

Question 14184

Topic: Biomechanics & Biomaterials

A 65-year-old male undergoes a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following best describes the primary mechanism by which highly cross-linked polyethylene reduces wear compared to conventional polyethylene?

. Decreased adhesive wear through free radical elimination
. Increased resistance to abrasive wear by increasing the elastic modulus
. Decreased adhesive wear by reducing the number of amorphous regions
. Increased resistance to third-body wear through strain hardening
. Decreased abrasive and adhesive wear due to restricted polymer chain mobility

Correct Answer & Explanation

. Decreased abrasive and adhesive wear due to restricted polymer chain mobility

Explanation

Highly cross-linked polyethylene reduces wear by restricting polymer chain mobility, which minimizes plastic deformation and alignment under stress. This significantly decreases both adhesive and abrasive wear, though it also reduces fatigue strength.

Question 14185

Topic: 1. General Principles & Basic Science

In the early stages of osteoarthritis, which of the following represents the most characteristic biochemical change in the articular cartilage matrix?

. Decreased water content and increased proteoglycan concentration
. Increased water content and decreased proteoglycan concentration
. Decreased water content and decreased collagen synthesis
. Increased water content and increased proteoglycan concentration
. Unaltered water content with increased type II collagen breakdown

Correct Answer & Explanation

. Increased water content and decreased proteoglycan concentration

Explanation

The earliest biochemical change in osteoarthritis is the disruption of the collagen network, which allows the tissue to swell, resulting in increased water content. Concurrently, there is a depletion of proteoglycans as they are degraded and lost into the synovial fluid.

Question 14186

Topic: Biomechanics & Biomaterials

A patient presents with pain and a sterile effusion 5 years after receiving a modular total hip arthroplasty with a cobalt-chromium head and a titanium femoral stem. Aspirate reveals dark fluid and metal debris. What type of corrosion is most likely occurring at the head-neck junction?

. Pitting corrosion
. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Uniform corrosion

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at modular junctions like the head-neck taper due to micromotion disrupting the protective oxide layer. This is often combined with crevice corrosion in a process termed mechanically assisted crevice corrosion (MACC).

Question 14187

Topic: 1. General Principles & Basic Science

During arthroscopic rotator cuff repair, a surgeon aims to optimize tendon-to-bone healing. Which of the following describes the ideal biologic progression of primary healing at the repair site?

. Direct formation of Sharpey fibers without an intermediate fibrovascular scar
. Formation of a fibrovascular interface followed by progressive remodeling into a distinct tidemark
. Endochondral ossification of the tendon edge bridging to the cancellous bone
. Intramembranous ossification originating from the bursal side of the tendon
. Avascular necrosis of the tendon stump followed by creeping substitution

Correct Answer & Explanation

. Formation of a fibrovascular interface followed by progressive remodeling into a distinct tidemark

Explanation

Tendon-to-bone healing after rotator cuff repair typically occurs via secondary healing, initially forming a fibrovascular scar that remodels over months. Direct regeneration of the native four-zone enthesis is rarely fully achieved.

Question 14188

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) induce bone formation primarily by signaling through which of the following intracellular pathways?

. Wnt/beta-catenin pathway
. RANK/RANKL pathway
. JAK/STAT pathway
. Smad 1/5/8 pathway
. cAMP/PKA pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate and activate intracellular Smad proteins (specifically Smad 1, 5, and 8). These form a complex to enter the nucleus and regulate transcription of osteogenic genes.

Question 14189

Topic: 1. General Principles & Basic Science

Which of the following best describes the incorporation process of a structural cortical bone allograft compared to a cancellous autograft?

. Faster revascularization and higher early mechanical strength
. Initial osteoblastic formation followed by slow osteoclastic resorption
. Initial osteoclastic resorption leading to temporary structural weakness
. Relies primarily on osteoinduction driven by native BMPs
. Independent of creeping substitution

Correct Answer & Explanation

. Initial osteoclastic resorption leading to temporary structural weakness

Explanation

Structural cortical allografts undergo initial osteoclastic resorption causing temporary mechanical weakness before new bone formation. Cancellous grafts incorporate faster via creeping substitution with early osteoblastic activity.

Question 14190

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone is responsible for the highest resistance to shear stress due to its specific collagen fiber orientation?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone contains collagen fibers arranged parallel to the joint surface. This specific orientation provides the highest resistance to shear forces within the joint.

Question 14191

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel plate with titanium screws for fracture fixation. Which of the following types of corrosion is most likely to occur at the screw-plate interface?

. Fretting corrosion
. Galvanic corrosion
. Crevice corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals, such as stainless steel and titanium, are placed in contact within an electrolytic solution (body fluid). The less noble metal (stainless steel) acts as an anode and preferentially corrodes.

Question 14192

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size and bilateral thigh pain. Laboratory studies show markedly elevated alkaline phosphatase with normal calcium and phosphorus. What is the primary cellular defect in this condition?

. Impaired osteoid mineralization
. Hyperactive, multinucleated osteoclasts
. Decreased osteoblastic bone formation
. Defective Type I collagen synthesis
. Parathyroid adenoma

Correct Answer & Explanation

. Hyperactive, multinucleated osteoclasts

Explanation

Paget disease of bone is driven by primary hyperactive, multinucleated osteoclasts leading to chaotic bone resorption. This is followed by disorganized osteoblastic bone formation, resulting in weak woven bone.

Question 14193

Topic: Infection, Pharmacology & VTE
A 45-year-old farmer sustains a highly contaminated Gustilo-Anderson Grade IIIA open tibia fracture from a tractor rollover. According to evidence-based guidelines, which antibiotic regimen is most appropriate for initial management?
. Cefazolin alone
. Cefazolin and gentamicin
. Cefazolin, gentamicin, and penicillin
. Vancomycin and ceftriaxone
. Clindamycin alone

Correct Answer & Explanation

. Cefazolin, gentamicin, and penicillin

Explanation

For farm injuries with gross soil contamination, high-dose penicillin is added to a first-generation cephalosporin and an aminoglycoside. This provides necessary coverage for Clostridium species to prevent gas gangrene.

Question 14194

Topic: Infection, Pharmacology & VTE

A 60-year-old male presents with a swollen, acutely painful knee. Synovial fluid aspiration reveals a white blood cell count of 65,000 cells/mm3 with 85% polymorphonuclear leukocytes. Crystals are absent. What is the most likely diagnosis?

. Osteoarthritis
. Rheumatoid arthritis flare
. Gouty arthropathy
. Septic arthritis
. Lyme arthritis

Correct Answer & Explanation

. Septic arthritis

Explanation

A synovial fluid WBC count greater than 50,000 cells/mm3 with a high percentage of PMNs strongly suggests septic arthritis. The absence of crystals further lowers the likelihood of gout or pseudogout.

Question 14195

Topic: 1. General Principles & Basic Science
During the remodeling phase of ligament healing, which biochemical transition is most responsible for the gradual increase in tensile strength?
. Replacement of Type I collagen with Type III collagen
. Replacement of Type III collagen with Type I collagen
. Increased proteoglycan synthesis
. Transition from cellular to acellular matrix
. Upregulation of matrix metalloproteinases

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

During the remodeling phase, the initially deposited disorganized Type III collagen is gradually replaced by stronger, highly cross-linked Type I collagen. This transition is essential for restoring the ligament's tensile strength.

Question 14196

Topic: 1. General Principles & Basic Science
Following a peripheral nerve transection injury, Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for clearing myelin debris and guiding regenerating axons in the peripheral nervous system?
. Astrocytes
. Oligodendrocytes
. Schwann cells
. Microglia
. Fibroblasts

Correct Answer & Explanation

. Schwann cells

Explanation

In the peripheral nervous system, Schwann cells are crucial for clearing myelin debris and forming the Bands of Bรผngner. These bands create a supportive microenvironment that guides regenerating axonal sprouts.

Question 14197

Topic: Biology, Genetics & Bone Healing

A 70-year-old female presents with severe back pain and a purely lytic lesion in the L3 vertebral body. Laboratory tests show anemia and hypercalcemia. Which of the following mechanisms is responsible for the bone destruction in this disease?

. Direct tumor cell phagocytosis of bone
. Osteoblast inhibition via decreased Wnt signaling
. Secretion of osteoclast-activating factors (e.g., RANKL) by myeloma cells
. Ectopic parathyroid hormone (PTH) secretion
. Defective osteoid mineralization due to Bence Jones proteins

Correct Answer & Explanation

. Secretion of osteoclast-activating factors (e.g., RANKL) by myeloma cells

Explanation

Multiple myeloma cells secrete osteoclast-activating factors such as RANKL, MIP-1 alpha, and IL-6, which stimulate rampant osteoclastic bone resorption. Concurrently, they inhibit osteoblast activity, resulting in purely lytic bone lesions.

Question 14198

Topic: Biomechanics & Biomaterials

A 55-year-old female undergoes a revision total hip arthroplasty. During the procedure, the surgeon utilizes a stainless steel cerclage wire around a titanium femoral stem. Which type of corrosion is most likely to occur at the interface of these two different metals?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within a conductive fluid environment, leading to an electrochemical gradient. The less noble metal (stainless steel) acts as the anode and corrodes preferentially.

Question 14199

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with a 12-year history of alendronate use presents with sudden onset thigh pain after a minor misstep. Radiographs demonstrate lateral cortical thickening and a transverse fracture with a medial spike in the subtrochanteric region. What is the primary pathophysiologic mechanism of this specific fracture type?

. Osteoclast overactivity
. Severe generalized osteopenia
. Suppression of targeted bone remodeling
. Hyperparathyroidism
. Vitamin D deficiency

Correct Answer & Explanation

. Suppression of targeted bone remodeling

Explanation

Long-term bisphosphonate use heavily suppresses osteoclast function, leading to a suppression of targeted bone remodeling. This prevents the normal repair of skeletal microdamage, resulting in the accumulation of microcracks and eventual atypical femur fractures.

Question 14200

Topic: Surgical Anatomy & Approaches

A 25-year-old male sustains a closed, isolated midshaft humerus fracture and is treated non-operatively with a functional fracture brace. At his 12-week follow-up, the fracture is radiographically healing, but he demonstrates an inability to actively extend his wrist or digits. Finger flexion and intrinsic function are normal. What is the most appropriate next step in management?

. Immediate surgical nerve exploration
. EMG/NCS and continued observation
. Tendon transfers for radial nerve palsy
. Upper extremity MRI
. Open reduction internal fixation of the humerus

Correct Answer & Explanation

. EMG/NCS and continued observation

Explanation

Secondary radial nerve palsy or palsy failing to recover by 12 weeks during conservative management warrants an EMG/NCS to establish a baseline and determine if reinnervation is occurring. Continued observation is generally appropriate for up to 3 to 6 months before considering surgical exploration.

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