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1. General Principles & Basic Science MCQs

Practice Set 621 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 12401

Topic: Biomechanics & Biomaterials

During a primary THA, the surgeon chooses a 36-mm femoral head over a 28-mm femoral head to improve hip stability. Assuming the same head-neck ratio, what is the primary biomechanical advantage that decreases the risk of dislocation with the larger femoral head?

. It increases the combined anteversion of the hip
. It decreases the volumetric wear of the polyethylene
. It increases the jump distance required for the head to dislocate
. It creates a more medialized center of rotation
. It directly increases the tension in the abductor musculature

Correct Answer & Explanation

. It increases the jump distance required for the head to dislocate

Explanation

Larger femoral heads provide greater stability primarily by increasing the 'jump distance'โ€”the distance the femoral head must translate laterally before it completely escapes the acetabular rim. A larger head also increases the head-neck ratio (assuming the neck diameter remains constant), which improves the impingement-free range of motion. However, the direct mechanical barrier to dislocation once subluxation begins is the increased jump distance. Note that larger heads increase (not decrease) volumetric wear, though modern highly cross-linked polyethylene handles this well.

Question 12402

Topic: Surgical Anatomy & Approaches

During hip arthroscopy, establishing the anterior portal requires careful anatomic knowledge. Placing the anterior portal too medial or deep puts which of the following nerves at highest risk?

. Sciatic nerve
. Superior gluteal nerve
. Lateral femoral cutaneous nerve
. Obturator nerve
. Pudendal nerve

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

The anterior portal for hip arthroscopy is established slightly lateral to the intersection of a vertical line from the ASIS and a horizontal line from the tip of the greater trochanter. It carries a significant risk of injury to the lateral femoral cutaneous nerve (LFCN) branches and the femoral nerve if placed too medial.

Question 12403

Topic: Surgical Anatomy & Approaches

The direct anterior approach (Smith-Petersen) for total hip arthroplasty utilizes a true internervous and intermuscular plane. This plane separates muscles innervated by which two nerves?

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

Correct Answer & Explanation

. Femoral nerve and Superior gluteal nerve

Explanation

The direct anterior approach uses the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep dissection passes between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 12404

Topic: Biomechanics & Biomaterials

Kinematic studies of the normal human knee demonstrate specific coupled motions during deep flexion. Which of the following best describes the normal kinematic movement of the femoral condyles on the tibia from 0 to 120 degrees of flexion?

. Symmetrical posterior rollback of both the medial and lateral femoral condyles
. Anterior translation of the lateral femoral condyle with a fixed medial condyle
. A medial pivot pattern with significant posterior translation (rollback) of the lateral femoral condyle
. A lateral pivot pattern with significant posterior translation (rollback) of the medial femoral condyle
. Pure rotation around a fixed transverse axis with no anteroposterior translation

Correct Answer & Explanation

. A medial pivot pattern with significant posterior translation (rollback) of the lateral femoral condyle

Explanation

Normal knee kinematics follow a 'medial pivot' pattern. The medial femoral condyle acts as a ball-and-socket joint with minimal anteroposterior translation, while the lateral femoral condyle undergoes significant posterior translation (rollback) as the knee flexes. This coupled internal rotation of the tibia (or external rotation of the femur) aids in maximizing deep flexion.

Question 12405

Topic: Biology, Genetics & Bone Healing

A 38-year-old male on long-term systemic corticosteroids for lupus presents with atraumatic hip pain. MRI confirms osteonecrosis of the femoral head. What is the primary cellular pathophysiology underlying corticosteroid-induced osteonecrosis?

. Direct toxicity resulting in massive osteoclast apoptosis
. Mesenchymal stem cell differentiation into adipocytes leading to marrow hypertrophy and increased intraosseous pressure
. Hypervascularity leading to rapid subchondral bone resorption and collapse
. Direct mechanical disruption of the ligamentum teres arterial supply
. Systemic formation of intravascular nitrogen gas emboli

Correct Answer & Explanation

. Mesenchymal stem cell differentiation into adipocytes leading to marrow hypertrophy and increased intraosseous pressure

Explanation

Corticosteroids alter the differentiation pathway of mesenchymal stem cells, favoring adipogenesis over osteogenesis. The resulting hypertrophy of fat cells within the rigid bony confines of the femoral head increases intraosseous pressure, which compresses thin-walled venules and arterioles, ultimately leading to ischemia and osteonecrosis.

Question 12406

Topic: Biomechanics & Biomaterials

Antibiotic-loaded acrylic bone cement (ALABC) is commonly used for prophylaxis and treatment of periprosthetic joint infection. Which of the following antibiotics is NOT appropriate for incorporation into PMMA bone cement due to its severe heat lability?

. Tobramycin
. Vancomycin
. Gentamicin
. Erythromycin
. Penicillin G

Correct Answer & Explanation

. Penicillin G

Explanation

The polymerization of polymethyl methacrylate (PMMA) bone cement is a highly exothermic reaction that can reach temperatures over 80-100 degrees Celsius in vivo. Antibiotics mixed into PMMA must be heat-stable, water-soluble, and available in powder form. Penicillins and most cephalosporins are heat-labile and degrade during polymerization, whereas aminoglycosides (tobramycin, gentamicin) and vancomycin are heat-stable.

Question 12407

Topic: Biology, Genetics & Bone Healing

In the process of bone remodeling, the activation of osteoclasts requires the binding of Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL) to RANK on osteoclast precursors. Which of the following cell types is the primary source of RANKL expression in bone?

. Osteoblasts
. Mature osteoclasts
. Macrophages
. Osteocytes
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Osteoblasts and their precursors (stromal cells) express RANKL on their surface. When RANKL binds to RANK on the surface of osteoclast precursors, it stimulates their differentiation and fusion into mature, active multinucleated osteoclasts. Osteoblasts also secrete osteoprotegerin (OPG), a decoy receptor that binds RANKL to inhibit osteoclastogenesis, thus regulating bone resorption.

Question 12408

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely utilized in major orthopedic procedures, such as total joint arthroplasty and spinal fusion, to minimize perioperative blood loss. Which of the following best describes the specific pharmacological mechanism of action of TXA?
. Irreversibly inhibits cyclooxygenase-1 and 2
. Competitively inhibits the activation of plasminogen to plasmin
. Directly inhibits coagulation factor Xa
. Binds directly to antithrombin III to enhance its activity
. Promotes the release of von Willebrand factor from endothelial cells

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly binds to the lysine-binding sites on plasminogen, which competitively prevents plasminogen from binding to fibrin and being activated to plasmin. By inhibiting plasmin formation, TXA effectively inhibits the breakdown of fibrin clots (fibrinolysis), thereby reducing surgical blood loss.

Question 12409

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive bone pain, increasing hat size, and unilateral hearing loss. Laboratory investigations reveal an isolated, marked elevation of serum alkaline phosphatase, with normal serum calcium and phosphorus levels. The initial pathophysiological phase of this disorder is primarily driven by an abnormality in which of the following?

. Osteoblast synthetic function
. Type I collagen cross-linking
. Parathyroid hormone receptor sensitivity
. Osteoclast function and morphology
. Vitamin D hydroxylation in the kidney

Correct Answer & Explanation

. Osteoclast function and morphology

Explanation

The patient's clinical presentation is classic for Paget's disease of bone (osteitis deformans). The primary cellular defect in Paget's disease originates in the osteoclasts, which are increased in number, abnormally large, and possess numerous nuclei (up to 100 per cell). The disease begins with an intense osteoclastic resorptive phase, followed by a compensatory but disorganized osteoblastic phase (mixed phase), and finally a sclerotic phase.

Question 12410

Topic: 1. General Principles & Basic Science

Normal articular cartilage is highly organized into distinct architectural zones. Which zone is biomechanically adapted to resist high compressive loads, characterized by the lowest concentration of water, the highest concentration of proteoglycans, and collagen fibers oriented perpendicularly to the joint surface?

. Deep (radial) zone
. Superficial (tangential) zone
. Middle (transitional) zone
. Calcified cartilage zone
. The tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is specifically structured to resist compressive forces. It contains the lowest water content, the highest concentration of proteoglycans (which provide compressive resistance through osmotic swelling pressure), and large type II collagen fibrils that are oriented perpendicular to the articular surface to anchor the uncalcified cartilage to the underlying calcified zone.

Question 12411

Topic: Biology, Genetics & Bone Healing

A transverse diaphyseal fracture of the radius is surgically treated with anatomic reduction and rigid fixation using a dynamic compression plate (absolute stability). Under these specific biomechanical conditions, the fracture will predominantly heal via primary bone healing (contact healing). This process is mediated directly by which of the following?

. Chondrocyte hypertrophy and apoptosis
. Formation of a fibrocartilaginous soft callus
. Intramembranous ossification from the periosteum
. Cutting cones (Haversian remodeling)
. Endochondral ossification

Correct Answer & Explanation

. Cutting cones (Haversian remodeling)

Explanation

Primary bone healing (also known as direct bone healing) occurs only under conditions of absolute mechanical stability and direct bone-to-bone contact, effectively bypassing the intermediate callus formation stage. It relies entirely on normal Haversian remodeling, where osteoclasts at the leading edge form 'cutting cones' that tunnel across the fracture line, followed immediately by osteoblasts laying down new lamellar bone.

Question 12412

Topic: Biology, Genetics & Bone Healing

A 72-year-old female is prescribed oral alendronate for the treatment of postmenopausal osteoporosis following a low-energy distal radius fracture. Nitrogen-containing bisphosphonates, such as alendronate, reduce bone turnover primarily by inhibiting which of the following intracellular targets within the osteoclast?

. Cathepsin K
. Farnesyl pyrophosphate (FPP) synthase
. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Matrix metalloproteinase-9 (MMP-9)

Correct Answer & Explanation

. Farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate, zoledronate, risedronate) inhibit farnesyl pyrophosphate (FPP) synthase, a crucial enzyme in the mevalonate pathway. This inhibition prevents the prenylation of small GTPase proteins (like Ras, Rho, Rab) essential for osteoclast function and survival, ultimately leading to osteoclast apoptosis and decreased bone resorption.

Question 12413

Topic: Biomechanics & Biomaterials

During a revision trauma surgery, a surgeon contemplates using a titanium alloy plate in direct contact with stainless steel screws. This combination of dissimilar metals within the body's electrolyte-rich fluid environment initiates a process known as galvanic corrosion. Which of the following describes the most likely electrochemical outcome of this pairing?

. Both metals will corrode at an equally accelerated rate
. The titanium will act as the cathode and undergo rapid corrosion
. The stainless steel will act as the anode and undergo accelerated corrosion
. The titanium will act as the anode and undergo accelerated corrosion
. The stainless steel will act as the cathode and remain completely protected

Correct Answer & Explanation

. The stainless steel will act as the anode and undergo accelerated corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conductive solution (like body fluid). The metal with the lower corrosion potential (the less noble metal) becomes the anode and corrodes, while the metal with the higher potential (more noble) becomes the cathode and is protected. Stainless steel is less noble than titanium; therefore, the stainless steel acts as the anode and undergoes accelerated corrosion.

Question 12414

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with persistent knee pain. Radiographs demonstrate an eccentric, completely lytic epiphyseal lesion extending into the metaphysis of the proximal tibia, lacking a sclerotic rim. Biopsy confirms a Giant Cell Tumor of bone (GCT). In cases where the tumor is deemed un-resectable or causes severe morbidity upon resection, which of the following targeted systemic therapies is FDA-approved for treatment?

. Imatinib mesylate
. Denosumab
. Rituximab
. Bevacizumab
. Trastuzumab

Correct Answer & Explanation

. Denosumab

Explanation

Giant Cell Tumor of bone (GCT) is characterized histologically by multinucleated giant cells expressing RANK, intermixed with mononuclear neoplastic stromal cells that express high levels of RANKL. Denosumab, a humanized monoclonal antibody that binds to and inhibits RANKL, effectively halts the recruitment and activation of osteoclast-like giant cells. It is the FDA-approved medical treatment for unresectable or recurrent GCTs.

Question 12415

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent causative organism in chronic periprosthetic joint infections due to its robust ability to adhere to inert implant surfaces. This adherence and subsequent resistance to host immune clearance and systemic antibiotics is primarily mediated by the pathogen's production of which of the following?

. Coagulase
. Protein A
. Alpha-toxin
. A polysaccharide glycocalyx
. Panton-Valentine leukocidin

Correct Answer & Explanation

. A polysaccharide glycocalyx

Explanation

Staphylococcus epidermidis (a coagulase-negative staphylococcus) is an opportunistic pathogen known for its ability to form a dense biofilm on foreign materials, such as orthopedic implants. This biofilm formation relies on the secretion of an extracellular polymeric substance, predominantly a polysaccharide glycocalyx (often referred to as 'slime'), which mediates firm adhesion and shields the bacteria from antibiotics and phagocytosis.

Question 12416

Topic: Biology, Genetics & Bone Healing

A surgeon opts to use demineralized bone matrix (DBM) to supplement a posterolateral lumbar fusion. DBM is derived from allograft bone processed with an acid bath to remove the mineral component. Consequently, which of the following precise combinations of biologic bone grafting properties does DBM possess?

. Osteoconduction only
. Osteoinduction only
. Osteogenesis only
. Osteoconduction and osteogenesis
. Osteoconduction and osteoinduction

Correct Answer & Explanation

. Osteoconduction and osteoinduction

Explanation

Demineralized bone matrix (DBM) possesses both osteoconductive and osteoinductive properties. The remaining type I collagen matrix provides a scaffold for new bone growth (osteoconduction), while the acid demineralization process exposes trapped noncollagenous proteins, particularly bone morphogenetic proteins (BMPs), conferring the ability to stimulate mesenchymal stem cell differentiation into osteoblasts (osteoinduction). Because it contains no living cells, DBM is entirely devoid of osteogenic capability.

Question 12417

Topic: Biomechanics & Biomaterials

During the intraoperative tensioning phase of an anterior cruciate ligament (ACL) reconstruction, the soft-tissue graft is pulled to a specific, constant length and secured. The surgeon notes that over several minutes, the tension dynamically measured within the graft progressively decreases. This specific viscoelastic behavior is termed:

. Creep
. Stress relaxation
. Hysteresis
. Strain rate dependency
. Fatigue failure

Correct Answer & Explanation

. Stress relaxation

Explanation

Viscoelastic materials (such as ligaments and tendons) exhibit time-dependent mechanical properties. 'Stress relaxation' is the phenomenon where the internal stress (tension) of a material decreases over time when it is held at a constant strain (constant length). Conversely, 'creep' refers to the progressive increase in strain (elongation) over time when the material is subjected to a constant applied stress (constant load).

Question 12418

Topic: Biology, Genetics & Bone Healing

A 5-year-old child presents with progressive varus bowing of the lower extremities, waddling gait, and short stature. Laboratory workup reveals normal serum calcium, markedly low serum phosphate, and elevated alkaline phosphatase. Genetic testing confirms X-linked hypophosphatemic rickets (XLH). The pathogenesis of this disorder is fundamentally driven by an excess of which circulating endocrine factor?

. Parathyroid hormone (PTH)
. 1,25-dihydroxyvitamin D
. Fibroblast growth factor-23 (FGF-23)
. Calcitonin
. Osteoprotegerin

Correct Answer & Explanation

. Fibroblast growth factor-23 (FGF-23)

Explanation

X-linked hypophosphatemic rickets (XLH) is the most common heritable form of rickets. It is caused by an inactivating mutation in the PHEX gene. Normally, PHEX degrades fibroblast growth factor-23 (FGF-23). The mutation leads to unchecked, elevated levels of FGF-23, which acts potently on the kidneys to downregulate sodium-phosphate cotransporters (causing severe renal phosphate wasting) and inhibits 1-alpha-hydroxylase (reducing active Vitamin D formation).

Question 12419

Topic: Infection, Pharmacology & VTE

To minimize surgical site infections during clean orthopedic operations, prophylactic intravenous antibiotics must be maintained at therapeutic tissue concentrations throughout the case. For an adult patient receiving standard cefazolin prophylaxis, which intraoperative redosing protocol is recommended by the AAOS and CDC guidelines?

. Every 2 hours or after 500 mL of intraoperative blood loss
. Every 3 hours or after 1000 mL of intraoperative blood loss
. Every 4 hours or after 1500 mL of intraoperative blood loss
. Every 6 hours or after 2000 mL of intraoperative blood loss
. Every 8 hours regardless of intraoperative blood loss

Correct Answer & Explanation

. Every 4 hours or after 1500 mL of intraoperative blood loss

Explanation

Cefazolin is a first-generation cephalosporin with a half-life of approximately 1.8 to 2 hours. Current clinical practice guidelines from the AAOS, CDC, and WHO recommend redosing cefazolin every 4 hours during prolonged surgical procedures (measured from the time of the initial preoperative dose) or if major intraoperative blood loss (> 1,500 mL) occurs, to ensure tissue concentrations remain above the minimum inhibitory concentration (MIC) for target pathogens.

Question 12420

Topic: 1. General Principles & Basic Science

A massive transfusion protocol is initiated for a polytrauma patient with a complex acetabular fracture and liver laceration. Thromboelastography (TEG) is utilized to guide targeted resuscitation. The TEG tracing demonstrates a severely prolonged R-time, with a normal K-time, normal alpha angle, and normal Maximum Amplitude (MA). Based strictly on this tracing, what is the most appropriate initial, targeted intervention?

. Transfuse packed red blood cells (PRBCs)
. Transfuse platelet concentrate
. Administer intravenous tranexamic acid (TXA)
. Transfuse fresh frozen plasma (FFP)
. Administer recombinant factor VIIa

Correct Answer & Explanation

. Transfuse fresh frozen plasma (FFP)

Explanation

In a Thromboelastography (TEG) tracing, the R-time (reaction time) represents the time to initial fibrin formation and is primarily dependent on the activity of coagulation factors. A prolonged R-time indicates a deficiency in clotting factors, making the targeted transfusion of fresh frozen plasma (FFP) the most appropriate intervention. K-time and alpha angle reflect fibrinogen levels (treated with cryoprecipitate). MA reflects platelet function and number (treated with platelets).

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