Synovial plica syndromes: a comprehensive overview from embryology to pathology

Synovial plicae are folds of synovial tissue in the knee, hip, elbow, and shoulder, representing embryonic remnants of synovial septa. They are usually asymptomatic, but trauma, repetitive microtrauma, or prior surgery can render them thickened and fibrotic, producing pain and mechanical symptoms collectively termed plica syndrome. It is easily overlooked or misdiagnosed because the symptoms are nonspecific and other intra-articular disorders often coexist. This review addresses the embryology, histology, anatomy, clinical presentation, imaging, and treatment of synovial plicae across these joints, with emphasis on magnetic resonance imaging (MRI) features. MRI is the preferred imaging modality for evaluating suspected plica syndrome, characterizing the fold and associated abnormalities, and excluding alternative causes of joint pain. Pathologic plicae appear thickened and irregular, with increased signal intensity and frequently associated focal synovitis or adjacent chondral damage. Plica thickness alone has limited diagnostic value, as measurements overlap between symptomatic and asymptomatic individuals. Establishing a diagnosis of symptomatic plica syndrome requires correlation of the imaging findings with the clinical presentation. When joint effusion is absent, magnetic resonance (MR) or computed tomography (CT) arthrography improves delineation of the synovial folds and associated lesions. Plica syndrome occurs most often in young, physically active patients, and management is initially conservative. When symptoms are refractory, arthroscopic resection relieves symptoms, particularly when the plica is the only abnormality and the cartilage is preserved. Most outcome data derive from the knee and the elbow.