It is common to notice bumps on knuckles, which can raise questions about their origin. These changes might cause concern, as they can feel unusual or become noticeable. Various factors contribute to their formation, from superficial skin conditions to underlying joint structures. Understanding the potential causes helps determine if a bump is harmless or requires medical attention.
Bumps from Skin-Surface Conditions
Bumps on knuckles often arise from changes in the outermost skin layers. Warts are a common type, small, rough growths caused by the human papillomavirus (HPV). They typically appear as flesh-colored, grainy bumps, sometimes with tiny black dots. Warts form when the virus infects skin cells, causing them to grow rapidly.
Calluses are another frequent cause, appearing as thickened, hardened areas of skin. They usually form on knuckles in response to repeated friction or pressure, such as from manual tasks. Calluses serve as a protective response, making the skin more resilient. These bumps tend to be firm and may have a yellowish tint.
Psoriasis plaques can also appear as distinct, raised patches on knuckles. Psoriasis is an autoimmune condition where skin cells grow too quickly, leading to an accumulation on the surface. These plaques are typically reddened, scaly, and well-defined, often appearing silvery-white. They can be itchy or painful.
Bumps Related to Joints and Underlying Tissues
Knuckle bumps frequently stem from issues within the joints or soft tissues beneath the skin. Osteoarthritis, a degenerative joint disease, can lead to bony enlargements known as nodes. Heberden’s nodes develop on the distal interphalangeal (DIP) joints (closest to fingertips), while Bouchard’s nodes appear on the proximal interphalangeal (PIP) joints (middle finger joints). These nodes are hard, often symmetrical, and can cause stiffness or a loss of range of motion.
Rheumatoid arthritis, an autoimmune condition causing chronic inflammation, can result in bumps called rheumatoid nodules. These firm, non-tender lumps form under the skin, often over bony prominences like the knuckles. Unlike the bony nodes of osteoarthritis, rheumatoid nodules are soft tissue growths that can vary in size and may sometimes be mobile.
Fluid-filled sacs, such as ganglion cysts and mucoid cysts, are another category of bumps originating from deeper structures. Ganglion cysts are non-cancerous lumps that typically form near joints or tendons and contain a jelly-like fluid. They can appear on the wrist or near finger joints, feeling soft or firm. Mucoid cysts, a specific type of ganglion cyst, usually occur at the end finger joint (DIP joint) and may be associated with osteoarthritis. These cysts can sometimes cause a groove in the fingernail.
Bumps Caused by Injury or Specific Deposits
One example is “boxer’s knuckles,” a traumatic injury often sustained from impact, such as punching. This can involve damage to the tendons or ligaments around the metacarpophalangeal (MCP) joints, the knuckles at the base of the fingers. The injury typically results in swelling and a noticeable bump, accompanied by pain and difficulty moving the finger.
Gout, a form of inflammatory arthritis, can lead to tophi: deposits of uric acid crystals. These tophi often form as firm, sometimes chalky, lumps under the skin, particularly around joints like the knuckles. They can be painful and inflamed, especially during a gout flare-up. Tophi typically appear years after gout onset, indicating chronic elevation of uric acid levels.
Xanthomas are another type of deposit that can cause knuckle bumps; they are fatty deposits under the skin. These appear as yellowish, soft, and sometimes slightly raised bumps. Xanthomas are often associated with high levels of lipids, such as cholesterol, in the blood. They may be observed on the knuckles, particularly in certain genetic conditions or metabolic disorders.
Key Characteristics to Observe
When a bump appears on a knuckle, noting specific characteristics provides valuable clues. Observe changes in the bump’s size; rapid growth or significant changes warrant attention. The bump’s color and surrounding skin can indicate inflammation (redness) or trauma (bruising). Pain, tenderness, warmth, or limited joint movement (difficulty bending or straightening the finger) suggest an underlying issue. If a bump is persistent, doesn’t resolve, or has other concerning symptoms, seek medical guidance.