Ultrasound-detected lateral band snapping syndrome in proximal interphalangeal joint of small finger—A rare case report

Background: Snapping fingers resulting from flexor tendon tenosynovitis at the metacarpophalangeal (MCP) joint, is common. However lateral band snapping syndrome (LPSS) in the proximal interphalangeal joint (PIPJ) are extremely rare. Case presentation: A 43-year-old female was diagnosed with LPSS in the PIPJ of fifth finger which was confirmed by dynamic evaluation upon ultrasound. Repair of retinacular ligament of the extensor tendon was performed. At the six-month follow up, the patient had regained full ROM with no discomfort, without evidence of recurrence. Discussion: The diagnosis of LPSS at the PIPJ is challenging. Dynamic evaluation of the extensor tendon over PIPJ is necessary to diagnose LBSS. Ultrasound was used to assess the movement of the lateral band of the extensor tendon when the fingers flexed and to demonstrate dynamically the snapping and subluxation of the lateral band, so as to facilitate confirming the diagnosis of LBSS. Conclusion: Given clinical suspicion of LBSS, we recommend ultrasonography as a feasible tool to confirm the diagnosis. Patients with LBSS may thus benefit from prompt repair of the retinacular ligament without sequela.