Finding an unexpected bump on your wrist bone can be concerning, but these masses are usually benign. The wrist is a complex structure of eight carpal bones, tendons, and ligaments, allowing several types of growths to form. Knowing the characteristics of the lump is the first step toward understanding its origin and determining the appropriate next steps for evaluation.
Ganglion Cysts: The Leading Cause
The most frequent mass on the back of the wrist is a ganglion cyst, a non-cancerous lump developing near joints or along tendon sheaths. These soft tissue masses form when a small tear in the joint capsule or tendon lining allows synovial fluid to escape and collect in a sac-like structure. This fluid is thick and slippery, similar to the lubricating substance found naturally within your joints.
A ganglion cyst often presents as a smooth, rounded, or oval-shaped bump that can feel firm or spongy. A distinct feature is that their size can fluctuate, sometimes growing larger with increased wrist activity and shrinking with rest. They are most common on the dorsal (back) side of the wrist, but they can also appear on the volar (palm) side or near the joints of the fingers. While the exact cause is not fully known, they are common in individuals between 20 and 40 years old, especially women, and may be linked to previous joint injury or repetitive stress.
The bump itself is usually painless, but discomfort occurs if the cyst presses on an adjacent nerve or tendon. When this compression happens, a person may experience a dull ache, tingling, or muscle weakness in the hand. Despite their variable size, these cysts are harmless and do not spread.
Bony Protrusions and Structural Causes
When a lump on the wrist feels hard, immovable, and directly connected to the bone, it is likely a structural prominence. The most common bony cause is a carpal boss, also known as dorsal wrist bossing. This is an overgrowth of bone, or a small bone spur, that forms where the small hand bones meet the wrist bones, typically near the base of the second or third metacarpal.
Unlike a soft cyst, a carpal boss is a firm, rigid mass that will not change size or flatten when pressure is applied. It is a fixed bump on the skeleton, often becoming more noticeable when the wrist is flexed. While the precise trigger is unclear, it may result from degenerative changes, repetitive motion stress, or a past trauma to the area.
Other structural causes include osteophytes, which are bone spurs related to osteoarthritis, or a healed fracture callus. A callus is new bone tissue that forms during the healing process of a broken bone. These bony changes are distinct from soft tissue masses and are confirmed through imaging tests. A carpal boss is often painless, but if it becomes symptomatic, it is usually because the tendons are rubbing over the prominence, leading to localized tenderness.
Recognizing Warning Signs and Seeking Care
Although most wrist bumps are benign, a medical evaluation is advisable for any new or changing mass to ensure an accurate diagnosis. Providers typically begin with a physical examination, assessing the lump’s texture, mobility, and tenderness. For a suspected ganglion cyst, transillumination—shining a light through the mass—can often confirm its fluid-filled nature.
Diagnostic imaging is used to differentiate between soft tissue and bony causes. An X-ray identifies a carpal boss or skeletal issues like bone spurs or an old fracture. An ultrasound or MRI scan provides detailed images of the soft tissues, helping to confirm a cyst or rule out other masses. Seek prompt attention if the bump exhibits rapid growth, significant pain, numbness, tingling, or weakness in the hand or fingers.
For treatment, many wrist bumps, particularly painless ganglion cysts or asymptomatic carpal bosses, require only observation. If a cyst causes pain or functional limitations, non-surgical options include wearing a splint or aspiration, which involves draining the fluid with a needle. For a painful carpal boss, initial care focuses on rest, anti-inflammatory medication, or a steroid injection. Surgical removal is reserved for cases where conservative treatments fail to relieve persistent symptoms or if the mass causes considerable discomfort or nerve compression.