The acromion is a bony projection extending from the shoulder blade (scapula) that forms the roof of the shoulder joint. This structure creates the narrow subacromial space, through which the rotator cuff tendons and the bursa must pass. An anatomical variation, such as a Type 2 acromion, is often identified as a contributing factor to impingement syndrome, especially when shoulder pain occurs with overhead movement. While a Type 2 acromion is linked to discomfort, treatment decisions depend heavily on the severity of symptoms and the patient’s response to non-surgical methods.
Understanding the Type 2 Acromion Shape
The acromion’s shape is categorized using the Bigliani classification system. Type 1 has a flat undersurface, Type 3 is hooked, and Type 2 is defined by a curved shape. The Type 2 acromion’s undersurface is concave, running roughly parallel to the head of the humerus (upper arm bone).
This curved contour is the most common anatomical variant found in the general population. Its shape can reduce the available room in the subacromial space compared to the flat Type 1 acromion. This narrowing leads to mechanical friction, causing irritation, inflammation, and compression of the soft tissues, including the bursa and rotator cuff tendons.
This friction causes subacromial impingement syndrome, often manifesting as pain when lifting the arm overhead. Although the hooked Type 3 acromion is most strongly associated with rotator cuff tears, Type 2 is frequently present in patients diagnosed with impingement. Identifying this shape on imaging is diagnostic information, but it does not automatically confirm the need for surgery.
Non-Surgical Paths to Recovery
For patients with shoulder pain related to a Type 2 acromion, the initial approach is conservative, focusing on reducing inflammation and improving shoulder mechanics. The goal of non-surgical management is to resolve symptoms and restore function without surgery.
A structured physical therapy program is the core of conservative care, typically lasting six to twelve weeks before assessment. Therapy focuses on strengthening the rotator cuff muscles to stabilize the joint and prevent the humeral head from migrating upward, maximizing the subacromial space. Exercises also target the scapular stabilizers to ensure proper shoulder blade positioning and movement patterns.
Activity modification involves temporarily avoiding painful overhead movements. To manage pain and inflammation, nonsteroidal anti-inflammatory drugs (NSAIDs) may be recommended. For severe or persistent pain, a subacromial corticosteroid injection delivers anti-inflammatory medication directly into the compressed area. These conservative methods are highly successful, and few patients fail to achieve satisfactory pain relief and function.
Determining When Surgery Is Necessary
Surgery is considered a last resort for Type 2 acromion-related impingement. It is reserved for patients whose symptoms have not improved after an extended course of non-surgical treatment. The decision to operate is typically made after at least six months of failed conservative management, when persistent pain restricts daily activities and quality of life.
The most common procedure is arthroscopic subacromial decompression, or acromioplasty. This minimally invasive technique uses a camera and instruments to shave away a small portion of bone from the acromion’s undersurface. The intent is to convert the curved (Type 2) or hooked (Type 3) shape into a flatter contour, similar to a Type 1 acromion, physically increasing the space for the tendons and bursa.
If a patient has a significant rotator cuff tear confirmed by imaging, the surgery may include repairing the tear alongside the acromioplasty. However, recent research suggests that performing acromioplasty with a rotator cuff repair for a Type 2 acromion may not improve outcomes compared to repairing the tendon alone. Therefore, the necessity of the bone-shaving procedure depends on the individual’s overall pathology and the surgeon’s clinical assessment.