articular cartilage

Composition of Articular Cartilage

The composition of articular cartilage is unique, allowing it to effectively withstand the stress and strain of joint movement.

• Water: Comprises about 65-80% of the articular cartilage, providing resilience.
• Collagen fibers: Make up 10-20% of the cartilage, offering structural support.
• Proteoglycans: These proteins, around 10-15%, help to retain water, maintaining cartilage elasticity.
• Chondrocytes: Specialized cells responsible for maintaining and repairing the cartilage.

Function of Articular Cartilage

Articular cartilage serves several crucial roles in joint health and performance:

• Allows for smooth movement of joints, reducing friction between bones.
• Acts as a cushion to absorb shocks and stress during weight-bearing activities, such as walking or running.
• Distributes loads evenly to the underlying bone, minimizing wear and tear.

Importance in Joint Diseases

Articular cartilage damage or degeneration is a significant factor in joint diseases, such as osteoarthritis. When cartilage wears down, it leads to increased friction, pain, and reduced mobility. Understanding how articular cartilage functions can highlight the importance of its preservation in joint health management. Measures such as physical therapy, maintaining a healthy weight, and avoiding injury are often recommended to support cartilage health.

Structure of Articular Cartilage

The structure of articular cartilage is uniquely suited to support its function in joints. By examining its layers and components, you can appreciate how it maintains joint health.Articular cartilage is typically composed of four zones: superficial, middle, deep, and calcified. Each zone has distinct characteristics that contribute to the cartilage's ability to reduce friction and absorb shock.

Superficial Zone

The superficial zone is the outermost layer of articular cartilage, responsible for providing a smooth, gliding surface for joint movement. It also helps protect deeper layers from shear forces.Characteristics of this zone include:

• High water content to maintain smoothness.
• Tightly packed collagen fibers arranged parallel to the surface.
• Thin layer of chondrocytes.

Middle Zone

Beneath the superficial zone, the middle zone offers support and acts as a transition between the outer and deeper layers.Key features include:

• Randomly arranged collagen fibers to distribute load.
• Higher concentration of proteoglycans for shock absorption.
• Chondrocytes that are more spherical in shape.

Deep Zone

The deep zone is crucial for cartilage strength, anchoring the cartilage to the underlying bone.This layer includes:

• Collagen fibers organized perpendicular to the joint surface.
• Increased density of chondrocytes.
• Thicker arrangement of collagen for structural stability.

Calcified Zone

The calcified zone is the deepest layer, helping to secure the cartilage to the bone, preventing movement along the bone surface.Features of this zone include:

• Mineralization of the matrix for rigidity.
• Serves as the barrier between cartilage and subchondral bone.

Biomechanics of Articular Cartilage

Understanding the biomechanics of articular cartilage is essential to grasp its function in joint health. It involves studying the forces that cartilage withstands and how its structural components contribute to its resilience.

Load Distribution

Articular cartilage is adept at distributing loads across joint surfaces, which is fundamental in weight-bearing activities. Efficient load distribution minimizes stress concentrations, reducing potential damage.

• Collagen fibers help spread loads, preventing wear and tear.
• The high water content within proteoglycans provides resistance to compressive forces.

Friction Minimization

Minimizing friction is crucial for smooth joint movement, a task that articular cartilage handles excellently.The biomechanical properties enable:

• Low friction surfaces due to the smoothness of the superficial zone.
• Hydration maintenance by synovial fluid, reducing wear.

Shock Absorption

Shock absorption is a key biomechanical function of articular cartilage, protecting underlying bone from impact stresses.Mechanisms include:

• Proteoglycans interacting with water, creating a gel-like consistency that dampens shock.
• The elasticity of collagen fibers, allowing deformation under stress followed by a return to the original shape.

Mechanical Properties

The mechanical properties of articular cartilage contribute to its function. This includes:

• Elasticity, largely due to collagen, providing flexibility.
• Viscosity, derived from proteoglycans, giving resistance to flow and deformation.
• Permeability, allowing fluid transfer, crucial for nutrient exchange and joint lubrication.

Articular Cartilage Function

Articular cartilage plays a crucial role in joint function by acting as a cushion and reducing friction in articulating joints. It contributes to smooth and efficient movement while protecting bones from damage. Understanding its location and function is essential to appreciating its role in maintaining joint health.

Where is Articular Cartilage Located

Articular cartilage is located at the ends of bones that form synovial joints. These joints include:

• Knees: Facilitating motion between the femur, tibia, and patella.
• Hips: Allowing smooth articulation of the femoral head in the acetabulum.
• Shoulders: Enabling the humerus to move within the glenoid cavity.
• Hands and Feet: Providing mobility in smaller joints like those of fingers and toes.

Articular Cartilage Repair Techniques

Damage to articular cartilage can impair joint function, necessitating repair techniques to restore performance. Here are common strategies:

• Microfracture Surgery: Involves creating small holes in the bone to stimulate cartilage growth by encouraging blood supply.
• Osteochondral Grafting: Transforms healthy cartilage from a non-weight-bearing joint area to the damaged site.
• Autologous Chondrocyte Implantation (ACI): Uses the patient's own cultured cartilage cells to fill in cartilage defects.
• Stem Cell Therapy: Explored for its potential to regenerate damaged cartilage using stem cells.