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.

When temperatures soar, especially combined with high humidity, people are at risk for heat-related illness including heat exhaustion and heat stroke.

While it’s best to avoid going outside in extreme heat, not everyone can stay inside. Whether you work outdoors or need to get in your exercise routine, there are ways to reduce your risk of developing heat illness.

Michael Redlener, MD

In this Q&A, Michael Redlener, MD, Medical Director of the Mount Sinai West Emergency Department, explains how heat can affect you and how to stay safe.

What are the risks of being active outdoors when it’s very hot?

If you are exercising or working outside, your body is working harder and your metabolism (internal process of converting food to energy) increases.  Normally, your body can regulate the internal temperature even as your metabolism increases. However, when it is hot outside, the high environmental temperature makes it harder for your body to regulate its internal temperature, putting you at a higher risk of increasing your body temperature to dangerous levels.

Who is most at risk?

People who are 65 or older, children, people who have disabilities, and people who are generally working outside or spending a lot of time outside have a higher tendency to get heat illness. People who are overweight, on certain medications, living with heart disease or mental illness, and people who drink alcohol, are all at risk. Having a sunburn also increases your risk because it reduces your ability to control your temperature through your skin’s normal mechanism.

Concerning medications, certain drugs can affect your body’s ability to process heat, so it’s important to consult your doctor if you plan on being out in the heat. The Centers for Disease Control and Prevention provides guidance on heat and medications.

What signs indicate I’m developing heat illness when being active in the heat?

There’s a range of conditions to watch for. Painful heat cramps caused by dehydration and too much sweating are usually the first sign of danger. If you experience heat cramps, stop any physical activity, move to a cooler place, drink water or a sports drink with electrolytes, and wait for the cramps to go away before you restart physical activity.

If cramps last longer than an hour, or if you are for some reason on a low sodium diet, or if you have heart problems and these symptoms continue, seek medical help. If it progresses, it becomes heat exhaustion. You will experience heavy sweating, and feel cold and clammy. You may have a fast and weak pulse, some nausea or vomiting, and muscle cramps. You will also experience general fatigue and tiredness, dizziness, possibly a headache, and you may even pass out.

If this happens to you or someone else, move to a cooler place and loosen your clothing. If possible, apply cool wet cloths to your body or get into a cool bath to reduce your body temperature. Sip water if you feel nauseous, and to make sure you’re staying hydrated. If you are vomiting and can’t stop, or if your symptoms are getting worse or lasting longer than an hour, seek medical help.

How does heat stroke differ?

The next stage after heat illness is heat stroke, the worst heat-related medical condition that can happen to you. During heat stroke, your body temperature is 103 degrees or greater. Not only will you experience a headache, dizziness, and nausea, you also become confused. You don’t know where you are, or possibly even who you are, and you can pass out. Heat stroke is an extremely dangerous condition that can lead to permanent brain injury, and even death. If you are exercising and become confused or can no longer function, or notice this happening to someone else, get to a cooler place quickly and call 911. If possible, apply cool cloths or take a cool bath to get that temperature down.

How can I change my exercise routine to reduce my risk?

Here are some things you can do to reduce your risk:

• Limit outdoor activity as much as possible, especially during the middle of the day, the hottest period. If you need to exercise outdoors, do so in the early morning (before 10 am) or evening (after 4 pm).
• Wear sunscreen—SPF 30 or higher.
• Start slow and pace your activity, and slowly pick up the pace as you can tolerate.
• Keep hydrated during and after your workout.
• Wear loose, lightweight, light-colored clothing, which absorb less heat.

How can I stay properly hydrated?

There are a number of ways to make sure you drink enough fluids.

• Bring a water bottle and drink more water than usual.
• Drink sports drinks with electrolytes to maintain a balance between water and salt in your body.
• Don’t wait until you’re thirsty to drink. Once you are thirsty, you’re already dehydrated.
• Avoid very cold drinks, which can cause stomach cramps due to the dramatic shift in body temperature during extreme heat.
• Avoid very sugary or alcoholic drinks, which increase dehydration.

Any other suggestions on what I can do if I work or do physical activity outdoors?

If you have to be outside during the hottest hours, have a plan about what you are going to do should you start feeling badly. If you are with someone, such as a friend or coworker, check on each other to stay hydrated and get help if medical attention is needed.