Case of the Month - January

35 year old man twisted his knee.

Investigations

Left image: Lateral x-ray demonstrates a deep lateral sulcus (green arrow) and small effusion (red arrow).

Centre image: AP x-ray shows a Segond fracture (green arrow) and an additional avulsion fracture of the lateral tibial plateau (red arrow).

Right image: Selected image from an MRI demonstrates an anterior cruciate ligament (ACL) tear(green arrow) and confirms the Segond fracture (red arrow).

Discussion

Knee injuries are common injuries. Plain radiographs usually constitute the first phase of investigations after physical examination. The main purpose of the x-ray is to exclude a fracture, although some subtle fracture may be radiographically occult.

This case demonstrates three different fractures.

The lateral radiograph shows a compression fracture of the lteral femoral condyle in the region of the lateral sulcus or patello femoral sulcus. This injury results from the pivot shift pattern of impaction that frequently leads to ACL tears and is itself highly associated with a concomitant ACL injury.

The Segond fracture is an avulsion fracture of the lateral tibial plateau at the site of attachment of the lateral capsular ligament. This fracture is also highly associated with ACL tears, which should be expected in any patient with a Segond fracture.

The lateral tibial plateau fracture in this case was due to a bony avulsion injury at the site of attachment of the ilio tibial band onto Gerdys' tubercle.

The MRI confirmed the three fractures and demonstrated a full thickness tear of the ACL. MRI is pivotal in imaging assessment of the knee. It is extremely sensitive at detecting fractures and also allows assessment of soft tissues, including chondral, ligamentous and mensical injuries. It frequently detects meniscal and ligamentous injuries that were unsuspected clinically.