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1. General Principles & Basic Science MCQs

Practice Set 257 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 5121

Topic: Physiology & Rehabilitation

Which of the following physiological characteristics best distinguishes Type I (slow-twitch) skeletal muscle fibers from Type II (fast-twitch) skeletal muscle fibers?

. Higher reliance on glycolytic metabolism
. Lower capillary density
. Higher mitochondrial density and oxidative capacity
. Faster rate of myosin ATPase activity
. Greater peak force generation

Correct Answer & Explanation

. Higher mitochondrial density and oxidative capacity

Explanation

Type I muscle fibers are 'slow-twitch' and fatigue-resistant. They rely primarily on oxidative phosphorylation for energy production. Consequently, they possess a higher mitochondrial density, higher myoglobin content (giving them a red appearance), and greater capillary density. In contrast, Type II fibers have faster myosin ATPase activity, rely more on glycolysis, and generate greater peak force but fatigue much more rapidly.

Question 5122

Topic: Biology, Genetics & Bone Healing

A 32-year-old female is scheduled for curettage and cementation of a Giant Cell Tumor (GCT) of the distal femur. She was treated pre-operatively with denosumab. What is the primary mechanism of action of denosumab in the treatment of GCT of bone?

. Directly induces apoptosis of the neoplastic mononuclear stromal cells
. Binds to RANKL, inhibiting the recruitment and formation of osteoclast-like giant cells
. Binds directly to the RANK receptor on the surface of multinucleated giant cells
. Inhibits vascular endothelial growth factor (VEGF) preventing tumor angiogenesis
. Cross-links DNA in the rapidly dividing tumor cells

Correct Answer & Explanation

. Binds to RANKL, inhibiting the recruitment and formation of osteoclast-like giant cells

Explanation

In Giant Cell Tumor of bone, the neoplastic cells are the mononuclear stromal cells, which express high levels of RANK Ligand (RANKL). This RANKL recruits and stimulates normal host macrophages to fuse into osteoclast-like giant cells, which cause massive bone destruction. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclast precursors, thereby halting the formation and activity of the giant cells.

Question 5123

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs), such as BMP-2 and BMP-7, primarily promote osteoblastic differentiation by signaling through which of the following intracellular pathways?

. Wnt/beta-catenin pathway
. JAK-STAT pathway
. Smad 1/5/8 pathway
. MAP kinase pathway
. Notch signaling pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs are members of the TGF-beta superfamily. They initiate signaling by binding to heterodimeric serine/threonine kinase receptors on the cell surface. This activates the receptor, which phosphorylates receptor-regulated Smads (specifically Smad 1, 5, and 8). These phosphorylated Smads form a complex with the common-partner Smad (Smad 4) and translocate to the nucleus to regulate the transcription of osteogenic genes (like Runx2/Cbfa1).

Question 5124

Topic: 1. General Principles & Basic Science

Upon polarizing light microscopy of synovial fluid aspirated from an acutely swollen joint, Monosodium Urate (MSU) crystals are classically described as:

. Rhomboid-shaped and positively birefringent
. Needle-shaped and negatively birefringent
. Rhomboid-shaped and negatively birefringent
. Needle-shaped and positively birefringent
. Envelope-shaped and non-birefringent

Correct Answer & Explanation

. Needle-shaped and negatively birefringent

Explanation

Gout is caused by the deposition of Monosodium Urate (MSU) crystals. Under polarized light microscopy, MSU crystals appear needle-shaped and exhibit strong negative birefringence (appearing yellow when aligned parallel to the compensator axis). Calcium Pyrophosphate Dihydrate (CPPD) crystals, seen in pseudogout, are typically rhomboid-shaped and exhibit weak positive birefringence (appearing blue when aligned parallel).

Question 5125

Topic: Biology, Genetics & Bone Healing

The monoclonal antibody Romosozumab is utilized in the treatment of severe osteoporosis. Its primary mechanism of action in increasing bone mineral density is by binding to and inhibiting which of the following molecules?

. RANK Ligand (RANKL)
. Cathepsin K
. Sclerostin
. Osteoprotegerin (OPG)
. Parathyroid hormone receptor

Correct Answer & Explanation

. Sclerostin

Explanation

Romosozumab is a humanized monoclonal antibody that binds to and inhibits sclerostin. Sclerostin is normally produced by osteocytes and inhibits the Wnt/beta-catenin signaling pathway in osteoblasts, thus decreasing bone formation. By inhibiting sclerostin, Romosozumab has a dual effect: it significantly increases bone formation and mildly decreases bone resorption.

Question 5126

Topic: 1. General Principles & Basic Science

The main blood supply to the adult femoral head is provided by the deep branch of the medial femoral circumflex artery (MFCA). Prior to perforating the joint capsule, this vessel courses superiorly between which two anatomic structures?

. Pectineus and iliopsoas
. Obturator externus and quadratus femoris
. Superior gemellus and obturator internus
. Piriformis and gluteus medius
. Adductor longus and adductor brevis

Correct Answer & Explanation

. Obturator externus and quadratus femoris

Explanation

The deep branch of the medial femoral circumflex artery (MFCA) is the predominant blood supply to the femoral head. It courses posteriorly between the pectineus and iliopsoas muscles, and then heads superiorly, running consistently between the obturator externus and quadratus femoris muscles before piercing the capsule to form the retinacular vessels.

Question 5127

Topic: Infection, Pharmacology & VTE

Biofilm formation is a critical factor in the pathogenesis of periprosthetic joint infections, rendering bacteria highly resistant to systemic antibiotics. In Staphylococcus epidermidis infections, what is the primary extracellular polymeric substance responsible for intercellular adhesion and structural integrity of the biofilm?

. Hyaluronic acid
. Teichoic acid
. Polysaccharide intercellular adhesin (PIA)
. Fibronectin-binding protein
. Alpha-toxin

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Biofilm formation by Staphylococcus epidermidis largely depends on the production of Polysaccharide Intercellular Adhesin (PIA), which is synthesized by products of the icaADBC operon. PIA acts as the primary extracellular matrix component, facilitating intercellular adhesion and shielding the bacteria from the host immune response and antibiotics.

Question 5128

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with an acute monoarticular septic arthritis of the knee. Standard synovial fluid cultures are negative at 48 hours, but the ESR and CRP are significantly elevated. Which of the following organisms is most likely responsible and optimally requires inoculation into BACTEC blood culture bottles or PCR for detection?
. Staphylococcus aureus
. Haemophilus influenzae
. Kingella kingae
. Streptococcus pneumoniae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a gram-negative bacillus that has become recognized as the most common cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. It is notoriously fastidious and difficult to isolate on standard solid media; the diagnostic yield is significantly increased by inoculating joint fluid directly into BACTEC blood culture bottles or using specific PCR assays.

Question 5129

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing. Which of the following intracellular signaling pathways is primarily activated by BMP receptor binding?

. JAK/STAT pathway
. Wnt/beta-catenin pathway
. SMAD 1/5/8 pathway
. Notch/Hes pathway
. Hedgehog/Gli pathway

Correct Answer & Explanation

. SMAD 1/5/8 pathway

Explanation

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily. When a BMP binds to its cell surface serine-threonine kinase receptors, it induces the phosphorylation of receptor-regulated SMADs, specifically SMAD 1, 5, and 8. These phosphorylated SMADs form a complex with the common-mediator SMAD 4, which then translocates into the nucleus to regulate the transcription of osteogenic genes like Runx2.

Question 5130

Topic: 1. General Principles & Basic Science

A surgeon decides to exchange a solid 10 mm diameter intramedullary tibial nail for a solid 12 mm diameter intramedullary tibial nail. According to biomechanical principles of cylindrical structures, by approximately what factor will the bending rigidity of the nail increase?

. 1.20
. 1.44
. 1.73
. 2.07
. 2.48

Correct Answer & Explanation

. 2.07

Explanation

The bending rigidity (stiffness) of a solid cylinder is proportional to the area moment of inertia, which scales with the radius to the fourth power (r^4). Increasing the diameter from 10 mm to 12 mm increases the radius from 5 mm to 6 mm. The factor of increase is (6/5)^4 = 1.2^4 = 2.0736. Thus, the bending rigidity increases by approximately a factor of 2.07.

Question 5131

Topic: Surgical Anatomy & Approaches

During the anterior intrapelvic (modified Stoppa) approach for acetabular fracture fixation, the surgeon must be mindful of the 'corona mortis'. This vascular anastomosis most commonly connects the obturator vessels with which of the following vascular systems?

. Internal iliac vessels
. External iliac or inferior epigastric vessels
. Superior gluteal vessels
. Internal pudendal vessels
. Deep circumflex iliac vessels

Correct Answer & Explanation

. External iliac or inferior epigastric vessels

Explanation

The 'corona mortis' (crown of death) is a highly variable but clinically significant vascular anastomosis located over the superior pubic ramus, typically 4 to 6 cm from the pubic symphysis. It represents an anastomotic connection between the external iliac vascular system (often the inferior epigastric artery/vein) and the obturator vascular system (which arises from the internal iliac system). Injury to it can cause catastrophic bleeding retracting into the pelvis.

Question 5132

Topic: Biomechanics & Biomaterials
The introduction of highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) has significantly reduced volumetric wear rates in total hip arthroplasty. However, the radiation cross-linking process introduces a clinically relevant trade-off by reducing which of the following material properties?
. Oxidation resistance
. Surface wettability
. Elastic modulus
. Yield strength and fatigue resistance
. Thermal conductivity

Correct Answer & Explanation

. Yield strength and fatigue resistance

Explanation

Irradiation of UHMWPE creates free radicals that form cross-links, heavily increasing the material's resistance to adhesive and abrasive wear. However, this process alters the crystalline structure and polymer chain mobility, which results in a reduction of mechanical properties, specifically yield strength, ultimate tensile strength, and fatigue resistance. This makes it more susceptible to fracture, particularly in thin liners or high-stress applications.

Question 5133

Topic: 1. General Principles & Basic Science

Historically, the arcuate branch of the anterior circumflex humeral artery was considered the primary blood supply to the humeral head. However, modern quantitative cadaveric studies have demonstrated that the predominant blood supply to the humeral head actually arises from which of the following vessels?

. Anterior circumflex humeral artery
. Posterior circumflex humeral artery
. Thoracoacromial artery
. Suprascapular artery
. Subscapular artery

Correct Answer & Explanation

. Posterior circumflex humeral artery

Explanation

A landmark quantitative study by Hettrich et al. (JBJS Am 2010) demonstrated that the posterior circumflex humeral artery (PCHA) provides the majority (approximately 64%) of the blood supply to the humeral head, specifically supplying the posterior, inferior, and medial aspects. The anterior circumflex humeral artery provides only about 36%. This shifted the traditional paradigm that the arcuate artery (from the ACHA) was the dominant supply.

Question 5134

Topic: Surgical Anatomy & Approaches

The 'Corona Mortis' is an important vascular anastomosis encountered during the ilioinguinal approach to the pelvis. It typically connects which two vascular systems?

. External iliac/inferior epigastric and Obturator
. Internal iliac and Superior gluteal
. External pudendal and Obturator
. Femoral and Inferior gluteal
. Deep circumflex iliac and Internal pudendal

Correct Answer & Explanation

. External iliac/inferior epigastric and Obturator

Explanation

The Corona Mortis is a vascular anastomosis between the external iliac or inferior epigastric vessels and the obturator vessels. It crosses the superior pubic ramus and is highly susceptible to injury during pelvic approaches or screw placement, leading to severe hemorrhage.

Question 5135

Topic: Biomechanics & Biomaterials

Trunnionosis, observed at the head-neck modular junction in total hip arthroplasty, is predominantly initiated by which of the following mechanisms?

. Galvanic corrosion
. Fretting corrosion
. Pitting corrosion
. Intergranular corrosion
. Uniform corrosion

Correct Answer & Explanation

. Fretting corrosion

Explanation

Trunnionosis is primarily an example of mechanically assisted crevice corrosion, initiated by fretting corrosion. Micromotion at the modular head-neck taper (fretting) mechanically breaks down the protective passive oxide layer of the metal, exposing raw metal to the body fluids and leading to accelerated localized crevice corrosion.

Question 5136

Topic: 1. General Principles & Basic Science

When performing a primary repair of a flexor tendon laceration in Zone II, the ultimate tensile strength of the repair before healing is most directly proportional to the:

. Caliber of the core suture material
. Number of core suture strands crossing the repair site
. Configuration of the epitendinous suture
. Number of locking loops in the core suture
. Strictness of postoperative immobilization

Correct Answer & Explanation

. Number of core suture strands crossing the repair site

Explanation

Biomechanical studies have consistently shown that the initial tensile strength of a flexor tendon repair is most directly proportional to the number of core suture strands that cross the repair site (e.g., a 4-strand repair is stronger than a 2-strand repair).

Question 5137

Topic: Biomechanics & Biomaterials

The scapholunate interosseous ligament is the primary stabilizer of the scapholunate articulation. Which anatomical subregion of this ligament possesses the greatest tensile strength and is biomechanically the most important to repair?

. Volar portion
. Dorsal portion
. Proximal (membranous) portion
. Central portion
. Distal portion

Correct Answer & Explanation

. Dorsal portion

Explanation

The scapholunate interosseous ligament has three distinct regions: dorsal, proximal (membranous), and volar. The dorsal portion is the thickest and biomechanically the strongest, being the most critical region to repair to restore normal kinematics. Conversely, the volar portion is the strongest for the lunotriquetral ligament.

Question 5138

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four distinct structural zones. Which zone is characterized by having the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibrils aligned parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage comprises 10-20% of articular cartilage thickness. It possesses the highest water content, the lowest proteoglycan concentration, and collagen fibrils (mostly Type II) oriented parallel to the joint surface to resist shear forces.

Question 5139

Topic: 1. General Principles & Basic Science

In the microstructure of normal hyaline articular cartilage, which zone possesses the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibrils that are oriented strictly perpendicular to the articular surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. Its collagen fibers run perpendicular to the joint surface, providing significant resistance to compressive forces.

Question 5140

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, successful fracture healing depends on the deformation limits of different tissues within the fracture gap. What is the maximum interfragmentary strain threshold that permits the formation of lamellar bone (primary bone healing)?

. 2%
. 10%
. 20%
. 30%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that tissue can only form in a fracture gap if the strain does not exceed the elongation tolerance of that specific tissue. Lamellar bone requires an ultra-low strain environment of less than 2% to form. Cartilage can tolerate up to 10% strain (allowing secondary healing), and granulation tissue tolerates up to 100% strain.

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