Comprehensive review of the anatomy, function, and imaging of the popliteus and associated pathologic conditions.

The popliteus is a relatively small but unique muscle of the knee. It is a component of the posterolateral corner of the knee and acts as a major stabilizer of the posterolateral knee. It is important to be aware of the normal magnetic resonance (MR) imaging appearance of the popliteus musculotendinous complex and its relation to other structures of the posterolateral corner for accurate diagnosis. It is also important to be aware of the pitfalls in imaging of the popliteus. Dysfunction of the popliteus is often underappreciated and is usually secondary to direct or indirect trauma. Injuries of the popliteus can be classified as first-, second-, or third-degree strains. Injuries of the popliteus are often associated with other posterolateral corner injuries. Pathologic conditions of the popliteus may be a clue to other injuries in the knee. The site and pattern of popliteus tear can be helpful to the orthopedic surgeon in deciding whether repair is warranted and determining the approach to surgery and has prognostic implications. Undiagnosed popliteus injuries can lead to poor functional results after knee reconstructive surgery. Inflammatory pathologic conditions of the popliteus may cause knee pain and can be diagnosed with MR imaging. The popliteus is an important component of the posterolateral corner that needs closer attention for optimal diagnosis and patient care.