Recurrent Knee Effusion After Penetrating Trauma in a Child: A Case Report

Recurrent knee effusion after penetrating trauma is unusual in children and should prompt a search for occult intra-articular foreign bodies to prevent cartilage damage and repeated procedures. A 12-year-old girl suffered a glass-induced penetrating injury to the right knee. Initial radiographs were normal and the patient's wound was irrigated and debrided. However, the patient presented three weeks after with persistent knee effusion; Magnetic resonance imaging showed synovitis, joint fluid and an impacted osteochondral lesion of the medial femoral condyle. Laboratory evaluation demonstrated elevated inflammatory markers and septic arthritis was a clinical concern. Diagnostic arthroscopy and joint washout was performed 24 days after the index injury. Synovial fluid (800 WBC mm-3, 12 % neutrophils) and cultures were negative.. However, knee effusion recurred after 30 days. A repeat MRI performed revealed only postoperative changes; Patient was put on a brief course of steroids with transient improvement. Six months after the original injury, the patient still presented a large knee effusion. Thin-slice CT plus repeat MRI demonstrated two radiodense foci (≈ 5 mm and 2 mm) in the posterolateral and lateral parapatellar recesses and small chondral loose bodies. Arthroscopy using a shaver-mounted collector (GraftNet™; Arthrex, Naples, Florida, USA) enabled retrieval of all fragments - four glass shards were removed. Concomitant grade 3 osteochondral injury of the medial femoral condyle and grade 4 lesion of the medial tibial plateau (10 mm) were debrided. At six-month follow-up the patient was pain-free, had no effusion and had returned unrestrictedly to volleyball. Persistent or recurrent effusion after penetrating knee trauma warrants high suspicion for retained foreign material. Thin-slice CT complements MRI by localizing fine radiodense bodies such as glass. Using appropriate arthroscopic retrieval devices enables successful and complete arthroscopic removal of foreign bodies - preventing chronic synovitis and secondary cartilage degeneration.