Infrapatellar Bursa: Anatomy, Function, Bursitis Symptoms, and Treatment

What is infrapatellar bursa?

The infrapatellar bursa is a small, fluid-filled sac located in the knee, positioned just below the kneecap and superficial to the patellar tendon. Its primary function is to reduce friction and cushion the tendon as it glides over the tibial tubercle during knee movement.

Anatomy and Location

The knee joint contains several bursae, which are thin, slippery sacs filled with a small amount of synovial fluid. These structures are strategically placed throughout the body where tendons, muscles, or skin move over bony prominences. Their purpose is to minimize friction and provide cushioning, facilitating smooth movement.

The infrapatellar bursa is specifically located in the front of the knee, beneath the patella (kneecap). It is often referred to in two forms:

• Superficial Infrapatellar Bursa: This bursa lies between the skin and the patellar tendon, just above the tibial tubercle. While less commonly affected, it can become inflamed from direct trauma or prolonged kneeling.
• Deep Infrapatellar Bursa: This is the more frequently discussed and clinically relevant of the two. It is situated between the distal part of the patellar tendon and the anterior surface of the tibia (shin bone), just above the tibial tubercle. It also lies close to Hoffa's fat pad, a significant fat pad within the knee.

Understanding its precise location is crucial because its inflammation can mimic or coexist with other common knee conditions.

Function of the Infrapatellar Bursa

The primary roles of the infrapatellar bursa are biomechanical:

• Friction Reduction: It allows the patellar tendon to glide smoothly over the underlying bone (tibia) during knee flexion and extension, preventing wear and tear.
• Cushioning: It acts as a shock absorber, protecting the patellar tendon and surrounding structures from direct impact or pressure.
• Facilitates Movement: By minimizing friction, it contributes to the efficient and pain-free range of motion of the knee joint, particularly during activities that involve bending and straightening the leg.

Infrapatellar Bursitis

When the infrapatellar bursa becomes inflamed, the condition is known as infrapatellar bursitis. This inflammation causes the bursa to swell and fill with excess fluid, leading to pain and discomfort. It is distinct from patellar tendinopathy (Jumper's Knee), which involves inflammation or degeneration of the patellar tendon itself, although the symptoms can sometimes overlap due to their close proximity.

Causes of Infrapatellar Bursitis

Several factors can contribute to the development of infrapatellar bursitis:

• Repetitive Stress or Overuse: Activities that involve repeated knee bending, kneeling, or squatting can irritate the bursa. This is common in certain occupations (e.g., plumbers, roofers, gardeners) or sports (e.g., running, jumping, cycling).
• Direct Trauma: A direct blow or fall onto the front of the knee can cause inflammation of the bursa.
• Prolonged Pressure: Sustained pressure on the knee, such as prolonged kneeling without adequate padding, can irritate the bursa.
• Biomechanical Issues: Imbalances in lower limb mechanics, such as tight quadriceps or hamstrings, poor foot mechanics, or muscle weakness, can alter knee joint kinematics and increase stress on the bursa.
• Underlying Medical Conditions: Systemic inflammatory conditions like rheumatoid arthritis, gout, or pseudogout can cause inflammation in various bursae, including the infrapatellar bursa.
• Infection (Septic Bursitis): Although less common, the bursa can become infected if bacteria enter through a cut, scrape, or puncture wound near the knee. Septic bursitis is a serious condition requiring immediate medical attention.

Symptoms of Infrapatellar Bursitis

The symptoms of infrapatellar bursitis typically include:

• Pain: Localized pain just below the kneecap, often worsened by activity (especially running, jumping, or squatting), direct pressure, or prolonged kneeling.
• Swelling: Noticeable swelling or a palpable lump just below the patella.
• Tenderness: The area immediately below the kneecap is tender to the touch.
• Warmth and Redness: If the bursa is infected (septic bursitis), the skin over the bursa may feel warm and appear red.
• Limited Range of Motion: While less common than with other knee pathologies, severe swelling can sometimes limit full knee flexion or extension.
• Crepitus: A grinding or crackling sensation may be felt with movement in some cases, though this is more typical of joint surface issues.

Diagnosis

Diagnosing infrapatellar bursitis typically involves:

• Clinical Examination: A healthcare professional will assess your symptoms, palpate the area below the kneecap for tenderness and swelling, and evaluate your knee's range of motion. They will also look for signs of infection (redness, warmth, fever).
• Medical History: Discussing your activity levels, occupation, and any history of trauma or underlying medical conditions.
• Imaging Studies:
  • Ultrasound: Often the first-line imaging modality, as it can clearly visualize the inflamed bursa, fluid accumulation, and distinguish it from tendon pathology.
  • Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues and can help differentiate infrapatellar bursitis from other conditions like patellar tendinopathy, Hoffa's fat pad impingement, or meniscal tears.
  • X-rays: Typically not useful for visualizing bursitis itself but can rule out bony abnormalities or fractures.
• Bursa Aspiration: If infection is suspected, a sample of the bursa fluid may be drawn with a needle (aspiration) and sent for laboratory analysis to check for bacteria or crystals (e.g., uric acid crystals in gout).

Treatment and Management

Treatment for infrapatellar bursitis aims to reduce inflammation, alleviate pain, and restore function.

Conservative Management

Most cases of infrapatellar bursitis respond well to conservative measures:

• Rest and Activity Modification: Avoiding activities that aggravate the bursa, such as kneeling, squatting, or high-impact exercises.
• Ice Application: Applying ice packs to the affected area for 15-20 minutes several times a day to reduce swelling and pain.
• Compression: Using a compression bandage or sleeve can help reduce swelling.
• Elevation: Elevating the leg can help reduce fluid accumulation.
• Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Over-the-counter medications like ibuprofen or naproxen can help manage pain and inflammation.
• Physical Therapy: A physical therapist can provide exercises to improve flexibility, strengthen surrounding muscles (quadriceps, hamstrings, glutes), correct biomechanical imbalances, and offer advice on activity modification and proper form.
• Corticosteroid Injections: In cases of persistent, non-septic bursitis, a corticosteroid injection directly into the bursa can provide significant pain relief and reduce inflammation. This is typically done under ultrasound guidance.

Medical Intervention

• Antibiotics: If septic bursitis is diagnosed, a course of antibiotics is essential to clear the infection.
• Aspiration: Draining the excess fluid from the bursa can relieve pressure and pain, especially in cases of large effusions or septic bursitis.
• Surgical Excision (Bursectomy): Rarely, if conservative treatments fail and chronic, debilitating bursitis persists, surgical removal of the bursa may be considered. This is usually a last resort.

Prevention Strategies

Preventing infrapatellar bursitis involves minimizing stress and trauma to the bursa:

• Use Knee Pads: When performing activities that require prolonged kneeling, wear appropriate knee pads to cushion the joint.
• Warm-up and Cool-down: Always perform a proper warm-up before exercise and cool-down afterward to prepare muscles and tendons for activity and aid recovery.
• Gradual Progression: Increase the intensity, duration, or frequency of physical activities gradually to allow the body to adapt.
• Maintain Flexibility and Strength: Regularly stretch the quadriceps and hamstrings, and strengthen the muscles around the knee to ensure proper joint mechanics.
• Address Biomechanical Issues: Work with a physical therapist to identify and correct any underlying gait abnormalities or muscle imbalances.
• Proper Footwear: Wear supportive shoes appropriate for your activity.
• Maintain a Healthy Weight: Excess body weight can increase stress on the knee joints.

Conclusion

The infrapatellar bursa is a vital, yet often overlooked, component of knee joint health, playing a critical role in facilitating smooth, pain-free movement. While small, its inflammation can lead to significant discomfort and functional limitation. Understanding its anatomy, function, and the causes of bursitis is key to both effective treatment and proactive prevention, ensuring the longevity and optimal performance of your knees. If you experience persistent pain or swelling below your kneecap, consult a healthcare professional for an accurate diagnosis and appropriate management plan.