What Causes Radiating Pain in the Knee?

The knee joint is the biggest movable, or synovial, joints in the body. Being the largest movable joint means that the joint has many moving parts that can easily get damaged due to wear and tear or injury. Knee pain can occur in people of all ages for a wide variety of reasons. However, when you experience radiating knee pain, the pain is not limited just to the knee. It spreads to the areas around the knee as well, causing more discomfort and pain. There can be many reasons for radiating knee pain.

The knee is the joint located between the bones of the lower and upper leg. It is this joint that allows your leg to bend while also providing stability to support the weight of the entire body. This is why there is a lot of stress on the knee joint. At the same time, the knee also supports motions like walking, running, jumping, turning, and crouching.^{(1, 2, 3)}

The knee is made up of many parts that help it do its job, including:

• Muscles
• Bones
• Cartilage
• Tendons
• Ligaments

All these parts are prone to injury and disease, which can cause knee pain, especially radiating knee pain.

Although the knee is a supportive joint, it is not made for the harsh demands that a person puts on it. The knee was never designed for activities like playing soccer or football or for doing the work of a plumber or carpenter.^{(4, 5)} Of course, there is no way one can anticipate everything that a knee would have to do, and frequent abuse of this joint can cause pain, especially radiating pain.

Apart from the actual knee itself, there are a number of structures associated with the knee that can cause this type of radiating knee pain. As mentioned above, these structures include the bone, ligaments, tendons, and the meniscus.

Aside from these parts of the knee, other parts of the body can also be the cause of radiating knee pain. The lower back is one such area as it shares a common nerve with the knee. Due to this, your doctor will carry out a thorough physical exam when you complain of radiating knee pain.

Here’s a look at some of the causes of radiating knee pain.

1. Trauma

   According to the Arthritis Foundation, the knee is one of the most injury-prone joints. ⁽⁶⁾ The overall structure and parts of the knee joint increase the risk of getting certain types of injury, which can cause radiating pain and even prevent the joint from functioning properly.

   Some of the common knee injuries that occur because of tears in one of the three major ligaments of the knee include:

   • An anterior cruciate ligament (ACL)
   • Medial collateral ligament (MCL)
   • A posterior cruciate ligament (PCL)

   Injuries to these crucial ligaments are pretty common in athletes.^{(7, 8, 9)} Ligament injuries often need surgical intervention.

   Trauma to the knee can also cause injuries as a result of overstretching or overworking a tendon. Tendinitis, inflammation, or even ruptures can cause radiating knee pain. Furthermore, engaging in activities like lifting heavy items, jumping, running, and others that involve the tendons can also cause tendon injuries that cause knee pain.

   Patellar tendinitis is a term that refers to inflammation and irritation of the patellar tendon in the knee. In such a case, if the tendon gets severely ruptured, it generally needs to be repaired surgically.^{(10, 11, 12)}

   Less serious cases of patellar tendinitis can be treated with a splint which provides rigid support to keep the knee in place and prevents it from moving during the healing process.

2. Fractures

   Trauma from a collision or fall can cause a fracture in the knee bone. There are several bones in the knee that can break, including the kneecap, which is known as the patella.^{(13, 14)}

   People with degenerative disorders like osteoporosis that cause your bones to become weak and fragile can end up developing a fracture in the knee even if they have a minor injury or just step off the stairs in the wrong way.^{(15, 16)}

   Severe fractures need surgical intervention to repair, though many people with knee fractures only need to be treated with physical therapy.

3. Connective Tissue Disorders

   Conditions like rheumatoid arthritis (RA) affect the joints. RA is an autoimmune inflammatory disorder in which the immune system mistakenly attacks the joint tissues thinking it is a foreign invader. Unlike degenerative tissue disorders, rheumatoid arthritis and other connective tissue conditions impact the lining of the joints. This can cause painful swelling in the knee joints and lead to radiating knee pain. If a person with RA does not seek treatment in time, it can eventually lead to bone erosion and joint deformity over time.^{(17, 18)}

   There is no cure for RA, but medication and treatment options can help provide relief from the symptoms.

4. Degenerative Tissue Disorders

   Degenerative tissue disorders are a common knee problem that causes radiating knee pain.^{(19, 20)} Conditions like osteoarthritis bring about degeneration in the cartilage as well as the surrounding tissues of the knee.⁽²¹⁾ This produces pain, joint dysfunction, and stiffness in the joints.

   Osteoarthritis usually happens as a result of aging and occurs in around 13 percent of women and 10 percent of men over the age of 60 years in the US.⁽²²⁾ Though there is no cure for osteoarthritis, it is possible to manage the symptoms of the disease with pain relief medications and gentle but regular exercises.

   Severe damage to the knee or any joint in the body due to this degenerative condition may require joint replacement or other types of surgery.

5. Dislocated Kneecap

   The kneecap may move out of place owing to an injury, trauma, or accident. Usually, a doctor is able to replace the kneecap without any major issue. You will have to undergo an X-ray to identify if there are any other fractures in the area. You may have to use a splint to allow the soft tissue around the kneecap to keep it in place so that it can regain strength and heal. In some cases, a person might have to undergo surgery to prevent any more dislocations.^{(23, 24)}

   A dislocated knee is a rare but dangerous injury. This is not the same as a dislocated kneecap. However, this can only happen due to a severely powerful blow to the knee to cause such kind of damage. Even though a dislocated knee is reversible, this condition is excruciatingly painful and can produce radiating knee pain.^{(25, 26)}

Apart from a thorough physical exam, your doctor is likely to use several testing techniques to locate the source of radiating knee pain. These include computed tomography, X-rays, MRIs, and ultrasound. All these tests examine different structures in the body that might be causing the radiating pain. A blood test may also be done to identify the presence of any infection in and around the knee joint.

If you experience radiating knee pain after an injury, especially if you hear a soft pop sound while exercising, the most likely reason is a torn ligament or cartilage, or even both.

For radiating pain of the knee that slowly gets worse, you may use over-the-counter pain medications for relief. Of course, the RICE technique (rest, ice, compression, and elevation) when you experience such type of radiating knee pain can help. If the pain continues to persist or it gets worse, your doctor may administer medications and steroid injections, or the last resort might be joint replacement surgery.

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