Articular Cartilage

Articular Cartilage and Fibrocartilage

General Information on Articular Cartilage

  • Definitions:

    • Articular cartilage: Smooth tissue covering the ends of bones at joints.

    • Fibrocartilage: A tougher form of cartilage found in specific areas, such as the intervertebral discs and menisci.

Purpose of Articular Cartilage

  • Decrease Bone-to-Bone Contact:

    • Reduces stress by increasing surface area, thereby distributing loads more evenly.

  • Decrease Friction:

    • Allows for smooth movement between joint surfaces.

  • Composition:

    • Solid content: 13% - 40%

    • Water content: 60% - 87%

Response of Articular Cartilage to Loading

  • Elastic Behavior:

    • Responds quickly to loads, behaving like a solid.

  • Viscoelastic Behavior:

    • Under slower loading rates, exhibits properties of both solid and fluid, allowing time-dependent deformation.

    • Reference: Oloyede et al. (1992) discusses deformation characteristics.

Articular Cartilage Health

  • Healthy cartilage relies on the movement for nourishing synovial fluid, which is vital for joint health.

Microfracture Surgery

  • Definition: Surgical procedure to repair cartilage defects by creating small fractures in the underlying bone, promoting bleeding and the growth of new cartilage.

  • Process:

    • Drill holes into the bone to encourage blood supply and tissue growth.

  • Follow-up: For example, a case study shows a 1.5-year follow-up on a trochlear condral defect.

Autologous Chondrocyte Implantation (ACI)

  • Process: Involves two surgeries where a cartilage sample is taken, cultured in a lab, and then sutured back into the defect area.

    • Follow-up shows improved smoothness and reduced defects.

Mosaicplasty Procedure

  • Definition: A technique to repair cartilage defects by transplanting plugs of cartilage from a healthy area to the damaged area.

  • Follow-up: One year post-operation shows filling of defect area with plugs; still some imperfections present.

Fibrocartilage Structure and Characteristics

Properties of Fibrocartilage

  • Composition:

    • Colagenous tissue: 75% of dry weight.

    • Main type is Type I collagen, differing from articular cartilage which contains Type II collagen.

  • Mechanical Properties:

    • Behavior under tension: Stiffer in circumferential direction, weaker radially by nearly 100 times.

    • The surface of fibrocartilage is generally 5 times stronger than that of articular cartilage.

  • Importance of Fiber Orientation:

    • Circumferential fibers critical for managing hoop stress and load distribution.

Functions of the Menisci

  • Load Bearing:

    • Contributes 50% of compressive load area in full extension and 85% in 90° flexion.

    • Removal of meniscus can lead to a 50% reduction in contact area.

  • Shock Absorption:

    • Acts as a viscoelastic structure to dampen loads over a longer time.

  • Joint Stability:

    • Wedge shape deepens joint space and improves bony congruency, preventing tibia translation and contributing to stability.

Tendons and Ligaments

Definitions

  • Tendons:

    • Structures that transfer muscle force to bones, facilitating movement.

  • Ligaments:

    • Connects bones to provide stability to joint structures.

Structural Characteristics

  • Composition:

    • Cellular: 20%

    • Matrix: 80%, containing 70% water, 30% collagen, glycosaminoglycans (GAGs), and elastin.

  • Tendons have greater collagen content compared to ligaments, enhancing their strength.

Mechanical Properties

  • Tendons exhibit significant strength under tension in both directions of loading.

  • Structure allows for increased stiffness when loaded rapidly or with greater cross-sectional area.

  • Both tendons and ligaments have anisotropic properties, meaning their mechanical response varies based on the direction of the load.

Rehabilitation and Reconstruction

  • Emphasis on realigning fibers post-injury or during reconstruction of ligaments (e.g., ACL rehabilitation) to restore function and minimize stiffness.