Patellar Cysts: Understanding Types, Causes, Symptoms, and Management

What is a cyst on the patella?

A cyst on the patella, or kneecap, refers to an abnormal, fluid-filled sac that can develop either within the patella bone itself, in the soft tissues overlying it, or adjacent to its associated tendons and ligaments, often causing localized swelling, pain, or restricted movement.

Understanding the Patella and Knee Anatomy

The patella, commonly known as the kneecap, is a small, triangular-shaped bone embedded within the quadriceps tendon. It plays a crucial role in knee biomechanics by increasing the leverage of the quadriceps muscle, thereby enhancing its ability to extend the lower leg. The patella articulates with the femur (thigh bone) to form the patellofemoral joint, and is protected by articular cartilage. Surrounding the patella are various soft tissues, including bursae (fluid-filled sacs that reduce friction), tendons (like the patellar tendon connecting the patella to the tibia), and ligaments. Understanding these structures is key to comprehending where and why a cyst might form in this region.

What is a Cyst?

In a medical context, a cyst is a sac-like pocket of membranous tissue that contains fluid, air, or other substances. Cysts can form almost anywhere in the body and are typically benign (non-cancerous). They arise from various mechanisms, including inflammation, trauma, degenerative processes, or sometimes without a clear cause. Their presence around the patella can be a source of discomfort and functional limitation, especially for individuals engaged in physical activity.

Types of Cysts Associated with the Patella

While the term "cyst on the patella" might suggest a single entity, several distinct types of cysts and fluid collections can occur in or around the kneecap.

• Prepatellar Bursitis (Housemaid's Knee): This is perhaps the most common "cyst-like" swelling directly over the patella. The prepatellar bursa is a fluid-filled sac located between the skin and the front of the patella. Inflammation or irritation of this bursa, often due to repetitive kneeling or direct trauma, leads to excessive fluid production, resulting in a noticeable, soft, fluctuant swelling. While technically an inflamed bursa and not a true cyst, it presents as a localized fluid collection directly on the kneecap.
• Intraosseous Patellar Cysts: These are less common and are true cysts located within the patella bone itself. They are typically benign bone lesions, often discovered incidentally during imaging for other knee issues. They can be a result of degenerative changes, trauma, or developmental anomalies. While often asymptomatic, larger cysts or those causing structural weakness might lead to pain.
• Ganglion Cysts: These are benign, fluid-filled sacs that typically arise from a joint capsule or tendon sheath. While more common in the wrist or ankle, they can occur around the knee, including near the patellar tendon or surrounding retinacula (fibrous bands supporting the patella). They contain a thick, jelly-like fluid similar to synovial fluid.
• Synovial Cysts: Similar to ganglion cysts, synovial cysts are out-pouchings of the synovial membrane, which lines joints. If there is a weakness in the joint capsule, synovial fluid can protrude, forming a cyst. These can occur in various locations around the knee, including near the patellofemoral joint.
• Baker's Cyst (Popliteal Cyst): While not on the patella, a Baker's cyst is a common knee-related cyst that forms at the back of the knee (popliteal fossa). It's an accumulation of joint fluid that has extruded through a defect in the posterior joint capsule, often secondary to intra-articular pathology like meniscal tears or osteoarthritis. It's important to distinguish it from cysts directly on the patella.

Causes and Risk Factors

The formation of a cyst on or around the patella is often multifactorial:

• Trauma: Direct blows to the kneecap or repetitive microtrauma can irritate bursae or other soft tissues, leading to fluid accumulation.
• Repetitive Stress/Overuse: Activities involving frequent kneeling, squatting, or jumping can strain the structures around the patella, predisposing to inflammation and cyst formation (e.g., prepatellar bursitis).
• Degenerative Conditions: Osteoarthritis in the patellofemoral joint can lead to increased synovial fluid production and, in some cases, the formation of synovial or intraosseous cysts.
• Underlying Joint Pathology: Meniscal tears, ligament injuries, or other intra-articular issues can alter joint mechanics and fluid dynamics, sometimes contributing to cyst formation (especially relevant for Baker's cysts).
• Inflammatory Conditions: Systemic inflammatory conditions like rheumatoid arthritis can also contribute to bursitis or synovial cyst formation.
• Idiopathic: In some cases, particularly with ganglion cysts, the exact cause remains unknown.

Common Symptoms

The symptoms of a patellar cyst vary depending on its type, size, and location:

• Visible Swelling: A noticeable lump or bulge on or around the kneecap is the most common symptom, especially with prepatellar bursitis.
• Pain: Localized pain, which may worsen with activity, direct pressure (e.g., kneeling), or movement of the knee.
• Tenderness: The area over the cyst may be tender to the touch.
• Restricted Range of Motion: Larger cysts can mechanically impede full knee flexion or extension.
• Stiffness: A feeling of stiffness or tightness around the knee.
• Warmth and Redness: In cases of acute inflammation or infection (e.g., septic bursitis), the area may be warm, red, and exquisitely tender.

Diagnosis

Diagnosing a patellar cyst typically involves a combination of:

• Clinical Examination: A healthcare professional will visually inspect the knee, palpate the area to assess the size, consistency, and tenderness of the swelling, and evaluate the knee's range of motion.
• Medical History: Information about recent injuries, activities, and pre-existing medical conditions is crucial.
• Imaging Studies:
  • X-rays: Primarily used to rule out bone abnormalities, fractures, or significant osteoarthritis. They can identify intraosseous patellar cysts.
  • Ultrasound: An excellent tool for visualizing soft tissue fluid collections, differentiating between solid masses and cysts, and assessing the size and contents of bursal or ganglion cysts.
  • Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues, including tendons, ligaments, cartilage, and fluid collections. MRI is highly effective in identifying and characterizing various types of cysts around the knee, including their connection to joint structures.

Treatment Approaches

Treatment for a cyst on the patella depends on its type, size, symptoms, and underlying cause.

• Conservative Management:
  • Rest and Activity Modification: Avoiding activities that aggravate the cyst (e.g., kneeling for prepatellar bursitis).
  • Ice Application: To reduce pain and swelling.
  • Compression: Using a compression bandage can help reduce swelling.
  • Elevation: Elevating the leg can also aid in reducing swelling.
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Over-the-counter medications like ibuprofen can help manage pain and inflammation.
  • Physical Therapy: May be recommended to address underlying biomechanical issues, strengthen surrounding muscles, and improve flexibility, especially once acute symptoms subside.
• Aspiration: For larger, symptomatic fluid collections (e.g., prepatellar bursitis, ganglion cysts), the fluid can be drained using a needle. This often provides temporary relief, but the cyst may recur.
• Corticosteroid Injections: After aspiration, a corticosteroid may be injected into the bursa or cyst to reduce inflammation and recurrence, though this is used cautiously due to potential side effects.
• Surgical Excision: If conservative treatments fail, if the cyst is large and severely symptomatic, or if there's a concern about its nature, surgical removal may be considered. This is more common for recurrent or persistent ganglion cysts, or for chronic, problematic bursitis. Intraosseous cysts are rarely surgically removed unless they are very large and symptomatic.
• Addressing Underlying Causes: If the cyst is secondary to another condition (e.g., osteoarthritis, meniscal tear), treatment of the primary issue is essential.

Implications for Exercise and Rehabilitation

For fitness enthusiasts and trainers, understanding patellar cysts is crucial for safe and effective exercise programming:

• Acute Phase: During acute inflammation or pain, exercise involving the affected knee should be modified or temporarily ceased. Focus on pain-free range of motion and isometric exercises if tolerated.
• Rehabilitation: Once pain subsides, a progressive rehabilitation program is vital. This includes:
  • Restoring Range of Motion: Gentle stretches and mobility exercises.
  • Strengthening: Focus on quadriceps, hamstrings, and gluteal muscles to improve knee stability and mechanics. Exercises should be low-impact initially (e.g., cycling, swimming) and gradually progress to weight-bearing activities.
  • Proprioception and Balance: Exercises to improve neuromuscular control around the knee.
  • Activity Modification: Identifying and modifying activities or techniques that may have contributed to the cyst's formation (e.g., using knee pads for kneeling, optimizing squat depth).
• Return to Activity: A gradual return to sport or higher-impact activities is essential, guided by symptom resolution and functional capacity. Listen to your body and avoid pushing through pain.

When to Seek Medical Attention

It is advisable to consult a healthcare professional if you experience:

• A new or rapidly growing lump on or around your kneecap.
• Significant pain, redness, warmth, or tenderness around the cyst, which could indicate infection.
• Fever, chills, or general malaise accompanying the knee symptoms.
• Difficulty bending or straightening your knee due to the cyst.
• Symptoms that do not improve with rest and conservative measures.

Conclusion

A cyst on the patella can manifest in various forms, from common fluid collections like prepatellar bursitis to rarer intraosseous lesions. While often benign, they can cause significant discomfort and interfere with daily activities and exercise. Accurate diagnosis by a healthcare professional is essential to determine the type of cyst and guide appropriate treatment. With proper management, including conservative measures, and a thoughtful approach to rehabilitation, individuals can often achieve significant relief and return to their desired level of physical activity.