This study aims to evaluate whether adding a fenestration procedure to standard ultrasound-guided aspiration and corticosteroid-lidocaine injection provides additional clinical benefits for patients with symptomatic Baker's cyst associated with knee osteoarthritis. Baker's cyst is a fluid-filled swelling located behind the knee that may cause pain, stiffness, swelling, and limited mobility. Although aspiration with medication injection is commonly used to relieve symptoms, recurrence of the cyst is frequent.
Fenestration is a minimally invasive technique in which small controlled openings are created in the cyst wall under ultrasound guidance to improve internal drainage and potentially reduce recurrence. In this prospective, randomized, double-blind, controlled study, participants will be assigned to one of two groups:
1. aspiration with corticosteroid and lidocaine injection, or 2. aspiration with corticosteroid and lidocaine injection plus fenestration.
Pain, functional scores, cyst measurements, and recurrence will be assessed at follow-up visits at 2 weeks, 1 month, and 3 months. The purpose of this study is to determine whether the addition of fenestration results in better symptom improvement and lower rates of recurrence compared with standard aspiration alone.
Adults aged 40 to 75 years
Diagnosis of knee osteoarthritis according to the 2010 American College of Rheumatology (ACR) criteria
Presence of a symptomatic Baker's cyst confirmed by ultrasonography
Ability to understand study procedures and provide written informed consent
Presence of inflammatory arthritis, septic arthritis, crystal arthropathy, or secondary causes of knee osteoarthritis
Kellgren-Lawrence grade 4 knee osteoarthritis
Active systemic infection
History of malignancy
Parallel
Baker's Cyst Aspiration
Procedure/SurgeryWith the patient in the prone position, the ultrasound probe is placed transversely over the gastrocnemius-semimembranosus bursa. Under real-time ultrasound guidance, the needle is advanced while visualizing neurovascular structures to avoid injury. Aspiration of the cyst content is performed in all participants.
Steroid-Lidocaine Injection
DrugFollowing aspiration, an injection mixture consisting of 1 mL betamethasone, 1 mL of 2% lidocaine, and 1 mL of 0.9% isotonic sodium chloride is administered into the decompressed cyst cavity under ultrasound guidance.
Ultrasound-Guided Fenestration
Procedure/SurgeryAfter aspiration, fenestration of the cyst wall is performed under ultrasound guidance. The cyst wall is punctured at a minimum of six different points using a needle to create communication with surrounding tissues and reduce recurrence. Following fenestration, the same steroid and local anesthetic mixture is administered.
Change in Baker's Cyst Volume
Baker's cyst volume measured by ultrasonography using three-dimensional linear measurements (height × width × depth) and calculated in cubic millimeters (mm³). Volume measurements will be compared between the two study groups (Aspiration + Steroid-Lidocaine vs. Aspiration + Steroid-Lidocaine + Fenestration). All measurements will be performed by a blinded physician using a 7-13 MHz linear transducer. Lower values indicate a reduction in cyst size.
Change in Pain Severity (NRS Score)
Pain severity will be assessed using the Numeric Rating Scale (NRS; 0-10), where 0 indicates "no pain" and 10 indicates "worst imaginable pain." Pain levels will be recorded at each follow-up visit, and changes over time will be compared between the two study groups.
Change in Rauschning-Lindgren Classification (RLC)
Clinical severity of Baker's cyst-related knee symptoms assessed using the Rauschning-Lindgren Classification, a 4-grade clinical scale ranging from Grade 0 to Grade 3. Grade 0 indicates no swelling, pain, limitation of range of motion, instability, or functional restriction. Grade 1 represents mild symptoms such as slight swelling or discomfort after strenuous activity with minimal functional limitation. Grade 2 corresponds to moderate swelling and pain following moderate exertion, with measurable limitation of knee range of motion and reduced participation in physical activities. Grade 3 reflects severe symptoms, including marked swelling, pain at rest or interfering with activities of daily living, significant limitation of knee motion, instability, and inability to participate in work or sports activities. Higher grades indicate greater clinical severity of symptoms.
Change in Knee Injury and Osteoarthritis Outcome Score (KOOS)
The Knee Injury and Osteoarthritis Outcome Score (KOOS) consists of five subscales: Pain (9 items), Symptoms (7 items), Activities of Daily Living (17 items), Sport and Recreation Function (5 items), and Knee-related Quality of Life (4 items).Each item is scored on a 5-point Likert scale from 0 to 4. Raw subscale scores are calculated by summing the item scores within each subscale and are subsequently transformed to a 0-100 scale using the standard KOOS transformation formula, where 0 represents extreme knee problems and 100 represents no knee problems. The KOOS total score is calculated as the arithmetic mean of the five normalized subscale scores. Higher total scores indicate better knee-related symptoms, function, and quality of life.
Change in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)
The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) is a disease-specific, patient-reported outcome measure consisting of 24 items grouped into three subscales: Pain (5 items), Stiffness (2 items), and Physical Function (17 items). Each item is scored on a 5-point Likert scale ranging from 0 (none) to 4 (extreme). Raw subscale scores are calculated by summing the item scores within each subscale, with maximum possible scores of 20 for Pain, 8 for Stiffness, and 68 for Physical Function, resulting in a total raw score ranging from 0 to 96. For analysis, raw scores are summed to generate the WOMAC total score. Higher total scores indicate worse pain, stiffness, and physical dysfunction related to knee osteoarthritis.
Post-Procedure Pain Change (Short-Term Response)
Immediate post-procedural pain assessed using the Numeric Rating Scale (NRS), ranging from 0 to 10, where 0 indicates no pain and 10 indicates the worst imaginable pain. Higher scores indicate worse pain.
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