Joint pain in a single joint in the leg has many possible causes, ranging from simple muscular or tendon sprains to the more serious septic arthritis, which is an infection of the entire joint that can cause permanent damage. A health-care professional can help determine the cause and start appropriate treatment.
Infectious Causes
According to FamilyPracticeNotebook.com, some infections of the joint can destroy it in less than 48 hours, making a bad infection in the joint, called septic arthritis, a medical emergency. The joint may be swollen, warm and extremely tender. Infectious agents causing joint pain may be viral, parasitic, bacterial or fungal.
Immune Causes
Problems with the immune system can also cause joint pain in the leg. The Mayo Clinic notes that in a condition called reactive arthritis, a person will contract an infection, often an illness causing diarrhea, and the immune system will resolve it. However, some of the proteins on the bacteria that the immune system recognized will be similar in the joint, and the immune system may attack the joint as well after several weeks. The condition usually resolves on its own.
Trauma
Trauma is a common source of joint pain. It may affect the bone, the muscle, the tendons attaching bone to muscle, or the ligaments attaching bone to bone. It can be sudden during activity, or occur from chronic overuse, leading to osteoarthritis. In addition, trauma to a blood vessel near the joint can cause bleeding into the joint and subsequent joint pain.
Nervous System Causes
Nerves leaving the spinal cord in the back may be a source of joint pain, as in a herniated disc in the back. Most often this will cause back pain, but the pain may also radiate to the leg, or cause numbness or weakness. A nerve can also be damaged or entrapped at the joint to cause pain, according to Family Practice Notebook.
Metabolic Causes
The National Institutes of Health notes that metabolic problems can cause joint pain in the leg. These include two diseases that form crystals that are deposited in the leg. Gout is a condition of excessive uric acid in the blood, which deposits in joints to cause inflammation and pain, according to Gout.com. Psuedogout is similar, but the crystals are made of a different substance, calcium pyrophosphate.
Multiple Joints
There are many other causes of joint pain. Some of these tend to occur in multiple joints. Viral and bacterial infections may affect multiple joints. Systemic conditions such as rheumatoid arthritis or lupus may affect multiple joints as well.
