Baker’s Cyst Aspiration

Baker’s Cyst Aspiration and steroid injection is a treatment option for patients with knee joint OA that develops a cyst behind the knee.

Baker’s Cyst is an obvious swelling in the popliteal fossa, often quite large; limited active and passive knee flexion.

Baker’s cysts tend to occur most commonly in adults aged 35 to 70 and most often are associated with inflammatory joint diseases such as rheumatoid arthritis, osteoarthritis, or as a result of overuse or injury to the knee. As they are asymptomatic, Baker’s cysts are most often detected incidentally on physical examination or imaging studies (e.g., MRI in an adult with suspected osteoarthritis or internal abnormalities of the knee). Prevalence typically increases with age, most likely due to the increase in knee-bursal communication with age.

Equipment Needed

• Syringe: 10 ml
• Needle: White, 19 gauge / 1.5 inches (40 mm)
• Kenalog 40

Related Anatomy

A Baker’s cyst is an enlarged sac of synovial fluid caused by seepage through a defect in the posterior wall of the capsule of the knee joint or by effusion within the semimembranosus bursa. The popliteal artery and vein and posterior tibial nerve pass centrally in the popliteal fossa and must be avoided when injecting.

See Also: Knee Muscles Anatomy

Baker’s Cyst Aspiration Technique

• Patient lies prone,
• Mark spot two fingers medial to midline of fossa and two fingers below popliteal crease,
• Insert needle at marked spot and angle laterally at a 45 degree angle,
• Aspirate excess fluid.

A firm compression bandage can be applied for 1 or 2 days after Baker’s Cyst Aspiration.

If anything other than clear synovial fluid is removed, a specimen should be sent for culture and the appropriate treatment instigated. The swelling frequently returns at some point but can be reaspirated if the patient wishes.

A Baker’s cyst is often found in association with a knee effusion and disappears on aspirating the knee, implying that they communicate. Refrain from putting a needle into a pulsatile Baker’s cyst; this is almost certainly a popliteal artery aneurysm.

Ruptured Baker’s cyst may mimic deep vein thrombosis of the calf.

References & More

1. Leib AD, Roshan A, Foris LA, et al. Baker’s Cyst. [Updated 2022 Sep 4]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430774/
2. Fredericksen K, Kiel J. Bedside ultrasound-guided aspiration and corticosteroid injection of a baker’s cyst in a patient with osteoarthritis and recurrent knee pain. J Am Coll Emerg Physicians Open. 2021 Apr 29;2(2):e12424. doi: 10.1002/emp2.12424. PMID: 33969342; PMCID: PMC8082707.