MCQs – Basic 2

Modern Study Review (AI-Generated)

High-Yield Summary

Cartilage and bone allografts, implant biomechanics, cartilage physiology, and compartment syndrome are core topics frequently tested in orthopaedic board exams. This topic is a staple of the Royal College exam, focusing heavily on graft immunogenicity, implant wear mechanisms, cartilage zonal anatomy, and compartment syndrome pressure thresholds. The single most important clinical trade-off often tested is the interpretation of compartment pressure values—absolute pressure ?30 mm Hg versus delta pressure (diastolic minus compartment pressure) <20 mm Hg—to decide on fasciotomy. While classic teaching emphasizes steroid-induced avascular necrosis (AVN), modern evidence suggests steroids may paradoxically decrease AVN risk post-radiation therapy.

High-Yield Decision Matrix

Active Recall Q&A

Cartilage Allografts & Osteochondral Grafts

Q: Are chondrocytes in cartilage allografts immunogenic?
A: No, chondrocytes are not immunogenic because they are protected by the cartilage matrix.
Related Pearl: This immune privilege allows osteochondral allografts to be transplanted without systemic immunosuppression.

Q: What is a common cause of failure in osteochondral allografts?
A: Failure is often due to surface incongruity and failure of the interface to heal properly.
Related Pearl: Precise matching of graft surface geometry is critical to prevent mechanical failure.

Q: Do cortical allografts undergo stress fractures?
A: Yes, cortical allografts can undergo stress fractures.
Related Pearl: Stress fractures in cortical allografts reflect their load-bearing role and remodeling dynamics.

Radiation Therapy & Sarcomas

Q: How do steroids affect avascular necrosis (AVN) rates after radiation therapy?
A: Steroids may paradoxically decrease the rate of AVN post-radiation therapy.
Related Pearl: This counterintuitive effect may relate to steroids’ anti-inflammatory properties modulating microvascular injury.

Q: What are the most common sarcomas after radiation therapy?
A: Osteosarcoma, fibrosarcoma, and malignant fibrous histiocytoma (MFH) are the most common post-XRT sarcomas.
Related Pearl: Radiation-induced sarcomas typically develop years after exposure and require high suspicion in irradiated bone.

Biodegradable Implants & Joint Lubrication

Q: What is the incidence of osteolysis around biodegradable implants by 12 weeks?
A: Up to 50% of patients show large amounts of surrounding osteolysis by 12 weeks.
Related Pearl: Early osteolysis may reflect inflammatory response to implant degradation products.

Q: What is the primary role of hyaluronic acid in joints?
A: Hyaluronic acid is essential for weeping lubrication, being squeezed out of the cartilage matrix during joint loading.
Related Pearl: Weeping lubrication reduces friction and protects cartilage surfaces during motion.

UHMW Polyethylene & Acetabular Wear

Q: How does the modulus of elasticity of UHMW polyethylene change over time?
A: The modulus decreases over time because UHMWP is viscoelastic.
Related Pearl: Viscoelastic creep contributes to long-term implant deformation under load.

Q: How does the modulus of elasticity of UHMW polyethylene compare to metals?
A: The modulus of UHMW polyethylene is less than that of all metals.
Related Pearl: This lower stiffness allows some shock absorption but may contribute to wear debris generation.

Q: What is the approximate rate of acetabular wear per year?
A: About 0.1 mm per year, with wear decreasing with age; much may be creep rather than true wear.
Related Pearl: Differentiating creep from wear is important for implant longevity assessment.

Q: What type of wear predominates in acetabular components?
A: Abrasive wear predominates; third-body wear is a subtype of abrasive wear.
Related Pearl: Abrasive wear generates polyethylene particles that can induce osteolysis.

Chondrocyte Physiology & Cartilage Zones

Q: How do chondrocytes tolerate oxygen levels compared to synovial cells?
A: Chondrocytes tolerate lower PO2 than synovial cells and many other cell types.
Related Pearl: Cartilage is avascular and adapted to hypoxic conditions, influencing metabolism and repair.

Q: What are the characteristics of cells and matrix in the superficial zone of cartilage?
A: Cells are flat and spindle-shaped; very little proteoglycan; collagen fibers are tangential to the surface.
Related Pearl: The superficial zone resists shear forces and provides a smooth articulating surface.

Q: How do cells and matrix differ in the transitional zone of cartilage?
A: Cells are more round and hypertrophied compared to the superficial zone.
Related Pearl: Transitional zone acts as a buffer between superficial and deep zones, adapting to compressive forces.

Q: Describe the deep zone of cartilage in terms of cells and matrix.
A: Cells are plump and spherical with abundant proteoglycan; collagen fibers are perpendicular to the surface.
Related Pearl: The deep zone resists compressive loads and anchors cartilage to subchondral bone.

Q: Where is the tide mark located in cartilage?
A: Between the deep zone and the zone of calcified cartilage.
Related Pearl: The tide mark represents the mineralization front and is critical for cartilage-bone interface integrity.

Q: What is the thickness range of the tide mark?
A: Between 100 nanometers and 5 micrometers, depending on the source.
Related Pearl: Variability in measurement reflects differences in histological techniques and species.

Proteoglycans & Cartilage Composition

Q: What glycosaminoglycans (GAGs) compose proteoglycans in cartilage?
A: Predominantly chondroitin sulfate, dermatan sulfate, and keratan sulfate; 90% of proteoglycans are aggrecan.
Related Pearl: Negative charges on GAGs attract water, providing cartilage its compressive resilience.

Q: How does the ratio of GAGs in proteoglycans change with age?
A: Chondroitin-4 sulfate decreases; chondroitin-6 sulfate and keratan sulfate increase with age.
Related Pearl: These changes contribute to decreased cartilage hydration and elasticity in aging.

Q: What percentage of cartilage tissue volume and wet weight do chondrocytes constitute?
A: Less than 10% of tissue volume and less than 5% of wet weight.
Related Pearl: The extracellular matrix dominates cartilage composition, reflecting its mechanical function.

Q: What proportion of cartilage dry weight is collagen?
A: Over 50% of dry weight is collagen.
Related Pearl: Type II collagen provides tensile strength and structural framework.

Q: What is the water content of cartilage as a percentage of wet weight?
A: Approximately 65-80%.
Related Pearl: High water content is essential for load distribution and nutrient diffusion.

Osteoarthritis & Chondrocyte Metabolism

Q: How does osteoarthritis affect cartilage matrix components?
A: There is increased degradation of aggrecan and type II collagen fibers, with a compensatory increase in synthesis that eventually fails.
Related Pearl: Matrix breakdown leads to cartilage thinning and joint dysfunction.

Q: What is the metabolic activity of chondrocytes over time?
A: Chondrocytes have a high metabolic rate but enlarge and lose the ability to divide with age.
Related Pearl: Limited chondrocyte proliferation impairs cartilage repair capacity.

Q: How does cartilage change mechanically and biochemically with aging?
A: Cartilage becomes stiffer; protein content increases; water and proteoglycan content decrease in mass and size.
Related Pearl: These changes reduce cartilage resilience and increase susceptibility to degeneration.

Piezoelectric Bone & Bone Remodeling

Q: What generates piezoelectric potentials in bone?
A: Strain in the organic components (collagen and proteoglycans), independent of tissue viability.
Related Pearl: Piezoelectricity influences bone remodeling by modulating cellular activity.

Q: Where do negative and positive charges localize during bone bending?
A: Negative charges on concavity (compression) stimulate bone formation; positive charges on convexity (tension) stimulate resorption.
Related Pearl: This charge distribution guides adaptive bone remodeling to mechanical loads.

Compartment Syndrome

Q: What are the two critical pressure definitions for compartment syndrome?
A: Absolute compartment pressure ?30 mm Hg, or a difference between diastolic and compartment pressure <20 mm Hg.
Related Pearl: Both criteria help identify ischemic risk and guide timely fasciotomy.

Classic Clinical Notes

• In cartilage allografts, the chondrocytes are NOT immunogenic – they are protected from the immune system by the matrix.

• Failure in osteochondral allografts is often related to surface incongruity and failure for this interface to heal.

• Cortical allografts DO undergo stress fracture.

• Regarding XRT – steroids may paradoxically DECREASE the rate of AVN.

• The most common sarcomas post XRT are osteosarcoma, fibrosarcoma, and MFH.

• Biodegradable implants often show huge amounts of surrounding osteolysis by 12 weeks (in up to 50% of patients).

• Hyaluronic acid is important for weeping lubrication (the primary type of lubrication in joints) – it gets squeezed out of the cartilage matrix.

• The modulus of elasticity of UHMWP may decrease with time, as it is a viscoelastic substance.

• The modulus of UHMWP is less than all metals.

• In terms of acetabular wear: wear tends to decrease with age, and is calculated to be about 0.1 mm per year, although much of this might be creep, not wear.

• Acetabular wear is almost always ABRASIVE. 3rd body wear may also occur, but this is just a specific type of abrasive wear.

• Chondrocytes tolerate a lower PO2 than synovial cells – in fact, chondrocytes probably tolerate a lower PO2 than a lot of cells!

• In the zones of cartilage:
• Superficial – cells are flat, spindle shaped; very little proteoglycan; collagen tangential to surface
• Transitional – cells are more round, hypertrophied
• Deep – cells are plump, spherical, with lots of proteoglycan; collagen perpendicular to surface
• Zone of calcified cartilage
• Subchondral bone

• The tide mark is between the deep zone and zone of calcified cartilage. It is somewhere between 100 nanometers to 5 micrometers (microns) in thickness, depending on who you read.

• Glycosaminoglycans that make up proteoglycans are predominantly chondroitin sulfate, dermatan sulfate, and keratan sulfate. They join with a core protein to make proteoglycan (90% are called aggrecan). They are negatively charged and thus hydrophilic.

• The ratio of glycosaminoglycans in proteoglycans changes with age – chondroitin-4 sulfate decreases with age, while chondroitin-6 sulfate and keratan sulfate increase with age. Certainly, the aging process leads to less proteoglycans in general and thus a loss of some of the water carrying capacity of the cartilage.

• Hyaline cartilage – chondrocytes make up less than 10% of tissue volume and less than 5% of wet weight, while the collagen makes up over 50% of the dry weight. The water content of cartilage is about 65-80% the total wet weight.

• Remember: chondroitin-4 sulfate DECREASES with age; chondroitin-6 sulfate and keratan sulfate INCREASE with age.

• In osteoarthritis, there is an increased degradation of aggrecan and type II collagen fibers, and the cells try to keep up with this by increasing the synthesis of aggrecan and collagen (eventually doesn’t keep up though).

• In general, chondrocytes have a high metabolic rate as they maintain the extracellular matrix. Over time, they become larger and no longer divide.

• With aging, cartilage becomes stiffer; the protein content increases, the water content decreases, and cartilage proteoglycans decrease in mass and size.

• In piezoelectric materials (such as bone), the electric potentials are produced by strain in the ORGANIC COMPONENTS – i.e., the collagen and proteoglycans. This does not depend on tissue viability.

• When bending is applied to the bone, the negative charges are on the concavity (compression side), the positive charges on the convexity (tensile side). The negative charges are associated with bone formation, the positive with bone resorption.

• For compartment syndrome – two definitions of critical pressure: 30 mm Hg, or a difference between diastolic and compartment pressure of less than 20 (i.e., the compartment pressure creeps up to within 20 of diastolic pressure).

Last Updated on January 25, 2026 by Christian Veillette