Segond fracture

The Segond fracture is a type of avulsion fracture (soft tissue structures tearing off bits of their bony attachment) of the lateral tibial plateau of the knee, immediately beyond the surface which articulates with the femur.

History and incidence
Originally described by Dr. Paul Segond in 1879 after a series of cadaveric experiments, the Segond fracture occurs in association with tears of the anterior cruciate ligament (ACL) (75–100%) and injury to the medial meniscus (66–75%), as well as injury to the structures behind the knee.

A rare, mirror image of the Segond fracture has also been described. The so-called "reverse Segond fracture" can occur after an avulsion fracture of the tibial component of the medial collateral ligament (MCL) in association with posterior cruciate ligament (PCL) and medial meniscal tears.

Mechanism
Segond fracture is typically the result of abnormal varus, or "bowing", stress to the knee, combined with internal rotation of the tibia. Reverse Segond fracture, as its name suggests, is caused by abnormal valgus, or "knock-knee", stress and external rotation.

Originally thought to be a result of avulsion of the medial third of the lateral collateral ligament, the Segond fracture has been shown by more recent research to relate also to the insertion of the iliotibial tract (ITT) and the anterior oblique band (AOB), a ligamentous attachment of the fibular collateral ligament (FCL), to the midportion of the lateral tibia.

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

Imaging findings
Segond and reverse Segond fractures are characterized by a small avulsion, or "chip", fragment of characteristic size that is best seen on plain radiography in the anterior-posterior, or "front-to-back", plane. The chip of bone 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 bone marrow edema of the underlying tibial plateau on fat- saturated T2W and STIR images, as well as the associated findings of ligamentous and/or meniscal injury.