Pea-Sized Lump on Kneecap: Causes, Diagnosis, and Treatment Options

What is the pea-sized lump on my knee cap?

A pea-sized lump on your kneecap (patella) can arise from various causes, most commonly benign conditions like bursitis or cysts, but it always warrants professional medical evaluation to ensure an accurate diagnosis and appropriate management.

Understanding Lumps on the Kneecap

The knee joint is a complex structure, and the patella, or kneecap, is a sesamoid bone embedded within the quadriceps tendon, serving as a fulcrum to enhance the leverage of the thigh muscles. Due to its superficial location and exposure to impact and repetitive stress, lumps can occasionally develop on or around it. While many are benign, understanding the potential causes is crucial.

Common Causes of a Pea-Sized Lump on the Kneecap

When evaluating a lump on the kneecap, several conditions are commonly considered:

• Prepatellar Bursitis: Often referred to as "housemaid's knee" or "carpenter's knee," this is arguably the most frequent cause of a lump directly on the kneecap. The prepatellar bursa is a small, fluid-filled sac located between the skin and the front of the kneecap. Its purpose is to reduce friction during knee movement.
  • Cause: Repetitive kneeling, direct trauma, or sometimes infection.
  • Characteristics: The lump is typically soft, fluid-filled, and can range from pea-sized to much larger. It may be painful, warm, and red, especially if inflamed or infected.
• Ganglion Cyst: These are non-cancerous, fluid-filled sacs that typically form on joints or tendon sheaths. While more common on the wrist or ankle, they can occur around the knee joint, including the front of the patella.
  • Cause: Often unknown, but can be related to joint or tendon irritation.
  • Characteristics: Usually firm but can be slightly yielding, often painless unless pressing on a nerve, and fixed in position.
• Lipoma: A lipoma is a benign (non-cancerous) fatty tumor that grows slowly beneath the skin. They can occur anywhere on the body, including the knee.
  • Cause: Unknown, but often genetic.
  • Characteristics: Soft, movable to the touch, and usually painless.
• Cystic Lesions: Beyond ganglion cysts, other types of benign cysts, such as synovial cysts, can sometimes present as a localized lump around the patella.
  • Cause: Related to joint fluid leakage or degeneration.
  • Characteristics: Typically soft to firm, often non-tender unless inflamed.
• Trauma-Related Swelling (Hematoma or Seroma): A direct blow or fall onto the kneecap can cause localized bleeding (hematoma) or fluid accumulation (seroma) under the skin, forming a lump.
  • Cause: Acute injury or repeated minor trauma.
  • Characteristics: Can be painful, bruised, and firm or boggy depending on the fluid type.
• Osteochondroma: This is a benign bone tumor that typically develops during childhood or adolescence, forming an outgrowth of bone covered by cartilage. While usually arising from the ends of long bones, they can rarely occur near the patella.
  • Cause: Developmental anomaly.
  • Characteristics: Hard, fixed lump, often painless unless it irritates surrounding tissues.
• Other Rare Causes: Less common possibilities include tendinopathy (thickening of the patellar tendon, though typically below the kneecap), gouty tophi (crystal deposits in chronic gout), or, very rarely, malignant tumors.

Associated Symptoms to Consider

When a lump appears, it's important to note any accompanying symptoms, as these provide critical clues for diagnosis:

• Pain: Is the lump tender to touch? Does it hurt with movement or at rest?
• Redness and Warmth: These are signs of inflammation or infection.
• Swelling: Is it localized to the lump, or is there generalized knee swelling?
• Limited Range of Motion: Does the lump impede your ability to bend or straighten your knee?
• Fever or Chills: These systemic symptoms can indicate an infection.
• Changes in Size or Texture: Has the lump grown rapidly, or changed from soft to hard?

Diagnosis and Medical Evaluation

Given the range of potential causes, a thorough medical evaluation is essential for any persistent or concerning lump. A healthcare professional, such as a sports medicine physician, orthopedic surgeon, or physical therapist, will typically follow these steps:

• Medical History: They will ask about your activities, any recent injuries, the onset and duration of the lump, and associated symptoms.
• Physical Examination: This involves palpating the lump to assess its size, consistency (soft, firm, hard), mobility, tenderness, and whether it's attached to deeper structures. Your knee's range of motion and stability will also be assessed.
• Imaging Studies:
  • X-ray: Useful for evaluating bone involvement, such as an osteochondroma or ruling out fractures.
  • Ultrasound: Excellent for visualizing soft tissue structures like bursae, cysts, and fluid collections. It can differentiate between solid and fluid-filled masses.
  • MRI (Magnetic Resonance Imaging): Provides detailed images of soft tissues, including tendons, ligaments, muscles, and bursa, offering a comprehensive view of the lump and surrounding structures.
• Aspiration: If a fluid-filled lump (like bursitis or a cyst) is suspected, a needle may be used to withdraw fluid for analysis (e.g., to check for infection or crystals).
• Blood Tests: May be ordered if infection or inflammatory conditions (like gout) are suspected.

Treatment Approaches

Treatment for a pea-sized lump on the kneecap varies significantly depending on the underlying cause:

• Conservative Management:
  • RICE Protocol: Rest, Ice, Compression, and Elevation can help manage pain and swelling, especially for bursitis or post-traumatic swelling.
  • NSAIDs: Non-steroidal anti-inflammatory drugs (e.g., ibuprofen) can reduce pain and inflammation.
  • Activity Modification: Avoiding activities that exacerbate the lump, particularly repetitive kneeling.
  • Physical Therapy: For conditions like bursitis, physical therapy can address underlying biomechanical issues, improve flexibility, strengthen surrounding muscles, and provide strategies for preventing recurrence.
• Medical Interventions:
  • Aspiration: Draining fluid from a bursa or cyst can relieve pressure and pain.
  • Corticosteroid Injections: Injecting corticosteroids into an inflamed bursa can reduce inflammation.
  • Antibiotics: If an infection is present (e.g., septic bursitis), antibiotics are crucial.
• Surgical Intervention:
  • Bursectomy: In cases of chronic, recurrent, or infected bursitis that doesn't respond to conservative treatment, surgical removal of the bursa may be necessary.
  • Cyst Excision: Large, symptomatic, or recurrent cysts may be surgically removed.
  • Tumor Removal: Benign tumors like lipomas or osteochondromas are typically removed if they are symptomatic, growing, or causing functional impairment.

Prevention and Self-Care

While not all causes are preventable, some measures can reduce the risk of certain lumps:

• Use Knee Pads: When performing activities that involve prolonged kneeling (e.g., gardening, construction), protective knee pads can prevent prepatellar bursitis.
• Gradual Activity Progression: Slowly increasing the intensity and duration of physical activities can help prevent overuse injuries.
• Proper Biomechanics: Working with a physical therapist to ensure proper form during exercise and daily activities can reduce undue stress on the knee.
• Maintain a Healthy Weight: Reducing excess load on the knee joints can prevent various musculoskeletal issues.

When to See a Doctor

It's important to seek medical attention for any new, persistent, or changing lump on your kneecap. Specifically, consult a healthcare professional if the lump:

• Is accompanied by significant pain, redness, warmth, or fever.
• Grows rapidly or changes in shape or texture.
• Interferes with your ability to move your knee or bear weight.
• Is hard, fixed, and immovable.
• Is accompanied by unexplained weight loss, fatigue, or other systemic symptoms.

While most pea-sized lumps on the kneecap are benign, a professional diagnosis is the only way to determine the exact cause and ensure you receive the most appropriate and effective treatment.