Saturday night, Nationals right fielder Bryce Harper slipped on 1st base and sustained what looked like a gruesome left knee injury.
You can clearly see his left knee buckle awkwardly on the video as it hyperextends. When we see an injury like this, our initial biggest concern is a ligamentous injury. In this case, we could see that the ACL, possibly the PCL, and the posterolateral corner (the ligament complex formerly known as the LCL) could have all been stressed. An MRI confirmed that Harper does NOT have any ligamentous damage but he does have significant bone bruises in his knee.
When the knee buckles like his did, the ligaments (small, rubber-band like structures that stabilize the joint when the muscles can’t do the job) are stressed. Sometimes that stretch/stress is enough to tear them. Other times, like in Bryce Harper’s fortunate case, the ligaments do not tear (although, after seeing that video I have to imagine that they were at least sprained). Although there was no permanent damage to the ligaments in the knee, the femur (thigh bone) and tibia (shin bone) hit forcefully into each other. This causes injury to the bone. In mild cases, that injury is called a bone contusion (bruise). Bone contusions are INCREDIBLY painful – remember Gronk’s dramatic reaction to his knee bruise? Dez Bryant suffered a similar knee contusion last season. If the bones hit each other hard enough, the bones can dent. This occurs when the bone just below the joint surface is fractured (cracked), causing the the joint surface to collapse.
Here’s an MRI image of a knee that buckled. Normal bone looks black on the images. Bone bruises look bright white.
You can see where the tibia and femur hit each other, there is a resultant white bone bruise on both sides of the joint. The areas of “white” bruised bone are fragile. Therefore, to prevent further injury to the bone, an athlete needs to rest and allow that bone to heal. For a moderate bone bruise to heal usually takes anywhere from 4-6 weeks. Sometimes if there is a significant crack or fracture in the bruised bone it can take longer. If the bone is not allowed to heal, the major risk is that a portion of the bone under the joint surface will collapse like in this MRI image.
When this occurs the thick lacquer paint-like articular cartilage which coats the joint surface can crack. An articular cartilage injury like that could be career-ending.
Bone contusions don’t sound like a very big deal – it’s just a bruise, right? I hope that reading this helps to understand why these athletes need to be treated aggressively with rest and protected until their bones heal.