Diagnostic Radiology/Musculoskeletal Imaging/Trauma/Segond fracture

Avulsion fracture of the lateral tibial plateau immediately distal to the articular surface. Originally described by Dr. Paul Segond in 1879 after a series of cadaveric experiements, the Segond fracture occurs in association with ACL tears (75-100%) and medial meniscal injury (66-75%), as well as injury to the posteriolateral knee structures.

Originally thought to be a result of avulsion of the medial third of the lateral collateral ligament, more recent research suggests that the insertion of the iliotibial tract (ITT) and the anterior oblique band (AOB), a ligamentous attachment of the fibular collateral ligament to the midportion of the lateral tibia, also play an important role.

A rare, mirror image of the Segond fracture has also been described. The so-called "reverse Segond" fracture is comprised of avulsion fracture of the tibial component of the medial collateral ligament in association with posterior cruciate ligamentous injury and medial meniscal tears.

Mechanism
Segond fracture is typically the result of abnormal varus stress and internal rotation. Reverse Segond fracture, as its name suggests, is caused by abnormal valgus stress and external rotation.

Clinical Significance
Because of the high rate of associated ligamentous and meniscal injury, the presence of a Segond or reverse Segond fracture requires these other pathologies must be specifically ruled out.

Radiologic Findings
Segond and reverse Segond fractures are characterized by a small avulsion fragment of characteristic size that is best seen on plain radiography in the AP plane. Nonetheless, the avulsion fragment may be very difficult to see, and the only direct imaging evidence of this pathology may be by MRI. MRI findings include improved visualization of the fracture fragment on T1W images and marrow edema of the underlying tibial plateau on fat saturated T2W and STIR images, as well as the associated findings of meniscoligamentous injury.