Articular Cartilage: Function, Damage & Treatment

What is Articular Cartilage?

Articular cartilage (Latin: Cartilago articularis) is a specialized form of hyaline cartilage that covers the contact surfaces of bones in movable joints. It is composed primarily of type II collagen, proteoglycans, and water, which together form an elastic, shock-absorbing matrix. Because articular cartilage contains no blood vessels, it receives nutrients through the synovial fluid that fills the joint cavity. This unique structure allows cartilage to absorb compressive forces and enable smooth joint motion.

Structure and Function

Articular cartilage is organized into several distinct layers, each with specific mechanical properties:

• Superficial zone: Contains flat, parallel collagen fibers and provides a smooth surface to minimize friction.
• Middle zone (transitional zone): Provides compressive strength through obliquely arranged collagen fibers.
• Deep zone (radial zone): Collagen fibers run perpendicular to the bone, anchoring the cartilage firmly.
• Calcified zone: Connects the cartilage to the underlying subchondral bone.

The main functions of articular cartilage are load distribution, shock absorption during movement, and ensuring nearly frictionless gliding of joint surfaces.

Common Diseases of Articular Cartilage

Due to its limited regenerative capacity, articular cartilage is susceptible to several conditions:

• Osteoarthritis: The most common joint disease, characterized by progressive cartilage breakdown leading to pain, stiffness, and reduced mobility.
• Chondropathy: A general term for degenerative or inflammatory changes in cartilage, commonly affecting the kneecap (chondromalacia patellae).
• Osteochondritis dissecans: A condition where a segment of cartilage and underlying bone can die and detach from the joint surface.
• Traumatic cartilage injuries: Damage caused by sports accidents or excessive mechanical loading.

Causes of Cartilage Damage

Cartilage damage can result from a variety of factors:

• Overuse and chronic wear (e.g., from sports or physical labor)
• Acute injuries and trauma (e.g., sports accidents)
• Joint malalignment (e.g., valgus or varus deformities)
• Inflammatory joint diseases such as rheumatoid arthritis
• Genetic predisposition and natural aging processes
• Excess body weight, which increases joint loading

Symptoms of Cartilage Damage

Because articular cartilage itself contains no pain receptors, symptoms often appear only once surrounding structures are affected:

• Joint pain and discomfort, especially during physical activity
• Joint swelling and stiffness, particularly in the morning
• Clicking or grinding sensations in the joint (crepitus)
• Reduced range of motion in the affected joint
• Joint effusion (accumulation of fluid within the joint)

Diagnosis

Several diagnostic methods are available to assess articular cartilage:

• MRI (Magnetic Resonance Imaging): The gold standard for imaging cartilage defects, providing detailed visualization of soft tissues.
• X-ray: Indicates indirect cartilage loss through joint space narrowing and bony changes.
• Arthroscopy: Direct visual inspection of cartilage through minimally invasive joint surgery.
• Ultrasound: Can provide limited assessment of joint effusion and cartilage thickness.

Treatment

Treatment of articular cartilage damage depends on the severity and underlying cause:

Conservative Treatment

• Physiotherapy and targeted muscle strengthening to reduce joint loading
• Pain management with anti-inflammatory medications (e.g., NSAIDs)
• Intra-articular hyaluronic acid injections to improve joint lubrication
• Weight reduction to decrease mechanical stress on the joint
• Orthotic devices and insoles to correct malalignment

Surgical Treatment

• Microfracture: Small perforations in the bone stimulate the formation of fibrocartilage repair tissue.
• Autologous Chondrocyte Implantation (ACI): The patient's own cartilage cells are harvested, cultured in a laboratory, and reimplanted into the defect.
• Osteochondral Autograft Transfer (OATS): Cartilage-bone cylinders are taken from less load-bearing areas and transplanted into the defect.
• Joint replacement (endoprosthesis): A last resort for advanced cartilage degeneration.

Regeneration and Prevention

Due to its avascular nature, articular cartilage has very limited self-healing capacity. Preventive measures are therefore especially important:

• Regular, joint-friendly physical activity (e.g., swimming, cycling)
• Maintaining a healthy body weight
• A balanced diet rich in vitamin C, vitamin D, and omega-3 fatty acids
• Avoiding excessive joint overloading
• Seeking medical advice early for persistent joint complaints

References

1. Buckwalter, J. A. & Mankin, H. J. (1998): Articular cartilage: degeneration and osteoarthritis, repair, regeneration, and transplantation. In: Instructional Course Lectures, 47, pp. 487–504.
2. World Health Organization (WHO): Musculoskeletal conditions. Available at: https://www.who.int/news-room/fact-sheets/detail/musculoskeletal-conditions
3. Mow, V. C. & Huiskes, R. (Eds.) (2005): Basic Orthopaedic Biomechanics and Mechano-Biology. 3rd edition. Lippincott Williams & Wilkins, Philadelphia.