I was saddened to hear last week that Mariano Rivera, one of the greatest closers in baseball of all-time (Rivera career stats), tore his ACL in a freak accident shagging fly balls in the outfield.
We hear commentators on SportsCentre talk about ACL injuries fairly frequently in various sports, and you may hear guys throw the term around as well, but, really, what the heck is an ACL anyway?
Some Basic Anatomy.
The ACL, or anterior cruciate ligament, is the critical ligament that prevents the shin bone from separating from the thigh bone above. Secondarily, it also keeps the lower leg from twisting too much. Think of it like a rope that keep the bones from separating. Too much strain on it, and the ACL might tear.
The "anterior" part of the acronym is because it sits in front of the PCL (posterior cruciate), and "cruciate", which means "cross", because the ACL and PCL criss-cross each other in the centre of the knee.
There you go. Might win you a bar bet some night.
So, who typically tears their ACL? And how? And how often?
Well, ACL tears certainly are common. 1 in 3000 people tear their ACL per year, and appproximately 70% of those occur during some sort of sporting activity.
For whatever reason, Females tend to tear the ACL significantly more than men. For example, Linendfeld et al (http://ajs.sagepub.com/content/22/3/364.short) reported a SIX-FOLD increase in ACL injuries in female soccer players than men, and Ferreti et al, (http://ajs.sagepub.com/content/20/2/203.short) noted a FOUR-FOLD increased incidence in women Volleyball players.
Mechanisms of Injury.
When I'm taking a history from a patient about their injury, if I've done my job right, I usually have a pretty good idea of what they might have done to themselves, even before examining them. This is crucial in eliciting the history of a possible ACL injury, as they can be easily missed, if you're not careful.
The classic injury, is very much what Rivera did. The athlete will describe a non-contact, sudden decelerating move. Very often the player will plant their foot and hyperextend and/or twist the knee, while trying to cut, or change direction. If the foot doesn't slide, (ie, a cleat or shoe gets stuck), the knee may strain and injure the ACL.
The patient may describe a "POPPING" sensation, as the ACL finally gives out and tears. If the injury is isolated, there may be very little swelling associated.
In this case, raw video footage demonstrates one of the mechanisms of injury; hyperextending the knee.
It's Torn. Now What?
At our sport clinic, after the diagnosis is made, the question then becomes, should this be fixed or not?
Watching ESPN, or TSN, or any of the other SN's, you'd think it's "to the operating room as soon as possible".
It actually shouldn't be. The human body is a funny thing. For some people, their proprioceptive ability (or position sense), can compensate for the loss of the ACL dramatically. If their activity or sport consists mostly of straight ahead running only, they may do ok without fixing it. I'm thinking of runners, cylcists, swimmers, and perhaps a few others.
However, sports that are stop and go, like basketball, soccer, football and the like, do depend on the ACL greatly, and probably require fixing, no matter how good your proprioception is.
Our usual protocol following an ACL injury, is quieting the knee down (ie getting any swelling settled),
getting as much range of motion back, and getting the knee (especially the hamstrings) as strong as possible, before an operation. A good physiotherapist is your best friend.
The operation to fix the ACL, usually involves replacing it with a hamstring or part of the quadriceps tendon from the patient. This can be done as day-surgery, but then the true work for the athlete begins.
Rehab should be intensive, with reasonable time lines being about 3 months to get back to straight ahead activity, and 6 months to stop and go sport.
Best wishes to Rivera. I'd hate to see him end his career this way.