Your knee is a complex joint with many components, making it vulnerable to a variety of injuries. Some of the most common knee injuries include fractures, dislocations, sprains, and ligament tears.
The knee is the largest joint of the body, and is also one of the most commonly injured joints. Bones, cartilage, ligaments, and tendons work together to form your knee joint and allow you to bend your leg. Because of all the moving parts on the knee and the sensitive nature of the joint, it’s very prone to multiple types of injuries.
If you’re experiencing knee pain, it’s likely that you’re suffering from one of the most common knee injuries. We’ll help you understand the makeup of the knee, as well as how to identify the symptoms of a knee injury. However, only your orthopaedic doctor can determine what injury you’re dealing with.
Many knee injuries can be successfully treated with simple measures, such as bracing and rehabilitation exercises. Other injuries may require surgery to correct.
Most of these visits were due to the same common problems. Knee injuries can often be treated at home, but some are serious enough to need surgical intervention.
Read on to learn about knee injuries that can occur after a fall and how to tell the difference between minor injuries that can be treated at home and more severe ones that require medical attention
What Is the Anatomy of the Knee?
The knee is a hinge joint that has a simple purpose. It needs to flex (bend) or extend (straighten) to allow the body to perform many activities, like running, walking, kicking, and sitting. Imagine standing up from a chair if your knees couldn’t bend.
While there are four bones that come together at the knee, only the femur (thighbone) and the tibia (shinbone) form the joint itself. The head of the fibula (strut bone on the outside of the leg) provides some stability, and the patella (kneecap) helps with joint and muscle function. Movement and weight-bearing occur where the ends of the femur called the femoral condyles match up with the top flat surfaces of the tibia (tibial plateaus).
There are two major muscle groups that are balanced and allow movement of the knee joint. When the quadriceps muscles on the front of the thigh contract, the knee extends or straightens. The hamstring muscles on the back of the thigh flex or bend the knee when they contract. The muscles cross the knee joint and are attached to the tibia by tendons. The quadriceps tendon is special, in that it contains the patella within its fibers. The patella allows the quadriceps muscle/tendon unit to work more efficiently. The quadriceps tendon is renamed the patellar tendon from the kneecap to its attachment in the tibia.
The stability of the knee joint is maintained by four ligaments, thick bands of tissue that stabilize the joint. The medial collateral ligament (MCL) and lateral collateral ligament (LCL) are on the sides of the knee and prevent the joint from sliding sideways. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) form an “X” on the inside of the knee and prevent the knee from sliding back and forth. These limitations on knee movement allow the knee to concentrate the forces of the muscles on flexion and extension.
Inside the knee, there are two shock-absorbing pieces of cartilage called menisci (singular meniscus) that sit on the top surface of the tibia. The menisci allow the femoral condyle to move on the tibial surface without friction, preventing the bones from rubbing on each other. Without this cartilage covering, the friction of bone on bone would cause inflammation, or arthritis.
Bursas surround the knee joint and are fluid-filled sacs that cushion the knee during its range of motion. In the front of the knee, there is a bursa between the skin and the kneecap called the prepatellar bursa and another above the kneecap called the suprapatellar bursa (supra=above).
Each part of the anatomy needs to function properly for the knee to work. Acute injury or trauma as well as chronic overuse may cause inflammation and its accompanying symptoms of pain, swelling, redness, and warmth.
Common Knee Injuries
The knee is one of the most commonly injured parts of the body. Sports, falls, and motor-vehicle accidents account for the vast majority of knee pain and injuries to the knee.
The different types of common knee injuries to the knee are defined by the affected anatomy of the knee and the mechanism by which it’s injured.
Knee sprains are injuries to the ligaments that hold the knee together. There are multiple ligaments that stabilize the knee and keep it in alignment. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) stabilize the knee in movement from front to back and cross each other in the middle of the knee joint. The medial collateral ligament (MCL) and lateral collateral ligament (LCL) stabilize the knee so that the bones do not slide from side to side.
Ligament sprains are graded by the amount of stretching or tearing of the ligament fibers and how much instability it causes as follows:
- Grade 1 knee sprain: The ligament is stretched and painful, but fibers are not torn and no instability is present.
- Grade 2 knee sprain: The ligament fibers are torn partially, mild instability may be evident.
- Grade 3 knee sprain: The ligament fibers are completely torn and the knee is unstable.
Knee strains occur when tendons or muscles surrounding the knee are stretched, usually due to hyperflexion or hyperextension of the knee. These strains can lead to pain outside of the knee joint but can cause dysfunction of the normal range of motion of the knee. The patellar tendon stretches from the lower kneecap to the front of the tibia bone at the front of the leg.
Knee bursitis occurs when a fluid-filled pouch (called a bursa) in the knee is irritated, inflamed, or infected. Bursas are fluid-filled sacs located around joints that act as shock absorbers that minimize the friction between various tissues, such as the muscles and tendons around the joints. In the knee, there are two main bursas, one above the kneecap (patella), and one below the knee joint near the front of the tibia bone.
Tears of the meniscus can occur from damage to the inside of the knee. The medial and lateral menisci (plural of meniscus) are semi-round, articular cartilage that act as shock absorbers and smooth cushions for the thighbone (femur). These menisci can be injured acutely or can become dysfunctional gradually due to overuse and/or aging.
Knee joint dislocation can occur due to high-impact, large-force injuries to the knee (sports, motor vehicle accidents). This is a rare injury but causes severe damage to all the anatomical components of the knee and can include damage to the blood vessels and nerves about the knee. This requires emergency treatment or surgery.
The kneecap (patella) can dislocate to the side of the knee. Patellar dislocation can be very painful but is generally not life-threatening and can be treated by popping it back into place (reduction of the patella), splinting, and physical therapy.
Knee fractures occur from direct blows to the bones. Patella, or kneecap, fractures occur when a person falls directly down onto the knees and the kneecap cracks due to the force. Collapse of the top of the tibia bone in the knee (tibia plateau fracture) can occur from sudden compression injury to the knee, especially in people with osteoporosis. Other fractures of the long bones (fibula, tibia, and femur) are rare with isolated injures to the knee.
Other overuse injuries of the knee include patellofemoral pain syndrome (often referred to as “runner’s knee,” which causes pain on the front of the knee) and weakness and degeneration of the cartilage under the kneecap (chondromalacia patella). These injuries are due to an accumulation of repetitive damage to the knee structures. Congenital knee problems or improper mechanics of the knee movement may cause this.
Osteochondritis dissecans is a joint disorder that occurs most commonly in children. Bone and cartilage beneath the joints loses its blood supply, resulting in joint pain and stiffness. This condition typically affects the knees, but it can also affect other joints such as elbows and ankles.
Osgood-Schlatter disease is a condition in children caused by growth spurts that cause knee pain and swelling below the kneecap.
What Are Risk Factors for Knee Injuries?
Accidents happen, and injuries occur on the football field, on the basketball court, on the soccer pitch, and in daily life. Often knee injuries cannot be prevented. Maintaining a healthy weight, keeping fit, staying strong, and stretching may be helpful in minimizing the risk of many injuries, including those that involve the knee.
Imbalances of muscles that surround and support the knee can lead to knee injuries. If either the quadriceps or hamstring muscle groups become weak, the stability of the knee and ability to withstand an injury is decreased.
Similarly, an imbalance between muscles within the quadriceps muscles of the thigh may cause the kneecap (patella) to track improperly, causing patellofemoral syndrome or increasing the risk of patellar dislocation.
Pregnant women are at higher risk for knee injury and pain because of increased weight, the body’s shifted center of gravity, and hormonal changes that can weaken ligaments and make them more lax.
The knee joint absorbs a significant amount of the force that is generated with each step with walking or running. People who are significantly overweight may develop knee pain because of the excess weight that needs to be supported.
What Are Knee Injury Symptoms and Signs?
Acute knee injuries can cause pain and swelling with difficulty bending the knee and weight-bearing. Acute knee injuries often may be considered as falling into two groups: those where there is almost immediate swelling in the joint associated with the inability to bend the knee and bear weight, and those in which there is discomfort and perhaps localized pain to one side of the knee, but with minimal swelling and minimal effects on walking.
If the swelling occurs immediately, it may suggest a ligament tear or fracture. If the swelling arises over a period of many hours, meniscal or cartilage injuries may be the cause. However, injuries to the knee may involve more than one structure and the symptoms may not present classically.
Longer-term symptoms that point to knee problems will include pain and swelling in addition to other complaints. Inflammation in the joint may be caused by even minor activity. Swelling may be intermittent, brought on by activity, and may gradually resolve as the inflammation decreases.
Pain, too, may come and go. It may not occur right away with activity but might be delayed as the inflammation develops. Pain can also be felt with specific activities. Pain while climbing stairs is a symptom of meniscus injury, where the cartilage is being pinched in the joint as the joint space narrows with knee bending. Pain with walking down stairs suggests patellar pain, where the kneecap is being forced onto the femur.
Giving way, or a feeling of instability of the knee, or popping or grinding in the knee is associated with cartilage or meniscus tears. Locking is the term used when the knee joint refuses to completely straighten, and this is almost always due to torn cartilage. In this situation, the torn piece of cartilage folds upon itself and doesn’t allow the knee to extend.
How Do Health Care Professionals Diagnose A Knee Injury?
The diagnosis of a knee injury is made by a physician on the basis of history, physical examination, and sometimes the use of X-rays or MRIs.
Depending on the how the knee was injured and whether or not there are accompanying medical issues, the doctor will perform specific tests involving bending or twisting the knee to test the stability of the ligaments and check for damage to the cartilage. Knee-bending tests done by your doctor are designed to isolate specifically which ligament or part of the cartilage has been damaged.
Further testing with X-rays, CT scans, or MRIs may be necessary to evaluate the extent of the injury and help determine treatment and prognosis. X-rays and CT scans are used to asses for bony injuries (fractures), and MRIs are used to evaluate soft-tissue damage (ligaments and cartilage).
Treatment Of Knee Injuries
When you are first injured, the RICE method — rest, ice, gentle compression and elevation – can help speed your recovery.
Be sure to seek treatment as soon as possible, especially if you:
- Hear a popping noise and feel your knee give out at the time of injury
- Have severe pain
- Cannot move the knee
- Begin limping
- Have swelling at the injury site
The type of treatment your doctor recommends will depend on several factors, such as the severity of your injury, your age, general health, and activity level.
Many knee injuries can be treated with simple measures, such as:
- Immobilization. Your doctor may recommend a brace to prevent your knee from moving. If you have fractured a bone, a cast or brace may hold the bones in place while they heal. To further protect your knee, you may be given crutches to keep you from putting weight on your leg.
- Physical therapy. Specific exercises will restore function to your knee and strengthen the leg muscles that support it.
- Nonsteroidal anti-inflammatory medicines. Drugs like aspirin and ibuprofen reduce pain and swelling.
Many fractures and injuries around the knee require surgery to fully restore function to your leg. In some cases – such as many ACL tears — surgery can be done arthroscopically using miniature instruments and small incisions. Many injuries require open surgery with a larger incision that provides your surgeon with a more direct view and easier access to the injured structures.
Preventing knee injuries is not always possible, but a person can take precautions to reduce the risk. For instance, people who run or play sports should wear the appropriate shoes and protective gear.
In cases of iliotibial band syndrome and overuse injuries, a person may want to consider reducing the number of miles they run.
Certain exercises also help strengthen the smaller leg muscles, which may help prevent injury. Finally, stretching before and after exercise can help prevent injury to the knees.
Proper nutrition, especially for athletes, is also important. Protein, calcium, and vitamin D are essential for maintaining healthy bones, muscles, and ligaments.
Strong muscles stabilize joints. With the knee, having strong and flexible quadriceps and hamstring muscles can prevent minor stresses to the knee from causing significant injury. Routine stretching exercises or yoga are able to increase muscle flexibility and maintain joint mobility and range of motion.
Proper footwear can also minimize the risk for knee injury. Wearing shoes that are appropriate for the activity can lessen the risk of twisting and other forces that can stress the knee.
or specific information on prevention of anterior cruciate ligament (ACL) injury, check out the ACL Prevention Project training program by the Santa Monica Orthopaedic and Sports Medicine Foundation. It is a 15-minute training session that consists of a warm-up, stretching, strengthening, plyometrics, and sport specific agility training.
Read more Knee Injuries From Falling Accidents