A bump appearing on a knuckle is a frequent occurrence that prompts concern. These lumps vary widely in origin, texture, and significance, ranging from soft, fluid-filled sacs to hard, bony outgrowths. Determining the nature of the lump requires looking closely at its location, consistency, and whether it is associated with pain or other symptoms. The causes generally fall into distinct categories: soft tissue formations, chronic joint deterioration, and acute trauma or infection.
Soft Tissue Cysts and Growths
The most common soft tissue masses found near the knuckles are fluid-filled sacs that originate from the joint or tendon sheaths. A ganglion cyst is a non-cancerous lump resulting from the weakening of a joint capsule or tendon lining, allowing fluid to pool outside the joint space. This cyst contains a thick, gelatinous material, which gives it a dense, yet sometimes moveable, consistency under the skin.
A specific form is the mucous cyst, which appears exclusively on the dorsal aspect of the distal interphalangeal joint (the knuckle closest to the fingernail). Mucous cysts frequently develop in older adults and are often linked to underlying osteoarthritis in that specific joint. As the cyst grows, it can sometimes press on the nail matrix, leading to a noticeable groove or deformity in the fingernail.
Another type of soft tissue mass is a lipoma, a benign growth composed of fatty tissue. Unlike cysts, lipomas are generally soft and doughy to the touch and are not typically spherical or connected to the joint capsule. They usually feel mobile beneath the skin and rarely cause symptoms unless they grow large enough to press on a nerve or restrict movement.
Bumps Related to Joint Deterioration
Some of the hardest and most permanent bumps on the knuckles are a direct consequence of long-term joint disease, specifically osteoarthritis. This degenerative condition leads to the formation of bony enlargements, or osteophytes, as the body attempts to repair damaged cartilage. These hard, non-mobile bumps are known by specific names depending on their location.
Heberden’s nodes are osteophytes that form on the distal interphalangeal joints (the knuckles nearest the fingertip). Bouchard’s nodes occur on the proximal interphalangeal joints (the middle knuckles of the fingers). Both types of nodes are signs of hand osteoarthritis. While they may be painful and inflamed when they first develop, they often become painless, permanent, and hard deformities.
Inflammatory forms of arthritis also cause distinct lumps, such as the rheumatoid nodules associated with rheumatoid arthritis (RA). These nodules are firm, rubbery masses made of inflammatory tissue, and they tend to form over pressure points, including the knuckles and elbows. Tophi are characteristic lumps seen in chronic gout, resulting from the accumulation of monosodium urate crystals in and around the joints. Tophi appear as swollen growths that can erode bone and may even rupture to release a chalky, white material.
Trauma, Calluses, and Acute Causes
Bumps can also arise from acute events like friction, injury, or infection, rather than from chronic conditions. A common cause is the development of knuckle pads, which are localized thickenings of the skin and underlying fibrous tissue. These are essentially deep calluses that form over the knuckles due to repetitive, frictional trauma, often seen in specific occupations or habits like finger chewing.
A direct, acute injury can result in a post-traumatic lump, such as scar tissue or a localized collection of fluid, or it may lead to a serious infection. Bacterial infections can cause a painful, rapidly developing bump, which may present as cellulitis or an abscess. Cellulitis is a deep skin infection characterized by rapidly spreading warmth, redness, and tenderness, sometimes accompanied by systemic symptoms like fever.
An abscess is a localized pocket of pus that forms a raised, tender lump, distinct from the diffuse swelling of cellulitis. Both infections require prompt medical attention, as the small, enclosed spaces in the hand allow infection to spread quickly and cause damage to nearby tendons and joints.
When a Knuckle Bump Requires a Doctor
While many knuckle bumps are benign, such as small calluses or asymptomatic cysts, certain features warrant medical evaluation. You should consult a doctor if the bump appears suddenly and grows rapidly in size, or if it is associated with signs of acute infection. These infectious signs include worsening pain, spreading redness, warmth, or the presence of pus, especially if accompanied by a fever.
Any lump that causes significant pain or restricts the range of motion in the finger joint should be examined. Symptoms suggesting nerve compression require urgent attention. These include new or persistent numbness, tingling (paresthesia), or muscle weakness in the finger or hand, as this indicates the mass may be pressing on a peripheral nerve. An accurate diagnosis is necessary to determine if the bump is a sign of an underlying systemic disease, like arthritis, or a localized issue requiring drainage or surgical removal.