Menu

1. General Principles & Basic Science MCQs

Practice Set 261 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 5201

Topic: Biomechanics & Biomaterials

In orthopedic implant metallurgy, what specific type of corrosion occurs in restricted spaces, such as under the head of a bone screw, where the oxygen concentration becomes locally depleted compared to the surrounding fluid environment?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Crevice corrosion occurs in shielded areas, such as the interface between a screw head and a plate. In these crevices, oxygen is quickly depleted, preventing the reformation of the protective passive oxide layer (passivation). The resulting oxygen concentration gradient between the crevice and the surrounding fluid causes the crevice to become anodic, leading to localized metal dissolution.

Question 5202

Topic: Biology, Genetics & Bone Healing

Which of the following cytokines is most directly responsible for the final activation of osteoclasts in the pathogenesis of aseptic loosening secondary to polyethylene wear debris?

. Interleukin-1 (IL-1)
. Tumor Necrosis Factor-alpha (TNF-alpha)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Osteoprotegerin (OPG)
. Bone Morphogenetic Protein-2 (BMP-2)

Correct Answer & Explanation

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

Explanation

While macrophages phagocytose particulate wear debris and release inflammatory mediators such as IL-1, IL-6, and TNF-alpha, these cytokines act to stimulate osteoblasts and other local cells to express RANKL. RANKL then binds to RANK on the surface of osteoclast precursors, representing the final direct and necessary step for osteoclast differentiation, activation, and subsequent bone resorption (osteolysis).

Question 5203

Topic: Surgical Anatomy & Approaches

A 40-year-old man sustains a closed, high-energy distal tibia intra-articular fracture (AO/OTA 43-C3). On presentation, he has massive soft tissue swelling and hemorrhagic fracture blisters over the medial ankle. A spanning external fixator is placed. Which of the following is the most reliable clinical indicator that the soft tissues are amenable to definitive open reduction and internal fixation?

. Re-epithelialization of hemorrhagic blisters
. Re-epithelialization of clear fluid blisters
. Return of skin wrinkles and a positive 'pinch test'
. Decrease in compartment pressures below 30 mmHg
. Normalization of the erythrocyte sedimentation rate (ESR)

Correct Answer & Explanation

. Return of skin wrinkles and a positive 'pinch test'

Explanation

In high-energy pilon fractures, definitive open internal fixation should be delayed until the soft tissue envelope has recovered, to minimize the risk of wound breakdown and deep infection. The most reliable clinical sign of sufficient edema resolution is the return of normal skin wrinkles and a positive 'pinch test' (the ability to pinch the skin over the planned surgical approach). Hemorrhagic blisters represent a full-thickness epidermal injury and require extensive time to heal; incisions should ideally bypass them.

Question 5204

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct histomorphological zones. Which of the following characteristics best describes the superficial (tangential) zone?

. Highest concentration of proteoglycans and lowest water content
. Collagen fibers oriented perpendicular to the articular surface
. Contains chondrocytes that are round and arranged in vertical columns
. Highest concentration of water and collagen fibers oriented parallel to the articular surface
. Represents the tidemark separating hyaline cartilage from calcified cartilage

Correct Answer & Explanation

. Highest concentration of water and collagen fibers oriented parallel to the articular surface

Explanation

The superficial (tangential) zone of articular cartilage is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers (primarily Type II) oriented parallel to the joint surface. This parallel arrangement provides high tensile strength to resist shear forces during joint loading. The deep zone, conversely, has the highest proteoglycan content and collagen oriented perpendicular to the surface.

Question 5205

Topic: 1. General Principles & Basic Science

Following a Zone II flexor tendon laceration, a multi-strand core suture repair is planned to allow for early active motion rehabilitation. According to biomechanical studies, which of the following factors has the greatest influence on the initial tensile strength of a flexor tendon repair?

. The caliber of the suture material used
. The type of knot used (e.g., surgical vs. square)
. The use of a continuous epitendinous suture
. The number of suture strands crossing the repair site
. The distance of the core suture purchase from the laceration edge

Correct Answer & Explanation

. The number of suture strands crossing the repair site

Explanation

Biomechanical studies of flexor tendon repairs definitively demonstrate that the initial ultimate tensile strength of the repair is most directly proportional to the number of core suture strands crossing the repair site. For example, a 4-strand repair is substantially stronger than a 2-strand repair, and a 6-strand is stronger than a 4-strand. An epitendinous suture also adds significant strength, but the core strand count is the primary determinant of ability to withstand early active motion.

Question 5206

Topic: Biomechanics & Biomaterials

Which of the following biomechanical terms best describes the phenomenon where a constant force applied to a viscoelastic material over a prolonged period results in increasing deformation?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a material under a constant load over time. Stress relaxation is the decrease in stress over time when the material is held at a constant strain (constant deformation). Hysteresis relates to the loss of energy (usually as heat) during the loading and unloading cycles of a viscoelastic material. Orthopedic tissues like ligaments and cartilage exhibit both creep and stress relaxation.

Question 5207

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal-metaphyseal lesion of the distal femur extending to the subchondral bone without a sclerotic rim. Biopsy shows multinucleated giant cells and mononuclear stromal cells. If treating with Denosumab, what is the precise cellular target of the drug?

. VEGF on endothelial cells
. RANKL produced by mononuclear stromal cells
. RANK receptor on multinucleated giant cells
. RANKL produced by multinucleated giant cells
. RANK receptor on mononuclear stromal cells

Correct Answer & Explanation

. RANKL produced by mononuclear stromal cells

Explanation

In Giant Cell Tumor (GCT) of bone, the actual neoplastic cells are the mononuclear spindle-like stromal cells. These cells express excess RANK Ligand (RANKL). This RANKL binds to the RANK receptors on the non-neoplastic multinucleated giant cells (which are osteoclast-like), recruiting them and causing massive bone resorption. Denosumab is a monoclonal antibody that targets and binds RANKL, effectively halting this destructive process.

Question 5208

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing, the process transitions through several distinct phases. Which type of collagen is synthesized primarily during the soft callus (cartilaginous) phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Secondary fracture healing relies on endochondral ossification. During the soft callus phase, chondrocytes proliferate and synthesize a cartilaginous matrix rich in Type II collagen. Later, during the hard callus phase, these chondrocytes hypertrophy (secreting Type X collagen) and undergo apoptosis, while osteoblasts move in and deposit woven bone, which is primarily Type I collagen.

Question 5209

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the treatment of unresectable or recurrent Giant Cell Tumor of bone (GCT). What is its precise mechanism of action?

. Binds directly to the RANK receptor on osteoclasts, inhibiting their activation
. Binds to RANK Ligand (RANKL), preventing its interaction with the RANK receptor
. Inhibits the osteoclast proton pump, preventing an acidic resorption environment
. Cross-links DNA in the multinucleated osteoclast-like giant cells
. Inhibits matrix metalloproteinases in the neoplastic mononuclear stroma

Correct Answer & Explanation

. Binds to RANK Ligand (RANKL), preventing its interaction with the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to RANK Ligand (RANKL), which is overexpressed by the mononuclear neoplastic stromal cells of GCT. By binding RANKL, denosumab prevents it from activating the RANK receptor on the reactive osteoclast-like giant cells, thereby halting bone resorption and tumor progression.

Question 5210

Topic: 1. General Principles & Basic Science

Biomechanical studies have demonstrated that an un-repaired complete posterior root tear of the medial meniscus results in which of the following alterations in knee mechanics?

. Increased anterior tibial translation comparable to a complete ACL tear
. Articular contact pressures virtually equivalent to those following a total medial meniscectomy
. A minor decrease in contact area but no significant change in peak pressure
. Severe posteromedial rotatory instability during walking
. Cartilage loading concentrated exclusively on the lateral compartment

Correct Answer & Explanation

. Articular contact pressures virtually equivalent to those following a total medial meniscectomy

Explanation

Complete radial tears of the meniscus at its posterior root cause a loss of hoop stresses, leading to medial extrusion of the meniscus during axial loading. Biomechanically, this failure mechanism results in articular contact pressures equivalent to a knee that has undergone a total medial meniscectomy, accelerating the onset of osteoarthritis.

Question 5211

Topic: 1. General Principles & Basic Science

In normal articular cartilage, the collagen fibrils in the superficial zone (lamina splendens) are oriented in which direction relative to the joint surface?

. Perpendicular to the joint surface
. Oblique to the joint surface
. Parallel to the joint surface
. Randomly arranged with no predominant orientation
. In concentric whorls around chondrocytes

Correct Answer & Explanation

. Parallel to the joint surface

Explanation

In the superficial zone of articular cartilage, collagen fibers (predominantly Type II) are arranged parallel to the articular surface. This orientation provides maximum tensile strength to resist shear forces within the joint. In the deep zone, fibers are perpendicular to resist compressive forces, and in the middle zone, they are oblique/random.

Question 5212

Topic: Biomechanics & Biomaterials

In orthopaedic biomechanics, which of the following terms describes the time-dependent increase in strain (deformation) of a viscoelastic material when subjected to a constant stress (load)?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Young's modulus

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (strain) of a viscoelastic material over time when it is subjected to a constant force (stress). This is a foundational concept in the serial casting of deformities (e.g., clubfoot). Stress relaxation, conversely, is the decrease in stress over time when a material is held at a constant strain.

Question 5213

Topic: Infection, Pharmacology & VTE

A 65-year-old man is diagnosed with an acute staphylococcal periprosthetic joint infection (PJI) of his total hip arthroplasty. He is treated with irrigation, debridement, and modular exchange. His post-operative antibiotic regimen includes Rifampin. What is the primary reason for including Rifampin, and what is its mechanism of action?

. High penetration into bone; inhibits bacterial cell wall synthesis by binding PBPs
. Synergistic effect with vancomycin on planktonic bacteria; inhibits protein synthesis at the 30S ribosomal subunit
. Prevention of deep vein thrombosis; inhibits folate synthesis
. Ability to penetrate bacterial biofilms; inhibits DNA-dependent RNA polymerase
. Promotes osteoblast differentiation; inhibits DNA gyrase

Correct Answer & Explanation

. Ability to penetrate bacterial biofilms; inhibits DNA-dependent RNA polymerase

Explanation

Rifampin is utilized in the treatment of staphylococcal periprosthetic joint infections due to its exceptional ability to penetrate established bacterial biofilms and eradicate sessile organisms. Its mechanism of action is the inhibition of DNA-dependent RNA polymerase, which disrupts bacterial RNA transcription.

Question 5214

Topic: Biology, Genetics & Bone Healing

Giant Cell Tumor (GCT) of bone is a locally aggressive benign tumor. Which of the following accurately describes the cellular pathophysiology and the targeted mechanism of the biological agent Denosumab in treating this condition?

. The neoplastic multinucleated giant cells express RANK, which is inhibited by Denosumab
. The neoplastic mononuclear stromal cells express RANKL; Denosumab is a monoclonal antibody against RANKL
. The neoplastic osteoblasts express osteoprotegerin (OPG); Denosumab binds and neutralizes OPG
. The neoplastic macrophages express TNF-alpha; Denosumab acts as a TNF-alpha inhibitor
. The neoplastic spindle cells express VEGF; Denosumab inhibits angiogenesis via VEGF blockade

Correct Answer & Explanation

. The neoplastic mononuclear stromal cells express RANKL; Denosumab is a monoclonal antibody against RANKL

Explanation

In Giant Cell Tumor (GCT) of bone, the actual neoplastic cells are the mononuclear spindle-like stromal cells. These cells express high levels of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). The multinucleated giant cells are reactive (osteoclast-like) and express RANK. Denosumab is a human monoclonal antibody that binds and inhibits RANKL, effectively halting the recruitment and activation of the destructive giant cells.

Question 5215

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a biologically active Giant Cell Tumor (GCT) of the distal femur. She is scheduled for curettage but is treated preoperatively with Denosumab to consolidate the tumor margins. What is the mechanism of action of this medication?

. Direct cytotoxicity to the neoplastic mononuclear cells
. Monoclonal antibody that binds and inhibits RANKL
. Inhibition of vascular endothelial growth factor (VEGF)
. Stimulation of osteoblast proliferation and bone formation
. Matrix metalloproteinase (MMP) inhibitor

Correct Answer & Explanation

. Monoclonal antibody that binds and inhibits RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By inhibiting RANKL, it prevents the activation of the RANK receptor on osteoclast-like giant cells, thereby profoundly reducing osteolysis and promoting ossification of the tumor matrix.

Question 5216

Topic: Biology, Genetics & Bone Healing
Which type of collagen is the predominant structural protein found in the extracellular matrix of normal mature articular (hyaline) cartilage?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Type II collagen makes up 90-95% of the collagen in normal articular (hyaline) cartilage, providing tensile strength. Type I is found in bone, tendon, and fibrocartilage (such as the meniscus or scar cartilage). Type X is specific to the hypertrophic zone of the growth plate during endochondral ossification.

Question 5217

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (modified Stoppa) approach for the fixation of an acetabular fracture, meticulous dissection is required over the superior pubic ramus to avoid injury to the 'corona mortis'. This vascular structure represents an anastomosis between which of the following?

. Obturator vessels and inferior epigastric vessels
. Internal iliac and external iliac arteries directly
. Internal pudendal and external pudendal vessels
. Superior gluteal and internal iliac vessels
. Inferior gluteal and obturator vessels

Correct Answer & Explanation

. Obturator vessels and inferior epigastric vessels

Explanation

The 'corona mortis' (crown of death) is a highly variable but critical vascular anastomosis between the external iliac system (inferior epigastric artery/vein) and the internal iliac system (obturator artery/vein). It is located over the posterior aspect of the superior pubic ramus and is at significant risk of iatrogenic injury during anterior intrapelvic approaches, leading to massive, difficult-to-control hemorrhage.

Question 5218

Topic: 1. General Principles & Basic Science

During a latissimus dorsi flap transfer for soft tissue coverage, the surgeon must isolate the thoracodorsal nerve. In brachial plexus anatomy, the thoracodorsal nerve arises directly from which of the following structures?

. Lateral cord
. Medial cord
. Upper trunk
. Roots (C5-C7)
. Posterior cord

Correct Answer & Explanation

. Posterior cord

Explanation

The thoracodorsal nerve (middle subscapular nerve) branches directly off the posterior cord of the brachial plexus. The posterior cord (formed by the posterior divisions of all three trunks) gives rise to the upper subscapular, thoracodorsal, and lower subscapular nerves, before terminating into the axillary and radial nerves.

Question 5219

Topic: Biomechanics & Biomaterials

A 22-year-old collegiate baseball pitcher presents with profound shoulder pain during the 'late cocking' phase of throwing. MRI arthrogram demonstrates a Type II SLAP (Superior Labrum Anterior to Posterior) lesion. After 6 months of targeted physical therapy, he remains unable to throw. What is the primary surgical recommendation?

. Open biceps tenodesis
. Arthroscopic biceps tenotomy
. Arthroscopic debridement of the superior labrum
. Arthroscopic repair of the superior labrum and biceps anchor
. Open capsular shift

Correct Answer & Explanation

. Arthroscopic repair of the superior labrum and biceps anchor

Explanation

A Type II SLAP lesion involves detachment of the superior labrum and the origin of the long head of the biceps tendon from the glenoid. In a young, high-demand, overhead throwing athlete, the standard of care after failed conservative management is arthroscopic repair of the labrum back to the glenoid footprint. Biceps tenodesis or tenotomy is generally reserved for older patients, non-throwers, or salvage after failed repairs, as it alters the normal throwing kinematics.

Question 5220

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely incorporated into orthopedic protocols to significantly reduce perioperative blood loss. Which of the following accurately describes its primary pharmacological mechanism of action?
. Direct inhibition of Factor Xa in the coagulation cascade
. Competitive inhibition of plasminogen activation
. Irreversible antagonism of Vitamin K-dependent clotting factors
. Inhibition of cyclooxygenase to prevent platelet aggregation
. Enhancement of antithrombin III activity

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation

Explanation

Tranexamic acid (TXA) is a synthetic derivative of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly and competitively binding to the lysine-binding sites on plasminogen molecules. This prevents plasminogen from converting into plasmin, which in turn prevents the degradation of fibrin clots, thereby stabilizing the clot and reducing bleeding.

Test Yourself

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

On this Page