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1. General Principles & Basic Science MCQs

Practice Set 427 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 8521

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopaedic implants occurs when dissimilar metals are in physical contact within a conductive physiological fluid. Which of the following combinations of implant materials is most strongly contraindicated due to the high risk of severe galvanic corrosion?

. Commercially pure titanium and titanium alloy (Ti-6Al-4V)
. Cobalt-chromium-molybdenum alloy and titanium alloy
. 316L stainless steel and titanium alloy
. Cobalt-chromium-molybdenum alloy and oxidized zirconium
. Tantalum and commercially pure titanium

Correct Answer & Explanation

. 316L stainless steel and titanium alloy

Explanation

Mixing 316L stainless steel and titanium alloy in direct contact is contraindicated due to a significant difference in their electrochemical potentials on the anodic index. This leads to severe galvanic corrosion of the less noble metal (stainless steel). Conversely, cobalt-chromium and titanium alloys are closer in the galvanic series and are frequently combined safely, such as in modular total hip arthroplasty.

Question 8522

Topic: Physiology & Rehabilitation

Eccentric muscle contractions occur when a muscle lengthens while under tension. Compared to concentric contractions, which of the following is a characteristic feature of eccentric contractions?

. They generate significantly less maximum tension or force
. They require greater metabolic energy expenditure (ATP) per unit of force produced
. They are associated with a higher incidence of delayed onset muscle soreness (DOMS)
. They primarily involve the recruitment of type I muscle fibers before type II fibers
. The cross-bridge cycling rate is much higher than in concentric contractions

Correct Answer & Explanation

. They are associated with a higher incidence of delayed onset muscle soreness (DOMS)

Explanation

Eccentric contractions can generate up to twice the force of isometric or concentric contractions while utilizing less ATP, reflecting a higher mechanical efficiency. However, this high force generation induces greater mechanical stress on the muscle fibers and surrounding connective tissue, leading to microtrauma and a significantly higher incidence of delayed onset muscle soreness (DOMS).

Question 8523

Topic: 1. General Principles & Basic Science

During activities characterized by high articular loads and extremely low sliding velocities, such as initiating movement from a prolonged standing position, which type of lubrication mechanism primarily protects the articular cartilage surfaces?

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

Correct Answer & Explanation

. Boundary lubrication

Explanation

Under conditions of high load and low sliding velocity, fluid-film lubrication mechanisms (like elastohydrodynamic or squeeze-film) break down. In these situations, boundary lubrication predominates. This mechanism relies on a protective monolayer of specific molecules, primarily lubricin (PRG4) and surface-active phospholipids, chemically bound to the articular surface to prevent direct cartilage-on-cartilage contact.

Question 8524

Topic: Biology, Genetics & Bone Healing

Osteoclastogenesis and the resorptive activity of osteoclasts are heavily regulated by the osteoblast lineage. Which of the following systemic hormones exerts its catabolic bone effect by directly binding to osteoblasts, subsequently upregulating RANKL expression and downregulating osteoprotegerin (OPG)?

. Calcitonin
. Parathyroid hormone (PTH)
. 1,25-dihydroxyvitamin D3
. Estrogen
. Transforming growth factor-beta (TGF-beta)

Correct Answer & Explanation

. Parathyroid hormone (PTH)

Explanation

Parathyroid hormone (PTH) regulates serum calcium by stimulating bone resorption. Because osteoclasts lack PTH receptors, PTH binds to PTH1R receptors on osteoblasts. This stimulates the osteoblasts to increase their expression of RANKL and decrease the secretion of OPG. The elevated RANKL/OPG ratio promotes osteoclast differentiation, maturation, and survival, leading to increased bone resorption.

Question 8525

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with chronic knee pain. Imaging demonstrates an eccentric, purely lytic lesion in the distal femoral epiphysis, extending precisely to the subchondral bone plate. Biopsy reveals numerous multinucleated giant cells within a background of mononuclear stromal cells. Which of the following molecular targets is primarily expressed by the true neoplastic cells in this condition?

. Receptor Activator of Nuclear factor Kappa-B (RANK)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Osteoprotegerin (OPG)
. Runt-related transcription factor 2 (RUNX2)
. SRY-box transcription factor 9 (SOX9)

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

The clinical and histological presentation defines a Giant Cell Tumor (GCT) of bone. In GCT, the actual neoplastic elements are the mononuclear spindle-shaped stromal cells, not the giant cells themselves. These neoplastic stromal cells aberrantly express high levels of RANKL, which subsequently recruits normal monocyte-macrophage precursors and induces them to fuse into reactive, multinucleated giant cells expressing RANK. This pathway is the pharmacological target for Denosumab in unresectable GCT cases.

Question 8526

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman is evaluated for persistent right knee pain. Radiographs demonstrate an eccentrically located, purely lytic lesion in the proximal tibial epiphysis extending to the subchondral bone, with cortical thinning but no matrix calcification. Biopsy confirms a giant cell tumor of bone. Due to the proximity to the joint space and the size of the defect, she is treated preoperatively with denosumab to downstage the tumor and reconstitute the cortical rim. What is the primary mechanism of action of this pharmacological agent?

. Induction of direct apoptosis in the neoplastic mononuclear stromal cells
. Inhibition of the vascular endothelial growth factor (VEGF) pathway
. Monoclonal antibody targeting and binding to RANK ligand (RANKL)
. Selective inhibition of the tyrosine kinase c-Kit receptor
. Agonism of the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Monoclonal antibody targeting and binding to RANK ligand (RANKL)

Explanation

Giant cell tumor of bone (GCTB) is characterized by neoplastic mononuclear stromal cells that express high levels of RANK ligand (RANKL). RANKL recruits and activates non-neoplastic, multinucleated giant cells (osteoclast-like cells) which are responsible for the aggressive local bone destruction. Denosumab is a fully human monoclonal antibody that binds directly to RANKL, preventing it from interacting with the RANK receptor on the surface of osteoclast precursors. This effectively halts osteoclastogenesis and subsequent bone resorption, leading to stabilization and calcification of the tumor margin, which can facilitate surgical curettage.

Question 8527

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with generalized bone pain, profound fatigue, and a recent pathological fracture of the left humerus. Laboratory tests reveal normocytic anemia, hypercalcemia, and an elevated serum monoclonal paraprotein spike. Skeletal survey shows multiple 'punched-out' lytic lesions in the skull, spine, and pelvis. Which of the following best explains the specific mechanism driving the uncoupled bone remodeling and severe lack of osteoblastic bone formation seen in this disease process?

. Overexpression of bone morphogenetic protein 2 (BMP-2) by tumor cells
. Inhibition of the Wnt/beta-catenin signaling pathway by Dickkopf-1 (Dkk-1)
. Decreased systemic production of interleukin-6 (IL-6)
. Increased expression of osteoprotegerin (OPG) within the bone marrow microenvironment
. Activating mutation in the fibroblast growth factor receptor 3 (FGFR3)

Correct Answer & Explanation

. Inhibition of the Wnt/beta-catenin signaling pathway by Dickkopf-1 (Dkk-1)

Explanation

Multiple myeloma is characterized by purely osteolytic bone lesions due to severely uncoupled bone remodeling: there is robust osteoclast activation alongside profound suppression of osteoblast activity. Myeloma cells secrete factors such as Dickkopf-1 (Dkk-1) and sclerostin, which potently inhibit the Wnt/beta-catenin signaling pathway. The Wnt pathway is essential for osteoblast differentiation and function; its inhibition results in the failure of bone formation. Additionally, myeloma cells upregulate RANKL and downregulate osteoprotegerin (OPG), further driving osteoclast-mediated bone destruction. IL-6 is actually increased in myeloma and serves as a major growth and survival factor for the malignant plasma cells.

Question 8528

Topic: 1. General Principles & Basic Science

In normal mature articular cartilage, which zone is characterized by the highest concentration of proteoglycans and the presence of the largest diameter collagen fibrils oriented perpendicular to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage features large-diameter collagen fibrils aligned perpendicular to the surface to resist compressive forces. It also contains the highest proteoglycan content and the lowest water content.

Question 8529

Topic: Biomechanics & Biomaterials



If a stainless steel screw is placed through a titanium alloy plate in a saline physiological environment, galvanic corrosion may occur. Which of the following best describes the resulting electrochemical process?

. Titanium acts as the anode and corrodes
. Titanium acts as the cathode and corrodes
. Stainless steel acts as the anode and corrodes
. Stainless steel acts as the cathode and corrodes
. Both metals act as anodes and corrode equally

Correct Answer & Explanation

. Stainless steel acts as the anode and corrodes

Explanation

In a mixed-metal galvanic couple between stainless steel and titanium, the less noble stainless steel acts as the anode and undergoes accelerated corrosion. Titanium is more noble and acts as the cathode.

Question 8530

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, absolute stability constructs (such as a properly applied lag screw and neutralization plate) promote primary bone healing. What is the maximum interfragmentary strain threshold compatible with primary bone healing?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing (Haversian remodeling without visible callus) requires an absolute stability environment with less than 2% interfragmentary strain. Strains between 2% and 10% result in secondary healing with callus formation.

Question 8531

Topic: 1. General Principles & Basic Science
Low molecular weight heparin (LMWH) is frequently utilized for deep vein thrombosis prophylaxis following major orthopedic surgery. Its primary mechanism of action involves binding to antithrombin III, which then predominantly inactivates which of the following coagulation factors?
. Factor IIa (Thrombin)
. Factor VIIa
. Factor VIII
. Factor Xa
. Factor XII

Correct Answer & Explanation

. Factor Xa

Explanation

LMWH binds to antithrombin III and preferentially accelerates its inhibition of Factor Xa with minimal effect on thrombin (Factor IIa). This contrasts with unfractionated heparin, which equally inhibits both Factor Xa and Factor IIa.

Question 8532

Topic: Infection, Pharmacology & VTE



Biofilm formation is a critical and devastating step in the pathogenesis of periprosthetic joint infection. Which extracellular component makes up the vast majority of the biofilm's volume and protects the sessile bacteria from host defenses?

. Fibrinogen networks
. Extracellular DNA matrices
. Peptidoglycan layers
. Polysaccharide glycocalyx
. Lipopolysaccharide envelopes

Correct Answer & Explanation

. Polysaccharide glycocalyx

Explanation

The biofilm matrix is predominantly composed of a highly hydrated polysaccharide glycocalyx. This thick slime layer shields the embedded sessile bacteria from antibiotics, antibodies, and immune cell phagocytosis.

Question 8533

Topic: 1. General Principles & Basic Science
A patient suffers a severe stretch injury to the brachial plexus, and a specific nerve lesion is categorized histologically as a Sunderland Grade III injury. Which of the following best describes the anatomical extent of this injury?
. Myelin disruption with intact axon continuity
. Axon and myelin disruption with an intact endoneurial tube
. Axon and endoneurium disruption with an intact perineurium
. Axon, endoneurium, and perineurium disruption with an intact epineurium
. Complete nerve transection involving all layers

Correct Answer & Explanation

. Axon and endoneurium disruption with an intact perineurium

Explanation

A Sunderland Grade III nerve injury involves loss of continuity of both the axon and the endoneurium, while the perineurium remains intact. Spontaneous recovery is highly variable and often compromised by intrafascicular scarring.

Question 8534

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman presents with severe back pain and is found to have multiple osteolytic bone lesions. Biopsy reveals sheets of monoclonal plasma cells. Which of the following cell-signaling molecules is most directly responsible for the massive osteoclast activation seen in this disease process?

. Interleukin-2 (IL-2)
. Transforming growth factor-beta (TGF-b)
. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Interferon-gamma

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Multiple myeloma cells stimulate local osteoblasts and marrow stromal cells to overexpress RANKL while downregulating OPG. RANKL binds directly to RANK on osteoclast precursors, driving extensive osteoclastogenesis and subsequent lytic bone destruction.

Question 8535

Topic: Biology, Genetics & Bone Healing



A 60-year-old man with increasing hat size and bowing of his tibiae is diagnosed with Paget's disease of bone. During the active mixed phase of this metabolic disease, which of the following is the pathognomonic histological finding?

. Empty lacunae with surrounding necrotic adipocytes
. A chaotic mosaic pattern of woven and lamellar bone with prominent cement lines
. Sheets of atypical, hyperchromatic chondrocytes
. Mononuclear cell infiltration in the synovial subintima
. Diffuse unmineralized osteoid seams thicker than 15 micrometers

Correct Answer & Explanation

. A chaotic mosaic pattern of woven and lamellar bone with prominent cement lines

Explanation

The hallmark histologic feature of Paget's disease is a chaotic "mosaic" pattern of woven and lamellar bone, separated by irregular, heavily stained cement lines. This reflects the excessively rapid, uncoordinated turnover driven by hyperactive osteoclasts and osteoblasts.

Question 8536

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized effectively for treating severe osteoporosis and preventing skeletal-related events in metastatic bone disease. What is the specific molecular mechanism of action of this pharmacological agent?

. Binds directly to bone hydroxyapatite and disrupts the osteoclast ruffled border
. Stimulates osteoblast differentiation directly via the Wnt/beta-catenin signaling pathway
. Acts as a recombinant parathyroid hormone analog to intermittently promote bone formation
. Functions as a monoclonal antibody that binds and neutralizes RANKL
. Acts as a selective estrogen receptor modulator to decrease bone resorption

Correct Answer & Explanation

. Functions as a monoclonal antibody that binds and neutralizes RANKL

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to and inhibits RANKL. By neutralizing RANKL, it prevents the activation and survival of osteoclasts, profoundly decreasing bone resorption.

Question 8537

Topic: 1. General Principles & Basic Science

A thorough understanding of normal gait biomechanics is essential. During the normal human gait cycle, which muscle undergoes an eccentric contraction during the initial contact (heel strike) to loading response phase to safely lower the foot to the ground?

. Gastrocnemius
. Tibialis anterior
. Soleus
. Tibialis posterior
. Peroneus brevis

Correct Answer & Explanation

. Tibialis anterior

Explanation

The tibialis anterior muscle fires eccentrically immediately following heel strike to control plantarflexion and smoothly lower the forefoot to the floor. Weakness or paralysis of this muscle results in an uncontrolled "slap foot" gait.

Question 8538

Topic: Biomechanics & Biomaterials

During the toe region of a tendon's stress-strain curve, which of the following events is primarily occurring?

. Microscopic failure of collagen fibers
. Uncrimping of collagen fibers
. Macroscopic failure of the tendon
. Plastic deformation of the tendon
. Elastic deformation of isolated collagen fibrils

Correct Answer & Explanation

. Uncrimping of collagen fibers

Explanation

The 'toe region' of the stress-strain curve corresponds to the uncrimping of collagen fibers. As the tendon is stretched further, it enters the linear elastic region where actual fiber stretching occurs.

Question 8539

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants due to its biocompatibility. Compared to cobalt-chromium alloys, titanium has which of the following biomechanical properties?

. Higher modulus of elasticity and lower fatigue strength
. Lower modulus of elasticity and greater notch sensitivity
. Higher ultimate tensile strength and lower ductility
. Increased galvanic corrosion when coupled with stainless steel
. Superior wear characteristics in articulation with polyethylene

Correct Answer & Explanation

. Lower modulus of elasticity and greater notch sensitivity

Explanation

Titanium has a lower modulus of elasticity (closer to bone) compared to cobalt-chrome, which reduces stress shielding. However, it is highly notch-sensitive and has poor wear characteristics when articulating with polyethylene.

Question 8540

Topic: 1. General Principles & Basic Science

In which zone of articular cartilage are the collagen fibers oriented parallel to the joint surface and contain the highest concentration of water?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone features collagen fibers oriented parallel to the joint surface to resist shear forces. It also has the highest water concentration but the lowest proteoglycan content.

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