Following 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.

After 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.

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.

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.

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.

Baseline knee ultrasound assessment will be performed according to the OMERACT (Outcome Measures in Rheumatology) ultrasound definitions for knee osteoarthritis.

Synovitis will be assessed in the suprapatellar and medial/lateral parapatellar recesses using standardized longitudinal and transverse scanning planes and graded from Grade 0 to Grade 3, where higher grades indicate greater synovial distension by abnormal hypoechoic or anechoic material.

Synovial hypertrophy will be graded from Grade 0 to Grade 1 based on the presence of non-displaceable intra-articular tissue. Joint effusion will be evaluated in the parapatellar recesses and graded as Grade 0 (absent) or Grade 1 (present). Power Doppler signal will be recorded as present or absent.

Baseline structural findings including cartilage damage (Grade 0-3), meniscal extrusion (Grade 0-2), and osteophytes (Grade 0-3) will be documented. Higher grades indicate more severe pathology.

Radiographic severity of knee osteoarthritis will be assessed using the Kellgren-Lawrence (K-L) classification based on standard anteroposterior knee radiographs. The K-L grading system ranges from Grade 0 to Grade 4, where Grade 0 indicates no radiographic features of osteoarthritis; Grade 1 indicates doubtful joint space narrowing with possible osteophyte formation; Grade 2 indicates definite osteophytes with possible joint space narrowing; Grade 3 indicates multiple osteophytes, definite joint space narrowing, sclerosis, and possible bony deformity; and Grade 4 indicates large osteophytes, marked joint space narrowing, severe sclerosis, and definite bony deformity.

Higher grades indicate more severe radiographic osteoarthritis. Baseline K-L grade will be used for descriptive and subgroup analyses, as structural radiographic change is not expected during short-term follow-up.

Baker's cyst morphology will be classified as simple or complex based on ultrasound appearance. A simple cyst is defined as an anechoic, unilocular structure without internal septations or echogenic material, whereas a complex cyst is defined by the presence of internal septations, echogenic contents, wall thickening, or irregular morphology.

Changes in cyst complexity over time will be compared between the two study groups.

Total volume of aspirated Baker's cyst fluid measured in milliliters (mL) during the procedure. Higher volumes indicate greater cyst content.

Joint effusion assessed by ultrasonography using the OMERACT semiquantitative grading system for knee osteoarthritis, ranging from Grade 0 to Grade 1. Grade 0 indicates no effusion, while Grade 1 indicates the presence of abnormal hypoechoic or anechoic intra-articular fluid that is displaceable and compressible and does not exhibit Power Doppler signal.

Changes in effusion grade over time will be compared between the two study groups. Higher grades indicate greater joint effusion.