Knee Swelling: Causes of a Swollen Knee Joint

The knee bears the body's weight with every step. When the knee joint swells, the person sees the result of a process occurring inside a closed cavity. Let us break down where the fluid there comes from, what causes lie behind it, and when a visit to the doctor cannot be postponed.

What knee swelling looks like and what happens in the joint

The knee joint is assembled from bones, cartilage, ligaments and fluid, and muscles and tendons help it move. Any of these structures, damaged or diseased, makes itself known through pain and difficulty walking. The synovial membrane lines the joint cavity; its inflammation is called synovitis — the process is confined to its limits and manifests as an accumulation of effusion in the cavity it lines. Synovitis most often occurs in the knee, elbow, wrist and ankle joints.

Traumatic causes of knee swelling

Sprains cause pain after overloading, excessive stretching or twisting, often during exercise. Tendinitis manifests as pain between the patella and the shin; it is often provoked by repetitive running and jumping. A tear of a ligament, tendon or meniscus and cartilage damage look different: the joint is unstable, gives way when trying to stand up, the leg cannot be straightened, and a pop may occur at the moment of injury. Patellar dislocation changes its shape after a collision or a sudden change of direction. Hemorrhage into the joint cavity causes swelling, warmth and bruising; it is more likely in people on anticoagulants.

Knee swelling in arthrosis and inflammatory joint diseases

The most common knee disease is osteoarthritis: cartilage gradually wears away, causing pain and swelling. The picture is recognizable: pain and stiffness in both knees, moderate swelling, more often in older people. Synovitis is present in many cases of osteoarthritis, and in rheumatoid arthritis it occurs more often than in other variants; the membrane also becomes inflamed in lupus and gout. A warm red knee in which kneeling or bending increases pain and swelling is described in bursitis. A hot red joint with sudden attacks of very severe pain is the picture of gout or septic arthritis. In adolescents, swelling below the patella is associated with Osgood-Schlatter disease.

Knee swelling with pain when walking: what to look at first

In descriptions of causes, swelling more often goes together with pain, stiffness or warmth around the joint. A simple dividing line then helps — whether there was an obvious injury. After overloading, twisting or a collision, one thinks of a sprain, ligament and meniscus tears, patellar dislocation, hemorrhage into the joint. If there was no injury, the range of causes is different: arthrosis, bursitis, gout, septic arthritis, and in adolescents — Osgood-Schlatter disease.

Diagnosis and which doctor to see

If the pain does not go away within a few weeks or the knee is swollen, see a doctor: they examine the joint and decide what to do next. Further direction is determined by the doctor after the examination: it may be physical therapy, medications, a scan or specialized treatment, including surgery.

• examination by a doctor;
• X-ray;
• MRI;
• arthroscopy;
• arthrography.

Urgent medical attention is needed if the knee is very painful, cannot move, cannot be leaned on, is severely swollen or has changed shape, locks, gives way or clicks painfully. Painless clicking is normal.

A swollen knee by itself is not a reason to call an ambulance. 103/112 — if a very high temperature (or chills) is combined with redness and heat around the knee: this may be a sign of infection.

The material is for reference: it explains the mechanics of swelling but does not replace a doctor's consultation — the final answer is given by examination.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer