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 Introduction to the Biology of the Musculoskeletal System The musculoskeletal system provides form, stability, and movement to the human body. It consists of the body's bones (which make up the skeleton), muscles, tendons, ligaments, joints, cartilage... read more ). Examples of such disorders are bursitis Bursitis Bursitis is painful inflammation of a bursa (a flat, fluid-filled sac that provides cushioning where skin, muscles, tendons, and ligaments rub over bones). Movement is usually painful, and bursae... read more 
, tendinitis Tendinitis and Tenosynovitis Tendinitis is inflammation of a tendon. Tenosynovitis is tendinitis accompanied by inflammation of the protective covering around the tendon (tendon sheath). The cause is not always known. Tendons... read more , sprains Overview of Sprains and Other Soft-Tissue Injuries Sprains are tears in ligaments (tissues that connect one bone to another). Other soft-tissue injuries include tears in muscles (strains) and tears (ruptures) in tendons (tissues that connect... read more 
, 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 Infectious Arthritis Infectious arthritis is infection in the fluid and tissues of a joint usually caused by bacteria but occasionally by viruses or fungi. Bacteria, viruses, or fungi may spread through the bloodstream... read more , gout Gout and Calcium Pyrophosphate Arthritis and related disorders, and osteoarthritis Osteoarthritis (OA) Osteoarthritis is a chronic disorder that causes damage to the cartilage and surrounding tissues and is characterized by pain, stiffness, and loss of function. Arthritis due to damage of joint... read more 
. Joint pain may be the first symptom of a disorder that affects other organs in the body, such as an autoimmune disorder Overview of Autoimmune Disorders of Connective Tissue In an autoimmune disorder, antibodies or cells produced by the body attack the body’s own tissues. Many autoimmune disorders affect connective tissue and a variety of organs. Connective tissue... read more 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 Joint Pain: Many Joints Pain that involves more than just one joint is called polyarticular joint pain. A joint may simply be painful (arthralgia) or may also be inflamed (arthritis). Pain that seems to be coming from... read more ).
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 Infectious Arthritis Infectious arthritis is infection in the fluid and tissues of a joint usually caused by bacteria but occasionally by viruses or fungi. Bacteria, viruses, or fungi may spread through the bloodstream... read more (often caused by gonorrhea Gonorrhea Gonorrhea is a sexually transmitted infection caused by the bacteria Neisseria gonorrhoeae, which infect the lining of the urethra, cervix, rectum, or throat, or the membranes that cover... read more
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 Gout and Calcium Pyrophosphate Arthritis )
Among older adults who have not been injured, the most common causes are
Crystal-induced arthritis (gout Gout and Calcium Pyrophosphate Arthritis or calcium pyrophosphate arthritis Calcium Pyrophosphate (CPP) Arthritis Calcium pyrophosphate (CPP) arthritis (previously called pseudogout) is a disorder caused by deposits of calcium pyrophosphate dihydrate crystals in the joint cartilage, leading to intermittent... read more )
The most dangerous cause at any age is acute infectious arthritis Infectious Arthritis Infectious arthritis is infection in the fluid and tissues of a joint usually caused by bacteria but occasionally by viruses or fungi. Bacteria, viruses, or fungi may spread through the bloodstream... read more . 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 .
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 Osteonecrosis Osteonecrosis is the death of a segment of bone caused by an impaired blood supply. Osteonecrosis is most commonly caused by an injury but can also occur without an injury. Typical symptoms... read more ), joint tumors Joint Tumors Tumors rarely affect joints unless a bone tumor or soft-tissue tumor is near a joint. However, two conditions—synovial chondromatosis and tenosynovial giant cell tumors—occur in the lining ... read more 
(such as pigmented villonodular synovitis Tenosynovial giant cell tumor Tumors rarely affect joints unless a bone tumor or soft-tissue tumor is near a joint. However, two conditions—synovial chondromatosis and tenosynovial giant cell tumors—occur in the lining ... read more ), blood in the joint (hemarthrosis), and disorders that usually cause pain in more than one joint, such as reactive arthritis Reactive Arthritis Reactive arthritis (previously called Reiter syndrome) is a spondyloarthritis causing inflammation of the joints and tendon attachments at the joints, often related to an infection. Joint pain... read more 
.
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
Presence of a bleeding disorder, use of anticoagulants ("blood thinners," for example, warfarin), or abnormal blood hemoglobin (for example, sickle cell disease)
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 ).
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 Joint Noises Joint noises (crepitus) describes a popping, cracking, or clicking sound in a joint. Joint noises, such as creaks and clicks, are common among many people without any joint disorders, but they... read more ). 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 Joint aspiration (arthrocentesis) A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more 
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 X-rays A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more 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 Computed tomography (CT) and magnetic resonance imaging (MRI) A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more (MRI) or computed tomography Computed tomography (CT) and magnetic resonance imaging (MRI) A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more (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 Laboratory Tests A doctor can often diagnose a musculoskeletal disorder based on the history and the results of a physical examination. Laboratory tests, imaging tests, or other diagnostic procedures are sometimes... read more 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 Nonsteroidal Anti-Inflammatory Drugs Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more (NSAIDs) or, for very severe inflammation, sometimes corticosteroids Corticosteroids Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more 
. Joint pain without inflammation, regardless of the cause, can be relieved with NSAIDs, although acetaminophen Acetaminophen Pain relievers (analgesics) are the main drugs used to treat pain. Doctors choose a pain reliever based on the type and duration of pain and on the drug's likely benefits and risks. Most pain... read more 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 Cold therapy (cryotherapy) Professional rehabilitation therapists treat pain and inflammation. Such treatment makes movement easier and enables people to participate more fully in rehabilitation. Techniques used include... read more (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 Heat therapy Professional rehabilitation therapists treat pain and inflammation. Such treatment makes movement easier and enables people to participate more fully in rehabilitation. Techniques used include... read more (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 Physical Therapy (PT) Physical therapy, a component of rehabilitation, involves exercising and manipulating the body with an emphasis on the back, upper arms, and legs. It can improve joint and muscle function, helping... read more 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.
