Hyperextension of the knee is a condition where the back of the knee joint opens too widely, allowing the tibia (shinbone) to slip backwards, beyond its normal limit.
The knee is a complex, hinged joint. It is formed where the femur (thighbone), the tibia and the patella (kneecap) meet. These bones articulate with each other to allow the leg to bend and, to a limited degree, twist. The parts of the bones that come into contact with each other are covered with a smooth cartilage that prevents friction as the bones move over each other. Also within the joint are cushions of cartilage that act as shock absorbers to protect the bones. Several ligaments connect the bones, keeping them in alignment and limiting the extent of movement. Surrounding the joint is a capsule lined with synovium, a membrane that secretes a nourishing and lubricating fluid that flows throughout the joint.
If for any reason the ligaments are too loose, or are damaged, they cannot maintain the position of the bones and therefore the stability of the knee, which can then no longer support the weight of the body.
Knee hyperextension is thought to cause as much as a fivefold increase in the risk of injuring the ACL.
A common cause is a straight leg receiving a severe blow that forces the knee backwards, for example during a car crash. This usually results in injury to several knee ligaments and possibly dislocation of the knee.
Hyperextension can also happen as a result of a fall, or while playing a sport that puts great stress on the knee. Examples of such sports are volleyball, football, basketball or gymnastics. This happens less frequently and usually only the anterior cruciate ligament (ACL) within the knee is damaged.
If the quadriceps muscles at the front of the thigh are weak, the hamstring muscles at the back of the thigh will compensate, leading to an imbalance between the two and an increased likelihood of the joint being pulled out of position backwards - hyperextension.
Depending on the severity of the injury, your symptoms may include:
- Pain felt at the back and sides of the knee
- Possible ‘pop’ sound or feeling at the moment of injury
- Swelling that begins within three hours of injury
- Instability of the knee and a feeling that it might give way
- Decreased range of motion of the knee
Because the knee is an intricate joint and can be damaged easily, it is important to seek professional help if your knee has been injured. Correct treatment is necessary to achieve a full recovery.
Your doctor will ask you questions relating to the injury, such as how and when it happened, the position that your leg was in at the time, and the onset and duration of symptoms. He or she will also need to know about any previous knee injuries. A complete medical history will include questions about your general health, lifestyle, activities, and sports participation.
During the physical examination the doctor will carefully evaluate your knee, and compare it with your unaffected leg. Swelling, discoloration, and any obvious deformity will be noted. The range of motion will be tested and, if pain and swelling allow, the doctor will bend your knee and gently push and pull on the shin to assess the strength of the ligaments.
Depending on the suspected damage, you may need to have some diagnostic tests. These will probably include x-rays to view the bones, and CT or MRI scans, which clearly show the soft tissues. Arthroscopy (camera-guided knee surgery) is sometimes used for diagnostic purposes.
Treatment for knee hyperextension depends on which ligaments or other knee structures are damaged and, if so, the severity of the damage.
For mild cases, time and conservative treatment will usually be sufficient, with recovery taking only a few weeks. For more severe injuries surgery may be necessary, in which case your orthopedic surgeon will discuss all the available options with you. Recovery and rehabilitation of the knee would take several months.
Your doctor or physiotherapist will develop an exercise program to restore mobility to your knee and strengthen the quadriceps muscles. It is important that you follow professional advice in order to achieve full recovery and prevent further injury.
- Rest: Avoid putting weight on the knee or bending it. Use crutches when walking. Your doctor may recommend a temporary knee brace.
- Ice: Apply ice, crushed in a bag and covered with a towel, to the sides and back of the knee for as long as is comfortable, several times a day.
- Compression: Wrap the knee in an ace bandage for support.
- Elevation: Raise the knee above the level of your heart, whenever possible.
- NSAIDs: Over the counter pain and anti-inflammatory medicine will relieve some of your symptoms.
Make sure that you exercise both legs equally to avoid creating imbalance.
Sitting on the floor with your injured leg straight out in front of you and the unaffected leg bent with the foot on the floor, contract the quadriceps of the injured leg by pressing the knee towards the floor. Hold the position for 5-10 seconds then relax. Repeat 10 times.
Place a rolled towel under the injured knee. Lie on your back with your unaffected leg bent, the foot flat on the floor. Slowly straighten the injured leg by engaging the quadriceps. Hold the position for 5-10 seconds then lower. Repeat 10 times.
Lying on your back, bend the injured knee and keep the foot on the floor. Slide the heel towards the buttocks as far as you can without pain. Repeat 10-20 times.
Straight leg raise:
Lying on your back on the floor, bend your unaffected knee and rest the foot on the floor. Keeping the knee of the injured leg straight, contract the thigh muscles and lift the leg up until the heel is about 6 inches off the ground. Hold for 5-10 seconds then relax. Repeat 10 times.
What to look for in a brace:
Your doctor will probably recommend a particular brace for you. There are many brands available, but you may want to consider a hinged knee brace that can be locked to prevent any hyperextension. The brace should be properly fitted so that it provides comfortable support without being constricting.