A joint is a point where bones make contact, connecting the skeletal system. Most joints are mobile, which allows the body to make different types of movement. There are three kinds of joint: fibrous, cartilaginous, and synovial.
Fibrous joints are usually immovable. They include the cranium in the skull, the joints between the teeth and the sockets in the jaw, and the joints between the bones of the lower leg.
Cartilaginous joints are those where cartilage joins two bones. These joints are partially movable. One example is the joint between the right and left pubic bone.
Synovial joints are the joints that allow limbs to move freely. These joints have a cavity in them that contains synovial fluid. This fluid allows the bones that connect the joint to move around with ease. Some examples include the knee, elbow, hip, and shoulder.
Many conditions and factors can cause a person to experience joint pain. If a person has pain in multiple joints, it is known as polyarthralgia. Usually, joint pain is the result of injury, infection, illness, or inflammation.
Below are some of the common causes of joint pain:
Injury is a common cause of joint pain. Injuries can result from the excessive use or effort of the joints or from an impact that causes a fracture, sprain, or strain.
For example, a common knee injury is damage to the anterior cruciate ligament (ACL). People who play certain sports, such as soccer, basketball, or football, are more at risk of injuring their ACL.
Some infections may result in joint pain. For example, the hepatitis C virus (HCV) can cause complications that result in joint pain. It is common for people with HCV to have related rheumatic diseases, which can cause problems, including pain in the joints.
Some diseases can cause joint pain. Lupus is a chronic autoimmune disease, and common symptoms include muscle and joint pain. In fact, joint pain is the first symptom for more than half of those who develop lupus.
People develop lupus because their body’s immune system becomes hyperactive and attacks normal, healthy tissue.
Arthritis and arthralgia are very similar but have key differences. Both describe joint pain, but arthralgia occurs without the distinct inflammation in the joint that characterizes arthritis. Nearly half of adults with arthritis report persistent joint pain.
There are more than 100 different kinds of arthritis, including:
- osteoarthritis (OA)
- rheumatoid arthritis (RA)
- septic arthritis
The cause of arthritis varies among the different types.
OA results from cartilage loss in the joints. Calcification of the cartilage around the joints eventually makes the cartilage thinner before damaging it. Older adults are more likely to develop OA.
RA is an autoimmune response to a trigger. The body tries to fight off what it thinks is an invader but instead degrades the cartilage and bones in the joints.
Gout occurs due to the crystallization of uric acid in the body. Uric acid gets into the joint spaces, causing inflammation.
In most cases, septic arthritis results from a bacterial infection. Bacteria get into the synovial fluid in the joints, which eventually degrades the cartilage, leading to arthritis.