All photos shown are actual patients of AIM Medical Imaging, obtained with personal consent. The information below is for information purposes only, and is not to be considered as medical advice.
A MRI of the knee is one of the most common body regions requested for imaging. Injuries to the knee can be caused by twisting, direct impact and can even occur spontaneously. MRI of the knee is invaluable in assessing the joint, and is recommended whenever ligamentous or cartilaginous injury is suspected. Shown below are some high resolution images taken at AIM Medical Imaging showing the normal appearance of structures as well as various injuries and conditions involving the knee.
The anterior cruciate ligament (ACL) is the ligament most commonly injured in the knee . Injuries are often associated with high torsion forces involved with athletic sports, contact sports and snow sports. Patients often report hearing a “pop” at the time of the injury. A complete tear is generally repaired via surgical means by rebuilding the ligament often with a tissue graft.
Figure 1 (above) shows a Sagittal T2 of the knee showing the normal appearing ACL. The ACL is the cluster of black diagonal lines coursing from the back of the femur to the front of the tibia (red arrows). High resolution imaging of the knee is able to show the bundles of the ACL. Compare this to Figure 2 which shows a complete tear of the ACL (blue arrow) with the lower part of the ACL laying in the knee joint (red arrow).
A tear in the medial collateral ligament (MCL) is the second most common ligamentous injury. The MCL derives its name from its position on the medial side of the knee (closest to the midline). Tear are often partial, which do not require surgical intervention, however, a full tear must be excluded. Partial and complete tears of the MCL commonly occur simultaneously with tears of the medial meniscus (described later) A partial MCL tear of the knee is shown in Figure 3. Note the fluid (white region) surrounding the ligament indicating traumatic injury.
Injuries to the meniscus in the knee are relatively commonly and are often associated with a torsion type injury. This can cause locking in the knee joint, and the knee “giving way” especially when walking up or down stairs. Tears of the meniscus, especially those involving the medial meniscus are usually treated surgically. Figure 4 is a series of ultra-high resolution (600micron thin) images of the meniscus. Image a) shows a healthy medial meniscus. The outline of the medial meniscus is shown in b). Image c) shows a tear in the posterior horn of the medial meniscus (different patient’s meniscus)*.
Figure 4a (left), b(middle) and c(right)
Injuries to the PCL are less common than the ACL. The PCL is stronger and able to tolerate more force than the ACL.This can be understood by comparing the appearance of the PCL in Figure 5 to the ACL images in Figure 1. The PCL is responsible for preventing the tibia from moving backwards when the knee is bent.
Figure 6 a) shows a normal appearing quadriceps femoris tendon. Figure 6 b) shows a full tear of the quadriceps insertion with the patellar tendon remaining intact.
As well as assessing all of the soft tissues of the knee, an MRI is also able to show subtle fractures of the knee which may not be seen by x-ray. As MRI is able to identify different tissue composition, it is able to show areas of tissue repair, including that of bone. Figure 7 shows a undisplaced fracture which was not seen on x-ray. The subtle fracture is shown with the red arrows.
Sometimes the knee can cause pain and discomfort for no apparent reason. This can be due to numerous factors e.g. osteoarthritis, meniscal degeneration or a condition interestingly named SONK. While this name is humerous to say aloud (you will sound like a goose!) it actually stands for Spontaneous Osteo Necrosis of the Knee. SONK (Figure 8) more often affects the older population, especially female patients and may necessitates a knee replacement .