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Arthritis is the most common cause of metacarpophalangeal joint pain, though the condition can be attributed to a number of different problems, including trauma, either from repetitive use or injury, bone cysts, and other underlying conditions like gout. People typically have one metacarpophalangeal joint, also known as an MCP or MC joint, per finger. These joints play a critical role in finger and hand movement, and pain can inhibit a number of everyday tasks. Most of the time the pain happens all at once, which it to say that all the joints in a single hand flare up together, but not always. A lot depends on a person’s structural anatomy and the underlying cause of the pain.
In people, the MCP joints are essentially the knuckles where the bones of the hands first connect to the long middle bones of the fingers. Speaking more scientifically, they are where the heads of the metacarpal bones meet the bases of the proximal phalanges. The meeting involves a number of ligaments and small tendons and plays a critical role in finger movement and precision. Metacarpophalangeal joint pain is often disabling because these "hinge" joints are essential to a number of both fine motor tasks and larger power, or grip, activities.
The most common cause of metacarpophalangeal joint pain is rheumatoid arthritis. This inflammatory disease happens when the lining of joints, particularly those in the hands and fingers, produces substances that erode the cartilage, ligaments, and tendons of the area. When rheumatoid arthritis happens in the MCP joints it can cause not only pain but also lasting damage, sometimes causing a shift of the fingers toward the ulnar side of the hand — the little finger's side. This can be disfiguring and can dramatically impair movement and hand functionality.
Other Forms of Arthritis
Osteoarthritis and post-traumatic arthritis are generally the second-most common causes of pain in this joint. These are more general forms of joint deterioration that typically happen as a facet of old age or, in the case of post-traumatic flare-ups, accident or injury. The main symptom is a wearing down or deterioration of the protective cartilage covering the bone at the joint. These types of arthritis typically impact larger joints before they hit the fingers, but not always, particularly not when the hands have been injured or somehow compromised.
Repetitive Use and Trauma
Trauma or injury to the hands and fingers can also cause pain, stemming from either the soft tissue edema limiting the joint movement or actual damage to the joint. This sort of pain will sometimes go away on its own once the fingers have healed, particularly if the injury wasn’t severe enough to cause lasting damage. A hand bruised by being smashed in a door, for instance, is more likely to make a full recovery than one requiring surgery or one in which the bones were actually broken. In these cases joint pain may be longer lasting, particularly if the joints healed improperly.
Repetitive use can also wear down the cartilage of the joints, though this often happens slowly over time so it’s harder for people to pinpoint a specific cause. People with repetitive injuries often complain of an aching or deep joint pain during fine motor activity, but the pain isn’t necessarily always present and it rarely comes with the deformity that is apparent with rheumatoid arthritis.
Gout and Skin Disorders
Another non-traumatic cause of pain is gout. Gout is a very painful accumulation of uric acid that most often occurs in the joint of the big toe, but it can also manifest in the MCP joints, particularly where the thumb joins the hand. Joints impacted by gout tend to be bright red, swollen, and often hot to the touch.
Psoriasis is an autoimmune disorder that is best known for its impact on the skin, but it sometimes causes pain and disability in the body’s joints before the reddened skin lesions so characteristic of the disease appear. People who suffer from this condition typically have scaly, flakey skin over large swaths of their bodies. The discomfort and itchiness of the condition sometimes causes them to overlook MCP joint pain because their attention is more focused on the external symptoms, but in many cases, if there is psoriasis on the hands there is likely inflammation in the finger joints, too.
Benign bone cysts might also be the culprit, particularly if the sufferer is a young boy or teenager. Young men are more prone to bone cysts than young women in part because of the rate at which their bones shift and develop during puberty. A cyst is basically a errant bobble of fluid that builds up and forms a growth; when this happens on or near the finger joints, people often feel pain until the area is drained or the cyst is otherwise removed.
Other types of cysts, such as ganglion or dermoid cysts, might also be to blame, though diagnosing these can be more invasive and are usually only considered when health care providers have ruled out most other potential causes. Even known joint conditions that are rarely seen in the hands and fingers, such as osteochondromatosis, might need to be investigated in really perplexing cases, and sometimes even rarer conditions like Systemic lupus erythematosus may be diagnosed as the true cause in the process.