Knee Arthritis
The knee is one of the largest and most complex joints in the body, comprised of the femur (thigh bone), tibia (shin bone) and patella (kneecap). Between the bones are two C-shaped menisci and a smooth layer of cartilage that cushions and protects the bones during movement. When cartilage wears down, the bones begin to rub against each other, leading to pain, inflammation and restricted motion. Over time, this process alters the normal biomechanics of the knee and can result in deformity.
Knee arthritis is a common and progressive condition that affects millions of people worldwide. At its core, arthritis in the knee involves inflammation and degradation of the joint structures that allow the knee to move smoothly. It can lead to significant pain, stiffness, loss of function and diminished quality of life if left unmanaged.
There are several types of knee arthritis, but the most prevalent in adults is osteoarthritis.
- Osteoarthritis is often described as “wear-and-tear” arthritis because it develops gradually and is associated with aging and repetitive stress on the joint.
- Another form of knee arthritis is rheumatoid arthritis, an autoimmune disease in which the body’s immune system mistakenly attacks the joint lining, causing inflammation and joint damage.
- Post-traumatic arthritis can occur after a serious knee injury, such as a fracture or ligament tear, and may accelerate cartilage loss.
- Inflammatory arthritis is less common. Infections and metabolic disorders can contribute to inflammatory arthritis affecting the knee.
Symptoms of knee arthritis vary depending on the severity of joint damage but typically include pain, stiffness, swelling and reduced range of motion. Pain is often the most noticeable symptom and may be present during activity, at rest or at night. It may begin as mild discomfort and progress to a constant ache that interferes with daily activities. Stiffness is especially noticeable after periods of inactivity, such as upon waking in the morning or after sitting for a long time. This stiffness can limit the ability to fully bend or straighten the knee.
Swelling around the knee joint is another hallmark feature. In osteoarthritis, the joint may feel warm and appear enlarged due to inflammation. Individuals with inflammatory types of arthritis, such as rheumatoid arthritis, may notice more pronounced swelling and warmth as part of a systemic process. Mechanical symptoms, such as catching, locking or a sensation of instability, can also occur when loose fragments of cartilage or bone interfere with normal joint movement. A grinding or crunching sensation known as crepitus may be felt or heard when the knee moves.
The causes of knee arthritis are multifactorial. Aging is a significant risk factor, as cartilage naturally becomes thinner and less resilient over time. Genetics also influence susceptibility; some individuals inherit traits that make their cartilage more prone to breakdown. Previous knee injuries, including meniscus tears, ligament injuries or fractures, significantly increase the risk of developing post-traumatic arthritis later in life. Repetitive stress from occupational or athletic activities that load the knee joint can accelerate cartilage wear.
Obesity is a major contributing factor because excess body weight places additional stress on the knee with every step. Metabolic conditions, such as diabetes, have been associated with cartilage degeneration and inflammation, although the precise mechanisms remain under study. Autoimmune inflammatory diseases, including rheumatoid arthritis and psoriatic arthritis, lead to systemic inflammation that targets joint tissues, causing rapid structural damage if not appropriately controlled.
Diagnosing knee arthritis involves a comprehensive clinical evaluation that begins with a detailed medical history and physical examination. During the history, the clinician will ask about the onset, duration and pattern of symptoms, as well as any prior knee injuries, underlying medical conditions and lifestyle factors such as activity level and weight. The physical examination focuses on assessing knee alignment, range of motion, swelling, tenderness and stability. Specific maneuvers can help differentiate between arthritis and other sources of knee pain, such as tendon or ligament pathology.
Imaging studies are essential to confirming the diagnosis and assessing the extent of joint damage. Plain radiographs (X-rays) are typically the first imaging modality used and can reveal characteristic features of arthritis. Magnetic resonance imaging (MRI) provides a more detailed view of soft tissues, meniscal integrity and cartilage, and is valuable when the diagnosis is uncertain or when surgical planning is being considered.
Laboratory tests may be ordered when an inflammatory or systemic cause of arthritis is suspected. Blood tests can identify markers of inflammation and specific antibodies associated with autoimmune diseases. Joint aspiration, in which fluid is drawn from the knee with a needle, may be performed to analyze the fluid for infection, crystals or inflammatory cells, especially when there is significant swelling or concern for a septic or crystal-induced arthritis.
In summary, knee arthritis is a progressive condition marked by cartilage loss, pain, stiffness and functional decline. It arises from aging, injury, inflammatory diseases, mechanical stress and metabolic factors. Early recognition of symptoms and a structured diagnostic approach, including history, physical examination, imaging and selective laboratory tests, are essential for accurate diagnosis and appropriate management. Individuals experiencing persistent knee pain or functional limitations should seek evaluation by specialists skilled in joint preservation to develop individualized treatment plans that address both symptoms and underlying joint health.
