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1. General Principles & Basic Science MCQs

Practice Set 702 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 14021

Topic: 1. General Principles & Basic Science

Osteoclasts degrade the inorganic mineralized component of bone tissue by secreting which of the following into the sealed subosteoclastic resorption pit (Howship's lacuna)?

. Cathepsin K
. Matrix metalloproteinases
. Hydrogen ions via carbonic anhydrase II
. Alkaline phosphatase
. Tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. Hydrogen ions via carbonic anhydrase II

Explanation

Osteoclasts secrete hydrogen ions into the resorption pit via an ATP-dependent proton pump, utilizing carbonic anhydrase II to generate the protons. The highly acidic environment dissolves the inorganic hydroxyapatite, while enzymes like Cathepsin K degrade the organic collagen matrix.

Question 14022

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely used in total joint arthroplasty to reduce perioperative blood loss. Which of the following best describes its mechanism of action?

. Directly inhibits thrombin
. Inhibits cyclooxygenase, promoting platelet aggregation
. Competitively inhibits the activation of plasminogen to plasmin
. Promotes the release of von Willebrand factor from endothelial cells
. Inhibits factor Xa

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic antifibrinolytic agent that acts as an analog of the amino acid lysine. It competitively inhibits the activation of plasminogen to plasmin, thereby preventing the premature degradation of fibrin clots.

Question 14023

Topic: Biology, Genetics & Bone Healing

A surgeon utilizes demineralized bone matrix (DBM) during a spinal fusion. Which of the following properties does DBM inherently possess to facilitate bone formation?

. Osteoconductive and osteoinductive
. Osteoconductive and osteogenic
. Osteoinductive and osteogenic
. Osteoconductive only
. Osteogenic only

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

Demineralized bone matrix (DBM) provides a collagenous structural scaffold (osteoconductive) and retains bone morphogenetic proteins (BMPs) that stimulate local cells to differentiate into bone-forming cells (osteoinductive). However, it lacks viable cells, so it is not osteogenic.

Question 14024

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for a ductile orthopedic material like stainless steel, which of the following points marks the transition from elastic to plastic deformation?

. Proportional limit
. Ultimate tensile strength
. Yield point
. Failure point
. Toughness threshold

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the transition from elastic (reversible) to plastic (irreversible) deformation on a stress-strain curve. Prior to this point, the material will return to its original shape if the load is removed.

Question 14025

Topic: 1. General Principles & Basic Science

In healthy adult articular cartilage, which zone is characterized by the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest proteoglycan content and the lowest water content. Its collagen fibers (primarily Type II) are oriented perpendicularly to the subchondral bone to resist compressive loads.

Question 14026

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with a history of recurrent fractures, blue sclerae, and early-onset hearing loss. A structural defect in which of the following molecular processes is the primary pathophysiology?

. Defective mineralization of osteoid
. Abnormal endochondral ossification
. Impaired hydroxylation of proline
. Substitution of glycine in the collagen triple helix
. Overactivity of osteoclast remodeling

Correct Answer & Explanation

. Substitution of glycine in the collagen triple helix

Explanation

The patient has Osteogenesis Imperfecta (OI), which is most commonly caused by an autosomal dominant point mutation in the COL1A1 or COL1A2 genes. This results in the substitution of glycine by a bulkier amino acid in the procollagen triple helix, disrupting Type I collagen assembly.

Question 14027

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with increasing hat size and bilateral hip pain. Radiographs reveal extensive cortical thickening and coarsened trabeculae. Bone biopsy demonstrates a mosaic pattern of lamellar bone. What is the primary cellular defect initiating this condition?

. Decreased osteoblast activity
. Increased osteoblast activity
. Decreased osteoclast activity
. Increased osteoclast activity
. Impaired osteocyte mechanotransduction

Correct Answer & Explanation

. Increased osteoclast activity

Explanation

Paget disease of bone is initiated by an intense phase of overactive, increased osteoclastic bone resorption (the lytic phase), followed by disorganized osteoblastic bone formation. The resulting woven bone has a characteristic 'mosaic' or 'jigsaw puzzle' appearance on histology.

Question 14028

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy is diagnosed with X-linked hypophosphatemic rickets. Which of the following laboratory profiles is most characteristic of his untreated condition?

. Normal calcium, decreased phosphate, normal PTH, elevated FGF23
. Decreased calcium, normal phosphate, elevated PTH, normal FGF23
. Elevated calcium, decreased phosphate, decreased PTH, normal FGF23
. Normal calcium, elevated phosphate, normal PTH, decreased FGF23
. Decreased calcium, decreased phosphate, elevated PTH, elevated FGF23

Correct Answer & Explanation

. Normal calcium, decreased phosphate, normal PTH, elevated FGF23

Explanation

X-linked hypophosphatemic rickets (XLH) is caused by a PHEX gene mutation that leads to excess Fibroblast Growth Factor 23 (FGF23). Elevated FGF23 causes renal phosphate wasting, leading to hypophosphatemia. Serum calcium and Parathyroid Hormone (PTH) levels are typically normal.

Question 14029

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a third-degree injury involves disruption of which of the following structures?

. Myelin sheath only
. Axon and myelin sheath, leaving endoneurium intact
. Axon, myelin, and endoneurium, leaving perineurium intact
. Axon, myelin, endoneurium, and perineurium, leaving epineurium intact
. Complete transection of the nerve including epineurium

Correct Answer & Explanation

. Axon, myelin, and endoneurium, leaving perineurium intact

Explanation

In the Sunderland classification, a 3rd-degree injury involves disruption of the axon, myelin, and endoneurium, while the perineurium and epineurium remain intact. The loss of endoneurial tubes leads to disorganized axonal regeneration and a high risk of neuroma-in-continuity.

Question 14030

Topic: Biomechanics & Biomaterials

A surgeon inadvertently uses a titanium screw to secure a stainless steel plate during fracture fixation. Months later, the implant site becomes painful, and revision surgery reveals localized tissue reaction with dark metallic debris. What is the primary mechanism of implant degradation in this scenario?

. Fretting corrosion
. Galvanic corrosion
. Crevice corrosion
. Pitting corrosion
. Fatigue failure

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (like titanium and stainless steel) are in physical contact within an electrolytic solution (body fluid). An electrochemical cell is created, leading to accelerated corrosion of the less noble metal (anodic dissolution).

Question 14031

Topic: Biomechanics & Biomaterials
In modern total joint arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is extensively used to decrease adhesive and abrasive wear. Which of the following mechanical properties is most significantly reduced as a direct consequence of the cross-linking process?
. Ultimate tensile strength
. Hardness
. Fatigue resistance (Toughness)
. Elastic modulus
. Yield strength

Correct Answer & Explanation

. Fatigue resistance (Toughness)

Explanation

While high-dose irradiation cross-linking dramatically decreases the wear rate of UHMWPE, it significantly decreases its mechanical toughness, fatigue resistance, and ductility, making it more vulnerable to fracture or failure under high-stress conditions.

Question 14032

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with a lytic, epiphyseal-metaphyseal lesion in her proximal tibia. Biopsy reveals multinucleated giant cells intermixed with mononuclear stromal cells. Systemic therapy with denosumab is considered. What is the specific target of this medication?

. VEGF
. RANKL
. mTOR
. Tyrosine kinase
. PD-1

Correct Answer & Explanation

. RANKL

Explanation

Giant cell tumor of bone is driven by neoplastic mononuclear stromal cells that express high levels of Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL). Denosumab is a monoclonal antibody that targets RANKL, preventing the recruitment and activation of the destructive multinucleated giant cells.

Question 14033

Topic: 1. General Principles & Basic Science

During the initiation of skeletal muscle contraction, the release of calcium from the sarcoplasmic reticulum triggers cross-bridge cycling by directly binding to which of the following structural proteins?

. Tropomyosin
. Troponin I
. Troponin T
. Troponin C
. Myosin heavy chain

Correct Answer & Explanation

. Troponin C

Explanation

Calcium ions bind to Troponin C. This binding causes a conformational change in the troponin complex, moving tropomyosin away from the myosin-binding sites on the actin filament, thus allowing the myosin head to bind and cross-bridge cycling to commence.

Question 14034

Topic: Biology, Genetics & Bone Healing

During secondary (indirect) fracture healing, which of the following stages is characterized by the highest peak in oxygen consumption, chondrogenesis, and cellular proliferation?

. Hematoma formation
. Inflammation
. Soft callus formation
. Hard callus formation
. Remodeling

Correct Answer & Explanation

. Soft callus formation

Explanation

Soft callus formation is the most metabolically active phase of fracture healing. It is characterized by peak cellular proliferation, active chondrogenesis, aggressive angiogenesis, and the highest peak in overall oxygen consumption as the cartilaginous framework is laid down.

Question 14035

Topic: Biomechanics & Biomaterials

When optimizing the biomechanics of a cortical bone screw, which of the following design modifications will most effectively increase its pullout strength?

. Decreasing the outer diameter
. Increasing the inner (root) diameter
. Decreasing the thread pitch
. Increasing the screw length beyond the far cortex by 10mm
. Decreasing the working length

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the outer diameter and the total surface area of thread engagement. Decreasing the thread pitch increases the number of threads per unit length, thereby increasing the amount of bone engaged and maximizing pullout strength.

Question 14036

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently administered in orthopedic surgery to reduce perioperative blood loss. What is the primary mechanism of action of TXA?
. Inhibition of cyclooxygenase-1 (COX-1)
. Activation of the extrinsic coagulation cascade
. Competitive inhibition of plasminogen activation
. Direct inhibition of Factor Xa
. Irreversible binding to antithrombin III

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine. It acts as an antifibrinolytic by reversibly and competitively binding to the lysine receptor sites on plasminogen, thereby preventing its activation to plasmin and subsequent fibrin degradation.

Question 14037

Topic: Physiology & Rehabilitation

Which type of joint lubrication predominates in healthy human articular cartilage during the normal walking cycle when the joint surfaces are undergoing relative motion at high speeds and low loads?

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

Correct Answer & Explanation

. Elastohydrodynamic lubrication

Explanation

Elastohydrodynamic lubrication (a form of fluid film lubrication) predominates under dynamic conditions of high speed and low load (such as the swing phase of gait). The deformation of the elastic articular cartilage increases the surface area and maintains a continuous thin fluid film, minimizing friction.

Question 14038

Topic: Biomechanics & Biomaterials

Among common metallic orthopedic implants, which has a modulus of elasticity that most closely approximates that of cortical bone?

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

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity (approx. 110 GPa) that is closer to cortical bone (15-20 GPa) compared to stainless steel (200 GPa) and cobalt-chromium (220 GPa). This closer biomechanical match helps minimize stress shielding.

Question 14039

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, in which of the following stages does the peak expression of Type II collagen occur?

. Hematoma formation
. Soft callus formation
. Hard callus formation
. Remodeling
. Inflammation

Correct Answer & Explanation

. Soft callus formation

Explanation

Type II collagen is primarily produced by chondrocytes during the soft callus phase of secondary bone healing. It forms the cartilaginous framework that is subsequently replaced by woven bone (Type I collagen) during hard callus formation.

Question 14040

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following wear mechanisms is fundamentally responsible for the generation of ultra-high-molecular-weight polyethylene (UHMWPE) wear debris at the articulating interface?
. Adhesive wear
. Abrasive wear
. Corrosive wear
. Galvanic wear
. Third-body wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary continuous wear mechanism for UHMWPE. It occurs when microscopic asperities on the hard metal surface temporarily bond with the softer polyethylene, tearing off submicron particles during motion.

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