Menu

1. General Principles & Basic Science MCQs

Practice Set 622 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 12421

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, primary (direct) bone healing without callus formation occurs under conditions of absolute stability. What is the maximum allowable interfragmentary strain that permits primary bone healing to occur via cutting cones?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory states that the type of tissue that forms between fracture fragments depends on interfragmentary strain. Primary (direct) bone healing via Haversian remodeling (cutting cones) requires absolute stability, meaning the strain must be less than 2%. Strains between 2% and 10% result in secondary bone healing with callus formation.

Question 12422

Topic: Surgical Anatomy & Approaches

During surgical approach for an acetabular fracture utilizing the ilioinguinal approach, the surgeon must be cautious of the 'corona mortis'. This anatomical structure is a vascular anastomosis between which two vascular systems?

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

Correct Answer & Explanation

. External iliac and internal iliac (obturator) systems

Explanation

The 'corona mortis' (crown of death) is an important vascular anastomosis situated over the superior pubic ramus, connecting the external iliac system (inferior epigastric vessels) and the internal iliac system (obturator vessels). It can be either arterial, venous, or both, and is at risk of iatrogenic injury during anterior pelvic approaches.

Question 12423

Topic: Biology, Genetics & Bone Healing

A 72-year-old female presents with progressive groin pain 10 years after a total hip arthroplasty. Radiographs show eccentric wear of the polyethylene liner and massive periprosthetic osteolysis. The biological cascade leading to this osteolysis is primarily mediated by macrophages phagocytosing wear debris. Which molecule is ultimately secreted to activate osteoclasts and drive bone resorption in this process?

. Interleukin-10 (IL-10)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Transforming growth factor-beta (TGF-beta)
. Osteoprotegerin (OPG)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Particle-induced osteolysis is driven by macrophages that phagocytose polyethylene wear debris and release pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6). These cytokines stimulate osteoblasts and fibroblasts to upregulate RANKL. RANKL binds to RANK receptors on osteoclast precursors, leading to osteoclast differentiation and massive bone resorption (osteolysis). OPG acts as a decoy receptor to inhibit this process.

Question 12424

Topic: 1. General Principles & Basic Science
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is used to distinguish necrotizing fasciitis from other soft tissue infections. Which of the following parameters is heavily weighted (yields the most points) in the LRINEC scoring system?
. C-reactive protein (CRP) > 150 mg/L
. Serum sodium < 135 mmol/L
. White blood cell count > 25 cells/mm3
. Serum creatinine > 141 umol/L
. Blood glucose > 10 mmol/L

Correct Answer & Explanation

. C-reactive protein (CRP) > 150 mg/L

Explanation

The LRINEC score utilizes CRP, WBC, hemoglobin, sodium, creatinine, and glucose. A C-reactive protein (CRP) level > 150 mg/L yields the highest single point value (4 points) in the scoring system. A total score of 6 or higher raises the suspicion for necrotizing fasciitis, and a score of 8 or higher is strongly predictive.

Question 12425

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, the Young's modulus (modulus of elasticity) of an implant is a crucial factor in load sharing with host bone. Titanium alloy (Ti-6Al-4V) is frequently chosen for femoral stems over Cobalt-Chromium (Co-Cr) alloys primarily to reduce 'stress shielding'. Which of the following accurately compares their Young's moduli relative to cortical bone?

. Titanium has a higher modulus than Co-Cr, closer to cortical bone
. Titanium has a lower modulus than Co-Cr, closer to cortical bone
. Cortical bone has a higher modulus than both Titanium and Co-Cr
. Titanium and Co-Cr have identical moduli, but Titanium is less toxic
. Co-Cr has a lower modulus than Titanium, matching cancellous bone

Correct Answer & Explanation

. Titanium has a lower modulus than Co-Cr, closer to cortical bone

Explanation

Young's modulus represents the stiffness of a material. Cortical bone has a modulus of approx. 15-20 GPa. Titanium alloy has a modulus of approx. 110 GPa, while Cobalt-Chromium has a modulus of approx. 210-240 GPa. Because Titanium's modulus is lower than Co-Cr (making it more flexible and closer to the modulus of cortical bone), it transfers more mechanical stress to the adjacent bone, thereby reducing bone resorption due to stress shielding.

Question 12426

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, 'soap-bubble' lesion in the epiphysis of the distal femur extending to the subchondral bone. Biopsy shows mononuclear cells and numerous multinucleated giant cells. The neoplastic cells in this tumor are known to express high levels of which surface marker, providing a target for medical therapy with Denosumab?

. CD99
. RANKL
. Vimentin
. S-100
. Estrogen receptor

Correct Answer & Explanation

. RANKL

Explanation

The clinical and histologic description is diagnostic of a Giant Cell Tumor (GCT) of bone. The true neoplastic cells in GCT are the spindle-shaped mononuclear stromal cells, which express high levels of RANKL. This RANKL over-expression recruits and activates normal multinucleated osteoclast-like giant cells, leading to massive bone destruction. Denosumab, a monoclonal antibody against RANKL, is an effective medical treatment for inoperable or recurrent GCTs.

Question 12427

Topic: 1. General Principles & Basic Science

A 28-year-old female presents with an acute zone II flexor tendon laceration of her right index finger. To safely allow for an early active mobilization rehabilitation protocol, which of the following core repair techniques is required biomechanically?

. A 2-strand core repair with an epitendinous suture
. A 4-strand (or greater) core repair with an epitendinous suture
. A 2-strand core repair without an epitendinous suture
. A figure-of-eight single strand repair
. Early active mobilization is strictly contraindicated in all zone II repairs

Correct Answer & Explanation

. A 4-strand (or greater) core repair with an epitendinous suture

Explanation

To safely permit early active mobilization following a flexor tendon repair (which is beneficial for reducing adhesions and improving excursion), a mechanically robust repair is required. Biomechanical studies dictate that a minimum of a 4-strand core repair, supplemented by an epitendinous suture, provides the requisite tensile strength to withstand the forces of early active motion.

Question 12428

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective targeted medical therapy utilized in the management of unresectable or metastatic giant cell tumors of bone (GCTB). What is the specific mechanism of action of Denosumab in this disease?

. Inhibition of vascular endothelial growth factor (VEGF)
. Inhibition of the mammalian target of rapamycin (mTOR) pathway
. Monoclonal antibody against RANKL, preventing osteoclast activation
. Direct cytotoxicity to the neoplastic mononuclear cells
. Inhibition of tyrosine kinase receptors

Correct Answer & Explanation

. Monoclonal antibody against RANKL, preventing osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In Giant Cell Tumor of Bone, the neoplastic mononuclear stroma cells secrete RANKL, which aggressively recruits and activates the multinucleated giant cells (osteoclast-like cells) that cause bone destruction. Denosumab binds RANKL, effectively halting this destructive process.

Question 12429

Topic: Biology, Genetics & Bone Healing
During secondary bone healing, endochondral ossification is responsible for the formation of the fracture soft callus. Which type of collagen is predominantly synthesized by the cells within this soft callus?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

The soft callus in endochondral fracture healing is primarily composed of cartilage, which is produced by proliferating chondrocytes. The extracellular matrix of cartilage is predominantly composed of Type II collagen. As healing progresses to the hard callus phase, osteoblasts deposit woven bone, which is predominantly composed of Type I collagen.

Question 12430

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, galvanic corrosion can lead to significant implant failure or adverse local tissue reactions. Which of the following exact conditions is required for galvanic corrosion to occur?

. Cyclic mechanical loading of a single uniform metal type
. Fretting wear between a polyethylene liner and a metal cup
. Contact between two dissimilar metals in the presence of an electrolytic fluid
. Exposure of titanium to highly oxygenated arterial blood
. Sterilization of stainless steel hardware with gamma irradiation

Correct Answer & Explanation

. Contact between two dissimilar metals in the presence of an electrolytic fluid

Explanation

Galvanic corrosion is an electrochemical process that is driven by differences in the electrical potential of distinct materials. It occurs strictly when two dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact with one another while simultaneously immersed in a conductive electrolytic solution (such as human extracellular fluid or blood). The metal with the lower electrical potential acts as an anode and undergoes accelerated corrosion.

Question 12431

Topic: 1. General Principles & Basic Science

A 40-year-old male undergoes a flexor tendon repair in Zone II of the index finger. To optimize outcomes and prevent tendon adhesions, which rehabilitation protocol is currently considered the gold standard in the early postoperative period?

. Immobilization for 6 weeks followed by active motion
. Early active mobilization protocols (e.g., Belfast or synergistic motion)
. Continuous passive motion (CPM) for 4 weeks
. Immediate resisted active flexion exercises
. Passive flexion and passive extension only

Correct Answer & Explanation

. Early active mobilization protocols (e.g., Belfast or synergistic motion)

Explanation

Early active mobilization protocols involve controlled active flexion and extension within a splint. This approach improves tendon excursion, reduces adhesions, and maintains repair strength better than prolonged immobilization.

Question 12432

Topic: Biomechanics & Biomaterials

In the biomechanical evaluation of tendons and ligaments, the phenomenon where a tissue subjected to a constant load deforms continuously over time is best described by which of the following terms?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent continuous deformation of a viscoelastic material under a constant load. Stress relaxation refers to the decrease in stress over time when the material is held at a constant length.

Question 12433

Topic: Biomechanics & Biomaterials

A researcher is studying articular cartilage biomechanics. Which zone of articular cartilage is characterized by the highest concentration of proteoglycans and collagen fibers oriented perpendicular to the joint 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 contains the highest concentration of proteoglycans and features collagen fibers aligned vertically to resist compressive loads. The superficial zone has horizontal fibers to resist shear stress.

Question 12434

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in bone healing and remodeling. Upon BMP binding to its cell surface receptor, which intracellular signaling pathway is primarily activated to stimulate osteoblast differentiation?

. Wnt/beta-catenin
. JAK/STAT
. Smad 1/5/8
. MAPK/ERK
. Notch/Hes

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs signal primarily through the canonical Smad pathway, specifically phosphorylating Smads 1, 5, and 8. These complex with Smad 4 to translocate into the nucleus and upregulate osteogenic genes like Runx2.

Question 12435

Topic: Surgical Anatomy & Approaches

A 25-year-old male sustains a closed humerus fracture and subsequent radial nerve palsy. Electromyography (EMG) at 4 weeks shows fibrillation potentials, but the nerve sheath remains intact. According to Sunderland's classification, this corresponds to a 2nd-degree injury. What is the equivalent Seddon classification and prognosis?

. Neurapraxia; complete recovery expected within days
. Axonotmesis; recovery expected at 1 mm/day
. Neurotmesis; no spontaneous recovery
. Axonotmesis; no spontaneous recovery
. Neurapraxia; recovery expected at 1 mm/day

Correct Answer & Explanation

. Axonotmesis; recovery expected at 1 mm/day

Explanation

A 2nd-degree Sunderland injury corresponds to Seddon's axonotmesis, where the axon is disrupted but the endoneurium is intact. Wallerian degeneration occurs, but spontaneous recovery is expected at approximately 1 mm/day.

Question 12436

Topic: Biomechanics & Biomaterials

A surgeon revises a failed internal fixation of a femur fracture where a stainless steel plate was used with titanium screws. Extensive black debris and localized osteolysis are noted. What specific type of corrosion is primarily responsible for this failure?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in contact within an electrolytic fluid medium like blood. This electrochemical process accelerates the corrosion of the less noble metal.

Question 12437

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, absolute stability (strain less than 2%) is required to promote which type of bone healing?

. Primary bone healing via Haversian remodeling
. Secondary bone healing via endochondral ossification
. Secondary bone healing via intramembranous ossification
. Callus formation and maturation
. Woven bone bridging

Correct Answer & Explanation

. Primary bone healing via Haversian remodeling

Explanation

Primary bone healing (contact healing) requires absolute stability with strain below 2%, allowing osteoclasts to form cutting cones followed by osteoblasts laying down new osteons. Secondary bone healing involves callus formation and tolerates higher strain.

Question 12438

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with severe osteoporosis and a recent distal radius fracture is started on denosumab. Which of the following accurately describes the mechanism of action of this medication?

. It mimics pyrophosphate and binds to hydroxyapatite crystals
. It is a monoclonal antibody that binds to and inhibits RANKL
. It directly stimulates osteoblasts by activating the Wnt pathway
. It is a selective estrogen receptor modulator
. It inhibits the enzyme cathepsin K in osteoclasts

Correct Answer & Explanation

. It is a monoclonal antibody that binds to and inhibits RANKL

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to Receptor Activator of Nuclear Factor Kappa-B Ligand (RANKL). This prevents RANKL from activating RANK on osteoclasts, thereby inhibiting bone resorption.

Question 12439

Topic: 1. General Principles & Basic Science

During a prolonged lower extremity orthopedic surgery with a pneumatic tourniquet inflated to 300 mmHg, what is the earliest predictable cellular consequence within the ischemic skeletal muscle?

. Irreversible mitochondrial damage
. Depletion of ATP and progression to anaerobic metabolism
. Myonecrosis and rhabdomyolysis
. Microvascular thrombosis
. Apoptosis of muscle satellite cells

Correct Answer & Explanation

. Depletion of ATP and progression to anaerobic metabolism

Explanation

The earliest physiological change during tourniquet-induced ischemia is the shift from aerobic to anaerobic metabolism, leading to ATP depletion and lactic acidosis. Irreversible damage (myonecrosis) typically requires ischemia lasting beyond 2 to 3 hours.

Question 12440

Topic: 1. General Principles & Basic Science

A surgeon is designing a new cortical screw to maximize pullout strength in osteoporotic bone. Which of the following geometric modifications will most significantly increase the screw's pullout strength?

. Increasing the inner root diameter
. Decreasing the outer thread diameter
. Increasing the thread pitch
. Increasing the outer thread diameter
. Decreasing the thread length

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

Screw pullout strength is primarily determined by the outer thread diameter, thread engagement length, and the shear strength of the bone. Increasing the outer thread diameter provides the largest increase in bone purchase and pullout resistance.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page