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1. General Principles & Basic Science MCQs

Practice Set 260 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 5181

Topic: Infection, Pharmacology & VTE

During a total knee arthroplasty for a patient with a severe, fixed varus deformity, the surgeon must perform a sequential medial release to achieve a balanced extension and flexion gap. Which of the following represents the most accepted sequence of release after osteophyte removal?

. Superficial MCL, Deep MCL, Pes anserinus, Posteromedial capsule
. Pes anserinus, Deep MCL, Superficial MCL, Posteromedial capsule
. Deep MCL, Posteromedial capsule, Superficial MCL, Pes anserinus
. Posteromedial capsule, Pes anserinus, Deep MCL, Superficial MCL
. Deep MCL, Pes anserinus, Posteromedial capsule, Superficial MCL

Correct Answer & Explanation

. Deep MCL, Posteromedial capsule, Superficial MCL, Pes anserinus

Explanation

In a severe varus knee, sequential release of the tight medial structures is necessary. Following the removal of medial osteophytes, the classic stepwise release begins with the deep MCL, followed by the posteromedial corner/capsule, then the superficial MCL (often subperiosteally off the tibia), and finally the pes anserinus tendons if further correction is required.

Question 5182

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is used off-label in various nonunion surgeries. Following the binding of rhBMP-2 to its transmembrane serine/threonine kinase receptors, which of the following intracellular signaling pathways is primarily activated to upregulate osteogenic gene expression?

. Wnt/beta-catenin pathway
. Smad 1/5/8 pathway
. JAK/STAT pathway
. MAPK/ERK pathway
. Notch/Hes pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily. When BMPs bind to their specific heterodimeric receptors, they primarily signal through the canonical Smad pathway, specifically phosphorylating Smad 1, 5, and 8. These complex with Smad 4 and translocate to the nucleus to induce transcription of osteoblastic genes like Runx2.

Question 5183

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach to the acetabulum, the surgeon must carefully identify and ligate the 'corona mortis' to prevent life-threatening hemorrhage. This vascular structure is an anastomosis between the obturator vessels and which of the following vascular systems?

. Internal iliac or superior gluteal vessels
. External iliac or inferior epigastric vessels
. Internal pudendal vessels
. Femoral or deep circumflex iliac vessels
. Superior vesical vessels

Correct Answer & Explanation

. External iliac or inferior epigastric vessels

Explanation

The corona mortis ('crown of death') is a retropubic vascular anastomosis between the obturator system and the external iliac or inferior epigastric systems. It is found traversing the superior pubic ramus at an average distance of 5-6 cm from the pubic symphysis and is at high risk of iatrogenic injury during anterior pelvic surgical exposures.

Question 5184

Topic: Biomechanics & Biomaterials
What is the primary mechanism by which highly cross-linked polyethylene (HXLPE) achieves significantly reduced wear rates compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE) in total hip arthroplasty?
. Addition of vitamin E to increase surface hardness
. Reduction of free radicals through remelting or annealing
. Creation of transverse covalent bonds between polymer chains via gamma or electron beam irradiation
. Increasing the crystalline structure density through cold forging
. Sterilization in an oxygen-rich environment

Correct Answer & Explanation

. Creation of transverse covalent bonds between polymer chains via gamma or electron beam irradiation

Explanation

Highly cross-linked polyethylene is manufactured by exposing UHMWPE to high doses of gamma or electron beam irradiation. This radiation breaks carbon-hydrogen bonds, allowing free radicals to combine and form strong transverse covalent bonds (cross-links) between adjacent polymer chains. This highly interlinked network vastly improves resistance to adhesive and abrasive wear. Post-irradiation melting or annealing is then done to eliminate residual free radicals and prevent long-term oxidation.

Question 5185

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the collagen fibers in the superficial zone (lamina splendens) are tightly packed and oriented parallel to the articular surface. What is the primary biomechanical function of this specific structural alignment?

. To resist compressive forces from weight bearing
. To provide a semi-permeable barrier for hydrostatic pressure maintenance
. To resist torsional forces during pivoting
. To resist shear forces generated during joint articulation
. To resist tensile forces strictly at the tidemark

Correct Answer & Explanation

. To resist shear forces generated during joint articulation

Explanation

Articular cartilage is divided into zones. The superficial zone (lamina splendens) contains densely packed Type II collagen fibers oriented parallel to the joint surface. This parallel orientation provides high tensile strength in the plane of the joint, which functions primarily to resist the extreme shear forces generated during joint articulation.

Question 5186

Topic: 1. General Principles & Basic Science
A peripheral nerve injury is classified as a Sunderland Grade III. Which of the following structural components of the nerve remains intact?
. Axon only
. Endoneurium
. Perineurium
. Epineurium only
. Myelin sheath only

Correct Answer & Explanation

. Endoneurium

Explanation

A Sunderland Grade III injury involves disruption of the axon and the endoneurium, but the perineurium and epineurium remain intact. Grade I is neurapraxia (focal demyelination). Grade II involves axon disruption with intact endoneurium. Grade IV involves disruption of the axon, endoneurium, and perineurium, leaving only the epineurium intact. Grade V is a complete nerve transection.

Question 5187

Topic: 1. General Principles & Basic Science

Following a Zone II flexor digitorum profundus (FDP) repair, which of the following rehabilitation protocols primarily relies on active extension and passive flexion utilizing rubber band traction attached to a dorsal blocking splint?

. Kleinert protocol
. Duran protocol
. Early active motion protocol
. Strickland protocol
. Immobilization protocol

Correct Answer & Explanation

. Kleinert protocol

Explanation

The Kleinert protocol utilizes a dorsal blocking splint with dynamic rubber band traction attached to the involved finger's nail. This allows the patient to perform active extension (pulling against the rubber band) while flexion is entirely passive (via the recoil of the rubber band). The Duran protocol relies on passive flexion and extension exercises performed by the patient or therapist without dynamic traction.

Question 5188

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft extender in orthopedic surgery. Which of the following best describes its primary biologic properties?

. Osteogenic and osteoconductive
. Osteoinductive and osteoconductive
. Osteogenic only
. Osteoconductive only
. Osteoinductive only

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) is osteoinductive (due to the release of bone morphogenetic proteins [BMPs] during the acid demineralization process) and osteoconductive (providing a collagen scaffold for bone growth). It is not osteogenic, because the sterilization and processing steps destroy all viable cells (osteoblasts and osteoprogenitor cells).

Question 5189

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach for fixation of an acetabular fracture, life-threatening hemorrhage is encountered just posterior to the superior pubic ramus. This is most likely due to an iatrogenic injury to the 'corona mortis,' which represents an abnormal vascular anastomosis between which two systems?

. Internal iliac vein and external iliac vein
. External iliac and obturator vessels
. Superior gluteal and inferior gluteal vessels
. Internal pudendal and obturator vessels
. Deep circumflex iliac and inferior epigastric vessels

Correct Answer & Explanation

. External iliac and obturator vessels

Explanation

The corona mortis ('crown of death') is a common and clinically significant anatomical variant representing an anastomosis between the external iliac system (or its inferior epigastric branch) and the obturator system (a branch of the internal iliac). It crosses the superior pubic ramus approximately 4-5 cm lateral to the symphysis pubis and is at high risk of injury during anterior pelvic and acetabular exposures.

Question 5190

Topic: Biology, Genetics & Bone Healing

In bone biology, the Wnt signaling pathway is crucial for osteoblastogenesis and bone formation. Sclerostin is a key negative regulator of this pathway. By binding to which of the following receptors does sclerostin exert its inhibitory effect?

. RANKL
. Osteoprotegerin
. LRP5/LRP6 coreceptors
. Runx2
. Bone morphogenetic protein 2 (BMP-2)

Correct Answer & Explanation

. LRP5/LRP6 coreceptors

Explanation

Sclerostin, a glycoprotein secreted primarily by osteocytes, acts as a potent inhibitor of the canonical Wnt signaling pathway. It does so by binding to the LRP5 and LRP6 coreceptors on the osteoblast surface, preventing Wnt ligands from binding. This inhibition reduces intracellular accumulation of beta-catenin, thereby decreasing bone formation. Monoclonal antibodies targeting sclerostin (e.g., romosozumab) exploit this mechanism to treat osteoporosis.

Question 5191

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) stimulates osteoblastic differentiation primarily through binding to cell surface serine/threonine kinase receptors. Upon activation, which intracellular signaling molecules are phosphorylated and translocated to the nucleus to regulate gene transcription?

. JAK and STAT proteins
. Smad 1, 5, and 8
. NF-kappaB and IKK
. Wnt and beta-catenin
. ERK and MAPK

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

Bone Morphogenetic Proteins (BMPs) signal through cell surface serine/threonine kinase receptors. Once bound, they phosphorylate receptor-regulated Smads (R-Smads), specifically Smads 1, 5, and 8. These complex with Smad 4 to translocate to the nucleus and upregulate osteogenic genes like Runx2.

Question 5192

Topic: 1. General Principles & Basic Science

During a zone II flexor digitorum profundus (FDP) tendon repair, the surgeon elects to increase the number of suture strands crossing the repair site from two to four. What is the primary biomechanical advantage of this technique?

. Decreased work of flexion
. Decreased tendon gliding resistance
. Increased gap formation resistance
. Decreased risk of postoperative tenosynovitis
. Increased intrinsic tendon healing rate

Correct Answer & Explanation

. Increased gap formation resistance

Explanation

The ultimate tensile strength and resistance to gap formation of a flexor tendon repair are directly proportional to the number of core suture strands crossing the repair site. Increasing from a 2-strand to a 4-strand repair provides the necessary strength to withstand the forces of early active mobilization protocols.

Question 5193

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct structural zones. Which zone contains the highest concentration of collagen, with fibrils aligned strictly parallel to the articular surface to resist shear forces?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains the highest concentration of collagen (primarily Type II) and the lowest concentration of proteoglycans. The collagen fibrils in this zone are aligned parallel to the joint surface specifically to resist shear forces.

Question 5194

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a third-degree nerve injury involves the physical disruption of which of the following structures?

. Myelin sheath only (axon remains fully intact)
. Axon and endoneurium, with an intact perineurium
. Axon only, with an intact endoneurium
. Perineurium and endoneurium, with an intact epineurium
. Complete physical transection of the nerve including the epineurium

Correct Answer & Explanation

. Perineurium and endoneurium, with an intact epineurium

Explanation

The Sunderland classification expands on Seddon's classification. 1st degree: neurapraxia (myelin injury). 2nd degree: axonotmesis with intact endoneurium (excellent recovery). 3rd degree: axon and endoneurium are disrupted, but the perineurium is intact (recovery is variable and often incomplete due to intrafascicular scarring). 4th degree: perineurium disrupted, fascicles disorganized, but epineurium intact (requires surgery). 5th degree: neurotmesis/complete nerve transection.

Question 5195

Topic: Infection, Pharmacology & VTE

Vancomycin is frequently administered in orthopedic surgery for both prophylaxis and treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. What is the precise mechanism of action by which vancomycin exerts its bactericidal effect?

. Inhibits protein synthesis by reversibly binding to the 50S ribosomal subunit
. Inhibits protein synthesis by irreversibly binding to the 30S ribosomal subunit
. Inhibits DNA gyrase and topoisomerase IV, preventing DNA replication
. Inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine terminus of peptidoglycan precursors
. Inhibits folic acid synthesis by competitively inhibiting dihydropteroate synthase

Correct Answer & Explanation

. Inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine terminus of peptidoglycan precursors

Explanation

Vancomycin is a glycopeptide antibiotic that bactericidally inhibits cell wall synthesis. It works by binding non-covalently but very tightly to the D-alanyl-D-alanine terminal dipeptide of the peptidoglycan precursors, preventing their cross-linking by transpeptidases. This differs from beta-lactam antibiotics (like penicillins and cephalosporins), which bind directly to the penicillin-binding proteins (transpeptidases) themselves.

Question 5196

Topic: Biomechanics & Biomaterials

A researcher is testing the viscoelastic properties of the anterior cruciate ligament in a laboratory setting. When a constant tensile force is applied to the ligament over an extended period, the ligament is observed to gradually elongate. Which biomechanical term best describes this phenomenon?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation (elongation) of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation is the time-dependent decrease in internal stress when the tissue is held at a constant deformation/strain. Hysteresis is the energy lost (as heat) during the loading and unloading cycle.

Question 5197

Topic: Biology, Genetics & Bone Healing

Demineralized Bone Matrix (DBM) is widely used in orthopedic surgery as a bone graft substitute. DBM primarily facilitates bone healing by providing which of the following biological properties?

. Osteogenesis and Osteoconduction
. Osteoinduction and Osteoconduction
. Osteogenesis only
. Structural mechanical support
. Osteopromotion via viable mesenchymal stem cells

Correct Answer & Explanation

. Osteoinduction and Osteoconduction

Explanation

Demineralized bone matrix (DBM) is created by acid extraction of allograft bone, leaving a collagenous matrix (which provides osteoconduction) and exposing naturally occurring growth factors like Bone Morphogenetic Proteins (BMPs) (which provide osteoinduction). DBM has no living cells, so it is not osteogenic, and its processing removes its structural/mechanical integrity.

Question 5198

Topic: Biology, Genetics & Bone Healing
Which of the following bone morphogenetic proteins (BMPs) is actually a procollagen C-proteinase and does not belong to the transforming growth factor-beta (TGF-beta) superfamily?
. BMP-1
. BMP-2
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-1

Explanation

BMP-1 is unique among the bone morphogenetic proteins. While initially discovered alongside other BMPs, it was later identified as a metalloproteinase (specifically a procollagen C-proteinase) that facilitates cartilage and bone formation by cleaving the C-termini of procollagens I, II, and III. Unlike BMP-2, BMP-4, and BMP-7 (which are osteoinductive factors), BMP-1 does not belong to the TGF-beta superfamily and does not signal through SMAD pathways.

Question 5199

Topic: Biology, Genetics & Bone Healing

A 25-year-old female presents with a painful, lucent, eccentrically located lesion in the distal femur metaphysis extending to the subchondral bone. Biopsy reveals a population of neoplastic mononuclear cells and reactive multinucleated giant cells. Which of the following describes the mechanism of action of the targeted medical therapy (Denosumab) used for severe or recurrent cases of this condition?

. Inhibiting the RANK receptor directly on the surface of osteoblasts
. Binding to RANKL to prevent the activation and differentiation of osteoclast-like cells
. Directly inducing apoptosis of the multinucleated giant cells via p53 pathways
. Inhibiting vascular endothelial growth factor (VEGF) to reduce tumor vascularity
. Stimulating osteoprotegerin (OPG) production by the neoplastic mononuclear cells

Correct Answer & Explanation

. Binding to RANKL to prevent the activation and differentiation of osteoclast-like cells

Explanation

Giant Cell Tumor (GCT) of bone is characterized by neoplastic mononuclear stromal cells that express high levels of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This recruits and activates reactive multinucleated giant cells (osteoclasts) that cause bone destruction. Denosumab is a humanized monoclonal antibody that binds to RANKL, preventing its interaction with the RANK receptor on the osteoclast precursor cells, thereby inhibiting their differentiation and activation.

Question 5200

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue divided into distinct structural zones. Which of the following zones contains the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented perpendicular to the articular 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 is responsible for resisting compressive forces. It has the highest concentration of proteoglycans (which provide compressive stiffness), the lowest water content, and thick collagen fibrils arranged perpendicular to the joint surface to anchor the uncalcified cartilage to the tidemark and calcified zone. The superficial zone has the highest water content and collagen oriented parallel to the joint.

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