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1. General Principles & Basic Science MCQs

Practice Set 670 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 13381

Topic: Biology, Genetics & Bone Healing

During secondary (indirect) fracture healing, the cartilaginous soft callus is eventually replaced by hard woven bone. This specific biological transition most closely resembles which normal process of skeletal development?

. Intramembranous ossification
. Endochondral ossification
. Appositional bone growth
. Creeping substitution
. Osteonal remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing involves the intermediate formation of a cartilaginous soft callus that subsequently mineralizes and is replaced by bone. This process mechanically and biologically mirrors endochondral ossification observed in the physeal growth plate.

Question 13382

Topic: Biomechanics & Biomaterials
Which sterilization method for ultra-high-molecular-weight polyethylene (UHMWPE) components is most highly associated with long-term oxidative degradation and increased wear rates?
. Gamma irradiation in an inert gas environment
. Gamma irradiation in air
. Ethylene oxide gas sterilization
. Gas plasma sterilization
. Electron beam irradiation in a vacuum

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation in air creates free radicals that react with ambient oxygen over time. This leads to oxidative chain scission, decreasing the molecular weight and significantly increasing the wear rate of the polyethylene.

Question 13383

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with osteoporosis is started on denosumab. What is the primary mechanism of action of this medication?

. Inhibition of farnesyl pyrophosphate synthase
. Inhibition of sclerostin to promote Wnt signaling
. Monoclonal antibody binding to RANKL
. Recombinant parathyroid hormone analogue
. Selective estrogen receptor modulation

Correct Answer & Explanation

. Monoclonal antibody binding to RANKL

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). This prevents RANKL from binding to RANK on osteoclasts, thereby potently inhibiting osteoclast maturation, function, and survival.

Question 13384

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, a second-degree nerve injury (axonotmesis) is characterized by disruption of the axon with preservation of which of the following structures?

. Epineurium only
. Endoneurium
. Perineurium only
. Myelin sheath
. Fascicular architecture only

Correct Answer & Explanation

. Endoneurium

Explanation

A second-degree Sunderland injury involves disruption of the axon and myelin sheath, resulting in Wallerian degeneration, but the endoneurium remains intact. This intact endoneurial tube allows for complete, guided axonal regeneration.

Question 13385

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct histomorphologic zones. Which zone is characterized by collagen fibers oriented parallel to the joint surface and the highest water content?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Tidemark
. Calcified cartilage zone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone contains collagen fibers aligned parallel to the articular surface to resist shear forces. It also has the highest concentration of water and collagen, but the lowest concentration of proteoglycans.

Question 13386

Topic: Biology, Genetics & Bone Healing

Scurvy results from a dietary deficiency of Vitamin C, leading to impaired collagen synthesis. Vitamin C acts as an essential cofactor for which of the following processes in collagen production?

. Cleavage of procollagen to tropocollagen
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Glycosylation of hydroxylysine residues
. Assembly of three alpha chains into a triple helix

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Vitamin C (ascorbic acid) is a required cofactor for prolyl hydroxylase and lysyl hydroxylase. Without hydroxylation of proline and lysine residues, the collagen alpha chains cannot form stable triple helices, leading to weak connective tissue.

Question 13387

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is frequently used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its mechanism of action?
. Directly inhibits thrombin formation
. Activates the extrinsic coagulation cascade
. Competitively inhibits the activation of plasminogen to plasmin
. Increases the release of von Willebrand factor from endothelial cells
. Inhibits Factor Xa via antithrombin III

Correct Answer & Explanation

. Competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is a synthetic lysine analog that competitively binds to the lysine-binding sites on plasminogen. This blocks the conversion of plasminogen to plasmin, thereby inhibiting the degradation of fibrin clots (fibrinolysis).

Question 13388

Topic: 1. General Principles & Basic Science

When optimizing the biomechanical properties of a cortical bone screw, which of the following design modifications will most significantly increase its pull-out strength?

. Decreasing the thread pitch
. Decreasing the inner (root) diameter
. Increasing the outer thread diameter
. Increasing the length of the screw head
. Using a cannulated screw design

Correct Answer & Explanation

. Increasing the outer thread diameter

Explanation

The pull-out strength of a bone screw is most directly proportional to its outer thread diameter. While pitch and length of engagement also play roles, maximizing the outer diameter provides the largest increase in purchase.

Question 13389

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing via endochondral ossification, the early soft callus is primarily composed of which type of collagen?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

Secondary fracture healing involves a cartilaginous intermediate. The soft callus is composed of fibrocartilage and hyaline cartilage, which primarily consists of Type II collagen. This is eventually replaced by Type I collagen as hard callus forms.

Question 13390

Topic: Infection, Pharmacology & VTE

According to the original Kocher criteria for differentiating pediatric septic arthritis of the hip from transient synovitis, which of the following is NOT one of the classic four predictive variables?

. Temperature greater than 38.5 degrees Celsius
. Inability to bear weight on the affected limb
. Erythrocyte sedimentation rate (ESR) greater than 40 mm/hr
. Serum C-reactive protein (CRP) greater than 2.0 mg/dL
. White blood cell (WBC) count greater than 12,000 cells/mm3

Correct Answer & Explanation

. Serum C-reactive protein (CRP) greater than 2.0 mg/dL

Explanation

The original four Kocher criteria are non-weight-bearing status, ESR > 40, WBC > 12,000, and Temperature > 38.5 C. CRP > 2.0 mg/dL was later added as a fifth independent predictor by Caird et al., but was not part of the original Kocher study.

Question 13391

Topic: Biology, Genetics & Bone Healing

Osteomalacia is characterized by a high ratio of unmineralized osteoid to mineralized bone. What is the primary pathophysiologic defect in this condition?

. Abnormal osteoclast resorption of mineralized bone
. Defective mineralization of the newly formed osteoid matrix
. Impaired synthesis of Type I collagen by osteoblasts
. A defect in the RANKL-OPG signaling axis
. Overproduction of alkaline phosphatase

Correct Answer & Explanation

. Defective mineralization of the newly formed osteoid matrix

Explanation

Osteomalacia (and rickets in children) is caused by a failure of calcium and phosphate deposition into the bone matrix. This results in an accumulation of unmineralized osteoid tissue.

Question 13392

Topic: Biomechanics & Biomaterials

To avoid galvanic corrosion in orthopedic implants, dissimilar metals should generally not be mixed. Which of the following combinations is most likely to result in significant galvanic corrosion?

. Titanium alloy and Cobalt-Chromium alloy
. 316L Stainless Steel and Titanium alloy
. Tantalum and Titanium alloy
. Cobalt-Chromium alloy and Zirconium
. Ceramic (Alumina) and Titanium alloy

Correct Answer & Explanation

. 316L Stainless Steel and Titanium alloy

Explanation

Stainless steel is significantly less noble than titanium on the galvanic series. When placed in contact within a conductive fluid (body tissue), stainless steel acts as the anode and corrodes rapidly, making this combination strictly contraindicated.

Question 13393

Topic: 1. General Principles & Basic Science

Following a primary flexor tendon repair, at what time point does the repaired tendon generally experience its lowest tensile strength, making it most susceptible to rupture?

. 0 to 3 days
. 5 to 21 days
. 4 to 6 weeks
. 8 to 10 weeks
. 12 to 16 weeks

Correct Answer & Explanation

. 5 to 21 days

Explanation

A repaired tendon is at its weakest between days 5 and 21 post-operation. During this inflammatory/early proliferative phase, the native collagen softens before new collagen synthesis and cross-linking can provide significant structural strength.

Question 13394

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, induce osteoblastic differentiation. These growth factors initiate their primary intracellular signaling cascade by activating which of the following pathways?

. Wnt/beta-catenin pathway
. JAK/STAT signaling pathway
. Smad 1/5/8 pathway
. MAP kinase pathway
. cAMP/Protein Kinase A pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase cell-surface receptors, which subsequently phosphorylate intracellular Smad proteins (specifically Smad 1, 5, and 8). These activated Smads translocate to the nucleus to upregulate osteogenic gene transcription.

Question 13395

Topic: Infection, Pharmacology & VTE

An orthopedic study reports that a new deep vein thrombosis (DVT) prophylaxis protocol reduces the absolute risk of DVT from 8% to 3% compared to the standard protocol. What is the Number Needed to Treat (NNT) to prevent one DVT?

. 5
. 10
. 20
. 50
. 100

Correct Answer & Explanation

. 20

Explanation

The Number Needed to Treat (NNT) is calculated as the inverse of the Absolute Risk Reduction (ARR). The ARR here is 8% - 3% = 5% (0.05). Therefore, NNT = 1 / 0.05 = 20.

Question 13396

Topic: Biology, Genetics & Bone Healing

In primary hyperparathyroidism, continuous hypersecretion of parathyroid hormone (PTH) leads to net bone resorption. Which cell type possesses the primary PTH receptor that initiates this catabolic cascade?

. Osteocytes
. Osteoclasts
. Osteoblasts
. Chondrocytes
. Macrophages

Correct Answer & Explanation

. Osteoblasts

Explanation

PTH binds to specific receptors on the surface of osteoblasts. In response to continuous PTH exposure, osteoblasts upregulate the expression of RANKL, which then binds to RANK on osteoclasts to stimulate bone resorption.

Question 13397

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel cerclage wire in combination with a titanium plate for a femoral fracture fixation. Months later, localized bone resorption and implant failure are noted at the junction of the two metals. Which type of corrosion is most likely responsible for this failure?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in electrical contact within an electrolytic environment, such as the human body. The less noble metal acts as an anode and undergoes accelerated corrosion. Using implants of the same material prevents this complication.

Question 13398

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, absolute stability and primary bone healing can only occur when the strain at the fracture gap is maintained below what threshold?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires a stable mechanical environment with strain less than 2%, allowing osteons to cross the fracture site without intermediate callus formation. Granulation tissue tolerates up to 100% strain, while secondary bone healing (callus) occurs between 2% and 10% strain.

Question 13399

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis is started on Denosumab. What is the precise mechanism of action of this pharmacological agent?

. Binds directly to osteoclasts causing premature apoptosis
. Inhibits RANKL from binding to the RANK receptor
. Binds to osteoprotegerin (OPG) to increase its half-life
. Inhibits sclerostin to promote osteoblastogenesis
. Directly stimulates the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Inhibits RANKL from binding to the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By preventing RANKL from binding to its receptor (RANK) on osteoclasts, it effectively inhibits osteoclast maturation, function, and survival.

Question 13400

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by the highest water content, lowest proteoglycan content, and collagen fibers arranged parallel to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone of articular cartilage contains the highest proportion of water and the lowest concentration of proteoglycans. Its type II collagen fibers are arranged parallel to the articular surface to resist shear forces during joint motion.

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