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1. General Principles & Basic Science MCQs

Practice Set 399 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 7961

Topic: 1. General Principles & Basic Science

A basic science researcher is studying the tribology of healthy articular cartilage during the stance phase of the gait cycle. Under these conditions of high physiological load and extremely low sliding speeds, the fluid film is largely depleted. Which lubrication regime primarily protects the articular surfaces from wear under these specific conditions?

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

Correct Answer & Explanation

. Boundary lubrication

Explanation

Joint lubrication relies on multiple mechanisms depending on loads and sliding speeds. Under high-load and low-speed conditions (such as the stance phase of gait or standing), fluid films break down, and Boundary Lubrication predominates. This is mediated by surface-active molecules, primarily lubricin (PRG4) and hyaluronic acid, which are bound to the superficial zone of the cartilage, preventing direct cartilage-to-cartilage contact and wear.

Question 7962

Topic: Infection, Pharmacology & VTE

A 55-year-old male develops a chronic periprosthetic joint infection of the knee caused by Staphylococcus epidermidis. The persistence of this organism on the implant surface is primarily facilitated by a highly adherent biofilm. Which of the following is the key component of the extracellular polymeric substance (EPS) that affords structural integrity and antibiotic resistance in S. epidermidis biofilms?

. Peptidoglycan
. Polysaccharide intercellular adhesin (PIA)
. Lipopolysaccharide (LPS)
. Teichoic acid
. Fibronectin-binding protein

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

In Staphylococcus epidermidis, biofilm formation and structural integrity are heavily dependent on Polysaccharide Intercellular Adhesin (PIA), which is synthesized by enzymes encoded in the icaADBC operon. PIA forms the main volume of the extracellular polymeric substance (EPS) matrix, shielding the bacterial colony from host immune responses and systemic antibiotics, necessitating surgical removal of the hardware.

Question 7963

Topic: Physiology & Rehabilitation

A 30-year-old weightlifter feels a sharp 'pop' in his distal arm during a heavy preacher curl exercise. According to the sliding filament theory and the length-tension relationship of skeletal muscle, at what sarcomere length is maximum active isometric force generated?

. When actin and myosin filaments are completely non-overlapping
. When the sarcomere is maximally stretched beyond resting length
. At intermediate lengths with optimal overlap of actin and myosin cross-bridges
. When the Z-lines are abutting the myosin filaments causing maximal shortening
. When the muscle is undergoing rapid concentric isokinetic contraction

Correct Answer & Explanation

. At intermediate lengths with optimal overlap of actin and myosin cross-bridges

Explanation

The length-tension curve of skeletal muscle demonstrates that maximal active tension is generated at an intermediate (resting) sarcomere length (approx. 2.0-2.2 micrometers). At this length, there is optimal overlap between actin and myosin filaments, allowing the maximum number of cross-bridges to form. Extreme stretch eliminates filament overlap, and extreme shortening causes physical interference between filaments and the Z-discs, both of which reduce active tension.

Question 7964

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a midshaft tibial fracture and is treated with a dynamically locked intramedullary nail. The fracture gap is 2 mm. According to Perren's strain theory, what is the maximum interfragmentary strain that will still permit the direct formation of lamellar bone across the fracture gap?

. 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 dictates that a specific tissue will only form in a fracture gap if the tissue can tolerate the strain (deformation) present. Lamellar bone is brittle and can only form under very low strain conditions (less than 2%). Woven bone can tolerate up to 10% strain, cartilage can tolerate between 10% and 30% strain, and granulation tissue can tolerate up to 100% strain. Absolute stability (strain < 2%) is required for primary (lamellar) bone healing.

Question 7965

Topic: Surgical Anatomy & Approaches

A 28-year-old patient sustains a closed midshaft humerus fracture resulting in an immediate radial nerve palsy. EMGs performed at 4 weeks show fibrillation potentials but no motor unit action potentials. Which of the following describes the correct order of the connective tissue layers in a peripheral nerve, from innermost (surrounding individual axons) to outermost (surrounding the entire nerve)?

. Epineurium, Perineurium, Endoneurium
. Endoneurium, Epineurium, Perineurium
. Endoneurium, Perineurium, Epineurium
. Perineurium, Endoneurium, Epineurium
. Epineurium, Endoneurium, Perineurium

Correct Answer & Explanation

. Endoneurium, Perineurium, Epineurium

Explanation

The connective tissue layers of a peripheral nerve, from deep to superficial, are: the Endoneurium (surrounds individual axons and their Schwann cells), the Perineurium (surrounds groups of axons to form fascicles, providing primary mechanical strength and maintaining the blood-nerve barrier), and the Epineurium (the outermost layer surrounding the entire nerve and the interfascicular spaces).

Question 7966

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman with severe osteoporosis is treated with romosozumab to reduce her risk of fragility fractures. Which of the following best describes the molecular mechanism of action of this medication?

. Inhibition of the RANKL-RANK interaction
. Binding and inhibition of sclerostin
. Direct agonism of the parathyroid hormone (PTH) receptor
. Direct inhibition of the osteoclast ruffled border H+-ATPase
. Stimulation of endogenous osteoprotegerin (OPG) production

Correct Answer & Explanation

. Binding and inhibition of sclerostin

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin. Sclerostin is a glycoprotein produced primarily by osteocytes that naturally inhibits the Wnt/beta-catenin signaling pathway. By blocking sclerostin, romosozumab disinhibits the Wnt pathway, leading to increased osteoblast differentiation and bone formation, while also secondarily decreasing bone resorption.

Question 7967

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament reconstruction, the surgeon tensions the soft tissue graft and secures it at a constant length for several minutes before final fixation. The surgeon notices that the force required to hold the graft at this specific length gradually decreases over time. Which biomechanical property does this phenomenon represent?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the viscoelastic property defined as a time-dependent decrease in stress (or force) when a material is held at a constant strain (or length). Creep, conversely, is the gradual increase in strain (deformation) when a material is held under a constant stress (load). Hysteresis refers to the energy lost as heat during a loading and unloading cycle.

Question 7968

Topic: 1. General Principles & Basic Science

A basic science researcher is studying a full-thickness osteochondral defect model in an animal. Histologic evaluation of normal articular cartilage demonstrates the tidemark. Which of the following best describes the predominant collagen orientation and primary biomechanical function of the zone located immediately superficial to the tidemark?

. Parallel to the joint surface; resists shear stress
. Randomly oriented; resists compressive stress
. Perpendicular to the joint surface; resists compressive stress
. Randomly oriented; resists shear stress
. Parallel to the joint surface; resists tensile stress

Correct Answer & Explanation

. Perpendicular to the joint surface; resists compressive stress

Explanation

The zone immediately superficial to the tidemark is the deep zone of articular cartilage. In the deep zone, collagen fibers are oriented perpendicular to the joint surface and anchor the cartilage to the underlying calcified zone and subchondral bone. The primary biomechanical role of this zone and its structural arrangement is to resist high compressive loads.

Question 7969

Topic: Biomechanics & Biomaterials

A 55-year-old male undergoes a total hip arthroplasty using highly cross-linked polyethylene (HXLPE). During manufacturing, the polyethylene is subjected to gamma irradiation followed by a remelting process. What is the primary purpose of the remelting step?

. To increase the ultimate tensile strength of the polyethylene
. To extinguish free radicals and reduce long-term oxidation
. To increase the crystalline content to improve elasticity
. To promote chain scission to allow smoother articulation
. To decrease the overall density of the polyethylene bearing

Correct Answer & Explanation

. To extinguish free radicals and reduce long-term oxidation

Explanation

Irradiation is used to create highly cross-linked polyethylene to significantly improve wear resistance. However, irradiation cleaves polymer chains, generating free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidation, embrittlement, and catastrophic failure. Remelting the plastic above its melting temperature extinguishes these free radicals, preventing oxidation, though it slightly decreases the ultimate yield and fatigue strength.

Question 7970

Topic: Surgical Anatomy & Approaches

A 28-year-old patient sustains a closed midshaft humerus fracture and presents with a complete radial nerve palsy. Electromyography (EMG) performed at 4 weeks shows fibrillation potentials and positive sharp waves in the brachioradialis, but no motor unit action potentials. What pathophysiologic process best accounts for these findings distal to the injury site?

. Neuropraxia with intact axonal continuity
. Primary demyelination without axonal loss
. Retrograde chromatolysis extending to the dorsal root ganglion
. Wallerian degeneration due to loss of axoplasmic transport
. Segmental demyelination at the nodes of Ranvier

Correct Answer & Explanation

. Wallerian degeneration due to loss of axoplasmic transport

Explanation

The presence of fibrillation potentials and positive sharp waves on EMG 3 to 4 weeks after injury indicates muscle denervation, signifying a loss of axonal continuity (axonotmesis or neurotmesis) rather than a simple conduction block (neuropraxia). Severed axons undergo Wallerian degeneration distal to the site of injury. Macrophages and Schwann cells clear the myelin and axonal debris, preparing the endoneurial tubes for regenerating axons.

Question 7971

Topic: Biomechanics & Biomaterials

A surgeon secures a titanium alloy plate with a stainless steel screw to stabilize a complex periarticular fracture. Over the next year, the patient develops localized pain and swelling. Radiographs show lucency around the screw without signs of infection. Which of the following electrochemical processes is most likely responsible for this complication?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as titanium and stainless steel) are placed in direct physical contact within an electrolytic environment (like body fluids). The metal with the lower electrochemical potential (anodic metal) undergoes accelerated corrosion to protect the more noble (cathodic) metal. Mixing implant metals should generally be avoided to prevent this complication.

Question 7972

Topic: Biomechanics & Biomaterials

According to the Blix length-tension curve for skeletal muscle biomechanics, maximum active isometric tension is generated at an optimal sarcomere resting length. This peak in force production is directly attributed to which of the following?

. Actin filaments completely overlapping and colliding in the center of the sarcomere
. Maximal overlap between actin filaments and myosin cross-bridges
. The muscle being stretched to the point of zero overlap between actin and myosin
. Complete relaxation of the series elastic components within the tendon
. Maximum plastic deformation of the titin filaments

Correct Answer & Explanation

. Maximal overlap between actin filaments and myosin cross-bridges

Explanation

The length-tension relationship dictates that maximum active tension in a muscle fiber is produced at the resting length where there is optimal spatial overlap between the actin and myosin filaments. This allows for the maximum number of cross-bridge formations. If the sarcomere is overly shortened, actin filaments overlap and interfere with each other; if excessively stretched, overlap decreases, reducing cross-bridge potential.

Question 7973

Topic: Physiology & Rehabilitation

During normal human gait, the center of mass undergoes specific kinematic displacements. Evaluation of the vertical ground reaction force (vGRF) curve reveals a 'double-hump' pattern. Which phases of the gait cycle correspond to the highest magnitudes of vertical ground reaction force?

. Mid-stance
. Initial contact (Heel strike) and toe-off
. Terminal swing
. Loading response and terminal stance
. Pre-swing

Correct Answer & Explanation

. Loading response and terminal stance

Explanation

During normal walking, the vertical ground reaction force (vGRF) exhibits a characteristic two-peak (double-hump) pattern. The first peak occurs during the loading response (weight acceptance) as the limb absorbs the downward acceleration of the body's mass. The second peak occurs during terminal stance as the plantarflexors forcefully push off, accelerating the body upward and forward. Mid-stance is represented by the trough between these two peaks.

Question 7974

Topic: 1. General Principles & Basic Science
To reduce perioperative blood loss in a patient undergoing bilateral total knee arthroplasty, the surgical team administers intravenous tranexamic acid (TXA). What is the specific molecular mechanism of action of this pharmacologic agent?
. Irreversible inhibition of cyclooxygenase-1 in platelets
. Direct binding and inhibition of Factor Xa in the coagulation cascade
. Competitive inhibition of plasminogen activation to plasmin
. Enhancement of antithrombin III activity
. Cross-linking of fibrin monomers to stabilize the primary clot

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation to plasmin

Explanation

Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly and competitively binding to the lysine-binding sites on plasminogen. This interaction prevents plasminogen from binding to fibrin and being activated into plasmin, thereby inhibiting fibrinolysis and stabilizing the existing blood clot.

Question 7975

Topic: Biomechanics & Biomaterials

A 25-year-old athlete undergoes an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft. During graft preparation, the surgeon applies a constant load of 20 Newtons to the graft for 10 minutes on the back table, observing that the graft slowly elongates over time before its length stabilizes. Which of the following viscoelastic properties does this phenomenon describe?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is a classic viscoelastic property defined as the time-dependent increase in strain (deformation) of a material when subjected to a constant stress (load). In ligament reconstruction, pre-tensioning the graft relies on the principle of creep to reduce post-implantation elongation. Stress relaxation, conversely, is the time-dependent decrease in stress under a constant strain. Hysteresis refers to the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 7976

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman with a history of osteoporosis sustains a distal radius fracture. She has been on denosumab for 2 years prior to the injury. At the cellular and molecular level, how does this specific pharmacological agent primarily inhibit bone resorption?

. Binding directly to the ruffled border of mature osteoclasts to prevent acid secretion
. Inducing targeted apoptosis of mature osteoclasts by inhibiting farnesyl pyrophosphate synthase
. Binding to RANKL to prevent its interaction with the RANK receptor on osteoclast precursors
. Acting as a synthetic decoy receptor directly mimicking the action of osteoprotegerin (OPG) on RANK
. Inhibiting the differentiation of mesenchymal stem cells into the osteoclast lineage

Correct Answer & Explanation

. Binding to RANKL to prevent its interaction with the RANK receptor on osteoclast precursors

Explanation

Denosumab is a human monoclonal antibody that directly targets and binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on the surface of osteoclast precursors and mature osteoclasts. This effectively halts osteoclastogenesis, decreases mature osteoclast function, and reduces survival. Bisphosphonates act by inhibiting farnesyl pyrophosphate synthase (nitrogenous) or inducing apoptosis. Osteoprotegerin (OPG) is the body's natural decoy receptor for RANKL; denosumab mimics the function of OPG but does not act on the RANK receptor itself.

Question 7977

Topic: Biomechanics & Biomaterials

In the design and selection of femoral stems for total hip arthroplasty, varying metal alloys are utilized based on their distinct mechanical properties. Compared to Cobalt-Chromium (CoCr) alloys, Titanium (Ti-6Al-4V) alloys exhibit which of the following characteristics?

. Higher modulus of elasticity
. Lower notch sensitivity
. Greater ultimate tensile strength
. Lower modulus of elasticity
. Increased resistance to abrasive wear

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloys (e.g., Ti-6Al-4V) have a lower modulus of elasticity compared to Cobalt-Chromium (CoCr) and stainless steel alloys. This lower modulus closer approximates the stiffness of cortical bone, which is highly beneficial for reducing stress shielding around femoral implants. However, titanium is highly notch sensitive (scratches act as significant stress risers) and has poor resistance to abrasive wear, making it inappropriate for use as a bearing surface (e.g., femoral heads).

Question 7978

Topic: 1. General Principles & Basic Science

Articular cartilage relies on multiple distinct lubrication mechanisms depending on the load applied and the velocity of the joint articulation. During prolonged standing, which represents a high-load and zero-velocity state, which of the following lubrication mechanisms primarily protects the articular surfaces?

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

Correct Answer & Explanation

. Boundary lubrication

Explanation

Boundary lubrication is the primary mechanism protecting articular cartilage under extreme conditions of high loads and low or zero velocities (e.g., prolonged standing). It depends entirely on a monolayer of protective lubricant molecules, primarily lubricin (PRG4) and surface-active phospholipids, physically bound to the articular surface to prevent direct surface-to-surface adhesion. Fluid-film mechanisms (elastohydrodynamic, hydrodynamic, and squeeze-film) require joint motion or dynamic loading to maintain a wedge or film of fluid between the surfaces.

Question 7979

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is the standard bearing surface in modern total hip arthroplasty due to its superior wear characteristics. Which of the following mechanical properties is significantly decreased as a direct consequence of increasing the cross-linking of UHMWPE?
. Fatigue crack propagation resistance
. Oxidation resistance
. Modulus of elasticity
. Melting temperature
. Adhesive wear resistance

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

While highly cross-linking UHMWPE dramatically improves its resistance to adhesive and abrasive wear (thereby reducing osteolysis), it negatively impacts several bulk mechanical properties. The most significant decreases are seen in ductility, ultimate tensile strength, fracture toughness, and fatigue crack propagation resistance. This reduction in fatigue strength makes highly cross-linked polyethylene more susceptible to mechanical failure, such as rim fracture in thin acetabular liners or post breakage in posterior-stabilized knee designs.

Question 7980

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory regarding the biomechanics of fracture fixation, what is the maximum mechanical strain tolerated by lamellar bone tissue before it will fail to form across a fracture gap?

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

Correct Answer & Explanation

. 1%

Explanation

Perren's strain theory dictates that the type of tissue that forms within a fracture gap is strictly determined by the local mechanical strain it can withstand without rupturing. Lamellar bone can only tolerate up to 2% strain. Therefore, absolute stability (strain < 2%) is required for primary bone healing. Woven bone tolerates up to 10% strain, cartilage up to 30%, and granulation tissue up to 100% strain.

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