'The Sneaky Plica' revisited: morphology, pathophysiology and treatment of synovial plicae of the knee.

PURPOSE: To comprise current knowledge on morphology, embryology and pathophysiology of synovial plicae as well as on clinical and therapeutic aspects of the plica syndrome.

METHODS: Review of the literature combined with a meta-analysis of studies assessing the outcome of open or arthroscopic plica excision including the author's own series.

RESULTS: The term synovial plica has been devised to describe a number of intra-capsular folds thought to represent remnants of a membranous knee joint partition present during foetal development. Although four such folds have been defined, it is mainly the medial patellar plica which is implicated in carrying clinical significance as a potential cause of anteromedial knee pain particularly in adolescents. Blunt trauma, a sudden increase in athletic activity or any form of transient synovitis are associated with plica inflammation leading to tissue fibrosis and subsequent loss of elasticity. A plica affected in this way may impinge against intra-articular structures in its proximity, often creating localised chondromalacia particularly of the patello-femoral joint. The diagnosis is based on history and clinical examination although MRI can be of value. Twenty-three studies assessing the clinical out-come of 969 patients following open or arthroscopic plica excision were identified. The average age was 25 years with equal male-to-female ratio. Trauma was considered the cause in 57 %. At a mean follow-up of 27.5 months, 64 % of patients were symptom free, 26 % improved and 10 % considered failures.

CONCLUSION: Symptomatic plicae may initially be treated with physiotherapeutic measures and structured exercise regimes but success rates are generally low. Intra-plical or intra-articular corticosteroid injections may be beneficial if administered early in the disease process. Arthroscopic excision of the entire plical fold becomes indicated in recalcitrant cases and once a plica has undergone irrevocable morphological changes. The procedure carries low morbidity, and results are universally good especially if the plica is the sole pathology. Factors associated with a favourable outcome are young patient age, localised symptoms of short duration and absence of plica induced chondromalacia.