A bump on the knee refers to any noticeable bump or swelling on or around the knee joint. While many are benign, their presence often causes concern. They can arise from various tissues, including fluid-filled sacs, fatty deposits, or bony growths. Understanding their common causes can provide clarity and guide appropriate next steps.
Common Causes of Knee Bumps
Knee bumps can stem from several distinct conditions. One frequent cause is bursitis, an inflammation of bursae, which are small, fluid-filled sacs that cushion bones, tendons, and muscles around joints. The prepatellar bursa, in front of the kneecap, is often affected, leading to a visible, fluid-filled lump, sometimes called “housemaid’s knee” due to prolonged kneeling. Inflammation causes the bursa’s lining to thicken and produce excess fluid, leading to swelling.
Another common bump is a Baker’s cyst (popliteal cyst), a fluid-filled sac behind the knee. It develops when underlying knee issues, like arthritis or cartilage tears, cause excess synovial fluid production. This fluid collects, creating the bulge.
Ganglion cysts are fluid-filled sacs that can appear near joints or tendons. While less common directly on the knee joint surface, they can occur around the knee, sometimes associated with ligaments or meniscal tears. They are generally benign and contain gelatinous fluid.
Lipomas are soft, non-cancerous fatty lumps that can develop anywhere, including around the knee. They feel soft and rubbery, range in size from a pea to several centimeters, and may move slightly under the skin when pressed. These slow-growing bumps are usually painless unless they press on a nerve.
Osteoarthritis, a degenerative joint disease, can lead to the formation of bone spurs. They form along the knee joint margins as cartilage wears away, causing bones to rub. These hard bumps can restrict movement and cause pain.
Rheumatoid nodules are firm lumps that can occur in individuals with rheumatoid arthritis, an autoimmune condition. They typically form under the skin near affected joints, including the knees, and vary in size. While usually not painful, they indicate systemic inflammation.
Infections can manifest as warm, red, and painful swelling around the knee. Skin infections (e.g., cellulitis, abscesses) or joint infections can cause such bumps. Septic bursitis, a bacterial infection of a bursa, is serious and requires immediate medical attention.
Accompanying Symptoms to Note
A knee bump can appear alongside various symptoms, which often provide clues about the underlying cause. Pain is a common symptom, which can be localized to the bump, radiate to other areas, or intensify with movement or at rest. The pain’s nature (e.g., sharp or dull) can also be indicative.
Swelling is frequently observed, either generalized around the knee or localized to the bump. Redness and warmth over the bump suggest inflammation or possible infection.
Limited range of motion or stiffness can make it difficult to bend or straighten the knee. Stiffness might be more noticeable after inactivity, such as in the morning. Tenderness to touch is common, indicating sensitivity in the affected area.
Some individuals might experience clicking, popping, or grinding sensations within the knee, particularly during movement. While sometimes harmless, these sounds can point to issues like cartilage damage or meniscal tears. Fever or chills alongside a knee bump indicate a potential infection and warrant prompt medical attention.
When to Seek Medical Advice
While many knee bumps are harmless, certain signs indicate the need for medical evaluation. Seek medical advice if a knee bump appears suddenly or grows rapidly. Consult a doctor if the bump is accompanied by severe pain, significant redness, or warmth, as these can signal inflammation or infection.
Fever or chills with a knee bump are particularly concerning and suggest possible infection. If the bump limits knee movement, makes weight-bearing difficult, or causes instability, consult a doctor. If the lump feels firm, immobile, attached to underlying structures, or causes numbness, tingling, or weakness in the leg, medical assessment is important. Any new or unusual lump that causes concern, does not improve, or worsens over time should also be evaluated.
Understanding Diagnosis and Management
When evaluating a knee bump, medical professionals begin with a physical examination. This involves assessing the bump’s size, consistency, tenderness, and impact on knee movement. The doctor also checks for warmth, redness, and associated pain.
Further diagnostic tools may be utilized. X-rays can identify bone issues, such as bone spurs or fractures. Ultrasound imaging is effective for visualizing fluid-filled cysts (e.g., Baker’s cysts, bursitis) and other soft tissue abnormalities. Magnetic Resonance Imaging (MRI) provides detailed images of soft tissues, cartilage, ligaments, and the joint, aiding in diagnosing complex conditions or internal derangements. If infection or inflammatory conditions are suspected, blood tests or fluid aspiration from the bump for laboratory analysis may be performed.
Management varies by diagnosis but often begins with conservative measures, such as rest, ice, compression, and elevation (RICE protocol). Over-the-counter pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs), can manage discomfort and inflammation. Physical therapy may improve knee strength, flexibility, and range of motion. For persistent symptoms, medical interventions like fluid aspiration from a cyst or bursa, or corticosteroid injections to reduce inflammation, might be considered. In certain situations, particularly for persistent, symptomatic, or problematic bumps unresponsive to conservative treatments, surgical intervention may be necessary.