Finding a new lump or bump on the body can cause immediate concern, but the majority of masses that develop on the shoulder are benign and treatable. The shoulder is a complex region involving multiple layers of muscle, bone, joints, and soft tissue, which contributes to the wide range of potential causes for a visible protrusion. Understanding whether a bump appeared suddenly after an event or developed slowly over time can offer the first clue toward identifying its origin.
Bumps Caused by Acute Injury or Trauma
A bump that appears immediately following a fall, a direct blow, or a heavy lifting incident often indicates a disruption to the underlying bone or joint structure. One common cause is an acromioclavicular (AC) joint separation, sometimes called a “shoulder separation,” which results from a tear in the ligaments connecting the collarbone (clavicle) to the highest point of the shoulder blade (acromion). When these stabilizing ligaments are torn, the weight of the arm pulls the shoulder blade down, causing the end of the clavicle to protrude upward and create a distinct, visible bump on the top of the shoulder. This type of injury is typically accompanied by severe pain and limited movement in the arm.
Another acute cause is a fracture, most commonly of the clavicle, where the broken bone fragments can displace and push against the skin, creating a sharp, painful prominence. Swelling itself can also mimic a bump, particularly with a severe soft tissue injury like a complete rotator cuff tear, where the immediate inflammation and bruising create a visible mass. In these traumatic cases, the sudden onset of the bump, coupled with intense pain and an inability to use the arm normally, requires prompt medical attention.
Common Soft Tissue and Skin-Related Bumps
When a bump develops slowly and is not associated with an injury, it often originates in the superficial soft tissues of the shoulder. A lipoma is one of the most frequently encountered benign growths, consisting of an overgrowth of fatty tissue located just beneath the skin. These lumps are generally soft, rubbery, and easily movable when pressed, and they are usually painless unless they grow large enough to press on a nerve. Lipomas are slow-growing and typically measure less than five centimeters across.
Epidermal cysts are another common type of soft-tissue mass, forming a closed sac filled with keratin, a protein found in skin cells. These cysts are usually firm, flesh-colored, and benign, often forming due to a clogged hair follicle or minor skin trauma. A different type of soft lump can be caused by bursitis, which is the inflammation of a bursa, a small, fluid-filled sac that cushions bones and tendons around the joint. If the subacromial bursa becomes inflamed, it can swell and create a soft, spongy lump that is tender to the touch.
Structural Changes and Joint-Related Bumps
Some shoulder prominences are not discrete lumps but rather the result of gradual, long-term changes to the joint or posture. Osteoarthritis, a degenerative condition where joint cartilage wears down, frequently leads to the formation of bone spurs, known as osteophytes. These bony projections develop along the edges of the joint as the body attempts to repair the damaged area, and they can create a noticeable, hard bump, especially around the acromioclavicular joint. This slow growth is often accompanied by chronic stiffness, pain that increases with movement, and a grinding sensation within the joint.
Another type of visible change is muscle atrophy, which occurs in cases of long-standing, massive rotator cuff tears. The wasting of the supraspinatus or infraspinatus muscles leaves a depression, making the underlying bony structures of the shoulder blade appear more prominent, resulting in a distinct visual asymmetry. Postural issues, such as kyphosis, can also create a visible hump in the upper back, which alters the contour of the shoulder area. This forward curvature of the spine, sometimes called a “dowager’s hump,” is a skeletal change that makes the shoulders look rounded and the shoulder blades uneven.
When to Seek Medical Evaluation
While most shoulder bumps are benign, certain signs indicate the need for a professional medical evaluation to rule out more significant conditions. A prompt visit to a healthcare provider is warranted if the bump exhibits any of the following characteristics:
- Systemic symptoms, such as an unexplained fever or chills.
- Rapidly increasing in size.
- Signs of infection, including increasing redness, heat, or drainage.
- Hard, fixed in place, and unmovable under the skin, especially if it is larger than five centimeters.
- Severe, persistent pain, or is associated with numbness, tingling, or weakness in the arm or hand.