Medial patellar instability describes a condition in which the lateral restraints to medial patellar translation are compromised.1 Patients may experience debilitating symptoms that preclude the ability to perform even basic activities of daily living. Hughston et al. reported that 85% of patients with medial patellar instability could not perform “light recreational activities” and 69% of patients had “severe” or “disabling” knee pain.2

Unlike the more prevalent lateral patellar instability, which may be due to a variety of etiologies, medial instability is almost exclusively due to iatrogenic causes, specifically seen following a lateral retinacular release (LRR) in the setting of patellofemoral disorders such as patellofemoral pain, patellar maltracking and patellofemoral instability.2, 3, 4 Biomechanical studies have further supported this specific but dreaded risk of an isolated LRR. Huddleston et al. demonstrated medial patellar translation significantly increased following LRR throughout knee flexion.5 Clinically, a double-blind prospective study by Pagenstert et al. found lateral retinacular lengthening (LRL) resulted in less medial instability, less quadriceps atrophy and better clinical outcomes compared to LRR at two-year follow-up.6 Due to the dysfunction associated with medial patellar instability, several treatment techniques have been described, including lateral retinaculum imbrication,3 soft tissue augmentation using the fascia lata,7 or lateral patellofemoral ligament (LPFL) reconstruction (using allograft or autograft, either with soft tissue or osseous techniques).5,8

Given the increasing clinical recognition and commensurate increase in research of medial patellar instability, the purpose of this article is to provide a comprehensive review of the more recent evidence regarding the anatomy of the lateral restraints to medial patellar translation, its associated biomechanics, and treatment options for medial instability, including LPFL reconstruction.