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1. General Principles & Basic Science MCQs

Practice Set 247 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 4921

Topic: Biomechanics & Biomaterials

In a viva on orthopedic biomaterials, an examiner asks about the consequences of combining different metals in an implant construct. If a 316L stainless steel screw is placed through a titanium alloy plate in a physiologic environment, what is the most likely outcome based on the galvanic series?

. The titanium plate undergoes accelerated galvanic corrosion.
. The stainless steel screw undergoes accelerated galvanic corrosion.
. Both metals undergo equal rates of crevice corrosion.
. Galvanic corrosion is completely prevented by the passivation layers of both metals.
. Fretting corrosion occurs, but galvanic corrosion is impossible in vivo.

Correct Answer & Explanation

. The stainless steel screw undergoes accelerated galvanic corrosion.

Explanation

In a galvanic couple, the less noble (more anodic) metal undergoes accelerated corrosion. Stainless steel is more anodic than titanium alloy, making the stainless steel screw susceptible to accelerated galvanic corrosion in the physiologic electrolyte environment.

Question 4922

Topic: Biology, Genetics & Bone Healing

Romosozumab is a monoclonal antibody utilized in the treatment of osteoporosis. It exerts its anabolic effect on bone by directly inhibiting Sclerostin. What is the primary mechanism by which Sclerostin normally acts to decrease bone formation?

. It stimulates RANKL expression by osteoblasts
. It inhibits the differentiation of osteoclast precursors
. It binds to osteoprotegerin (OPG), preventing its action
. It activates the BMP signaling pathway in osteocytes
. It binds to LRP5/6, inhibiting the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. It binds to LRP5/6, inhibiting the Wnt/beta-catenin signaling pathway

Explanation

Sclerostin, a glycoprotein encoded by the SOST gene and produced primarily by osteocytes, acts as a negative regulator of bone formation. It does this by binding to the LRP5/6 coreceptors on osteoblasts, which competitively inhibits the canonical Wnt/beta-catenin signaling pathway necessary for osteoblast differentiation and bone formation. Romosozumab blocks Sclerostin, thereby disinhibiting Wnt signaling and promoting bone formation.

Question 4923

Topic: Surgical Anatomy & Approaches

During the anterior intrapelvic (modified Stoppa) approach for an acetabular fracture, an aberrant vessel traversing the superior pubic ramus is encountered and ligated. This 'corona mortis' represents an anastomosis between which two vascular systems?

. External iliac (or inferior epigastric) artery and the obturator artery
. Internal iliac artery and the superior gluteal artery
. External pudendal artery and the obturator artery
. Femoral artery and the inferior gluteal artery
. Inferior epigastric artery and the deep circumflex iliac artery

Correct Answer & Explanation

. External iliac (or inferior epigastric) artery and the obturator artery

Explanation

The corona mortis ('crown of death') is an important anatomical variant consisting of a vascular anastomosis between the external iliac (or its branch, the inferior epigastric) system and the internal iliac (obturator) system. It lies on the posterior aspect of the superior pubic ramus, approximately 4-9 cm from the pubic symphysis. It can be arterial, venous, or both, and is highly susceptible to injury during anterior pelvic approaches, necessitating careful identification and ligation.

Question 4924

Topic: Biomechanics & Biomaterials

In evaluating the biochemical changes in articular cartilage, how does early osteoarthritis (OA) uniquely differ from the changes seen in normal aging?

. Early OA exhibits increased water content, whereas aging exhibits decreased water content
. Early OA exhibits increased chondroitin sulfate, whereas aging exhibits increased water content
. Early OA exhibits decreased collagen synthesis, whereas aging exhibits increased collagen synthesis
. Early OA exhibits an increase in total proteoglycan content, whereas aging exhibits a decrease
. Early OA exhibits decreased keratin sulfate, whereas aging exhibits increased water content

Correct Answer & Explanation

. Early OA exhibits increased water content, whereas aging exhibits decreased water content

Explanation

A hallmark of early osteoarthritis (OA) is the disruption of the collagen meshwork, leading to increased permeability and swelling of the cartilage matrix, thereby increasing the water content. Conversely, normal aging of cartilage is characterized by a decrease in water content due to changes in proteoglycan size and aggregation. In both aging and OA, the total proteoglycan content generally decreases and the modulus of elasticity changes, but the divergent direction of water content change is a classic differentiating factor.

Question 4925

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMPs) are used clinically to enhance bone healing. BMPs belong to the TGF-beta superfamily. They initiate intracellular signaling primarily by binding to transmembrane receptors that activate which of the following downstream molecules?

. JAK/STAT pathway
. cAMP/PKA pathway
. Smad proteins
. Wnt/beta-catenin
. MAP kinases

Correct Answer & Explanation

. Smad proteins

Explanation

Bone morphogenetic proteins (BMPs) bind to serine/threonine kinase receptors (Type I and Type II) on the cell surface. This binding phosphorylates and activates receptor-regulated Smads (R-Smads, specifically Smad 1, 5, and 8), which then complex with Co-Smad (Smad 4) and translocate to the nucleus to regulate the transcription of osteogenic genes.

Question 4926

Topic: 1. General Principles & Basic Science
Following surgical repair of a zone II flexor tendon injury, early active motion protocols are frequently utilized to prevent adhesion formation. What is the primary biological mechanism by which these protocols promote intrinsic tendon healing over extrinsic healing?
. By increasing the invasion of fibroblasts from the surrounding tendon sheath
. By stimulating epitenon cells to migrate and proliferate into the repair site
. By enhancing the vascular ingrowth from the vincular system
. By promoting the deposition of type III collagen rather than type I collagen
. By completely halting the inflammatory phase of wound healing

Correct Answer & Explanation

. By stimulating epitenon cells to migrate and proliferate into the repair site

Explanation

Tendon healing occurs via intrinsic and extrinsic pathways. Extrinsic healing relies on cells from the surrounding sheath and leads to adhesions. Intrinsic healing is mediated by epitenon and endotenon cells. Early controlled mobilization stimulates the intrinsic healing pathway, causing epitenon cells to migrate into the repair site and synthesize collagen, while simultaneously mechanically preventing extrinsically derived tissue adhesions from stabilizing.

Question 4927

Topic: 1. General Principles & Basic Science

Articular cartilage is highly specialized to withstand compressive and shear forces. It is structurally divided into four distinct zones. Which of the following zones contains the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers oriented perpendicular to the articular surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils arranged perpendicular to the articular surface, which provides the greatest resistance to compressive forces. It also has the highest concentration of proteoglycans and the lowest water content of the uncalcified zones. The superficial zone has collagen parallel to the joint surface and the highest water content.

Question 4928

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits viscoelastic properties during mechanical loading. Which of the following statements best defines the biomechanical phenomenon of 'stress relaxation'?

. A constant load is applied, leading to a slow, progressive increase in deformation over time.
. A constant deformation is applied, leading to a slow, progressive decrease in the internal stress over time.
. The energy lost as heat during a single continuous loading and unloading cycle.
. The point at which a material transitions from elastic to plastic deformation.
. The application of cyclic loading causing failure at a stress lower than the ultimate tensile strength.

Correct Answer & Explanation

. A constant deformation is applied, leading to a slow, progressive decrease in the internal stress over time.

Explanation

Stress relaxation occurs when a viscoelastic material is subjected to a constant deformation (strain), resulting in a gradual decrease in internal stress over time as the fluid within the matrix redistributes. Creep, by contrast, is the gradual increase in deformation when a constant load (stress) is applied.

Question 4929

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) play a critical role in osteoinduction and are members of the transforming growth factor-beta (TGF-beta) superfamily. Following the binding of a BMP ligand to its transmembrane serine/threonine kinase receptor, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus and initiate transcription of osteogenic genes?

. MAP kinases (ERK, JNK)
. JAK and STAT proteins
. Smad 1, 5, and 8
. Beta-catenin and TCF/LEF
. NF-kappa B

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMP signaling operates primarily through the canonical Smad pathway. When BMP binds to its type I and type II serine/threonine kinase receptors, it induces phosphorylation of the receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These phosphorylated R-Smads then form a complex with the common-partner Smad (co-Smad, Smad 4) and translocate to the nucleus to regulate the transcription of target genes necessary for osteoblast differentiation.

Question 4930

Topic: Surgical Anatomy & Approaches

A 24-year-old male presents with radial-sided wrist pain after a fall onto an outstretched hand. Imaging reveals a displaced fracture of the proximal pole of the scaphoid. Surgical fixation with a headless compression screw is planned. Which of the following surgical approaches is most appropriate for optimal screw placement and preservation of the scaphoid blood supply in this specific fracture pattern?

. Volar approach utilizing the interval between the flexor carpi radialis and radial artery
. Volar approach utilizing the interval between the flexor pollicis longus and palmaris longus
. Dorsal approach between the third and fourth extensor compartments
. Dorsal approach through the anatomic snuffbox (between the first and second extensor compartments)
. Direct lateral approach excising the radial styloid

Correct Answer & Explanation

. Dorsal approach between the third and fourth extensor compartments

Explanation

The blood supply to the scaphoid is primarily retrograde, entering the distal pole and dorsal ridge via branches of the radial artery. The proximal pole relies entirely on intraosseous blood flow from distal to proximal. For proximal pole fractures, a dorsal approach (typically between the 3rd and 4th extensor compartments) is preferred because it avoids damage to the dominant volar/distal blood supply (the palmar radiocarpal branches), prevents division of critical volar ligaments (e.g., radioscaphocapitate ligament), and provides direct, collinear access to the proximal pole for screw trajectory along the central axis of the scaphoid.

Question 4931

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones: superficial, middle (transitional), deep, and calcified. Which of the following biochemical and structural descriptions is most accurate regarding the deep zone of normal adult articular cartilage?

. It has the highest water content and collagen fibers oriented parallel to the joint surface.
. It contains the highest concentration of proteoglycans and collagen fibers oriented perpendicular to the joint surface.
. It has randomly oriented collagen fibers and the highest concentration of chondrocytes.
. It is separated from the subchondral bone by the tidemark and composed primarily of Type I collagen.
. It has the highest tensile strength due to a dense network of elastin fibers.

Correct Answer & Explanation

. It contains the highest concentration of proteoglycans and collagen fibers oriented perpendicular to the joint surface.

Explanation

The deep (or radial) zone of articular cartilage represents the layer closest to the tidemark (which separates it from the calcified cartilage). It is characterized by having the lowest water content, the highest concentration of proteoglycans (which provides excellent resistance to compressive forces), and thick Type II collagen fibers that are oriented perpendicular to the joint surface. The superficial zone has the highest water content and parallel collagen fibers to resist shear stress.

Question 4932

Topic: Surgical Anatomy & Approaches

A patient presents with an irreversible high radial nerve palsy following a humerus fracture. The surgeon elects to perform a tendon transfer to restore wrist, finger, and thumb extension. The classic Boyes transfer specifically utilizes which of the following tendon transpositions to restore finger extension (Extensor Digitorum Communis)?

. Pronator Teres to Extensor Carpi Radialis Brevis
. Flexor Carpi Radialis to Extensor Digitorum Communis
. Flexor Carpi Ulnaris to Extensor Digitorum Communis
. Flexor Digitorum Superficialis (middle finger) to Extensor Digitorum Communis
. Palmaris Longus to Extensor Pollicis Longus

Correct Answer & Explanation

. Flexor Digitorum Superficialis (middle finger) to Extensor Digitorum Communis

Explanation

The Boyes transfer relies on the flexor digitorum superficialis (FDS) of the middle finger transferred through the interosseous membrane to the EDC to restore finger extension. It also uses the FDS of the ring finger to the EIP and EPL. In contrast, standard transfers (like the modified Green transfer) use the FCU or FCR to EDC.

Question 4933

Topic: Biomechanics & Biomaterials

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment, such as the human body. Which of the following combinations of orthopedic implants poses the highest risk for significant galvanic corrosion and is thus generally contraindicated?

. Titanium alloy and commercially pure Titanium
. Cobalt-chromium alloy and Titanium alloy
. Cobalt-chromium alloy and oxidized Zirconium
. Stainless steel and Titanium alloy
. Tantalum and Titanium alloy

Correct Answer & Explanation

. Cobalt-chromium alloy and Titanium alloy

Explanation

Stainless steel and Titanium (or Cobalt-chromium) have vastly different electrochemical potentials (anodic indices). Mixing stainless steel with Titanium or CoCr in the same construct leads to severe galvanic corrosion, preferentially degrading the more anodic metal (stainless steel). Titanium and Cobalt-chromium are frequently used together (e.g., modular THA) because their electrochemical potentials are similar, making the risk of clinical galvanic corrosion minimal.

Question 4934

Topic: Surgical Anatomy & Approaches

A surgeon is performing a total hip arthroplasty using an approach that exploits the internervous plane between the superior gluteal nerve and the femoral nerve. Which of the following describes the muscles defining this surgical interval?

. Tensor fasciae latae and sartorius
. Tensor fasciae latae and gluteus medius
. Gluteus medius and minimus
. Gluteus maximus and medius
. Rectus femoris and vastus lateralis

Correct Answer & Explanation

. Tensor fasciae latae and sartorius

Explanation

The anterior approach to the hip (Smith-Petersen) uses the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve) superficially.

Question 4935

Topic: Biology, Genetics & Bone Healing

During fracture healing via endochondral ossification, undifferentiated mesenchymal stem cells are directed to differentiate along various lineages. Which of the following transcription factors is considered the essential "master regulator" for the differentiation of mesenchymal stem cells into osteoblasts?

. SOX9
. Runx2 (Cbfa1)
. PPAR-gamma
. HIF-1 alpha
. MyoD

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the core transcription factor required for osteoblast differentiation and bone formation. A deficiency in Runx2 leads to cleidocranial dysplasia. SOX9 directs chondrogenic differentiation, PPAR-gamma directs adipogenesis, and MyoD directs myogenesis.

Question 4936

Topic: Biology, Genetics & Bone Healing

A 28-year-old female undergoes curettage for a giant cell tumor (GCT) of the distal femur. The histology demonstrates multinucleated giant cells within a stroma of mononuclear cells. The neoplastic mononuclear cells express a specific ligand that promotes the recruitment and formation of the reactive osteoclast-like giant cells. What is this ligand?

. Osteoprotegerin (OPG)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Bone Morphogenetic Protein-2 (BMP-2)
. Fibroblast Growth Factor-23 (FGF-23)
. Transforming Growth Factor-beta (TGF-beta)

Correct Answer & Explanation

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

Explanation

In Giant Cell Tumor of bone, the neoplastic cells are actually the spindled mononuclear stromal cells. These cells highly express RANKL, which binds to RANK on normal macrophages, driving them to fuse and differentiate into the massive, bone-destroying osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is utilized therapeutically for unresectable GCT.

Question 4937

Topic: 1. General Principles & Basic Science

In the principles of internal fixation, several design parameters of a screw influence its biomechanical performance. Which of the following factors is the primary determinant of a screw's pullout strength from bone?

. Outer (major) diameter
. Inner (minor/core) diameter
. Thread pitch
. Head design
. Cannulation diameter

Correct Answer & Explanation

. Outer (major) diameter

Explanation

The pullout strength of a bone screw is directly proportional to the outer (major) diameter of the screw, the length of thread engagement, and the shear strength of the bone. The inner (minor) diameter determines the screw's tensile and torsional strength (resistance to breakage/fatigue), not its pullout strength.

Question 4938

Topic: Biology, Genetics & Bone Healing

The osteoinductive properties of bone grafts are heavily mediated by Bone Morphogenetic Proteins (BMPs). Which of the following BMPs is an FDA-approved recombinant product specifically indicated for the treatment of acute open tibial shaft fractures treated with an intramedullary nail?

. BMP-2 (rhBMP-2)
. BMP-3
. BMP-4
. BMP-7 (rhOP-1)
. BMP-9

Correct Answer & Explanation

. BMP-2 (rhBMP-2)

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for acute open tibial shaft fractures (and anterior lumbar interbody fusions). rhBMP-7 (also known as Osteogenic Protein-1 or OP-1) previously held a Humanitarian Device Exemption for recalcitrant tibial nonunions.

Question 4939

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage has the highest concentration of water and lowest concentration of proteoglycans?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone contains the highest water content (approximately 80%), the lowest proteoglycan concentration, and collagen fibers oriented parallel to the joint surface to effectively resist shear stress.

Question 4940

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal-metaphyseal lesion in the proximal tibia extending to the subchondral bone without a sclerotic rim. Biopsy shows multinucleated giant cells in a stroma of mononuclear cells. Which of the following is the primary neoplastic cell in this lesion?

. Multinucleated giant cell
. Osteoblast
. Spindle-shaped stromal cell
. Chondrocyte
. Histiocyte

Correct Answer & Explanation

. Spindle-shaped stromal cell

Explanation

In Giant Cell Tumor of bone (GCT), the true neoplastic cells are the mononuclear spindle-shaped stromal cells which express RANKL. The multinucleated giant cells are reactive osteoclast-like cells expressing RANK, recruited by the neoplastic stromal cells.

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