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 later with persistent knee effusion. Magnetic resonance imaging (MRI) 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 white blood cell mm^-3, 12% neutrophils) and cultures were negative. However, knee effusion recurred after 30 days. A repeat MRI performed revealed only postoperative changes. The 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 computed tomography (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.