Sports Medicine
Autumn Dach, DO
Resident Physician
Mayo Clinic
Rochester, Minnesota, United States
Cara Prideaux, MD
Residency Program Director
Mayo Clinic Rochester
Rochester, Minnesota, United States
Autumn Dach, DO
Resident Physician
Mayo Clinic
Rochester, Minnesota, United States
A 34-year-old ballet dancer presented with a five-year history of intermittent, activity-limiting painful medial knee snapping, right greater than left. She had a remote right medial meniscus tear and bilateral parameniscal cysts. Symptoms were reproducible with dynamic open-chain knee flexion and extension in hip abduction and external rotation but absent during weightbearing. Conservative management - including physical therapy and activity modification - provided limited relief. Examination revealed palpable, visible snapping at the medial knee with reverberation into the medial thigh. MRI demonstrated complex bilateral medial meniscal tears with large, loculated parameniscal cysts tracking deep and superficial to the medial collateral ligament (MCL). Dynamic ultrasound confirmed snapping of the gracilis and sartorius tendons over the parameniscal cyst, with knee flexion and extension (with maximum hip abduction and external rotation). Ultrasound-guided parameniscal cyst aspiration with intra-articular knee joint and parameniscal cyst PRP injections have been offered.
Discussions: Snapping of the pes anserinus tendons over a parameniscal cyst is a rare etiology of medial knee snapping. Most cases report semitendinosus or gracilis subluxation over bony prominences rather than cysts. Dynamic ultrasound was crucial in this case, allowing real-time visualization of tendon - cyst interaction during provocative movements. Initial treatment is conservative, including physical therapy, activity modification, and cyst aspiration. If symptoms persist, ultrasound-guided platelet rich plasma injections may be considered. Surgical interventions are reserved for refractory cases.
Conclusions: This case highlights a rare cause of medial knee snapping due to gracilis and sartorius tendons subluxing over a large parameniscal cyst, confirmed by dynamic ultrasound. Dynamic ultrasound should be considered the gold standard for evaluating snapping phenomena around the knee, as it provides direct visualization of symptomatic structures in motion.
