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1. General Principles & Basic Science MCQs

Practice Set 311 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 6201

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) exert their potent osteoinductive effects by binding to cell-surface receptors and primarily activating which of the following intracellular signaling molecules?

. STAT proteins
. Smad proteins
. Beta-catenin
. MAP kinases
. NF-kappa B

Correct Answer & Explanation

. STAT proteins

Explanation

BMPs bind to serine/threonine kinase receptors on the cell membrane, which subsequently phosphorylate and activate downstream intracellular Smad proteins (typically Smads 1, 5, and 8) to upregulate osteogenic gene expression.

Question 6202

Topic: Biomechanics & Biomaterials

Galvanic corrosion of orthopedic implants is most likely to occur under which of the following specific conditions?

. A titanium screw is used in combination with a titanium plate
. A stainless steel screw is used in combination with a cobalt-chromium femoral head
. A stainless steel screw is placed in direct contact with a titanium plate
. Fretting motion occurs between a screw and plate of the identical material
. A ceramic head articulates directly with a cross-linked polyethylene liner

Correct Answer & Explanation

. A titanium screw is used in combination with a titanium plate

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium) are in direct contact within an electrolytic environment, leading to accelerated corrosion of the less noble metal.

Question 6203

Topic: Biology, Genetics & Bone Healing

While most of the appendicular skeleton develops via an intermediate cartilage model, which of the following bones develops primarily via intramembranous ossification?

. Femur
. Radius
. Clavicle
. Vertebral body
. Tibia

Correct Answer & Explanation

. Femur

Explanation

The clavicle, along with the flat bones of the skull and portions of the mandible, develops primarily via intramembranous ossification, where mesenchymal stem cells differentiate directly into osteoblasts without a cartilaginous template.

Question 6204

Topic: 1. General Principles & Basic Science

During prolonged standing, which exposes a joint to high static loads at zero or very low speeds, which mechanism is primarily responsible for the lubrication of articular cartilage?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Squeeze-film lubrication
. Weeping lubrication

Correct Answer & Explanation

. Hydrodynamic lubrication

Explanation

Boundary lubrication is the primary mechanism protecting articular cartilage under high-load, low-speed conditions. It relies on a monolayer of molecules, such as lubricin and superficial zone protein, bound to the articular surface.

Question 6205

Topic: Biology, Genetics & Bone Healing

Osteoclasts are specialized multinucleated giant cells responsible for the resorption of bone matrix. From which distinct cellular lineage do osteoclasts originate?

. Mesenchymal stem cells
. Hematopoietic macrophage-monocyte lineage
. Neural crest cells
. Endodermal precursor cells
. Chondrogenic precursor cells

Correct Answer & Explanation

. Mesenchymal stem cells

Explanation

Osteoclasts are derived from hematopoietic stem cells of the monocyte-macrophage lineage. In contrast, osteoblasts, chondrocytes, and adipocytes share a common origin from mesenchymal stem cells.

Question 6206

Topic: 1. General Principles & Basic Science

The biomechanical function of the nucleus pulposus within the intervertebral disc is primarily designed to resist and distribute which type of applied force?

. Tension
. Shear
. Compression
. Torsion
. Bending

Correct Answer & Explanation

. Tension

Explanation

The nucleus pulposus is a highly hydrated, gel-like center rich in Type II collagen and aggrecan, perfectly adapted to resist and uniformly distribute compressive axial loads. The surrounding annulus fibrosus handles tensile and torsional forces.

Question 6207

Topic: Physiology & Rehabilitation

Because mature articular cartilage is avascular and hypoxic, chondrocytes must rely predominantly on which metabolic pathway for their cellular energy (ATP) production?

. Oxidative phosphorylation
. Beta-oxidation of fatty acids
. Anaerobic glycolysis
. Gluconeogenesis
. Pentose phosphate pathway

Correct Answer & Explanation

. Oxidative phosphorylation

Explanation

Due to the avascular nature of mature articular cartilage, chondrocytes reside in a hypoxic environment and rely almost entirely on anaerobic glycolysis for ATP synthesis, a process regulated by hypoxia-inducible factor 1-alpha (HIF-1 alpha).

Question 6208

Topic: Biology, Genetics & Bone Healing

During the intracellular biosynthesis of collagen, vitamin C (ascorbic acid) is an absolute requirement as a cofactor for which specific enzymatic process?

. Cleavage of procollagen C-propeptides
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen by lysyl oxidase
. Glycosylation of hydroxylysine residues
. Transcription of COL1A1 genes

Correct Answer & Explanation

. Cleavage of procollagen C-propeptides

Explanation

Vitamin C is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Defective hydroxylation of proline and lysine leads to structurally unstable collagen triple helices, resulting in scurvy.

Question 6209

Topic: Biomechanics & Biomaterials

According to the principles of external fixation biomechanics, which of the following modifications will most significantly increase the bending stiffness of a half-pin?

. Increasing the core diameter of the pin
. Decreasing the distance from the bone to the external bar
. Increasing the total number of pins
. Placing pins in multiple different planes
. Changing the pin material from titanium to stainless steel

Correct Answer & Explanation

. Increasing the core diameter of the pin

Explanation

While bringing the bar closer to the bone increases construct stiffness, increasing the core diameter of the pin has the most profound effect on the individual pin's bending stiffness, as it is proportional to the radius to the fourth power (r^4).

Question 6210

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest water content, highest collagen concentration, and lowest proteoglycan concentration?

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

Correct Answer & Explanation

. Superficial zone

Explanation

The superficial zone of articular cartilage has the highest water and collagen content, but the lowest proteoglycan concentration. Its collagen fibers are oriented parallel to the joint surface to primarily resist shear forces.

Question 6211

Topic: Biology, Genetics & Bone Healing

What process characterizes creeping substitution during the incorporation of a cortical bone graft?

. Direct enchondral ossification
. Osteoclast resorption followed by osteoblast formation via cutting cones
. Rapid revascularization without structural resorption
. Membranous ossification from the periosteum
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Direct enchondral ossification

Explanation

Creeping substitution in cortical bone grafts involves osteoclastic resorption of the dead graft bone followed closely by osteoblastic bone formation. This process relies on cutting cones and proceeds much slower than the incorporation of cancellous bone grafts.

Question 6212

Topic: Biology, Genetics & Bone Healing

What is the primary cellular mechanism of action for nitrogen-containing bisphosphonates?

. Inhibition of cathepsin K
. Direct activation of osteoprotegerin
. Inhibition of farnesyl pyrophosphate synthase
. Binding to RANK ligand
. Inhibition of sclerostin

Correct Answer & Explanation

. Inhibition of cathepsin K

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of small GTPases that are essential for normal osteoclast function and survival.

Question 6213

Topic: Biomechanics & Biomaterials

On a load-deformation or stress-strain curve for a structural material, what biomechanical property is represented by the slope of the linear portion?

. Toughness
. Yield strength
. Ultimate tensile strength
. Stiffness (Young's modulus)
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

Young's modulus (or modulus of elasticity) is the slope of the linear, elastic portion of the stress-strain curve. It represents the intrinsic stiffness of the material being tested.

Question 6214

Topic: Biomechanics & Biomaterials

The time-dependent increase in strain of articular cartilage when subjected to a constant, prolonged compressive load is termed:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the progressive time-dependent deformation (increase in strain) of a viscoelastic material under a constant load. In contrast, stress relaxation is the decrease in stress over time when held at a constant strain.

Question 6215

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopedic implants is most likely to result in significant galvanic corrosion if placed in direct physical contact in vivo?

. Titanium alloy and Commercially pure titanium
. Cobalt-chromium and Cobalt-chromium
. Titanium alloy and Stainless steel
. Stainless steel and Stainless steel
. Titanium alloy and Tantalum

Correct Answer & Explanation

. Titanium alloy and Commercially pure titanium

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct contact within an electrolytic environment. The combination of titanium and stainless steel is highly prone to severe galvanic corrosion and must be avoided.

Question 6216

Topic: 1. General Principles & Basic Science

Which design modification to a cortical bone screw will most effectively increase its pull-out strength?

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

Correct Answer & Explanation

. Increasing the inner core diameter

Explanation

The pull-out strength of a screw is increased by maximizing the volume of bone caught between the threads. This is achieved by increasing the outer diameter, decreasing the inner core diameter, increasing engagement length, and decreasing the thread pitch.

Question 6217

Topic: Biology, Genetics & Bone Healing

Which type of fracture healing is characterized by the sequential formation of a soft cartilaginous callus followed by a hard bony callus?

. Primary bone healing
. Intramembranous ossification
. Secondary bone healing
. Creeping substitution
. Osteonal remodeling

Correct Answer & Explanation

. Primary bone healing

Explanation

Secondary bone healing occurs via enchondral ossification, proceeding through stages of hematoma formation, soft (cartilaginous) callus, hard (woven bone) callus, and remodeling. Primary bone healing occurs without callus formation under conditions of absolute stability.

Question 6218

Topic: Biology, Genetics & Bone Healing

Osteoclasts are multinucleated giant cells derived from which of the following cellular lineages?

. Mesenchymal stem cells
. Hematopoietic macrophage-monocyte lineage
. Neural crest cells
. Endodermal precursors
. Endothelial progenitor cells

Correct Answer & Explanation

. Mesenchymal stem cells

Explanation

Osteoclasts are derived from the fusion of mononuclear precursors of the hematopoietic macrophage-monocyte lineage. In contrast, osteoblasts, chondrocytes, and fibroblasts are derived from mesenchymal stem cells.

Question 6219

Topic: 1. General Principles & Basic Science

Which mechanism of joint lubrication operates primarily under conditions of low speeds and high loads, relying on surface-active molecules like lubricin?

. Elastohydrodynamic lubrication
. Boundary lubrication
. Weeping lubrication
. Squeeze-film lubrication
. Hydrodynamic lubrication

Correct Answer & Explanation

. Elastohydrodynamic lubrication

Explanation

Boundary lubrication relies on a thin molecular layer of glycoproteins (like lubricin) attached to the articular surface to reduce friction, operating best under low speeds and high loads. Fluid-film mechanisms predominate at higher speeds.

Question 6220

Topic: Biomechanics & Biomaterials

On a stress-strain curve of a normal human tendon, what does the initial non-linear "toe region" represent?

. Yielding of collagen fibers
. Uncrimping of collagen fibers
. Microscopic failure of fascicles
. Macroscopic failure of the tendon
. Plastic deformation

Correct Answer & Explanation

. Yielding of collagen fibers

Explanation

The initial toe region occurs at low strains and represents the straightening or "uncrimping" of the naturally wavy collagen fibers in the resting tendon. Beyond this region, the curve becomes linear as the fibers themselves begin to stretch.

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