A Rare Presentation of Idiopathic Medial Patellar Instability: Case Report and Review of the Literature.

INTRODUCTION: Idiopathic medial patellar subluxation (MPS) is an exceptionally rare and frequently underdiagnosed cause of anterior knee pain and instability. Unlike the more common lateral patellar instability, MPS is usually reported as an iatrogenic complication following excessive lateral retinacular release. Spontaneous non-traumatic MPS without prior surgery is uncommon and poses significant diagnostic and therapeutic challenges. We report a rare case of idiopathic MPS in a patient without previous trauma or surgical intervention. CASE REPORT: A 44-year-old female presented with a 2-year history of progressive anterior-medial left knee pain and recurrent "giving-way" episodes. She had previously been treated for patellofemoral pain syndrome without improvement. Clinical examination revealed excessive medial patellar translation, a positive medial patellar apprehension test, and symptom relief with lateral patellar support. Magnetic resonance imaging demonstrated medial patellar tilt with grade IV chondromalacia of the medial patellar facet. Due to persistent symptoms despite prolonged physiotherapy and bracing, the patient underwent arthroscopic medial retinacular release. Postoperatively, she completed structured rehabilitation and demonstrated complete resolution of instability with excellent functional recovery at 18-months of follow-up. CONCLUSION: This case highlights the importance of recognizing idiopathic MPS as a differential diagnosis for persistent anterior knee pain and instability. Early clinical recognition and appropriate management may prevent prolonged disability and progressive patellofemoral cartilage degeneration.