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1. General Principles & Basic Science MCQs

Practice Set 314 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 6261

Topic: 1. General Principles & Basic Science

According to Perren's strain theory of fracture healing, which of the following tissues can tolerate the highest interfragmentary strain before rupturing?

. Lamellar bone
. Woven bone
. Fibrocartilage
. Granulation tissue
. Hyaline cartilage

Correct Answer & Explanation

. Lamellar bone

Explanation

Perren's strain theory posits that tissues will only form in a fracture gap if the local strain is below their yield point. Granulation tissue tolerates up to 100% strain, fibrocartilage up to 15%, and lamellar bone only about 2%.

Question 6262

Topic: 1. General Principles & Basic Science

An empty 3 mm unicortical drill hole is accidentally made in the anterior cortex of a tibia during surgery. Under torsional loading, how much does this defect approximately reduce the bone's torsional strength?

. It has no significant effect
. 10%
. 30%
. 50%
. 90%

Correct Answer & Explanation

. It has no significant effect

Explanation

An empty cortical hole acts as a significant stress riser. A defect as small as 20% of the bone's diameter can decrease the bone's torsional strength by up to 50% due to stress concentration at the margins.

Question 6263

Topic: Biomechanics & Biomaterials

Which of the following material properties represents the total energy absorbed by a material before it fails, corresponding to the total area under the stress-strain curve?

. Toughness
. Stiffness
. Ductility
. Fatigue limit
. Viscoelasticity

Correct Answer & Explanation

. Toughness

Explanation

Toughness is the energy absorbed by a material prior to failure, represented by the total area under the stress-strain curve. Stiffness refers to the elastic region's slope (Young's modulus), while ductility is the amount of plastic deformation before failure.

Question 6264

Topic: Biology, Genetics & Bone Healing

Mesenchymal stem cells differentiate into osteoblasts through the activation of specific transcription factors. Which of the following is considered the master transcription factor essential for osteoblast lineage commitment?

. SOX9
. RUNX2 (Cbfa1)
. PPAR-gamma
. MyoD
. HIF-1 alpha

Correct Answer & Explanation

. SOX9

Explanation

RUNX2 (Cbfa1) is the master transcription factor required for the differentiation of mesenchymal stem cells into osteoblasts. SOX9 is essential for chondrogenesis, and PPAR-gamma drives adipogenesis.

Question 6265

Topic: 1. General Principles & Basic Science

In cortical bone screw fixation, which geometric modification to the screw design will most significantly increase its pull-out strength?

. Increasing the inner (core) diameter
. Increasing the outer (thread) diameter
. Decreasing the thread pitch
. Increasing the screw head size
. Decreasing the screw length

Correct Answer & Explanation

. Increasing the inner (core) diameter

Explanation

The outer diameter is the most significant geometric determinant of screw pull-out strength. While increasing the core diameter improves fatigue strength, it minimally impacts pull-out strength compared to changes in the outer diameter.

Question 6266

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated for primary (contact) bone healing to occur via cutting cones?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2%. Strains between 2% and 10% promote secondary bone healing via callus formation, while strains >10% lead to fibrous nonunion.

Question 6267

Topic: 1. General Principles & Basic Science

Which zone of normal articular cartilage contains the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone of articular cartilage is designed to resist shear forces, characterized by a high water content, low proteoglycan content, and densely packed collagen fibers parallel to the articular surface.

Question 6268

Topic: Biology, Genetics & Bone Healing

When utilizing a bridging plate for a comminuted diaphyseal fracture, what is a direct biomechanical consequence of increasing the working length (the distance between the closest inner screws) of the construct?

. Increased torsional stiffness
. Decreased overall axial and bending stiffness
. Increased risk of plate failure due to increased rigidity
. Decreased interfragmentary movement
. Increased stress concentration at the innermost screws

Correct Answer & Explanation

. Increased torsional stiffness

Explanation

Increasing the working length of a bridging plate decreases the overall axial and bending stiffness of the construct. This increased flexibility permits more interfragmentary motion, which stimulates secondary bone healing via callus formation.

Question 6269

Topic: Biomechanics & Biomaterials

Which structural property is the primary determinant of torsional rigidity in a solid intramedullary nail?

. Nail length
. Wall thickness
. Radius to the fourth power
. Radius to the third power
. Material modulus of elasticity squared

Correct Answer & Explanation

. Nail length

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, small increases in the diameter of an IM nail result in massive increases in torsional rigidity.

Question 6270

Topic: Biology, Genetics & Bone Healing
During the soft callus phase of secondary fracture healing, the initial cartilaginous matrix is predominantly composed of which type of collagen?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

The soft callus primarily consists of hyaline cartilage and fibrocartilage, which are rich in Type II collagen. As the healing progresses to the hard callus phase, Type II is replaced by Type I collagen during endochondral ossification.

Question 6271

Topic: Biomechanics & Biomaterials

A dynamic splint is applied to a patient's contracted elbow, delivering a constant force. Over several days, the joint progressively gains extension. Which biomechanical property of viscoelastic materials does this best describe?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation of a viscoelastic material over time when subjected to a constant load. Stress relaxation, in contrast, is the decrease in stress over time when a material is held at a constant length or deformation.

Question 6272

Topic: Biomechanics & Biomaterials

To minimize stress shielding in total joint arthroplasty, engineers seek materials that match the mechanical properties of bone. Which of the following implant materials has a modulus of elasticity closest to that of human cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy (Ti-6Al-4V)
. Alumina ceramic
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Stainless steel

Explanation

Titanium alloy has a modulus of elasticity (approx. 110 GPa) that is closer to cortical bone (15-20 GPa) than stainless steel (200 GPa) or CoCr (210 GPa). This closer match reduces the extent of stress shielding.

Question 6273

Topic: 1. General Principles & Basic Science

Which of the following medications is known to impair early fracture healing by specifically inhibiting a pathway critical for the differentiation of osteoblasts during early endochondral ossification?

. Alendronate
. Celecoxib
. Denosumab
. Teriparatide
. Methotrexate

Correct Answer & Explanation

. Alendronate

Explanation

Celecoxib, a selective COX-2 inhibitor, blocks the synthesis of prostaglandins (like PGE2) that are essential for osteoblast differentiation and the early stages of endochondral ossification, thereby impairing fracture healing.

Question 6274

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological agent for treating osteoporosis. What is its specific molecular mechanism of action?

. It binds directly to the RANK receptor on osteoclasts.
. It acts as a monoclonal antibody that binds to and neutralizes RANKL.
. It inhibits farnesyl pyrophosphate synthase in the mevalonate pathway.
. It directly stimulates Wnt/beta-catenin signaling in osteoblasts.
. It inhibits cathepsin K activity within the osteoclast sealing zone.

Correct Answer & Explanation

. It binds directly to the RANK receptor on osteoclasts.

Explanation

Denosumab is a fully human monoclonal antibody that binds specifically to RANKL. By neutralizing RANKL, it prevents it from binding to the RANK receptor on osteoclasts, severely inhibiting osteoclastogenesis and bone resorption.

Question 6275

Topic: Biomechanics & Biomaterials

When a tendon is tested in tension, the initial region of its stress-strain curve demonstrates low stiffness before becoming linear. What is responsible for this initial 'toe region'?

. Microfailure of individual collagen fibers
. Uncrimping of the wavy collagen fibers
. Plastic deformation of the tendon matrix
. Viscoelastic creep under constant load
. Extrusion of water from the proteoglycan matrix

Correct Answer & Explanation

. Microfailure of individual collagen fibers

Explanation

The toe region corresponds to the initial uncrimping or straightening of the naturally wavy collagen fibers at low strains. Once the fibers are straight, the curve enters the linear (elastic) region.

Question 6276

Topic: Biology, Genetics & Bone Healing

Which of the following non-collagenous bone matrix proteins contains an RGD (Arg-Gly-Asp) sequence that is essential for osteoclast attachment via alpha-v beta-3 integrins?

. Osteocalcin
. Osteopontin
. Osteonectin
. Sclerostin
. Decorin

Correct Answer & Explanation

. Osteocalcin

Explanation

Osteopontin and bone sialoprotein both contain the RGD sequence, which binds specifically to the alpha-v beta-3 integrin on the osteoclast membrane, facilitating the formation of the sealing zone for bone resorption.

Question 6277

Topic: 1. General Principles & Basic Science

When designing an external fixator, a surgeon opts to increase the diameter of the Schanz pins from 4 mm to 5 mm. How does this specific change mathematically alter the bending stiffness of the pins?

. Increases it linearly in proportion to the diameter
. Increases it to the second power of the radius
. Increases it to the third power of the radius
. Increases it to the fourth power of the radius
. Has a negligible effect compared to decreasing the bone-to-rod distance

Correct Answer & Explanation

. Increases it linearly in proportion to the diameter

Explanation

The bending stiffness of a pin is proportional to its area moment of inertia, which correlates with the radius to the fourth power (r^4). Thus, a minor increase in pin diameter yields a profound increase in construct stiffness.

Question 6278

Topic: Biology, Genetics & Bone Healing

Romosozumab has recently been utilized for the treatment of severe osteoporosis. What is the precise mechanism of action of this agent?

. It binds and neutralizes RANKL, preventing osteoclast activation.
. It acts as an analog of parathyroid hormone, stimulating bone formation.
. It binds to and inhibits sclerostin, thereby enhancing Wnt/beta-catenin signaling.
. It inhibits cathepsin K, preventing degradation of the organic bone matrix.
. It directly stimulates the secretion of BMP-2 from osteoblasts.

Correct Answer & Explanation

. It binds and neutralizes RANKL, preventing osteoclast activation.

Explanation

Romosozumab is a monoclonal antibody that binds and inhibits sclerostin. Since sclerostin is an endogenous inhibitor of the Wnt/beta-catenin pathway, neutralizing it increases osteoblast activity and dramatically enhances bone formation.

Question 6279

Topic: 1. General Principles & Basic Science

Which of the following parameters most significantly increases the pullout strength of a cortical screw?

. Increasing the core diameter
. Decreasing the pitch
. Increasing the outer thread diameter
. Increasing the length of the screw head
. Decreasing the length of engagement

Correct Answer & Explanation

. Increasing the core diameter

Explanation

Pullout strength is most significantly determined by the outer thread diameter, as it is proportional to the square of the thread diameter. Other secondary factors include the length of engagement and shear strength of the surrounding bone.

Question 6280

Topic: Biology, Genetics & Bone Healing

In the context of bone healing, primary (strain-free) bone healing relies fundamentally on which of the following processes?

. Endochondral ossification
. Intramembranous ossification
. Haversian remodeling via cutting cones
. Soft callus formation followed by hard callus
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Endochondral ossification

Explanation

Primary bone healing occurs strictly under conditions of absolute stability and relies on direct Haversian remodeling via cutting cones. Unlike secondary healing, it progresses without intermediate cartilaginous callus formation.

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