Accessory Cartilage: Definition, Types, Function, and Clinical Significance

What is accessory cartilage?

Accessory cartilage refers to specialized cartilaginous structures found within or around joints that are distinct from the primary articular cartilage lining the bone ends. These structures play crucial roles in enhancing joint function, stability, and load distribution, acting as vital secondary components of the musculoskeletal system.

Understanding Cartilage

To grasp the concept of accessory cartilage, it's essential to first understand cartilage itself. Cartilage is a resilient, semi-rigid connective tissue found throughout the body, providing support, flexibility, and smooth surfaces for joint movement. There are three main types of cartilage:

• Hyaline Cartilage: The most common type, found on the ends of bones in synovial joints (articular cartilage), in the nose, trachea, and ribs. It provides a smooth, low-friction surface for articulation.
• Elastic Cartilage: More flexible than hyaline cartilage, found in structures requiring high elasticity, such as the external ear and epiglottis.
• Fibrocartilage: The strongest and most durable type, rich in collagen fibers, found in areas subjected to high compressive forces, such as intervertebral discs, menisci of the knee, and pubic symphysis.

Defining Accessory Cartilage

Accessory cartilage, while not a universally standardized anatomical term, generally refers to fibrocartilaginous structures that are not the primary articular cartilage, but rather serve an auxiliary or supplementary role within a joint. These structures are typically composed of fibrocartilage due to its superior strength and ability to withstand significant mechanical stress. They are strategically positioned to optimize joint mechanics, enhance stability, and distribute forces more effectively.

It's important to distinguish accessory cartilage from supernumerary cartilage, which refers to extra or anomalous cartilaginous structures that may develop in unusual locations, often without a specific functional role or as part of an accessory bone formation. While some accessory cartilages might be considered supernumerary in developmental terms, the context of exercise science typically focuses on their functional contribution within joints.

Common Locations and Examples

Accessory cartilaginous structures are vital components in several key joints, especially those subjected to high loads and complex movements:

• Menisci of the Knee: The medial and lateral menisci are crescent-shaped fibrocartilaginous discs located between the femur and tibia. They deepen the articular surface, improve congruence, distribute load across the joint, absorb shock, and contribute to joint stability.
• Labra (Glenoid and Acetabular):
  • The glenoid labrum is a fibrocartilaginous ring that deepens the shallow glenoid fossa of the scapula, increasing the surface area for articulation with the humeral head in the shoulder joint. This enhances stability without sacrificing mobility.
  • The acetabular labrum is a similar ring that deepens the acetabulum of the pelvis, providing greater stability to the hip joint by increasing the contact area with the femoral head.
• Articular Discs/Meniscoids: Found in joints like the temporomandibular joint (TMJ) and sternoclavicular joint. These discs divide the joint cavity, allowing for multiple movements and distributing forces across the joint surfaces.
• Intervertebral Discs (Annulus Fibrosus): While often considered a primary structure of the spine, the outer fibrous ring (annulus fibrosus) of the intervertebral disc is a prime example of a fibrocartilaginous structure designed for shock absorption and load distribution between vertebrae.

Function and Biomechanical Role

The presence of accessory cartilage significantly impacts joint biomechanics and overall function:

• Enhanced Joint Congruence: By deepening or shaping joint surfaces, these cartilages improve the fit between bones, leading to more stable and efficient movement.
• Load Distribution and Shock Absorption: They spread compressive forces over a larger area, reducing peak stresses on the underlying articular cartilage and bone. This cushioning effect is crucial for protecting joints during high-impact activities.
• Joint Stability: Accessory cartilages contribute to joint stability by acting as wedges or bumpers, limiting excessive motion and preventing dislocation.
• Lubrication and Nutrition: They help facilitate the even distribution of synovial fluid across the joint surfaces, aiding lubrication and nutrient delivery to the articular cartilage.
• Proprioception: Some accessory cartilages, particularly menisci and labra, contain mechanoreceptors that contribute to proprioception, providing the brain with information about joint position and movement.

Clinical Significance and Common Issues

Given their critical functional roles, accessory cartilages are susceptible to injury and degeneration, which can significantly impair joint function:

• Tears: Acute traumatic injuries, such as twisting motions in the knee, can lead to meniscal tears. Repetitive overhead movements can cause labral tears in the shoulder.
• Degeneration: Over time, or due to chronic stress, these cartilages can undergo degenerative changes, leading to fraying, thinning, and reduced mechanical integrity. This is common in conditions like osteoarthritis.
• Pain and Dysfunction: Injuries or degeneration of accessory cartilage can cause localized pain, clicking, popping, locking, instability, and reduced range of motion.
• Impact on Primary Cartilage: Damage to accessory cartilage can alter joint mechanics, leading to increased stress on the primary articular cartilage and accelerating the progression of osteoarthritis.

Maintaining Cartilage Health

While accessory cartilage has limited capacity for self-repair, certain strategies can help maintain its health and reduce the risk of injury:

• Proper Exercise Technique: Executing movements with correct form minimizes undue stress on joints and their accessory structures.
• Progressive Overload: Gradually increasing training intensity allows cartilage to adapt and strengthen, rather than being overwhelmed.
• Strength and Stability Training: Strengthening muscles surrounding a joint provides dynamic support and can offload accessory cartilages.
• Mobility and Flexibility: Maintaining healthy joint ranges of motion prevents stiffness and abnormal loading patterns.
• Balanced Nutrition: A diet rich in anti-inflammatory foods, collagen-supporting nutrients (e.g., Vitamin C, protein), and adequate hydration can support overall tissue health.
• Weight Management: Reducing excess body weight significantly decreases the load on weight-bearing joints.
• Listen to Your Body: Acknowledging and addressing joint pain promptly can prevent minor issues from escalating into significant injuries.

Conclusion

Accessory cartilage, primarily composed of robust fibrocartilage, represents a crucial set of structures within our joints. Far from being mere "accessories," these menisci, labra, and discs are integral to optimizing joint congruence, distributing mechanical loads, absorbing shock, and enhancing stability. Understanding their vital roles and adopting strategies to protect their integrity is fundamental for maintaining long-term joint health and maximizing athletic performance.