Knee Bursitis: Understanding, Symptoms, and Differentiating Conditions

What can be mistaken for knee bursitis?

Knee bursitis, characterized by inflammation of the fluid-filled sacs around the knee, often presents with localized pain and swelling; however, many other knee conditions can mimic these symptoms, necessitating a precise diagnosis.

Understanding Knee Bursitis

The knee joint is surrounded by several bursae, small, fluid-filled sacs that reduce friction between bones, tendons, and muscles. When these bursae become inflamed, a condition known as bursitis occurs. Common knee bursae affected include:

• Prepatellar bursa: Located in front of the kneecap, often inflamed by direct trauma or repetitive kneeling ("housemaid's knee").
• Infrapatellar bursa: Located below the kneecap, either superficial (between skin and patellar tendon) or deep (between patellar tendon and tibia). Often associated with jumping or prolonged kneeling ("clergyman's knee").
• Pes anserine bursa: Located on the inner side of the knee, about 2-3 inches below the joint line. Commonly affected in runners, obese individuals, or those with osteoarthritis.

Key Symptoms of Knee Bursitis

While symptoms can vary depending on the affected bursa, common signs of knee bursitis include:

• Localized swelling: A noticeable lump or puffiness, often soft and fluid-filled, directly over the inflamed bursa.
• Pain: Tenderness to touch, especially over the bursa, and pain that worsens with direct pressure, kneeling, or specific movements.
• Warmth and redness: The skin over the affected bursa may feel warm to the touch and appear reddish.
• Pain with activity: Discomfort may increase with activity and decrease with rest, though severe cases can cause pain at rest.
• Restricted range of motion: Swelling and pain can sometimes limit the knee's ability to bend or straighten fully.

Conditions Commonly Mistaken for Knee Bursitis

Due to overlapping symptoms like pain and swelling, several other knee conditions can be confused with bursitis. Accurate differentiation is crucial for effective treatment.

• Patellofemoral Pain Syndrome (Runner's Knee):
  • Similarities: Anterior knee pain.
  • Differences: Pain is typically diffuse, around or behind the kneecap, often worsened by activities like squatting, climbing stairs, or prolonged sitting. Swelling is less common and, if present, is usually diffuse joint effusion, not a localized bursa swelling. Tenderness is more over the patella facets or general anterior knee, not a specific bursa.
• Meniscus Tear:
  • Similarities: Knee pain, swelling (though often delayed or diffuse), and sometimes limited range of motion.
  • Differences: Often characterized by mechanical symptoms like clicking, popping, locking, or giving way. Pain is typically along the joint line (medial or lateral) and can be sharp with twisting or pivoting movements. Swelling is usually intra-articular (within the joint capsule) rather than a distinct superficial lump.
• Ligament Sprain (e.g., MCL, LCL):
  • Similarities: Localized pain, swelling, and tenderness.
  • Differences: Pain is directly over the injured ligament (e.g., medial collateral ligament on the inner knee, lateral collateral ligament on the outer knee). Instability or a feeling of the knee "giving out" is a hallmark symptom. Swelling may be diffuse within the joint or along the ligament path, but not typically a discrete bursal sac.
• Osteoarthritis:
  • Similarities: Knee pain, stiffness, and sometimes swelling.
  • Differences: Pain is typically gradual in onset, worsens with activity, and is associated with morning stiffness that improves with movement. Crepitus (grinding sensation) is common. Swelling, if present, is usually diffuse joint effusion rather than localized bursal swelling. Pain is often deep within the joint.
• Patellar Tendinopathy (Jumper's Knee):
  • Similarities: Anterior knee pain, tenderness below the kneecap.
  • Differences: Pain is specifically at the inferior pole of the patella or along the patellar tendon, not a distinct bursa. It's an overuse injury of the tendon, worsened by jumping, landing, or explosive movements. Swelling is typically minimal, and tenderness is focused on the tendon itself.
• Iliotibial Band (ITB) Syndrome:
  • Similarities: Lateral knee pain.
  • Differences: Pain is usually on the outer side of the knee, often aggravated by repetitive knee flexion and extension, common in runners and cyclists. Tenderness is along the IT band where it crosses the lateral epicondyle of the femur. Swelling is rare and not a localized fluid sac.
• Baker's Cyst (Popliteal Cyst):
  • Similarities: Swelling and pain in the knee area.
  • Differences: A Baker's cyst is a fluid-filled sac that develops at the back of the knee (popliteal fossa). It's often secondary to other intra-articular problems like meniscal tears or arthritis. The swelling is posterior, whereas common knee bursitis is typically anterior or medial.
• Gout or Pseudogout:
  • Similarities: Acute, severe pain, marked swelling, redness, and warmth.
  • Differences: These are inflammatory arthropathies caused by crystal deposition. The onset is typically very sudden and intensely painful, often affecting the joint itself rather than just a bursa. Diagnosis is confirmed by aspiration of joint fluid and crystal identification.
• Cellulitis/Infection:
  • Similarities: Diffuse redness, warmth, pain, and swelling.
  • Differences: Cellulitis is a bacterial infection of the skin and subcutaneous tissue, typically more widespread and less localized than bursitis. It's often accompanied by systemic symptoms like fever and malaise. While septic bursitis (infected bursa) can occur, cellulitis is a broader skin infection.
• Referred Pain:
  • Similarities: Knee pain without obvious local injury.
  • Differences: Pain originating from the hip joint or lumbar spine can sometimes be perceived in the knee. A thorough examination of the hip and lower back can help identify the true source, as the knee itself will typically lack local signs of inflammation or injury.

Differentiating Factors and When to Seek Medical Attention

Accurately diagnosing the cause of knee pain requires a comprehensive approach. A healthcare professional will typically:

• Conduct a detailed history: Inquire about the onset, nature, aggravating/alleviating factors, and specific activities that trigger pain.
• Perform a physical examination: This includes palpating specific structures, assessing range of motion, performing special tests to evaluate ligaments and menisci, and observing gait. The ability to pinpoint the exact location of tenderness and swelling is key to differentiating bursitis from other conditions.
• Utilize imaging studies:
  • X-rays: Can rule out fractures, arthritis, or bone spurs.
  • Ultrasound: Excellent for visualizing fluid collections, confirming bursitis, or identifying tendon pathology.
  • MRI: Provides detailed images of soft tissues, including ligaments, menisci, tendons, and cartilage, helping to rule out or confirm other injuries.
• Consider aspiration: In cases of significant swelling or suspected infection (septic bursitis), fluid can be drawn from the bursa or joint for analysis.

It is crucial to seek medical attention if you experience:

• Severe pain or swelling that prevents weight-bearing.
• Inability to bend or straighten your knee fully.
• Marked redness, warmth, or fever, which could indicate infection.
• Any signs of instability or a feeling of the knee giving way.
• Persistent pain or swelling that does not improve with rest and conservative measures.

Conclusion

The knee is a complex joint, and pain in this area can stem from a multitude of causes. While bursitis is a common culprit, its symptoms can closely mirror those of various other conditions, ranging from ligament sprains and meniscal tears to arthritis and tendinopathies. For fitness enthusiasts, trainers, and students of kinesiology, understanding these differential diagnoses is paramount. A precise diagnosis, often requiring professional medical evaluation, is the first step toward an effective treatment plan and a safe return to activity.