You may know someone who has torn their ACL, or you may have heard about this injury while watching sports on TV. In fact, a tear in the anterior cruciate ligament (ACL) is one of the most common knee injuries, and it can happen to professional athletes, to those exercising just for fun, or those just living their daily lives.
The ligament, located in the middle of your knee, connects the bottom of the thigh bone (femur) to the top of the shinbone (tibia). It provides critical stability for your knee, making it important for sports performance, as well as walking down the street.
In this Q&A, orthopedic surgeon Shawn Anthony, MD, MBA, Associate Chief of Sports Medicine, explains what happens if you tear your ACL and describes treatments, including a new approach that repairs your torn ligament by regrowing your own tissue rather than removing the torn tissue and rebuilding it.
How common are ACL tears?
ACL tears happen often. A quick pivot or contact injury can cause this ligament to tear. I see patients from teens, to young adults, all the way to people in their 60s and 70s with ACL tears. It can affect professional athletes, weekend warriors, and even those who just misstep while walking down the street.
What does an ACL tear feel like?
An ACL tear is one of the more painful knee injuries at the moment it happens, when the ligament actually tears. The pain is followed by swelling, difficulty walking, and a sense of instability where your knee feels like it’s going to buckle under you. Over the first week or two after the ACL injury, the pain and swelling calms down, and patients regain their range of motion. They feel fairly normal by about three to four weeks after the injury. Patients can run straight ahead with an ACL tear, even run a marathon, with minimal to no symptoms. But they will experience a sense of instability whenever they do activities that engage the ACL—whenever they try to turn or pivot.
How do you diagnose an ACL tear?
We start with a physical exam, and if the ligament feels loose, then we follow with a magnetic resonance imaging (MRI) scan. This shows us the size and location of the tear. But there are some limitations to the information we get with an MRI, especially with partial tears.
How do you treat ACL tears?
The first step after an ACL tear is to start rehabilitation to regain range of motion and reduce swelling. Some partial ACL tears can heal just with time and physical therapy; we can usually get a sense whether this is likely based on the MRI. But patients who are active and engage in pivoting sports will choose surgical intervention to improve knee stability. There are two ways to surgically treat a torn ACL: reconstruction and repair. Both of these techniques are performed through a knee arthroscopy, or key-hole minimally invasive surgery. ACL reconstruction is the traditional approach. We remove the torn tissue and reconstruct the ACL using either the patient’s own tissue or material from a tissue bank. ACL repair, particularly using the BEAR implant, helps guide the ACL to heal itself.
How does BEAR ACL repair work?
BEAR ACL stands for bridge-enhanced ACL repair. We use a collagen scaffolding, which looks like a giant marshmallow and helps regrow the patient’s ACL. (Collagen is a protein and a fiber like structure that makes up your connective tissues.) We hydrate it with the patient’s blood, then insert it inside the knee, between the torn parts of the ligament. The BEAR implant guides the patient’s own ACL tissue as it regrows (called regeneration) and then it dissolves within two months.
With both approaches, most patients can return to normal daily activities in two to four weeks, running in about four months, and pivoting sports in about nine months. Both surgeries are effective, but clinical studies have found that patients who had the BEAR ACL repair reported that their knees feel more natural. In addition, the BEAR approach offers advantages in case the patient re-tears the ACL. Re-tearing the ACL happens in about five percent of cases, regardless of how it was treated. If a patient had a BEAR repair surgery, it is much easier to do a second surgery since BEAR does not involve harvesting the patient’s own tissue or drilling holes in the bone.
Do ACL tears lead to osteoarthritis?
After an ACL injury, about one in three patients will develop osteoarthritis, which means loss of cartilage in the knee, within 10 years of the injury. This is slightly higher in patients who have untreated ACL tears. We believe that’s due to the initial injury, the trauma to the knee cartilage when the ACL is torn. Animal studies have shown promising results of less osteoarthritis in those treated with BEAR ACL repair surgery; that is an area of ongoing research in the clinical studies of BEAR patients.