Pain in Back of the Knee
Can Mean Several Things

Pain in Back of the Knee

Pain in back of the knee is usually due to a ligament injury, a Baker's cyst, or arthritis. The best treatment is often rest and elevation, along with mild pain medications.

This pain is often due to arthritis. Arthritis pain in the knee is usually felt in the front, around the kneecap. But if the joint becomes filled with fluid due to synovium inflammation the entire knee can swell and become painful. The knee is one of the most common joints for developing osteoporosis.

In the back of knee is found the posterior cruciate ligament (PCL). It's just one of four ligaments that help the knee joint remain stable. The cruciate ligaments connect the knee joint to the thigh bone and the shin bone. The PCL is a thick, very strong ligament that can be injured or stressed leading to a painful condition in the rear of the knee.

When the PCL is damaged, the knee can feel odd because it's not able to be fully stabilized. This is often described as the knee "giving out". The swelling and pain lead to reduced motion and knee flexibility.

Fluid in the Knee

Most of the time, the real pain in back of the knee comes from inflammation and swelling. Arthritis can cause inflammation in the joint when the synovium lining is irritated and produces fluid. This fluid can fill the front and back of the knee joint and make it very painful to use, and it can become chronic.

What causes knee swelling?
A swollen knee is a common problem. Many people call this "water on the knee." However, determining the cause of knee swelling can be a challenge. Swelling may be acute or chronic. It may be associated with a recent injury or may have a gradual onset. The swelling can be within the knee or around the knee.

Sometimes the swelling causing the pain in back of the knee is due to a Baker's Cyst. This is not a tumor despite the name. It's a collection of fluid in just the rear of the knee joint. This condition is usually the result of arthritis, ligament injury, or a tear in the cartilage called the meniscus.

People who have a swollen knee can either have fluid within the knee joint itself, or in the surrounding soft tissue. The first step in determining the cause of the fluid accumulation is to determine where the fluid is located.

The knee joint is surrounded by a capsule. This capsule forms the "joint space." The joint space normally has a small amount of lubricating fluid within the knee to help keep the knee moving easily. Some conditions cause an accumulation of this fluid.

This is what most people consider a swollen knee, also called a knee effusion. If it is determined that fluid is inside the knee joint, the next step is to determine if there was an associated injury.

As you can see, most of the pain in back of the knee, is due to fluid accumulation in the joint. It's the cause of the fluid accumulation that varies.

Living with Knee Pain

Everyday people are living with knee pain which can be difficult, because the knee bears much of the body's weight. The pain in back of the knee can be aggravated with just simple walking, and then can force someone to compensate for the pain by "walking funny". It's really not funny though because walking with an odd gait, can lead to many other joint problems.

Knee Arthritis
Knee arthritis causes the body to produce extra fluid in the knee joint. The amount of fluid tends to fluctuate over time. Patients with knee arthritis often notice the affected knee is larger than the other. The amount of fluid often corresponds with the amount of activity the patient has been doing--more significant activities cause more swelling.

One category of swelling is the rapid onset of fluid within the joint, but no recent injury to the knee. The most common causes of this type of fluid accumulation are due to infection or gout.

  • Infections can cause fluid to accumulate within the knee joint. Infections can be caused by contamination in the knee, such as from surgery or a wound to the knee, or a systemic infection that spreads to the joint. Infections inside a joint are problematic because your body has a hard time fighting infections within this space. Surgery may be needed to clean out the infection.
  • Gout and Pseudogout is due to the accumulation of uric acid crystals within the fluid of your knee. Uric acid is a substance produced as part of digestion. In order to properly digest food, and rid our body of waste, our bodies produce substances such as uric acid to transport waste material. People with gout accumulate uric acid crystals within joints, leading to inflammation and swelling.
  • Pseudogout is a similar problem, only a different type of crystals accumulates within the joint. In patients with pseudogout, calcium crystals simulate an inflammatory reaction within the joint, leading to a swollen knee.
  • Fluid Outside The Knee Joint when fluid is outside of the actual joint space, and in the soft tissues surrounding the knee, the most common cause is prepatellar bursitis. This condition causes fluid accumulation in the bursa just on top of the kneecap. Usually the fluid can be felt on top of the kneecap, rather than underneath the kneecap.

Fluid can also accumulate in the soft tissue around the knee after an injury such as a contusion to the knee. A forceful injury to the soft tissue surrounding the knee can cause fluid and/or blood to accumulate, giving the appearance of a swollen knee.

Treatments for pain in back of the knee include:

  • Anti-inflammatory medications
  • Cortisone injections
  • Ice packs
  • Rest and elevation of the knee

Often the fluid that accumulates must be drained by a doctor and then treatments work to prevent a re occurrence. Pain in back of the knee isn't the most common knee problem, but that's no consolation to anyone experiencing the pain.

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