Menu

1. General Principles & Basic Science MCQs

Practice Set 395 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 7881

Topic: 1. General Principles & Basic Science

Osteopetrosis is a rare genetic disorder characterized by dense, poorly remodeled bones. The infantile malignant form is most commonly caused by a mutation in the TCIRG1 gene, which encodes the a3 subunit of the vacuolar H+-ATPase. Dysfunction of this pump directly impairs which critical step in osteoclast-mediated bone resorption?

. Differentiation of mononuclear precursors into multinucleated osteoclasts
. Binding of RANKL to the RANK receptor
. Sealing zone formation via alphav-beta3 integrins
. Acidification of the Howship's lacuna to dissolve hydroxyapatite
. Secretion of Cathepsin K to degrade Type I collagen

Correct Answer & Explanation

. Acidification of the Howship's lacuna to dissolve hydroxyapatite

Explanation

The vacuolar H+-ATPase resides on the ruffled border of an actively resorbing osteoclast and actively pumps protons (H+) into the sealed microenvironment known as the Howship's lacuna. This acidification (achieving a pH of ~4.5) is absolutely necessary to dissolve the inorganic hydroxyapatite mineral component of bone. Mutations in the TCIRG1 gene impair this pump, causing osteoclast-rich osteopetrosis, where osteoclasts are abundant but functionally defective.

Question 7882

Topic: Biomechanics & Biomaterials



A load-deformation (stress-strain) curve for a standard orthopedic structural construct is evaluated. The specific point on the curve where the construct permanently transitions from elastic deformation to plastic deformation is known as the:

. Yield point
. Ultimate failure point
. Proportional limit
. Point of catastrophic failure
. Endurance limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the precise transition between the elastic region (where removal of the load results in full recovery of the material's original shape) and the plastic region (where microscopic structural changes occur, and permanent deformation remains after load removal). The proportional limit is slightly earlier on the curve, representing the true end of the linear elastic relationship (Hooke's Law), though the two points are typically located very close together.

Question 7883

Topic: Biology, Genetics & Bone Healing

Osteopetrosis is a genetic disease characterized by dense, brittle bones due to defective osteoclastic bone resorption. A mutation in the gene encoding for which of the following enzymes is most commonly associated with the failure of osteoclasts to create the necessary acidic microenvironment?

. Alkaline phosphatase
. Cathepsin K
. Carbonic anhydrase II
. Matrix metalloproteinase 9
. Tartrate-resistant acid phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II (CA II) is essential for producing the protons needed to acidify the resorption lacuna beneath the osteoclast's ruffled border. Mutations in CA II cause a subtype of autosomal recessive osteopetrosis that is characteristically associated with renal tubular acidosis and cerebral calcification. Cathepsin K degrades the organic matrix (type I collagen) but does not acidify the environment.

Question 7884

Topic: 1. General Principles & Basic Science

Articular cartilage relies on its highly organized structure for biomechanical function. Reviewing the histological zones of articular cartilage, which of the following best describes the structural and biochemical characteristics of the deep (calcified and uncalcified) zone compared to the superficial (tangential) zone?

. Higher water content, parallel collagen fibers, and lowest proteoglycan concentration
. Lower water content, perpendicular collagen fibers, and highest proteoglycan concentration
. Highest water content, random collagen orientation, and high cellularity
. Lowest water content, parallel collagen fibers, and lowest proteoglycan concentration
. Equal water content, perpendicular collagen fibers, and intermediate proteoglycan concentration

Correct Answer & Explanation

. Higher water content, parallel collagen fibers, and lowest proteoglycan concentration

Explanation

Articular cartilage varies significantly by zone. The superficial zone has the highest water content (approx. 80%), collagen fibers parallel to the joint surface (to resist shear forces), and the lowest proteoglycan content. The deep zone has the lowest water content (approx. 65%), the highest proteoglycan concentration, and collagen fibers oriented perpendicular to the joint surface to resist compressive loads.

Question 7885

Topic: Biomechanics & Biomaterials

Tendons and ligaments exhibit distinct viscoelastic properties, meaning their biomechanical response depends heavily on the rate and duration of loading. Which of the following best describes the phenomenon of 'creep' in an orthopaedic viscoelastic tissue?

. Progressive and increasing deformation over time under a constant load
. Progressive decrease in load over time required to maintain a constant deformation
. Energy loss during a cyclical loading and unloading cycle
. The failure of a material after repeated loading below its ultimate tensile strength
. The nonlinear initial portion of a load-deformation curve where collagen fibers un-crimp

Correct Answer & Explanation

. Progressive and increasing deformation over time under a constant load

Explanation

Creep is a fundamental viscoelastic property defined as the progressive deformation of a material over time when subjected to a constant load. Option B describes stress relaxation. Option C describes hysteresis. Option D describes fatigue failure. Option E describes the 'toe region' of the load-deformation curve.

Question 7886

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, the type of tissue that forms in a fracture gap is dictated by the amount of mechanical strain at the local cellular level. What is the maximum strain environment that permits the formation of primary lamellar bone?

. 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 postulates that a specific tissue can only form under conditions where the local mechanical strain does not exceed its failure strain. Lamellar bone is highly intolerant of strain and requires an environment with less than 2% strain to form (primary bone healing). Cartilage can tolerate up to 10% strain (allowing secondary callus formation), while granulation tissue can tolerate up to 100% strain.

Question 7887

Topic: Biomechanics & Biomaterials

A 45-year-old patient requires a revision of a previously placed plate and screw construct for a nonunion. Intraoperatively, black metallosis debris is noted specifically at the screw-plate interface.

Assuming both the plate and the screws are composed of the exact same 316L stainless steel alloy, which of the following represents the primary mechanism for this localized corrosion?

. Galvanic corrosion
. Crevice corrosion
. Pitting corrosion
. Fretting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs when there is micromotion between two closely apposed surfaces of the same material, such as the interface between a screw head and a plate hole. This mechanical micromotion repeatedly destroys the self-passivating oxide layer, leading to localized corrosion and black debris. Galvanic corrosion requires dissimilar metals. Crevice corrosion occurs in oxygen-depleted zones but is not primarily driven by the mechanical micromotion described.

Question 7888

Topic: Surgical Anatomy & Approaches
Following a severe crush injury to the sciatic nerve, the distal nerve segment undergoes Wallerian degeneration. Which of the following cell types is primarily responsible for the phagocytosis of myelin debris and the subsequent formation of the bands of Büngner to guide regenerating axonal sprouts in the peripheral nervous system?
. Oligodendrocytes
. Astrocytes
. Microglia
. Schwann cells
. Fibroblasts

Correct Answer & Explanation

. Schwann cells

Explanation

In the peripheral nervous system, Schwann cells are the primary glia responsible for coordinating Wallerian degeneration and regeneration. Alongside infiltrating macrophages, Schwann cells phagocytose myelin debris, proliferate, and align to form longitudinal tubes known as the bands of Büngner. They also secrete essential neurotrophic factors to guide regenerating axons. Oligodendrocytes and microglia perform similar functions in the CNS, but oligodendrocytes typically inhibit axonal regeneration.

Question 7889

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the management of severe osteoporosis. Which of the following best describes its mechanism of action when administered via daily subcutaneous injections?

. Inhibition of the mevalonate pathway in osteoclasts
. Binding to RANKL, preventing osteoclast activation
. Intermittent activation of parathyroid hormone (PTH) receptors, predominantly stimulating osteoblasts
. Continuous activation of parathyroid hormone (PTH) receptors, predominantly stimulating osteoclasts
. Direct inhibition of Cathepsin K

Correct Answer & Explanation

. Intermittent activation of parathyroid hormone (PTH) receptors, predominantly stimulating osteoblasts

Explanation

Teriparatide is a recombinant form of human parathyroid hormone (PTH 1-34). While continuous elevation of endogenous PTH (as seen in hyperparathyroidism) leads to increased osteoclast activity and bone resorption, the intermittent administration (daily subcutaneous injection) of Teriparatide has a net anabolic effect on bone by predominantly stimulating osteoblast proliferation, differentiation, and activity. Bisphosphonates inhibit the mevalonate pathway, and Denosumab binds to RANKL.

Question 7890

Topic: Physiology & Rehabilitation

A marathon runner sustains a partial gastrocnemius tear. The predominant muscle fibers in this athlete's gastrocnemius are optimized for sustained endurance. Which of the following biochemical and physiological profiles best characterizes Type I muscle fibers compared to Type II fibers?

. High mitochondrial density, aerobic metabolism, and slow twitch properties
. Low mitochondrial density, anaerobic metabolism, and fast twitch properties
. High glycogen content, rapid fatigue, and high peak tension
. Low myoglobin content, high glycolytic enzyme activity, and slow twitch properties
. High capillary density, anaerobic metabolism, and fast twitch properties

Correct Answer & Explanation

. High mitochondrial density, aerobic metabolism, and slow twitch properties

Explanation

Type I muscle fibers are 'slow-twitch' fibers optimized for endurance and postural control. They rely primarily on oxidative (aerobic) metabolism, possess a high density of mitochondria and myoglobin (giving them a red appearance), have an extensive capillary network, and are highly resistant to fatigue. Conversely, Type II fibers ('fast-twitch') rely heavily on glycolytic (anaerobic) metabolism, have lower mitochondrial density, and fatigue much more rapidly but generate higher peak tension.

Question 7891

Topic: 1. General Principles & Basic Science

An orthopedic surgeon is evaluating the biomechanical stability of pedicle screws for a complex lumbar fusion.

According to established biomechanical principles, the pullout strength of a cortical screw is most directly proportional to which of the following variables?

. Outer (major) thread diameter
. Inner (root) thread diameter
. Thread pitch
. Core thickness
. Screw head size

Correct Answer & Explanation

. Outer (major) thread diameter

Explanation

The pullout strength of a screw depends directly on the volume of bone engaged between the threads. It is mathematically proportional to the outer (major) thread diameter, the length of thread engagement, and the shear strength of the surrounding bone. It is inversely proportional to the pitch. The inner (root) diameter is the primary determinant of the screw's torsional and bending strength, but not its pullout strength.

Question 7892

Topic: Biomechanics & Biomaterials
A patient undergoes a total hip arthroplasty using a highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) liner. Evaluation of the liner mechanics in a laboratory model shows dimensional changes over time when subjected to a constant physiological load, without the generation of particulate debris. Which of the following biomechanical phenomena best describes this finding?
. Abrasive wear
. Creep
. Adhesive wear
. Fatigue failure
. Galvanic corrosion

Correct Answer & Explanation

. Creep

Explanation

Creep, or cold flow, is the progressive deformation of a viscoelastic material under a constant load over time. In UHMWPE components, this dimensional change occurs without the generation of wear debris. This is distinct from abrasive or adhesive wear, which involve the physical removal of material and generation of particulate debris that can lead to osteolysis.

Question 7893

Topic: Biology, Genetics & Bone Healing

A novel pharmacological agent designed to accelerate fracture healing is found to act by directly inhibiting sclerostin. Which of the following best describes the downstream cellular effect of this medication?

. Increased osteoclast apoptosis
. Decreased RANKL expression by osteoblasts
. Increased beta-catenin translocation to the nucleus
. Inhibition of Runx2 transcription
. Direct activation of osteoprotegerin (OPG)

Correct Answer & Explanation

. Increased beta-catenin translocation to the nucleus

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes that acts as an antagonist to the Wnt/beta-catenin signaling pathway. By binding to LRP5/6 receptors, it prevents Wnt signaling, thereby inhibiting bone formation. Medications that inhibit sclerostin (e.g., romosozumab) allow Wnt to bind to its receptors, leading to intracellular stabilization and accumulation of beta-catenin, which then translocates to the nucleus to upregulate target genes that drive osteoblastogenesis and bone formation.

Question 7894

Topic: Biomechanics & Biomaterials

When comparing a solid titanium alloy (Ti-6Al-4V) intramedullary nail to a solid stainless steel (316L) intramedullary nail of the identical diameter and cross-sectional design, which of the following biomechanical statements is most accurate?

. The titanium nail has a higher modulus of elasticity.
. The titanium nail has a lower modulus of elasticity.
. The stainless steel nail provides superior biocompatibility and osteointegration.
. The stainless steel nail is more susceptible to galvanic corrosion when used in isolation.
. The titanium nail exhibits higher yield strength but lower ultimate tensile strength.

Correct Answer & Explanation

. The titanium nail has a lower modulus of elasticity.

Explanation

Titanium alloys have a lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel. This property makes titanium more flexible and reduces stress shielding at the fracture site. Stainless steel has a much higher modulus of elasticity, making it significantly stiffer. Both materials are highly biocompatible, though titanium generally exhibits superior osteointegration.

Question 7895

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture and presents immediately with a secondary complete radial nerve palsy. Electromyography (EMG) is performed at 4 weeks post-injury and reveals abundant fibrillation potentials and positive sharp waves in the brachioradialis. What is the clinical significance of this EMG finding?

. It represents intact motor end plates indicative of a pure neuropraxia.
. It indicates active muscle denervation resulting from Wallerian degeneration.
. It demonstrates early physiological reinnervation with nascent motor units.
. It implies a primary myopathic process mimicking a peripheral nerve injury.
. It signifies axonotmesis with a guarantee of full spontaneous recovery.

Correct Answer & Explanation

. It indicates active muscle denervation resulting from Wallerian degeneration.

Explanation

Fibrillation potentials and positive sharp waves on an EMG are classic indicators of active muscle denervation. They arise spontaneously from individual denervated muscle fibers. These findings typically appear 3 to 4 weeks after a nerve injury severe enough to cause axonal loss and distal Wallerian degeneration (axonotmesis or neurotmesis). In contrast, neuropraxia (conduction block) involves an intact axon and does not produce fibrillation potentials.

Question 7896

Topic: Biology, Genetics & Bone Healing
A novel therapeutic agent is being studied for the treatment of Paget's disease. The drug targets the sealing zone of osteoclasts, preventing the creation of the isolated acidic microenvironment necessary for bone resorption. Which cell surface receptor is primarily targeted by this medication to disrupt osteoclast attachment to the bone matrix?
. Integrin alpha-5 beta-1 (α5β1)
. Integrin alpha-v beta-3 (αvβ3)
. Integrin alpha-2 beta-1 (α2β1)
. Cadherin-11
. CD44

Correct Answer & Explanation

. Integrin alpha-v beta-3 (αvβ3)

Explanation

Osteoclasts attach firmly to the bone matrix to form a 'sealing zone,' isolating the resorption pit (Howship's lacuna). This attachment is primarily mediated by the transmembrane receptor integrin alpha-v beta-3 (αvβ3), which recognizes and binds to RGD (Arginine-Glycine-Aspartic acid) amino acid sequences present on bone matrix proteins such as osteopontin and bone sialoprotein.

Question 7897

Topic: Biology, Genetics & Bone Healing

Which of the following accurately describes the mechanism of action of osteoprotegerin (OPG) in bone metabolism?

. It binds directly to the RANK receptor on osteoclasts to stimulate bone resorption
. It acts as a soluble decoy receptor for RANKL, preventing it from binding to RANK
. It upregulates sclerostin production by osteocytes to inhibit Wnt signaling
. It binds directly to hydroxyapatite and inhibits osteoclast ruffled border formation
. It promotes the differentiation of mesenchymal stem cells into mature osteoblasts

Correct Answer & Explanation

. It acts as a soluble decoy receptor for RANKL, preventing it from binding to RANK

Explanation

Osteoprotegerin (OPG) is a soluble decoy receptor produced primarily by osteoblasts. By binding to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), OPG prevents RANKL from interacting with its physiologic receptor, RANK, located on the surface of osteoclast precursors and mature osteoclasts. This effectively inhibits osteoclast differentiation, activation, and survival, leading to decreased bone resorption.

Question 7898

Topic: 1. General Principles & Basic Science

Figure 1 shows a histological section of normal articular cartilage. Which of the following biochemical changes is characteristic of the normal aging process in articular cartilage, distinguishing it from early osteoarthritis?

. Increased total water content
. Decreased chondroitin sulfate to keratin sulfate ratio
. Increased synthesis and concentration of Type II collagen
. Increased total proteoglycan content
. Increased hydraulic permeability

Correct Answer & Explanation

. Decreased chondroitin sulfate to keratin sulfate ratio

Explanation

Normal aging of articular cartilage is characterized by a decrease in total water content, a decrease in cellularity, and a decrease in the ratio of chondroitin sulfate to keratin sulfate (as keratin sulfate concentrations remain stable or increase relative to the declining chondroitin sulfate). In contrast, early osteoarthritis is characterized by an increase in water content, increased hydraulic permeability, and a fragmented collagen network.

Question 7899

Topic: Biomechanics & Biomaterials

A surgeon is revising a failed subtrochanteric femur fracture fixation. The original construct consisted of a titanium intramedullary nail and a stainless steel cerclage wire. Upon removal, significant dark tissue staining and localized metal degradation are noted precisely at the contact point between the wire and the nail. Which of the following principles best explains this phenomenon?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., titanium and stainless steel) are in direct physical contact within an electrolytic medium (such as human body fluids). This creates a galvanic cell, leading to accelerated corrosion of the less noble (more anodic) metal. Fretting corrosion is a mechanically induced process caused by micromotion, while crevice corrosion occurs in oxygen-depleted micro-environments like the interface between a screw head and a plate of the same material.

Question 7900

Topic: Biomechanics & Biomaterials

Stress-shielding around a rigid femoral stem is a well-known cause of aseptic loosening and proximal femoral bone resorption. To minimize stress shielding based on material properties, an implant should theoretically possess a modulus of elasticity that closely mimics that of cortical bone. Which of the following structural implant biomaterials has a modulus of elasticity closest to that of human cortical bone?

. Cobalt-chromium-molybdenum alloy
. Titanium alloy (Ti-6Al-4V)
. 316L Stainless steel
. Alumina ceramic
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

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

Explanation

Cortical bone has a modulus of elasticity of roughly 15-20 GPa. Titanium alloys (e.g., Ti-6Al-4V) have a modulus of elasticity of approximately 110 GPa. While still stiffer than bone, titanium is much closer to cortical bone's modulus than other structural metals such as 316L stainless steel (~200 GPa) or cobalt-chromium alloys (~220 GPa). Ceramics like alumina have even higher stiffness (~380-400 GPa). Thus, titanium alloy is widely used for cementless femoral stems to help decrease stress shielding.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page