Knuckles are complex anatomical structures where skin, tendons, and joint capsules converge, making them susceptible to a wide variety of growths and enlargements. When a bump appears on one of your finger joints, the cause is often benign. The appearance, location, and consistency of the bump—whether it is soft, bony, or fluid-filled—provide initial clues to its origin. Understanding the differences between these common causes can help guide your next steps.
Superficial Skin and Soft Tissue Causes
Many growths on the knuckles originate in the layers just beneath the skin, often involving fluid sacs or fibrous tissue. A ganglion cyst is a common lump found near joints and tendons in the hand, forming a small sac filled with a thick, jelly-like fluid. These cysts are typically firm or rubbery, are usually painless, and can change in size, sometimes even disappearing on their own.
A related type is the mucous cyst, which is a specific form of ganglion cyst that appears near the distal interphalangeal (DIP) joint. Mucous cysts often occur in people with underlying hand osteoarthritis and can cause a groove or ridge to form in the fingernail due to pressure on the nail matrix. Knuckle pads are another benign cause, presenting as firm, skin-colored or slightly rosy nodules that form over the proximal interphalangeal (PIP) joints. These are fibrous growths that can sometimes be linked to repetitive friction.
Warts, caused by the Human Papillomavirus (HPV), appear on the knuckles and fingers, often presenting as rough, raised bumps with tiny black dots. Unlike cysts, warts are a viral infection of the skin itself. Repeated pressure or friction can lead to the formation of calluses, which are thickened patches of hard, dead skin that can sometimes be mistaken for a deeper lump.
Bumps Related to Osteoarthritis and Joint Wear
Bumps that are hard and immovable often signal changes within the joint structure itself, primarily caused by osteoarthritis (OA). Osteoarthritis is a degenerative condition resulting from the breakdown of cartilage, which leads to the formation of new bone. These bony enlargements are known as osteophytes, or bone spurs, and they cause the characteristic knobby appearance of arthritic hands.
These bony growths have specific names based on their location on the fingers. Bumps that form on the distal interphalangeal (DIP) joints are called Heberden’s nodes. They are firm, permanent swellings that are considered a telltale sign of hand OA. Similarly, bumps that appear on the proximal interphalangeal (PIP) joints are known as Bouchard’s nodes.
Both Heberden’s and Bouchard’s nodes can cause stiffness, limited range of motion, and pain. These nodes are hard to the touch because they are composed of bone, distinguishing them from the softer, fluid-filled cysts. While these nodes are common in older adults, their development is strongly linked to genetics and can affect individuals before the age of 65.
Inflammatory and Systemic Conditions
Knuckle bumps are a manifestation of a systemic inflammatory or metabolic disease. Rheumatoid arthritis (RA) is an autoimmune condition that can cause firm, non-tender lumps called rheumatoid nodules. These nodules are masses of inflammatory tissue that form beneath the skin, often over bony prominences like the knuckles or elbows. They are typically rubbery and movable, helping to differentiate them from the fixed, bony nodes of osteoarthritis.
Gout results from the buildup of uric acid crystals in the joints and surrounding soft tissues. The deposits of these crystals form hard, inflammatory nodules called tophi. Tophi can appear on the knuckles, ears, or elbows and are often associated with episodes of intense joint pain, redness, and swelling.
Psoriatic arthritis (PsA), a condition linked to the skin disorder psoriasis, can also affect the knuckles, causing swelling, pain, and redness. PsA can lead to a characteristic “sausage-like” swelling of the entire finger, known as dactylitis. The involvement of the distal interphalangeal joints is particularly common in PsA, and it is often asymmetric, meaning it does not affect the same joints on both hands.
When to Consult a Healthcare Professional
While many knuckle bumps are harmless, certain signs indicate the need for medical evaluation to rule out a more serious underlying condition. You should seek consultation if a bump is rapidly growing, changes color, or becomes suddenly painful, hot, or red. These symptoms can suggest an infection, an inflammatory flare-up, or a tumor.
A doctor’s visit is also appropriate if the bump limits your ability to move your finger or hand, or if you experience associated symptoms like fever, unexplained weight loss, or numbness and tingling. The presence of bumps on both hands in a symmetrical pattern, especially when accompanied by stiffness that is worse in the morning, may suggest an inflammatory form of arthritis. A healthcare provider can perform a physical examination and may order imaging tests, such as X-rays, to determine if the bump is bony, fluid-filled, or composed of soft tissue.