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1. General Principles & Basic Science MCQs

Practice Set 374 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 7461

Topic: Biology, Genetics & Bone Healing

A 72-year-old male presents with deep, aching thigh pain, progressive hearing loss, and noticeable anterior bowing of his femur. Laboratory studies reveal an isolated, significantly elevated serum alkaline phosphatase level with normal calcium and phosphorus. A bone biopsy of the affected femur is most likely to demonstrate which of the following histological hallmarks?

. Extensive unmineralized osteoid seams surrounding normal osteoblast morphology
. A disorganized mosaic pattern of lamellar bone interspersed with prominent, haphazard cement lines
. Extremely dense cortical bone with absent Haversian systems and fibrous replacement of the medullary marrow space
. Collections of malignant, pleomorphic spindle cells producing delicate, lace-like malignant osteoid
. Subperiosteal bone resorption, dissecting osteitis, and numerous multi-nucleated giant cells forming 'brown tumors'

Correct Answer & Explanation

. Extensive unmineralized osteoid seams surrounding normal osteoblast morphology

Explanation

The clinical scenario (bone pain, bowing, hearing loss, isolated elevated alk phos in an elderly male) is classic for Paget's disease of bone (osteitis deformans). The disease involves phases of excessive osteoclastic resorption followed by frantic, disorganized osteoblastic bone formation. The resulting histologic hallmark, particularly during the mixed or sclerotic phase, is a 'mosaic' or 'jigsaw puzzle' pattern of woven and lamellar bone with prominent, haphazard cement lines reflecting the chaotic remodeling process.

Question 7462

Topic: Biomechanics & Biomaterials

A surgeon is deciding between a solid and a hollow intramedullary nail of the exact same outer diameter and material for a diaphyseal tibia fracture. Compared to the solid nail, the hollow nail possesses which of the following mechanical characteristics?

. Higher bending rigidity
. Lower torsional rigidity
. Higher area moment of inertia
. Increased susceptibility to galvanic corrosion
. Greater resistance to fatigue failure

Correct Answer & Explanation

. Higher bending rigidity

Explanation

Torsional rigidity is proportional to the polar moment of inertia. For a cylinder, a hollow core reduces the polar moment of inertia compared to a solid cylinder of the identical outer diameter, thus lowering its torsional rigidity. Bending rigidity (determined by the area moment of inertia) is also lower for a hollow nail compared to a solid nail of the exact same outer diameter.

Question 7463

Topic: 1. General Principles & Basic Science

Intravenous tranexamic acid (TXA) is administered to a patient undergoing a complex spinal fusion to reduce perioperative blood loss. Which of the following best describes the precise molecular mechanism of action of this agent?

. Direct inhibition of factor Xa
. Competitive inhibition of plasminogen activation
. Irreversible inhibition of cyclooxygenase
. Enhancement of antithrombin III activity
. Direct stimulation of von Willebrand factor release

Correct Answer & Explanation

. Direct inhibition of factor Xa

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin and being activated into plasmin, thereby effectively inhibiting fibrinolysis and stabilizing clots.

Question 7464

Topic: Biology, Genetics & Bone Healing

During the reparative phase of secondary fracture healing, a cartilaginous soft callus forms and is subsequently replaced by bone. Which specific type of collagen is most predominantly synthesized by the cells during the peak of this soft callus formation?

. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Secondary fracture healing involves endochondral ossification. During the soft callus phase, chondrocytes rapidly proliferate and synthesize a cartilage matrix that is predominantly rich in Type II collagen. Later in the process, hypertrophic chondrocytes express Type X collagen to facilitate calcification, before osteoblasts finally lay down Type I collagen to form woven bone.

Question 7465

Topic: Physiology & Rehabilitation

During the normal human gait cycle, the peak force across the hip joint can reach up to 2.5 to 3 times body weight. During which specific phase of the gait cycle does the maximum joint reaction force across the hip occur?

. Heel strike (Initial contact)
. Mid-stance
. Terminal stance (Heel off)
. Initial swing
. Terminal swing

Correct Answer & Explanation

. Heel strike (Initial contact)

Explanation

The maximum joint reaction force at the hip occurs during the late stance phase, specifically terminal stance (heel off). During this phase, the hip abductor muscles contract forcefully to stabilize the pelvis as the body's center of mass accelerates forward over the supporting limb, creating the highest compressive forces across the joint articulation.

Question 7466

Topic: Biomechanics & Biomaterials

A patient presents with localized pain and swelling two years after internal fixation of a distal radius fracture with a stainless steel plate and screws. Radiographs show extensive peri-implant radiolucency. Revision surgery reveals dark grey tissue staining and loosening of one screw, which was found to be inadvertently made of titanium. What type of corrosion primarily caused this phenomenon?

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

Correct Answer & Explanation

. Pitting corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within an electrolytic medium (such as human body fluids). An electrochemical cell is created, and the less noble (more anodic) metal corrodes preferentially and rapidly. This is why mixing different implant metals in a single construct is contraindicated.

Question 7467

Topic: 1. General Principles & Basic Science

Following a severe stretch injury to the brachial plexus, a patient exhibits a delayed protective muscle reflex to sudden elongation. Which specialized mechanoreceptor is primarily responsible for detecting both the rate and magnitude of muscle stretch to initiate the myotatic (stretch) reflex?

. Golgi tendon organ
. Muscle spindle
. Ruffini ending
. Pacinian corpuscle
. Free nerve ending

Correct Answer & Explanation

. Golgi tendon organ

Explanation

The muscle spindle is an encapsulated sensory receptor located parallel to extrafusal muscle fibers. It detects changes in muscle length and the rate of that change, initiating the myotatic (stretch) reflex via Ia afferent fibers. Conversely, the Golgi tendon organ is located in series at the musculotendinous junction, detecting muscle tension to initiate the inverse myotatic reflex (autogenic inhibition).

Question 7468

Topic: 1. General Principles & Basic Science

Demineralized bone matrix (DBM) is frequently used in orthopedic surgery to augment spinal fusions. The primary biologic property of DBM that makes it beneficial for bone healing is directly attributed to the presence of which of the following?

. Viable osteoprogenitor cells
. Structural hydroxyapatite for immediate load-bearing
. Bone morphogenetic proteins (BMPs)
. Exogenous vascular endothelial growth factor (VEGF)
. High concentrations of Type II collagen

Correct Answer & Explanation

. Viable osteoprogenitor cells

Explanation

Demineralized bone matrix (DBM) is an allograft processed by acid extraction to remove the mineral component (hydroxyapatite). This process exposes the underlying osteoinductive proteins, primarily Bone Morphogenetic Proteins (BMPs). DBM is predominantly osteoinductive and osteoconductive, but lacks viable cells (it is non-osteogenic) and provides minimal structural support.

Question 7469

Topic: Biomechanics & Biomaterials

A 65-year-old patient receives a total hip arthroplasty with a highly cross-linked polyethylene liner. What is the primary purpose of remelting the polyethylene after gamma irradiation during the manufacturing process?

. To increase the degree of cross-linking
. To eliminate free radicals and reduce oxidation
. To increase the yield strength and fatigue resistance
. To sterilize the component before packaging
. To improve the modulus of elasticity

Correct Answer & Explanation

. To increase the degree of cross-linking

Explanation

Gamma irradiation induces cross-linking in ultra-high-molecular-weight polyethylene (UHMWPE) to improve wear characteristics, but it also generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidative degradation and subsequent implant failure. Remelting allows trapped free radicals to recombine and be eliminated, though it slightly decreases the mechanical properties (such as yield strength and fatigue resistance) compared to annealing.

Question 7470

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of early osteoarthritis, which of the following represents the earliest biochemical change in the articular cartilage matrix?

. Increase in total proteoglycan content
. Decrease in total water content
. Increase in total water content
. Increase in collagen type II synthesis
. Decrease in chondrocyte metabolism

Correct Answer & Explanation

. Increase in total proteoglycan content

Explanation

The earliest recognizable biochemical change in osteoarthritis is an increase in the water content of the articular cartilage. This occurs due to the breakdown of the superficial collagen meshwork, which normally constrains the hydrophilic proteoglycans. Once the collagen network is damaged, the proteoglycans swell and absorb more water. As the disease progresses to later stages, the total proteoglycan content eventually decreases.

Question 7471

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain that allows for the formation of lamellar bone during fracture healing?

. 1 to 2 percent
. 10 percent
. 30 percent
. 50 percent
. 100 percent

Correct Answer & Explanation

. 1 to 2 percent

Explanation

Perren's strain theory dictates that a specific tissue will not form if the interfragmentary strain exceeds the maximum strain that the tissue can tolerate before failure. Lamellar bone is rigid and can only tolerate up to 2% strain. Woven bone can tolerate up to 10% strain, cartilage can tolerate 10-30%, and granulation tissue can tolerate up to 100%. Therefore, absolute stability (strain <2%) is required for primary (lamellar) bone healing.

Question 7472

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis and a recent vertebral compression fracture is started on teriparatide. Which of the following best describes the cellular mechanism of action of this medication?

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Binding to RANKL to prevent interaction with RANK on osteoclasts
. Intermittent activation of osteoblast PTH receptors stimulating bone formation
. Downregulation of sclerostin leading to increased Wnt signaling
. Selective estrogen receptor modulation in bone tissue

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently (e.g., via daily subcutaneous injection), it exerts an anabolic effect by directly stimulating osteoblasts via the PTH/PTHrP receptor, leading to increased bone formation. Continuous exposure to endogenous PTH (as in hyperparathyroidism) leads to net bone resorption. Option A describes bisphosphonates, Option B describes denosumab, and Option D describes romosozumab.

Question 7473

Topic: Biomechanics & Biomaterials

During tensile testing of a healthy flexor tendon, the stress-strain curve initially exhibits a non-linear 'toe region'. Which microscopic structural characteristic is primarily responsible for this specific region of the curve?

. Rupture of intermolecular cross-links
. Uncrimping of type I collagen fibrils
. Plastic deformation of the elastin matrix
. Microfailure of individual collagen fascicles
. Viscoelastic stress relaxation

Correct Answer & Explanation

. Rupture of intermolecular cross-links

Explanation

The stress-strain curve of tendons and ligaments typically begins with a non-linear 'toe region' at low strains (up to approximately 2%). This is anatomically due to the straightening, or 'uncrimping', of the naturally crimped type I collagen fibrils. Once straightened, the tendon enters the linear (elastic) region, where stiffness increases significantly until microscopic failure (yield point) and eventual macroscopic rupture occur.

Question 7474

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel plate with titanium alloy screws for the internal fixation of a diaphyseal fracture. Which of the following types of corrosion is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in physical contact within an electrolytic medium (such as blood or interstitial fluid). In this scenario, mixing stainless steel and titanium creates a galvanic cell, resulting in accelerated corrosion of the more anodic metal (typically the stainless steel). To avoid this, orthopedic implants of different metal alloys should generally not be mixed.

Question 7475

Topic: Surgical Anatomy & Approaches

A 28-year-old male sustains a closed midshaft humerus fracture with an associated radial nerve palsy. If the nerve has undergone Wallerian degeneration but the endoneurial tubes remain completely intact, what is the approximate expected rate of axonal regeneration?

. 0.1 mm/day
. 1 mm/day
. 5 mm/day
. 10 mm/day
. 25 mm/day

Correct Answer & Explanation

. 0.1 mm/day

Explanation

The scenario describes axonotmesis (Sunderland second degree), where the axon is disrupted leading to distal Wallerian degeneration, but the endoneurium, perineurium, and epineurium remain intact. Axonal regeneration in humans proceeds at a rate of approximately 1 mm/day (or about 1 inch per month). This physiologic constant is critical for clinically predicting the timeline of expected motor and sensory recovery.

Question 7476

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibrils 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

The superficial (tangential) zone comprises the top 10-20% of articular cartilage. It is characterized by the highest water content (up to 80%), the lowest proteoglycan content, and densely packed type II collagen fibers arranged parallel to the articular surface. This structural arrangement is uniquely suited to withstand the high shear forces experienced at the joint surface.

Question 7477

Topic: Physiology & Rehabilitation

During a prolonged, low-intensity orthopedic rehabilitation exercise (such as endurance cycling), which muscle fiber type is predominantly recruited, and what is its primary metabolic pathway for energy production?

. Type I fibers; Anaerobic glycolysis
. Type I fibers; Oxidative phosphorylation
. Type IIa fibers; Creatine phosphate
. Type IIb fibers; Anaerobic glycolysis
. Type IIb fibers; Oxidative phosphorylation

Correct Answer & Explanation

. Type I fibers; Anaerobic glycolysis

Explanation

Type I muscle fibers are 'slow-twitch' fibers characterized by high endurance, abundant mitochondria, and high myoglobin content. They are fatigue-resistant and recruited primarily during prolonged, low-intensity activities. Their primary source of ATP is aerobic metabolism via oxidative phosphorylation. Conversely, Type IIb fibers are 'fast-twitch', fatigue quickly, and rely mainly on anaerobic glycolysis for rapid bursts of power.

Question 7478

Topic: Biomechanics & Biomaterials

A modular revision total hip arthroplasty fails due to significant wear and metal debris at the head-neck taper junction. Which type of corrosion is primarily responsible for this specific mode of failure at the modular interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs at the contact sites between materials under load, such as the modular head-neck taper junction (trunnionosis) in a total hip arthroplasty. Micromotion disrupts the passive protective oxide layer, leading to mechanical wear and subsequent corrosive attack.

Question 7479

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is frequently utilized in major orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its primary mechanism of action?

. Direct inhibition of thrombin
. Activation of Factor Xa
. Reversible blockade of lysine binding sites on plasminogen
. Irreversible inhibition of cyclooxygenase-1 in platelets
. Direct conversion of fibrinogen to cross-linked fibrin

Correct Answer & Explanation

. Direct inhibition of thrombin

Explanation

Tranexamic acid is a synthetic derivative of the amino acid lysine. It competitively and reversibly inhibits the activation of plasminogen to plasmin by binding to lysine receptor sites on plasminogen. This prevents plasmin from breaking down fibrin clots, thereby inhibiting fibrinolysis.

Question 7480

Topic: Biomechanics & Biomaterials

During mechanical tensile testing of a healthy human anterior cruciate ligament, the initial non-linear 'toe region' observed on the stress-strain curve is primarily due to which of the following phenomena?

. Plastic deformation of collagen cross-links
. Microfailure of individual collagen fibrils
. Uncrimping of the naturally wavy collagen fibers
. Elastic deformation of hydroxyapatite crystals
. Viscoelastic creep of the ligament

Correct Answer & Explanation

. Plastic deformation of collagen cross-links

Explanation

The initial 'toe region' of the stress-strain curve for ligaments and tendons represents the uncrimping or straightening of the naturally wavy collagen fibers. Once the fibers are straight, the curve enters the linear (elastic) region where further stress causes proportional strain.

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