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1. General Principles & Basic Science MCQs

Practice Set 589 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 11761

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for the fixation of an anterior column acetabular fracture, significant arterial hemorrhage is encountered upon dissection over the superior pubic ramus. This bleeding is most likely originating from an aberrant anastomotic vessel known as the 'corona mortis'. Between which two vascular systems does this anastomosis typically occur?

. Obturator artery and internal iliac vein
. Internal iliac artery and superior gluteal artery
. External iliac artery/vein (or inferior epigastric) and the obturator artery/vein
. Inferior epigastric artery and internal pudendal artery
. Superior gluteal artery and obturator artery

Correct Answer & Explanation

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

Explanation

The corona mortis ('crown of death') is a significant vascular anastomosis between the external iliac system (or inferior epigastric vessels) and the obturator system. It is located over the superior pubic ramus at a distance of roughly 4-9 cm from the pubic symphysis. Disruption of this vessel during the ilioinguinal approach or Stoppa approach can lead to massive, difficult-to-control hemorrhage, as the vessel can retract into the true pelvis.

Question 11762

Topic: Biology, Genetics & Bone Healing

A 65-year-old female who has been taking alendronate for 8 years complains of prodromal aching pain in her left thigh for 3 months. Radiographs demonstrate focal lateral cortical thickening of the proximal femoral diaphysis with a subtle transverse radiolucent line, without complete fracture. What is the most appropriate next step in management?

. Discontinue the bisphosphonate and start teriparatide exclusively
. Prophylactic intramedullary nailing of the left femur
. Core decompression of the femoral shaft
. Switch from alendronate to denosumab and allow weight-bearing as tolerated
. Strict observation with serial radiographs every 6 months

Correct Answer & Explanation

. Prophylactic intramedullary nailing of the left femur

Explanation

The patient presents with a symptomatic incomplete atypical femur fracture (AFF), classically associated with long-term bisphosphonate use (lateral cortical thickening, transverse radiolucency, prodromal thigh pain). Because she is symptomatic (thigh pain), the risk of progression to a complete, displaced fracture is very high. The standard of care for a symptomatic incomplete AFF is prophylactic intramedullary nailing. Bisphosphonates should also be discontinued, and anabolic agents (like teriparatide) may be considered adjunctively, but surgery is the definitive management.

Question 11763

Topic: 1. General Principles & Basic Science

In the Masquelet technique for managing segmental bone defects, the first stage involves placing a polymethylmethacrylate (PMMA) spacer. Six to eight weeks later, the spacer is removed, and bone graft is placed inside the newly formed 'induced membrane'. What is the critical biological function of this induced membrane?

. It acts purely as a mechanical barrier to prevent soft tissue prolapse into the defect
. It releases high-dose antibiotics indefinitely to sterilize the bed
. It secretes osteoinductive growth factors (like VEGF and BMP-2) and prevents graft resorption
. It transforms directly into cortical bone via intramembranous ossification
. It negates the requirement for autologous cancellous bone grafting

Correct Answer & Explanation

. It acts purely as a mechanical barrier to prevent soft tissue prolapse into the defect

Explanation

The Masquelet technique relies on a biologically active 'induced membrane' that forms around the PMMA spacer. This membrane is not just a physical barrier; it is highly vascularized and actively secretes key osteogenic and angiogenic growth factors, including Vascular Endothelial Growth Factor (VEGF), Bone Morphogenetic Protein 2 (BMP-2), and TGF-beta. When the spacer is removed, this membrane creates an optimal biological chamber that supports the consolidation of the subsequently placed autologous bone graft and prevents its rapid resorption.

Question 11764

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is treated with a monoclonal antibody that targets a key cytokine involved in bone resorption. Which of the following is the specific mechanism of action of this drug at the cellular level?

. Binds to the ruffled border of osteoclasts
. Inhibits the Wnt/beta-catenin pathway
. Binds RANKL preventing its interaction with RANK
. Directly inhibits cathepsin K
. Stimulates osteoprotegerin (OPG) production by osteoblasts

Correct Answer & Explanation

. Binds to the ruffled border of osteoclasts

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclast precursors, thereby inhibiting osteoclast differentiation, activation, and survival. It acts as a pharmacologic mimic of osteoprotegerin (OPG).

Question 11765

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of a novel orthopedic implant alloy, a load-deformation curve is generated. What biomechanical property is represented by the total area under the stress-strain curve up to the point of failure?

. Elasticity
. Yield strength
. Toughness
. Brittleness
. Young's modulus

Correct Answer & Explanation

. Elasticity

Explanation

Toughness is defined as the total amount of energy a material can absorb before it fractures, which corresponds to the entire area under the stress-strain curve. Young's modulus is the slope of the elastic region, measuring stiffness. Yield strength is the point where plastic (irreversible) deformation begins.

Question 11766

Topic: 1. General Principles & Basic Science

In normal human articular cartilage, which zone is characterized by the largest diameter collagen fibrils oriented strictly perpendicular to the joint surface and the lowest water content?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils, which are oriented perpendicular to the joint surface to resist compressive loads. It also has the highest concentration of proteoglycans and the lowest water content of the uncalcified zones.

Question 11767

Topic: Biology, Genetics & Bone Healing

During the proliferative phase of fracture healing, mesenchymal stem cells differentiate into osteoblasts. Which of the following intracellular signaling pathways is most essential for committing these mesenchymal precursors exclusively to the osteoblast lineage?

. Notch signaling pathway
. Wnt/beta-catenin pathway
. Hedgehog signaling pathway
. Smad1/5/8 pathway
. JAK/STAT pathway

Correct Answer & Explanation

. Notch signaling pathway

Explanation

The Wnt/beta-catenin signaling pathway is critical for promoting osteoblast differentiation from mesenchymal stem cells while simultaneously inhibiting chondrogenic and adipogenic lineages. LRP5/6 are key co-receptors in this pathway.

Question 11768

Topic: Biomechanics & Biomaterials

When a constant sustained load is applied to an anterior cruciate ligament allograft over a prolonged period, the ligament slowly elongates over time without any increase in the applied force. Which of the following viscoelastic properties does this describe?

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

Correct Answer & Explanation

. Hysteresis

Explanation

Creep is defined as the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. Stress relaxation, conversely, is the decrease in stress (force) within a material over time when it is held at a constant length or strain.

Question 11769

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel screw to secure a titanium plate during the open reduction and internal fixation of a distal radius fracture. Which type of corrosion is most likely to occur at the interface of these two different metals?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in electrical contact within a conductive fluid. The less noble metal (anode) undergoes accelerated corrosion. Stainless steel and titanium should generally not be mixed to prevent this electrochemical process.

Question 11770

Topic: Biology, Genetics & Bone Healing

Fibroblast Growth Factor 23 (FGF-23) plays a critical role in phosphate homeostasis. Which of the following actions is a direct physiological effect of elevated circulating FGF-23 levels?

. Increased intestinal absorption of calcium
. Increased synthesis of 1,25-dihydroxyvitamin D
. Decreased renal reabsorption of phosphate
. Decreased secretion of parathyroid hormone
. Increased osteoblastic bone formation

Correct Answer & Explanation

. Increased intestinal absorption of calcium

Explanation

FGF-23 is a hormone primarily secreted by osteocytes in response to hyperphosphatemia. It acts on the kidneys to decrease phosphate reabsorption (by downregulating NaPi-IIa and NaPi-IIc cotransporters) and decreases the synthesis of active 1,25-dihydroxyvitamin D by inhibiting 1-alpha-hydroxylase.

Question 11771

Topic: Physiology & Rehabilitation

During the stance phase of normal human gait, the peak compressive loads across the articular cartilage of the knee can exceed several times body weight. Under these high-load, high-motion conditions, what is the primary mode of joint lubrication?

. Boundary lubrication
. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Weeping lubrication
. Squeeze-film lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Under high load and motion conditions, articular cartilage relies on elastohydrodynamic lubrication. The pressure of the fluid film causes elastic deformation of the articular cartilage, increasing the surface area of contact and distributing the load over a wider area.

Question 11772

Topic: 1. General Principles & Basic Science
A patient suffers a closed crush injury to the forearm. Electromyography and nerve conduction studies performed 4 weeks later suggest a nerve injury characterized by axonal disruption and loss of endoneurial tube continuity, but an intact perineurium and epineurium. According to the Sunderland classification, what grade is this nerve injury?
. Grade I
. Grade II
. Grade III
. Grade IV
. Grade V

Correct Answer & Explanation

. Grade III

Explanation

A Sunderland Grade III injury involves loss of continuity of the axon and the endoneurium, but the perineurium and epineurium remain intact. Because the endoneurial tubes are disrupted, regenerating axons may become misdirected, leading to incomplete or aberrant recovery compared to Grade II injuries.

Question 11773

Topic: Biology, Genetics & Bone Healing

An orthopaedic surgeon utilizes a massive structural cortical allograft for a segmental defect reconstruction following tumor resection. Which of the following best describes the classical sequence of events during the creeping substitution of this cortical bone graft?

. Osteoclastic resorption followed immediately by osteoblastic new bone formation within Haversian canals
. Initial osteoblastic apposition on dead trabeculae followed by osteoclastic resorption
. Rapid revascularization followed by widespread chondrogenesis and endochondral ossification
. Immediate vascular ingrowth without an intermediate resorptive phase
. Initial fibrous encapsulation followed by intramembranous ossification

Correct Answer & Explanation

. Osteoclastic resorption followed immediately by osteoblastic new bone formation within Haversian canals

Explanation

Creeping substitution in cortical bone grafts involves osteoclastic resorption cutting cones that bore through the dead cortical bone, closely followed by osteoblasts that lay down new lamellar bone. This process temporarily weakens the graft mechanically before it incorporates and regains strength.

Question 11774

Topic: Biology, Genetics & Bone Healing
While reviewing the histological properties of dense regular connective tissue, it is noted that ligaments and tendons have slightly different ultrastructural compositions. Compared to a typical tendon, a typical ligament contains a higher proportion of which of the following?
. Type I collagen
. Type II collagen
. Proteoglycans and elastin
. Fibroblasts in parallel rows
. Water content

Correct Answer & Explanation

. Proteoglycans and elastin

Explanation

Tendons and ligaments are both primarily composed of Type I collagen. However, ligaments generally have slightly less Type I collagen and a higher proportion of proteoglycans, elastin, and Type III collagen compared to tendons, giving them slightly more extensibility.

Question 11775

Topic: Infection, Pharmacology & VTE
A 68-year-old male is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. At which specific point in the coagulation cascade does this agent exert its primary therapeutic effect?
. Directly inhibits thrombin (Factor IIa)
. Inhibits the synthesis of vitamin K-dependent clotting factors
. Activates antithrombin III
. Directly inhibits Factor Xa
. Prevents the conversion of fibrinogen to fibrin

Correct Answer & Explanation

. Directly inhibits Factor Xa

Explanation

Rivaroxaban is a direct oral anticoagulant (DOAC) that functions by directly and reversibly inhibiting Factor Xa, preventing the conversion of prothrombin to thrombin. Dabigatran directly inhibits thrombin (Factor IIa). Heparins work by activating antithrombin III.

Question 11776

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with multiple unexplained fractures and a radiograph showing a 'bone-within-bone' appearance.

Genetic testing reveals a mutation in the gene encoding Carbonic Anhydrase II. Which of the following best describes the resulting cellular dysfunction?

. Inability of osteoblasts to synthesize type I collagen
. Failure of osteoclasts to generate hydrogen ions for ruffled border secretion
. Defective mineralization of osteoid leading to rickets
. Overproduction of osteoprotegerin (OPG) blocking RANKL
. Inhibition of chondrocyte proliferation in the resting zone

Correct Answer & Explanation

. Inability of osteoblasts to synthesize type I collagen

Explanation

Carbonic Anhydrase II mutation causes an autosomal recessive form of osteopetrosis. This enzyme is essential for osteoclasts to produce protons, which are pumped into Howship's lacuna to dissolve bone mineral.

Question 11777

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel screw through a titanium locking plate to treat a periarticular fracture. What specific biomechanical or biomaterial phenomenon is most likely to occur at the screw-plate interface?

. Fretting corrosion
. Galvanic corrosion with titanium acting as the anode
. Galvanic corrosion with stainless steel acting as the anode
. Crevice corrosion due to low oxygen tension
. Stress shielding of the underlying bone

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment. Stainless steel is less noble (more anodic) than titanium, causing the stainless steel to corrode while the titanium is protected.

Question 11778

Topic: Biomechanics & Biomaterials

During a biomechanical study, a human Achilles tendon is subjected to tensile testing at varying strain rates. According to the viscoelastic properties of ligaments and tendons, what is the expected result when the tendon is loaded at a very high strain rate compared to a low strain rate?

. Decreased stiffness and decreased ultimate failure load
. Increased stiffness and increased ultimate failure load
. Increased deformation before failure
. A prolonged toe region on the stress-strain curve
. Decreased Young's modulus

Correct Answer & Explanation

. Decreased stiffness and decreased ultimate failure load

Explanation

Ligaments and tendons exhibit viscoelasticity, meaning their biomechanical behavior is strain-rate dependent. At high strain rates, they become stiffer and can withstand a higher ultimate failure load before rupturing.

Question 11779

Topic: Biology, Genetics & Bone Healing

A patient undergoes spinal fusion using a massive structural cortical bone allograft. Compared to a cancellous autograft, which of the following accurately describes the incorporation process of the cortical allograft?

. It undergoes initial osteoblastic bone formation followed by resorption
. It incorporates via creeping substitution with osteoclasts leading the cutting cones
. It provides superior osteoinduction compared to cancellous autografts
. It achieves maximum mechanical strength 6 weeks after implantation
. It relies entirely on woven bone formation without remodeling

Correct Answer & Explanation

. It undergoes initial osteoblastic bone formation followed by resorption

Explanation

Structural cortical grafts incorporate via creeping substitution, where osteoclasts first resorb the dead bone (cutting cones) before osteoblasts lay down new bone. This causes the graft to become temporarily weaker before full incorporation.

Question 11780

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is frequently utilized to improve longevity. What is the primary biomechanical tradeoff of increasing the radiation dose to increase cross-linking in UHMWPE?
. Increased volumetric wear
. Decreased oxidation resistance
. Decreased yield strength and fatigue crack propagation resistance
. Increased adhesive wear
. Decreased elastic modulus

Correct Answer & Explanation

. Decreased yield strength and fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene significantly reduces volumetric and adhesive wear in joint arthroplasty. However, the cross-linking process decreases the material's ductility, fracture toughness, and resistance to fatigue crack propagation.

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