Unusual Case of Lateral Knee Pain: Magnetic Resonance Imaging Evidence of Isolated Lateral Patellotibial Ligament Enthesopathy.

Introduction: Patellofemoral stability is maintained by a complex interplay of osseous, muscular, and ligamentous structures, with the retinacular system playing a central role. While the medial patellofemoral and patellotibial ligaments are well characterized, the lateral patellotibial ligament (LPTL) has been less frequently described, and isolated pathology involving this structure is rarely reported in the literature. Case Report: We report the case of a 23-year-old athletic male presenting with a 2-week history of activity-related lateral knee pain without preceding trauma. Clinical examination revealed focal tenderness at the tibial attachment of the LPTL without effusion, instability, or meniscal signs. Magnetic resonance imaging (MRI) demonstrated linear thickening of the lateral patellar retinaculum extending from the inferolateral patella to the anterolateral proximal tibia, consistent with the LPTL, which appeared thickened compared to the medial counterpart. Associated bone marrow edema at the tibial attachment near Gerdy's tubercle suggested enthesopathy. Other intra-articular structures were normal. The patient was treated conservatively with physiotherapy, activity modification, and non-steroidal anti-inflammatory drugs, resulting in significant symptomatic improvement. Conclusions: This case highlights isolated LPTL enthesopathy as a rare but important cause of lateral knee pain in athletes. Recognition of this entity on MRI is essential to prevent misdiagnosis and to facilitate appropriate conservative management.