Pain or discomfort in the knees can occur for various reasons and it is not uncommon for most of us to experience a knee ache at some point or the other. Often this is related to strain and in younger people a knee ache is usually not a cause for concern unless it occurred due to a severe injury. However, a knee ache in older people could be a sign of a chronic problem which can progress to cause significant disability in the long run.
Why do knees ache?
Aching is a term used to describe a discomfort or mild pain. Sometimes the term ache or aching is used interchangeably with pain. Joint ache or joint pain is also known as arthralgia. It should not be confused with arthritis which means joint inflammation. However, most of the time joint inflammation (arthritis) leads to joint pain (arthralgia). This applies to any joint in the body, including the knee.
The knees bear intense force among most other joints of the body. The weight of the head, upper limbs, torso and thighs bear down on the knees, especially when standing and to a greater degree when walking or running. With or without the range of joint diseases that can affect the knee, the force that the knee has to bear on a constant basis often makes it prone to strain and injury. Therefore the aches in the knees or even knee pain is not uncommon.
Other Signs and Symptoms
Aching knees and knee pain are only symptoms of various knee conditions. There may be other symptoms such as:
- Swelling of the knee
- Heat and/or redness of the skin over the knee
- Stiffness of the knee joint
- Cracking, grating or popping sounds from the knee
Read more on knee stiffness.
Depending on the underlying condition, severity and duration there may also be other signs and symptoms such as nodules and deformity of the joint. Sometimes there may be other knee symptoms without pain. For example in some cases of a Baker’s cyst there may be no pain despite the swelling behind the knee.
Causes of Aching Knees
There are host of different causes of aching knees and knee pain. Most of these causes lead to inflammation of the joint (arthritis). It is important to note that arthritis is not a single knee condition. There are various different types of arthritis, depending on the underlying cause and mechanism of disease.
Injury to the knee is one of the most common conditions to affect the knee, resulting in aches and pains. This can occur with blunt or sharp force trauma to the knee joint, repetitive stress and physical strain. Injury does not only cause inflammation of the soft tissue and bones of the knee joint. It can also result is joint dislocation or fractures of one or more bones when the trauma is severe.
Sometimes the surrounding structures, like muscles, tendons and ligaments, may also be strained or injured. This can result in pain in and around the knee. In these cases the pain may not arise from the knee joint itself but is still felt in the knee. For example, anterior cruciate ligament (ACL) injury or iliotibial band syndrome are two conditions that may cause pain in or near the knee.
Infections can also cause knee pain, and the infection may not always infect the knee or surrounding tissue to result in pain. Systemic viral infections for example may present with joint ache like knee pain even though the knee joint is not infected. This is known as viral athralgia. An infection of the knee or surrounding tissue may also cause pain due to inflammation. Most of the time this is due to bacteria which may enter the knee tissue from a piercing injury. This is known as septic arthritis. If the bones are infected then it is known as osteomyelitis.
Knee pain may occur with several autoimmune diseases, like systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). These are diseases where the immune system attacks certain tissues or organs in the body. The exact cause is unknown but it is believed to be due to a combination of genetic and environmental factors, like viral infections. Rheumatoid arthritis is the second most common arthritis and usually affects the small joints but may involve the knee as well.
Osteoarthritis is the most common type of knee problem although it is not a typical arthritis. The condition is a result of degeneration of the joint, initially the cartilage and eventually the underlying bone. It more commonly affects the elderly as the wear and tear of the knee joint cannot be completely counteracted by the body’s reparative abilities. A portion of the cartilage or bone can break off and limit joint movement as well as elicit pain. This is known as a loose body and can also occur with a knee injury.
The knee joint is broadly composed of four bones. The bottom of the femur (thigh bone), the tibia and fibula (lower leg bones) and the overlying patella (kneecap). Any of these bones that comprise the knee joint may be fracture with the patella being particularly prone. Fractures arise with any blow to the knee joint, as may be sustained with a forward fall, in a motor vehicle accident, with an assault or from playing contact sports. Knee pain is usually severe with fractures of the knee bones.
Read more about knee cap pain.
Gout and pseudogout are two conditions that arise from crystals in the joint. Gout is due to uric acid crystals while pseudogout is caused by calcium pyrophosphate dihydrate crystals. The knee is the most commonly affected joint in pseudogout, which is not the case with gout where the big toe joints are more commonly affected. The exact cause of pseudogout is unclear but the condition is more common in older people. However, even when calcium pyrophosphate dihydrate crystals are present in the joint, not every person will experience symptoms of pseudogout.
Read more on knee pain relief.