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1. General Principles & Basic Science MCQs

Practice Set 717 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 14321

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate, are first-line treatments for osteoporosis. At the cellular level, what is the principal mechanism by which they decrease bone resorption?

. Inhibition of farnesyl pyrophosphate synthase
. Direct stimulation of osteoblast differentiation
. Competitive binding and neutralization of RANKL
. Irreversible inhibition of osteoclast proton pumps
. Direct activation of the calcium-sensing receptor

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase, a key enzyme in the mevalonate pathway. This disruption prevents the prenylation of small GTPases that are essential for osteoclast function and survival, ultimately leading to osteoclast apoptosis.

Question 14322

Topic: 1. General Principles & Basic Science

Normal articular cartilage possesses remarkable biomechanical properties to withstand physiological joint loads. The cartilage matrix derives its ability to resist high compressive loads primarily from which of its structural components?

. The highly oriented Type II collagen network
. The interaction between aggrecan and water molecules
. The spatial orientation of Type I collagen fibrils
. The rapid metabolic activity of deep zone chondrocytes
. The dense tangential fibers of the superficial zone

Correct Answer & Explanation

. The interaction between aggrecan and water molecules

Explanation

The compressive stiffness of articular cartilage is primarily due to the osmotic swelling pressure generated by highly negatively charged aggrecan (proteoglycan) molecules drawing water into the tissue matrix. The Type II collagen network primarily functions to resist tensile and shear forces.

Question 14323

Topic: Biomechanics & Biomaterials

In the context of internal fixation biomechanics, maximizing the radius of a solid intramedullary nail will increase its torsional rigidity by a factor proportional to the radius raised to what power?

. First power
. Second power
. Third power
. Fourth power
. Fifth power

Correct Answer & Explanation

. Fourth power

Explanation

The torsional rigidity of a solid cylindrical implant is determined by its polar moment of inertia, which is proportional to the radius raised to the fourth power (r^4). Therefore, even a small increase in the nail diameter dramatically enhances its resistance to torsional deformation.

Question 14324

Topic: Biology, Genetics & Bone Healing

Following rigid internal fixation of a transverse radius fracture with a dynamic compression plate resulting in absolute stability, successful bone healing occurs primarily via which of the following biological mechanisms?

. Endochondral ossification
. Intramembranous ossification
. Primary osteonal reconstruction
. Robust fibrocartilage callus formation
. Woven bone apposition without remodeling

Correct Answer & Explanation

. Primary osteonal reconstruction

Explanation

Absolute stability minimizes interfragmentary strain (keeping it under 2%), which suppresses external callus formation and allows for primary bone healing. This process involves direct osteonal reconstruction across the fracture gap via the advancement of cutting cones.

Question 14325

Topic: 1. General Principles & Basic Science

During an electromyography (EMG) evaluation of a patient with a traumatic peripheral nerve injury, the presence of fibrillation potentials and positive sharp waves typically indicates which of the following neural states?

. Normal resting skeletal muscle activity
. Early signs of successful axonal reinnervation
. Active axonal denervation
. A pure demyelinating conduction block without axonal loss
. Normal motor unit action potential recruitment

Correct Answer & Explanation

. Active axonal denervation

Explanation

Fibrillation potentials and positive sharp waves represent spontaneous, spontaneous electrical discharges of individual denervated muscle fibers. They are the classic electromyographic hallmark of active axonal denervation, typically appearing 2 to 3 weeks after the initial nerve injury.

Question 14326

Topic: Biology, Genetics & Bone Healing

A patient with end-stage renal disease presents with intractable bone pain. Laboratory evaluation reveals hypocalcemia, hyperphosphatemia, and markedly elevated parathyroid hormone (PTH). The most likely advanced skeletal manifestation in this patient is characterized histologically by:

. Defective mineralization of osteoid leading to widened growth plates
. Increased osteoid volume with severe peritrabecular marrow fibrosis
. Woven bone replacement associated with absent osteoclastic activity
. Normal bone turnover kinetics with globally decreased mineralization
. Pure osteomalacia with a marked decrease in unmineralized osteoid

Correct Answer & Explanation

. Increased osteoid volume with severe peritrabecular marrow fibrosis

Explanation

This patient exhibits secondary hyperparathyroidism as a result of advanced renal osteodystrophy. The classic advanced histologic finding is osteitis fibrosa cystica, which is characterized by profoundly increased bone turnover, osteoclastic resorption, and pathognomonic peritrabecular marrow fibrosis.

Question 14327

Topic: Infection, Pharmacology & VTE

During the development of a periprosthetic joint infection, biofilm formation protects the offending bacteria from host immune defenses and systemic antibiotics. What is the initiating biological step in the formation of a bacterial biofilm on an orthopedic implant?

. Maturation of the extracellular polymeric substance
. Irreversible adhesion of sessile bacterial colonies
. Reversible attachment of planktonic bacteria to the surface
. Quorum sensing activation and subsequent bacterial dispersal
. Enzymatic degradation of the host-derived glycocalyx

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria to the surface

Explanation

Biofilm formation is a sequential process that begins with the reversible attachment of free-floating (planktonic) bacteria to the implant surface. This initial stage is followed by irreversible adhesion, extracellular matrix production, structural maturation, and eventual bacterial dispersal.

Question 14328

Topic: Biomechanics & Biomaterials

During hardware removal, a surgeon notes significant degradation around a stainless steel screw that was inadvertently placed through a titanium plate. This accelerated localized degradation is primarily an example of which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct electrical contact within an electrolytic physiological fluid. The metal with the lower electrochemical potential (more anodic) corrodes at an accelerated rate, while the more cathodic metal is protected.

Question 14329

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently utilized for the fixation of total joint arthroplasty components. Which of the following statements is true regarding its fundamental biomechanical properties and clinical function?

. It acts as a true adhesive, bonding chemically directly to the surrounding bone
. It possesses its highest strength in tension and its lowest strength in compression
. It functions purely as a mechanical grout to evenly distribute compressive loads
. It undergoes significant volumetric expansion during the exothermic polymerization phase
. It promotes direct cellular osseointegration over its long-term lifespan

Correct Answer & Explanation

. It functions purely as a mechanical grout to evenly distribute compressive loads

Explanation

PMMA bone cement does not possess true adhesive properties; rather, it acts as a mechanical grout that creates an interlocking fit with the cancellous bone to transfer and distribute compressive loads. It is mechanically strongest in compression and highly vulnerable to failure under tension and shear forces.

Question 14330

Topic: Physiology & Rehabilitation

Understanding the dynamic joint reaction forces across the hip is critical for arthroplasty design and rehabilitation. During a normal gait cycle, the greatest joint reaction force across the hip occurs during which specific phase?

. Heel strike
. Mid-stance
. Toe-off
. Mid-swing
. Terminal swing

Correct Answer & Explanation

. Mid-stance

Explanation

The maximum joint reaction forces across the hip joint occur during the stance phase, particularly around mid-stance. During this phase, the abductor musculature must fire forcefully to balance the pelvis against the body weight, generating forces that can exceed three times body weight.

Question 14331

Topic: Infection, Pharmacology & VTE

Deep vein thrombosis (DVT) prophylaxis is a critical component of postoperative orthopedic care. Which of the following commonly utilized oral prophylactic agents exerts its anticoagulant effect via direct, reversible inhibition of thrombin (Factor IIa)?

. Rivaroxaban
. Apixaban
. Dabigatran
. Warfarin
. Enoxaparin

Correct Answer & Explanation

. Dabigatran

Explanation

Dabigatran is a direct oral anticoagulant (DOAC) that specifically and reversibly binds to and inhibits the active site of thrombin (Factor IIa). In contrast, rivaroxaban and apixaban exert their anticoagulant effects by directly inhibiting Factor Xa.

Question 14332

Topic: 1. General Principles & Basic Science

Which enzyme is primarily secreted by the osteoclast ruffled border to degrade the organic matrix of bone?

. Alkaline phosphatase
. Cathepsin K
. Tartrate-resistant acid phosphatase
. Carbonic anhydrase II
. Matrix metalloproteinase-3

Correct Answer & Explanation

. Cathepsin K

Explanation

Osteoclasts secrete hydrogen ions via carbonic anhydrase to dissolve the inorganic hydroxyapatite. Once the mineral is dissolved, Cathepsin K is secreted to degrade the organic type I collagen matrix.

Question 14333

Topic: Biomechanics & Biomaterials

A surgeon places a titanium screw through a stainless steel plate. What type of corrosion is most likely to occur at the interface of these two metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in a conductive fluid, creating an electrochemical gradient. The less noble metal acts as an anode and selectively corrodes.

Question 14334

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with a bowing deformity of his tibia and an elevated serum alkaline phosphatase. A bone biopsy reveals a mosaic pattern of lamellar bone. What is the primary cellular defect initiating this condition?

. Decreased osteoblast activity
. Hyperactive osteoclasts with multiple nuclei
. Defective mineralization of osteoid
. Abnormal type I collagen synthesis
. Monoclonal plasma cell proliferation

Correct Answer & Explanation

. Hyperactive osteoclasts with multiple nuclei

Explanation

Paget's disease is initiated by an intensely osteolytic phase driven by hyperactive, highly multinucleated osteoclasts. This is followed by a mixed phase of disorganized osteoblast activity, resulting in the classic mosaic woven and lamellar bone pattern.

Question 14335

Topic: 1. General Principles & Basic Science

Which of the following screw design modifications will most effectively increase the pullout strength of a cortical screw?

. Increasing the core diameter
. Increasing the thread pitch
. Decreasing the thread pitch
. Increasing the screw head diameter
. Decreasing the outer diameter

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the outer diameter, length of thread engagement, and thread density. Decreasing the thread pitch increases the number of threads engaged in the bone, maximizing pullout strength.

Question 14336

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its primary mechanism of action?
. Direct inhibition of factor Xa
. Competitive inhibition of plasminogen activation
. Irreversible inhibition of cyclooxygenase
. Activation of antithrombin III
. Cross-linking of fibrin monomers

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

TXA is a synthetic analog of the amino acid lysine. It reversibly binds to plasminogen, preventing its conversion to plasmin, thereby competitively inhibiting fibrin degradation and stabilizing clots.

Question 14337

Topic: Surgical Anatomy & Approaches

A 30-year-old sustains a closed midshaft humerus fracture with an immediate complete radial nerve palsy. At what time point after the injury will electromyography (EMG) first show fibrillation potentials in the brachioradialis muscle?

. Immediately after injury
. 3 to 5 days
. 2 to 3 weeks
. 6 to 8 weeks
. 3 months

Correct Answer & Explanation

. 2 to 3 weeks

Explanation

Wallerian degeneration occurs distal to the site of nerve injury but takes time to manifest electrically in the muscle. Fibrillation potentials and positive sharp waves, indicating active muscle denervation, typically first appear on EMG 2 to 3 weeks post-injury.

Question 14338

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, Staphylococcus epidermidis evades the host immune system and antibiotics primarily through biofilm formation. What is the major structural component of this biofilm?

. Peptidoglycan
. Lipopolysaccharide
. Polysaccharide intercellular adhesin (PIA)
. Teichoic acid
. Hyaluronic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix produced by Staphylococcus epidermidis is primarily composed of poly-N-acetylglucosamine, commonly known as polysaccharide intercellular adhesin (PIA). This protective glycocalyx severely limits antibiotic penetration and efficacy.

Question 14339

Topic: 1. General Principles & Basic Science
During the normal phases of tendon healing, which biochemical change during the remodeling phase is primarily responsible for the increased tensile strength of the tissue?
. Replacement of Type I collagen with Type III collagen
. Increased synthesis of extracellular proteoglycans
. Transition of Type III collagen to Type I collagen
. Proliferation of inflammatory macrophages
. Increased overall water content of the tendon

Correct Answer & Explanation

. Transition of Type III collagen to Type I collagen

Explanation

The initial reparative phase deposits a highly cellular matrix predominantly consisting of weaker Type III collagen. During the remodeling phase, Type III collagen is gradually replaced by stronger Type I collagen, which cross-links and aligns along the axis of tension.

Question 14340

Topic: Biology, Genetics & Bone Healing

In rheumatoid arthritis, progressive destruction of subchondral bone is driven by hypertrophic synovial tissue known as pannus. Which cell type in the pannus is primarily responsible for driving osteoclastogenesis via high RANKL expression?

. Chondrocytes
. Fibroblast-like synoviocytes
. B lymphocytes
. Neutrophils
. Osteoblasts

Correct Answer & Explanation

. Fibroblast-like synoviocytes

Explanation

Fibroblast-like synoviocytes (FLS) and activated T-cells within the rheumatoid pannus produce massive amounts of RANKL. This stimulates the differentiation and activation of osteoclasts, leading to the hallmark periarticular bone erosions.

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