Acromial Types and Their Role in Shoulder Dysfunction

What Are Acromial Types?

The acromion is a bony projection on the scapula (shoulder blade) that forms the top of the shoulder. It creates the roof over the rotator cuff and shoulder joint. Acromial types refer to the shapes or configurations of this bone, which vary between individuals. These variations potentially have clinical significance, especially concerning shoulder impingement and rotator cuff injuries.

There are four widely recognised acromial types, first of such was classified by Bigliani et al. in 1986. Simple X-ray view from the side, referral to as Lateral (outlet) view is suitable for seeing the acromion relative to the humeral head (ball of the shoulder). From this you can distinguish type I-III acromions. 

The 4 Types of Acromion

1. Type I – The Flat Acromion
This shape has a flat undersurface and is the least likely to cause impingement. It offers more space for the rotator cuff tendons to occupy beneath the acromion during shoulder movement.

2. Type II – The Curved Acromion
This is the most common acromial shape. The underside of the acromion curves downward, potentially narrowing the subacromial space. This can increase the risk of impingement. Particularly so in individuals with poor posture or altered shoulder mechanics for other reasons.

3. Type III – A Hooked Acromion
The hook-shaped end projects downward with this variation which theoretically increases the likelihood of compression of the rotator cuff tendons. Type III is strongly associated with subacromial impingement and rotator cuff tears. Research has shown a higher incidence of full-thickness rotator cuff tears in individuals with this Type III acromion morphology.

4. Type IV – A Convex Upturned Acromion
A less commonly encountered acromial type, features an upward tilt. The clinical implications are not as well documented due to the rarity of this variation but it’s likely it would pose less risk of impingement than the hooked variant.

What Is a Type 1 and Type 2 Acromion?

Type 1 and Type 2 acromion morphologies are considered more benign than Type 3.

• A Type 1 (flat) acromion provides ample space for tendon movement and is considered unlikely to be associated with impingement symptoms.
• A Type 2 (curved) acromion theoretically may reduce the subacromial space enough to irritate the rotator cuff tendons over time. Especially so with repetitive overhead activities or poor shoulder mechanics. Ideally symptoms considered related to a Type 2 acromion can be managed conservatively with physio treatment focusing on appropriate postural correction, scapular stabilisation, and shoulder strengthening.

Is Type 3 Acromion Serious?

A Type 3 (hooked) acromion is generally considered more likely to cause issues due to its stronger association with rotator cuff pathology. Research suggests that this acromial shape can increase mechanical compression on the rotator cuff tendons, particularly the supraspinatus. Over time, this repeated compression may lead to tendon irritation, beginning with inflammation and potentially progressing to degeneration and tearing.

While the presence of a Type 3 acromion does not guarantee shoulder problems, it does increase the risk of persistent pain when combined with other contributing factors. These may include:

• Poor shoulder biomechanics

• Repetitive overhead activities

• Age-related changes and tendon degeneration

Physiotherapy is typically the first-line treatment. At Sydney Physio Clinic, we focus on improving shoulder mechanics and reducing impingement through targeted rehabilitation. If symptoms persist despite conservative care, surgical options such as subacromial decompression may be considered.

Does a Type 2 Acromion Require Surgery?

Most individuals with a Type 2 acromion manage an active life perfectly fine.  At Sydney Physio Clinic, we frequently assess and treat patients with this morphology and shoulder impingement symptoms. A tailored program targeting scapular control, postural retraining, and rotator cuff strength can significantly reduce symptoms and improve function. With surgical intervention being unwarranted in all but the most stubborn of situations. 

Physiotherapy Management for Different Acromial Types

Understanding the role of acromial types in shoulder dysfunction helps tailor treatment. At Sydney Physio Clinic typically an approach to shoulder impingement regardless of acromial morphology includes:

• Postural correction rehabilitation where indicated to assist in “opening” the subacromial space
• Strengthening of scapular stabilisers to improve shoulder biomechanics
• Rotator cuff loading to build tendon load tolerance and humeral head control
• Manual therapy to reduce any soft tissue restrictions
• Education to avoid aggravating positions and overuse. It is amazing the number of patients with a concerted effort to adjust their sleeping posture who improve dramatically from this relatively simple lifestyle change. 

For symptomatic individuals with Type 2 and Type 3 acromions, early intervention can be important in avoiding chronic tendon changes. Imaging can be useful in many circumstances to help guide treatment, but clinical assessment still remains the foundation of the physiotherapy approach.

Acromial types can play a significant role in shoulder health, particularly in impingement syndromes and rotator cuff pathology. While a flat Type 1 acromion is generally not problematic, the curved and hooked variations may contribute to shoulder pain symptoms. At Sydney Physio Clinic, we focus on conservative management to help restore function and reduce pain. Creating a personalised program based on your lifestyle and functional demands.