Acromial Spurs: Types, Clinical Significance, and Management

What are the different types of acromial spurs?

Acromial spurs are bony growths (osteophytes) that develop on the undersurface of the acromion, a bony projection of the shoulder blade. These spurs are primarily categorized into three types—Type I (Flat), Type II (Curved), and Type III (Hooked)—based on their morphology, with the "hooked" type being most commonly associated with shoulder impingement syndrome and rotator cuff pathology.

Understanding Acromial Spurs: An Overview

The shoulder joint is a marvel of biomechanical engineering, allowing for an extensive range of motion. Critical to this function is the subacromial space, a narrow passageway located beneath the acromion and above the rotator cuff tendons. Acromial spurs are bony outgrowths that can develop on the anterior (front) or anteroinolateral (front and side) aspect of the acromion's undersurface.

These spurs are typically a result of degenerative changes, chronic stress, or repetitive microtrauma to the shoulder joint. Their presence can significantly reduce the already limited subacromial space, leading to compression and irritation of the underlying structures, most notably the rotator cuff tendons (supraspinatus, infraspinatus, teres minor, subscapularis) and the subacromial bursa. This compression is a primary mechanical cause of subacromial impingement syndrome, a common source of shoulder pain and dysfunction.

Neer's Classification System: The Three Primary Types

The most widely accepted and clinically relevant classification system for acromial morphology, including the presence and type of spurs, was developed by Dr. Charles S. Neer II. This system categorizes the acromion based on its shape as viewed on a lateral (side) X-ray of the shoulder, directly influencing the likelihood and severity of impingement.

• Type I Acromion (Flat):

  • Description: This type features a relatively flat undersurface of the acromion. There are no significant spurs or anterior downward angulation.
  • Clinical Significance: A Type I acromion is considered the most favorable morphology. It is associated with the lowest risk of subacromial impingement syndrome and rotator cuff tears because it provides ample space for the rotator cuff tendons to glide freely during arm movements.
  • Incidence: Found in approximately 17-27% of the population.

• Type II Acromion (Curved):

  • Description: The undersurface of a Type II acromion exhibits a smooth, concave curve that parallels the curvature of the humeral head. While curved, it lacks a distinct anterior hook. Spurs, if present, are typically small and subtle.
  • Clinical Significance: This type carries a moderate risk of subacromial impingement. The curved shape inherently reduces the subacromial space compared to a flat acromion, making the rotator cuff tendons more susceptible to compression, especially during overhead activities.
  • Incidence: The most common type, found in approximately 43-56% of the population.

• Type III Acromion (Hooked):

  • Description: A Type III acromion is characterized by a prominent, anteriorly directed hook or spur extending from the undersurface of the acromion. This hook is often well-defined and can be quite sharp.
  • Clinical Significance: This is the most clinically significant type, as it is strongly correlated with a high incidence of subacromial impingement syndrome and rotator cuff pathology, including tendinopathy and full-thickness tears. The prominent hook significantly encroaches upon the subacromial space, leading to chronic friction and wear on the underlying tendons.
  • Incidence: Found in approximately 27-30% of the population and is present in a vast majority of patients undergoing surgery for rotator cuff tears.

Clinical Significance and Implications

The type of acromial spur has profound implications for both diagnosis and treatment of shoulder pain.

• Impingement Severity: A hooked (Type III) acromion mechanically predisposes individuals to more severe and persistent impingement symptoms due to constant irritation of the rotator cuff.
• Rotator Cuff Pathology: The chronic mechanical abrasion caused by spurs, particularly Type III, can lead to fraying, degeneration, and ultimately, tearing of the rotator cuff tendons. The supraspinatus tendon is most commonly affected due to its position directly beneath the acromion.
• Diagnostic Imaging: X-rays are crucial for identifying the acromial type. MRI scans can further assess the extent of soft tissue damage (tendinopathy, bursitis, tears) associated with the spur.
• Treatment Considerations:
  • Conservative Management: For less severe cases or Type I/II with mild symptoms, physical therapy, anti-inflammatory medications, and corticosteroid injections may be effective.
  • Surgical Intervention: In cases of persistent pain, significant functional limitation, or confirmed rotator cuff tears, especially with a Type III acromion, surgical decompression (acromioplasty) may be recommended. This procedure involves removing the spur and a small portion of the acromion to decompress the subacromial space.

Beyond Neer: Other Considerations

While Neer's classification is foundational, other factors can also contribute to impingement and should be considered:

• Acromial Thickness: A thicker acromion, regardless of its type, can reduce the subacromial space.
• Acromial Angulation: The angle at which the acromion projects can also influence impingement.
• Os Acromiale: This is a condition where the acromion fails to fuse completely during development, resulting in a separate bone segment that can move and cause impingement.

It's important to remember that the mere presence of an acromial spur, even a Type III, does not automatically guarantee pain or dysfunction. Many individuals have spurs but remain asymptomatic. However, the presence of these morphological variations significantly increases the risk, particularly in those engaging in repetitive overhead activities.

Conclusion

Understanding the different types of acromial spurs, particularly through Neer's classification, is fundamental for clinicians, fitness professionals, and individuals experiencing shoulder pain. A Type III (Hooked) acromion is the most concerning due to its strong association with rotator cuff impingement and tears. While anatomical predisposition plays a role, appropriate exercise mechanics, strength training, and mobility work are crucial for managing and mitigating the risks associated with these bony variations. If you experience persistent shoulder pain, a thorough evaluation by a healthcare professional is essential to determine the underlying cause and guide appropriate management.