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1. General Principles & Basic Science MCQs

Practice Set 259 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 5161

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone has the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented strictly perpendicular to the articular surface?

. 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 represents about 30% of the cartilage volume. It provides the greatest resistance to compressive forces, possesses the highest proteoglycan concentration, the lowest water content, and features large diameter Type II collagen fibrils arranged perpendicular to the joint surface to anchor the cartilage to the underlying bone.

Question 5162

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach to the acetabulum, severe hemorrhage is encountered just superior to the superior pubic ramus. This bleeding is most likely originating from the corona mortis, which is an anastomotic connection between which two vascular systems?

. Internal iliac artery and internal pudendal artery
. External iliac (or inferior epigastric) vessels and the obturator vessels
. Femoral artery and external iliac artery
. Superior gluteal artery and inferior gluteal artery
. Deep circumflex iliac artery and the external iliac vein

Correct Answer & Explanation

. External iliac (or inferior epigastric) vessels and the obturator vessels

Explanation

The corona mortis ('crown of death') is an anatomical variant representing a vascular anastomosis between the external iliac (or its inferior epigastric branch) and the obturator vessels (a branch of the internal iliac). It crosses 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 exposures.

Question 5163

Topic: Biomechanics & Biomaterials

In the context of preparing polymethylmethacrylate (PMMA) bone cement, which of the following modifications significantly decreases the mechanical strength and fatigue life of the cement mantle?

. Adding antibiotics in powder form rather than liquid form
. Vacuum mixing the cement
. Centrifuging the cement prior to application
. Adding liquid antibiotics or excessive fluid
. Pre-chilling the monomer

Correct Answer & Explanation

. Adding liquid antibiotics or excessive fluid

Explanation

Adding aqueous/liquid substances (like liquid antibiotics) or excessive fluid significantly increases porosity and radically decreases the ultimate mechanical strength and fatigue life of PMMA bone cement. Antibiotics should only be added in fine powder form. Vacuum mixing and centrifugation both decrease porosity and thereby increase fatigue life. Pre-chilling the monomer prolongs the working time but does not weaken the cement.

Question 5164

Topic: Surgical Anatomy & Approaches

A 55-year-old male sustains a traumatic anterior shoulder dislocation. After a successful closed reduction, he complains of profound weakness in shoulder abduction and external rotation. Electromyography (EMG) at 6 weeks confirms an isolated peripheral nerve injury. Which of the following nerve roots primarily contribute to the affected nerve?

. C5, C6
. C6, C7
. C7, C8
. C8, T1
. C5, C6, C7

Correct Answer & Explanation

. C5, C6

Explanation

Anterior shoulder dislocations are frequently associated with axillary nerve palsy. The axillary nerve innervates the deltoid (shoulder abduction) and teres minor (external rotation). The axillary nerve arises from the posterior cord of the brachial plexus and carries nerve fibers primarily from the C5 and C6 nerve roots.

Question 5165

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) compared to conventional ultra-high molecular weight polyethylene (UHMWPE) results in which of the following material property changes?
. Increased ultimate tensile strength
. Increased resistance to abrasive wear
. Increased fatigue crack propagation resistance
. Increased oxidation resistance post-gamma irradiation in air
. Increased risk of osteolysis at 10 years

Correct Answer & Explanation

. Increased fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured to significantly increase resistance to adhesive and abrasive wear, thereby reducing wear debris and subsequent osteolysis. However, the cross-linking process and subsequent thermal treatments decrease mechanical properties such as ultimate tensile strength, yield strength, and fatigue crack propagation resistance.

Question 5166

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the treatment of unresectable or metastatic Giant Cell Tumor of bone (GCTB). What is the specific molecular target of this medication?

. Vascular Endothelial Growth Factor (VEGF)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Tumor Necrosis Factor alpha (TNF-alpha)
. Osteoprotegerin (OPG)
. Sclerostin

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to and inhibits RANK Ligand (RANKL). In GCTB, the neoplastic mononuclear stromal cells express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclast-like cells) that cause extensive bone osteolysis.

Question 5167

Topic: Physiology & Rehabilitation

During the descent phase of a squat exercise, the quadriceps muscle actively lengthens while remaining under tension to control knee flexion. What type of muscle contraction does this describe?

. Concentric
. Isometric
. Eccentric
. Isokinetic
. Plyometric

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when the muscle lengthens while actively producing force (e.g., the quadriceps during the descent phase of a squat acting as a brake). Concentric contractions occur when the muscle shortens, and isometric contractions occur when there is no change in muscle length.

Question 5168

Topic: Surgical Anatomy & Approaches

A 6-year-old boy sustains a completely displaced, extension-type supracondylar humerus fracture with posterolateral displacement of the distal fragment. On examination, he is unable to make an 'OK' sign. Which nerve is most likely injured?

. Radial nerve
. Ulnar nerve
. Anterior interosseous nerve (AIN)
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Anterior interosseous nerve (AIN)

Explanation

The anterior interosseous nerve (AIN), a branch of the median nerve, is the most commonly injured nerve in extension-type supracondylar humerus fractures, particularly those with posterolateral displacement. The inability to flex the IP joint of the thumb and DIP joint of the index finger (the 'OK' sign) indicates AIN palsy.

Question 5169

Topic: Infection, Pharmacology & VTE

A 20-year-old man presents with nocturnal thigh pain that is completely relieved by ibuprofen. Imaging shows a 1 cm radiolucent nidus with surrounding sclerosis in the femoral diaphysis. What is the primary biochemical mechanism underlying the effectiveness of NSAIDs for this specific lesion?

. Reduction of interleukin-6 production
. Inhibition of excessive cyclooxygenase-2 (COX-2) expression by the nidus
. Direct suppression of osteoclast activity
. Inhibition of vascular endothelial growth factor (VEGF)
. Blockade of substance P release in the periosteum

Correct Answer & Explanation

. Inhibition of excessive cyclooxygenase-2 (COX-2) expression by the nidus

Explanation

Osteoid osteomas characteristically cause severe nocturnal pain that is relieved by NSAIDs. This is because the nidus cells produce high levels of prostaglandins (specifically PGE2) due to marked expression of cyclooxygenase-2 (COX-2) enzymes. NSAIDs inhibit this COX-2 activity, directly eliminating the source of the pain.

Question 5170

Topic: Biomechanics & Biomaterials

During biomechanical testing of a tendon graft, the graft is rapidly stretched to a specific length and held at that constant length. Over time, the force required to maintain that length progressively decreases. This viscoelastic property is termed:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (force) over time when a viscoelastic material is held at a constant strain (length). Creep is the progressive increase in strain (length) over time when the material is held at a constant stress (load).

Question 5171

Topic: Biomechanics & Biomaterials

In the metallurgical design of titanium alloys for orthopaedic implants (such as Ti-6Al-4V), specific elements are added to stabilize different phases of the metal at room temperature. What is the primary role of vanadium in this alloy?

. It stabilizes the alpha-phase, increasing tensile strength.
. It stabilizes the beta-phase, lowering the modulus of elasticity.
. It promotes passivation by forming a dense oxide layer.
. It acts as an interstitial strengthener to prevent galvanic corrosion.
. It limits stress shielding by increasing the metal's density.

Correct Answer & Explanation

. It stabilizes the beta-phase, lowering the modulus of elasticity.

Explanation

In the Ti-6Al-4V alloy, titanium undergoes an allotropic phase transformation. Aluminum is added to stabilize the alpha-phase (hexagonal close-packed structure), which provides strength. Vanadium is a beta-phase (body-centered cubic) stabilizer. Retaining the beta-phase at room temperature lowers the overall modulus of elasticity of the implant, bringing it closer to that of cortical bone and thereby reducing stress shielding.

Question 5172

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach to the acetabulum for an anterior column fracture, the surgeon must be careful to identify and ligate the 'corona mortis'. This vascular structure represents an anastomosis between the external iliac (or deep inferior epigastric) and obturator vessels. Over which bony structure is this anastomosis most commonly found?

. Superior pubic ramus
. Inferior pubic ramus
. Iliopectineal eminence
. Ischial spine
. Symphysis pubis

Correct Answer & Explanation

. Superior pubic ramus

Explanation

The corona mortis is a vascular anastomosis between the external iliac (or deep inferior epigastric) and the obturator systems. It typically crosses the superior pubic ramus at an average of 5 to 7 cm from the pubic symphysis. Iatrogenic injury during the ilioinguinal or intrapelvic approaches can cause massive, difficult-to-control hemorrhage.

Question 5173

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones, each with unique biomechanical properties. Which zone is characterized by the highest concentration of proteoglycans, the lowest water content, and type II collagen fibrils oriented perpendicularly to the subchondral bone?

. 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 is responsible for providing the greatest resistance to compressive forces. It is characterized by the highest proteoglycan content, the lowest water content, and collagen fibrils that are arranged perpendicular to the articular surface, anchoring the cartilage to the underlying calcified zone and subchondral bone.

Question 5174

Topic: 1. General Principles & Basic Science

When massive cortical bone allografts are used in reconstructive orthopaedic surgery, they incorporate into the host skeleton via a process known as 'creeping substitution'. Which of the following sequences best describes this mechanism at the host-graft interface?

. Simultaneous bone formation by donor osteoblasts and host osteoblasts
. Osteoblastic new bone formation followed by delayed osteoclastic resorption
. Osteoclastic resorption of the allograft followed by osteoblastic new bone formation
. Formation of a dense avascular fibrous capsule that undergoes cartilaginous ossification
. Direct endochondral ossification mediated by bone morphogenetic proteins in the graft

Correct Answer & Explanation

. Osteoclastic resorption of the allograft followed by osteoblastic new bone formation

Explanation

Creeping substitution describes the process by which cortical bone allografts and structural autografts are incorporated. It begins with revascularization and osteoclastic resorption of the dead bone of the graft (creating 'cutting cones'), followed by osteoblastic deposition of new living bone on the remaining graft framework. Because resorption precedes formation, cortical grafts temporarily lose mechanical strength before regaining it.

Question 5175

Topic: Biology, Genetics & Bone Healing

Romosozumab is currently utilized in the treatment of severe osteoporosis. What is the specific cellular mechanism of action of this medication?

. Inhibits RANKL to prevent osteoclastogenesis
. Binds to sclerostin to disinhibit Wnt/beta-catenin signaling
. Directly stimulates osteoblast parathyroid hormone receptors
. Binds to cathepsin K to prevent bone resorption
. Acts as a selective estrogen receptor modulator (SERM)

Correct Answer & Explanation

. Binds to sclerostin to disinhibit Wnt/beta-catenin signaling

Explanation

Romosozumab is a humanized monoclonal antibody that binds to and inhibits sclerostin. By inhibiting sclerostin, it disinhibits the Wnt/beta-catenin signaling pathway, leading to increased bone formation and decreased bone resorption (a dual-acting anabolic agent).

Question 5176

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a destructive, expansile lytic lesion in the distal femur epimetaphysis. Biopsy confirms a Giant Cell Tumor of Bone. She is started on Denosumab preoperatively. Which of the following describes the primary histological effect of Denosumab on this tumor?

. Elimination of the neoplastic mononuclear stromal cells
. Elimination of the reactive multinucleated giant cells
. Induction of massive ischemic necrosis of the tumor bed
. Inhibition of vascular endothelial growth factor (VEGF)
. Promotion of chondroid differentiation in the stromal cells

Correct Answer & Explanation

. Elimination of the reactive multinucleated giant cells

Explanation

Denosumab is a RANKL inhibitor. In Giant Cell Tumor of Bone, the neoplastic mononuclear stromal cells express RANKL, which recruits reactive multinucleated osteoclast-like giant cells. Denosumab inhibits this recruitment, leading to the rapid depletion of the giant cells and subsequent woven bone formation, but the neoplastic stromal cells often remain viable.

Question 5177

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 configurations provides the greatest tensile strength and resistance to gap formation during early active rehabilitation?

. A 2-strand core suture with a running epitendinous suture
. A 4-strand core suture without an epitendinous suture
. A 4-strand core suture with a running epitendinous suture
. A 6-strand core suture with a running epitendinous suture
. An 8-strand core suture without an epitendinous suture

Correct Answer & Explanation

. A 6-strand core suture with a running epitendinous suture

Explanation

The ultimate tensile strength of a flexor tendon repair is directly proportional to the number of core strands crossing the repair site. A 6-strand core provides excellent strength. The addition of a peripheral epitendinous suture significantly improves resistance to initial gap formation and adds approximately 20-30% to the overall strength of the construct.

Question 5178

Topic: Biology, Genetics & Bone Healing

During the incorporation of a cortical structural allograft, the process of 'creeping substitution' occurs. Which of the following correctly describes the sequence of cellular events in this process?

. Direct lamellar bone formation by circulating mesenchymal stem cells
. Osteoclast resorption followed immediately by osteoblast new bone deposition
. Chondrocyte hypertrophy followed by endochondral ossification
. Osteoblast woven bone formation followed by osteoclast resorption
. Fibrous tissue interposition followed by intramembranous ossification

Correct Answer & Explanation

. Osteoclast resorption followed immediately by osteoblast new bone deposition

Explanation

Creeping substitution is the process by which a bone graft is slowly resorbed and simultaneously replaced with new living bone. For dense cortical grafts, this occurs via a 'cutting cone' mechanism, where osteoclasts lead the way by resorbing the Haversian canals, followed closely by osteoblasts laying down new osteoid.

Question 5179

Topic: Biology, Genetics & Bone Healing
Osteoclasts are multinucleated giant cells that create a sealed zone to isolate the resorptive pit (Howship's lacuna) on the bone surface. Which of the following integrins is primarily responsible for forming this sealing zone by binding to osteopontin and bone sialoprotein?
. Alpha-5 Beta-1
. Alpha-V Beta-3
. Alpha-2 Beta-1
. Alpha-M Beta-2
. Alpha-L Beta-2

Correct Answer & Explanation

. Alpha-V Beta-3

Explanation

The alpha-v beta-3 (αvβ3) integrin is highly expressed on the osteoclast cell membrane. It binds specifically to RGD (Arg-Gly-Asp) amino acid sequences found in bone matrix proteins like osteopontin and bone sialoprotein. This interaction is essential for the tight attachment of the osteoclast to the bone and the formation of the actin sealing zone.

Question 5180

Topic: Biomechanics & Biomaterials

A 45-year-old patient undergoes revision osteosynthesis of a nonunion using a titanium locking plate and stainless steel screws. Which of the following best describes the likely electrochemical outcome at the implant interface?

. The titanium plate undergoes rapid galvanic corrosion
. The stainless steel screws undergo rapid galvanic corrosion
. Fretting corrosion is completely eliminated
. Crevice corrosion occurs preferentially at the diaphyseal bone
. Both metals are passivated equally due to the formation of a titanium dioxide layer

Correct Answer & Explanation

. The stainless steel screws undergo rapid galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (e.g., bodily fluids). Stainless steel is anodic (less noble) relative to titanium. Therefore, when they are in direct contact, the stainless steel acts as the anode and preferentially corrodes, releasing ions, while the titanium acts as the cathode and remains protected.

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