Exploring the Acromial Region: Key Concepts and Classifications

By Ron Wamumali Written by Ron Wamumali
Updated on September 12, 2023

The acromial region is one of the most significant parts of the human anatomy. It is located in the shoulder region, playing a crucial role in the movement and stability of the shoulder joint. While this part of the human body may seem a tad complex, it sure does come with its fair share of uses. Without further ado, let’s start with defining the term acromion.

What’s the definition of the term acromion?

For those who aren’t quite familiar with the term, the acromion is part of the shoulder blade that’s found on the scapular region, to be specific. The acromia, or acromion if singular, extends over the shoulder joint, making it easy for the articulation to the clavicle. One of its functions is to serve as a connection point for various ligaments and muscles. The shape and size of the acromion can vary among individuals, which may have implications for shoulder health.


Two acromion regions

What are the functions of the acromial region?

The acromial region plays a vital role in shoulder movement and stability. Here are some of its key functions:

1. Muscle attachment

You can find a number of important muscles that attach to the acromial region, including the deltoid, trapezius, and rotator cuff muscles. The said muscles help move the shoulder joint, as well as keep it stable when needed. They contribute to shoulder movement and stability, and their proper functioning relies on the integrity of the acromial region.

2. Range of motion

The acromion, along with other structures, allows for a wide range of motion in the shoulder joint. It enables various movements, including flexion, extension, abduction, adduction, and rotation of the arm.

3. Joint stability

The acromion and the acromioclavicular joint provide stability to the shoulder joint. They help prevent excessive movement and dislocation of the joint during various activities, such as performing sports-related movements or lifting heavy objects.

The location of the acromion region

What’s the reason for the Bigliani classification of acromia?

The curved interior of the shoulder bone, or the clavicle in layman’s terms, can be divvied up into three variations, which is now four. The latter was also known as the Bigliani classification. The whole point of the Bigliani classification was to determine whether or not the acromial process (or acromial region) was responsible for rotator cuff tears – a common injury in sports.

The research revealed different results as far as the three variations of acromia were concerned. The three variations in question included Type I Acromia, Type II Acromia, and Type III Acromia. Type IV Acromia was most recently added to the list.

Of course, the Bigliani Classification didn’t come without its fair share of doubts and drawbacks. The latter explains why most clinicians still use it but with caution. According to Bigliani, approximately 69% of rotator cuff tears cases had Type III Acromia while 24.4% of these were Type II Acromia.

These three sections have a very complex relationship whose constant interaction results in movement in different directions. There are also muscles and tendons involved thus increasing movement and stability. The experts would encourage regular exercise to ensure flexibility as well as strength and stability.

If you follow the doctor’s instructions, then your acromion should do a great job when it comes to protecting the glenoid cavity. It’ll also do a great job in articulating the clavicle thus giving your entire frame more stability and overall strength.

What’s the most recent acromial classification and the distinction between each class?

A lot of confusion arises when it comes to differentiating the variations and types of acromia. As I mentioned earlier, there are three variations of acromia. But, when it comes to the types of acromia, then there are four in total. The only way for you to tell the difference between the four types of acromial, or acromion morphology as the experts would like to call it, is through a comprehensive sagittal oblique MRI.

The first type of acromial is the flat inferiorly acromial. According to relevant studies, the latter accounts for approximately 12% of the total cuff tear cases in the acromion region. The second type of acromial is the curved acromial. The curved acromial accounts for at least 56% of the total cases of cuff tears in the acromion region. The curved acromial comes with a concave undersurface and it can be found lying parallel to the humeral head.

The third and most recent discovery (and classification) of the acromion shape process is the upturned (convex) acromiale. The latter accounts for about 3% of the total cases of cuff tears in the acromion region. Studies show that the convex acromiale is shaped like one near its distal end, hence its name. 

The fourth and final classification of the acromial region is the hooked acromial. The latter can be found in the most anterior part of the acromion and accounts for approximately 29% of the entire region. The latter area is responsible for increasing shoulder impingement. The region is shaped like a hook.

Is the acromial region in humans similar to that of other mammals?

Even though all mammals come with a morphology that’s made of flesh and bone, it’s quite plausible that they do differ and that’s the case due to several variables. For starters, mammals that live in water may have a different bone structure than those on land simply because they tend to swim instead of walk or slither (in the case of mammals without limbs).


The acromion region in humans


That said, it’s safe to conclude that the acromial region in humans is slightly different from those of other mammals for the same reason stated above. Also, the acromial region in humans is believed to have evolved thus making it a tad more complex (or at least a few notches more complex than the rest).

If you compare the acromial region between humans and that of the primates, the human acromion appears steeply sloped. The latter is the case because humans walk upright while most primates alternate from walking straight to walking on fours. That said, it’s safe to conclude that the acromial region in humans is slightly different from that of other mammals.

Key takeaway

The acromial region is a key part of the shoulder joint, contributing to its movement and stability. Understanding its anatomy, function, and different classifications can help us appreciate its importance and its potential impact on shoulder health. Common conditions and injuries in the acromial region can significantly affect shoulder function, highlighting the need for proper care and treatment.