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1. General Principles & Basic Science MCQs

Practice Set 244 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 4861

Topic: Biomechanics & Biomaterials
A new highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) acetabular liner is being evaluated for total hip arthroplasty. To reduce the risk of oxidative degradation while maintaining wear resistance, which of the following processes is most commonly utilized during manufacturing?
. Gamma irradiation in air
. Addition of vitamin C
. Doping with Vitamin E (alpha-tocopherol)
. Increasing the molecular weight above 10 million g/mol
. Cold drawing of the polymer

Correct Answer & Explanation

. Doping with Vitamin E (alpha-tocopherol)

Explanation

Vitamin E (alpha-tocopherol) acts as a free radical scavenger in highly cross-linked UHMWPE. This prevents oxidative degradation without the need for melting, which can otherwise decrease the mechanical strength of the polymer.

Question 4862

Topic: Biology, Genetics & Bone Healing

A novel biologic therapy targets the prevention of osteoclast-mediated bone resorption in metastatic bone disease by acting as a decoy receptor for a specific activating ligand. Which of the following endogenous molecules does this therapy functionally mimic?

. Receptor Activator of Nuclear Factor Kappa-B (RANK)
. RANK Ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is an endogenous decoy receptor that binds to RANKL, preventing it from interacting with RANK on osteoclasts. Medications like Denosumab mimic the action of OPG to inhibit osteoclastogenesis and bone resorption.

Question 4863

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone possesses the highest concentration of water and collagen, with collagen fibrils specifically aligned parallel to the joint surface to maximally resist shear stress?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone contains the highest water and collagen content. Its collagen fibrils are oriented parallel to the articular surface to resist shear forces.

Question 4864

Topic: 1. General Principles & Basic Science

A surgeon is evaluating the pull-out strength of cortical bone screws. According to basic biomechanical principles, the pull-out strength of a bone screw is most directly proportional to which of the following variables?

. Pitch of the screw
. Core diameter
. Outer (thread) diameter
. Length of the unthreaded shaft
. Screw head diameter

Correct Answer & Explanation

. Outer (thread) diameter

Explanation

Screw pull-out strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the bone. Conversely, it is inversely proportional to the pitch of the screw.

Question 4865

Topic: Physiology & Rehabilitation

During rehabilitation of a quadriceps tendon rupture, the physiotherapist emphasizes specific muscle contractions. According to muscle physiology, which type of muscle contraction generates the highest maximal tension within the muscle fibers?

. Isometric contraction
. Concentric isotonic contraction
. Eccentric isotonic contraction
. Isokinetic concentric contraction
. Tetanic contraction

Correct Answer & Explanation

. Eccentric isotonic contraction

Explanation

Eccentric contractions (muscle lengthening under tension) generate the highest maximal force compared to isometric or concentric contractions. This mechanism is crucial in deceleration activities and is frequently implicated in tendon ruptures.

Question 4866

Topic: Infection, Pharmacology & VTE

A patient develops a deep periprosthetic joint infection due to Staphylococcus epidermidis. The chronicity of this infection is primarily mediated by a protective biofilm. Which bacterial communication mechanism is most critical for coordinating the formation and maturation of this biofilm?

. Phagocytosis evasion
. Quorum sensing
. Chemotaxis
. Opsonization
. Plasmid conjugation

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is a cell-to-cell communication system based on bacterial population density. It regulates gene expression essential for biofilm maturation, allowing bacteria to adapt and survive against host defenses and antibiotics.

Question 4867

Topic: 1. General Principles & Basic Science
A patient sustains a peripheral nerve injury resulting in axonal disruption and endoneurial tube damage, but with an intact perineurium and epineurium. According to the Sunderland classification, what grade of nerve injury has occurred?
. Grade I
. Grade II
. Grade III
. Grade IV
. Grade V

Correct Answer & Explanation

. Grade III

Explanation

A Sunderland Grade III injury involves loss of continuity of the axon and endoneurium, but the perineurium and epineurium remain intact. Recovery is variable and often incomplete due to intrafascicular scarring.

Question 4868

Topic: Biomechanics & Biomaterials

To minimize stress shielding following total hip arthroplasty, a femoral stem material with a Young's modulus closest to that of cortical bone is theoretically ideal. Which of the following orthopedic materials has a Young's modulus most similar to cortical bone?

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

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a Young's modulus (approximately 110 GPa) much closer to cortical bone (15-20 GPa) compared to Cobalt-chromium (approx 210 GPa) or Stainless steel (approx 200 GPa). This closer match helps reduce the degree of stress shielding.

Question 4869

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, the type of tissue that forms within a fracture gap is dictated by the local mechanical strain. What is the maximum percentage of strain that can be tolerated within the fracture gap for lamellar bone formation to occur without intermediate tissues?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory dictates that lamellar bone can only form under strain conditions of less than 2%. Higher strain (2-10%) leads to woven bone or fibrocartilage, while excessive strain (>10%) results in granulation tissue.

Question 4870

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III activation
. Direct, reversible inhibition of Factor Xa
. Inhibition of vitamin K epoxide reductase
. Irreversible inhibition of cyclooxygenase-1 (COX-1)

Correct Answer & Explanation

. Direct, reversible inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa. This interrupts the intrinsic and extrinsic pathway cascade, preventing thrombin generation.

Question 4871

Topic: 1. General Principles & Basic Science

During normal human gait, articular cartilage relies on various lubrication mechanisms depending on load and speed. Under high-load, low-speed conditions (such as standing from a seated position), which lubrication mechanism is predominantly responsible for reducing friction?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Squeeze-film lubrication
. Weeping lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication relies on molecules like lubricin directly adhering to the articular surfaces to prevent contact. It is the primary mechanism reducing friction under high-load and low-speed conditions when a fluid film cannot be maintained.

Question 4872

Topic: Biology, Genetics & Bone Healing

A surgeon utilizes Demineralized Bone Matrix (DBM) to augment a posterolateral lumbar fusion. DBM relies primarily on which of the following biological combinations to promote bone healing?

. Osteogenesis and osteoconduction
. Osteoinduction and osteoconduction
. Osteoconduction only
. Osteogenesis and osteoinduction
. Osteoinduction only

Correct Answer & Explanation

. Osteoinduction and osteoconduction

Explanation

Demineralized Bone Matrix (DBM) contains an exposed collagen matrix (osteoconductive) and native bone morphogenetic proteins (BMPs) making it highly osteoinductive. However, because it is acellular, it lacks osteogenic properties.

Question 4873

Topic: Biology, Genetics & Bone Healing

Osteoclasts are specialized multinucleated giant cells responsible for the physiologic resorption of bone matrix. From which of the following precursor cell lineages are osteoclasts primarily derived?

. Mesenchymal stem cells
. Hematopoietic macrophage-monocyte lineage
. Neural crest cells
. Endodermal progenitor cells
. Endothelial progenitor cells

Correct Answer & Explanation

. Hematopoietic macrophage-monocyte lineage

Explanation

Unlike osteoblasts which are derived from mesenchymal stem cells, osteoclasts differentiate from the hematopoietic macrophage-monocyte lineage. Their differentiation is highly dependent on RANKL and M-CSF.

Question 4874

Topic: Biology, Genetics & Bone Healing
During the soft callus phase of secondary fracture healing, the predominant collagen synthesized by chondrocytes is:
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type II

Explanation

During the soft callus stage, chondrocytes proliferate and predominantly secrete Type II collagen to form a cartilaginous template. This is later replaced by woven bone (Type I collagen) during hard callus formation.

Question 4875

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological treatment for unresectable Giant Cell Tumors of bone. It exerts its effect by acting as a monoclonal antibody against:

. VEGF
. RANKL
. Osteoprotegerin (OPG)
. TNF-alpha
. IL-6

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing its interaction with RANK on osteoclasts and giant cells. This effectively inhibits tumor-mediated osteolysis and giant cell formation.

Question 4876

Topic: 1. General Principles & Basic Science

In a healthy human hip joint, which lubrication mechanism is dominant during the brief, high-load period of heel strike?

. Squeeze-film lubrication
. Boundary lubrication
. Hydrodynamic lubrication
. Weeping lubrication
. Elastohydrodynamic lubrication

Correct Answer & Explanation

. Squeeze-film lubrication

Explanation

Squeeze-film lubrication occurs when two joint surfaces move perpendicular to each other under high loads for a short duration, such as during heel strike. Synovial fluid is momentarily trapped, preventing surface-to-surface contact.

Question 4877

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, the addition of molybdenum to 316L stainless steel primarily serves to:

. Increase the ultimate tensile strength
. Improve the fatigue life of the implant
. Reduce the modulus of elasticity
. Make the alloy MRI compatible
. Enhance resistance to pitting corrosion

Correct Answer & Explanation

. Enhance resistance to pitting corrosion

Explanation

The addition of 2-3% molybdenum to 316L stainless steel helps create a stable, protective passive oxide layer. This significantly enhances the metal's resistance to localized pitting and crevice corrosion in the chloride-rich physiological environment.

Question 4878

Topic: Biomechanics & Biomaterials
A 65-year-old female with a conventional ultra-high-molecular-weight polyethylene (UHMWPE) total hip arthroplasty placed 15 years ago presents with massive asymmetric head penetration on radiographs and severe osteolysis. The polyethylene was sterilized via gamma irradiation in air. What is the primary mechanism of this catastrophic failure?
. Adhesive wear
. Abrasive wear
. Oxidative degradation
. Third-body wear
. Galvanic corrosion

Correct Answer & Explanation

. Oxidative degradation

Explanation

Historically, gamma irradiation of UHMWPE in air led to free radical formation. Over time, these free radicals reacted with oxygen, causing oxidative degradation, chain scission, embrittlement, and subsequent catastrophic wear.

Question 4879

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum amount of interfragmentary strain that can be tolerated for primary lamellar bone formation to occur?

. 100%
. 50%
. 30%
. 10%
. 2%

Correct Answer & Explanation

. 2%

Explanation

According to Perren's strain theory, lamellar bone can only form in stable environments with less than 2% interfragmentary strain. Fibrocartilage can tolerate up to 10% strain, and granulation tissue can tolerate up to 100% strain.

Question 4880

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective medical treatment for advanced or unresectable Giant Cell Tumor of bone. What is its exact mechanism of action?

. Inhibits the farnesyl pyrophosphate synthase pathway
. Tyrosine kinase inhibitor targeting VEGF
. Induces direct apoptosis of osteoclasts
. Monoclonal antibody against the RANK receptor
. Monoclonal antibody against RANKL

Correct Answer & Explanation

. Monoclonal antibody against RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds specifically to the RANK Ligand (RANKL). By neutralizing RANKL, it prevents the activation of the RANK receptor on osteoclasts, halting bone destruction and tumor progression.

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