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1. General Principles & Basic Science MCQs

Practice Set 233 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 4641

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with persistent knee pain.

Radiographs demonstrate an eccentric, purely lytic lesion in the distal femur that extends directly to the subchondral bone without a distinct sclerotic margin. Core needle biopsy confirms a Giant Cell Tumor of bone. The formation of the multinucleated giant cells characteristic of this tumor is mediated by a specific signaling pathway. Which of the following systemic medications specifically targets and inhibits this pathway?

. Imatinib
. Denosumab
. Bisphosphonates
. Doxorubicin
. Methotrexate

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express RANKL. RANKL recruits osteoclast precursors and stimulates their differentiation into multinucleated, bone-resorbing giant cells via the RANK receptor. Denosumab is a human monoclonal antibody that specifically binds and inhibits RANKL, effectively halting osteoclastogenesis, reducing tumor size, and allowing for intralesional ossification. It is often used as a neoadjuvant or primary treatment for unresectable cases.

Question 4642

Topic: Physiology & Rehabilitation

A 28-year-old competitive weightlifter feels a sudden, sharp 'tearing' sensation in his anterior axilla while performing heavy bench presses. This is followed by immediate weakness, swelling, and extensive ecchymosis. Physical examination reveals a loss of the normal anterior axillary fold contour and pronounced weakness in internal rotation and adduction. Which specific portion of the pectoralis major muscle complex is most commonly ruptured in this classic mechanism of injury?

. Clavicular head at the musculotendinous junction
. Sternal head at or near the humeral insertion
. Clavicular head at the clavicular origin
. Sternal head at the sternal origin
. Abdominal head at the musculotendinous junction

Correct Answer & Explanation

. Sternal head at or near the humeral insertion

Explanation

Pectoralis major ruptures almost exclusively occur in young, active males during eccentric contraction activities, most notoriously the bench press. The sternal (sternocostal) head undergoes maximal stretch and tension when the arm is extended and externally rotated, making it mechanically the most vulnerable to rupture. The injury most commonly occurs at the humeral insertion (tendon avulsion) or at the musculotendinous junction of the sternal head. The clavicular head is often spared.

Question 4643

Topic: Biomechanics & Biomaterials



In the manufacturing of modern orthopedic implants, titanium alloys are frequently utilized due to their excellent biocompatibility and mechanical profile. Which of the following best explains the primary mechanism underlying titanium's exceptional corrosion resistance in vivo?

. Galvanic coupling with surrounding soft tissues and bone
. Spontaneous formation of a passive, inert titanium dioxide (TiO2) layer on its surface
. Its extremely high modulus of elasticity closely matching cortical bone
. Constant release of osteoinductive titanium ions inhibiting macrophage activation
. A low coefficient of friction when articulating against ultra-high-molecular-weight polyethylene

Correct Answer & Explanation

. Spontaneous formation of a passive, inert titanium dioxide (TiO2) layer on its surface

Explanation

Titanium and its alloys owe their high biocompatibility and excellent corrosion resistance to the spontaneous formation of a thin, passive, adherent oxide layer (primarily titanium dioxide, TiO2) on their surface when exposed to air or bodily fluids. This inert layer prevents further oxidation and interaction with the surrounding biological environment.

Question 4644

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing in a long bone, the repair process transitions through several highly coordinated phases. Which type of collagen is predominantly synthesized during the soft callus phase, and which cell type is primarily responsible for its production?
. Type I collagen; osteoblasts
. Type II collagen; chondrocytes
. Type III collagen; fibroblasts
. Type X collagen; hypertrophic chondrocytes
. Type I collagen; chondroblasts

Correct Answer & Explanation

. Type II collagen; chondrocytes

Explanation

Secondary fracture healing involves endochondral ossification. During the soft callus phase, the hematoma is replaced by fibrocartilage, predominantly composed of Type II collagen synthesized by proliferating chondrocytes. This cartilaginous template is later calcified (involving Type X collagen) and finally replaced by woven bone (Type I collagen produced by osteoblasts) during the hard callus phase.

Question 4645

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) initiate intracellular signaling through which of the following receptor types?

. Tyrosine kinase receptors
. Serine/threonine kinase receptors
. G-protein coupled receptors
. Intracellular nuclear receptors
. Ion channel-linked receptors

Correct Answer & Explanation

. Serine/threonine kinase receptors

Explanation

BMPs are members of the TGF-beta superfamily. They initiate intracellular signaling cascades by binding to specific Type I and Type II transmembrane serine/threonine kinase receptors, which leads to the phosphorylation and activation of intracellular Smad proteins.

Question 4646

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a distal femur lytic lesion that is diagnosed as a Giant Cell Tumor of Bone. She is started on Denosumab prior to surgery to help downstage the tumor. What is the mechanism of action of this medication?

. Direct cytotoxicity to neoplastic osteoblasts
. Monoclonal antibody against RANKL, inhibiting osteoclast formation
. Bisphosphonate that inhibits farnesyl pyrophosphate synthase
. VEGF inhibitor blocking tumor angiogenesis
. Monoclonal antibody against the RANK receptor directly

Correct Answer & Explanation

. Monoclonal antibody against RANKL, inhibiting osteoclast formation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding RANKL, it prevents it from interacting with the RANK receptor on osteoclasts and osteoclast precursors, thereby profoundly inhibiting osteoclast formation, function, and survival.

Question 4647

Topic: Biomechanics & Biomaterials

Trunnionosis in total hip arthroplasty is a phenomenon of mechanically assisted crevice corrosion. It is historically most strongly associated with which of the following combinations of head and stem materials?

. Cobalt-chrome head on titanium stem
. Ceramic head on titanium stem
. Ceramic head on cobalt-chrome stem
. Oxidized zirconium head on titanium stem
. Cobalt-chrome head on cobalt-chrome stem

Correct Answer & Explanation

. Cobalt-chrome head on titanium stem

Explanation

Trunnionosis, or mechanically assisted crevice corrosion at the modular head-neck junction, has been most commonly observed in combinations utilizing a large cobalt-chrome (CoCr) femoral head on a titanium alloy stem due to galvanic and fretting corrosion mechanics.

Question 4648

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the superficial (tangential) zone is functionally and structurally characterized by which of the following properties?

. Highest concentration of proteoglycans
. Collagen fibers oriented perpendicular to the joint surface
. Highest concentration of water and collagen fibers oriented parallel to the joint surface
. Chondrocytes arranged in columns
. Highest compressive strength

Correct Answer & Explanation

. Highest concentration of water and collagen fibers oriented parallel to the joint surface

Explanation

The superficial zone of articular cartilage is characterized by the highest water content, lowest proteoglycan content, and densely packed collagen fibers that are oriented parallel to the joint surface to resist sheer stress.

Question 4649

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. What is its primary biochemical mechanism of action?
. Activates the extrinsic coagulation cascade via Factor VII
. Promotes platelet aggregation by binding to von Willebrand factor
. Directly inhibits Factor Xa
. Inhibits the breakdown of fibrin by competitively blocking plasminogen activation
. Enhances the activity of antithrombin III

Correct Answer & Explanation

. Inhibits the breakdown of fibrin by competitively blocking plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly binding four to five lysine receptor sites on plasminogen, which prevents plasmin from binding to and degrading fibrin, thereby stabilizing the blood clot.

Question 4650

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach for the fixation of an acetabular fracture, the surgeon encounters significant bleeding from a vascular anastomosis situated over the superior pubic ramus.

What two main vessels typically form this specific anastomosis (Corona Mortis)?

. Obturator artery and internal iliac artery
. Superior gluteal artery and external iliac artery
. Inferior epigastric artery and obturator artery
. Internal pudendal artery and inferior gluteal artery
. External pudendal artery and medial circumflex femoral artery

Correct Answer & Explanation

. Inferior epigastric artery and obturator artery

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the external iliac and internal iliac vascular systems. Specifically, it connects the inferior epigastric artery or vein (from the external iliac system) to the obturator artery or vein (from the internal iliac system). It is located on the posterior aspect of the superior pubic ramus, approximately 4-7 cm from the pubic symphysis, and is at high risk of iatrogenic injury during the modified Stoppa or ilioinguinal approaches.

Question 4651

Topic: Biology, Genetics & Bone Healing

Romosozumab is a monoclonal antibody utilized in the treatment of severe osteoporosis. It functions by inhibiting sclerostin, thereby promoting bone formation. Sclerostin normally inhibits osteoblastogenesis by antagonizing which of the following signaling pathways?

. RANK/RANKL pathway
. Wnt/beta-catenin pathway via LRP5/6 receptors
. Transforming Growth Factor-beta (TGF-b) pathway
. Bone Morphogenetic Protein-2 (BMP-2) pathway
. Fibroblast Growth Factor (FGF) pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway via LRP5/6 receptors

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes. It acts as a negative regulator of bone formation by binding to the LRP5/6 coreceptors on osteoblasts, thereby inhibiting the canonical Wnt/beta-catenin signaling pathway. By blocking sclerostin, medications like romosozumab allow Wnt signaling to proceed, leading to increased osteoblast activity and bone formation.

Question 4652

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, improper tunnel placement can lead to graft failure or loss of motion. If the femoral tunnel is placed too far anteriorly (shallow) in the intercondylar notch, which of the following graft tension patterns will result?

. Tight in extension and tight in flexion
. Tight in flexion and lax in extension
. Lax in flexion and tight in extension
. Lax in both extension and flexion
. Isotropic tension throughout the entire range of motion

Correct Answer & Explanation

. Tight in flexion and lax in extension

Explanation

Proper femoral tunnel placement is critical for ACL graft isometry. If the femoral tunnel is placed too far anteriorly (shallow, moving away from the anatomic footprint towards the anterior cortex), the distance between the femoral and tibial attachments increases as the knee flexes. This results in the graft being overly tight in flexion (often restricting flexion or leading to graft stretch/failure) and lax in extension. Conversely, placement too far posteriorly leads to a graft that is tight in extension and lax in flexion.

Question 4653

Topic: Infection, Pharmacology & VTE

When executing a posteromedial approach to the knee for open reduction and internal fixation of a posteromedial tibial plateau fracture, the surgeon must develop a plane. The optimal inter-nervous/inter-muscular interval is primarily developed by retracting the medial head of the gastrocnemius laterally and which structure medially?

. Semimembranosus
. Popliteus
. Soleus
. Tibialis posterior
. Pes anserinus

Correct Answer & Explanation

. Pes anserinus

Explanation

The posteromedial approach to the tibial plateau typically utilizes the interval between the medial head of the gastrocnemius (which is retracted laterally, protecting the neurovascular bundle in the popliteal fossa) and the pes anserinus (sartorius, gracilis, semitendinosus), which is retracted medially/anteriorly. The semimembranosus can also be retracted medially. The pes anserinus forms the medial boundary of this superficial dissection window.

Question 4654

Topic: Biomechanics & Biomaterials

Articular cartilage is a highly specialized connective tissue. The primary structural proteoglycan of articular cartilage is aggrecan. Which of the following is the most abundant glycosaminoglycan (GAG) attached to the aggrecan core protein?

. Type I collagen
. Chondroitin sulfate
. Fibronectin
. Elastin
. Hydroxyapatite

Correct Answer & Explanation

. Chondroitin sulfate

Explanation

Aggrecan is the major proteoglycan in articular cartilage and provides the osmotic properties necessary to resist compressive loads. It consists of a core protein with numerous covalently attached glycosaminoglycan (GAG) side chains. The two primary GAGs on aggrecan are chondroitin sulfate and keratan sulfate, with chondroitin sulfate being the most abundant. Type I collagen is primarily found in bone and tendon; articular cartilage is predominantly Type II collagen.

Question 4655

Topic: Biomechanics & Biomaterials
To reduce wear rates in total hip arthroplasty, highly cross-linked polyethylene (HXLPE) was developed. However, the process of irradiation creates free radicals that can lead to long-term oxidation and material degradation. Which of the following manufacturing processes is specifically utilized to neutralize or eliminate these free radicals without requiring post-irradiation thermal treatment (melting or annealing)?
. Gamma irradiation in an inert argon environment
. Ethylene oxide gas sterilization
. Blending or diffusing with Vitamin E (alpha-tocopherol)
. Cold drawing of the ultra-high molecular weight polyethylene
. Addition of barium sulfate to the polymer matrix

Correct Answer & Explanation

. Blending or diffusing with Vitamin E (alpha-tocopherol)

Explanation

Irradiation of UHMWPE creates cross-links that improve wear resistance but also generates free radicals that predispose the material to oxidation. Historically, thermal treatments like remelting or annealing were used to quench these free radicals, but remelting reduces mechanical strength. The addition of Vitamin E (alpha-tocopherol) acts as an antioxidant, quenching free radicals without the need for thermal treatment, thereby preserving the material's mechanical properties while preventing oxidative degradation.

Question 4656

Topic: 1. General Principles & Basic Science

A 35-year-old carpenter lacerates his index finger with a utility knife, sustaining a Zone II injury to the flexor digitorum profundus (FDP) and superficialis (FDS) tendons. A primary multi-strand core suture repair is planned. Which of the following factors is most significantly responsible for increasing the work of flexion and gliding resistance following this repair?

. Use of a 4-strand repair instead of a 2-strand repair
. Epitendinous suture placement
. Increased cross-sectional bulk of the repair site
. Venting of the A4 pulley
. Excision of one slip of the FDS tendon

Correct Answer & Explanation

. Increased cross-sectional bulk of the repair site

Explanation

The most significant factor affecting the work of flexion and gliding resistance after flexor tendon repair is the increased cross-sectional bulk (volume) of the repaired tendon. Increased bulk causes friction and impingement as the tendon attempts to glide under the intact annular pulleys (A2 and A4). While multi-strand repairs (4-strand, 6-strand) increase tensile strength, if they are not performed meticulously, they can increase tendon bulk. An epitendinous suture actually reduces gliding resistance by smoothing the repair site. Venting pulleys or excising an FDS slip generally decreases resistance.

Question 4657

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs reveal an eccentric, expansile, purely lytic lesion in the distal femoral epiphysis extending to the subchondral bone. Biopsy shows multinucleated giant cells interspersed among mononuclear spindle cells. In the pathogenesis of this tumor, the neoplastic mononuclear cells overexpress a specific surface molecule that drives the recruitment and differentiation of the reactive giant cells. Which of the following is that molecule?

. RANK
. RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand)
. Osteoprotegerin (OPG)
. Vascular Endothelial Growth Factor (VEGF)
. Fibroblast Growth Factor Receptor 3 (FGFR3)

Correct Answer & Explanation

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

Explanation

The clinical picture describes a Giant Cell Tumor (GCT) of bone. The true neoplastic cells in a GCT are the spindle-shaped mononuclear stromal cells. These cells highly express RANKL (Receptor Activator of Nuclear Factor Kappa-B Ligand). RANKL binds to the RANK receptor found on the surface of normal circulating monocyte/macrophage precursors, driving them to fuse and form the prominent, reactive osteoclast-like multinucleated giant cells that cause the extensive osteolysis. This pathway is the target of the monoclonal antibody Denosumab.

Question 4658

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a highly organized extracellular matrix for its biomechanical properties. In which specific histologic zone of normal hyaline articular cartilage are the collagen fibers oriented primarily perpendicular to the articular surface, and the chondrocytes arranged in distinct vertical columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Articular cartilage is divided into four main zones. In the superficial (tangential) zone, collagen fibers are parallel to the joint surface to resist shear forces. In the middle (transitional) zone, collagen fibers are randomly oriented. In the deep (radial) zone, collagen fibers are oriented perpendicular to the joint surface and chondrocytes are arranged in vertical columns, providing high resistance to compressive forces. The tidemark separates the deep zone from the calcified zone.

Question 4659

Topic: 1. General Principles & Basic Science



Articular cartilage relies on a highly organized extracellular matrix to resist compressive and shear forces. In the superficial (tangential) zone of articular cartilage, what is the primary orientation of the Type II collagen fibrils and the relative proteoglycan content compared to the deeper zones?

. Collagen fibrils are parallel to the joint surface; proteoglycan content is lowest.
. Collagen fibrils are perpendicular to the joint surface; proteoglycan content is lowest.
. Collagen fibrils are parallel to the joint surface; proteoglycan content is highest.
. Collagen fibrils are perpendicular to the joint surface; proteoglycan content is highest.
. Collagen fibrils are randomly oriented; proteoglycan content is uniform throughout.

Correct Answer & Explanation

. Collagen fibrils are parallel to the joint surface; proteoglycan content is lowest.

Explanation

Articular cartilage is divided into zones. In the superficial (tangential) zone, Type II collagen fibrils are aligned parallel to the joint surface to resist shear forces. This zone has the highest water content but the lowest proteoglycan concentration. Conversely, the deep zone has collagen fibrils aligned perpendicular to the subchondral bone, highest proteoglycan content, and lowest water content, optimizing resistance to compressive loads.

Question 4660

Topic: Biology, Genetics & Bone Healing
Bone morphogenetic proteins (BMPs), particularly recombinant human BMP-2 and BMP-7, are utilized in orthopedic surgery to promote osteoinduction and bone healing. These signaling molecules exert their cellular effects primarily through which of the following intracellular signaling pathways?
. Wnt/β-catenin pathway
. JAK/STAT signaling pathway
. MAPK/ERK pathway
. Serine/threonine kinase receptors and Smad proteins
. Tyrosine kinase receptors and the Ras/Raf pathway

Correct Answer & Explanation

. Serine/threonine kinase receptors and Smad proteins

Explanation

BMPs belong to the Transforming Growth Factor-beta (TGF-β) superfamily. They bind to cell surface type I and type II serine/threonine kinase receptors. Upon activation, these receptors phosphorylate intracellular Smad proteins (specifically R-Smads 1, 5, and 8), which then form a complex with Smad4. This complex translocates to the nucleus to regulate transcription of osteogenic genes (e.g., Runx2, Osterix).

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