Kissing contusion | Radiology Signs

Answer:

Kissing contusions are paired bone marrow oedema lesions on opposing articular surfaces, and in the knee the classic pattern is oedema in the mid portion of the lateral femoral condyle and the posterolateral tibial plateau. This is the footprint of the pivot-shift injury and, when present, it indicates an anterior cruciate ligament tear with high probability even before the ligament itself is assessed. The two bruises are produced at the same instant as the tibia subluxes anteriorly and rotates internally and the lateral femoral condyle impacts the posterior tibial plateau. Associated findings that should be sought are a deep lateral femoral notch deeper than about 1.5 to 2 mm, a Segond fracture, a posterolateral corner injury, and meniscal tears, particularly of the lateral meniscus posterior horn acutely and of the medial meniscus in the chronic knee. Different contusion patterns indicate different mechanisms and should be read that way: a medial patellofemoral pattern with oedema in the inferomedial patella and the anterolateral femoral condyle indicates transient patellar dislocation, a dashboard pattern in the anterior tibia indicates posterior cruciate ligament injury, and a hyperextension pattern with kissing anterior femoral and tibial contusions indicates hyperextension with possible bicruciate injury.

Why is it called so?

The two bruises lie directly opposite one another on the impacting surfaces, as if the bones had kissed.

Pathophysiology

Bone contusion is a trabecular microfracture with haemorrhage and oedema in the marrow, invisible on radiographs and visible as high signal on fluid-sensitive fat-suppressed MRI sequences and low signal on T1. During the pivot shift, failure of the anterior cruciate ligament allows the tibia to translate anteriorly, so the convex lateral femoral condyle strikes the posterior slope of the lateral tibial plateau with considerable force. The impact compresses the subchondral trabeculae of both surfaces at their point of contact, producing mirror-image lesions. These bruises resolve over weeks to months, which is why their presence dates the injury as recent, and severe impaction may leave a permanent deep lateral femoral notch and predispose to later chondral loss.

Alternative names: Kissing bone bruises; pivot shift contusion pattern

Other associated named signs: Deep lateral femoral notch sign, the Segond fracture and the empty notch sign

References

1. Pringle L, Wissman RD. Imaging of Noncontact Anterior Cruciate Ligament Injuries and Associated Bone Marrow Contusion Patterns. J Knee Surg. 2022;35(5):475-481. PMID: 34902869.