Knee Update

This month, we will focus on new information regarding the knee. The following questions will be answered:

• Are there radiographic signs of anterior cruciate ligament injury?

• Does osteochondrities dissecans in the knee occur only at the medial femoral condyle?

• Are there newly discovered knee stabilizing structures?

Until recently, the two indirect indicators of ACL injury or rupture have been: (1) tibial spine fractures (best seen on the AP view and tunnel view and common in bicycle injuries) and (2) the lateral capsular sign, or Segund fractures, of the lateral tibial plateau (best seen on the anterior view).

This recent article evaluated in acute patients what has been observed in patients with chronic ACL injury: the lateral notch sign (LNS). The LNS represents a depression usually measuring more than 2mm on the lateral femoral condyle. This is best visualized on a standard lateral view. The terminal sulcus (where the anterior horn of the lateral meniscus articulates with the femur in full knee extension) of the lateral femoral condyle is usually less than 10mm posterior to Blumensaat's line. The LNS is seen more than 10mm posteriorly to this line, and therefore should not be confused with this normal depression.

In this study, the LNS was seen in 7.5% of acute ACL injuries. Also, of those with a LNS, the vast majority had an associated lateral meniscus tear.

Osteochondritis dissecans (OD) represents a separation of the joint cartilage and its underlying vascular supply. This may lead to a fragment that is connected or dislodged. OD of the knee is usually found at the medial femoral condyle (85%).

This study demonstrates that mainly young athletes with a complaint of anterior knee pain may have OD, although, on the whole, it is uncommon. Radiographically, the lesions are best seen on the skyline view and lateral view. Occasionally, an oblique view or Hughston patellar view may help. The appearance is usually a crater with or without separation, but may also have a cystic or lytic appearance. Most lesions were central or superolateral.

The patients in this study were young, competitive athletes, with over half having open physes. Symptoms were related to activity and generally involved complaints of anterior knee pain or patellar pain. Locking occurred in those with loose fragments. The physical exmaination was generally unremarkable, with crepitus commonly present. Most patients had functional patellar and lower limb malalignment. Most patients responded to a conservative approach including vastus medialis obliquus exercises, lateral retinacular stretching and McConnel taping.

Most textbooks describe the anterior and posterior cruciate ligaments (ACL and PCL) as separate structures divided by a fold of synovium. Occasionally, an anterior meniscofemoral ligament is present.

This study found that all cadaver knees evaluated had a structure made up of bands of collagen fibers within the synovium connecting the ACL and PCL. This interconnecting band connected the anterolateral border of the ACL with the posteromedial border of the PCL in a "lazy S" shape with a twist. The researchers also found that the intercruciate band contained nerve fibers and free nerve endings. They postulate that there are also mechanoreceptors present. They further posit that this completes a neurological and mechanical link that converts the ACL and PCL into a "cruciate complex."