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1. General Principles & Basic Science MCQs

Practice Set 696 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 13901

Topic: Biology, Genetics & Bone Healing

A 6-year-old child presents with bowed legs, widening of the physes, and metaphyseal cupping on radiographs. The primary pathophysiological defect in this condition involves:

. Defective synthesis of Type I collagen
. Failure of osteoid mineralization
. Impaired osteoclast ruffled border formation
. Defective hydroxylation of proline
. Mutation in the FGFR3 gene

Correct Answer & Explanation

. Failure of osteoid mineralization

Explanation

This presentation is classic for Rickets, which is characterized by a failure of mineralization of newly formed osteoid and growing cartilage matrix. Defective Type I collagen is seen in Osteogenesis Imperfecta, while defective hydroxylation occurs in Scurvy.

Question 13902

Topic: Biology, Genetics & Bone Healing

Scurvy leads to weakened connective tissue and bone due to a deficiency in Vitamin C. This deficiency directly impairs which of the following intracellular processes in collagen synthesis?

. Cleavage of procollagen C-terminals
. Glycosylation of hydroxylysine
. Hydroxylation of proline and lysine residues
. Formation of disulfide bonds in tropocollagen
. Extracellular cross-linking by lysyl oxidase

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Vitamin C (ascorbic acid) is a required cofactor for prolyl hydroxylase and lysyl hydroxylase. Deficiency impairs the hydroxylation of proline and lysine residues, preventing the formation of stable triple-helical collagen molecules.

Question 13903

Topic: Biology, Genetics & Bone Healing

Osteoclastogenesis and subsequent bone resorption are primarily driven by the interaction of RANKL with its receptor, RANK. Which of the following proteins acts as a soluble decoy receptor to competitively inhibit this interaction?

. Cathepsin K
. Sclerostin
. Osteoprotegerin (OPG)
. Osteocalcin
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from binding to RANK on osteoclast precursors. This inhibits osteoclast differentiation and activation, thereby reducing bone resorption.

Question 13904

Topic: Biology, Genetics & Bone Healing

Denosumab is a pharmacological agent utilized in the treatment of osteoporosis and giant cell tumors of bone. Its mechanism of action most closely mimics which of the following endogenous molecules?

. Osteoprotegerin (OPG)
. Parathyroid hormone (PTH)
. Bisphosphonates
. Sclerostin
. Bone morphogenetic protein-2

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Denosumab is a monoclonal antibody that binds to and neutralizes RANKL, effectively mimicking the action of endogenous Osteoprotegerin (OPG). This prevents osteoclast activation and reduces bone turnover.

Question 13905

Topic: Biomechanics & Biomaterials

When mixing different metals in orthopedic implants, galvanic corrosion is a significant concern. Which of the following material combinations possesses the highest risk for severe galvanic corrosion in vivo?

. Titanium alloy and Cobalt-Chromium
. Stainless steel and Cobalt-Chromium
. Stainless steel and Titanium alloy
. Titanium alloy and Tantalum
. Ceramic and Titanium alloy

Correct Answer & Explanation

. Stainless steel and Titanium alloy

Explanation

Combining stainless steel and titanium alloy creates a strong electrochemical potential difference, leading to severe galvanic corrosion of the less noble metal (stainless steel). Titanium and cobalt-chromium can often be used together safely.

Question 13906

Topic: 1. General Principles & Basic Science

The primary nutritional supply for mature articular cartilage is derived via which of the following mechanisms?

. Direct arterial supply from subchondral vessels
. Capillary beds within the menisci
. Diffusion from synovial fluid
. Epiphyseal nutrient artery branches
. Venous retrograde flow

Correct Answer & Explanation

. Diffusion from synovial fluid

Explanation

Mature articular cartilage is avascular and relies entirely on the diffusion of nutrients and oxygen from the surrounding synovial fluid. This process is facilitated by cyclic loading and unloading of the joint.

Question 13907

Topic: Biology, Genetics & Bone Healing

Intermittent daily administration of teriparatide (recombinant human parathyroid hormone) exerts its beneficial effect on osteoporotic bone primarily by:

. Stimulating osteoclast apoptosis
. Inhibiting RANKL production
. Stimulating osteoblastic bone formation
. Directly mineralizing osteoid
. Increasing renal calcium excretion

Correct Answer & Explanation

. Stimulating osteoblastic bone formation

Explanation

While continuous high levels of PTH cause net bone resorption, intermittent daily administration of PTH analogs (like teriparatide) disproportionately stimulates osteoblast activity. This leads to a net increase in bone formation and mass.

Question 13908

Topic: Biomechanics & Biomaterials

During total joint arthroplasty, antibiotic-loaded polymethylmethacrylate (PMMA) bone cement is often utilized. To be effective and not compromise the cement properties, the chosen antibiotic must primarily be:

. Thermostable and available in powder form
. Highly protein-bound and liquid
. Thermolabile and bacteriostatic
. Anaerobic specific and granular
. Hydrophobic and available in liquid form

Correct Answer & Explanation

. Thermostable and available in powder form

Explanation

Antibiotics mixed into PMMA must be thermostable to survive the highly exothermic polymerization reaction of the cement. They must also be in powder form to allow uniform mixing and elution without severely compromising the cement's mechanical strength.

Question 13909

Topic: 1. General Principles & Basic Science

Following a primary flexor tendon repair, the repair site is biomechanically at its weakest point during which of the following postoperative timeframes?

. 1 to 3 days
. 5 to 21 days
. 4 to 6 weeks
. 8 to 10 weeks
. 12 to 16 weeks

Correct Answer & Explanation

. 5 to 21 days

Explanation

A repaired tendon is typically weakest between days 5 and 21 (the inflammatory to early fibroblastic phase) because the initial suture-holding capacity decreases before the new collagen framework gains significant tensile strength.

Question 13910

Topic: Biomechanics & Biomaterials

According to the principles of fracture biomechanics, how does increasing the distance between the near and far cortices at a fracture gap (increasing gap size) affect interfragmentary strain, assuming interfragmentary motion remains constant?

. Increases interfragmentary strain
. Decreases interfragmentary strain
. Has no effect on interfragmentary strain
. Eliminates all strain
. Reverses the strain direction

Correct Answer & Explanation

. Decreases interfragmentary strain

Explanation

Interfragmentary strain is defined as the change in gap length divided by the original gap length. Therefore, for a given amount of motion (change in length), increasing the original gap size mathematically decreases the overall strain.

Question 13911

Topic: 1. General Principles & Basic Science

A peripheral nerve injury is classified as axonotmesis (Sunderland second degree). Which of the following best describes the structural damage and expected recovery?

. Complete transection of the nerve requiring surgery
. Demyelination with intact axon and complete recovery
. Axonal disruption with intact endoneurium and predictable recovery
. Axonal and endoneurial disruption with unpredictable recovery
. Epineurial disruption with neuroma formation

Correct Answer & Explanation

. Axonal disruption with intact endoneurium and predictable recovery

Explanation

Axonotmesis involves Wallerian degeneration of the axon, but the supportive connective tissue (endoneurium) remains intact. This intact neural tube guides regenerating axons, leading to predictable and usually complete functional recovery.

Question 13912

Topic: Biomechanics & Biomaterials

A surgeon plans to revise a fractured femur using a titanium locking plate and stainless steel screws. What is the primary biomechanical and chemical risk of combining these two metals in vivo?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic fluid, causing an electrochemical potential difference. Using titanium and stainless steel together increases the risk of this specific type of corrosion, potentially leading to implant failure.

Question 13913

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone is characterized by the highest concentration of proteoglycans, lowest water content, and chondrocytes arranged in vertical columns?

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains vertically aligned chondrocytes and thick collagen fibrils oriented perpendicular to the joint line. It also holds the highest concentration of proteoglycans and the lowest water content of the uncalcified zones.

Question 13914

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum strain environment that allows for primary bone healing (direct osteonal remodeling) without intermediate callus formation?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which correlates to a tissue strain of less than 2%. Under these conditions, osteoclasts create cutting cones across the fracture followed immediately by osteoblasts laying down lamellar bone.

Question 13915

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is prescribed teriparatide. What is the primary mechanism of action of this medication?

. Inhibits osteoclast activity by binding to hydroxyapatite
. Binds RANK ligand to prevent osteoclast activation
. Recombinant PTH analog that stimulates osteoblast-mediated bone formation
. Selective estrogen receptor modulator that reduces bone resorption
. Sclerostin inhibitor that enhances Wnt signaling

Correct Answer & Explanation

. Recombinant PTH analog that stimulates osteoblast-mediated bone formation

Explanation

Teriparatide is a recombinant fragment of human parathyroid hormone (PTH 1-34). When administered via daily intermittent subcutaneous injections, it paradoxically acts as a potent anabolic agent by stimulating osteoblast activity over osteoclast activity.

Question 13916

Topic: 1. General Principles & Basic Science

Following an acute traumatic nerve transection (neurotmesis), Wallerian degeneration occurs in the distal stump. Which cell type is primarily responsible for clearing myelin debris and guiding regenerating axons?

. Fibroblasts
. Schwann cells
. Oligodendrocytes
. Astrocytes
. Macrophages

Correct Answer & Explanation

. Schwann cells

Explanation

Schwann cells, along with macrophages, play a critical role in Wallerian degeneration by clearing myelin debris. Schwann cells then align to form the bands of Bungner, which create endoneurial tubes that guide the regenerating axonal sprouts.

Question 13917

Topic: Infection, Pharmacology & VTE

A 45-year-old male presents with an acutely swollen knee. Synovial fluid analysis reveals a white blood cell count of 65,000 cells/mm3 with 85% polymorphonuclear leukocytes (PMNs), and a glucose level significantly lower than serum. What is the most likely diagnosis?

. Osteoarthritis
. Traumatic hemarthrosis
. Gout
. Septic arthritis
. Pigmented villonodular synovitis

Correct Answer & Explanation

. Septic arthritis

Explanation

Synovial fluid with a WBC count greater than 50,000 cells/mm3 (often >75% PMNs) and decreased glucose relative to serum is highly indicative of septic arthritis. Inflammatory arthropathies like gout typically present with WBC counts between 2,000 and 50,000 cells/mm3.

Question 13918

Topic: Biomechanics & Biomaterials

Stress shielding around a non-cemented total hip arthroplasty stem is primarily related to a mismatch in which of the following physical properties between the implant and native bone?

. Ultimate tensile strength
. Yield point
. Modulus of elasticity
. Fatigue strength
. Ductility

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Stress shielding occurs when a stiff implant bears the mechanical load instead of the surrounding bone, leading to adaptive osteopenia. This phenomenon is directly related to the mismatch in the modulus of elasticity (stiffness) between the metallic implant and the native bone.

Question 13919

Topic: Physiology & Rehabilitation

During a postoperative rehabilitation protocol, a patient uses a Cybex machine that maintains a constant speed of movement regardless of the force applied. What type of muscle contraction does this represent?

. Isometric
. Isotonic concentric
. Isotonic eccentric
. Isokinetic
. Plyometric

Correct Answer & Explanation

. Isokinetic

Explanation

Isokinetic exercises involve muscle contraction where the speed of movement is kept constant by a dynamometer machine throughout the range of motion. This allows for maximal mechanical resistance at every point in the arc of motion.

Question 13920

Topic: Infection, Pharmacology & VTE
According to recent guidelines for venous thromboembolism (VTE) prophylaxis following elective total joint arthroplasty in standard-risk patients, aspirin is considered non-inferior to other anticoagulants. What is the primary mechanism of action of aspirin?
. Direct factor Xa inhibition
. Direct thrombin inhibition
. Irreversible inhibition of cyclooxygenase (COX)
. Vitamin K epoxide reductase inhibition
. Activation of antithrombin III

Correct Answer & Explanation

. Irreversible inhibition of cyclooxygenase (COX)

Explanation

Aspirin acts by irreversibly inhibiting cyclooxygenase (COX-1 and COX-2) enzymes. This blocks the formation of thromboxane A2 in platelets, thereby producing a potent antiplatelet effect that lasts for the lifetime of the platelet (7-10 days).

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