Acromion Definition

Shoulder Joint Pictures
Picture 1 – The Shoulder Joint
Source – wikipedia

The Acromion is an anatomical feature on the scapula (the shoulder blade). It is a lateral of extension of the spine on the scapula, forming the highest point on the shoulder and is triangular in shape. It occurs along with the coracoids process over the shoulder joint.

Acromion Process

The acromion may also be called the acromion process. This acromion process, an extension of the scapular spine, extends laterally over the shoulder joint. The acromion process and the clavicle together make up the acriomioclavicular joint.

Acromion Anatomy

Acromion shoulder is the lateral extension of the spine of the scapula. Scapula is the scientific name for the shoulder blade. The spine leads to a ‘head’ and here it bears two processes – the acromion process and the carocoid process. The acromion process, when joins the clavicle, together with it provides the attachments for muscle of the arm and the chest.

The superior surface of the acromion bone is convex shaped and is directed to all three sides – upwards, laterally and backwards.  The surface is rough, so as to provide for the attachment of the Deltoideus fibres. The inferior surface is smooth and concave, whereas the superior one is rough and convex.

On the basis of the lateral and medial borders, we can explain the anatomy of the acromion process in a slightly different manner. The lateral border of the acromion is thick and irregular, lined by 3-4 tubercles. The medial one is concave, and comparatively shorter in length. To this medial border, we also find a part of the trapezius attached.

Acromion Fracture

The acromion fractures can be of many kinds –Type 1, Type 2, Type 3 and the Stress fractures.  They may be further sub-divided into Type 1a, 2a, 2b etc. The Types of Acromion are described in detail below.

Type 1 Acromion

This class of fracture is known as Flat Acromion. This kind of fracture records a comparatively low number of impingement cases. It is subdivided into type 1A and type 1B. Type 1A requires less time for healing. This kind of bone fracture is mainly caused due to tearing and pushing actions. So it is also known as Avulsion fractures. Type 1B is the kind in which the displacement of the bone is not much. The primary cause behind this type is trauma.

Type 2 Acromion

This is the curved kind of Acromion, also called the curved acromion, which records cases with a high impingement injury. This acromion appears on the occurrence of many kinds too many displacements in the bone, which may be lateral or anterior. There may or may not be the reduction in the subacromial space. The patient can recover within 6 weeks without any surgical or operative treatment.

Type 3 Acromion

This is the Hooked Acromion or the beaked acromion. This kind of fracture is the most commonly occurring one. It results into a kind of inferior displacement. The pain caused by this fracture is greater than the other two.  It may either be an anatomical feature, or degenerative. This fracture cannot be cured without surgical treatment. Surgery is indispensable if the acromion is a degenerative one.

Type 4 Acromion

This is the most recent classification of acromion process. In this type of acromion, the undersurface is convex near the distal end. The frequency of this acromion is increasing in the present day.

Acromion Morphology

One of the most important factors which are related to rotator cuff pathology is Acromion morphology. The surgeons who are performing angioplasty based on preoperative radiographs, base their surgery on this important rationale of acromion morphology. Variation of this moprphology has been related with the pathogenesis syndrome also.

Acromion Pain

When there is an acromion, it may lead to shoulder pain, and many other related ailments. The patient may have shoulder pain, rotator cuff injury, and other similar pain.

Shoulder Impingement Syndrome

The shoulder impingement syndrome is a result of the compression of the soft tissues between the acromion and the humerus head. It occurs on the glenohumeral joint, which has the greatest range of motion in the body. Due to this motion, and the increase in mechanical demands, there may be the occurrence of some injuries to the soft tissues in the body. This leads to shoulder pain, and is called the shoulder impingement syndrome.

These injuries are chronic in nature and may develop as a result of hyper activity such as swimming, tennis. It may also occur due to assorted occupations.

Rotator Cuff Injury

This syndrome is associated with the hooked acromion syndrome. The two are closely related tpo each other. So much so, that there are cases when they were often misdiagnosed for the other. The symptoms of this injury may be shoulder pain, loss of motion and weakness.

The main cause behind this disease is acromioclavicular join arthritis. It may also occur due to the calcificification of coracoacromial ligament, weakness of the rotator cuff muscles or the structural abnormality of the acromion process.

To treat this injury, the patient may have to go through MRI scan, X-ray scan so as to visualize the bone spurs, the acromion anatomy and arthritis. The MRI imagiging reveals the fluid ccumulation, and it also reveals the chronic cases of tears in the rotator cuff. Sometimes proper care and rest also ensures recovery.

Acromion Buristis

The Subacromial bursitis or the acromuion bursitis, as it is generally called, occurs as a result of the inflammation of the bursa, separating the superior edge of the supraspinatus tendon from the cocra-acromial ligament, the acromion and the coracoids from the deltoid muscle. The inflammation of the bursa is a rare condition, and therefore, this condition does not occur normally. Subacromial bursitis may also occur due to the nerve injury or instability.

Acromion Bone Spurs

The people with advancing age generally develop bone spurs on the front side of the acromion.  Bone spurs refers to the deposition of calcium along the edges of the bone. They may at times become quite complicated if they turn big, or are accompanied by conditions such as impingement. When the bone spurs are formed at the front at the side of the   acromion, the subacromial space is reduced, thereby increasing the risk of the impignment.

Acromion Scapula

Scapula is the scientific name for the shoulder blade. It is a kind of triangular, flat bone lying over the back of the upper ribs. The scapula serves as an attachment for the muscles of the arm, neck, chest and the back. The back of the scapula is divided into unequal portions by a spine. It is the back of the spine that bears the acromion process on it.

Lateral Downsloping Acromion

One of the several configurations of the relationship between the clavicle and the acromion is the laterally downsloping position of the acromion. Due to this lateral and downsloping shape of the acromion, there is a high probability of impingement and the thickening of the coracoacromial ligament. Some mildly reactive sclerosis on the postero-lateral aspect of the humerus, may indicate chronic contact of the acromion and the humerus.

Low Lying Acromion

The acromion is low lying, and is relative to the distal end of the clavicle. The low lying acromion may predispose certain impingement in the shoulder. It may be responsible for the shoulder pain. It produces encroachment to the supraspinatus. A partial tear may occur on the undersurface of the supraspinatus tendon. This low lying position may decrease the space between the acromion and the humerus. Sometimes, it is the cause of instability of the shoulder.

Acromion Joint

The acromion joint, or the acromioclavicular joint (the AC joint), is a joint at the top of the shoulder, a junction between the clavicle and the acromion. The stabilization of the joint is brought about by three ligaments:

  • The Acromioclavicular Ligament– this ligament attaches the head of the scapula to the clavicle.
  • The Coracoacromial Ligament – this ligament runs from the coracoids to the acromion process.
  • The Coraclavicular Ligament – this consists of the conoid and the trapezoid ligament, and serves as a connector for the clavicle to the coracoids process in the scapula.

The basic function of the Clavicle Acromion joint is to allow the ability to raise the arm above the head. Although it is a gliding synovial joint, yet it serves as a pivot joint and helps in arm rotation.

Acromion Dislocation

The acromion dislocation or the collarbone dislocation is the bruising of the skin and of the underlying tissues, generally caused by a direct blow. This may be accompanied by a bleeding of the capillaries and infiltration of the muscles, soft tissues and of the tendons. People generally call this dislocation as the Broken Acromion.

Whenever there is a dislocation of the collarbone, an injury also occurs in the shoulder joint or the breastbone. The dislocation may occur either upwards or downwards, however, mostly the dislocation occurs upwards. The displacement may be brought about by a direct violence.

Acromion Injury

There may be injuries to the acromion or to the acromion joint. A separated shoulder or Acromioclavicular separation and AC joint separation is one of the most common form of injury. But one thing must be kept in mind. This injury should not be confused with the shoulder dislocation. These two are not the same, as this injury involves the dislocation of the glenohumeral joint. The acromion clavicle disfunction may be of several types. They can be generally clasified into six broad heads or six types.

Acromion Injury Classification

The Acromion Injury can be classified into six types :

Type I

This type of separation is commonly known as a sprain, and does not involve any fracture or tearing to the joint, it simply involves a trauma to the ligament that forms the joint. Its treatment procedure is rather simpler; it can be treated with anti-inflammatory drugs or pain medications only.

Type II

This type of separation involves a complete tearing of the acromioclavicular ligament and partial tearing of the coracoclavicular ligament. These results in a bump being formed at the shoulder.Patients may experience pain in the shoulder. This separation can be treated with the help of a sling, bed rest or icepacks. Recovery may be complete within 6 weeks of injury.

Type III

This separation results when both the acromioclavicular joint and the coracoclavicular ligaments are torn. There is a formation of a bump at the lateral end of the clavicle. Recovry may occur within 12 weeks, surgery may be required in extreme cases.

Type IV

In this type of separation. There is an avulsion of the coraclavicular ligament from the clavicle. Treatment requires surgery.

Type V

When the type III separation is exaggerated, it may result in a vertical displacement of the clavicle. Surgery is required for recovery.

Type VI

It is a rare occurrence in which the lateral end of the clavicle is vertically displaced below the coracoid. It generally occurs due to accidents in motor vehicle collisions. Surgical methods are used for treatment.

Acrmion Surgery

Several techniques are recommended for surgery. Surgeries may be described to fix the acromioclavicular separations. The Modified Weaver-Dunn procedure is a common technique, in which the end of the clavicle is cut, sacrificing a part of the coracoaclavicular ligament, and artificially providing some additional support to it.  Other methods of surgery include insertion of rockwood screw and removing it after 12 weeks, until the bone is stabilized.

The acromion is a bony prominence at the top of the shoulder blade. Any injury to the acromion should be given proper care and treatment. Too much stress or external pressure should not be given on this bone as it may lead to an injury or fracture to it. However, most forms of fracture are curable without surgery.


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