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1. General Principles & Basic Science MCQs

Practice Set 652 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 13021

Topic: 1. General Principles & Basic Science

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

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

Articular cartilage is structurally divided into zones. The superficial (tangential) zone contains the highest water content (approximately 80%), the lowest proteoglycan concentration, and Type II collagen fibers aligned parallel to the joint surface to resist shear forces. In contrast, the deep zone has the lowest water content, highest proteoglycan concentration, and vertically oriented collagen fibers to resist compression.

Question 13022

Topic: Biomechanics & Biomaterials
Which of the following modifications to ultra-high-molecular-weight polyethylene (UHMWPE) most effectively reduces adhesive and abrasive wear when used in total joint arthroplasty?
. Gamma irradiation in an oxygen-rich environment
. Ethylene oxide gas sterilization
. Highly cross-linking the polyethylene with subsequent thermal treatment
. Decreasing the molecular weight of the polymer
. Adding a pure cobalt-chromium backing to the liner

Correct Answer & Explanation

. Highly cross-linking the polyethylene with subsequent thermal treatment

Explanation

Highly cross-linking UHMWPE, typically achieved through gamma or electron beam irradiation followed by thermal treatment (remelting or annealing to eliminate free radicals), significantly improves its wear resistance. This process drastically decreases both adhesive and abrasive wear. However, highly cross-linking the material can slightly reduce its mechanical properties, such as fatigue strength and ductility.

Question 13023

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for a typical ductile metal used in orthopedic implants, which of the following best defines the yield point?

. The point of ultimate mechanical failure and fracture
. The transition point from elastic deformation to plastic deformation
. The maximum stress the material can withstand before necking begins
. The exact point where the modulus of elasticity reaches zero
. The region representing the material's toughness

Correct Answer & Explanation

. The transition point from elastic deformation to plastic deformation

Explanation

The yield point on a stress-strain curve marks the limit of elastic behavior and the beginning of plastic behavior. Prior to the yield point, deformation is completely reversible (elastic phase); once the load is removed, the material returns to its original shape. Beyond the yield point, the material undergoes permanent (plastic) deformation.

Question 13024

Topic: Biology, Genetics & Bone Healing

Secondary fracture healing proceeds via endochondral ossification. During the cartilaginous callus phase of this process, which specific cell type is primarily responsible for the production of Type X collagen?

. Proliferating chondrocytes
. Hypertrophic chondrocytes
. Osteoblasts
. Multinucleated osteoclasts
. Undifferentiated mesenchymal stem cells

Correct Answer & Explanation

. Hypertrophic chondrocytes

Explanation

During endochondral ossification in secondary fracture healing, the cartilaginous callus undergoes a maturation process. Hypertrophic chondrocytes are the primary cells responsible for secreting Type X collagen. This specialized collagen alters the extracellular matrix, making it permissive to calcification, which is a critical prerequisite for subsequent vascular invasion and replacement by osteoblasts.

Question 13025

Topic: Infection, Pharmacology & VTE

A 72-year-old patient develops a late chronic periprosthetic joint infection caused by Staphylococcus epidermidis. The pathogenesis heavily relies on the formation of a robust biofilm. What is the primary constituent of the extracellular polymeric substance (glycocalyx) produced by these bacteria?

. Lipopolysaccharides
. Polysaccharides
. Peptidoglycan
. Teichoic acid
. Fibronectin-binding proteins

Correct Answer & Explanation

. Polysaccharides

Explanation

Biofilm formation is a hallmark of orthopedic hardware infections. The biofilm is composed of a self-produced extracellular polymeric substance (EPS), often called the glycocalyx. The major structural components of this protective EPS matrix are complex exopolysaccharides, which shield the bacterial colony from both the host immune system and systemic antibiotics.

Question 13026

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly utilized in spinal fusion surgery. Based on its structural and biological profile, which of the following bone grafting properties does DBM inherently possess?

. Osteoconduction only
. Osteoinduction only
. Osteogenesis only
. Osteoconduction and osteoinduction
. Osteoconduction, osteoinduction, and osteogenesis

Correct Answer & Explanation

. Osteoconduction and osteoinduction

Explanation

Demineralized bone matrix (DBM) is produced by acid-extracting minerals from allograft bone. This process exposes osteoinductive growth factors, primarily Bone Morphogenetic Proteins (BMPs). The remaining type I collagen network serves as an osteoconductive scaffold. Because DBM is devoid of live cells, it lacks osteogenic properties.

Question 13027

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with increasing hat size, unilateral hearing loss, and bowing of his tibiae. Radiographs show pronounced cortical thickening and coarse trabeculae. What is the primary initial cellular abnormality in the pathophysiology of this patient's disease?

. Overactive osteoblasts producing an excess of woven bone
. Increased number and size of hyperactive osteoclasts
. Defective mineralization of the osteoid matrix
. A germline mutation in the Type I collagen gene
. T-cell mediated autoimmune destruction of the articular cartilage

Correct Answer & Explanation

. Increased number and size of hyperactive osteoclasts

Explanation

The clinical presentation is classic for Paget's disease of bone. The initial and primary cellular defect is an abnormality in osteoclasts, which become increased in number, abnormally large, and hyperactive, containing numerous nuclei. This intense resorptive phase triggers a subsequent, disorganized, and chaotic osteoblastic response, leading to structurally weak, woven bone.

Question 13028

Topic: 1. General Principles & Basic Science

According to Sunderland's classification of peripheral nerve injuries, a third-degree nerve injury involves complete disruption of the axon and which other histological structure?

. Myelin sheath only
. Endoneurium only
. Perineurium only
. Endoneurium and perineurium
. Epineurium

Correct Answer & Explanation

. Endoneurium and perineurium

Explanation

In Sunderland's classification: 1st degree is a localized conduction block (neuropraxia/myelin injury). 2nd degree is loss of axonal continuity with intact endoneurium (axonotmesis). 3rd degree involves loss of the axon and endoneurium, while the perineurium remains intact. 4th degree disrupts the axon, endoneurium, and perineurium. 5th degree is a complete nerve transection (epineurium disrupted).

Question 13029

Topic: 1. General Principles & Basic Science

During a knee arthroplasty utilizing a pneumatic tourniquet for 90 minutes, which of the following systemic physiological changes is most likely to occur immediately upon deflation of the tourniquet?

. Increase in central venous pressure
. Increase in core body temperature
. Decrease in end-tidal carbon dioxide (ETCO2)
. Decrease in systemic blood pressure
. Increase in arterial pH (alkalosis)

Correct Answer & Explanation

. Decrease in systemic blood pressure

Explanation

Upon tourniquet deflation, the sudden release of ischemic, acidotic, and hypercapnic blood back into systemic circulation causes marked vasodilation. This typically results in an immediate, transient decrease in systemic blood pressure. Additionally, the washout of metabolites causes a transient increase in end-tidal CO2, a decrease in core body temperature, and a decrease in arterial pH (acidosis).

Question 13030

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is revising a failed internal fixation and considers placing a titanium screw through a 316L stainless steel plate. Which of the following electrochemical principles explains why this specific mixing of metals should generally be avoided?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as stainless steel and titanium) are placed in direct physical contact within a conductive electrolyte environment (such as bodily fluids). The difference in their anodic index creates a small electrical current, leading to accelerated corrosion of the less noble metal (in this case, the stainless steel).

Question 13031

Topic: Physiology & Rehabilitation

During the normal human gait cycle, which muscle group undergoes a critical eccentric contraction during the initial contact to the loading response phase to control joint motion and absorb shock?

. Quadriceps
. Hamstrings
. Gastrocnemius
. Gluteus maximus
. Iliopsoas

Correct Answer & Explanation

. Quadriceps

Explanation

From initial contact (heel strike) to the loading response, the knee flexes slightly to absorb the shock of body weight. The quadriceps muscle group contracts eccentrically during this brief period to control the rate and extent of knee flexion, thereby stabilizing the limb as weight is accepted.

Question 13032

Topic: 1. General Principles & Basic Science

During the normal biological healing process of a completely lacerated and surgically repaired flexor tendon, at what time post-operatively does the repair tissue predictably reach its weakest point, making it most susceptible to iatrogenic rupture?

. 24 to 48 hours
. 7 to 14 days
. 3 to 4 weeks
. 6 to 8 weeks
. 12 weeks

Correct Answer & Explanation

. 7 to 14 days

Explanation

Tendon healing proceeds through inflammatory, proliferative, and remodeling phases. During the transition from the inflammatory phase to the early fibroblastic phase (approximately 7 to 14 days post-operatively), endogenous collagen is degraded by matrix metalloproteinases faster than new collagen is synthesized. This results in significant softening, and the repaired tendon is at its weakest.

Question 13033

Topic: 1. General Principles & Basic Science

The remarkable compressive stiffness and load-bearing capacity of normal articular cartilage are primarily provided by the interaction between interstitial fluid and which of the following structural macromolecules?

. Type II collagen
. Hyaluronic acid
. Aggrecan
. Decorin
. Fibronectin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant large proteoglycan in articular cartilage. It contains a core protein densely packed with chondroitin sulfate and keratan sulfate glycosaminoglycan (GAG) chains. The high concentration of negatively charged GAGs attracts cations and water via the Donnan osmotic effect. This creates a massive swelling pressure that resists compression, providing cartilage with its stiffness.

Question 13034

Topic: Infection, Pharmacology & VTE
A 68-year-old male is scheduled for a total hip arthroplasty. His cardiologist has instructed him to hold his daily Rivaroxaban, which he takes for non-valvular atrial fibrillation. What is the specific pharmacological mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibitor
. Vitamin K epoxide reductase antagonist
. Direct Factor Xa inhibitor
. Indirect Factor Xa inhibitor mediated via antithrombin III binding
. Irreversible ADP (P2Y12) receptor antagonist

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that functions as a highly selective direct Factor Xa inhibitor. By directly inhibiting Factor Xa, it interrupts both the intrinsic and extrinsic pathways of the blood coagulation cascade, preventing thrombin generation and thrombus formation. Unlike fondaparinux, it does not require antithrombin III to exert its effect.

Question 13035

Topic: 1. General Principles & Basic Science

In the repair of a zone II flexor tendon laceration using a multistrand core suture, what is the primary biomechanical advantage of adding a continuous epitendinous suture?

. It promotes intrinsic tendon healing by delaying angiogenesis
. It acts as the primary load-bearing structure during active flexion
. It decreases the work of flexion and increases repair strength by up to 50%
. It allows for immediate passive range of motion without core suture placement
. It primarily prevents the formation of an extrinsic cellular epitenon layer

Correct Answer & Explanation

. It decreases the work of flexion and increases repair strength by up to 50%

Explanation

Adding an epitendinous suture to a core flexor tendon repair significantly improves the construct. It smooths the repair site, decreasing gliding resistance (work of flexion), and provides a biomechanical advantage by increasing the tensile strength of the repair by 10% to 50%, reducing the risk of gap formation during early active motion protocols.

Question 13036

Topic: Biology, Genetics & Bone Healing

According to Perrenโ€™s strain theory of bone healing, what is the maximum amount of strain that lamellar bone can tolerate before failing?

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

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that different tissues tolerate different amounts of strain before failing. Lamellar bone can tolerate only up to 2% strain. Woven bone can tolerate up to 10% strain, and granulation tissue can tolerate up to 100% strain. Absolute stability (strain < 2%) is required for primary bone healing (direct Haversian remodeling).

Question 13037

Topic: 1. General Principles & Basic Science

When designing a cortical bone screw to maximize pullout strength in diaphyseal bone, which of the following geometric modifications will have the greatest direct effect?

. Decreasing the outer thread diameter
. Increasing the core (inner) diameter
. Increasing the outer thread diameter
. Decreasing the thread pitch (increasing threads per inch)
. Increasing the length of the screw head

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

Screw pullout strength is directly proportional to the outer diameter of the thread, the length of thread engagement, and the shear strength of the surrounding material, and inversely proportional to the thread pitch. Therefore, increasing the outer thread diameter provides the most significant structural increase in pullout strength among the given options. Increasing the core diameter increases the screw's bending or fatigue strength but does not primarily dictate pullout strength.

Question 13038

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, highly cross-linked polyethylene (HXLPE) has significantly reduced the rate of osteolysis compared to conventional ultra-high molecular weight polyethylene (UHMWPE). What is the primary mechanism by which vitamin E is utilized during the manufacturing of modern HXLPE?
. To increase the melting temperature of the polymer
. To prevent adhesive wear by increasing crystallinity
. To quench free radicals and prevent in vivo oxidation
. To promote protein binding and improve fluid film lubrication
. To substitute for gamma irradiation in the cross-linking process

Correct Answer & Explanation

. To quench free radicals and prevent in vivo oxidation

Explanation

Highly cross-linked polyethylene is manufactured using radiation to create cross-links that improve wear resistance, but this process generates free radicals. If left untreated, these free radicals react with oxygen, leading to oxidation and subsequent degradation of the polymer. Vitamin E (alpha-tocopherol) is an antioxidant added to HXLPE to quench these free radicals, thereby preventing oxidation without the need for post-irradiation remelting, which can decrease mechanical strength.

Question 13039

Topic: Surgical Anatomy & Approaches

During a direct anterior approach for a total hip arthroplasty, the surgeon develops the superficial internervous plane between the sartorius and the tensor fasciae latae (TFL). What are the respective motor innervations of these two muscles?

. Sartorius: Obturator nerve; TFL: Inferior gluteal nerve
. Sartorius: Femoral nerve; TFL: Inferior gluteal nerve
. Sartorius: Sciatic nerve; TFL: Superior gluteal nerve
. Sartorius: Femoral nerve; TFL: Femoral nerve
. Sartorius: Femoral nerve; TFL: Superior gluteal nerve

Correct Answer & Explanation

. Sartorius: Femoral nerve; TFL: Superior gluteal nerve

Explanation

The direct anterior approach (Smith-Petersen) to the hip utilizes a true internervous plane. Superficial to the fascia, the plane is between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (TFL, innervated by the superior gluteal nerve). Deep to the fascia, the plane is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 13040

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, the mechanical environment dictates the type of tissue that forms in a fracture gap. At a strain level of approximately 5%, which of the following tissues is expected to primarily form?

. Lamellar bone
. Woven bone
. Granulation tissue
. Fibrocartilage
. Hyaline cartilage

Correct Answer & Explanation

. Fibrocartilage

Explanation

Perren's strain theory states that tissues cannot form if the strain exceeds their tolerance limit. Granulation tissue can tolerate high strain (up to 100%). Fibrocartilage tolerates intermediate strain (up to 10%). Woven bone tolerates low strain (up to 2%). Thus, at a strain of 5%, fibrocartilage (cartilaginous callus) will form because the strain is too high for bone formation but within the tolerance of cartilage.

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