Segond fracture | Radiology Signs

Answer:

The Segond fracture is a small vertically orientated avulsion fragment from the lateral margin of the tibial plateau, just distal to the articular surface and proximal to Gerdy’s tubercle, seen on the frontal knee radiograph. Its importance is entirely in what accompanies it: it is associated with an anterior cruciate ligament tear in about 75 to 100 per cent of cases and with meniscal injury, most often of the medial meniscus, in a majority, so the finding of even a tiny fleck mandates MRI. The avulsed structure has been clarified by anatomical and MRI studies as the anterolateral complex, comprising the anterolateral ligament and the capsulo-osseous layer of the iliotibial band, rather than the middle third of the lateral capsular ligament as originally taught. The mechanism is internal rotation with varus stress, the same pivoting injury that ruptures the anterior cruciate ligament, and MRI typically shows the associated lateral compartment bone contusions in the posterolateral tibial plateau and the mid lateral femoral condyle. The reverse Segond fracture, an avulsion of the medial tibial plateau, is the analogous injury with posterior cruciate ligament and medial meniscal tears. Because the fragment itself is rarely fixed, treatment is directed at the ligament and meniscal injuries, and there is continuing interest in whether anterolateral reconstruction reduces residual rotatory instability.

Why is it called so?

The fracture is named after Paul Segond, the French surgeon who produced it experimentally in 1879 by forced internal rotation of the knee.

Pathophysiology

During a pivot-shift injury the tibia rotates internally on the femur while the knee is in slight flexion and varus, loading the anterolateral structures of the knee. The anterolateral ligament and the capsulo-osseous layer of the iliotibial band resist internal rotation, and when the force exceeds their strength the bone at their tibial attachment fails before the ligament substance does, producing a cortical avulsion. The same rotational displacement drives the lateral femoral condyle against the posterolateral tibial plateau, producing the characteristic kissing bone contusions, and stretches the anterior cruciate ligament beyond failure. The fragment is therefore not an isolated fracture but a radiographically visible marker of a complete rotatory injury pattern.

Alternative names: Lateral capsular sign; anterolateral ligament avulsion

Other associated named signs: Reverse Segond fracture, the arcuate sign, the deep lateral femoral notch sign and kissing contusions

References

1. Helito PVP, Bartholomeeusen S, Claes S, Rodrigues MB, Helito CP. Magnetic Resonance Imaging Evaluation of the Anterolateral Ligament and the Iliotibial Band in Acute Anterior Cruciate Ligament Injuries Associated With Segond Fractures. Arthroscopy. 2020;36(6):1679-1686. PMID: 32061976.