Knee pain is one of the most common musculoskeletal complaint that brings people to their doctor. With today's increasingly active society, the number of knee problems is increasing. Knee pain has a wide variety of specific causes and treatments.
Anatomy of the Knee
The knee joint's main function is to bend and straighten. The knee, more than just a simple hinge, however, also twists and rotates. In order to perform all of these actions and to support the entire body while doing so, the knee relies on a number of structures, including bones, ligaments, tendons, and cartilage.
- The knee joint involves three bones.
- The thighbone or femurcomprises the top portion of the joint.
- One of the bones in thelower leg (or calf area), the tibia, provides the bottom portion of the joint.
- The kneecap or patella rides along the front of the femur.
- The remaining bone in the calf, the fibula, is not involved in the knee joint but is close to the outer portion of the joint.
- Ligaments are fibrous bands that connect bones to each other.
- The knee includes four important ligaments, all four of which connect the femur to the tibia:
- The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) provide front and back (anterior and posterior) and rotational stability to the knee.
- The medial collateral ligament (MCL) and lateral collateral ligament(LCL) located along the inner (medial) and outer (lateral) sides of the knee provide medial and lateral stability to the knee.
- Tendons are fibrous bands similar to ligaments.
- Instead of connecting bones to other bones as ligaments do, tendons connect muscles to bones.
- The two important tendons in the knee are (1) the quadriceps tendon connecting the quadriceps muscle, which lies on the front of the thigh, to the patella and (2) the patellar tendon connecting the patella to the tibia (technically this is a ligament because it connects two bones).
- The quadriceps and patellar tendons as well as the patella itself are sometimes called the extensor mechanism, and together with the quadriceps muscle they facilitate leg extension (straightening).
- Cartilaginous structures called menisci (one is a meniscus) line the top of the tibia and lie between the tibia and the two knuckles at the bottom of the femur (called the femoral condyles).
- Menisci provide both space and cushion for the knee joint.
- Bursae (one is a bursa) are fluid-filled sacs that help to cushion the knee. The knee contains three important groups of bursae.
- The prepatellar bursae lie in front of the patella.
- The anserine bursae are located on the inner side of the knee about 2 inches below the joint.
- The infrapatellar bursae are located underneath the patella.
Here are some of the common knee pain symptoms that are experienced by patients, and what these symptoms may mean about the cause of your knee pain.
Location of Pain:
- Front of Knee: Pain over the front of the knee is most commonly related to the knee cap. Kneecap pain can be caused by several different problems.
- Inside of Knee: Pain on the inside, or medial side, of the knee is commonly caused by medial meniscus tears, MCL injuries, and arthritis.
- Outside of Knee: Pain on the outside of the knee, or lateral side, is commonly caused by lateral meniscus tears, LCL injuries, IT band tendonitis, and arthritis.
- Back of Knee: Pain in the back of the knee can be due to the collection of fluid, called a Baker's Cyst.
Timing of Pain:
- While going down stairs: Pain while walking down steps is very commonly associated withkneecap problems, such as chondromalacia.
- Morning pain: Pain after first waking in the morning that quickly resolves with gentle activity is typical of early arthritis.
Swelling of the knee is common with several different knee problems. When there is an effusion immediately after a knee injury, a possible cause is severe injury to an internal joint structure, like the anterior cruciate ligament or a fracture of the top of the shin bone.
When swelling develops gradually over hours to days after an injury, it is likely to be something less severe, like a tear of the meniscus or a ligament sprain.
Swelling that occurs without the presence of a known injury can be due to osteoarthritis (common), gout (less common), inflammatory arthritis, or a joint infection (uncommon).
Mobility of the knee can be affected by a number of common conditions. If mobility is chronically limited, often the cause is arthritis. When the surface of the joint becomes irregular as a result of the arthritis, the mobility of the joint may become limited.
If the mobility is limited after an acute injury, there is likely swelling limiting the motion, or a torn structure that is limiting the mobility.
The stability of the knee is provided by the ligaments that connect the shin bone (tibia) to the thigh bone (femur). When the ligaments are stretched or torn, the knee may feel as though it is giving way beneath the patient. A sensation that the knee may give out from beneath you is a common symptom of ligament injury.
Popping and snapping within the knee is common, and often not a symptom of any particular problem. When the pops are painless, there is usually no problem, but painful pops and snaps should be evaluated by your doctor. A pop is often heard or felt during an injury when a ligament, such as the ACL, is torn.
Grinding or crunching is a common symptom of cartilage problems. If the cartilage is damaged - a condition called chondromalacia - a crunching sensation is often felt by placing the hand over the kneecap and bending the knee. A similar grinding sensation may be felt with knee arthritis.
Locking is a symptom that occurs when a patient cannot bend or straighten their knee. The locking can either be due to something physically blocking motion of the knee, or by pain preventing normal knee motion.
One way to determine if there is something physically blocking knee motion is to inject the knee with a numbing medication. After the medication has taken effect, you can attempt to bend the knee to determine if pain was blocking the motion or if there is a structure, such as a torn meniscus, that is blocking normal motion.
Examining the Knee:
Determining the cause of knee pain relies on a proper examination of the knee joint. Learn about how your doctor can examine your knee to determine the source of your pain, and what tests can be performed to make the diagnosis.
Knee pain can be caused by injuries, mechanical problems, types of arthritis and other problems.
A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursae) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself.
Some of the more common knee injuries include:
- ACL injury. An ACL injury is the tearing of the anterior cruciate ligament (ACL) — one of four ligaments that connect your shinbone to your thighbone. An ACL injury is particularly common in people who play basketball or go downhill skiing, because it's linked to sudden changes in direction.
- Torn meniscus. The meniscus is formed of tough, rubbery cartilage and acts as a shock absorber between your shinbone and thighbone. It can be torn if you suddenly twist your knee while bearing weight on it.
- Knee bursitis. Some knee injuries cause inflammation in the bursae, the small sacs of fluid that cushion the outside of your knee joint so that tendons and ligaments glide smoothly over the joint.
- Patellar tendinitis. Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bones. Runners, skiers and cyclists are prone to develop inflammation in the patellar tendon, which connects the quadriceps muscle on the front of the thigh to the shinbone.
- Loose body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge.
- Knee 'locking'. This can occur from a cartilage tear. When a portion of cartilage from the tear flips inside the knee joint, you may not be able to fully straighten your knee.
- Dislocated kneecap. This occurs when the triangular bone (patella) that covers the front of your knee slips out of place, usually to the outside of your knee. You'll be able to see the dislocation, and your kneecap is likely to move excessively from side to side.
- Hip or foot pain. If you have hip or foot pain, you may change the way you walk to spare these painful joints. But this altered gait can interfere with the alignment of your kneecap and place more stress on your knee joint. In some cases, problems in the hip or foot can refer pain to the knee.
Types of arthritis
- Osteoarthritis. Sometimes called degenerative arthritis, osteoarthritis is the most common type of arthritis. It's a wear-and-tear condition that occurs when the cartilage in your knee deteriorates with use and age.
- Rheumatoid arthritis. The most debilitating form of arthritis, rheumatoid arthritis is an autoimmune condition that can affect almost any joint in your body, including your knees. Although rheumatoid arthritis is a chronic disease, it tends to vary in severity and may even come and go.
- Gout. This type of arthritis occurs when uric acid crystals build up in the joint. While gout most commonly affects the big toe, it can also occur in the knee.
- Pseudogout. Often mistaken for gout, pseudogout is caused by calcium pyrophosphate crystals that develop in the joint fluid. Knees are the most common joint affected by pseudogout.
- Septic arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. There's usually no trauma before the onset of pain. Septic arthritis often occurs with a fever.
- Iliotibial band syndrome. This occurs when the ligament that extends from the outside of your pelvic bone to the outside of your tibia (iliotibial band) becomes so tight that it rubs against the outer portion of your femur. Distance runners are especially susceptible to iliotibial band syndrome.
- Chondromalacia patellae (patellofemoral pain syndrome). This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It's common in young adults, especially those who have a slight misalignment of the kneecap; in athletes; and in older adults, who usually develop the condition as a result of arthritis of the kneecap.
- Osgood-Schlatter disease. This condition affects the softer area of bone near the top of the shinbone, where bone growth occurs. It's most common in boys who play games or sports that involve running or jumping. The discomfort can last a few months and may continue to recur until the child's bones stop growing.
- Osteochondritis dissecans. Caused by reduced blood flow to the end of a bone, osteochondritis dissecans is a joint condition in which a piece of cartilage, along with a thin layer of the bone beneath it, comes loose from the end of a bone. It occurs most often in young men, particularly after an injury to the knee.
Treatments will vary, depending upon what exactly is causing your knee pain.
Your doctor may prescribe medications to help relieve pain and to treat underlying conditions, such as rheumatoid arthritis or gout.
- Physical therapy. Strengthening the muscles around your knee will make it more stable. Training is likely to focus on the muscles on the front of your thigh (quadriceps) and the muscles in the back of your thigh (hamstrings). Exercises to improve your balance are also important.
- Orthotics and bracing. Arch supports, sometimes with wedges on the inner or outer aspect of the heel, can help to shift pressure away from the side of the knee most affected by osteoarthritis. Different types of braces may help protect and support the knee joint.
- Corticosteroids. Injections of a corticosteroid drug into your knee joint may help reduce the symptoms of an arthritis flare and provide pain relief that lasts a few months. The injections aren't effective in all cases. There is a small risk of infection.
- Hyaluronic acid. This thick fluid is normally found in healthy joints, and injecting it into damaged ones may ease pain and provide lubrication. Experts aren't quite sure how hyaluronic acid works, but it may reduce inflammation. Relief from a series of shots may last as long as six months to a year.
If you have an injury that may require surgery, it's usually not necessary to have the operation immediately. Before making any decision, consider the pros and cons of both nonsurgical rehabilitation and surgical reconstruction in relation to what's most important to you.
If you choose to have surgery, your options may include:
- Arthroscopic surgery. Depending on the nature of your injury, your doctor may be able to examine and repair your joint damage using a fiber-optic camera and long, narrow tools inserted through just a few small incisions around your knee. Arthroscopy may be used to remove loose bodies from your knee joint, repair torn or damaged cartilage and reconstruct torn ligaments.
- Partial knee replacement surgery. In this procedure (unicompartmental arthroplasty), your surgeon replaces only the most damaged portion of your knee with parts made of metal and plastic. The surgery can usually be performed with a small incision, and your hospital stay is typically just one night. You're also likely to heal more quickly than you are with surgery to replace your entire knee.
- Total knee replacement. In this procedure, your surgeon cuts away damaged bone and cartilage from your thighbone, shinbone and kneecap, and replaces it with an artificial joint made of metal alloys, high-grade plastics and polymers.