Knee Lumps: Causes, Types, Characteristics, and When to Seek Medical Attention

Why Is There a Big Lump On My Knee?

A lump on the knee can arise from various sources, ranging from benign fluid accumulations and soft tissue growths to bone abnormalities or inflammatory conditions, often signaling an underlying issue within the knee joint or surrounding structures.

Understanding Your Knee's Complex Anatomy

The knee is one of the body's largest and most complex joints, crucial for movement and weight-bearing. It's formed by the articulation of three bones: the femur (thigh bone), tibia (shin bone), and patella (kneecap). Supporting this structure are an intricate network of ligaments, tendons, muscles, cartilage (menisci), and bursae (small fluid-filled sacs that reduce friction). A lump can originate from any of these components, or from fat, blood vessels, or nerves in the vicinity. Understanding this complexity is key to identifying the potential cause of a new lump.

Common Causes of Knee Lumps: A Comprehensive Overview

Identifying the exact cause of a knee lump requires professional medical evaluation, but several common conditions account for the majority of cases.

• Bursitis: Inflammation of a bursa, a small fluid-filled sac that cushions bones, tendons, and muscles around joints.
  • Prepatellar Bursitis ("Housemaid's Knee"): Swelling over the kneecap, often caused by repetitive kneeling or direct trauma. The lump is typically soft and movable.
  • Infrapatellar Bursitis ("Clergyman's Knee"): Swelling just below the kneecap, often due to kneeling or direct impact.
  • Pes Anserine Bursitis: Swelling on the inner side of the knee, below the joint line, common in runners or those with osteoarthritis.
• Baker's Cyst (Popliteal Cyst): A fluid-filled sac that forms at the back of the knee. It's often a symptom of an underlying knee problem, such as arthritis, meniscus tear, or other inflammatory conditions, causing excess joint fluid to bulge into the bursa. It can feel soft or firm and may fluctuate in size.
• Meniscal Cyst: A firm, localized lump that develops on the joint line (either inner or outer side of the knee) and is directly associated with a meniscal tear. It's caused by synovial fluid leaking from the torn meniscus.
• Ganglion Cyst: While more common around the wrist or ankle, ganglion cysts can occasionally appear around the knee joint. These are benign, fluid-filled sacs that arise from a joint capsule or tendon sheath. They are typically soft, movable, and non-tender unless pressing on a nerve.
• Lipoma: A benign fatty tumor that can develop anywhere on the body, including around the knee. These are typically soft, movable, and painless lumps that grow slowly.
• Osteochondroma: A benign bone tumor that typically develops near the ends of long bones, often around the knee joint, especially in adolescents and young adults. It feels hard and fixed, as it's an outgrowth of bone.
• Tendonitis/Tendinopathy: Inflammation or degeneration of a tendon can cause localized swelling or thickening that feels like a lump.
  • Patellar Tendinopathy ("Jumper's Knee"): Swelling or thickening just below the kneecap, often due to overuse in jumping sports.
  • Quadriceps Tendinopathy: Swelling or thickening just above the kneecap.
• Arthritis-Related Swelling (Effusion) or Osteophytes:
  • Joint Effusion: General swelling of the knee joint due to excess synovial fluid, often from osteoarthritis, rheumatoid arthritis, or post-traumatic inflammation. This isn't a "lump" per se but can present as diffuse swelling.
  • Osteophytes (Bone Spurs): Bony growths that can develop around the joint margins due to osteoarthritis. While generally not a distinct "lump," a large spur might be palpable.
• Trauma-Related Swelling (Hematoma): A direct impact or injury to the knee can cause bleeding under the skin (hematoma), leading to a firm or soft lump that may be discolored (bruised).
• Malignant Tumors (Rare): While rare, cancerous tumors (e.g., osteosarcoma, soft tissue sarcoma) can present as a lump on or around the knee. These are often hard, fixed, and may be accompanied by persistent pain, night pain, or unexplained weight loss.

Characteristics of Knee Lumps: What to Observe

When you notice a lump, consider its characteristics as they can provide clues to its nature:

• Location: Is it over the kneecap, behind the knee, to the side, or on the joint line?
• Texture: Is it soft and squishy (fluid-filled), firm, or hard and bony?
• Mobility: Does it move freely under the skin, or is it fixed to underlying structures?
• Pain Level: Is it painless, tender to the touch, or painful with movement or at rest?
• Size Changes: Does it fluctuate in size, or has it been steadily growing?
• Associated Symptoms: Is there redness, warmth, bruising, fever, limited range of motion, or instability?

When to Seek Professional Medical Attention

While many knee lumps are benign, it's always prudent to have any new or concerning lump evaluated by a healthcare professional. Seek immediate medical attention if the lump is accompanied by:

• Severe pain, especially if it interferes with daily activities or sleep.
• Rapid increase in size.
• Redness, warmth, or fever, indicating possible infection.
• Inability to bear weight on the leg.
• Significant limitation of knee movement.
• Numbness or tingling in the leg or foot.
• The lump feels hard and fixed to the bone.
• You have a history of cancer.

Diagnosis and Treatment Approaches

A healthcare professional, such as a general practitioner, orthopedist, or sports medicine physician, will typically conduct a thorough physical examination, including palpation of the lump and assessment of knee range of motion and stability.

Diagnostic tools may include:

• X-ray: To evaluate bone structures and rule out bony growths or fractures.
• Ultrasound: Excellent for visualizing soft tissue structures, fluid collections (bursitis, cysts), and guiding aspiration.
• MRI (Magnetic Resonance Imaging): Provides detailed images of soft tissues, including ligaments, tendons, menisci, and cysts, offering the most comprehensive view.
• CT Scan: May be used for more detailed bone imaging in specific cases.
• Aspiration: Fluid may be drawn from a fluid-filled lump (e.g., bursa, cyst) for analysis to rule out infection or inflammatory conditions.
• Biopsy: In rare cases, if a solid mass is suspected to be a tumor, a biopsy may be performed to determine if it is benign or malignant.

Treatment depends entirely on the underlying cause:

• Conservative Management: Rest, ice, compression, elevation (RICE), anti-inflammatory medications (NSAIDs), physical therapy, and activity modification are common for inflammatory conditions like bursitis or tendinopathy.
• Aspiration and Injection: For large, symptomatic bursitis or cysts, fluid may be drained, and corticosteroids may be injected to reduce inflammation.
• Surgical Intervention: May be necessary for persistent Baker's cysts, symptomatic meniscal cysts, large lipomas, osteochondromas, or in cases of malignant tumors.

Prevention and Management Strategies

While not all knee lumps are preventable, general knee health practices can reduce the risk of some common causes:

• Maintain a Healthy Weight: Reduces stress on the knee joint.
• Strengthen Surrounding Muscles: Strong quadriceps, hamstrings, and glutes provide better knee support.
• Proper Warm-up and Cool-down: Prepare muscles and joints for activity and aid recovery.
• Gradual Increase in Activity: Avoid sudden increases in training intensity or volume.
• Use Proper Form: Especially during exercise or activities involving repetitive knee movements.
• Wear Appropriate Footwear: Support and cushioning can impact knee mechanics.
• Use Knee Pads: If your activities involve prolonged kneeling.

Conclusion

A lump on the knee is a common concern that can stem from a wide array of conditions, from benign fluid collections to more serious, though rare, pathologies. While many causes are harmless and respond well to conservative treatment, understanding the potential origins and knowing when to seek professional medical advice is paramount. Timely and accurate diagnosis by a healthcare professional is crucial for determining the underlying cause and establishing the most appropriate treatment plan to ensure optimal knee health and function.