Left Posterolateral Knee Pain - Water Polo

HISTORY: This case involves a 20-year-old female waterpolo athlete who presented for evaluation of left posterolateral knee pain. Athlete reported atraumatic left posterolateral knee pain, noted initially with all lateral aquatic movements. Land-based activities did not reportedly exacerbate symptoms. Athlete expressed concern of a palpable popliteal mass over the site of maximal tenderness, described as “popping in and out of place” during episodes of maximal pain. She endorses prior history of similar popliteal masses that typically self-resolve over 1-2 days. Athlete attempted physical rehabilitation with emphasis on posterior kinetic chain stretching in addition to ultrasound-based heart therapy with minimal symptomatic improvement and no change in popliteal mass size. PHYSICAL EXAMINATION: Physical examination revealed an approximate 2 cm x 2 cm solid, nontender, nonmobile mass within the popliteal fossa without overlying skin changes. Athlete demonstrated full knee range of motion in addition to full strength of surrounding structures. Specialized meniscal and ligamentous testing was unremarkable. Bedside point-of-care ultrasound revealed a solid, well-circumscribed, hyper echoic, nonvascularized round structure over the region of concern. DIFFERENTIAL DIAGNOSIS: Popliteal ganglion cyst vs Fabella vs Less likely abscess vs unlikely meniscal involvement TEST AND RESULTS: XR Left Knee - Fabella noted in popliteal area MRI Left Knee - Abnormal appearance to the fabella with abnormal signal in the fabella, reactive edema in the adjacent soft tissues, and thinning of the adjacent articular cartilage in the posterior lateral femoral condyle. FINAL WORKING DIAGNOSIS: Fabella Syndrome TREATMENT AND OUTCOMES: Orthopedic evaluation and ultimately underwent surgical excision of the fabella with overall improvement of symptoms.