(Kiosk 2) Differentiation of Traumatic Onset of Sinding-larsen-johansson Syndrome versus Patellar Sleeve Fracture: A Case Report

Case Diagnosis: Non-displaced patellar sleeve avulsion fracture

Case Description or Program Description: A 13-year-old male soccer player without pre-existing knee symptoms presented with acute right knee pain and inability to bear weight after landing on his flexed knee in gym. He felt a pop and had immediate pain at the distal pole of his patella. There was focal swelling and tenderness at the distal patella with crepitus on palpation, with pain worsened with active knee extension and passive knee flexion.

Setting: Outpatient Clinic

Assessment/Results: Plain radiographs showed distal patella bony change and thickening of the patellar tendon suggesting Sinding-Larsen-Johansson Syndrome (SLJS). Given acute onset without pre-existing knee symptoms, an MRI without contrast was obtained to assess for patellar sleeve fracture (PSF). MRI showed a small ossicle at the distal patella surrounded by increased signal on fluid-sensitive images. As imaging couldn't definitively distinguish between a non-displaced PSF versus acute-onset SLJS, he was treated for presumed acute avulsion. He had resolution of pain with immobilization and 4 sessions of physical therapy and returned to full activity within 6 weeks.

Discussion (relevance): SLJS is a traction apophysitis occurring non-traumatically in children aged 10-14, with activity-related symptoms at the distal pole of the patella. PSF also involves the patellar apophysis in the same age group, but occurs acutely, with typical history of a forceful quadriceps contraction with knee in flexion. MRI can be useful in distinguishing the two diagnoses as the cartilaginous sleeve injury in PSF is not visible on radiographs. Avulsion fragments with greater than 2 mm displacement are treated surgically, while non-displaced fragments are treated conservatively.

Conclusions: This case showcases the diagnostic challenges of overlapping presentations of distal patellar disorders in adolescents. Differentiation is more difficult when there is no extensive cartilaginous injury nor displaced avulsion fragment. A high degree of suspicion for PSF is suggested in acute onset injuries with typical history.