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1. General Principles & Basic Science MCQs

Practice Set 667 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 13321

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of orthopedic implant materials, the stiffness of a material is represented on the stress-strain curve. Which of the following best defines the Young's modulus of a material?

. The area under the entire stress-strain curve
. The slope of the curve in the elastic region
. The point at which the material undergoes permanent deformation
. The maximum stress a material can withstand before failure
. The area under the curve in the plastic region

Correct Answer & Explanation

. The slope of the curve in the elastic region

Explanation

Young's modulus (modulus of elasticity) is determined by the slope of the stress-strain curve in the linear, elastic region. It represents the inherent stiffness of the material, with a steeper slope indicating a stiffer material.

Question 13322

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with increasing right thigh pain and bowing of his femur. Radiographs show cortical thickening and trabecular coarsening. Serum alkaline phosphatase is markedly elevated, but calcium and phosphorus are normal. If a bone biopsy were performed, what characteristic histological finding would be expected?

. Woven bone with empty lacunae
. Mosaic pattern of lamellar bone with prominent cement lines
. Sheets of plasma cells with clock-face nuclei
. Non-mineralized osteoid seams surrounding trabeculae
. Multinucleated giant cells in a background of mononuclear stromal cells

Correct Answer & Explanation

. Mosaic pattern of lamellar bone with prominent cement lines

Explanation

Paget's disease of bone is characterized by increased, disorganized bone remodeling. Histologically, it presents as a mosaic pattern of lamellar bone with prominent, haphazardly arranged cement lines due to irregular periods of osteoclastic resorption and osteoblastic formation.

Question 13323

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman with a history of a vertebral fragility fracture is prescribed alendronate. At the cellular level, this medication inhibits bone resorption primarily by inhibiting which of the following enzymes?

. Cathepsin K
. Carbonic anhydrase II
. Farnesyl pyrophosphate synthase
. Tartrate-resistant acid phosphatase
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates, such as alendronate, inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This disruption prevents the prenylation of small GTPase proteins (like Ras and Rho), ultimately leading to osteoclast apoptosis and decreased bone resorption.

Question 13324

Topic: Biology, Genetics & Bone Healing

A 40-year-old woman with celiac disease presents with diffuse bone pain and proximal muscle weakness. Radiographs reveal bilateral pseudofractures (Looser zones) in the femoral neck. Which of the following serum laboratory profiles is most consistent with her diagnosis?

. Normal calcium, normal phosphorus, elevated alkaline phosphatase
. Low calcium, low phosphorus, elevated alkaline phosphatase
. Elevated calcium, low phosphorus, elevated alkaline phosphatase
. Normal calcium, elevated phosphorus, normal alkaline phosphatase
. Elevated calcium, elevated phosphorus, normal alkaline phosphatase

Correct Answer & Explanation

. Low calcium, low phosphorus, elevated alkaline phosphatase

Explanation

The patient has osteomalacia secondary to malabsorption of Vitamin D. This typically presents with low serum calcium, low serum phosphorus (due to secondary hyperparathyroidism), and elevated alkaline phosphatase.

Question 13325

Topic: Biomechanics & Biomaterials

An orthopedic surgeon plans to use a stainless steel screw to secure a titanium plate during fracture fixation. This combination of different metals in an electrolytic environment places the construct at highest risk for which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within a conductive fluid. This creates an electrochemical cell, leading to accelerated corrosion of the less noble metal.

Question 13326

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic, epiphyseal-metaphyseal lesion in the proximal tibia extending to the subchondral bone. Biopsy shows multinucleated giant cells. The targeted therapy (denosumab) for this specific tumor inhibits which of the following?

. Vascular endothelial growth factor (VEGF)
. RANK ligand (RANKL)
. Tumor necrosis factor-alpha (TNF-a)
. Bone morphogenetic protein 2 (BMP-2)
. Transforming growth factor-beta (TGF-b)

Correct Answer & Explanation

. RANK ligand (RANKL)

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear stromal cells that express high levels of RANKL, which recruits and activates the reactive multinucleated osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds and inhibits RANKL, effectively reducing osteoclastic bone destruction.

Question 13327

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a unique structural organization to withstand compressive and shear forces. In which zone of articular cartilage are the type II collagen fibers oriented perpendicular to the joint surface?

. Superficial zone
. Transitional (middle) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

In the deep (radial) zone of articular cartilage, chondrocytes are arranged in columns, and the Type II collagen fibers are oriented perpendicularly to the joint surface to resist compressive forces. The superficial zone has parallel fibers to resist shear, while the middle zone has randomly oriented fibers.

Question 13328

Topic: Infection, Pharmacology & VTE

A 65-year-old man presents with a delayed, low-grade periprosthetic joint infection of his total hip arthroplasty, caused by Staphylococcus epidermidis. The persistence and antibiotic resistance of this organism on the implant surface are primarily mediated by the production of which extracellular substance?

. Protein A
. Hyaluronidase
. Glycocalyx
. Coagulase
. Panton-Valentine leukocidin

Correct Answer & Explanation

. Glycocalyx

Explanation

Staphylococcus epidermidis is a common cause of indolent periprosthetic joint infections due to its ability to form a robust biofilm. The biofilm is composed of a self-produced extracellular polymeric substance known as glycocalyx, which shields the bacteria from host immune responses and antibiotics.

Question 13329

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is routinely used in total joint arthroplasty to reduce perioperative blood loss. Which of the following describes the specific mechanism of action of TXA?

. Directly inhibits thrombin
. Inhibits cyclooxygenase, preventing platelet aggregation
. Competitively inhibits the activation of plasminogen to plasmin
. Promotes the release of von Willebrand factor from endothelial cells
. Inhibits factor Xa

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is an antifibrinolytic agent that works as a synthetic analog of the amino acid lysine. It reversibly and competitively binds to the lysine receptor sites on plasminogen, preventing its activation into plasmin and thereby stabilizing the fibrin clot.

Question 13330

Topic: 1. General Principles & Basic Science

A massive structural cortical allograft is utilized for reconstruction following tumor resection. Compared to an autograft, what is the primary disadvantage regarding the biological incorporation of this massive allograft via creeping substitution?

. It rapidly resorbs before structural bridging occurs
. It induces a severe cell-mediated immune rejection
. It provides osteoinductive growth factors that cause ectopic ossification
. It incorporates slowly and incompletely, leaving necrotic bone centrally
. It undergoes early fatigue failure due to osteoclast hyperactivity

Correct Answer & Explanation

. It incorporates slowly and incompletely, leaving necrotic bone centrally

Explanation

Massive structural cortical allografts incorporate through creeping substitution, but this process is very slow and superficial. The central portion of the allograft typically remains necrotic and unremodeled for years, making it susceptible to late fatigue fractures and nonunions.

Question 13331

Topic: 1. General Principles & Basic Science

In the pathogenesis of Rheumatoid Arthritis joint destruction, what is the primary cell type within the hyperplastic synovium (pannus) responsible for the direct production of matrix metalloproteinases (MMPs) that degrade articular cartilage?

. Fibroblast-like synoviocytes
. Macrophage-like synoviocytes
. CD4+ T-lymphocytes
. B-lymphocytes
. Neutrophils

Correct Answer & Explanation

. Fibroblast-like synoviocytes

Explanation

In rheumatoid arthritis, the inflammatory pannus is driven by an interplay of immune cells. Fibroblast-like synoviocytes (Type B synoviocytes) are the primary effector cells that, once activated by cytokines, produce high levels of matrix metalloproteinases (MMPs) leading to cartilage destruction.

Question 13332

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel plate with titanium screws for a fracture fixation. Which of the following best describes the primary risk associated with mixing these two metals in vivo?

. Fretting corrosion
. Crevice corrosion
. Galvanic 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 body fluid, creating an electrochemical gradient. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 13333

Topic: 1. General Principles & Basic Science

In normal adult articular cartilage, what is the predominant orientation and type of collagen found in the deep zone (radiata)?

. Type I collagen, oriented parallel to the joint surface
. Type I collagen, oriented perpendicular to the joint surface
. Type II collagen, oriented randomly
. Type II collagen, oriented parallel to the joint surface
. Type II collagen, oriented perpendicular to the joint surface

Correct Answer & Explanation

. Type II collagen, oriented perpendicular to the joint surface

Explanation

The deep zone of articular cartilage is composed primarily of Type II collagen fibers oriented perpendicular to the joint surface. This arrangement provides high compressive strength and securely anchors the cartilage to the calcified zone across the tidemark.

Question 13334

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with multiple fractures and hepatosplenomegaly. Radiographs reveal diffuse osteosclerosis and a "bone-within-a-bone" appearance. A genetic defect in carbonic anhydrase II is identified. This mutation primarily impairs which of the following cellular functions?

. Osteoblast differentiation from mesenchymal stem cells
. Production of osteoid matrix by osteoblasts
. Acidification of the Howship lacuna by osteoclasts
. Synthesis of Type I collagen
. Mineralization of the epiphyseal plate

Correct Answer & Explanation

. Acidification of the Howship lacuna by osteoclasts

Explanation

Carbonic anhydrase II deficiency causes osteopetrosis by preventing osteoclasts from generating the protons needed to acidify the resorptive pit (Howship lacuna). This leads to defective bone resorption, resulting in overly dense but brittle bones.

Question 13335

Topic: Biology, Genetics & Bone Healing

During the incorporation of a cortical bone allograft, the process of "creeping substitution" is observed. Which of the following sequences best describes the initial cellular events in this process?

. Osteoblastic bone formation followed by osteoclastic resorption
. Osteoclastic resorption of Haversian canals followed by osteoblastic new bone deposition
. Chondrocyte proliferation followed by endochondral ossification
. Direct membranous ossification without prior resorption
. Fibroblast invasion followed by calcification

Correct Answer & Explanation

. Osteoclastic resorption of Haversian canals followed by osteoblastic new bone deposition

Explanation

Cortical bone grafts incorporate via creeping substitution, an extremely slow process where osteoclasts first resorb the existing Haversian canals. This is immediately followed by osteoblasts laying down new bone within these widened canals.

Question 13336

Topic: Infection, Pharmacology & VTE
A patient is prescribed subcutaneous enoxaparin for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the primary mechanism of action of this pharmacological agent?
. Directly inhibits thrombin (Factor IIa)
. Binds to antithrombin III, preferentially inhibiting Factor Xa over Factor IIa
. Inhibits the synthesis of vitamin K-dependent clotting factors
. Irreversibly binds to the ADP receptor on platelets
. Activates plasminogen to form plasmin

Correct Answer & Explanation

. Binds to antithrombin III, preferentially inhibiting Factor Xa over Factor IIa

Explanation

Enoxaparin is a low-molecular-weight heparin (LMWH) that binds to antithrombin III. This binding induces a conformational change that preferentially accelerates the inhibition of Factor Xa compared to thrombin (Factor IIa).

Question 13337

Topic: Infection, Pharmacology & VTE

A patient develops a periprosthetic joint infection caused by Staphylococcus epidermidis. The pathogenesis heavily relies on the formation of a biofilm. Which of the following primarily mediates the initial adherence of the bacteria to the orthopedic implant?

. Release of exotoxins
. Production of an extracellular polysaccharide glycocalyx
. Binding of fibronectin-binding proteins (FnBPs) to host proteins on the implant
. Phagocytosis by local macrophages
. Secretion of beta-lactamase

Correct Answer & Explanation

. Binding of fibronectin-binding proteins (FnBPs) to host proteins on the implant

Explanation

Initial adherence to an implant is mediated by bacterial adhesins like FnBPs binding to host proteins (such as fibronectin and fibrinogen) that immediately coat the implant surface. Following this attachment phase, the bacteria produce a polysaccharide glycocalyx to establish the mature biofilm.

Question 13338

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, which of the following statements regarding secondary bone healing is true?

. Woven bone can form only under conditions of high strain (>10%)
. Callus formation increases interfragmentary strain
. Granulation tissue tolerates up to 100% strain without rupturing
. Absolute stability is required for the formation of an external callus
. Cartilage forms under conditions of absolute zero strain

Correct Answer & Explanation

. Granulation tissue tolerates up to 100% strain without rupturing

Explanation

Perren's strain theory dictates that tissue will only form if the local strain is less than the tissue's tolerance. Granulation tissue can tolerate up to 100% strain, allowing it to initially bridge the fracture gap and stabilize the fragments so stiffer tissues can subsequently form.

Question 13339

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy is evaluated for bowing of the legs and short stature. Laboratory tests show low serum phosphate, normal calcium, normal PTH, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following is the primary pathophysiologic defect?

. Decreased intestinal absorption of calcium
. Defective mineralization of the organic bone matrix due to vitamin D deficiency
. Decreased renal tubular reabsorption of phosphate driven by excess FGF-23
. Primary hyperparathyroidism
. Inability to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D

Correct Answer & Explanation

. Decreased renal tubular reabsorption of phosphate driven by excess FGF-23

Explanation

The patient has X-linked hypophosphatemic rickets caused by a PHEX gene mutation, leading to unchecked elevation of FGF-23 levels. Excess FGF-23 inhibits renal phosphate reabsorption in the proximal tubule, resulting in severe renal phosphate wasting.

Question 13340

Topic: 1. General Principles & Basic Science

During the repair of a zone II flexor tendon laceration, a surgeon utilizes techniques to minimize adhesion formation. Adhesions in tendon healing are primarily associated with which of the following processes?

. Intrinsic healing driven by tenocytes
. Extrinsic healing driven by fibroblasts from the surrounding epitenon and peritenon
. Proliferation of synovial cells
. Excessive Type I collagen synthesis in the initial inflammatory phase
. Inadequate formation of the synovial diffusion barrier

Correct Answer & Explanation

. Extrinsic healing driven by fibroblasts from the surrounding epitenon and peritenon

Explanation

Tendon healing occurs via concurrent intrinsic (tenocytes within the tendon) and extrinsic pathways. The extrinsic healing pathway relies on inflammatory cells and fibroblasts invading from the surrounding peritendinous tissues, which is primarily responsible for scar adhesion formation.

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