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1. General Principles & Basic Science MCQs

Practice Set 697 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 13921

Topic: 1. General Principles & Basic Science

Which of the following physiologic changes occurs in skeletal muscle distal to an inflated pneumatic tourniquet after 60 minutes of ischemia?

. Intracellular pH increases
. Extracellular potassium decreases
. Intracellular accumulation of lactic acid
. Depletion of extracellular calcium
. Increased production of adenosine triphosphate (ATP)

Correct Answer & Explanation

. Intracellular accumulation of lactic acid

Explanation

Tourniquet-induced ischemia forces cellular metabolism to shift from aerobic to anaerobic glycolysis. This results in the depletion of ATP, an intracellular accumulation of lactic acid, and a subsequent decrease in intracellular pH (acidosis).

Question 13922

Topic: 1. General Principles & Basic Science
Following primary repair of an acute flexor tendon laceration, the healing process undergoes three overlapping phases. During the remodeling phase, which of the following cellular and matrix changes predominates?
. Influx of neutrophils and macrophages
. Peak proliferation of fibroblasts
. Random deposition of type III collagen
. Reorganization of type I collagen along lines of stress
. Peak angiogenesis and capillary budding

Correct Answer & Explanation

. Reorganization of type I collagen along lines of stress

Explanation

The remodeling phase of tendon healing, beginning around 6 weeks post-injury, is characterized by decreased cellularity and maturation of the scar. Type III collagen is gradually replaced by Type I collagen, which cross-links and aligns parallel to the axis of mechanical tension.

Question 13923

Topic: Infection, Pharmacology & VTE

In the pathogenesis of implant-related orthopedic infections, Staphylococcus epidermidis utilizes a specific extracellular structure to form a protective biofilm. What is the primary constituent of this structure?

. Peptidoglycan
. Lipopolysaccharide
. Polysaccharide glycocalyx
. Teichoic acid
. Flagellin

Correct Answer & Explanation

. Polysaccharide glycocalyx

Explanation

Staphylococcus epidermidis produces an extracellular polysaccharide slime layer, known as the glycocalyx. This matrix facilitates adherence to abiotic implant surfaces and protects the bacteria from host immune responses and systemic antibiotics by forming a mature biofilm.

Question 13924

Topic: 1. General Principles & Basic Science

According to the International Commission on Radiological Protection (ICRP), what is the recommended maximum annual occupational whole-body dose equivalent of ionizing radiation for an orthopedic surgeon?

. 5 mSv
. 20 mSv
. 50 mSv
. 150 mSv
. 500 mSv

Correct Answer & Explanation

. 20 mSv

Explanation

The ICRP recommends a maximum occupational whole-body radiation limit of 20 mSv per year, averaged over defined 5-year periods, with no single year exceeding 50 mSv. The lens of the eye also has a revised limit of 20 mSv per year to prevent cataracts.

Question 13925

Topic: Biomechanics & Biomaterials

Which type of corrosion is most likely to occur when a stainless steel screw is used to secure a titanium plate in fracture fixation?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution like bodily fluids, causing the less noble metal to corrode. Using stainless steel and titanium implants in direct contact should be avoided to prevent this complication.

Question 13926

Topic: Biology, Genetics & Bone Healing

Which of the following growth factors is primarily responsible for inducing the differentiation of mesenchymal stem cells into osteoblasts during early fracture healing?

. Insulin-like Growth Factor-1 (IGF-1)
. Fibroblast Growth Factor-2 (FGF-2)
. Bone Morphogenetic Protein-2 (BMP-2)
. Vascular Endothelial Growth Factor (VEGF)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Bone Morphogenetic Protein-2 (BMP-2)

Explanation

Bone Morphogenetic Proteins (especially BMP-2 and BMP-7) belong to the TGF-beta superfamily and strongly induce osteoblastic differentiation from mesenchymal stem cells. They are highly osteoinductive and critical for the early phases of bone regeneration.

Question 13927

Topic: 1. General Principles & Basic Science

In the postoperative rehabilitation of a Zone II flexor tendon repair, what is the primary biological rationale for utilizing early active motion protocols?

. To increase the ultimate tensile strength of the selected suture material
. To promote intrinsic healing while minimizing extrinsic adhesion formation
. To accelerate the enzymatic degradation of the epitenon
. To stimulate excessive granulation tissue formation at the repair site
. To completely bypass the inflammatory phase of wound healing

Correct Answer & Explanation

. To promote intrinsic healing while minimizing extrinsic adhesion formation

Explanation

Early active motion protocols promote intrinsic healing by encouraging tenocyte proliferation while stressing the tendon to glide. This controlled physical stress limits extrinsic healing, which otherwise relies on surrounding tissues and leads to restrictive scar adhesions.

Question 13928

Topic: Biomechanics & Biomaterials

Which of the following biomechanical terms accurately describes the progressive, time-dependent elongation of a ligament when it is subjected to a constant applied load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the viscoelastic property where a tissue gradually deforms (elongates) over time under a constant load. Conversely, stress relaxation is the progressive decrease in stress when a tissue is held at a constant length.

Question 13929

Topic: Biology, Genetics & Bone Healing

Rigid internal fixation utilizing compression plating for a transverse radius fracture primarily facilitates which specific type of bone healing?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with robust callus formation
. Chondrogenesis and subsequent enchondral bridging

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Rigid internal fixation with absolute stability (strain less than 2%) entirely bypasses callus formation, resulting in primary bone healing. This process occurs via direct Haversian remodeling where osteoclastic cutting cones traverse the fracture site, followed by osteoblastic bone deposition.

Question 13930

Topic: Biomechanics & Biomaterials

Which of the following material combinations in a modular total hip arthroplasty carries the highest risk of galvanic corrosion?

. Titanium alloy stem and cobalt-chromium head
. Cobalt-chromium stem and cobalt-chromium head
. Titanium alloy stem and ceramic head
. Cobalt-chromium stem and ceramic head
. Stainless steel stem and stainless steel head

Correct Answer & Explanation

. Titanium alloy stem and cobalt-chromium head

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment, such as bodily fluids. A titanium alloy stem coupled with a cobalt-chromium head represents a classic mixed-metal couple prone to galvanic and fretting corrosion at the trunnion.

Question 13931

Topic: 1. General Principles & Basic Science

During the incorporation of a cortical bone graft, which of the following biological processes best distinguishes its healing pattern from that of a cancellous bone graft?

. Rapid revascularization via existing trabecular pathways
. Osteoclastic resorption trailing osteoblastic bone formation
. Initial osteoclastic resorption followed by osteoblastic bone deposition
. Early structural weakening followed by prolonged creeping substitution
. Immediate osteoinduction without a recognizable inflammatory phase

Correct Answer & Explanation

. Initial osteoclastic resorption followed by osteoblastic bone deposition

Explanation

Cortical bone grafts undergo creeping substitution characterized by an initial phase of osteoclastic resorption out of proportion to bone formation, leading to early structural weakening. In contrast, cancellous grafts revascularize rapidly and are reinforced by early osteoblastic apposition on existing trabeculae.

Question 13932

Topic: Surgical Anatomy & Approaches
A patient sustains an anteroposterior compression (APC III) pelvic ring injury. During the surgical approach to the pubic symphysis, significant retropubic hemorrhage is encountered due to injury of the "corona mortis". This represents an anastomosis between which two vessels?
. External iliac artery and internal pudendal artery
. Inferior epigastric artery and obturator artery
. Superior gluteal artery and inferior epigastric artery
. Internal iliac artery and femoral artery
. Obturator artery and superior vesical artery

Correct Answer & Explanation

. Inferior epigastric artery and obturator artery

Explanation

The corona mortis is a potentially lethal vascular anastomosis between the external iliac (or inferior epigastric) and the obturator systems. It typically crosses the superior pubic ramus and is highly susceptible to iatrogenic or traumatic injury.

Question 13933

Topic: 1. General Principles & Basic Science

When performing a primary repair of a Zone II flexor digitorum profundus (FDP) laceration, which of the following suture constructs maximizes biomechanical strength to permit early active motion?

. 2-strand core suture with an epitendinous running suture
. 4-strand core suture without an epitendinous suture
. 4-strand core suture with an epitendinous running suture
. Bunnell 2-strand stitch with a locking loop
. Modified Kessler 2-strand stitch using absorbable suture

Correct Answer & Explanation

. 4-strand core suture with an epitendinous running suture

Explanation

A 4-strand (or greater) core suture repair combined with an epitendinous running suture provides the necessary tensile strength to safely withstand the forces of early active motion protocols. The epitendinous suture significantly reduces gap formation and adds up to 50% to the overall construct strength.

Question 13934

Topic: Biology, Genetics & Bone Healing

Articular cartilage derives its unique biomechanical properties from its extracellular matrix composition. Which component is primarily responsible for the tissue's high resistance to compressive forces?

. Type I collagen
. Type II collagen
. Aggrecan
. Fibronectin
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan, a large proteoglycan, binds to hyaluronic acid and entraps large amounts of water within the cartilage matrix. This osmotic swelling pressure provides the primary resistance to compressive loads, whereas Type II collagen resists tensile forces.

Question 13935

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly used as an adjuvant treatment for Giant Cell Tumor of Bone (GCTB). By which precise mechanism does this drug act to reduce tumor progression?

. Inhibiting the Wnt/beta-catenin signaling pathway
. Binding and neutralizing RANKL to prevent osteoclastogenesis
. Directly inducing apoptosis of the neoplastic mononuclear stromal cells
. Stimulating osteoprotegerin (OPG) production from osteoblasts
. Inhibiting vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Binding and neutralizing RANKL to prevent osteoclastogenesis

Explanation

Denosumab is a human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By neutralizing RANKL, it prevents the recruitment and maturation of giant cell osteoclasts, severely limiting the osteolytic behavior of the tumor.

Question 13936

Topic: Biology, Genetics & Bone Healing

In the biology of secondary fracture healing, the process is dependent on a specific sequence of overlapping phases. During which phase is endochondral ossification most active?

. Hematoma formation
. Inflammatory phase
. Soft callus formation
. Hard callus formation
. Remodeling phase

Correct Answer & Explanation

. Hard callus formation

Explanation

Hard callus formation represents the phase where the cartilaginous (soft) callus is converted into woven bone via endochondral ossification. This phase significantly increases the biomechanical stability of the healing fracture.

Question 13937

Topic: Biology, Genetics & Bone Healing

Which of the following orthopedic procedures relies primarily on intramembranous ossification for bone formation?

. Rigid plate fixation of a forearm fracture
. Cast immobilization of a distal radius fracture
. Distraction osteogenesis (Ilizarov technique)
. Intramedullary nailing of a femur fracture
. Secondary bone callus formation in a non-union

Correct Answer & Explanation

. Distraction osteogenesis (Ilizarov technique)

Explanation

Distraction osteogenesis primarily occurs via intramembranous ossification, which is characterized by the direct differentiation of mesenchymal stem cells into osteoblasts without a cartilaginous intermediate. Rigid fixation undergoes primary bone healing (cutting cones), while cast immobilization and IM nailing undergo secondary bone healing via endochondral ossification.

Question 13938

Topic: Biomechanics & Biomaterials
Which of the following factors most significantly increases the rate of volumetric wear of conventional ultra-high molecular weight polyethylene (UHMWPE) in total hip arthroplasty?
. Decreased femoral head size
. Increased polyethylene thickness
. Highly cross-linking the polyethylene
. Increased femoral head size
. Using a ceramic femoral head instead of cobalt-chrome

Correct Answer & Explanation

. Increased femoral head size

Explanation

Volumetric wear of conventional UHMWPE increases with larger femoral head sizes due to the increased sliding distance per step. Conversely, linear wear may increase with smaller heads due to higher focal contact pressures. Highly cross-linked polyethylene significantly reduces both volumetric and linear wear. Ceramic heads also reduce wear rates compared to cobalt-chrome.

Question 13939

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which structural zone contains the highest concentration of proteoglycans and the lowest concentration of water?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the highest concentration of proteoglycans and the lowest water content. The collagen fibers here are oriented vertically to resist compressive forces. In contrast, the superficial zone has the highest water content, highest collagen content, and lowest proteoglycan content.

Question 13940

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is frequently used in orthopedic surgery to minimize perioperative blood loss. What is the primary mechanism of action of TXA?

. Irreversible inhibition of cyclooxygenase
. Activation of the intrinsic coagulation cascade
. Competitive inhibition of plasminogen activation
. Direct inhibition of Factor Xa
. Cross-linking of fibrin monomers

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid is a synthetic lysine analog that acts as an antifibrinolytic agent. It competitively binds to the lysine-binding sites on plasminogen, preventing its activation to plasmin, thereby inhibiting the degradation of fibrin clots.

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