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1. General Principles & Basic Science MCQs

Practice Set 234 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 4661

Topic: Surgical Anatomy & Approaches

A 45-year-old male is undergoing an ilioinguinal approach for the treatment of an anterior column/posterior hemitransverse acetabular fracture.

During the dissection of the retropubic space (Space of Retzius), brisk arterial bleeding is encountered approximately 5 cm from the symphysis pubis, located posterior to the superior pubic ramus. Injury to which of the following structures is the most likely source of this hemorrhage?

. Internal pudendal artery
. Inferior epigastric artery
. Anastomosis between the external iliac and obturator vessels
. Lateral femoral circumflex artery
. Superior gluteal artery

Correct Answer & Explanation

. Anastomosis between the external iliac and obturator vessels

Explanation

The source of bleeding in this location is the 'corona mortis,' which is an anastomotic connection between the external iliac (or inferior epigastric) system and the obturator system. It traverses the superior pubic ramus at an average distance of 5 to 6 cm from the pubic symphysis. Surgeons must carefully dissect the posterior aspect of the superior pubic ramus and ligate these vessels during the ilioinguinal or intrapelvic approaches to avoid catastrophic hemorrhage.

Question 4662

Topic: Biomechanics & Biomaterials
When evaluating the biomaterials used in total hip arthroplasty, the sterilization process of ultra-high molecular weight polyethylene (UHMWPE) profoundly affects its long-term wear characteristics. Which of the following sterilization environments for UHMWPE is most strongly associated with free radical formation leading to oxidative chain scission, structural degradation, and accelerated clinical wear?
. Gamma irradiation in an inert gas (Argon)
. Gamma irradiation in air
. Ethylene oxide gas
. Hydrogen peroxide gas plasma
. Gamma irradiation in a vacuum

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation of UHMWPE in air (oxygen-containing environment) leads to the formation of free radicals that react with oxygen to form hydroperoxides. Over time, this oxidation leads to chain scission, decreased molecular weight, embrittlement, and catastrophic delamination and wear of the polyethylene bearing surface. Modern sterilization techniques use inert gases (like argon), vacuum packaging, or non-irradiation methods (like ethylene oxide) followed by highly cross-linking and annealing or remelting to eliminate free radicals.

Question 4663

Topic: Biology, Genetics & Bone Healing

Which of the following osteoinductive agents, members of the transforming growth factor-beta (TGF-beta) superfamily, is specifically FDA approved as an alternative to autogenous bone graft in acute, open tibial shaft fractures treated with an intramedullary nail?

. Bone Morphogenetic Protein-2 (BMP-2)
. Bone Morphogenetic Protein-3 (BMP-3)
. Bone Morphogenetic Protein-4 (BMP-4)
. Bone Morphogenetic Protein-7 (BMP-7)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Bone Morphogenetic Protein-2 (BMP-2)

Explanation

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is FDA approved for use in acute open tibial shaft fractures that have been stabilized with an intramedullary nail. Its use has been shown to reduce the need for secondary bone grafting procedures. rhBMP-7 (also known as Osteogenic Protein-1, or OP-1) was previously available under a Humanitarian Device Exemption for recalcitrant long bone nonunions, but BMP-2 is the specific agent approved for acute open tibias.

Question 4664

Topic: 1. General Principles & Basic Science

When evaluating the ultrastructure of normal adult articular cartilage, the tissue is anatomically divided into distinct layers or zones from the surface to the subchondral bone. Which zone is biomechanically characterized by having the highest concentration of proteoglycans, the lowest water content, and chondrocytes arranged in vertical columns?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. The tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is responsible for providing the greatest resistance to compressive loads. It contains the highest concentration of proteoglycans, the lowest water content, and type II collagen fibers arranged perpendicularly (vertically) to the joint surface. The chondrocytes in this zone are also characteristically arranged in vertical columns. The superficial zone has the highest water content and collagen fibers parallel to the surface to resist shear stress.

Question 4665

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the distal femur extending to the subchondral bone. Biopsy reveals multinucleated giant cells in a stroma of mononuclear cells. Due to the tumor's size and location, she is started on Denosumab prior to surgical intervention. What is the mechanism of action of this medication?

. Directly inhibits osteoblast apoptosis
. Monoclonal antibody that binds to and inhibits RANKL
. Monoclonal antibody that binds directly to RANK
. Nitrogen-containing bisphosphonate analog
. Tyrosine kinase inhibitor targeting VEGF receptors

Correct Answer & Explanation

. Monoclonal antibody that binds to and inhibits RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on osteoclasts and their precursors, thereby inhibiting osteoclast formation, function, and survival. It is highly effective in treating Giant Cell Tumors of bone.

Question 4666

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction and fracture healing. Which of the following describes the correct intracellular signaling pathway utilized by BMP-2?

. Wnt/beta-catenin pathway
. Smad 1/5/8 pathway
. MAP kinase pathway
. JAK/STAT pathway
. Notch signaling pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMP-2, BMP-4, and BMP-7 belong to the TGF-beta superfamily. They bind to cell-surface serine/threonine kinase receptors. Upon activation, these receptors phosphorylate intracellular Smad proteins, specifically Smads 1, 5, and 8. These phosphorylated Smads then form a complex with Smad 4 and translocate to the nucleus to regulate the transcription of osteogenic genes.

Question 4667

Topic: 1. General Principles & Basic Science

A 25-year-old male sustains a Zone II flexor tendon laceration of the index finger. Repair is performed with a 4-strand core suture and a running epitendinous repair. What is the primary biomechanical advantage of adding the epitendinous suture?

. Decreases gliding resistance and increases repair tensile strength
. Increases gap formation during active range of motion
. Primarily provides a physical barrier to extrinsic adhesions
. Allows for earlier removal of splinting
. Replaces the need for a core suture in Zone I

Correct Answer & Explanation

. Decreases gliding resistance and increases repair tensile strength

Explanation

In flexor tendon repairs, the addition of an epitendinous suture is crucial. It smooths the repair site by tucking in frayed tendon ends, which significantly decreases gliding resistance (work of flexion). Furthermore, it contributes mechanically by increasing the overall tensile strength of the repair by 10% to 50% and decreases gap formation under load.

Question 4668

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the management of osteoporosis to stimulate bone formation. Intermittent administration of this parathyroid hormone (PTH) analog exerts its primary anabolic effect by binding to receptors on which of the following cell types?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Intermittent administration of parathyroid hormone (PTH) or its analog (teriparatide) exerts a paradoxical anabolic effect on bone by directly binding to PTH1 receptors on osteoblasts, stimulating their proliferation, increasing their lifespan by preventing apoptosis, and increasing bone formation.

Question 4669

Topic: Biology, Genetics & Bone Healing
Sclerostin is a protein that negatively regulates bone formation. Monoclonal antibodies targeting sclerostin (e.g., romosozumab) are utilized in the treatment of severe osteoporosis. Sclerostin exerts its inhibitory effect on osteoblasts primarily by antagonizing which of the following intracellular signaling pathways?
. RANK/RANKL pathway
. Wnt/β-catenin pathway
. TGF-β/SMAD pathway
. Bone Morphogenetic Protein (BMP) pathway
. Notch signaling pathway

Correct Answer & Explanation

. Wnt/β-catenin pathway

Explanation

Sclerostin is secreted by osteocytes and inhibits bone formation by binding to LRP5/6 receptors on osteoblasts. This binding blocks the coreceptor function of LRP5/6, thereby antagonizing the canonical Wnt/β-catenin signaling pathway, which is essential for osteoblast differentiation and survival.

Question 4670

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are critical members of the TGF-beta superfamily that induce the differentiation of mesenchymal stem cells into osteoblasts. Which of the following recombinant BMPs is FDA-approved specifically for use in anterior lumbar interbody fusion (ALIF) with a metallic interbody cage?

. rhBMP-2
. rhBMP-3
. rhBMP-4
. rhBMP-7
. rhBMP-9

Correct Answer & Explanation

. rhBMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2, trade name Infuse) is FDA-approved for use in single-level anterior lumbar interbody fusion (ALIF) when used with an approved interbody fusion device. rhBMP-7 (OP-1) was previously approved for recalcitrant long bone nonunions under an HDE but is generally no longer commercially available in the US.

Question 4671

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a critical role in osteoinduction and bone healing. Recombinant human BMP-2 (rhBMP-2) is utilized in various spine and orthopedic trauma procedures. Upon binding to its transmembrane serine/threonine kinase receptor, which intracellular signaling pathway is primarily activated by BMP-2?

. Smad 2 and 3
. Smad 1, 5, and 8
. Wnt/Beta-catenin
. MAP kinase (MAPK)
. JAK/STAT

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMP-2 and BMP-7 act via cell surface receptors that have intrinsic serine/threonine kinase activity. Once activated, these receptors phosphorylate the intracellular R-Smads (Receptor-regulated Smads), specifically Smad 1, Smad 5, and Smad 8. These complex with Co-Smad (Smad 4) to translocate to the nucleus and induce osteogenic gene transcription. Smad 2 and 3 are primarily associated with the TGF-beta signaling pathway, not BMP.

Question 4672

Topic: Physiology & Rehabilitation

During normal human gait, the muscles of the lower extremity exhibit highly coordinated, phased activity. Peak concentric contraction and maximal electromyographic (EMG) activity of the gastrocnemius-soleus complex occurs during which specific phase of the gait cycle?

. Initial contact (Heel strike)
. Loading response (Foot flat)
. Mid stance
. Terminal stance (Heel off)
. Pre-swing (Toe off)

Correct Answer & Explanation

. Terminal stance (Heel off)

Explanation

The gastrocnemius-soleus complex is crucial for ankle plantarflexion. During mid stance, the triceps surae contracts eccentrically to control the forward progression of the tibia over the fixed foot (controlling ankle dorsiflexion). Its peak electrical activity and maximal concentric contraction occur during terminal stance (heel off) to provide the active push-off required for forward propulsion, right before pre-swing.

Question 4673

Topic: 1. General Principles & Basic Science
A 16-year-old male presents with a persistent, dull ache in his right tibia that is significantly worse at night. The pain is rapidly and completely relieved by ibuprofen. Imaging demonstrates a cortical thickening with a small (<1.5 cm) radiolucent nidus. What is the primary biochemical mechanism driving this patient's nocturnal pain?
. Release of substance P from surrounding reactive periosteum
. Elevated production of prostaglandin E2 (PGE2) by osteoblasts within the nidus
. High concentrations of interleukin-1 (IL-1) and TNF-alpha triggering osteoclasts
. Direct mechanical expansion of the medullary cavity by a growing cyst
. Histamine release from mast cells infiltrating the lytic lesion

Correct Answer & Explanation

. Elevated production of prostaglandin E2 (PGE2) by osteoblasts within the nidus

Explanation

The clinical presentation is classic for an osteoid osteoma. The pathognomonic symptom is severe, unrelenting night pain that is exquisitely responsive to nonsteroidal anti-inflammatory drugs (NSAIDs) or salicylates. This is because the cells within the nidus (active osteoblasts) contain very high levels of cyclooxygenase-2 (COX-2) and produce massive amounts of prostaglandin E2 (PGE2). PGE2 induces intense local vasodilation and directly stimulates local nerve endings.

Question 4674

Topic: Biology, Genetics & Bone Healing

A 35-year-old male sustains a transverse midshaft radius fracture. He undergoes open reduction and internal fixation with a 3.5 mm dynamic compression plate placed in absolute stability. Which of the following best describes the predominant mechanism of bone healing expected in this scenario?

. Endochondral ossification with a cartilaginous intermediate
. Primary bone healing characterized by osteoclast-led cutting cones followed by osteoblasts
. Intramembranous ossification with robust callus formation
. Chondroid metaplasia within the fracture hematoma
. Secondary bone healing driven by micromotion at the fracture site

Correct Answer & Explanation

. Primary bone healing characterized by osteoclast-led cutting cones followed by osteoblasts

Explanation

Absolute stability (rigid fixation with anatomic reduction and no gap) eliminates interfragmentary strain, bypassing callus formation. It leads to primary (direct) bone healing, which occurs via Haversian remodeling driven by osteoclast-led cutting cones followed immediately by osteoblasts laying down new bone.

Question 4675

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue designed to withstand significant compressive loads. The mechanical properties of cartilage vary across its depth. Which of the following correctly describes the biochemical composition of the deep zone of articular cartilage?

. Highest concentration of water and highest concentration of proteoglycans
. Highest concentration of water and lowest concentration of proteoglycans
. Lowest concentration of water and highest concentration of proteoglycans
. Lowest concentration of water and lowest concentration of proteoglycans
. Highest concentration of Type I collagen

Correct Answer & Explanation

. Lowest concentration of water and highest concentration of proteoglycans

Explanation

Articular cartilage composition varies by zone. The superficial zone has the highest water content and lowest proteoglycan content. In contrast, the deep zone has the lowest water content and the highest concentration of proteoglycans, allowing it to provide maximal resistance to compressive forces.

Question 4676

Topic: Surgical Anatomy & Approaches

A 65-year-old male is undergoing a total hip arthroplasty via the direct anterior approach. Which of the following best describes the deep internervous plane utilized during this approach?

. Between sartorius and tensor fasciae latae
. Between rectus femoris and gluteus medius
. Between gluteus medius and minimus
. Between tensor fasciae latae and gluteus medius
. Between pectineus and psoas

Correct Answer & Explanation

. Between sartorius and tensor fasciae latae

Explanation

The direct anterior (Smith-Petersen) approach to the hip utilizes a superficial and a deep internervous plane. The superficial plane is between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep interval is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 4677

Topic: Surgical Anatomy & Approaches

A trauma surgeon is performing an ilioinguinal approach to the anterior pelvis for the fixation of an anterior column acetabular fracture. During dissection over the superior pubic ramus, brisk arterial bleeding is encountered. This bleeding is most likely originating from an anastomosis between the obturator vessels and branches of which of the following?

. Internal iliac artery
. External iliac or inferior epigastric artery
. Superior gluteal artery
. Internal pudendal artery
. Deep circumflex iliac artery

Correct Answer & Explanation

. External iliac or inferior epigastric artery

Explanation

The 'corona mortis' (crown of death) is an important vascular anastomosis located over the posterior aspect of the superior pubic ramus, approximately 5-6 cm lateral to the pubic symphysis. It connects the obturator system (internal iliac system) with the external iliac or inferior epigastric vessels. It is vulnerable to injury during anterior pelvic approaches and can cause significant hemorrhage.

Question 4678

Topic: 1. General Principles & Basic Science

Articular cartilage is a complex tissue structured into distinct zones. Which zone contains chondrocytes arranged in vertical columns, has collagen fibers oriented perpendicular to the joint surface, and possesses the highest concentration of proteoglycans?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Articular cartilage consists of four structural zones. The deep (or radial) zone contains chondrocytes organized in vertical columns parallel to the collagen fibers, which are themselves oriented perpendicular to the articular surface. This architecture provides maximum resistance to compressive forces. The deep zone also contains the highest concentration of proteoglycans and the lowest water content of the uncalcified layers.

Question 4679

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage has the highest concentration of proteoglycans and the lowest concentration of water?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the lowest water content, highest proteoglycan concentration, and the largest diameter collagen fibrils which are oriented perpendicular to the joint surface to resist compressive forces.

Question 4680

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological agent used in the management of osteoporosis. What is its specific mechanism of action?

. Binds to RANKL and inhibits osteoclast activation
. Directly induces osteoclast apoptosis
. Stimulates osteoblast activity via PTH receptor
. Inhibits farnesyl pyrophosphate synthase
. Binds to sclerostin to promote bone formation

Correct Answer & Explanation

. Binds to RANKL and inhibits osteoclast activation

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), preventing it from interacting with RANK on osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

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