If you’re familiar with only one kind of knee injury, chances are the one you’ve heard of is a torn ACL – especially if you’re a sports fan or an athlete. But what exactly is the ACL, and how does it get torn?
“ACL” stands for “anterior cruciate ligament.” There are two cruciate ligaments, and they run diagonally through the middle of the knee in a cross shape (“cruciate” and “cross” come from the same Latin root that gives us the word “crucifix”). The posterior cruciate ligament (PCL) connects in the back of the knee, and the anterior cruciate ligament connects to the front.
Together, these two ligaments control the back and forth motion of your knee. Specifically, the ACL prevents your tibia (the larger bone in your lower leg) from sliding out in front of your femur (your thigh bone), and stabilizes the joint so it does not rotate too much. In addition to the ACL and PCL, ligaments running along the outer side of your knee and the inner side help to ensure your knee only bends in the direction it is meant to.
So how does the ACL get injured?
Changing direction rapidly, stopping suddenly, slowing down while running, landing from a jump incorrectly, and direct collision or other forceful contact are the most common culprits. If you think about the types of moves you see happening in sports such as football and skiing, it’s not surprising that the knee – and the ACL specifically – can become quite vulnerable to injury-causing sudden stress. Yet even something as “non-athletic” as a toddler falling on a parent’s outstretched leg can result in a torn ACL.
How do you know if you’ve injured your ACL?
An orthopedic provider can tell you for sure if you’ve torn your ACL. The primary diagnosis tool is to physically examine the structures of your injured knee and compare them to your non-injured knee. You doctor might also use an x-ray to be sure there are no broken bones associated with your injury. Although an MRI (magnetic resonance imaging) scan is not usually needed to diagnose an ACL injury, it does offer a detailed view of damage to ligaments and other soft tissues, and can help your provider determine your treatment options.
That said, here are some signals that you may have just injured your ACL:
- You hear a “popping” sound and your knee gives out
- Pain with swelling within 24 hours after injury
- Loss of full range of motion
- Tenderness along the joint line
- Discomfort while walking
How do ACL injuries get treated?
Most ACL tears in younger or athletic patients will require surgery to allow the person to return to full sports activity. However, ligaments such as an ACL cannot be stitched back together. Instead, they must be reconstructed using a tissue graft from elsewhere in the body – usually from one of the tendons in your leg. The tissue graft acts like a scaffold for the new ligament to grow on.
For ACL surgery, the orthopedic surgeon will insert instruments through two or three small incisions in the knee to make the repairs. Even though this is considered a less invasive procedure, it will still take six months or more before a patient can return to playing sports. Tissue regrowth takes time!
Not all ACL tears require surgery, however. If you are not very active or are elderly, your orthopedic doctor may recommend non-surgical treatments if your knee’s overall stability is intact. In this case, you may need to wear a brace to enhance knee stability and use crutches to minimize the weight you put on that leg. You’ll also carefully begin physical therapy exercises to regain function and strengthen the muscles that support and move your knee – an essential step with or without surgery.
If you’ve experienced an ACL tear or another kind of knee injury, our providers, physical therapists, and the rest of the care team at Spectrum Orthopaedics are ready to guide you through the uncertainties – and get you back on your feet.
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