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1. General Principles & Basic Science MCQs

Practice Set 429 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 8561

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with progressive hearing loss and an increasing hat size. Radiographs show mixed lytic and sclerotic changes in his skull and pelvis. Which of the following is the primary cellular abnormality initiating this condition?

. Defective osteoblast mineralization
. Excessive and disorganized osteoclast activity
. Decreased osteocyte apoptosis
. Increased chondrocyte proliferation
. Mutation in Type I collagen synthesis

Correct Answer & Explanation

. Excessive and disorganized osteoclast activity

Explanation

Paget disease of bone begins with an intensely destructive osteolytic phase driven by highly abnormal, multinucleated osteoclasts. This is followed by a disorganized blastic phase leading to structurally weak woven bone.

Question 8562

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is widely used in total joint arthroplasty to reduce wear rates. However, the cross-linking process results in which of the following mechanical trade-offs?
. Decreased oxidation resistance
. Decreased fatigue strength
. Increased adhesive wear
. Decreased modulus of elasticity
. Increased third-body wear

Correct Answer & Explanation

. Decreased fatigue strength

Explanation

While high cross-linking significantly decreases adhesive and abrasive wear, it concurrently reduces the material's fatigue strength, tensile strength, and fracture toughness. This can increase the risk of implant fracture, especially in thin components.

Question 8563

Topic: 1. General Principles & Basic Science
According to the Sunderland classification of nerve injury, a fourth-degree injury involves disruption of all neural and supporting elements EXCEPT the:
. Axon
. Endoneurium
. Perineurium
. Epineurium
. Myelin sheath

Correct Answer & Explanation

. Perineurium

Explanation

In a fourth-degree Sunderland nerve injury, the axon, endoneurium, and perineurium are disrupted, but the epineurium remains intact. Spontaneous recovery is extremely poor, and surgical intervention is usually required.

Question 8564

Topic: 1. General Principles & Basic Science
Which of the following enzymes is primarily responsible for the degradation of type II collagen in the pathogenesis of osteoarthritis?
. Matrix metalloproteinase-1 (MMP-1)
. Matrix metalloproteinase-3 (MMP-3)
. Matrix metalloproteinase-13 (MMP-13)
. Cathepsin K
. ADAMTS-4

Correct Answer & Explanation

. Matrix metalloproteinase-13 (MMP-13)

Explanation

MMP-13 (collagenase-3) is the primary enzyme responsible for the cleavage and degradation of Type II collagen in articular cartilage during osteoarthritis. ADAMTS enzymes are primarily aggrecanases.

Question 8565

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman undergoes biopsy of a lytic epiphyseal lesion in the proximal tibia. Pathology demonstrates multinucleated giant cells interspersed among mononuclear stromal cells. If systemic therapy is considered, which of the following is the primary cellular target of the most commonly used pharmacologic agent?

. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Vascular endothelial growth factor (VEGF)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

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

Explanation

Denosumab, a monoclonal antibody used for giant cell tumors, binds to RANKL. RANKL is produced by the neoplastic mononuclear stromal cells and recruits/activates the non-neoplastic osteoclast-like giant cells.

Question 8566

Topic: Biology, Genetics & Bone Healing

During the endochondral ossification process of fracture healing, mesenchymal stem cells must differentiate into chondrocytes to form the soft callus. Which of the following transcription factors is the essential master regulator for this specific chondrocytic differentiation?

. Runx2
. SOX9
. Osterix
. Sclerostin
. RANKL

Correct Answer & Explanation

. SOX9

Explanation

SOX9 is the primary transcription factor required for the differentiation of mesenchymal stem cells into chondrocytes. In contrast, Runx2 and Osterix are the key transcription factors necessary for osteoblastic differentiation.

Question 8567

Topic: Biomechanics & Biomaterials
A 65-year-old man undergoes a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following represents the primary biomechanical advantage of highly cross-linked polyethylene compared to conventional ultra-high molecular weight polyethylene (UHMWPE)?
. Increased fatigue strength
. Decreased adhesive and abrasive wear
. Improved resistance to oxidation without additives
. Increased ultimate tensile strength
. Increased ductility

Correct Answer & Explanation

. Decreased adhesive and abrasive wear

Explanation

Highly cross-linked polyethylene significantly reduces adhesive and abrasive wear rates compared to conventional UHMWPE, decreasing the risk of osteolysis. However, the cross-linking process sacrifices mechanical properties, leading to decreased fatigue strength, ductility, and ultimate tensile strength.

Question 8568

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the proximal tibial epiphysis extending to the subchondral bone.

Histology shows multinucleated giant cells in a stroma of mononuclear cells. The neoplastic cells in this lesion primarily express which of the following?

. Osteoprotegerin
. RANKL
. SOX9
. CD68
. p53

Correct Answer & Explanation

. RANKL

Explanation

In a Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear stromal cells, which heavily express RANKL. This overexpression stimulates the recruitment and fusion of normal host osteoclast precursors into the characteristic reactive multinucleated giant cells.

Question 8569

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a unique extracellular matrix to withstand physiological joint loads. Which of the following molecular components is primarily responsible for providing the compressive stiffness of articular cartilage?

. Type II collagen
. Aggrecan
. Decorin
. Fibronectin
. Elastin

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is a large proteoglycan that provides compressive stiffness to articular cartilage via its negatively charged glycosaminoglycan side chains, which attract water and create significant swelling pressure. Type II collagen, in contrast, primarily provides tensile strength and restrains the swelling pressure.

Question 8570

Topic: Infection, Pharmacology & VTE

A 45-year-old man develops a chronic prosthetic joint infection one year after a total knee arthroplasty. Intraoperative cultures yield Staphylococcus epidermidis. The organism's ability to persistently colonize the implant surface and evade the host immune system is primarily mediated by the production of which of the following?

. Panton-Valentine leukocidin
. Biofilm
. Protein A
. Alpha-toxin
. Endotoxin

Correct Answer & Explanation

. Biofilm

Explanation

Staphylococcus epidermidis forms a robust polysaccharide glycocalyx, or biofilm, that facilitates adherence to inert implant surfaces. This biofilm acts as a physical barrier, protecting the bacteria from both host cellular immunity and systemic antimicrobial therapy.

Question 8571

Topic: Biology, Genetics & Bone Healing

A 70-year-old man presents with progressive hearing loss and an increasing hat size. Radiographs show profound cortical thickening and coarsened trabeculae of the skull.

The primary cellular defect initiating this condition involves which of the following?

. Decreased osteoblast function
. Abnormal osteoclast activity
. Malignant transformation of chondrocytes
. Defective mineralization of osteoid
. Impaired type I collagen synthesis

Correct Answer & Explanation

. Abnormal osteoclast activity

Explanation

Paget's disease is initiated by an overactive, abnormal osteoclastic phase featuring large, hypermultinucleated osteoclasts. This intense resorption is followed by a disorganized compensatory osteoblastic response, resulting in weak, architecturally abnormal woven bone.

Question 8572

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed alendronate for the management of severe osteoporosis. At the cellular and molecular level, nitrogen-containing bisphosphonates inhibit osteoclast function primarily by disrupting which of the following metabolic pathways?

. Wnt/beta-catenin pathway
. Mevalonate pathway
. RANKL-RANK interaction
. Cytochrome P450 pathway
. Cyclooxygenase pathway

Correct Answer & Explanation

. Mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates (e.g., alendronate) inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of essential small GTP-binding proteins (like Ras and Rho), leading to osteoclast apoptosis and decreased bone resorption.

Question 8573

Topic: 1. General Principles & Basic Science

A biomechanical engineer is attempting to redesign a cortical bone screw to maximize its pull-out strength in osteoporotic bone. Which of the following specific design modifications will most effectively increase the screw's pull-out strength?

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

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pull-out strength is directly proportional to the volume of bone caught between the screw threads. It is maximized by increasing the outer thread diameter, decreasing the inner root diameter, and decreasing the thread pitch (resulting in more threads per unit length).

Question 8574

Topic: Biology, Genetics & Bone Healing

A 2-year-old boy presents with progressive lower extremity bowing and widened wrists. Laboratory tests show normal serum calcium, significantly low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. This specific genetic defect leads to excessive production of which of the following?

. Parathyroid hormone (PTH)
. Vitamin D3
. Fibroblast growth factor 23 (FGF23)
. Calcitonin
. RANKL

Correct Answer & Explanation

. Fibroblast growth factor 23 (FGF23)

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation, which leads to pathologically elevated levels of FGF23. Excess FGF23 causes severe renal phosphate wasting and decreases 1,25-dihydroxyvitamin D production, ultimately resulting in defective bone mineralization.

Question 8575

Topic: Surgical Anatomy & Approaches

A surgeon is performing a standard deltopectoral approach to the shoulder. Which of the following best defines the internervous plane utilized in this approach?

. Axillary nerve and Pectoral nerves
. Axillary nerve and Suprascapular nerve
. Musculocutaneous nerve and Radial nerve
. There is no true internervous plane in this approach
. Spinal accessory nerve and Axillary nerve

Correct Answer & Explanation

. Axillary nerve and Pectoral nerves

Explanation

The deltopectoral approach uses the internervous plane between the deltoid (innervated by the axillary nerve) and the pectoralis major (innervated by the medial and lateral pectoral nerves). This minimizes risk of denervating the anterior shoulder musculature.

Question 8576

Topic: Surgical Anatomy & Approaches

During an anterior intrapelvic (Stoppa) approach for an acetabular fracture, life-threatening hemorrhage occurs from an avulsed vascular anastomosis bridging over the superior pubic ramus. Which two vascular systems are connected by this "corona mortis"?

. Internal iliac and common femoral systems
. Obturator (internal iliac) and external iliac/inferior epigastric systems
. Superior gluteal and internal pudendal systems
. Inferior epigastric and internal pudendal systems
. Femoral and internal pudendal systems

Correct Answer & Explanation

. Obturator (internal iliac) and external iliac/inferior epigastric systems

Explanation

The corona mortis is a vascular connection between the obturator (internal iliac system) and the external iliac or inferior epigastric vessels. It crosses the superior pubic ramus and is highly vulnerable during anterior pelvic surgical approaches.

Question 8577

Topic: Surgical Anatomy & Approaches

A 35-year-old competitive weightlifter presents with vague posterior shoulder pain and paresthesias over the lateral deltoid, diagnosed as quadrangular space syndrome. What are the correct anatomical boundaries of this space?

. Teres minor (superior), teres major (inferior), long head of triceps (medial), surgical neck of humerus (lateral)
. Teres minor (superior), teres major (inferior), lateral head of triceps (medial), surgical neck of humerus (lateral)
. Infraspinatus (superior), teres minor (inferior), long head of triceps (medial), humerus (lateral)
. Subscapularis (superior), teres major (inferior), short head of biceps (medial), humerus (lateral)
. Teres major (superior), latissimus dorsi (inferior), long head of triceps (medial), humerus (lateral)

Correct Answer & Explanation

. Teres minor (superior), teres major (inferior), long head of triceps (medial), surgical neck of humerus (lateral)

Explanation

The quadrangular space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps, and laterally by the surgical neck of the humerus. It contains the axillary nerve and posterior circumflex humeral artery.

Question 8578

Topic: Biology, Genetics & Bone Healing

Histological analysis of an actively remodeling bone reveals multinucleated cells situated in Howship's lacunae. The specialized "ruffled border" of these cells, which facilitates bone resorption, is primarily formed by which structural elements?

. Extensive arrays of endoplasmic reticulum
. Microvilli supported by an actin filament cytoskeleton
. Hypertrophied Golgi apparatus networks
. Primary cilia protruding into the resorption pit
. Aggregations of lysosomal transport vesicles

Correct Answer & Explanation

. Microvilli supported by an actin filament cytoskeleton

Explanation

Osteoclasts create a sealed zone over bone, within which their cell membrane folds extensively to form a ruffled border. This border is structurally maintained by actin microfilaments and massively increases the surface area for secreting acid and proteolytic enzymes.

Question 8579

Topic: Surgical Anatomy & Approaches

During a regional block in the femoral triangle prior to anterior cruciate ligament reconstruction, the anesthesiologist identifies the vascular structures to avoid intravascular injection. What is the anatomical relationship of the femoral nerve to the femoral artery in this region?

. Medial
. Lateral
. Anterior
. Posterior
. Superior

Correct Answer & Explanation

. Lateral

Explanation

Within the femoral triangle, structures are oriented from lateral to medial according to the mnemonic NAVEL: Nerve, Artery, Vein, Empty space, Lymphatics. Thus, the femoral nerve is strictly lateral to the femoral artery.

Question 8580

Topic: Surgical Anatomy & Approaches

When performing an anterior (Smith-Petersen) approach to the hip, what is the superficial internervous plane utilized?

. Sartorius and tensor fasciae latae
. Rectus femoris and gluteus medius
. Pectineus and adductor longus
. Tensor fasciae latae and gluteus medius
. Gracilis and adductor magnus

Correct Answer & Explanation

. Sartorius and tensor fasciae latae

Explanation

The superficial internervous plane of the anterior (Smith-Petersen) approach lies between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep plane is between the rectus femoris and the gluteus medius.

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