Articular cartilage is a specialized tissue that lines the ends of the bones within the knee joint. This smooth, resilient covering is located on the surfaces of the femur (thighbone), tibia (shinbone), and patella (kneecap) where they meet. Its primary function is to provide a near-frictionless gliding surface, allowing the knee to bend and straighten easily. The cartilage also acts as a shock absorber, helping to evenly distribute the forces and pressures placed upon the joint during movement and weight-bearing activities.
Key Symptoms Indicating Cartilage Damage
One of the most common indicators of damaged knee cartilage is a persistent, deep ache that often worsens with activity. This pain may initially be a dull discomfort but can escalate to sharp, stabbing pain during specific movements like squatting, twisting, or climbing stairs. Unlike pain from a muscle strain, cartilage-related pain frequently feels like it originates from deep within the joint itself.
Mechanical symptoms are highly specific to cartilage issues, involving physical interference with the knee’s motion. The knee may experience “catching,” a brief, momentary snag or hesitation during movement, or “locking,” where the joint completely jams and cannot be fully straightened or bent. This locking sensation often results from a fragment of torn cartilage becoming momentarily trapped between the joint surfaces.
Another frequent sign is the sensation or sound of grinding, clicking, or popping, medically known as crepitus, when the knee moves. This noise occurs as the now-roughened cartilage surfaces scrape against each other, indicating a loss of the smooth protective layer. Swelling, or effusion, is also a common response to irritation within the joint, presenting as intermittent puffiness or chronic fluid buildup around the knee. This swelling can be a sign that the joint lining is inflamed by cartilage debris or increased friction.
Common Mechanisms of Injury
Cartilage damage typically results from one of two distinct processes: a sudden, high-force event or a gradual, long-term breakdown. Acute traumatic injury involves a specific, identifiable moment of damage, often occurring during sports or accidents. This can be caused by a direct blow to the knee, a severe fall, or a sudden, forceful twisting motion while the foot is planted on the ground. Such events can lead to a tear or a full-thickness lesion where the cartilage is sheared away from the underlying bone.
Conversely, damage can occur through degenerative wear and tear, which is a slow, progressive process. This gradual breakdown is often associated with aging and repetitive stress placed on the joint over many years. The continued friction and loading cause the articular cartilage to soften, flake, and thin out, eventually exposing the bone beneath. This degenerative process is the underlying mechanism that leads to the development of osteoarthritis, where the entire joint structure deteriorates.
How Doctors Confirm Cartilage Damage
Confirming cartilage damage begins with a thorough physical examination, where the physician assesses the patient’s range of motion, checks for tenderness along the joint line, and looks for signs of swelling. Specific maneuvers are performed to provoke symptoms like clicking or catching, which can help pinpoint the location and type of internal damage. The doctor also evaluates the knee’s stability to determine if ligaments are also affected.
Imaging studies are then used to visualize the joint’s internal structures. An X-ray is typically the first test ordered, though it cannot show cartilage directly, as cartilage is radiolucent. X-rays are useful for ruling out bone fractures and for observing signs of advanced degeneration, such as narrowing of the joint space, which suggests cartilage loss. Magnetic Resonance Imaging (MRI) is considered the most effective non-invasive method for diagnosing cartilage damage, providing detailed images of soft tissues. The MRI can clearly show the size and depth of a cartilage defect, identify irregularities on the joint surface, and detect any loose fragments.
For the most definitive diagnosis, especially when surgical repair is being considered, a procedure called arthroscopy may be performed. This involves inserting a tiny camera through small incisions into the joint, giving the surgeon a direct, real-time view of the cartilage surface. Arthroscopy allows the surgeon to accurately grade the severity of the damage, from minor softening to a full-thickness defect that exposes the bone.
Immediate Actions After Injury
If you suspect a sudden knee cartilage injury, the immediate first aid protocol to follow is Rest, Ice, Compression, and Elevation (RICE). Resting the joint means avoiding activities that cause pain and may involve using crutches to keep weight off the leg. Applying ice for about 15 to 20 minutes several times a day helps reduce pain and limit initial swelling in the joint.
Compression with a soft bandage or wrap helps control swelling, while elevating the leg above the level of the heart also assists in reducing fluid accumulation. Over-the-counter anti-inflammatory medications, such as ibuprofen or naproxen, can be used to manage pain and reduce the inflammatory response in the short term.
You should seek urgent medical attention if you experience an inability to bear any weight on the injured leg or if the knee appears visibly deformed. Severe, persistent pain or rapid, extensive swelling that develops immediately after the injury also warrants a prompt evaluation by a healthcare professional. If symptoms like pain, stiffness, or mechanical issues do not improve significantly after a few days of home care, a medical consultation is recommended for proper diagnosis.