Pain that is isolated to just one joint is called monoarticular joint pain. A joint may simply be painful (arthralgia) or may also be inflamed (arthritis).
Pain in a single joint may be caused by arthritis. Arthritis usually also causes warmth and swelling, and rarely redness of the overlying skin. Pain may occur only when the joint is moved or also be present at rest. Fluid may collect within the joint (called an effusion).
Pain that seems to be coming from a joint sometimes originates in a structure outside of the joint, such as a ligament, tendon, or muscle (see Introduction to the Biology of the Musculoskeletal System). Examples of such disorders are bursitis, tendinitis, sprains, and strains. Pains caused by these disorders are usually not considered true joint pains.
Causes of Pain in a Single Joint
Common causes of pain in a single joint include infectious arthritis, gout and related disorders, and osteoarthritis. Joint pain may be the first symptom of a disorder that affects other organs in the body, such as an autoimmune disorder or a bodywide infection. Symptoms of some autoimmune disorders can include fever, mouth sores, and rash. Pain that develops in one joint may also be the first symptom of a disorder that eventually affects many joints (see also Joint Pain: Many Joints).
Common causes
At all ages, injury, infection, and crystals in the joint (often called crystal-induced arthritis) are the most common causes of sudden pain in a single joint.
Among young adults, the most common causes are
Injury (most common)
Infection (often caused by gonorrhea that has spread throughout the body or bloodstream [disseminated gonococcal infection], particularly if the joint is warm and swollen)
Inflammation (caused by, for example, gout)
Among older adults who have not been injured, the most common causes are
Osteoarthritis (most common)
Crystal-induced arthritis (gout or calcium pyrophosphate arthritis)
The most dangerous cause at any age is acute infectious arthritis. Infectious arthritis can damage structures inside the joint within hours, which can lead to permanent arthritis. Rapid treatment can minimize permanent damage and prevent sepsis and death.
Common causes of pain in a single joint are listed in table Some Causes and Features of Pain in a Single Joint.
Less common causes
Less common causes of pain in a single joint include destruction of part of the nearby bone caused by poor blood supply (osteonecrosis), joint tumors (such as pigmented villonodular synovitis), blood in the joint (hemarthrosis), and disorders that usually cause pain in more than one joint, such as reactive arthritis.
Evaluation of Pain in a Single Joint
The following information can help people decide when a doctor’s evaluation is needed and help them know what to expect during the evaluation.
Warning signs
In people with pain in a single joint, certain symptoms and characteristics are cause for concern and are more likely to require immediate treatment. They include
Sudden or severe pain
Joint redness, warmth, swelling, or limitation of motion
Fever
Broken, red, warm, or tender skin near the joint
Signs of sudden illness other than joint pain
Possibility of a sexually transmitted infection (for instance, due to unprotected sex with a new partner)
When to see a doctor
People with warning signs should see a doctor right away. Doctors are better able to treat symptoms more rapidly and completely if treatment occurs early in certain disorders, including crystal-induced arthritis, hemarthrosis, and infectious arthritis. People without warning signs, particularly if the cause of pain is known (for example, if typical pain recurs in a joint affected by osteoarthritis or if pain occurs after a minor injury) and symptoms are mild, can wait a few days and see whether symptoms resolve before seeing a doctor.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the pain and the tests that may need to be done (see table Some Causes and Features of Pain in a Single Joint).
Doctors ask about the following:
When the pain started, how it has progressed, where it is located, and its severity
What makes the pain better or worse (for example, movement, weight-bearing exercise, or rest)
Previous injuries or previous joint pain
Symptoms in other joints (such as swelling)
Risk factors for sexually transmitted infections and Lyme disease
Known disorders, particularly those that could cause or contribute to joint pain (such as osteoarthritis, gout, or sickle cell disease)
The physical examination focuses on the joints for signs of inflammation (including swelling, warmth, and rarely redness), tenderness, limitation of motion, and noises made when the joint moves (called crepitus). Doctors compare the affected joint with the unaffected joint on the opposite side of the body to look for any subtle changes. Doctors may also look for signs of infection elsewhere on the body, particularly on the skin and genitals.
Several findings from the history and examination give clues to the cause of joint pain:
Based on the examination, doctors can usually tell whether the source of the pain is the joint or nearby structures. For example, if only one side of a joint seems abnormal, the source of the pain is probably outside of the joint.
Based on the examination, doctors can usually tell whether fluid is in the joint.
Inflammation that develops over hours is usually caused by crystal-induced arthritis, particularly if similar symptoms have occurred previously. Infectious arthritis is another major cause of acute arthritis.
Fever is most often caused by infectious arthritis or crystal-induced arthritis.
Testing
The need for tests depends on what doctors find during the history and physical examination, particularly whether warning signs are present.
Possible tests include
Testing of joint fluid
X-rays and other imaging tests
Sometimes blood tests
Doctors usually test the fluid in the joint if the joint is swollen. Doctors extract the fluid from the joint by first sterilizing the area with an antiseptic solution and then numbing the skin with an anesthetic. Then a needle is inserted into the joint and joint fluid is withdrawn (a procedure called joint aspiration or arthrocentesis). This procedure causes little or no pain. The fluid is usually tested for, among other things, bacteria that can cause infection and is examined under a microscope for crystals that cause gout and related disorders. Sometimes doctors do not test the fluid if the cause of the joint pain is obvious, for example, the pain occurs after an injury or fluid accumulates repeatedly in a joint with a chronic joint disorder such as osteoarthritis.
X-rays may be taken, but they are usually unnecessary in people with acute arthritis. X-rays do not show abnormalities of soft tissues or cartilage. X-rays are most helpful in diagnosing fractures and sometimes bone tumors or osteonecrosis.
Magnetic resonance imaging (MRI) or computed tomography (CT) can show abnormalities of bones, joints, tendons, and muscles in more detail than x-rays. Thus, MRI or CT is used to diagnose bone and joint abnormalities that may not be evident or clear on x-rays (for example, hip fractures that are too small to be seen on x-rays). MRI is used to diagnose certain soft-tissue abnormalities, such as rotator cuff abnormalities in the shoulder and ligament and meniscus cartilage abnormalities in the knee.
Blood tests are occasionally necessary, for example, to help diagnose or rule out Lyme disease.
Treatment of Pain in a Single Joint
The most effective way to relieve joint pain is to treat the disorder causing the pain. For example, antibiotics can be given to treat infectious arthritis. Bones with fractures may need to be immobilized (for example, set in a cast).
Drugs can also be used to relieve joint inflammation regardless of the cause. Such drugs include nonsteroidal anti-inflammatory drugs (NSAIDs) or, for very severe inflammation, sometimes corticosteroids. Joint pain without inflammation, regardless of the cause, can be relieved with NSAIDs, although tends to be as effective and safer for most people.
Immobilizing a joint with a splint or sling is sometimes a useful temporary way to relieve pain. Applying cold (for example, with ice) is the best treatment immediately after an injury has occurred and can be used for relieving pain caused by joint inflammation. Applying heat (for example, with a heating pad) may decrease pain by relieving spasms in the muscles around joints. However, people should protect their skin from extremes of heat and cold. For example, ice should be put in a rubber ice bag or a plastic bag wrapped in a towel and not applied to the skin directly. Also, hot and cold materials should be applied for at least 15 minutes at a time to penetrate deeply enough to affect the most painful or inflamed tissues.
After the severe pain has lessened, doctors may recommend people have physical therapy to regain or maintain range of motion and strengthen surrounding muscles.
Key Points
Single-joint pain in older adults is most often caused by osteoarthritis or gout.
Single-joint pain in young adults or adolescents may be caused by a sexually transmitted infection such as gonorrhea.
People who have sudden joint pain with swelling should be evaluated by a doctor as soon as possible so that infectious arthritis, if present, can be promptly treated.
Fluid from swollen joints is usually withdrawn and tested for infection and the presence of crystals.
