A lump on the side of your knee can be concerning. While many are harmless, some indicate underlying issues that warrant medical attention. Understanding the possible causes and accompanying symptoms helps determine when professional evaluation is appropriate.
Potential Causes of a Knee Lump
Meniscal cysts are a common cause of a lump on the side of the knee. These fluid-filled sacs typically form when there is a tear in the meniscus, the cartilage that cushions the knee joint. Fluid can leak out from the tear and collect, creating a noticeable bump, often on the lateral side of the knee. Meniscal cysts are usually associated with pain and tenderness along the joint line where the meniscus is torn.
Bursitis is another common cause, involving the inflammation of a bursa, a small, fluid-filled sac that reduces friction between bones, tendons, and muscles. While prepatellar bursitis typically affects the front of the kneecap, iliotibial bursitis can cause pain and swelling on the outside of the knee. This occurs when the iliotibial bursa, located between the shin bone and the iliotibial band, becomes inflamed.
Ganglion cysts can develop around the knee joint, though they are more common in the wrist. These are benign, fluid-filled masses that contain a thick, jelly-like substance. They can appear near joints or tendon sheaths and may or may not be painful, depending on their size and location. They can sometimes cause discomfort or interfere with knee movement.
Less commonly, a lipoma might present as a lump on the side of the knee. A lipoma is a benign growth of fatty tissue that forms just beneath the skin. These lumps are generally soft, movable, and usually painless, though they can cause discomfort if they press on a nerve or grow near a joint. While they can occur anywhere on the body, intra-articular lipomas within the knee joint are rare.
Though often located at the back of the knee, a Baker’s cyst, also known as a popliteal cyst, can occasionally present with a more lateral or posterolateral appearance. These fluid-filled sacs form when excess fluid from the knee joint, often due to arthritis or a meniscus tear, accumulates behind the knee. While typically found posteriorly, a lateral presentation, though unusual, has been reported. In rare instances, a lump could be a benign or malignant tumor, such as an osteochondroma or other soft tissue tumors. Their characteristics can vary, from painless bony masses to hard, immovable lumps.
Accompanying Symptoms to Note
A lump on the side of the knee can manifest with various accompanying symptoms that offer clues about its underlying cause. Pain is a common symptom, which can range from a dull ache to sharp, intense discomfort, and may worsen with specific movements or activities. The nature of the pain—whether constant, intermittent, or present only during weight-bearing—can be significant.
Tenderness to the touch is a frequent indicator, particularly if the lump is inflamed or irritated. The area around the lump might also feel warm to the touch or appear red, suggesting inflammation or, in some cases, an infection. Swelling that extends beyond the immediate area of the lump itself, affecting the entire knee joint or even the lower leg, can also occur.
Changes in the skin over the lump, such as discoloration or tightness, may be observed. The lump itself may change in size or consistency over time, becoming larger with activity and possibly smaller with rest. Restricted range of motion, difficulty bending or straightening the knee, or a feeling of stiffness can also accompany a knee lump, impacting daily activities and mobility.
When to Consult a Doctor
Consult a healthcare professional for any new or concerning lump on the side of your knee, especially if it appears suddenly or grows rapidly. Severe pain that limits your ability to bear weight or move your knee warrants prompt medical attention. Changes in the lump’s characteristics, such as it becoming hard, immovable, or developing new pain, require evaluation.
Signs of infection, including fever, chills, or spreading redness and warmth around the lump, require immediate medical attention. Numbness or tingling in the leg or foot, or any significant changes in skin color, are important symptoms to report. Even if the lump is painless, persistent presence or any worry about its nature warrants a doctor’s visit for accurate diagnosis.
Medical Evaluation and Management
When seeking medical attention for a knee lump, a healthcare professional begins with a thorough medical history, asking about the lump’s onset, associated symptoms, and general health. A physical examination follows, where the doctor inspects and palpates the lump to assess its size, consistency, mobility, and tenderness, also evaluating knee range of motion and stability.
Diagnostic imaging studies are utilized to further investigate the lump. An X-ray checks for bone involvement or abnormalities. Magnetic Resonance Imaging (MRI) provides detailed images of cysts, tumors, and other soft tissue structures. Ultrasound assesses fluid-filled masses and guides aspiration if needed.
Management varies based on the underlying cause of the lump. For many benign conditions, conservative treatments are the first approach. These include rest, ice, compression, and elevation (RICE protocol). Physical therapy may improve knee strength, flexibility, and overall function.
Medications, such as over-the-counter anti-inflammatory drugs, manage pain and inflammation. In some cases, aspiration of fluid from a cyst relieves pressure and confirms diagnosis. If conservative measures are insufficient or the lump causes significant symptoms, more invasive procedures like injections or surgical removal may be considered, depending on the diagnosis.