Cartilage is a specialized connective tissue that provides support and flexibility throughout the body. In the skeletal system, it covers the ends of bones in movable joints, facilitating smooth movement and contributing to the overall function of the joint.
What is Articular Hyaline Cartilage?
Articular hyaline cartilage covers the ends of bones within synovial joints. It measures between 2 to 4 millimeters in thickness and appears as a smooth, pearly white tissue. Unlike most body tissues, articular cartilage lacks blood vessels, nerves, and lymphatic vessels, which significantly impacts its ability to repair itself.
Its composition is primarily an extracellular matrix, making up about 95% of its volume. This matrix is largely water (70-80% of its weight), along with a network of collagen fibers and proteoglycans. Type II collagen is the predominant collagen type, providing tensile strength to the tissue. Proteoglycans, particularly aggrecan, are large molecules that attract and retain water, helping the tissue resist compressive loads. Specialized cells called chondrocytes are embedded within this matrix, maintaining the cartilage.
How Articular Cartilage Works
Articular hyaline cartilage performs two main biomechanical functions within a joint: providing a low-friction surface and absorbing shock. Its smooth, lubricated surface allows opposing bone ends to glide over each other with minimal resistance during movement. This low friction is partly due to the high fluid content within the cartilage and the presence of lubricin in the synovial fluid, which acts as a boundary lubricant.
The tissue’s ability to withstand and distribute compressive forces is attributed to its unique viscoelastic properties. When a load is applied, interstitial fluid within the cartilage pressurizes, supporting a significant portion of the load, often over 95%. This fluid flow through the porous solid matrix, along with interactions between macromolecules like proteoglycans and collagen, contributes to the cartilage’s elastic and resilient behavior. This allows it to deform under stress and then return to its original shape.
Causes of Cartilage Damage and Degeneration
Articular cartilage, despite its durability, is susceptible to damage and degeneration from various factors. Traumatic injuries, such as direct impacts from sports accidents or falls, can cause immediate and significant damage to the cartilage. These forceful events can lead to chondral injuries, where the damage is limited to the cartilage layer itself.
Repetitive stress or overuse also contributes to cartilage breakdown over time. This occurs in activities that involve repeated impacts or twisting motions on joints. Continuous mechanical loading can overwhelm the cartilage’s repair mechanisms, leading to gradual thinning and degradation. Prolonged periods of joint inactivity can also result in cartilage damage.
Age-related wear and tear is another cause of cartilage degeneration. As individuals age, cartilage can thin and become less resilient. This progressive loss of structure and function can lead to conditions like osteoarthritis, where cartilage progressively thins and fragments, eventually exposing the underlying bone. Due to its limited self-repair capacity, damaged areas often do not heal effectively on their own.
Strategies for Maintaining Cartilage Health
Maintaining a healthy weight reduces the load on weight-bearing joints, lessening stress on articular cartilage. Excess body weight increases joint pressure, accelerating cartilage wear and tear. Adopting a balanced diet that supports weight management can help preserve cartilage health.
Engaging in low-impact exercise is also beneficial for cartilage. Activities such as swimming, cycling, and brisk walking strengthen the muscles around joints, helping absorb shock and reduce direct stress on the cartilage. Movement also aids synovial fluid circulation, a natural lubricant that provides nutrients to the cartilage. Regular stretching and warming up before physical activity can help prevent injuries and protect cartilage.
A balanced, nutrient-rich diet can support overall joint health and cartilage maintenance. Foods rich in omega-3 fatty acids, antioxidants, and vitamins can help reduce inflammation and support collagen synthesis, benefiting cartilage function. Staying hydrated is also important, as cartilage relies on synovial fluid for smooth movement, and dehydration can hinder this. Early intervention for injuries and managing existing conditions are also important to slow cartilage degeneration.