Knee Lumps: Common Causes, Less Common Issues, and When to Seek Medical Attention

What Causes Knee Lump?

Knee lumps can arise from a diverse array of underlying conditions, ranging from benign fluid accumulation and inflammatory responses to structural issues or even rare growths, each necessitating a professional medical evaluation for accurate diagnosis and appropriate management.

Introduction to Knee Lumps

A lump around the knee can be a source of significant concern, given the knee's complex anatomy and its critical role in mobility. While some knee lumps are harmless and resolve on their own, others can indicate more serious underlying conditions requiring medical intervention. Understanding the potential causes is crucial for both individuals experiencing such symptoms and fitness professionals guiding their clients. This article will explore the most common and some less common causes of knee lumps, providing a foundational understanding of their origins and implications.

Common Causes of Knee Lumps

The majority of knee lumps are attributed to fluid accumulation, inflammation, or benign tissue changes.

• Bursitis:

  • What it is: Bursae are small, fluid-filled sacs that cushion bones, tendons, and muscles around joints. Inflammation of these sacs is called bursitis.
  • Location/Types: Common types around the knee include prepatellar bursitis (in front of the kneecap, often called "housemaid's knee" or "carpenter's knee"), infrapatellar bursitis (below the kneecap), and pes anserine bursitis (on the inner side of the knee, below the joint line).
  • Causes: Repetitive kneeling, direct trauma, overuse, or infection.
  • Symptoms: Localized swelling, tenderness, pain with movement, and sometimes warmth and redness if infected.

• Baker's Cyst (Popliteal Cyst):

  • What it is: A fluid-filled sac that forms at the back of the knee, often extending into the calf. It's typically a symptom of an underlying knee problem rather than a primary condition.
  • Causes: Often results from excess synovial fluid production due to conditions like osteoarthritis, rheumatoid arthritis, or meniscal tears, which then gets pushed into the gastrocnemius-semimembranosus bursa.
  • Symptoms: A palpable lump behind the knee, tightness, fullness, or pain, especially with knee extension or flexion. It may rupture, causing sudden pain and swelling in the calf.

• Ganglion Cyst:

  • What it is: A non-cancerous, fluid-filled lump that commonly develops near joints or along tendons. It contains a jelly-like fluid.
  • Location: Can occur around the knee, though less common than in the wrist or ankle.
  • Causes: Exact cause is unknown, but may be related to joint or tendon irritation or degeneration.
  • Symptoms: A visible, often firm, lump that may or may not be painful, depending on whether it presses on nerves.

• Meniscus Cyst:

  • What it is: A small, localized swelling that forms adjacent to a meniscal tear in the knee.
  • Causes: Synovial fluid leaking from a meniscal tear and accumulating in the surrounding soft tissues.
  • Symptoms: A palpable lump, often on the outer (lateral) aspect of the knee, accompanied by pain and other symptoms related to the underlying meniscal tear (e.g., clicking, locking).

• Fat Pad Impingement (Hoffa's Fat Pad Syndrome):

  • What it is: Inflammation and impingement of Hoffa's fat pad, a soft tissue structure located directly behind the patellar tendon and beneath the kneecap.
  • Causes: Direct trauma, hyperextension injuries, repetitive stress, or chronic irritation.
  • Symptoms: Anterior knee pain, especially with full extension, tenderness below the kneecap, and sometimes a localized swelling or fullness.

• Tendonitis/Tenosynovitis:

  • What it is: Inflammation of a tendon (tendonitis) or the sheath surrounding a tendon (tenosynovitis).
  • Location: Common around the knee are patellar tendonitis ("jumper's knee") and quadriceps tendonitis.
  • Causes: Overuse, repetitive activities, sudden increase in training intensity, or direct injury.
  • Symptoms: Pain, tenderness, and sometimes palpable swelling or thickening along the affected tendon.

Less Common but Significant Causes

While less frequent, certain other conditions can also manifest as a knee lump and require careful consideration.

• Osteochondroma:

  • What it is: The most common benign bone tumor, typically appearing as a hard, bony outgrowth near the growth plates of long bones, including those around the knee.
  • Causes: Believed to be a developmental anomaly.
  • Symptoms: A hard, fixed lump that may or may not be painful. Can sometimes press on nerves or blood vessels.

• Lipoma:

  • What it is: A common, benign tumor composed of fatty tissue.
  • Location: Can occur anywhere on the body, including around the knee.
  • Symptoms: A soft, movable, rubbery lump under the skin that is usually painless.

• Gout/Pseudogout:

  • What it is: Types of inflammatory arthritis caused by crystal deposition in joints. Gout involves uric acid crystals; pseudogout involves calcium pyrophosphate crystals.
  • Causes: Metabolic disorders leading to crystal accumulation.
  • Symptoms: Acute episodes of severe pain, swelling, redness, and warmth in the affected joint. Can lead to visible lumps (tophi in gout) in chronic cases.

• Arthritis (Rheumatoid Arthritis, Osteoarthritis):

  • What it is: Inflammatory or degenerative joint conditions.
  • Causes: Autoimmune response (RA) or wear-and-tear (OA).
  • Symptoms: Chronic joint pain, stiffness, and swelling. The swelling can sometimes present as a diffuse lump or contribute to conditions like Baker's cysts.

• Infection (Septic Arthritis, Cellulitis, Abscess):

  • What it is: Bacterial or fungal infection of the joint (septic arthritis), skin (cellulitis), or a localized collection of pus (abscess).
  • Causes: Bacteria entering the joint (e.g., from surgery, injection, or bloodstream) or skin breach.
  • Symptoms: Rapid onset of severe pain, warmth, redness, significant swelling, fever, and chills. This is a medical emergency.

• Trauma-Related Swelling (Hemarthrosis, Effusion):

  • What it is: Accumulation of blood (hemarthrosis) or general fluid (effusion) within the joint capsule following an injury.
  • Causes: Ligament tears (e.g., ACL), meniscal tears, fractures, or direct impact.
  • Symptoms: Swelling that develops rapidly after injury, pain, and restricted range of motion.

• Popliteal Artery Aneurysm:

  • What it is: A rare condition where the popliteal artery (behind the knee) weakens and bulges.
  • Symptoms: A pulsatile lump behind the knee, sometimes accompanied by pain, swelling, or symptoms of poor circulation in the lower leg if clots form. This is a serious vascular condition.

When to Seek Medical Attention

While some knee lumps are benign, it's always advisable to consult a healthcare professional for an accurate diagnosis, especially if you experience any of the following:

• Sudden onset of a lump or rapid growth.
• Severe pain or pain that interferes with daily activities.
• Warmth, redness, or tenderness over the lump, which could indicate infection or inflammation.
• Fever or chills accompanying the lump.
• Inability to bear weight on the affected leg.
• Changes in skin color or temperature around the lump.
• Numbness, tingling, or weakness in the leg or foot.
• The lump is pulsatile (you can feel a heartbeat in it).

Diagnostic Approaches

A healthcare provider will typically begin with a thorough physical examination, assessing the lump's size, consistency, mobility, and tenderness. They will also evaluate your knee's range of motion and stability. Further diagnostic tests may include:

• X-rays: To assess bone structure and rule out fractures or bony growths.
• Ultrasound: Excellent for visualizing soft tissue structures, fluid collections, cysts, and blood vessels.
• MRI (Magnetic Resonance Imaging): Provides detailed images of soft tissues, including ligaments, tendons, menisci, and fluid collections, offering a comprehensive view of the knee's internal structures.
• Aspiration: Drawing fluid from the lump with a needle for analysis, especially if infection or crystal deposition is suspected.

Conclusion

A lump around the knee can be caused by a wide range of conditions, from common inflammatory issues like bursitis and Baker's cysts to less frequent but potentially more serious concerns like tumors or vascular problems. Given the critical function of the knee and the varied nature of these causes, self-diagnosis is not recommended. If you notice a new or changing lump around your knee, particularly if accompanied by pain, swelling, redness, or functional limitations, prompt medical evaluation by a physician or orthopedic specialist is essential to ensure an accurate diagnosis and appropriate treatment plan.