Q: I saw a report on a health show that showed how many people who have an ACL tear also have bone bruising. Why is that such a big deal and how do I know if I had it?

A:  Bone contusion or bruising may be an indication of the severity of the injury. It can be viewed on MRI as edema or swelling inside the bone where the bone marrow is located.

Bone contusion has long been suspected as part of knee injuries severe enough to rupture the anterior cruciate ligament (ACL). And recently, a study from South Korea has been able to verify this theory.

The discovery that bone contusion occurs during ACL ruptures was made by looking at MRIs of 81 patients who had an ACL injury that required surgery. Most of the people in the study were athletes engaged in their sport (soccer, basketball, baseball, volleyball) at the time of the injury. But there were a few who were involved in a fall or car accident. Everyone in the study had MRIs taken within six weeks of the injury.

The MRIs were essential in determining that there had been bone bruising. By taking a closer look at the MRIs in relation to the patients' injuries, they were able to see how often bone contusions occurred. And, in fact, they found an 84 per cent rate of bone contusions in this group.

By breaking the data down further, they recorded 73 per cent of the bone contusions were located along the lateral side of the tibial plateau. The tibial plateau is the flat shelf of bone at the top of the tibia (shin bone). The tibial plateau forms the bottom half of the knee joint.

There were almost as many (68 per cent) of corresponding bone bruises along the lateral femoral condyle. The femoral condyle is the round end of the bottom of the femur. There is a lateral and a medial femoral condyle (one on each side of the femur). The femur forms the upper part of the knee joint.

In a smaller number of cases, there was bruising along the medial femoral condyle (24 per cent) and on the medial tibial plateau (26 per cent). Bruises along both the femoral and tibial sides of the joint on the same side (medial or lateral) are called kissing bone contusions.

The surgeons were also able to identify how many patients had meniscal injuries (and what type) at the time of the arthroscopic surgery. About half of the group had some type of meniscal injury. They compared how many patients with bone contusions also had a torn or damaged medial or lateral meniscus. The greater the bone contusions, the more the meniscal injuries.

Bone contusions aren't treated directly. But they are a sign of a more severe injury. And they serve as a signal to the orthopedic surgeon. Now the surgeon knows to look for associated knee injuries. The additional injuries likely involve the meniscus and ligaments. Finding and assessing these injuries will guide the surgeon in making all the necessary repairs during surgery.

Reference: Kyoung Ho Yoon, MD, et al. Bone Contusion and Associated Meniscal and Medial Collateral Ligament Injury in Patients with Anterior Cruciate Ligament Rupture. In The Journal of Bone and Joint Surgery. August 17, 2011. Vol. 93-A. No. 16. Pp. 1510-1518.