Menu

1. General Principles & Basic Science MCQs

Practice Set 352 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 7021

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials possesses a modulus of elasticity most closely resembling that of human cortical bone?

. Cobalt-chromium alloy
. Alumina ceramic
. Titanium alloy (Ti-6Al-4V)
. 316L Stainless steel
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

Titanium alloys have a modulus of elasticity (roughly 110 GPa) that is closer to cortical bone (15-20 GPa) than stainless steel (200 GPa) or cobalt-chromium (220 GPa). This closer biomechanical match helps reduce stress shielding around the implant.

Question 7022

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain that can be tolerated for primary (direct) bone healing to occur without the formation of an intermediate callus?

. < 2%
. 2% - 10%
. 10% - 30%
. 30% - 50%
. > 50%

Correct Answer & Explanation

. < 2%

Explanation

Primary bone healing requires absolute stability, corresponding to an interfragmentary strain of less than 2%. Strains between 2% and 10% typically promote secondary bone healing via endochondral ossification and visible callus formation.

Question 7023

Topic: Biology, Genetics & Bone Healing

Romosozumab is a monoclonal antibody used in the treatment of severe osteoporosis. It exerts its primarily anabolic bone effect by targeting and inhibiting which of the following proteins?

. Cathepsin K
. RANK Ligand
. Wnt/beta-catenin pathway
. Sclerostin
. Dickkopf-1 (DKK1)

Correct Answer & Explanation

. Cathepsin K

Explanation

Romosozumab binds to and inhibits sclerostin, a glycoprotein naturally secreted by osteocytes. Since sclerostin normally inhibits the osteogenic Wnt signaling pathway, blocking it leads to markedly increased bone formation.

Question 7024

Topic: Biomechanics & Biomaterials

Which of the following alterations occurs when a radiopacifier such as barium sulfate or zirconium dioxide is added to polymethylmethacrylate (PMMA) bone cement?

. Decreased fatigue strength
. Increased compressive strength
. Decreased exothermic reaction temperature
. Increased setting time
. Decreased volumetric shrinkage

Correct Answer & Explanation

. Decreased fatigue strength

Explanation

The addition of radiopacifiers creates microscopic inclusions and stress risers within the PMMA mantle. This significantly decreases the material's fatigue strength and tensile strength, though it remains highly resistant to compressive loads.

Question 7025

Topic: Biomechanics & Biomaterials

During tensile testing of a human anterior cruciate ligament, the initial non-linear 'toe region' of the load-deformation curve is primarily caused by:

. Microfailure of collagen fibrils
. Plastic deformation of elastin fibers
. Uncrimping of the naturally wavy type I collagen fibers
. Viscoelastic stress relaxation
. Fluid exudation from the proteoglycan matrix

Correct Answer & Explanation

. Microfailure of collagen fibrils

Explanation

The non-linear 'toe region' observed at low strains in the stress-strain curve of a ligament corresponds to the uncrimping and straightening of the naturally wavy collagen fibers. Once straightened, the ligament enters the steeper linear elastic region.

Question 7026

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) helps maintain calcium homeostasis through its action on bone, intestines, and kidneys. In the kidney, PTH stimulates the production of the active form of Vitamin D by upregulating which enzyme?

. 25-hydroxylase
. 1-alpha-hydroxylase
. 24-hydroxylase
. Alkaline phosphatase
. Tartrate-resistant acid phosphatase

Correct Answer & Explanation

. 25-hydroxylase

Explanation

In the proximal convoluted tubule of the kidney, PTH strongly stimulates 1-alpha-hydroxylase. This enzyme converts 25-hydroxyvitamin D into 1,25-dihydroxyvitamin D (calcitriol), the active hormone that promotes intestinal calcium absorption.

Question 7027

Topic: 1. General Principles & Basic Science

Osteoclasts resorb bone by creating an isolated, acidic microenvironment known as the Howship lacuna. Which of the following is primarily responsible for degrading the organic collagenous matrix of bone during this process?

. Carbonic anhydrase II
. Hydrogen-ATPase pumps
. Cathepsin K
. Matrix metalloproteinase 13 (MMP-13)
. Tissue non-specific alkaline phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

While hydrogen-ATPase pumps acidify the resorption pit to dissolve the inorganic mineral component (hydroxyapatite), the organic type I collagen matrix is subsequently degraded by the proteolytic enzyme Cathepsin K secreted by the osteoclast.

Question 7028

Topic: 1. General Principles & Basic Science

The 'screw-home' mechanism in the native knee is characterized by which of the following obligatory kinematic motions during terminal extension?

. Internal rotation of the tibia relative to the femur
. External rotation of the tibia relative to the femur
. Anterior translation of the femur on the tibia
. Varus angulation of the mechanical axis
. Medial translation of the patella

Correct Answer & Explanation

. Internal rotation of the tibia relative to the femur

Explanation

The screw-home mechanism dictates an obligate external rotation of the tibia relative to the femur during the final 15 to 20 degrees of knee extension. This rotation locks the knee for stability and is driven primarily by the asymmetry of the medial and lateral femoral condyles.

Question 7029

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is meticulously contouring a reconstruction plate for a complex pelvic ring injury. Which of the following implant materials is most notoriously susceptible to fatigue failure if deeply scratched or notched during bending?

. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Cobalt-chromium-molybdenum alloy
. Tantalum
. Commercially pure titanium

Correct Answer & Explanation

. 316L Stainless steel

Explanation

Titanium alloy (Ti-6Al-4V) is highly notch sensitive compared to stainless steel. Surface scratches or sharp bends create significant stress risers that drastically reduce its fatigue life, making it prone to sudden mechanical failure in load-bearing applications.

Question 7030

Topic: Biomechanics & Biomaterials

Which of the following best describes the phenomenon of stress relaxation in a viscoelastic material such as a tendon?

. Continued deformation over time under a constant load
. Decrease in stress over time when held at a constant strain
. Increased stiffness at higher strain rates
. Loss of energy during a loading and unloading cycle
. Failure of the material under cyclical loading below its yield strength

Correct Answer & Explanation

. Continued deformation over time under a constant load

Explanation

Stress relaxation is the decrease in internal stress over time when a viscoelastic material is held at a constant strain. Creep is continued deformation under a constant load.

Question 7031

Topic: Biomechanics & Biomaterials

Which of the following orthopaedic biomaterials has a Young's modulus closest to that of human cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Ultra-high-molecular-weight polyethylene (UHMWPE)

Correct Answer & Explanation

. Stainless steel

Explanation

Titanium alloy has a Young's modulus (approx. 110 GPa) closer to cortical bone (approx. 15-20 GPa) compared to Cobalt-chromium or Stainless steel. This reduces stress shielding of the host bone.

Question 7032

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological treatment for osteoporosis and giant cell tumor of bone. What is its specific mechanism of action?

. Direct inhibition of the osteoclast ruffled border proton pump
. Binding to the Wnt receptor to increase osteoblastogenesis
. Monoclonal antibody that binds to RANKL, preventing osteoclast activation
. Recombinant parathyroid hormone analog stimulating bone formation
. Inhibition of farnesyl pyrophosphate synthase in the mevalonate pathway

Correct Answer & Explanation

. Direct inhibition of the osteoclast ruffled border proton pump

Explanation

Denosumab is a monoclonal antibody that targets and binds to RANKL. This prevents RANKL from binding to RANK on the osteoclast precursor, thus inhibiting osteoclast differentiation and function.

Question 7033

Topic: Biomechanics & Biomaterials

Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) was developed primarily to address which of the following issues in total hip arthroplasty?

. Catastrophic fracture of the liner
. Squeaking during normal gait
. Adhesive and abrasive wear
. Fretting corrosion at the trunnion
. Impingement and early dislocation

Correct Answer & Explanation

. Catastrophic fracture of the liner

Explanation

Highly cross-linked polyethylene was developed to improve wear resistance against adhesive and abrasive wear. However, the cross-linking process decreases the material's fatigue strength and ductility.

Question 7034

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, what type of tissue forms first when the interfragmentary strain is between 2% and 10%?

. Woven bone
. Lamellar bone
. Cartilage
. Granulation tissue
. Fibrous tissue

Correct Answer & Explanation

. Woven bone

Explanation

Perren's strain theory states that the tissue forming in a fracture gap depends on the strain it can tolerate. Cartilage tolerates up to 10% strain, whereas bone formation requires a lower strain environment of less than 2%.

Question 7035

Topic: 1. General Principles & Basic Science

Which of the following geometric modifications to a cortical bone screw will most effectively increase its pull-out strength?

. Increasing the inner (root) diameter
. Increasing the thread pitch
. Decreasing the outer diameter
. Increasing the outer diameter
. Decreasing the length of engagement

Correct Answer & Explanation

. Increasing the inner (root) diameter

Explanation

Pull-out strength of a screw is most dependent on the outer thread diameter. Increasing the outer diameter, decreasing the inner diameter (which increases thread depth), and maximizing thread engagement all increase pull-out strength.

Question 7036

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopaedic implants is most likely to occur under which of the following circumstances?

. A titanium screw is used to secure a titanium plate.
. A stainless steel screw is used through a cobalt-chromium plate.
. A titanium screw is inserted into severely osteoporotic bone.
. A cobalt-chromium femoral head is placed on a cobalt-chromium stem.
. Repeated micro-motion occurs between a screw and a plate of the same material.

Correct Answer & Explanation

. A titanium screw is used to secure a titanium plate.

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within a conductive fluid environment. Mixing stainless steel with cobalt-chromium creates a strong galvanic couple, accelerating corrosion.

Question 7037

Topic: 1. General Principles & Basic Science

In which zone of normal articular cartilage are the collagen fibers oriented parallel to the joint surface to primarily resist shear forces?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains fine collagen fibers aligned parallel to the articular surface. This specific orientation primarily functions to resist shear stresses during joint motion.

Question 7038

Topic: Biology, Genetics & Bone Healing

Sclerostin, a protein product of the SOST gene, regulates bone mass primarily by acting as a negative regulator of which of the following pathways?

. RANK/RANKL pathway
. Osteoprotegerin (OPG) pathway
. Wnt/beta-catenin pathway
. TGF-beta pathway
. BMP/Smad pathway

Correct Answer & Explanation

. RANK/RANKL pathway

Explanation

Sclerostin is secreted by osteocytes and acts as a negative regulator of bone formation by binding to LRP5/6 receptors. This directly inhibits the canonical Wnt/beta-catenin signaling pathway in osteoblasts.

Question 7039

Topic: 1. General Principles & Basic Science

The "toe region" of the load-elongation curve for a normal ligament represents which of the following physiological events?

. Microscopic failure of collagen fibers
. Macroscopic failure of the ligament
. Uncrimping of collagen fibers
. Plastic deformation of the ligament
. The point of ultimate tensile strength

Correct Answer & Explanation

. Microscopic failure of collagen fibers

Explanation

The toe region is the initial, non-linear concave portion of the ligament's load-elongation curve. It corresponds to the uncrimping and straightening of the naturally wavy collagen fibers under initial low-level load.

Question 7040

Topic: Biomechanics & Biomaterials

Which of the following statements regarding the properties of polymethylmethacrylate (PMMA) bone cement is true?

. It provides rigid biologic fixation via osteointegration.
. Its curing process is a highly endothermic reaction.
. It is weakest in compression and strongest in tension.
. The addition of barium sulfate provides radiopacity but acts as a stress riser.
. Pre-cooling the monomer accelerates the polymerization time.

Correct Answer & Explanation

. It provides rigid biologic fixation via osteointegration.

Explanation

PMMA provides purely mechanical interlock rather than biologic fixation, and sets via an exothermic reaction. Additives like barium sulfate or zirconium dioxide act as stress risers, decreasing the cement's overall fatigue strength.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page