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1. General Principles & Basic Science MCQs

Practice Set 292 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 5821

Topic: Surgical Anatomy & Approaches

During a direct anterior approach for a total hip arthroplasty, the surgeon develops the superficial internervous plane. Which of the following nerves innervates the muscle that forms the medial boundary of this surgical interval?

. Superior gluteal nerve
. Femoral nerve
. Inferior gluteal nerve
. Obturator nerve
. Sciatic nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

The superficial interval for the direct anterior (Smith-Petersen) approach is between the tensor fasciae latae (laterally) and the sartorius (medially). The sartorius is innervated by the femoral nerve.

Question 5822

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is now routinely administered in total joint arthroplasty to reduce perioperative blood loss. Which of the following best describes its mechanism of action?
. It directly activates the coagulation cascade via Factor X
. It inhibits the cross-linking of fibrin polymers by blocking Factor XIII
. It competitively inhibits the activation of plasminogen to plasmin
. It promotes the release of von Willebrand factor from endothelial cells
. It irreversibly inhibits platelet cyclooxygenase

Correct Answer & Explanation

. It competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine-binding sites on plasminogen, preventing its conversion to plasmin and thus inhibiting fibrinolysis.

Question 5823

Topic: Surgical Anatomy & Approaches

During a direct anterior approach for a total hip arthroplasty, the surgeon utilizes the internervous plane between which of the following muscles?

. Gluteus medius and tensor fasciae latae
. Tensor fasciae latae and sartorius
. Sartorius and rectus femoris
. Rectus femoris and vastus lateralis
. Adductor longus and gracilis

Correct Answer & Explanation

. Tensor fasciae latae and sartorius

Explanation

The direct anterior (Smith-Petersen) approach to the hip exploits the internervous plane between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve). This allows access to the joint without detaching muscle insertions.

Question 5824

Topic: Biomechanics & Biomaterials

Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty to reduce wear rates. Which of the following manufacturing steps is primarily responsible for eliminating free radicals to prevent in vivo oxidation?

. Gamma irradiation in a vacuum
. Addition of calcium hydroxyapatite
. Electron beam cross-linking
. Remelting or annealing
. Ethylene oxide sterilization

Correct Answer & Explanation

. Remelting or annealing

Explanation

After irradiation generates cross-linking in polyethylene, residual free radicals are left behind that can cause oxidation and degradation. Remelting or annealing is performed to extinguish these free radicals and stabilize the material.

Question 5825

Topic: Biology, Genetics & Bone Healing

Which of the following genetic mutations results in high bone mass due to decreased inhibition of the Wnt/beta-catenin signaling pathway?

. Loss-of-function mutation in SOST
. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in RANK
. Gain-of-function mutation in COL1A1
. Loss-of-function mutation in LRP5

Correct Answer & Explanation

. Loss-of-function mutation in SOST

Explanation

Sclerostin (encoded by SOST) normally inhibits Wnt signaling by binding LRP5/6 receptors. Loss-of-function mutations in SOST lead to conditions like sclerosteosis, characterized by an uninhibited Wnt pathway and abnormally high bone mass.

Question 5826

Topic: Biomechanics & Biomaterials

On a typical stress-strain curve for a ductile orthopedic implant material, what term describes the point where the material begins to deform plastically rather than elastically?

. Ultimate tensile strength
. Yield point
. Failure point
. Modulus of elasticity
. Proportional limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the end of elastic deformation and the beginning of plastic deformation. Beyond this stress level, the material will sustain permanent deformation and will not return to its original shape.

Question 5827

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the mechanism of action of denosumab in the treatment of osteoporosis?

. Competitive inhibition of osteoclast proton pumps
. Monoclonal antibody binding directly to RANK ligand
. Stimulation of osteoblast proliferation via the Wnt pathway
. Selective estrogen receptor modulation
. Integration into the bone matrix resulting in osteoclast apoptosis

Correct Answer & Explanation

. Monoclonal antibody binding directly to RANK ligand

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL. This neutralizes RANKL, preventing it from activating RANK on osteoclasts, which profoundly inhibits osteoclast differentiation and bone resorption.

Question 5828

Topic: Biomechanics & Biomaterials

When a stainless steel plate is fixed with titanium screws in a fracture construct, which of the following electrochemical processes is most likely to cause early implant failure?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution, such as bodily fluids. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 5829

Topic: Biology, Genetics & Bone Healing

Intermittent administration of recombinant human parathyroid hormone (teriparatide) achieves its anabolic effect on bone primarily by preventing the apoptosis of which cell type?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Chondrocytes
. Mesenchymal stem cells

Correct Answer & Explanation

. Osteoblasts

Explanation

Intermittent PTH administration (teriparatide) exerts a net anabolic effect primarily by stimulating osteoblast activity and prolonging their lifespan by inhibiting osteoblast apoptosis. Continuous PTH exposure, conversely, promotes net bone resorption.

Question 5830

Topic: Biology, Genetics & Bone Healing

The acidification of the resorption pit by osteoclasts requires the secretion of protons across the ruffled border. Which intracellular enzyme primarily generates these protons?

. Alkaline phosphatase
. Tartrate-resistant acid phosphatase
. Carbonic anhydrase II
. Cathepsin K
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II catalyzes the conversion of carbon dioxide and water into carbonic acid, which rapidly dissociates into protons and bicarbonate. The protons are then actively pumped into the resorption lacuna to dissolve bone mineral.

Question 5831

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) signals through transmembrane serine-threonine kinase receptors. Which intracellular signaling molecules are directly phosphorylated following this activation?

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

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to specific serine-threonine kinase receptors that directly phosphorylate receptor-regulated Smads (Smads 1, 5, and 8). These phosphorylated Smads form a complex with Smad 4, translocate to the nucleus, and drive osteogenic gene transcription.

Question 5832

Topic: Biology, Genetics & Bone Healing

A patient presents with osteomalacia. Laboratory testing reveals low calcium, low phosphorus, and elevated parathyroid hormone (PTH) levels. Which of the following best explains the mechanism of low serum phosphorus in this patient?

. Decreased intestinal absorption of phosphorus
. PTH-mediated inhibition of renal phosphate reabsorption
. Decreased bone resorption of phosphorus
. Increased renal synthesis of 1,25-dihydroxyvitamin D
. Reduced FGF-23 secretion

Correct Answer & Explanation

. PTH-mediated inhibition of renal phosphate reabsorption

Explanation

In vitamin D deficiency (osteomalacia), secondary hyperparathyroidism develops to maintain serum calcium. The elevated PTH decreases phosphate reabsorption in the proximal renal tubule, causing phosphaturia and subsequent hypophosphatemia.

Question 5833

Topic: Biomechanics & Biomaterials

Which of the following modifications to a cortical bone screw most significantly increases its pullout strength?

. Decreasing the thread pitch
. Decreasing the outer (major) diameter
. Increasing the inner (core) diameter
. Decreasing the length of screw engagement
. Increasing the insertion torque past the yield point

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Screw pullout strength is directly proportional to the major diameter, thread engagement length, and bone density, and inversely proportional to thread pitch. Decreasing pitch means more threads per unit length are engaged in the bone, increasing pullout strength.

Question 5834

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to minimize perioperative blood loss. Which of the following best describes its primary mechanism of action?
. Inhibition of cyclooxygenase-1
. Reversible binding to the active site of thrombin
. Competitive inhibition of plasminogen activation
. Activation of tissue factor pathway inhibitor
. Enhancement of antithrombin III activity

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine-binding sites on plasminogen, preventing its conversion to plasmin and thus inhibiting fibrin clot degradation.

Question 5835

Topic: Biology, Genetics & Bone Healing

During endochondral ossification at the physis, in which histologic zone do chondrocytes undergo apoptosis as the extracellular matrix begins to calcify?

. Reserve zone
. Proliferative zone
. Zone of maturation
. Zone of hypertrophy
. Zone of provisional calcification

Correct Answer & Explanation

. Zone of provisional calcification

Explanation

In the zone of provisional calcification, the cartilage matrix undergoes calcification and the hypertrophic chondrocytes undergo apoptosis. This calcified matrix provides a temporary scaffold for osteoblasts to lay down primary woven bone.

Question 5836

Topic: Biomechanics & Biomaterials

When a ligament is subjected to a constant, sustained sub-failure load, it experiences a progressive increase in length over time. What is this time-dependent biomechanical property called?

. Stress relaxation
. Hysteresis
. Creep
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the time-dependent increase in strain (deformation) under a constant applied stress (load). This viscoelastic property is characteristic of tendons and ligaments.

Question 5837

Topic: 1. General Principles & Basic Science

Nonsteroidal anti-inflammatory drugs (NSAIDs) are thought to impair fracture healing primarily through the inhibition of which of the following?

. Prostaglandin E2 synthesis
. Leukotriene B4 synthesis
. Tumor necrosis factor-alpha
. Interleukin-1 beta
. Osteoprotegerin

Correct Answer & Explanation

. Prostaglandin E2 synthesis

Explanation

NSAIDs inhibit cyclooxygenase (COX) enzymes, resulting in decreased synthesis of prostaglandins, particularly PGE2. PGE2 is essential for early inflammatory signaling, osteoblast differentiation, and normal fracture callus formation.

Question 5838

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following manufacturing processes is most commonly used to decrease the adhesive and abrasive wear rates of ultra-high-molecular-weight polyethylene (UHMWPE)?
. High-dose gamma irradiation followed by remelting
. Increasing the amount of calcium hydroxyapatite coating
. Gamma sterilization in an oxygen-rich environment
. Decreasing the molecular weight of the polymer
. Adding a porous titanium backing

Correct Answer & Explanation

. High-dose gamma irradiation followed by remelting

Explanation

High-dose gamma irradiation induces cross-linking between polymer chains, drastically reducing the wear rate of UHMWPE. Subsequent thermal treatment (remelting or annealing) extinguishes residual free radicals to prevent oxidative degradation in vivo.

Question 5839

Topic: Biology, Genetics & Bone Healing

Which cell is considered the primary mechanosensor in bone tissue, responsible for orchestrating the remodeling process in response to changes in mechanical loading?

. Osteoblast
. Osteoclast
. Osteocyte
. Bone lining cell
. Mesenchymal stem cell

Correct Answer & Explanation

. Osteocyte

Explanation

Osteocytes, embedded deep within the bone matrix, are the primary mechanosensors of bone. They sense fluid shear stress within their canalicular networks during mechanical loading and direct osteoblast and osteoclast activity accordingly.

Question 5840

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate, inhibit bone resorption primarily by inhibiting which of the following enzymes?

. HMG-CoA reductase
. Farnesyl pyrophosphate (FPP) synthase
. Carbonic anhydrase II
. Cathepsin K
. Tyrosine kinase

Correct Answer & Explanation

. Farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates inhibit FPP synthase in the mevalonate pathway within osteoclasts. This prevents the prenylation of critical small GTP-binding proteins (e.g., Rab, Rho, Rac), leading to osteoclast apoptosis and loss of function.

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