HISTORY:
A 12-year-old male with a past medical history of Celiac’s disease and growth deficiency on hormone supplementation presented to sports medicine clinic with a large, painless bump on the medial aspect of his left knee. He noticed it three months prior, but reported enlargement over the last few weeks. He described it as firm and non-mobile. He denied any trauma or inciting event to the knee. He reported playing soccer 8 hours and squash 2 hours per week with both school and club teams. He did not describe any swelling around the knee itself and there was no history of locking or buckling of the knee. The bump did not limit his ambulation or mobility. He endorsed a mild decrease in his ability to flex the knee. He denied any other bumps or masses, fevers, chills, weight loss, erythema, ecchymosis, or edema.
PHYSICAL EXAMINATION:
Examination revealed an approximately 1x2cm firm, non-mobile mass over the superomedial aspect of the left tibia. No knee effusion was noted bilaterally. The left knee was non-tender to palpation along the medial and lateral joint lines as well as the patellar facets. There was no crepitus in the bilateral knees. The range of motion was minimally restricted in flexion on the left compared to the right. Full extension was intact without pain bilaterally. Sensation to light touch and motor strength was normal in the lower extremities. There was no varus or valgus laxity. McMurray’s and Lachman’s tests were negative bilaterally.
DIFFERENTIAL DIAGNOSIS:
1. Tumor (Osteosarcoma)
2. Ganglion Cyst
3. Parameniscal Cyst
4. Soft Tissue Sarcoma
TESTS AND RESULTS:
Left Knee X-ray: No acute fracture or traumatic malalignment. No bone mass visualized
Left Knee Bedside Ultrasound: Hypoechoic mass superficial to medial joint line and posterior to MCL
Left Knee MRI: 1.1 x 2.3 x 1.9cm multi-loculated parameniscal cyst. Tear in the posterior horn of the medial meniscus connecting to the parameniscal cyst
FINAL/WORKING DIAGNOSIS:
Multi-loculated parameniscal cyst secondary to a medial meniscus tear
TREATMENT AND OUTCOMES:
1. Referred to orthopedic surgery to rule out any surgical intervention
2. Consideration of ultrasound-guided percutaneous drainage of the parameniscal cyst
3. Instructed to current activity and exercise as tolerated
4. Counseled to report any pain or changes in symptoms
5. Follow up in 2 months