A Mutidisciplinary Evaluation Of A Large Knee Effusion And Calf Swelling In A 16-year-old Athlete

HISTORY: A 16-year-old male hockey and baseball athlete and active boy scout presented to sports medicine clinic with right knee and calf swelling and pain since injuring knee in recreational volleyball game 1.5 months prior. He initially presented to the emergency department where doppler ultrasound and knee radiographs were negative at that time. In the interim, he continued participating in baseball and hockey games and practice. He denied pain at rest or with walking but had pain (4/10) with running or skating. He denied any instability, catching or locking, rashes, fevers, or recent illness. PHYSICAL EXAMINATION: There was grade 2-3+ right knee effusion with swelling of the posteromedial calf. Flexion was limited to 120 degrees and extension was 5 degrees from full. Knee strength was full. Anterior and posterior drawer, and valgus and varus stress testing were all negative. Lachman’s and McMurray’s tests were negative however very limited due to the effusion and swelling. DIFFERENTIAL DIAGNOSIS: 1. Ligamentous Injury 2. Meniscal Injury 3. Patellar Subluxation/Dislocation 4. Intra-articular Fracture/Contusion 5. Rheumatologic Process 6. Infectious Process. TEST AND RESULTS: Four-view radiographs: Negative. MRI without contrast: Increased T2 signal within the ACL, tear of the lateral meniscus, and a ruptured Baker’s cyst. Diagnostic ultrasound: Cystic mass in the calf which appeared secondary to Baker’s cyst rupture with concern for a separate coalesced hematoma. Diagnostic arthroscopy: The ACL was fully intact. There was small fraying of the lateral meniscus which was debrided. There was also synovial hypertrophy throughout the knee, and a synovectomy with synovial biopsy was performed. This synovial biopsy showed extensive lymphocytic and plasma cell infiltrates and widespread neovascularization. CD4, CD20, and CD68 immunostains were positive. The patient was referred rheumatology: Lyme disease testing was positive. FINAL WORKING DIAGNOSIS: Lyme Arthritis TREATMENT AND OUTCOMES: The patient completed a 28-day course of doxycycline 100 mg twice per day. After 11 sessions of physical therapy, he graduated to home exercise program only. He returned to full participation in hockey (baseball season had since ended) with resolution of his pain and significant improvements in his effusion and swelling.