If you've ever sat on the sidelines with a knee injury, you probably appreciate how your knees power you through various sports and activities: kicking, jumping, running, and pivoting. To avoid knee injuries, it helps to understand how your knees work and what you can do to protect them.
What's in a Knee?
The knee is a joint, actually the largest joint in the body. Your knees provide stability and allow your legs to bend, swivel, and straighten.
The knee is made up of bones, cartilage, muscles, ligaments, and tendons, all working as one. What makes knee injuries complicated is they could be caused by stress or damage to any of these parts.
Bones and Cartilage
The knee sits in the middle of three bones: the tibia (your shinbone), the femur (your thighbone), and the patella (the kneecap). The patella is a flat, round bone that protects the knee joint.
The ends of the femur and the patella are covered in articular cartilage (think of the white stuff at the end of a chicken bone). Articular cartilage acts like a cushion and keeps the femur, patella, and tibia from grinding against each other. On the top of the tibia, extra pads of cartilage called menisci help absorb the body's weight (if you're talking about just one, it's called a meniscus). Each knee has two menisci — the inside (medial) meniscus and the outside (lateral) meniscus.
The muscles around the knee include the quadriceps, a group of four muscles at the front of the thigh, and the hamstring, located at the back of the thigh. The quadriceps help you straighten and extend your leg, and the hamstring helps you bend your knee.
Tendons and Ligaments
Tendons are like cables of strong tissue that connect muscles to bones. The tendons in the knee are the quadriceps, patellar, and hamstring tendons. All work together to allow the leg to extend.
Ligaments are rope-like cords that bind bones to bones or cartilage to bones. There are four ligaments in the knee that help connect the femur to the tibia and keep your legs stable:
- medial collateral ligament (MCL): The MCL connects your femur to your tibia along the inside of your knee. It keeps the inner part of your knee stable and helps control the sideways motion of your knee, like keeping it from bending inward.
- lateral collateral ligament (LCL): The LCL connects your femur to your tibia along the outside of your knee. It keeps the outer part of your knee stable and helps control the sideways motion of your knee, like keeping it from bending outward.
- anterior cruciate ligament (ACL): The ACL connects your femur to your tibia at the center of the knee. It helps control the knee's rotation.
- posterior cruciate ligament (PCL) — The PCL connects your femur to your tibia at the back of the knee. It helps control the knee's backward motion, like keeping the shinbone from sliding out under the thighbone.
Types of Knee Injuries
All those working parts mean there are a bunch of ways to injure a knee. Common causes for injuries are overuse (from repetitive motions, like in many sports), sudden stops or twists, or direct blows to the knee.
Here are some of the more common ways teens injure their knees:
A sprain means you've stretched or torn a ligament. Common knee sprains usually involve damage to the ACL and/or MCL. The most serious sprains involve complete tears of one or more of the knee ligaments. Symptoms of knee sprains include:
- a popping or snapping sound in the knee at the time of injury
- pain that seems to come from within the knee, especially with movement
- not being able to put any weight on that leg
- fluid behind the kneecap
- the knee feels loose or unstable or gives way
A strain means you've partly or completely torn a muscle or tendon. With knee strains, you may feel symptoms similar to a sprain and may see bruises around the injured area.
Tendonitis happens when a tendon gets irritated or inflamed. It is often caused by overuse. A person with tendonitis in the knee might have pain or discomfort when walking, or when bending, extending, or lifting a leg.
Damage to the menisci is a really common sports injury, especially in sports where sudden changes in speed or side-to-side movements can cause them to tear. Meniscus injuries often occur together with severe sprains, especially those involving the ACL.
Meniscus injuries can cause tenderness, tightness, and swelling around the front of the knee. Sometimes fluid collects around the knee (this is called effusion).
Fractures and Dislocations
A fracture is a cracked, broken, or shattered bone and is usually diagnosed by an X-ray. You may have trouble moving that bone and are likely to have a lot of pain.
Patellar dislocation happens when the patella (the kneecap) is knocked off to the side of the knee joint by twisting or some kind of impact. Sometimes it will go back to its normal position by itself, but usually it will need to be put back into place by a doctor. Symptoms include swelling and a lot of pain at the front of your knee. There will usually be an abnormal bulge on the side of your knee, and you may be unable to walk.
Sometimes a small piece of bone or cartilage softens or breaks off from the end of a bone, causing long-term knee pain. This is called osteochondritis dessicans (OCD). Symptoms of OCD include pain; swelling; an inability to extend the leg; and stiffness, catching, or popping sensations with knee movement. Treatment can include resting the knee, wearing a cast for a couple of months, and sometimes surgery in older teens.
Chondromalacia pattellae happens when the cartilage in the knee joint softens because of injury, muscle weakness, or overuse, and the patella and the thighbone may rub together. This causes pain and aching, especially when a person walks up stairs or hills. Treatment may involve surgery.
A bursa is a sac filled with fluid over a bony bump to prevent friction. If a bursa in the knee becomes irritated and swollen from overuse or constant friction, it can develop into a condition called bursitis. Symptoms of bursitis in the knee include warmth, tenderness, swelling, and pain on the front of the kneecap.
Osgood-Schlatter disease is a painful disorder caused by repetitive stress on the front end of the tibia where the patellar tendon connects to the bone. It happens most frequently in young athletes between the ages of 10 to 13 years. Symptoms include a bump below the knee joint that's painful to the touch and is also painful with activity. Pain is relieved with rest.
What Do Doctors Do?
A doctor may do different things to figure out whether someone has a knee injury. Treatment for a knee injury usually depends on the type of injury.
If you've injured your knee, the doctor will ask questions about your symptoms, including what your usual activities are, especially any sports you play. The doctor will also want to know about other health conditions that lead to knee pain.
The doctor will then examine the different parts of your knee, checking the bones, ligaments, and tendons for any signs of injury. The doctor will probably bend, twist, and turn your knee to look for any signs of an unstable knee joint. The doctor may ask you to walk, bend over, or squat so he or she can get a better look at your knee.
Sometimes doctors will order an X-ray to get a good picture of the knee bones. A CAT scan or MRI can give the doctor a better three-dimensional picture of the bones, ligaments, or cartilage.
For injuries like mild sprains, strains, and overuse, resting your knee might be one of the first treatments your doctor recommends. Remember RICE:
RICE means you should rest your knee as much as possible, use ice packs for a couple of days to bring down swelling, use compression (ACE) bandages, and prop your leg up on pillows or other soft objects. For inflammation and pain, your doctor may recommend anti-inflammatory medications like ibuprofen.
Other treatment for knee injuries may involve using a knee immobilizer (kind of like a brace or a sleeve that you wrap around your leg to keep it from moving too much) or wearing a cast for a few weeks. You also might have to use crutches to get around for awhile.
For more serious knee injuries, your doctor might recommend you see an orthopedic surgeon (a doctor specially trained in the care of bone and joint diseases; also called an orthopedist). Orthopedists take care of many kinds of knee injuries, especially those involving sports and different types of accidents.
If necessary, an orthopedist will perform arthroscopy, a type of surgery that takes a direct look at the inside of your knee joint.
During arthroscopy, the orthopedist first makes a small opening in the knee and inserts an arthroscope, a tiny tube-like tool, into the joint capsule. The arthroscope contains a lighted video camera on the end and is wired to a television screen that the surgeon watches while moving the scope to pinpoint the exact knee problem. Most of the time, the doctor is able to fix the problem during the procedure, like repairing a torn ACL ligament.
When used to treat ligament and meniscal tears and other types of serious knee injuries, arthroscopy decreases postoperative pain and recovery time.
An orthopedist also can perform open surgery on the knee, which allows him or her to see the injury without the aid of a television screen.
Depending on the type of knee injury you have, your doctor may recommend rehabilitative physical therapy. Working with a physical therapist, you'll do specific exercises designed to take your knee joint through its range of motion to prevent stiffness and scarring as your knee heals. You also may need to do regular exercises to stretch and strengthen the muscles surrounding the knee. Physical therapy is commonly used to help a person recover after surgery.
You may be anxious for your knee to heal so you can get back to your normal life. But trying to rush your recovery after an injury or surgery can put you at risk for future injury and may further extend the healing process. Take your doctor or physical therapist's instructions seriously, and don't put your health in jeopardy by returning to your usual activities before you get the go-ahead from a health pro.
Preventing Knee Injuries
Preventing knee injuries from the start is a lot less painful and a lot less hassle than undergoing surgery. If you play sports, always wear appropriate protective equipment during practices and competitions. Kneepads and shin guards (as well as helmets and other protective gear) will help to protect you from injury. You'll also want to make sure you wear supportive shoes that are in good condition and appropriate for your sport.
When it comes to your workouts, always warm up and cool down, and remember to work up to your training program slowly. Suddenly increasing the intensity or duration of your workouts can lead to overuse injuries. Try weightlifting to strengthen your muscles and stretching, Pilates, and yoga to improve your flexibility because strong, flexible muscles help support and protect joints.
If you play only one sport, try conditioning and training year-round — even if it's at a lower intensity than during your competitive season — to maintain coordination and balance. That way you'll be less likely to injure yourself during your competitive season.
In growing kids and teens, imbalances in muscle flexibility and strength can lead to injuries and inflammation from overuse. Regular stretching can help. After an injury or surgery has healed, it is also important to continue a regular stretching or conditioning program to prevent another injury.
The way you move also can help you prevent knee injuries. If your sport involves a lot of jumping, make sure to bend your knees when you land, which takes pressure off of the ACL. Do you have to cut laterally or pivot frequently in your sport? Use your joints to crouch and bend at the knees and hips, reducing your chance of a ligament injury.
If you notice any signs of knee injuries or knee pain, tell your coach, parent, or doctor. Limit your activities until you can get treatment or a diagnosis. Taking care of injuries right away saves a lot of trouble and hassle later.
Reviewed by: Alfred Atanda Jr., MD
Date reviewed: October 2012