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1. General Principles & Basic Science MCQs

Practice Set 531 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 10601

Topic: 1. General Principles & Basic Science

A 45-year-old male is involved in a high-speed rollover MVC. He complains of severe neck pain and bilateral upper extremity weakness. Cervical radiographs reveal 50% anterior translation of C5 over C6. Which mechanism of injury is most classically responsible for this specific pattern?

. Hyperextension
. Axial loading
. Hyperflexion with distraction
. Lateral bending
. Extension with rotation

Correct Answer & Explanation

. Hyperflexion with distraction

Explanation

Bilateral facet dislocations result from extreme hyperflexion and distraction forces. Radiographically, they are characterized by approximately 50% anterior translation of the superior vertebral body over the inferior one.

Question 10602

Topic: Biology, Genetics & Bone Healing

What biomechanical strain environment is required to achieve primary (direct) bone healing without the formation of a fracture callus?

. Strain less than 2%
. Strain between 2% and 10%
. Strain between 10% and 20%
. Strain greater than 20%
. Strain between 5% and 15%

Correct Answer & Explanation

. Strain less than 2%

Explanation

According to Perren's strain theory, primary bone healing requires absolute stability with a strain environment of less than 2%. Secondary bone healing, which involves callus formation, occurs in environments of relative stability with a strain between 2% and 10%.

Question 10603

Topic: Biomechanics & Biomaterials

To minimize stress shielding around an orthopedic implant, a biomaterial should ideally possess a modulus of elasticity similar to cortical bone. Among standard structural implant metals, which of the following is closest to the elastic modulus of cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Trabecular metal (Tantalum)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy

Explanation

Cortical bone has a modulus of elasticity of approximately 15-20 GPa. Titanium alloy (approx. 110 GPa) is closer to cortical bone than stainless steel (approx. 200 GPa) and CoCr (approx. 210-240 GPa), which helps reduce stress shielding. (Note: Trabecular metal has high porosity and a low bulk modulus, but among solid structural metals, titanium is standardly taught as the closest to bone).

Question 10604

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the medical management of Giant Cell Tumor of bone. What is its exact mechanism of action?

. Binds directly to the RANK receptor on osteoclasts
. Binds directly to RANKL to prevent receptor activation
. Acts as a recombinant Osteoprotegerin (OPG) analog
. Inhibits Macrophage colony-stimulating factor (M-CSF)
. Directly induces apoptosis in neoplastic stromal cells

Correct Answer & Explanation

. Binds directly to RANKL to prevent receptor activation

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). This prevents RANKL from binding to the RANK receptor on osteoclast precursors, thereby profoundly inhibiting osteoclastogenesis and osteoclast function.

Question 10605

Topic: 1. General Principles & Basic Science

The medial femoral circumflex artery (MFCA) is the primary blood supply to the adult femoral head. After giving off its trochanteric branch, the deep branch of the MFCA typically passes between which two muscles prior to piercing the joint capsule?

. Pectineus and iliopsoas
. Quadratus femoris and obturator externus
. Obturator internus and piriformis
. Gluteus medius and minimus
. Adductor longus and brevis

Correct Answer & Explanation

. Quadratus femoris and obturator externus

Explanation

The deep branch of the medial femoral circumflex artery courses posteriorly and passes between the quadratus femoris and the obturator externus to reach the trochanteric fossa, where it gives rise to the critical retinacular vessels supplying the femoral head.

Question 10606

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct anatomical zones. Which zone contains the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented perpendicular to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is characterized by having the lowest water content, the highest concentration of proteoglycans, and vertically oriented type II collagen fibers that securely anchor the cartilage to the underlying calcified zone.

Question 10607

Topic: 1. General Principles & Basic Science

Osteoclasts resorb bone by creating an acidic microenvironment at the ruffled border. Which enzyme is primarily responsible for intracellularly generating the hydrogen ions (H+) needed for this critical acidification process?

. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Cathepsin K
. Matrix metalloproteinase 9 (MMP-9)
. Alkaline phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II converts CO2 and H2O into carbonic acid, which readily dissociates into protons (H+) and bicarbonate. These protons are then actively pumped across the ruffled border via an H+-ATPase pump to create the highly acidic environment (pH ~4.5) necessary to dissolve hydroxyapatite.

Question 10608

Topic: Biology, Genetics & Bone Healing

What is the primary cellular target and mechanism of action of Denosumab in the treatment of giant cell tumors of bone?

. Inhibits osteoclast H+/K+ ATPase directly
. Binds directly to the RANK receptor on osteoclast precursors
. Binds to RANKL, preventing its interaction with the RANK receptor
. Stimulates Osteoprotegerin (OPG) production by osteoblasts
. Induces apoptosis of neoplastic spindle cells in the tumor stroma

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on osteoclast precursors and mature osteoclasts, thereby inhibiting osteoclastogenesis and function. This is highly effective in Giant Cell Tumors of bone, which are rich in RANKL-expressing stromal cells that recruit RANK-expressing osteoclast-like giant cells.

Question 10609

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high molecular weight polyethylene (UHMWPE) for arthroplasty, what is the primary adverse consequence of radiation cross-linking if it is not followed by a thermal treatment (melting or annealing)?
. Generation of residual free radicals leading to in vivo oxidation and embrittlement
. Significant decrease in the modulus of elasticity
. Increase in adhesive wear during articulation
. Inadequate cross-linking density for wear reduction
. Premature melting of the crystalline regions

Correct Answer & Explanation

. Generation of residual free radicals leading to in vivo oxidation and embrittlement

Explanation

Gamma or electron beam irradiation is used to cross-link UHMWPE, which significantly improves its wear resistance. However, irradiation cleaves polymer chains, leaving residual free radicals. If these free radicals are not eliminated through thermal treatment (re-melting or annealing) or stabilized (e.g., with Vitamin E), they will react with oxygen in vivo, leading to oxidation, chain scission, embrittlement, and ultimately mechanical failure or delamination.

Question 10610

Topic: Biomechanics & Biomaterials
Which of the following sequences correctly orders biomaterials from HIGHEST to LOWEST Young's modulus of elasticity?
. Cortical Bone > Titanium > Stainless Steel > Cobalt Chromium
. Titanium > Cobalt Chromium > Stainless Steel > Cortical Bone
. Cobalt Chromium > Titanium > Stainless Steel > Cortical Bone
. Cobalt Chromium > Stainless Steel > Titanium > Cortical Bone
. Stainless Steel > Cobalt Chromium > Cortical Bone > Titanium

Correct Answer & Explanation

. Cobalt Chromium > Stainless Steel > Titanium > Cortical Bone

Explanation

Young's modulus represents the stiffness of a material. The higher the modulus, the stiffer the material. Cobalt Chromium (CoCr) is the stiffest among standard orthopaedic metals (~220 GPa), followed by Stainless Steel (~200 GPa), then Titanium alloy (Ti-6Al-4V) (~110 GPa). Cortical bone is much less stiff, with a modulus of approximately 15-20 GPa. Stress shielding occurs when there is a significant mismatch in modulus between the implant and bone.

Question 10611

Topic: Infection, Pharmacology & VTE

Methicillin-resistant Staphylococcus aureus (MRSA) demonstrates resistance to standard beta-lactam antibiotics primarily through which of the following mechanisms?

. Production of an extended-spectrum beta-lactamase enzyme
. Upregulation of transmembrane efflux pumps to clear the antibiotic
. Alteration of penicillin-binding protein 2a (PBP2a) encoded by the mecA gene
. Mutation in the DNA gyrase target site
. Significant thickening of the peptidoglycan cell wall (glycocalyx)

Correct Answer & Explanation

. Alteration of penicillin-binding protein 2a (PBP2a) encoded by the mecA gene

Explanation

MRSA resistance is mediated by the mecA gene, which encodes for a novel penicillin-binding protein, PBP2a. This altered protein has a very low affinity for beta-lactam antibiotics (such as penicillins and cephalosporins), allowing the bacteria to synthesize its cell wall even in the presence of these drugs. DNA gyrase mutations relate to fluoroquinolone resistance.

Question 10612

Topic: Biology, Genetics & Bone Healing

Vitamin C (ascorbic acid) deficiency results in scurvy, which is characterized by bone pain, bleeding gums, and poor wound healing. Vitamin C serves as an essential cofactor for which of the following specific processes in bone and cartilage synthesis?

. Hydroxylation of proline and lysine residues in procollagen
. Glycosylation of hydroxylysine residues
. Cleavage of procollagen C-terminal and N-terminal propeptides
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Translation of alpha chains on the rough endoplasmic reticulum

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues in procollagen

Explanation

Vitamin C is a necessary cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes catalyze the hydroxylation of proline and lysine residues on the forming procollagen chains. This hydroxylation is critical for the subsequent formation of the stable triple-helix structure of collagen. Without it, collagen is structurally weak, leading to the clinical manifestations of scurvy.

Question 10613

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopaedic surgery to reduce perioperative blood loss. It achieves this effect primarily through which of the following mechanisms?
. Irreversible inhibition of cyclooxygenase in platelets
. Competitive inhibition of plasminogen activation
. Direct inhibition of Factor Xa in the coagulation cascade
. Enhancement of antithrombin III activity
. Inhibition of vitamin K epoxide reductase

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly binding to the lysine-binding sites on plasminogen. This competitive inhibition prevents plasminogen from binding to fibrin, thereby inhibiting its activation into plasmin and preventing the degradation of fibrin clots (fibrinolysis).

Question 10614

Topic: 1. General Principles & Basic Science

When evaluating the ultrastructure of normal articular cartilage, which zone is characterized by the highest water content and collagen fibrils oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (up to 80%), the lowest proteoglycan content, and a high concentration of densely packed collagen fibrils oriented parallel to the articular surface to resist shear forces. The deep zone has the highest proteoglycan content and vertical collagen fibrils. The tidemark separates the deep uncalcified cartilage from the calcified cartilage.

Question 10615

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, what is the maximum amount of interfragmentary tissue strain that permits the formation and survival of primary lamellar bone?

. < 2%
. 2% - 10%
. 10% - 30%
. 30% - 50%
. > 50%

Correct Answer & Explanation

. < 2%

Explanation

Perren's strain theory states that the type of tissue that forms in a fracture gap depends on the interfragmentary strain. Lamellar bone can only form under very low strain conditions (< 2%). Woven bone can tolerate strain up to 10%, cartilage up to 30%, and granulation tissue can tolerate up to 100% strain. Absolute stability (e.g., lag screw and compression plate) aims for < 2% strain to allow direct (primary) bone healing.

Question 10616

Topic: 1. General Principles & Basic Science

An orthopaedic surgeon is evaluating a new diagnostic test for periprosthetic joint infection. Which of the following statistical parameters is inherently dependent on the underlying prevalence of the disease in the tested population?

. Sensitivity
. Specificity
. Negative Likelihood Ratio
. Positive Predictive Value
. Power

Correct Answer & Explanation

. Positive Predictive Value

Explanation

Positive Predictive Value (PPV) and Negative Predictive Value (NPV) are highly dependent on the prevalence of the disease in the population being studied. As disease prevalence increases, PPV increases and NPV decreases. In contrast, Sensitivity, Specificity, and Likelihood Ratios are inherent characteristics of the test itself and are theoretically independent of disease prevalence.

Question 10617

Topic: Biology, Genetics & Bone Healing

During the initial active (lytic) phase of Paget's disease of bone, the primary pathological process is driven by abnormal cells that characteristically exhibit which of the following histological features?

. Spindle-shaped morphology actively producing disordered osteoid
. Mononuclear cells with abundant clear cytoplasm and distinct cell borders
. Small round blue cells with scant cytoplasm and prominent nucleoli
. Bizarre, atypical nuclei with frequent atypical mitoses
. Extremely large size with an increased number of nuclei (up to 100) and viral-like inclusions

Correct Answer & Explanation

. Extremely large size with an increased number of nuclei (up to 100) and viral-like inclusions

Explanation

Paget's disease of bone begins with an intensely osteolytic phase driven by abnormal osteoclasts. These osteoclasts are pathologically large and multinucleated, often containing up to 100 nuclei per cell (normal is 3-10). Ultrastructurally, they may contain viral-like inclusion bodies, which has led to theories of a paramyxovirus etiology. The subsequent mixed and sclerotic phases are characterized by chaotic osteoblast activity.

Question 10618

Topic: Surgical Anatomy & Approaches

When utilizing the volar approach (Henry approach) to the proximal third of the radius, the internervous plane developed during the superficial dissection lies between which two muscles?

. Brachioradialis and Pronator Teres
. Flexor Carpi Radialis and Palmaris Longus
. Extensor Carpi Radialis Brevis and Extensor Digitorum Communis
. Flexor Carpi Ulnaris and Flexor Digitorum Profundus
. Pronator Teres and Flexor Carpi Radialis

Correct Answer & Explanation

. Brachioradialis and Pronator Teres

Explanation

The superficial internervous plane of the volar (Henry) approach to the forearm is between the brachioradialis (innervated by the radial nerve) and the pronator teres (innervated by the median nerve) proximally. In the distal third, the plane is between the brachioradialis and the flexor carpi radialis (median nerve). It is a true internervous approach throughout its length.

Question 10619

Topic: 1. General Principles & Basic Science
A patient suffers a severe stretch injury to the brachial plexus. EMG/NCS and advanced imaging confirm a Sunderland Grade 3 nerve injury. By definition, which of the following structures remain physically INTACT in a Sunderland Grade 3 injury?
. Myelin sheath and axon only
. Axon and endoneurium
. Perineurium and epineurium
. Epineurium only
. No structures remain intact

Correct Answer & Explanation

. Perineurium and epineurium

Explanation

According to the Sunderland classification of nerve injuries: Grade 1 (Neuropraxia) is a local myelin block with intact axon. Grade 2 (Axonotmesis) involves axonal disruption but intact endoneurium. Grade 3 involves disruption of the axon and endoneurium, but the perineurium (and epineurium) remains intact. Grade 4 disrupts the perineurium, leaving only the epineurium intact. Grade 5 is complete nerve transection.

Question 10620

Topic: Biology, Genetics & Bone Healing

A radiograph of an infant presenting with multiple fractures and cranial nerve palsies demonstrates diffusely dense, 'marble-like' bones with an absence of normal medullary cavities. The most common malignant autosomal recessive form of this disease is fundamentally caused by a defect in which of the following?

. Type I collagen synthesis and assembly
. Fibroblast growth factor receptor 3 (FGFR3) regulation
. Runx2 transcription factor activity
. Carbonic anhydrase II leading to defective osteoclast ruffled border
. Lysosomal storage enzyme beta-galactosidase

Correct Answer & Explanation

. Carbonic anhydrase II leading to defective osteoclast ruffled border

Explanation

The disease is Osteopetrosis (Marble Bone Disease), characterized by dense but brittle bones due to failure of osteoclast resorptive function. The malignant autosomal recessive (infantile) form is most commonly associated with mutations in the TCIRG1 gene (vacuolar proton pump) or Carbonic Anhydrase II. These defects prevent the osteoclast from acidifying the resorption pit, manifested ultrastructurally by an absent or defective ruffled border.

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