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What is Articular Cartilage?
Articular cartilage is a highly specialized connective tissue found in all movable joints of the body. Its primary functions include cushioning, producing synovial fluid, and facilitating load transmission with low friction. It also serves a protective role for bones, maintaining proper distance between them, allowing smooth movement while absorbing shocks. Articular cartilage is white, shiny, and relatively hard, with a unique structure resistant to wear and compression. In the knee joint, it covers the lateral and medial femoral condyles, the upper part of the tibia, and the articular part of the patella.
The cartilage is approximately 2-4 mm thick and lacks blood vessels, lymphatics, and nerves. Unfortunately, it has limited self-healing and regeneration abilities. It is particularly sensitive and prone to rapid degradation once damaged, which makes maintaining it in good condition critical for joint health. Its complex structure makes the treatment and reconstruction of defects a challenge for the patient, surgeon, and physiotherapist.
Articular Cartilage Damage
The pathology of articular cartilage is a broad topic, encompassing both traumatic injuries and chronic disease processes. The primary component of the joint surface is hyaline cartilage. If it becomes damaged, the joint surface ceases to be smooth, which can lead to pain. Articular surface damage in the knee is relatively common. Several scenarios can lead to its damage, with the most frequent causes being various types of trauma or accelerated wear that results in osteoarthritis. The goal of cartilage repair procedures is to stimulate the growth of new hyaline cartilage, form a cartilage scar, or fix the damaged cartilage fragment.
Assessment of Cartilage Damage Using the Outerbridge Scale
- Grade 1: Softening and swelling (edema) of the cartilage.
- Grade 2: Partial-thickness cracks and fragmentation (fissures <1.25 mm).
- Grade 3: Full-thickness cracks (fissures >1.25 mm) extending to the subchondral bone without exposing the bone.
Grade 4: Defects exposing the subchondral bone.
Grades I and II are typically treated non-operatively, while Grades III and IV often require surgical intervention.
Causes of Articular Cartilage Damage
One of the primary causes is trauma leading to physical damage to the articular cartilage. This can be a sudden impact on the cartilage, resulting from falling directly on the knee, such as during sports or motor vehicle accidents. This injury can often occur in conjunction with damage to other knee structures, particularly ligaments and menisci. When ligament or meniscal injuries lead to limb axis misalignment, muscle weakness, and impaired joint mechanics, the risk of articular surface damage increases. If the knee joint is unstable, operates incorrectly, or the patella is displaced to one side, excessive pressure may be applied to specific parts of the articular surface, accelerating cartilage degeneration.
Most of these cases affect young or middle-aged people who are active or engage in professional sports. Another large group includes individuals whose cartilage damage is caused by osteoarthritis — knee degeneration. This primarily affects individuals over 50 years of age or those suffering from obesity. Prolonged limb immobilization can also affect cartilage condition. Articular cartilage is nourished through joint movement, so prolonged immobilization due to trauma or injury can result in cartilage damage.
Symptoms of Articular Cartilage Damage
- The most characteristic symptom is pain within the joint.
- Knee pain may force changes in gait, which can consequently lead to misalignment and hip pain.
- Inflammation causing the knee area to become warm, sensitive, and painful.
- Joint effusion (swelling).
- Joint stiffness.
- Limited range of motion – as the damage progresses, the affected limb will not move as freely as the healthy one.
- A sensation of "catching" during joint flexion.
- Knee joint instability.
- A feeling of weakness in the limb.
- In severe cases, a piece of cartilage may break off, leading to joint locking.
- Crepitus or grinding sounds during flexion or joint movement.
How is Cartilage Damage Diagnosed?
Distinguishing articular cartilage damage from sprains or ligament injuries is not easy, as symptoms can be similar. However, modern non-invasive tests make diagnosis much simpler than before. Diagnosis involves a patient interview, a clinical knee assessment, and a series of physical tests. Details about the history of the condition, such as a specific incident (e.g., an accident or sudden sports injury) or gradual onset of symptoms, are very informative.
After conducting a physical examination, the physician may order imaging tests. X-rays can rule out fractures within the joint and determine joint space width and alignment. Ultrasound (USG) is limited in assessing cartilage but can provide valuable information in the hands of an experienced diagnostician. MRI (Magnetic Resonance Imaging) allows precise diagnosis of the injury's extent and evaluates the condition of other knee structures, making it the gold standard in diagnosing cartilage damage.
How is Damaged Articular Cartilage Treated?
Conservative Treatment
For minor injuries with mild symptoms, initial steps can be taken at home. During the first few days, protect the joint from further damage using a knee brace, rest while elevating the affected limb, and apply ice packs regularly. Over-the-counter pain relievers like paracetamol or NSAIDs can be taken for severe pain. If symptoms persist after a few days, consult an orthopedic specialist for further treatment.
Non-surgical treatment focuses on returning the patient to daily activities and an active lifestyle, relieving pain, and improving joint function. The orthopedic surgeon selects the treatment method based on factors such as the cause, severity of the damage, patient age, overall health, and activity level. Conservative treatment, particularly for Grade I and II damage, involves physiotherapy exercises, strengthening surrounding muscles, improving stability, and enhancing range of motion. Hyaluronic acid injections can also lubricate the joint and reduce friction.
Surgical Treatment
When cartilage wear is significant and conservative methods fail, surgery becomes the best solution. The goal of surgical treatment is to eliminate symptoms and prevent degenerative changes through structural and biomechanical cartilage reconstruction. Depending on the damage grade, extent, and patient age, options include microfracture, drilling, advanced techniques like collagen membranes, autologous cartilage grafts, and cell cultures.
Cartilage Repair Using the AMIC Method
AMIC (Autologous Matrix-Induced Chondrogenesis) involves covering cartilage defects with collagen membranes and stimulating bone marrow-derived stem cells. The minimally invasive arthroscopic technique allows precise placement of collagen patches into damaged areas.
Rehabilitation After Cartilage Reconstruction
Rehabilitation is a critical factor in recovery, lasting approximately 32 weeks. It involves reducing pain and swelling, restoring full range of motion, and rebuilding muscle strength. Progress evaluations like the Biomechanical Functional Assessment (BOF) guide rehabilitation adjustments.
Prevention
Patient education on injury prevention, maintaining a healthy weight, and proper nutrition is crucial for avoiding cartilage damage. Early preventive measures can help avoid surgery.
Related Articles:
Explore other possible causes of knee pain in different areas of the joint.
References:
- National Library of Medicine - "The basic science of articular cartilage" - Alice J. Sophia Fox, MSc, Asheesh Bedi, MD, and Scott A. Rodeo 2009
- Orthoinfo - Articular Cartilage Restoration – 2009
- Medical News Today - "What you need to know about cartilage damage" - Medically reviewed by William Morrison, M.D. — Written by Tim Newman on December 15, 2017
