Bone Bruises in Athletes’ Knees

Did you know that the bone can get bruised? Now that we have technology like magnetic resonance imaging (MRI), discoveries like bone bruising are possible. What does it look like on the MRI? MRIs are made of signals that show up as an image on the computer screen. The signals have various levels of intensity from light to dark. Changes in the signal pattern alert the radiologist to any problems.

In the case of bone bruises, blood pooling, fluid build up (swelling), and increased blood flow to the area show up on the MRI. Water that moves seen within the bone marrow (center of the bone) is another sign of bone bruising. If the injury is severe enough, there can even be tiny fracture lines in the bone referred to as microfractures.

Traumatic bone bruises of the knee are the subject of this article written by two orthopedic surgeons. One surgeon is from Harvard Medical School (Boston). The other hails from Vanderbilt Sports Medicine Center at the Vanderbilt University Medical Center in Nashville, Tennessee.

Bone bruises of the knee from trauma in athletes affect the subchondral bone. This is the first layer of bone underneath the cartilage of the knee. The most common injury associated with bone bruising is a rupture of the anterior cruciate ligament (ACL).

You’ve probably heard of ACL injuries. The ACL is one of two ligaments that criss-cross each other inside the knee. An injury severe enough to pull the ligament off the bone where it attaches can also cause bone bruising. In fact, 80 per cent of all patients who suffer an ACL rupture also have evidence of bone bruising on MRIs.

Without the ACL to hold the tibia (lower leg bone) from sliding too far under the femur (thigh bone) the impact of the injury, the loss of the ligament, and the movement of bone-on-bone leaves the site of the rupture bruised. In fact, there’s even a telltale sign on the bone called the footprint that shows where the impact left the bruise.

Studies have shown that the severity of bone bruising is a direct result of the energy of the injury. Contact injuries (the athlete is hit by another player or falls and makes contact with the ground) have more energy behind them than noncontact injuries (the foot is planted on the ground and the player makes a sudden change in direction).

Recognizing the fact that bone bruising occurs is a fairly new discovery. Knowing what happens in the long-term is unclear. Repeat MRIs show that the bruising goes away over time (usually within 60 days).

Studies done so far don’t show any problem with returning to normal function after a bone bruise. Most athletes are back on the field within six months’ time. The real question on everyone’s minds is whether or not the bruising will result in arthritis later.

We know that damage to the articular cartilage lining the joint is a poor prognostic sign — that means when the cartilage is damaged, it’s very likely there will be problems with arthritis later. As time goes by, researchers will follow patients who have signs of bone bruising and see what happens years later.

Other injuries resulting in bone bruising such as dislocated or fractured patellae (plural for knee caps) will also be investigated. For now, radiologists are working hard to identify locations of bone bruises and the mechanisms behind them.

At the same time, they are categorizing any associated injuries and reporting on bone bruise patterns (what is actually seen on the MRI). In time, there will be some answers about the natural history (what happens over a period of months to years) of bone bruising.