There are four main ligaments in the knee that can become injured. During injury, a knee ligament may be sprained (stretched), or sometimes ruptured (torn). Ligament rupture can be partial (just some of the fibres that make up the ligament are torn) or complete (the ligament is torn through completely). Knee ligament injuries can cause pain, swelling, tenderness, bruising and reduced movement of your knee. Your knee joint may feel unstable and you may walk with a limp. Treatment of a knee ligament injury can depend on a number of things including which ligament is injured and how sporty and active you are.
Some anatomy of the knee joint
The diagrams above show the knee joint.
There are four bones around the area of the knee joint: the femur (thigh bone), the tibia (the main shin bone), the fibula (the outer shin bone) and the patella (the knee cap). But the main movements of the knee joint are between the femur, the tibia and the patella. Articular cartilage (tough connective tissue) lines the ends of the tibia and femur and the back of the patella around the knee joint. The articular cartilage reduces friction between the bones of the knee joint and helps smooth movement between them.
Each knee joint also contains a medial and lateral meniscus (inner and outer meniscus). These are thick rubbery pads of cartilage tissue. They are C-shaped and become thinner towards the middle of the joint. The menisci cartilages sit on top of, and are in addition to, the usual thin layer of articular cartilage which covers the top of the tibia. The menisci act like shock absorbers to absorb the impact of the upper leg on the lower leg and also help to improve smooth movement and stability of the knee.
There are also four ligaments around the knee joint. A ligament is a tough strip of connective tissue that joins one bone to another bone around a joint. The knee joint ligaments help to stabilise and support the knee when it is moved into different positions.
Each ligament has a different job to do:
• The anterior cruciate ligament (ACL) is one of the ligaments inside the knee joint. It runs diagonally connecting the anterior (front) of the tibia to the posterior (back) of the femur. This ligament helps to stabilise the knee joint by controlling backward and forward movements of the knee. It stops the tibia bone from moving forwards in front of the femur.
• The posterior cruciate ligament (PCL) is the other ligament inside the knee joint. It also runs diagonally across the knee connecting the posterior (back) of the tibia to the anterior (front) of the femur. The ACL and PCL cross each other inside the knee joint and some people call them the cross ligaments. The PCL helps to control the forward and backward movements of the knee.
• The medial collateral ligament (MCL) is one of the ligaments on the outside of the knee joint. It runs between the femur and the tibia on the inner side of the knee. It helps to protect and stabilise the knee joint against any blows or forces that may be directed on to the outer side of the knee. It helps to limit the amount that the knee moves from side to side.
• The lateral collateral ligament (LCL) is the other main ligament on the outside the knee joint. It runs between the femur and the fibula on the outer side of the knee. It helps to protect and stabilise the knee joint against any blows or forces that may be directed on to the inner side of the knee. This ligament also helps to limit the amount the knee moves from side to side.
The knee joint is surrounded by a protective joint capsule. This is lined by a special membrane called the synovial membrane. The synovial membrane produces synovial fluid which helps to lubricate and reduce friction within the knee joint. There are also muscles that help to support the knee joint. The main ones are the quadriceps (front thigh muscles) and hamstrings (rear thigh muscles) in the legs.
What are the symptoms of a knee ligament injury?
If you have injured one or more of the ligaments in your knee, the symptoms are likely to be similar regardless of the ligament that is injured. The severity of the symptoms depends on the degree of the injury to the ligament. For example, a ligament that is completely torn may produce more in the way of symptoms than a ligament that is just sprained (stretched).
Symptoms can include:
• A popping sound, or a popping or snapping feeling at the time of injury can sometimes be heard if a ligament is completely torn.
• Swelling of your knee. When a ligament is injured, there may be some bleeding inside your knee joint from the damaged ligament. This can lead to knee swelling. The degree of swelling will depend on the severity of the injury. Minor ligament sprains may cause little in the way of swelling, whereas completely torn ligaments may lead to a lot of knee swelling.
• Pain in your knee. Again, the degree of pain can depend on the severity of the knee injury.
• Tenderness around your knee on touching. This may be mild tenderness over the actual ligament in minor sprains, or more generalised and severe tenderness if a ligament is torn.
• Not being able to use or move your knee normally. In complete ligament tears, movement can be severely reduced, whereas in more minor sprains, you may have a relatively good amount of knee movement.
• A feeling that your knee is unstable or perhaps giving way if you try to stand on it. This may cause you to limp. Again, this depends on how severe the ligament injury is. You may be able to stand if you only have a minor sprain.
• Bruising around your knee can sometimes appear, although not always. It may take some time for bruising to develop.
For the first 48-72 hours think of:
• Paying the PRICE – Protect, Rest, Ice, Compression, Elevation; and
• Do no HARM – No Heat, Alcohol, Running or Massage.
Paying the PRICE:
• Protect your injured knee from further injury.
• Rest your affected knee for 48-72 hours following injury. Consider the use of crutches to keep the weight off your injured knee. However, many doctors say that you should actually not keep your injured knee immobile for too long. You can usually start some exercises to help keep your knee joint moving and mobile as soon as you can tolerate the exercises without them causing too much pain. You can ask your doctor when you can start to move your knee joint and what exercises you should do.
• Ice should be applied as soon as possible after your knee injury for 10-30 minutes. Less than 10 minutes has little effect. More than 30 minutes may damage the skin. Make an ice pack by wrapping ice cubes in a plastic bag or towel. (Do not put ice directly next to skin as it may cause ice-burn.) A bag of frozen peas is an alternative. Gently press the ice pack on to your injured knee. The cold from the ice is thought to reduce blood flow to the damaged ligament. This may limit pain and inflammation. After the first application, some doctors recommend reapplying for 15 minutes every two hours (during day time) for the first 48-72 hours. Do not leave ice on while asleep.
• Compression with a bandage will limit swelling, and help to rest your knee joint. A tubular compression bandage can be used. Mild pressure that is not uncomfortable or too tight, and does not stop blood flow, is ideal. A pharmacist will advise on the correct size. Remove before going to sleep. You may be advised to remove the bandage for good after 48 hours. This is because the bandage may limit movement of the joint which should normally be moving more freely after this time. However, bandages of the knee are sometimes kept on for longer to help keep swelling down and to keep the affected knee more comfortable. Ask your doctor what is best in your case.
• Elevation aims to limit and reduce any swelling. For example, keep your foot on the affected side up on a chair when you are sitting. It may be easier to lie on a sofa and to put your foot on some cushions. When you are in bed, put your foot on a pillow. The aim is that your affected knee should be above the level of your heart.
Avoid HARM for 72 hours after injury. That is, avoid:
• Heat – for example, hot baths, saunas, heat packs. Heat has the opposite effect on the blood flow to ice. That is, it encourages blood flow. So, heat should be avoided when inflammation is developing. However, after about 72 hours, no further inflammation is likely to develop and heat may then be soothing.
• Alcohol drinks, which can increase bleeding and swelling and decrease healing.
• Running or any other form of exercise which may cause further damage.
• Massage, which may increase bleeding and swelling. However, as with heat, after about 72 hours, gentle massage may be soothing.
• Paracetamol and codeine: paracetamol is useful to ease pain. It is best to take paracetamol regularly, for a few days or so, rather than every now and then. An adult dose is two 500 mg tablets, four times a day. If the pain is more severe, a doctor may prescribe codeine, which is more powerful, but can make some people drowsy and constipated.
• Anti-inflammatory painkillers: these drugs are also called non-steroidal anti-inflammatory drugs (NSAIDs). They relieve pain and may also limit inflammation and swelling. There are many types and brands. You can buy two types (aspirin and ibuprofen) at pharmacies without a prescription. You need a prescription for the others. Side-effects sometimes occur with anti-inflammatory painkillers. Stomach pain, and bleeding from the stomach, are the most serious. Some people with asthma, high blood pressure, kidney failure, bad indigestion and heart failure may not be able to take anti-inflammatory painkillers. So, check with your doctor or pharmacist before taking them in order to make sure they are suitable for you.
But note: Clinical Knowledge Summaries, a well-known source of guidance for doctors in the UK (cited below), do not recommend that anti-inflammatory painkillers be used in the first 48 hours after the injury. This is because of concerns that they may delay healing. The logic is that some inflammation is a necessary part of the healing process. So, it may be that decreasing inflammation too much by taking these drugs may impair the healing process. This may be a theoretical concern as no trials have proved this point. Further research is needed to clarify the use of these drugs following an injury.
Also, if you are having surgery to repair a torn ACL (see below), it is thought that, theoretically, NSAIDs may not be a good idea to take for a long period of time after the surgery because they may have an effect on the success of the surgery.
• Rub-on (topical) anti-inflammatory painkillers: again, there are various types and brands. You can buy one containing ibuprofen, without a prescription, at pharmacies . You need a prescription for the others. There is debate as to how effective rub-on anti-inflammatory painkillers are compared with tablets. Some studies suggest that they may be as good as tablets for treating sprains. Some studies suggest they may not be as good. However, the amount of the drug that gets into the bloodstream is much less than with tablets, and there is less risk of side-effects.
This may be helpful after some knee ligament injuries. Physiotherapy may help to improve the range of movement in your injured knee. Exercises may also be suggested to help strengthen the muscles that support your knee joint. If you are considering surgery to repair a torn knee ligament, you may be advised to have physiotherapy before the operation.
Depending on the knee ligament injury that you have, your doctor may advise you to wear a special brace to support your knee while the damaged ligament heals. Knee braces usually have a hinge mechanism that allows some bending and extending movement of your knee joint but not movement of your knee from side to side. However, a knee brace may not be advisable for all knee ligament injuries. You may like to discuss the use of a knee brace with your doctor.
Sometimes surgery may be suggested after a knee ligament injury. This is more likely if:
• You are someone who does a lot of sport or you are a very active person and you have injured your ACL.
• You have injured more than one knee ligament, or you have injured a knee ligament and have also injured another part of your knee.
• You have ruptured your LCL.
Surgery is most commonly suggested to repair ACL injuries. However, it is fair to say that the best way to treat a torn ACL is still debated. Physiotherapy and other measures may be all that is needed by some and may prevent the need for an operation. The decision about whether or not to use surgery depends on each individual person, the activities and sports that you do, how active your lifestyle is in general, your underlying health and any other knee injuries that you may also have. You may want to discuss the pros and cons of surgery with your doctor.
If surgery is carried out to repair a torn ACL, your doctor will usually advise that you wait some weeks after your initial injury. This is so that any swelling has had a chance to go down, you have got more movement back in your knee and you have built up the strength in the muscles of your thighs that help to support your knee joint. Your doctor may refer you for physiotherapy to help to prepare you for surgery.
The ACL ligament cannot simply be stitched back together. Instead, surgery to reconstruct, or rebuild, the ACL is usually carried out. Most often, part of a tendon, or tendons, from somewhere else in your body is used to reconstruct your ACL. For example, the following may be used:
• Part of your patellar tendon (the tendon at the bottom of your kneecap).
• Part of your quadriceps tendon (the tendon that attaches your kneecap to the quadriceps muscle at the front of your thigh).
• Part of your hamstring tendons (the tendons that run from the back of your knee up the back of your thigh).
• Sometimes, tendons from someone else (a donor) may also be used to repair your ACL.
The tendon is fixed in place inside your knee joint, using staples or screws. Once fixed in place, over time, a new ligament should grow over the tendon that has been used. Keyhole surgery is usually used to reconstruct your ACL.
There is currently some debate as to the best way to treat PCL injury – with surgery, or without surgery. You may like to discuss this with your doctor. If surgery is carried out, as with surgery for ACL injury, the damaged ligament is replaced using a tendon, or tendons, from elsewhere in your body, or using a donor tendon.
Surgery is not often needed for MCL injuries.
How long does a knee ligament injury take to heal?
This will depend on which knee ligament you have injured and also how severe your injury is. Also, if you have injured more than one ligament in your knee, recovery may take longer.
If you have surgery to repair your ACL, it usually takes around six months before your knee has recovered enough for you to return to your previous sporting activities but, in some people, it may be longer. In general, surgery to reconstruct an ACL has good results in around 8-9 out of 10 people.
If your PCL has been treated using surgery, it can take between 9 and 12 months before complete recovery.
After a sprain or partial tear to the MCL, the ligament has completely healed in most people after three months. If there is a complete tear, recovery may take a little longer but most people are back to their usual activities after 6-9 months.
Note: you should ask advice from your doctor or physiotherapist about when it is safe for you to start exercise or sport again after a knee ligament injury. It is important that you do not start exercising again until your knee is pain-free and completely stable. If you start exercising too early, you may cause further injury to your knee.
Knee ligament injuries can be unpredictable and can affect anyone, including fit people who do a lot of sport. However, if you exercise regularly and build up the strength in the muscles of your legs that help to support your knee joint (particularly your hamstring and quadriceps muscles), this may help to reduce your chance of knee ligament injury. If you are not used to exercising regularly, you should start gently and gradually build up the frequency and intensity of your exercise.
During an exercise session, or if you are playing sport, make sure that you warm up at the start of your training. This increases the flow of blood to your muscles and helps to loosen up your joint movements. Warming up may also help to prevent injury.
Some people wear a knee brace when they are exercising or doing sporting activities if they have previously had a knee ligament injury, or even just to prevent a knee injury in the first place. Some studies have shown that wearing a brace may help to reduce the chance of another injury whilst other studies have not shown this as the case. One particular study looked at people with previous injury to their ACL. The study found that those who wore a knee brace whilst skiing were less likely to have a further knee injury than those who did not wear a knee brace. In general, more research is needed to look at the use of knee braces for preventing knee injury.