What is the treatment for a cyst on the patella?

Treatment for a Cyst on the Patella

The treatment for a cyst on the patella depends on its type, with symptomatic cysts typically requiring surgical intervention through curettage and bone grafting or cement filling, especially for aneurysmal bone cysts.

Diagnostic Approach

Initial Imaging

• Plain radiographs (X-rays) are the first-line imaging modality to identify the cyst and assess for any associated bone abnormalities 1
• MRI without contrast is indicated to:
  • Characterize the cyst type (ganglion, aneurysmal bone cyst, unicameral bone cyst)
  • Evaluate surrounding soft tissue involvement
  • Assess for associated intra-articular pathology 1
• Ultrasound can be useful to:
  • Confirm the cystic nature of the lesion
  • Determine vascularity of the mass
  • Guide aspiration if needed 1

Types of Patellar Cysts

1. Aneurysmal bone cyst (ABC) - expansile, blood-filled lesion that can be primary or secondary to another lesion like giant cell tumor 2, 3
2. Unicameral (simple) bone cyst - fluid-filled cavity within the bone 4
3. Infrapatellar fat pad cyst/ganglion - multiloculated cyst in the fat pad adjacent to the patella 5

Treatment Algorithm

1. Conservative Management (for minimally symptomatic cysts)

• Activity modification to reduce activities that exacerbate pain
• NSAIDs for pain and inflammation
• Physical therapy focusing on quadriceps strengthening
• Monitoring with follow-up imaging

2. Minimally Invasive Procedures

• For soft tissue cysts (ganglion/fat pad cysts):
  • Ultrasound-guided aspiration is the treatment of choice for symptomatic ganglia 5
  • May include injection of corticosteroid after aspiration
  • Note: Recurrence is common with aspiration alone

3. Surgical Management (for persistent symptoms or bone cysts)

• For aneurysmal bone cysts or unicameral bone cysts:

  • Curettage (surgical scraping) of the cyst cavity 2, 3, 4
  • Filling the defect with either:
    • Bone cement (methylmethacrylate) 2
    • Autogenous bone graft harvested from proximal tibia or iliac crest 4

• For popliteal cysts with connection to the knee joint:

  • Arthroscopic treatment addressing both the cyst and any associated intra-articular pathology 6
  • Includes identification and enlargement of the valvular opening between joint and cyst
  • Intracystic debridement of fibrous membrane, nodules, and septa

Post-Treatment Considerations

Follow-up

• Clinical reassessment at 3-4 weeks post-treatment
• Follow-up imaging (X-ray or MRI) at 3-6 months to evaluate for recurrence
• Long-term monitoring may be necessary, especially for aneurysmal bone cysts

Prognosis

• Most patellar cysts treated surgically have good outcomes with appropriate treatment
• Recovery period typically ranges from 3-6 weeks for soft tissue cysts to 3-6 months for bone cysts
• Recurrence rates are higher with conservative treatment or aspiration alone compared to surgical intervention

Special Considerations

• Evaluate the integrity of the extensor mechanism (patellar tendon and quadriceps) as many patients present with malfunction of this system 3
• Consider the patient's age and activity level when determining treatment approach
• Histopathological examination of surgically removed tissue is essential to confirm diagnosis and rule out malignancy

Pitfalls to Avoid

• Misdiagnosing a malignant lesion as a benign cyst
• Inadequate curettage leading to recurrence
• Overlooking associated intra-articular pathology that may contribute to cyst formation
• Failure to address the valvular mechanism in popliteal cysts, resulting in high recurrence rates 6