A MRI uses a strong magnet to produce an image of the knee joint. For information about how a MRI works, click here. The image that the MRI creates looks black, white, and all shades of grey. This different shade is called "signal." High signal is a white appearing shade, and low signal is a dark shade. The radiologist and orthopedist use these signal characteristics to determine if the appearance in normal or abnormal.
Edema is another word for swelling and is indicative of injury to an area. Edema is commonly seen around an area that has sustained an injury. Therefore, the structure may appear normal, but the edema may show where the injury is located. Edema may be seen within a bone (a "bone bruise") or within the soft-tissues.
MRI machines use different sequences to help show different types of injuries. Common MRI sequences include T1 and T2 images, and sometimes notations such as "spin," "echo," and "STIR," will be used. These don't really matter for understanding the report; rather they are used by the radiologist to communicate which images show a characteristic finding, and how these images were obtained.
- Bone Bruise
A bone bruise is an area of bone that has been injured and has swelling, or edema, within the bone. This is a sign that the bone has been injured sufficiently to have inflammation within the bone itself. Specific bone bruises may not require any treatment themselves, but may be a sign of other injuries such as an ACL tear.
- Anterior or Posterior Horn
The anterior and posterior horns of the meniscus help the radiologist communicate where in the meniscus he or she sees an abnormality. The anterior horn of the meniscus is in the front of the knee, and the posterior horn is in back. The posterior horn of the meniscus is more commonly injured.
Keep in mind, the MRI report may indicate findings that are not necessarily "normal," but that does not mean those findings are causing your problem. The MRI must be used in association with the physical examination, history of injury, and other studies, in order to determine a proper treatment plan.