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1. General Principles & Basic Science MCQs

Practice Set 592 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 11821

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, direct or primary bone healing can occasionally occur if there is rigid internal fixation with absolute stability. This involves bone remodeling via cutting cones. Which of the following best describes the cellular arrangement at the advancing leading edge of a cortical cutting cone?

. Osteoblasts depositing osteoid
. Osteocytes communicating via canaliculi
. Osteoclasts resorbing bone
. Chondrocytes undergoing hypertrophy
. Mesenchymal stem cells differentiating

Correct Answer & Explanation

. Osteoblasts depositing osteoid

Explanation

In primary bone healing, remodeling occurs via cutting cones. The leading edge (head) of the cutting cone is composed of osteoclasts that bore through the necrotic bone. They are followed by a capillary loop and osteoblasts (in the trailing edge or closing cone) that lay down new concentric lamellae of bone.

Question 11822

Topic: Physiology & Rehabilitation

A biomechanical analysis of a normal adult gait cycle is performed in a gait laboratory. During which phase of the gait cycle does the gluteus maximus exhibit its peak electromyographic (EMG) activity?

. Initial contact (heel strike)
. Mid-stance
. Terminal stance
. Initial swing
. Terminal swing

Correct Answer & Explanation

. Initial contact (heel strike)

Explanation

The gluteus maximus reaches its peak EMG activity during initial contact (heel strike). Its main function at this stage is to decelerate the forward motion of the trunk and initiate hip extension to stabilize the pelvis as the body's weight is accepted onto the limb.

Question 11823

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely utilized in total joint arthroplasty to minimize perioperative blood loss. Which of the following accurately describes the primary mechanism of action of TXA?
. Direct inhibition of factor Xa
. Irreversible binding to cyclooxygenase
. Synthetic analog of lysine that competitively inhibits plasminogen activation
. Activation of antithrombin III
. Enhancement of von Willebrand factor binding to exposed collagen

Correct Answer & Explanation

. Synthetic analog of lysine that competitively inhibits plasminogen activation

Explanation

Tranexamic acid (TXA) is an antifibrinolytic agent. It is a synthetic analog of the amino acid lysine and reversibly binds to the lysine receptor sites on plasminogen. This competitive inhibition prevents plasminogen from converting into plasmin, thereby preventing the degradation of fibrin clots.

Question 11824

Topic: Biomechanics & Biomaterials
To improve the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) utilized in total joint arthroplasty, the material is subjected to irradiation to induce cross-linking. Which of the following is the primary purpose of subsequent remelting or the addition of Vitamin E during manufacturing?
. Increase the yield strength of the polymer
. Eliminate free radicals to prevent oxidative degradation
. Improve the hydrophilicity for better boundary lubrication
. Decrease the elastic modulus to match cortical bone
. Enhance the osteoinductivity of the eventual wear debris

Correct Answer & Explanation

. Eliminate free radicals to prevent oxidative degradation

Explanation

Irradiation of UHMWPE creates cross-links that vastly improve wear resistance, but it also generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidative degradation and embrittlement. Remelting or adding antioxidants like Vitamin E quenches these free radicals.

Question 11825

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a critical role in fracture healing by promoting osteoinduction and driving mesenchymal stem cells toward an osteoblastic lineage. BMPs transmit their intracellular signals primarily by phosphorylating which of the following downstream mediators?

. Beta-catenin
. STAT proteins
. Smad proteins
. Cyclic AMP
. Inositol triphosphate (IP3)

Correct Answer & Explanation

. Beta-catenin

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which subsequently phosphorylate intracellular Smad proteins (specifically Smad 1, 5, and 8). These form a complex with Smad 4, translocate to the nucleus, and regulate osteogenic gene transcription.

Question 11826

Topic: Biomechanics & Biomaterials

A basic science researcher is studying the biomechanical properties of the anterior cruciate ligament (ACL). A constant length of deformation (strain) is abruptly applied to the ligament in a testing machine, and the load (stress) required to maintain this specific length is observed to decrease exponentially over time. Which viscoelastic property is being demonstrated?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropic behavior

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is a classic viscoelastic property defined as the decrease in internal stress (or load) over time when a material is held at a constant strain (length). Creep, conversely, is an increase in strain (deformation) over time when the material is subjected to a constant load.

Question 11827

Topic: Biology, Genetics & Bone Healing

An 80-year-old man presents with increasing hat size, unilateral hearing loss, and bowing of his right tibia. Laboratory testing shows a significantly elevated serum alkaline phosphatase with normal calcium and phosphorus levels. The primary cellular defect initiating this disease process originates from an abnormality in which of the following?

. Osteoblast hyperactivity due to an FGFR3 mutation
. Osteocyte apoptosis due to chronic subchondral ischemia
. Osteoclast hyperactivity potentially linked to a paramyxovirus infection and SQSTM1 mutation
. Mesenchymal stem cell failure to differentiate into mature osteoblasts
. Chondrocyte hypertrophy arrest at the growth plate

Correct Answer & Explanation

. Osteoblast hyperactivity due to an FGFR3 mutation

Explanation

Paget's disease of bone is initiated by intensely overactive, abnormal osteoclasts that are larger and multinucleated. This primary osteoclastic phase is followed by disorganized, chaotic woven bone formation by osteoblasts. The exact etiology is believed to be a combination of genetic susceptibility (SQSTM1/p62 mutations) and potential viral triggers (paramyxovirus inclusions in osteoclasts).

Question 11828

Topic: Surgical Anatomy & Approaches

Following a closed midshaft humerus fracture, a patient develops a complete radial nerve palsy. Electromyography (EMG) performed at 4 weeks shows fibrillation potentials in the brachioradialis. If the nerve has sustained an injury where the axon and myelin sheath are disrupted, but the endoneurium, perineurium, and epineurium remain anatomically intact, this corresponds to which classification?

. Seddon's Neuropraxia
. Sunderland's First-Degree
. Sunderland's Second-Degree
. Sunderland's Third-Degree
. Sunderland's Fourth-Degree

Correct Answer & Explanation

. Seddon's Neuropraxia

Explanation

Sunderland's Second-Degree injury correlates with Seddon's Axonotmesis. In this injury, the axon and its myelin sheath are disrupted (leading to Wallerian degeneration), but the supporting endoneurial tubes remain intact. This intact structure guides spontaneous axonal regeneration at about 1 mm/day.

Question 11829

Topic: Biomechanics & Biomaterials

A 60-year-old male presents with an acute, severely painful, and swollen knee without antecedent trauma. Aspiration yields cloudy synovial fluid with 25,000 WBCs/mcL. Under compensated polarized light microscopy, weakly positively birefringent rhomboid-shaped crystals are visualized. What is the chemical composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Calcium hydroxyapatite
. Cholesterol
. Basic calcium phosphate

Correct Answer & Explanation

. Monosodium urate

Explanation

The diagnosis is pseudogout, which is caused by the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in the joint. They appear rhomboid-shaped and demonstrate weak positive birefringence under polarized light. Monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 11830

Topic: Infection, Pharmacology & VTE

In the setting of periprosthetic joint infection, Staphylococcus aureus forms a resilient biofilm on the metallic implant surface, rendering standard systemic antibiotics largely ineffective. Which of the following phases of biofilm development is characterized specifically by the mass production of an extracellular polymeric substance (EPS) matrix and inter-bacterial communication via quorum sensing?

. Reversible attachment
. Irreversible attachment
. Maturation phase
. Dispersion phase
. Planktonic phase

Correct Answer & Explanation

. Reversible attachment

Explanation

Biofilm formation occurs in stages: attachment (reversible then irreversible), maturation (growth), and detachment/dispersion. The maturation phase is defined by the robust secretion of the protective EPS matrix and the use of quorum sensing molecules that allow the bacterial colony to coordinate gene expression and defend against host immunity/antibiotics.

Question 11831

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue structured in distinct layers to resist both compressive and shear forces. In which zone of articular cartilage do the Type II collagen fibers align perpendicular to the subchondral bone surface, with chondrocytes characteristically arranged in vertical columns?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

In the deep (radial) zone of articular cartilage, collagen fibers are oriented perpendicularly to the articular surface to provide maximal resistance to compressive loads, and the chondrocytes align in columns between these fibers. The superficial zone has parallel fibers to resist shear stress.

Question 11832

Topic: 1. General Principles & Basic Science

Aggrecan is the most abundant proteoglycan in articular cartilage and provides critical osmotic resistance needed to absorb compressive loads. Which of the following molecules attaches the core protein of aggrecan to the hyaluronic acid backbone?

. Chondroitin sulfate
. Link protein
. Keratan sulfate
. Collagen type IX
. Fibronectin

Correct Answer & Explanation

. Chondroitin sulfate

Explanation

Aggrecan is the predominant proteoglycan in articular cartilage, providing osmotic resistance needed to absorb compressive loads. Aggrecan molecules bind noncovalently to a central hyaluronic acid backbone, and this interaction is stabilized by link proteins, forming a massive aggregate.

Question 11833

Topic: Biomechanics & Biomaterials

Placing a stainless steel screw through a titanium plate in a fracture fixation construct increases the risk of which type of implant corrosion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals, such as stainless steel and titanium, are placed in electrical contact within a conductive fluid (such as physiologic body fluid). The less noble metal undergoes accelerated corrosion. It is generally advised not to mix these metals in internal fixation constructs to prevent hardware failure and local tissue reactions.

Question 11834

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum strain tolerated by lamellar bone formation during fracture healing?

. 1%
. 2%
. 10%
. 30%
. 100%

Correct Answer & Explanation

. 1%

Explanation

Perren's strain theory postulates that the type of tissue that differentiates in a fracture gap is determined by the local mechanical strain. Lamellar bone requires a highly stable environment and forms only when strain is less than 2%. Woven bone can tolerate up to 10% strain, cartilage up to 30%, and granulation tissue can withstand up to 100% strain. Absolute stability techniques aim to keep strain <2%.

Question 11835

Topic: 1. General Principles & Basic Science
A 45-year-old male presents with acute knee pain. A synovial fluid aspirate demonstrates 45,000 WBC/mm³ with 85% PMNs. Polarized light microscopy reveals negatively birefringent needle-shaped crystals, and there are no organisms on Gram stain. What is the primary composition of these crystals?
. Calcium pyrophosphate dihydrate
. Monosodium urate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Monosodium urate

Explanation

Gout is an inflammatory arthropathy caused by the intra-articular deposition of monosodium urate crystals. Synovial fluid analysis reveals a high white blood cell count with predominantly neutrophils. Under polarized light microscopy, monosodium urate crystals are needle-shaped and exhibit strong negative birefringence. Calcium pyrophosphate dihydrate crystals, characteristic of pseudogout, are rhomboid-shaped and positively birefringent.

Question 11836

Topic: 1. General Principles & Basic Science
Following a peripheral nerve injury, Wallerian degeneration occurs distal to the transection. Which cells proliferate and align in longitudinal columns (bands of Büngner) to guide regenerating axons?
. Schwann cells
. Macrophages
. Fibroblasts
. Oligodendrocytes
. Astrocytes

Correct Answer & Explanation

. Schwann cells

Explanation

Following a peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Schwann cells and macrophages degrade and phagocytose the myelin sheath and axonal debris. Subsequently, Schwann cells proliferate and line up in columns, known as bands of Büngner, to guide regenerating axonal sprouts from the proximal stump back to their target tissues.

Question 11837

Topic: Biology, Genetics & Bone Healing

Sclerostin is a key negative regulator of bone formation secreted by osteocytes. Which of the following intracellular signaling pathways does sclerostin directly inhibit?

. RANK-RANKL signaling
. Wnt/beta-catenin signaling
. BMP-SMAD signaling
. Notch signaling
. Hedgehog signaling

Correct Answer & Explanation

. RANK-RANKL signaling

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes. It acts as a negative regulator of bone formation by binding to the LRP5/6 co-receptors on osteoblasts, thereby competitively inhibiting Wnt/beta-catenin signaling. This pathway is crucial for osteoblast differentiation and bone formation. Therapeutic monoclonal antibodies against sclerostin (e.g., romosozumab) exploit this mechanism to treat osteoporosis.

Question 11838

Topic: Physiology & Rehabilitation

Slow-twitch (Type I) muscle fibers are specialized for endurance activities. Compared to Type II (fast-twitch) fibers, Type I fibers have a higher intracellular concentration of which of the following?

. Glycogen
. Myosin ATPase
. Sarcoplasmic reticulum
. Mitochondria
. Glycolytic enzymes

Correct Answer & Explanation

. Glycogen

Explanation

Muscle fibers are broadly classified into Type I (slow-twitch) and Type II (fast-twitch) fibers. Type I fibers are specialized for aerobic metabolism and sustained endurance. They possess a high density of mitochondria, a rich capillary supply, and abundant myoglobin (giving them a red appearance). Type II fibers rely more on anaerobic glycolysis, have high myosin ATPase activity, and fatigue more quickly.

Question 11839

Topic: 1. General Principles & Basic Science
During the remodeling phase of tendon healing, the cellularity decreases, and the extracellular matrix becomes highly organized. Which of the following best describes the change in collagen composition during this phase?
. Increase in Type I collagen and decrease in Type III collagen
. Increase in Type III collagen and decrease in Type I collagen
. Increase in Type II collagen and decrease in Type I collagen
. Increase in Type I collagen and decrease in Type II collagen
. Increase in Type IX collagen and decrease in Type III collagen

Correct Answer & Explanation

. Increase in Type I collagen and decrease in Type III collagen

Explanation

Tendon healing occurs in overlapping phases: inflammation, proliferation, and remodeling. During the early proliferative phase, fibroblasts synthesize an abundant amount of disorganized Type III collagen. As healing progresses into the remodeling phase, Type III collagen is gradually replaced by the stronger, more longitudinally aligned Type I collagen, leading to an increase in tissue tensile strength.

Question 11840

Topic: 1. General Principles & Basic Science

The vascular supply to the peripheral 10-30% (red-red zone) of the medial and lateral menisci originates primarily from which of the following structures?

. Middle genicular artery
. Perimeniscal capillary plexus derived from the inferior and superior genicular arteries
. Synovial fluid diffusion
. Popliteal artery direct branches
. Sural arteries

Correct Answer & Explanation

. Middle genicular artery

Explanation

The menisci are critical load-sharing structures in the knee. The peripheral 10% to 30% of the medial and lateral menisci is vascularized, allowing for a robust healing response following repair. This blood supply originates from a perimeniscal capillary plexus formed by branches of the inferior and superior medial and lateral genicular arteries. The inner avascular zone relies entirely on diffusion from the synovial fluid for nutrition.

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