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1. General Principles & Basic Science MCQs

Practice Set 695 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 13881

Topic: Surgical Anatomy & Approaches

When performing a total hip arthroplasty via the direct anterior approach (Smith-Petersen), the superficial surgical internervous plane is located between muscles supplied by which two nerves?

. Superior gluteal and inferior gluteal nerves
. Femoral and superior gluteal nerves
. Femoral and sciatic nerves
. Obturator and femoral nerves
. Superior gluteal and sciatic nerves

Correct Answer & Explanation

. Femoral and superior gluteal nerves

Explanation

The direct anterior approach utilizes an internervous plane between the sartorius (femoral nerve) and tensor fasciae latae (superior gluteal nerve). The deep plane continues between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 13882

Topic: 1. General Principles & Basic Science
Which of the following stages of tendon healing is characterized by the highest content of Type III collagen?
. Inflammatory phase
. Early proliferative (fibroblastic) phase
. Remodeling phase
. Maturation phase
. Degenerative phase

Correct Answer & Explanation

. Early proliferative (fibroblastic) phase

Explanation

During the early proliferative (or fibroblastic) phase of tendon healing, fibroblasts rapidly synthesize Type III collagen to bridge the tissue gap. Over time, during the remodeling phase, this is gradually replaced by stronger Type I collagen.

Question 13883

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, highly cross-linked polyethylene (XLPE) inserts significantly reduce wear rates. However, increasing the radiation dose during cross-linking has which of the following detrimental effects on the material properties?

. Increases the rate of oxidation
. Decreases the ultimate tensile strength and fatigue resistance
. Increases the coefficient of friction
. Decreases its biocompatibility
. Increases the modulus of elasticity significantly

Correct Answer & Explanation

. Decreases the ultimate tensile strength and fatigue resistance

Explanation

While highly cross-linked polyethylene drastically reduces volumetric wear, the radiation cross-linking process alters its mechanical properties. Higher radiation doses decrease ultimate tensile strength, yield strength, and fatigue resistance, increasing the risk of mechanical failure.

Question 13884

Topic: Biology, Genetics & Bone Healing

During normal bone remodeling, osteoclast differentiation and activation are primarily stimulated by the binding of RANKL to its receptor, RANK. Which of the following proteins acts as a decoy receptor to inhibit this interaction?

. Osteocalcin
. Osteopontin
. Sclerostin
. Osteoprotegerin (OPG)
. Cathepsin K

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is secreted by osteoblasts and binds to RANKL, preventing it from interacting with RANK on osteoclast precursors. This inhibits osteoclastogenesis and prevents excessive bone resorption.

Question 13885

Topic: Biomechanics & Biomaterials

In orthopedic implants, the combination of a stainless steel screw with a titanium plate can lead to early implant failure. What specific type of corrosion is most likely to occur in this scenario?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic medium, such as body fluid. The less noble metal undergoes accelerated corrosion due to the electrochemical potential difference.

Question 13886

Topic: Biology, Genetics & Bone Healing

In fracture fixation, increasing the working length of a bridging plate has which of the following biomechanical effects?

. Increases axial stiffness and increases torsional stiffness
. Decreases axial stiffness and decreases torsional stiffness
. Increases axial stiffness but decreases torsional stiffness
. Decreases axial stiffness but increases torsional stiffness
. Does not alter stiffness but increases yield strength

Correct Answer & Explanation

. Decreases axial stiffness and decreases torsional stiffness

Explanation

Increasing the working length of a plate decreases both its axial and torsional stiffness. This allows for increased interfragmentary motion, which promotes secondary bone healing via callus formation.

Question 13887

Topic: 1. General Principles & Basic Science

Following a complete peripheral nerve transection (neurotmesis), Wallerian degeneration occurs. At what rate does the regenerating axon typically grow after the initial latent period?

. 0.1 mm/day
. 1 mm/day
. 5 mm/day
. 10 mm/day
. 1 inch/day

Correct Answer & Explanation

. 1 mm/day

Explanation

After an initial latent period, axonal regeneration typically proceeds at a rate of approximately 1 mm per day (or about 1 inch per month). This is a vital metric for estimating the timeline of clinical recovery following nerve repair.

Question 13888

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute. Which of the following best describes its biological properties?

. Osteoconductive only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteogenic and osteoinductive
. Osteogenic, osteoinductive, and osteoconductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM retains bone morphogenetic proteins (BMPs) providing osteoinductive properties, and its matrix acts as an osteoconductive scaffold. However, because it is acellular and lacks live osteoblasts, it does not possess osteogenic properties.

Question 13889

Topic: 1. General Principles & Basic Science

Galvanic corrosion of orthopedic implants occurs primarily when:

. Two identical metals are subjected to cyclical loading
. A single metal undergoes fatigue failure from micro-motion
. Two dissimilar metals are in direct contact within an electrolytic environment
. Polyethylene wear debris induces a localized acidic environment
. Bacterial biofilms produce localized changes in pH on the metal surface

Correct Answer & Explanation

. Two dissimilar metals are in direct contact within an electrolytic environment

Explanation

Galvanic corrosion happens when two dissimilar metals (e.g., stainless steel and titanium) are in physical contact within the body's electrolytic fluid environment. This causes an electrochemical potential difference, leading to accelerated corrosion of the less noble metal.

Question 13890

Topic: Infection, Pharmacology & VTE

Methicillin-resistant Staphylococcus aureus (MRSA) is a major concern in prosthetic joint infections. Its resistance to beta-lactam antibiotics is primarily mediated by the mecA gene, which encodes for:

. Beta-lactamase enzymes that degrade the antibiotic
. Efflux pumps that actively remove the antibiotic from the cell
. An altered penicillin-binding protein (PBP2a) with low affinity for beta-lactams
. Porin channel modifications that prevent antibiotic entry
. Ribosomal methylation preventing antibiotic binding

Correct Answer & Explanation

. An altered penicillin-binding protein (PBP2a) with low affinity for beta-lactams

Explanation

The mecA gene encodes for PBP2a, an altered penicillin-binding protein that has a significantly reduced affinity for beta-lactam antibiotics. This structural change allows MRSA to maintain cell wall synthesis even in the presence of these drugs.

Question 13891

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis utilizing an Ilizarov frame, bone generation in the distraction gap primarily occurs via which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional bone growth
. Creeping substitution
. Osteonal remodeling

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Bone formation during distraction osteogenesis primarily occurs via intramembranous ossification, characterized by direct differentiation of mesenchymal stem cells into osteoblasts without a cartilaginous intermediate. Endochondral ossification requires a cartilage model and is classically seen in secondary fracture healing (callus formation).

Question 13892

Topic: Infection, Pharmacology & VTE

According to the original Kocher criteria, the presence of four specific factors yields a 99% probability of septic arthritis in a pediatric hip. Which of the following is NOT one of the original four criteria?

. History of fever > 38.5 degrees Celsius
. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate > 40 mm/hr
. C-reactive protein > 2.0 mg/dL
. Serum white blood cell count > 12,000 cells/mm3

Correct Answer & Explanation

. C-reactive protein > 2.0 mg/dL

Explanation

The original Kocher criteria include: fever > 38.5 C, inability to bear weight, ESR > 40 mm/hr, and WBC > 12,000/mm3. While later studies (such as by Caird et al.) demonstrated that a CRP > 2.0 mg/dL is a strong independent predictor of septic arthritis, it was not part of the original four Kocher criteria.

Question 13893

Topic: 1. General Principles & Basic Science

Which zone of normal articular cartilage is characterized by having the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibrils aligned parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains the highest water content, the lowest proteoglycan concentration, and densely packed type II collagen fibers aligned parallel to the articular surface to resist shear forces.

Question 13894

Topic: Biomechanics & Biomaterials

Which of the following metallic orthopaedic biomaterials has a modulus of elasticity that most closely approximates that of human cortical bone, thereby reducing the effect of stress shielding?

. Cobalt-chromium-molybdenum alloy
. Stainless steel (316L)
. Titanium alloy (Ti-6Al-4V)
. Tantalum
. Zirconium

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

The modulus of elasticity of cortical bone is approximately 15-20 GPa. Titanium alloys (approx. 110 GPa) are much closer to cortical bone than stainless steel (approx. 200 GPa) or cobalt-chromium alloys (approx. 220-240 GPa). This closer match helps minimize stress shielding. Tantalum has a very low modulus closer to cancellous bone (approx. 3 GPa).

Question 13895

Topic: Biology, Genetics & Bone Healing
The normal meniscus provides load distribution, shock absorption, and secondary stability to the knee. Which structural protein constitutes the vast majority (greater than 90%) of the organic dry weight of a normal meniscus?
. Type I collagen
. Type II collagen
. Type III collagen
. Type X collagen
. Aggrecan

Correct Answer & Explanation

. Type I collagen

Explanation

The meniscus is primarily composed of fibrocartilage, not hyaline cartilage. As such, type I collagen makes up > 90% of its collagen content, giving it high tensile strength. In contrast, hyaline articular cartilage is predominantly type II collagen.

Question 13896

Topic: Infection, Pharmacology & VTE
For postoperative deep vein thrombosis (DVT) prophylaxis following total joint arthroplasty, multiple oral anticoagulants are now utilized. Which of the following agents exerts its clinical effect by directly and selectively inhibiting Factor Xa?
. Warfarin
. Dabigatran
. Apixaban
. Clopidogrel
. Enoxaparin

Correct Answer & Explanation

. Apixaban

Explanation

Apixaban and Rivaroxaban are direct oral anticoagulants (DOACs) that work by directly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin inhibits vitamin K-dependent factors (II, VII, IX, X). Enoxaparin (LMWH) primarily potentiates Antithrombin III, which indirectly inhibits Factor Xa.

Question 13897

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, an interosseous ligament is held at a constant deformed length over an extended period. The observation that the internal tension within the ligament progressively decreases over time is defined as:

. Creep
. Hysteresis
. Stress relaxation
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where a tissue subjected to a constant displacement (length) exhibits a decrease in stress (tension) over time. In contrast, creep refers to progressive deformation over time under a constant load.

Question 13898

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, lamellar bone can only form when the interfragmentary strain at the fracture gap is below which of the following thresholds?

. 2%
. 10%
. 15%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that lamellar bone can only tolerate and form in environments with less than 2% strain. Granulation tissue tolerates up to 100% strain, while fibrocartilage can tolerate up to 10% strain.

Question 13899

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four distinct histological zones. Which zone possesses the highest concentration of water and collagen, but the lowest concentration of proteoglycans?

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

Correct Answer & Explanation

. Superficial zone

Explanation

The superficial zone of articular cartilage contains the highest water content (up to 80%) and collagen arranged parallel to the joint surface. It has the lowest concentration of proteoglycans compared to the deeper zones.

Question 13900

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials exhibits a modulus of elasticity most closely approximating that of cortical bone?

. Cobalt-chromium alloy
. Stainless steel 316L
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloys have a modulus of elasticity (approx. 110 GPa) that is closer to cortical bone (approx. 15-20 GPa) than stainless steel (200 GPa) or cobalt-chromium (220 GPa). This closer match reduces the risk of stress shielding.

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