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1. General Principles & Basic Science MCQs

Practice Set 254 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 5061

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) are used clinically to enhance bone healing. They act as osteoinductive agents by binding to cell surface receptors and initiating an intracellular signaling cascade. Which of the following intracellular signaling molecules is the primary direct mediator of the canonical BMP pathway?

. Beta-catenin
. Smad 1/5/8
. NF-kappaB
. JAK/STAT
. Cyclic AMP

Correct Answer & Explanation

. Smad 1/5/8

Explanation

Bone Morphogenetic Proteins (BMPs) belong to the TGF-beta superfamily. The canonical signaling pathway for BMPs involves binding to serine/threonine kinase cell surface receptors, which then phosphorylate intracellular receptor-regulated Smads, specifically Smad 1, 5, and 8. These complex with the co-Smad (Smad 4) and translocate to the nucleus to regulate gene transcription for osteoblastic differentiation. Beta-catenin is involved in the Wnt signaling pathway. NF-kappaB is involved in RANKL/osteoclast signaling.

Question 5062

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, which factor is most crucial for the transition from a soft cartilaginous callus to a hard bony callus?

. Increased motion at the fracture site
. Decreased oxygen tension
. Angiogenesis and vascular ingrowth
. High levels of sclerostin
. Apoptosis of osteoblasts

Correct Answer & Explanation

. Angiogenesis and vascular ingrowth

Explanation

The transition from soft (cartilaginous) callus to hard (bony) callus during endochondral ossification requires adequate vascular ingrowth (angiogenesis), which brings in chondroclasts, osteoprogenitor cells, and oxygen required for matrix mineralization.

Question 5063

Topic: Infection, Pharmacology & VTE

A patient is scheduled for an elective total knee arthroplasty. He is currently taking Rivaroxaban for atrial fibrillation. What is the mechanism of action of this medication?

. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K antagonist
. Low molecular weight heparin
. COX-1 inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban (Xarelto) is a direct oral anticoagulant (DOAC) that functions as a direct and reversible inhibitor of Factor Xa, interrupting the intrinsic and extrinsic pathway of the blood coagulation cascade. Dabigatran, conversely, is a direct thrombin (Factor IIa) inhibitor.

Question 5064

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the epiphysis of the proximal tibia extending to the subchondral bone, with no sclerotic margin. Biopsy shows multinucleated giant cells in a stroma of mononuclear cells. Which monoclonal antibody is approved for treating unresectable or recurrent forms of this tumor?

. Infliximab
. Denosumab
. Rituximab
. Bevacizumab
. Trastuzumab

Correct Answer & Explanation

. Denosumab

Explanation

The lesion described is a Giant Cell Tumor of bone (GCT). The mononuclear stromal cells express RANKL, which recruits and stimulates osteoclast-like giant cells causing osteolysis. Denosumab is a monoclonal antibody against RANKL and is highly effective in treating unresectable or recurrent GCTs.

Question 5065

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a lytic, eccentrically located lesion in the distal femur extending to the subchondral bone. A biopsy confirms Giant Cell Tumor (GCT) of bone. She is treated preoperatively with denosumab. What is the exact mechanism of action of denosumab in this context?

. Inhibition of RANK ligand (RANKL)
. Direct induction of osteoclast apoptosis
. Inhibition of tyrosine kinase pathways
. Inhibition of vascular endothelial growth factor (VEGF)
. Selective estrogen receptor modulation

Correct Answer & Explanation

. Inhibition of RANK ligand (RANKL)

Explanation

Denosumab is a human monoclonal antibody that specifically binds to and inhibits RANK ligand (RANKL). In Giant Cell Tumors, the neoplastic stromal cells overexpress RANKL, which recruits and activates the multinucleated giant cells (osteoclast-like cells) responsible for massive bone resorption. Denosumab blocks this interaction, reducing the tumor's osteolysis and giant cell population.

Question 5066

Topic: 1. General Principles & Basic Science

Articular cartilage provides a nearly frictionless surface and absorbs tremendous loads. Which specific extracellular matrix component is primarily responsible for retaining water to provide compressive stiffness?

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

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant large proteoglycan in articular cartilage. Its highly negatively charged glycosaminoglycan (GAG) side chains (chondroitin sulfate and keratin sulfate) attract cations and water via the Donnan osmotic effect. This swelling pressure, constrained by the collagen network, provides cartilage with its compressive stiffness.

Question 5067

Topic: Biomechanics & Biomaterials
To significantly decrease the wear rate of ultra-high-molecular-weight polyethylene (UHMWPE) in total joint arthroplasty, it is subjected to high-dose irradiation. However, this process requires a secondary step to prevent long-term failure. What is the primary purpose of this secondary step (e.g., melting or annealing)?
. To restore the tensile strength to pre-irradiation levels
. To eliminate residual free radicals and improve oxidative stability
. To increase the crystallinity of the polyethylene
. To cross-link the amorphous regions of the polymer
. To sterilize the component before packaging

Correct Answer & Explanation

. To eliminate residual free radicals and improve oxidative stability

Explanation

Highly cross-linking UHMWPE via gamma irradiation significantly improves wear resistance but generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidation, delamination, and embrittlement. A secondary thermal treatment (melting or annealing) or doping with Vitamin E is necessary to quench these free radicals and ensure oxidative stability.

Question 5068

Topic: 1. General Principles & Basic Science

In the highly organized structure of healthy articular cartilage, which layer is characterized by the highest concentration of proteoglycans, the lowest water content, and collagen fibers arranged perpendicularly to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibers oriented perpendicular to the articular surface. It also has the highest concentration of proteoglycans and the lowest water content, optimizing it to resist compressive forces.

Question 5069

Topic: Biology, Genetics & Bone Healing
Following arthroscopic rotator cuff repair, healing at the tendon-bone interface progresses through inflammatory, proliferative, and remodeling phases. During the early proliferative phase of healing at the footprint, which type of collagen is predominately synthesized?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type III collagen

Explanation

During the proliferative phase of tendon-bone healing (and tendon healing in general), fibroblasts rapidly synthesize Type III collagen, which forms disorganized granulation tissue. During the remodeling phase, this is gradually replaced by stronger, highly organized Type I collagen.

Question 5070

Topic: Biomechanics & Biomaterials
Cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is heavily utilized in total hip arthroplasty to reduce wear. However, increasing the radiation dose to achieve higher cross-linking has which of the following detrimental effects on the mechanical properties of the polyethylene liner?
. Decreased fatigue strength and fracture toughness
. Increased oxidation potential over time
. Decreased elastic modulus leading to increased creep
. Increased adhesive wear against cobalt-chromium
. Increased melting temperature

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Highly cross-linked polyethylene drastically reduces volumetric wear. However, the radiation process used to induce cross-linking significantly decreases mechanical properties, most notably fatigue strength, ultimate tensile strength, and fracture toughness, which can increase the risk of rim fracture or structural failure in certain applications.

Question 5071

Topic: Biology, Genetics & Bone Healing

Denosumab is used as a medical treatment for large or unresectable giant cell tumors of bone (GCTB). By what specific molecular mechanism does denosumab halt the progression of this disease?

. Direct induction of apoptosis in the neoplastic mononuclear cells
. Inhibition of RANK ligand (RANKL) expressed by neoplastic mononuclear cells, preventing recruitment of reactive giant cells
. Inhibition of osteoprotegerin (OPG), leading directly to osteoclast death
. Inhibition of vascular endothelial growth factor (VEGF), cutting off tumor vascularity
. Direct binding to the RANK receptor on the surface of normal osteoblasts

Correct Answer & Explanation

. Inhibition of RANK ligand (RANKL) expressed by neoplastic mononuclear cells, preventing recruitment of reactive giant cells

Explanation

Giant cell tumor of bone consists of neoplastic mononuclear stromal cells that overexpress RANKL. This overexpression recruits and activates normal monocytes to become reactive, bone-resorbing multinucleated giant cells. Denosumab is a monoclonal antibody that binds directly to RANKL, halting this interaction and stopping bone destruction.

Question 5072

Topic: Biology, Genetics & Bone Healing

During secondary bone healing, endochondral ossification is heavily reliant on the differentiation of mesenchymal stem cells into chondrocytes within the soft callus. Which of the following transcription factors is the primary master regulator driving this chondrogenic differentiation?

. Runx2 (Cbfa1)
. Osterix (Osx)
. Sclerostin
. Sox9
. Beta-catenin

Correct Answer & Explanation

. Sox9

Explanation

Sox9 is the master transcription factor responsible for the commitment and differentiation of mesenchymal stem cells into chondrocytes during endochondral ossification. Runx2 and Osterix are master regulators for osteoblast differentiation.

Question 5073

Topic: Surgical Anatomy & Approaches

A 30-year-old male sustains a high radial nerve palsy following a mid-shaft humerus fracture. After 9 months with no electromyographic evidence of recovery, tendon transfers are planned. Using the classic Brand transfer for radial nerve palsy, which of the following tendon transfers is primarily used to restore thumb extension?

. Flexor carpi ulnaris (FCU) to Extensor pollicis longus (EPL)
. Flexor digitorum superficialis (FDS) to Extensor pollicis longus (EPL)
. Pronator teres (PT) to Extensor pollicis longus (EPL)
. Brachioradialis (BR) to Extensor pollicis longus (EPL)
. Palmaris longus (PL) to Extensor pollicis longus (EPL)

Correct Answer & Explanation

. Palmaris longus (PL) to Extensor pollicis longus (EPL)

Explanation

The classic Brand transfer for radial nerve palsy utilizes the Pronator Teres (PT) to Extensor Carpi Radialis Brevis (ECRB) for wrist extension, the Flexor Carpi Radialis (FCR) to the Extensor Digitorum Communis (EDC) for finger extension, and the Palmaris Longus (PL) to the Extensor Pollicis Longus (EPL) for thumb extension. Note that the FCR is transferred to the EPL in some modifications (like the modified Boyes transfer), but the standard Brand transfer uses PL to EPL.

Question 5074

Topic: Biology, Genetics & Bone Healing

Secondary fracture healing, which involves the formation of an intermediate cartilaginous callus, relies heavily on endochondral ossification. Which of the following mechanical environments most strongly promotes this type of bone healing?

. Rigid internal fixation with absolute stability
. Extensive stripping of the local periosteum
. Micromotion at the fracture site providing relative stability
. Application of high-dose local bisphosphonates
. Complete surgical removal of the fracture hematoma

Correct Answer & Explanation

. Micromotion at the fracture site providing relative stability

Explanation

Secondary fracture healing occurs via endochondral ossification, where a cartilage template is first formed and then replaced by bone (callus formation). This process is stimulated by relative stability, which allows for controlled micromotion at the fracture site. Techniques like intramedullary nailing or bridge plating provide relative stability. Absolute stability (e.g., rigid compression plating) eliminates micromotion and promotes primary bone healing via cutting cones, without callus formation.

Question 5075

Topic: 1. General Principles & Basic Science
A 55-year-old woman presents with adult acquired flatfoot deformity (AAFD) secondary to posterior tibial tendon dysfunction. On examination, she has a flexible hindfoot valgus and is unable to perform a single-leg heel rise on the affected side. Radiographs confirm a flexible pes planovalgus without severe arthritic changes. What is the most appropriate primary surgical intervention for this stage of disease?
. Custom orthotics and physical therapy
. Gastrocnemius recession alone
. Flexor digitorum longus (FDL) transfer and medial displacement calcaneal osteotomy (MDCO)
. Triple arthrodesis
. Tibiotalocalcaneal arthrodesis

Correct Answer & Explanation

. Flexor digitorum longus (FDL) transfer and medial displacement calcaneal osteotomy (MDCO)

Explanation

The patient has Stage II AAFD (flexible deformity, inability to perform single heel rise). The standard surgical treatment for Stage II disease involves soft tissue reconstruction (FDL transfer to the navicular to substitute for the dysfunctional PTT) combined with a bony procedure to correct the biomechanics and protect the transfer, most commonly a medial displacement calcaneal osteotomy (MDCO). Triple arthrodesis is reserved for Stage III (rigid deformity or significant arthritis).

Question 5076

Topic: 1. General Principles & Basic Science

Articular cartilage is organized into multiple histological zones, each with specific biomechanical properties. Which zone is characterized by the largest diameter collagen fibrils oriented perpendicular to the articular surface, the highest concentration of proteoglycans, and the lowest water content?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils, which are oriented perpendicular to the articular surface. This zone also possesses the highest concentration of proteoglycans and the lowest water content, providing significant resistance to compressive forces.

Question 5077

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum amount of interfragmentary strain that can be tolerated for primary (direct) bone healing to occur without the formation of a visible fracture callus?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Greater than 30%
. 100%

Correct Answer & Explanation

. Less than 2%

Explanation

According to Perren's strain theory, primary (direct) bone healing via cutting cones requires absolute stability. This corresponds to an interfragmentary strain of less than 2%. Secondary bone healing (which involves callus formation) occurs at strains between 2% and 10%. Granulation tissue forms at strains up to 100%.

Question 5078

Topic: Biology, Genetics & Bone Healing

A 32-year-old female with a recurrent Giant Cell Tumor (GCT) of the distal femur is started on neoadjuvant medical therapy to facilitate joint-salvage surgery. She is given Denosumab, a human monoclonal antibody. What is the exact cellular target and mechanism of action of this medication in the context of GCT?

. Binds to the RANK receptor on the reactive osteoclast-like giant cells
. Binds to RANKL expressed by the neoplastic mononuclear stromal cells
. Acts as an analogue to Osteoprotegerin (OPG) on osteoblasts
. Inhibits Vascular Endothelial Growth Factor (VEGF) preventing angiogenesis
. Inhibits tyrosine kinase receptors in the neoplastic giant cells

Correct Answer & Explanation

. Binds to RANKL expressed by the neoplastic mononuclear stromal cells

Explanation

Denosumab is a monoclonal antibody that targets Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). In Giant Cell Tumor of bone, the neoplastic cells are the mononuclear stromal cells, which express high levels of RANKL. Denosumab binds this RANKL, preventing it from binding to the RANK receptor on the reactive (non-neoplastic) osteoclast-like giant cells, thereby halting their recruitment, maturation, and bone-resorbing activity.

Question 5079

Topic: Biomechanics & Biomaterials

During an Anterior Cruciate Ligament (ACL) reconstruction, the surgeon tensions the quadrupled hamstring graft to a specific length and secures it. Over the next several minutes, the tension (force) required by the fixation device to maintain that exact length decreases. This physical phenomenon is characteristic of viscoelastic materials and is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the property of a viscoelastic material whereby the stress (internal force/tension) decreases over time when the material is held at a constant strain (length). Conversely, 'creep' is the increase in strain (deformation/length) over time when the material is subjected to a constant stress (load).

Question 5080

Topic: 1. General Principles & Basic Science

During a primary Zone II flexor tendon repair, a surgeon considers the biomechanical trade-offs of different suture configurations. Increasing the number of core suture strands crossing the repair site primarily improves which specific biomechanical property of the repaired tendon?

. Resistance to gap formation under cyclic loading
. Tendon glide during early active motion protocols
. Work of flexion
. Ultimate tensile strength of the repair
. Intrinsic cellular healing rate

Correct Answer & Explanation

. Ultimate tensile strength of the repair

Explanation

The ultimate tensile strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the repair site (e.g., a 4-strand repair is generally stronger than a 2-strand repair). However, increasing strands also increases the bulk of the repair, which can negatively impact tendon glide and increase the 'work of flexion' through the pulley system.

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