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1. General Principles & Basic Science MCQs

Practice Set 255 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 5081

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs), specifically BMP-2 and BMP-7, are utilized clinically for their potent osteoinductive capabilities. Upon binding to their respective cell surface receptors, which specific intracellular signaling pathway is primarily activated to upregulate osteogenic gene transcription?

. Wnt / beta-catenin pathway
. JAK-STAT signaling pathway
. Smad signaling pathway
. MAPK / ERK signaling pathway
. Notch signaling cascade

Correct Answer & Explanation

. Smad signaling pathway

Explanation

BMPs are members of the TGF-beta superfamily. When they bind to their specific serine/threonine kinase transmembrane receptors, they induce phosphorylation of receptor-regulated Smads (R-Smads, such as Smad 1, 5, and 8). These form a complex with the common-partner Smad 4, which then translocates to the nucleus to act as a transcription factor for osteogenic genes (e.g., Runx2).

Question 5082

Topic: Biomechanics & Biomaterials

Biomechanical testing of a human anterior cruciate ligament graft is performed. When a constant load (stress) is applied to the ligament over an extended period, the ligament undergoes a gradual increase in length (strain). This viscoelastic property is best defined as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is the viscoelastic property where a tissue undergoes continuous, time-dependent deformation (elongation or strain) under a constant applied load (stress). In contrast, stress relaxation is the decrease in stress over time when the tissue is held at a constant length (strain).

Question 5083

Topic: 1. General Principles & Basic Science
During the natural progression of tendon healing, the remodeling phase is characterized by the replacement of immature collagen with mature collagen. Which type of collagen transitions to which type during this phase?
. Type I transitions to Type II
. Type II transitions to Type I
. Type III transitions to Type I
. Type I transitions to Type III
. Type III transitions to Type IV

Correct Answer & Explanation

. Type II transitions to Type I

Explanation

Tendon healing occurs in three phases: inflammatory, proliferative, and remodeling. During the proliferative phase, fibroblasts synthesize a large amount of Type III collagen, which is disorganized and weaker. During the remodeling phase, this is gradually replaced by Type I collagen, which is organized linearly along the axis of tension, providing greater tensile strength to the healed tendon.

Question 5084

Topic: Biomechanics & Biomaterials

A trauma surgeon is selecting an intramedullary nail for a tibial fracture. Comparing titanium alloy (Ti-6Al-4V) to 316L stainless steel, titanium alloy exhibits:

. A higher modulus of elasticity, resulting in less stress shielding
. A lower modulus of elasticity, resulting in less stress shielding
. A higher modulus of elasticity, resulting in greater stress shielding
. A lower modulus of elasticity, resulting in greater stress shielding
. An identical modulus of elasticity but superior fatigue resistance

Correct Answer & Explanation

. A lower modulus of elasticity, resulting in less stress shielding

Explanation

Titanium alloy (Ti-6Al-4V) has a lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel or cobalt-chrome alloys. Because it is less stiff, it shares load better with the surrounding bone, thereby reducing stress shielding and theoretically promoting better fracture healing and minimizing bone resorption compared to the stiffer stainless steel implants.

Question 5085

Topic: Biomechanics & Biomaterials

The torsional rigidity of a solid cylindrical intramedullary nail is mathematically governed by its polar moment of inertia. Based on this formula, the torsional rigidity is proportional to which of the following regarding the radius of the nail?

. Radius
. Radius squared
. Radius to the third power
. Radius to the fourth power
. Inversely proportional to the radius

Correct Answer & Explanation

. Radius to the fourth power

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia (J), which is calculated as J = (pi * r^4) / 2. Therefore, the torsional rigidity is directly proportional to the radius to the fourth power (r^4).

Question 5086

Topic: Biology, Genetics & Bone Healing

Denosumab is an established targeted therapy used in the management of unresectable or recurrent Giant Cell Tumor of Bone (GCTB). What is its precise mechanism of action?

. It binds directly to the ruffled border of mature osteoclasts, inhibiting their function.
. It is a monoclonal antibody that binds to RANKL, preventing activation of the RANK receptor.
. It directly induces apoptosis of the neoplastic mononuclear stromal cells.
. It selectively inhibits vascular endothelial growth factor (VEGF) to starve the tumor.
. It is a tyrosine kinase inhibitor that blocks c-KIT signaling.

Correct Answer & Explanation

. It is a monoclonal antibody that binds to RANKL, preventing activation of the RANK receptor.

Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding RANKL, it prevents it from activating the RANK receptor on the surface of osteoclast precursors, thereby inhibiting the formation, function, and survival of the giant osteoclast-like cells characteristic of GCTB.

Question 5087

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory regarding fracture healing, what mechanical strain condition within a fracture gap is required to achieve primary (direct) bone healing via Haversian remodeling, bypassing cartilaginous callus formation?

. Strain less than 2%
. Strain between 2% and 10%
. Strain between 10% and 30%
. Strain greater than 30%
. Constant dynamic strain fluctuations

Correct Answer & Explanation

. Strain less than 2%

Explanation

Perren's strain theory posits that primary (direct) bone healing requires absolute stability, defined as a strain environment of < 2%. This environment prevents the disruption of crossing osteons and avoids callus formation. Strain between 2% and 10% allows for secondary healing (callus formation), while strain > 10% leads to nonunion or fibrous tissue formation.

Question 5088

Topic: Surgical Anatomy & Approaches

Which of the following accurately describes the 'corona mortis' anastomosis, a critical vascular structure that may be encountered and injured during the ilioinguinal approach to the acetabulum?

. Anastomosis between the external iliac or inferior epigastric vessels and the obturator vessels
. Anastomosis between the internal iliac artery and the superior gluteal artery
. Anastomosis between the deep circumflex iliac artery and the femoral artery
. Anastomosis between the internal pudendal artery and the middle rectal artery
. Anastomosis between the external pudendal artery and the medial femoral circumflex artery

Correct Answer & Explanation

. Anastomosis between the external iliac or inferior epigastric vessels and the obturator vessels

Explanation

The corona mortis ('crown of death') is a vascular connection between the obturator and external iliac (or inferior epigastric) systems. It is located over the superior pubic ramus at an average distance of 5 to 6 cm from the pubic symphysis. Injury to this structure during an ilioinguinal approach or placement of superior pubic ramus screws can result in severe, difficult-to-control hemorrhage.

Question 5089

Topic: Biomechanics & Biomaterials

During the repair of a Zone II flexor tendon injury in the hand, preservation or reconstruction of which of the following annular pulleys is most critical to prevent bowstringing and maintain proper finger biomechanics?

. A1 and A3 pulleys
. A2 and A4 pulleys
. A3 and A5 pulleys
. A1 and A5 pulleys
. A2 and A3 pulleys

Correct Answer & Explanation

. A2 and A4 pulleys

Explanation

The flexor tendon sheath contains five annular (A1-A5) and three cruciform (C1-C3) pulleys. The A2 and A4 pulleys are the most mechanically critical. They originate directly from the periosteum of the proximal and middle phalanges, respectively. Loss of the A2 or A4 pulleys leads to clinically significant bowstringing of the flexor tendons, resulting in a loss of active flexion at the IP joints and an overall decrease in the work capacity of the finger.

Question 5090

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) play a crucial role in osteoinduction during fracture healing and spinal fusion. The cellular signaling cascade of BMPs is primarily initiated by the ligand binding to which of the following types of receptors on the cell surface?

. Tyrosine kinase receptors
. G-protein coupled receptors
. Serine/threonine kinase receptors
. Intracellular nuclear receptors
. Ion channel-linked receptors

Correct Answer & Explanation

. Serine/threonine kinase receptors

Explanation

Bone Morphogenetic Proteins (BMPs) are members of the TGF-beta superfamily. They bind to type I and type II transmembrane receptors, which are serine/threonine kinase receptors. Upon ligand binding, these receptors phosphorylate intracellular Smad proteins (typically Smad 1, 5, and 8), which then complex with Smad 4, translocate to the nucleus, and regulate the transcription of osteogenic genes (e.g., Runx2).

Question 5091

Topic: Biology, Genetics & Bone Healing

A 28-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femoral epiphysis extending to the subchondral bone, with no sclerotic margin. Biopsy confirms a giant cell tumor of bone (GCTB). Which of the following statements regarding the pathogenesis and targeted medical therapy for this tumor is true?

. The multinucleated giant cells are the primary neoplastic cells and express high levels of RANK
. The mononuclear stromal cells are the primary neoplastic cells and secrete excessive amounts of RANKL
. Imatinib mesylate is the preferred targeted therapy for unresectable lesions
. Denosumab therapy is a monoclonal antibody directed against the RANK receptor on the surface of the mononuclear stromal cells
. The tumor cells characteristically exhibit the t(X;18) chromosomal translocation

Correct Answer & Explanation

. The mononuclear stromal cells are the primary neoplastic cells and secrete excessive amounts of RANKL

Explanation

In Giant Cell Tumor of Bone (GCTB), the neoplastic cells are actually the mononuclear stromal cells, not the multinucleated giant cells. The neoplastic stromal cells secrete large amounts of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which recruits and activates normal osteoclast precursors into the reactive, multinucleated giant cells that cause the characteristic bone destruction. Denosumab is a monoclonal antibody that targets and binds RANKL (not the RANK receptor), inhibiting this process and is used for advanced or unresectable GCTB.

Question 5092

Topic: Biomechanics & Biomaterials

'Trunnionosis' in modern total hip arthroplasty primarily occurs at the modular head-neck taper junction. This phenomenon, which can lead to adverse local tissue reactions (ALTR) even with metal-on-polyethylene bearings, is mechanically initiated by micro-motion at the taper interface. This micro-motion primarily leads to which of the following modes of implant degradation?

. Pitting corrosion
. Galvanic corrosion
. Fretting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Fretting corrosion

Explanation

Trunnionosis refers to the wear and corrosion at the modular head-neck taper junction in a total hip arthroplasty. It is initiated by micro-motion under load, which constantly disrupts the protective passive oxide layer on the metal surface. This specific process of mechanically assisted crevice corrosion initiated by oscillatory micro-motion is termed 'fretting corrosion'. While galvanic corrosion plays a secondary role once the passivating layer is breached (especially with mixed metals like CoCr on Ti), the mechanical initiator is fretting.

Question 5093

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, what term describes the progressive deformation of a viscoelastic material over time when it is subjected to a constant load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the property of a viscoelastic material wherein it undergoes progressive, time-dependent deformation when subjected to a constant force or stress. Conversely, stress relaxation refers to the decrease in stress over time when a material is held at a constant strain.

Question 5094

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction and fracture healing. They exert their primary intracellular osteogenic effects through which of the following signaling pathways?

. Wnt/beta-catenin pathway
. JAK-STAT pathway
. Smad signaling pathway
. cAMP-dependent protein kinase pathway
. MAPK/ERK pathway

Correct Answer & Explanation

. Smad signaling pathway

Explanation

BMPs are members of the TGF-beta superfamily. Upon binding to their specific transmembrane serine/threonine kinase receptors, they induce phosphorylation of intracellular Smad proteins (specifically receptor-regulated Smads 1, 5, and 8). These form a complex with the co-Smad (Smad 4), which translocates to the nucleus to regulate the transcription of osteogenic target genes like Runx2.

Question 5095

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in bone healing and osteoinduction. Following the binding of BMP to its cell surface receptor, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus and regulate gene expression?

. Wnt proteins
. Smad 1, 5, and 8
. MAP kinases
. Beta-catenin
. RANKL

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs signal primarily through a Smad-dependent pathway. Binding of BMP to its specific serine/threonine kinase receptors leads to the phosphorylation of receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These R-Smads then form a complex with the common-mediator Smad (Smad 4) and translocate into the nucleus to activate the transcription of osteogenic target genes.

Question 5096

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant combinations is most likely to result in clinically significant galvanic corrosion if placed in direct physical contact within the human body?

. Cobalt-Chromium (Co-Cr) alloy and ultra-high-molecular-weight polyethylene
. Stainless steel (316L) and Titanium alloy (Ti-6Al-4V)
. Commercially pure Titanium and Titanium alloy (Ti-6Al-4V)
. Cobalt-Chromium (Co-Cr) alloy and Titanium alloy (Ti-6Al-4V)
. Stainless steel (316L) and Tantalum

Correct Answer & Explanation

. Stainless steel (316L) and Titanium alloy (Ti-6Al-4V)

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different electrochemical potentials (anodic index) are placed in direct physical contact within an electrolytic solution like body fluids. Stainless steel and titanium have a large difference in their electrochemical potentials, making them highly susceptible to severe galvanic corrosion when mixed. Titanium and Co-Cr have closer potentials and are routinely mixed safely in modular arthroplasty components.

Question 5097

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a recurrent Giant Cell Tumor (GCT) of the distal femur. Surgical curettage is deemed highly morbid, and she is started on Denosumab. What is the mechanism of action of this medication?

. It acts as a decoy receptor for macrophage colony-stimulating factor (M-CSF)
. It directly induces apoptosis of the neoplastic stromal cells within the tumor
. It is a monoclonal antibody that binds directly to RANK Ligand (RANKL)
. It is a bisphosphonate that inhibits the farnesyl pyrophosphate synthase pathway
. It selectively modulates estrogen receptors to inhibit osteoclast activity

Correct Answer & Explanation

. It is a monoclonal antibody that binds directly to RANK Ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from activating the RANK receptor on the surface of osteoclasts and their precursors, thereby inhibiting osteoclastogenesis and drastically reducing bone resorption in conditions like GCT and osteoporosis.

Question 5098

Topic: Surgical Anatomy & Approaches

A surgeon is performing a Direct Anterior Approach (Smith-Petersen) to the hip for a primary total hip arthroplasty. What muscles define the deep internervous plane in this approach?

. Sartorius and Tensor Fasciae Latae (TFL)
. Rectus femoris and Gluteus medius
. Gluteus medius and Gluteus minimus
. Tensor Fasciae Latae (TFL) and Gluteus medius
. Iliopsoas and Pectineus

Correct Answer & Explanation

. Sartorius and Tensor Fasciae Latae (TFL)

Explanation

The Smith-Petersen (Direct Anterior) approach exploits true internervous planes. The superficial plane is between the Sartorius (femoral nerve) and the Tensor Fasciae Latae (superior gluteal nerve). The deep plane lies between the Rectus femoris (femoral nerve) and the Gluteus medius (superior gluteal nerve).

Question 5099

Topic: Biomechanics & Biomaterials

Normal articular cartilage is divided into distinct structural zones. Which of the following best describes the histologic and biochemical characteristics of the superficial (tangential) zone?

. Highest proteoglycan content and vertically aligned collagen fibers
. Highest water content and collagen fibers aligned parallel to the joint surface
. Lowest water content and randomly oriented collagen fibers
. Highest cell density and purely Type I collagen
. Lowest cell density and highest concentration of hydroxyapatite crystals

Correct Answer & Explanation

. Highest water content and collagen fibers aligned parallel to the joint surface

Explanation

The superficial (tangential) zone of articular cartilage represents 10-20% of the thickness. It has the highest water content (up to 80%), lowest proteoglycan content, and features densely packed collagen fibers aligned parallel to the joint surface to resist shear forces. The deep zone features vertically aligned collagen fibers, lowest water content, and highest proteoglycan content to resist compressive loads.

Question 5100

Topic: Biology, Genetics & Bone Healing

In the process of bone remodeling, what is the primary biochemical role of osteoprotegerin (OPG)?

. It binds to RANKL, preventing it from interacting with RANK, thereby inhibiting osteoclast differentiation and activation.
. It binds directly to the RANK receptor on osteoclasts, stimulating osteoclastogenesis.
. It acts as a decoy receptor for macrophage colony-stimulating factor (M-CSF), preventing precursor maturation.
. It upregulates the production of sclerostin by mature osteocytes.
. It is an enzyme secreted by osteoclasts that degrades the organic bone matrix directly.

Correct Answer & Explanation

. It binds to RANKL, preventing it from interacting with RANK, thereby inhibiting osteoclast differentiation and activation.

Explanation

Osteoprotegerin (OPG) is a glycoprotein produced by osteoblasts that acts as a soluble decoy receptor. It competitively binds to RANK Ligand (RANKL), preventing RANKL from binding to the RANK receptor on the surface of osteoclast precursors. This interaction strongly inhibits the differentiation, activation, and survival of osteoclasts, thereby decreasing bone resorption.

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