Shoulder Injuries: Bankart vs. ALPSA Lesions, MRI Differences, and Clinical Impact

What is the Difference Between ALPSA and Bankart MRI?

Both ALPSA (Anterior Labroligamentous Periosteal Sleeve Avulsion) and Bankart lesions are types of glenoid labral injuries commonly associated with anterior shoulder instability, but they differ in the specific nature of the labral detachment and its relationship to the periosteum, which is crucial for their appearance on MRI and subsequent surgical planning.

Understanding Shoulder Instability and the Glenoid Labrum

The shoulder joint, or glenohumeral joint, is a ball-and-socket joint known for its remarkable range of motion. This mobility, however, comes at the cost of stability. Key to its stability is the glenoid labrum, a fibrocartilaginous rim that deepens the shallow glenoid socket, providing an attachment point for the glenohumeral ligaments. When the shoulder dislocates, particularly anteriorly, these stabilizing structures can be damaged, leading to recurrent instability. Two common injuries identified on Magnetic Resonance Imaging (MRI) following such events are Bankart and ALPSA lesions, both impacting the anterior-inferior aspect of the labrum.

What is a Bankart Lesion?

A Bankart lesion is the most common type of traumatic anterior-inferior labral tear resulting from an anterior shoulder dislocation.

• Definition: It involves the avulsion (tearing away) of the anterior-inferior portion of the glenoid labrum from the glenoid rim. Critically, the periosteum (the fibrous membrane covering the bone) in this region is also typically torn, allowing the labrum to retract.
• Mechanism: Typically occurs when the humeral head dislocates anteriorly and inferiorly, impacting and tearing the labrum from the bony glenoid rim.
• MRI Appearance: On MRI, a Bankart lesion is characterized by:
  • Detached or avulsed labrum: The labrum is clearly separated from the anterior-inferior aspect of the glenoid.
  • Retraction: The torn labrum often retracts, creating a gap between the labrum and the glenoid.
  • Fluid signal: Increased fluid signal (bright on T2-weighted images) is often seen in the gap, indicating the tear.
  • Associated bony injury: A bony Bankart lesion occurs when a fragment of bone from the glenoid rim is avulsed along with the labrum. This is a more severe injury, often indicative of greater instability.
• Clinical Significance: A Bankart lesion significantly compromises anterior shoulder stability, often leading to recurrent dislocations or subluxations if not surgically repaired.

What is an ALPSA Lesion?

An ALPSA (Anterior Labroligamentous Periosteal Sleeve Avulsion) lesion is a variant of an anterior-inferior labral tear that also results from anterior shoulder dislocation, but with a distinct characteristic regarding the periosteum.

• Definition: In an ALPSA lesion, the anterior-inferior labrum is avulsed from the glenoid, similar to a Bankart, but it remains attached to the intact anterior periosteum. Instead of fully detaching and retracting, the labrum is displaced medially and inferiorly, often flipping or rolling over, creating a "sleeve" of tissue.
• Mechanism: While also caused by anterior dislocation, the mechanism often involves a rotational component or a less direct avulsion, allowing the periosteum to remain intact and act as a hinge.
• MRI Appearance: On MRI, an ALPSA lesion is characterized by:
  • Medial displacement: The torn labrum is displaced medially, away from the glenoid rim, but it is not retracted into the joint.
  • Intact periosteum: The key differentiating feature is the presence of an intact periosteal sleeve that tethers the displaced labrum.
  • "Sleeve" or "Mass" appearance: The displaced labrum, still attached to the periosteum, can appear as a thickened or folded "mass" of tissue lying on the anterior glenoid neck, medial to its anatomical position.
  • No bony avulsion: Typically, ALPSA lesions do not involve an avulsed bone fragment from the glenoid rim.
• Clinical Significance: Like Bankart lesions, ALPSA lesions contribute to shoulder instability. However, their unique morphology can make surgical repair more challenging, as the displaced labrum may be scarred down in its abnormal position, requiring more extensive mobilization. They also carry a high risk of recurrent instability if not addressed.

Key Differences on MRI

The distinction between Bankart and ALPSA lesions on MRI is crucial for accurate diagnosis and surgical planning.

• Bankart Lesion:
  • Labrum is avulsed and often retracted from the glenoid rim.
  • There is a clear gap between the labrum and the glenoid.
  • The periosteum is typically torn.
  • May involve an associated bony avulsion (bony Bankart).
• ALPSA Lesion:
  • Labrum is medially displaced but remains attached to the intact anterior periosteum.
  • The labrum appears as a "sleeve" or "mass" lying on the anterior glenoid neck.
  • There is no significant gap between the displaced labrum and the glenoid rim, as it's tethered by the periosteum.
  • No associated bony avulsion is typically seen.

Clinical Implications and Management

Both Bankart and ALPSA lesions are significant injuries that contribute to chronic shoulder instability.

• Recurrent Instability: Both types of lesions compromise the static stabilizers of the shoulder, predisposing individuals to repeated dislocations or subluxations.
• Surgical Repair: Surgical intervention, typically an arthroscopic Bankart repair, is often required for both. The goal is to reattach the torn labrum to the glenoid rim, restoring the integrity of the joint capsule and ligaments.
• Surgical Complexity: ALPSA lesions can be more challenging to repair than simple Bankart lesions. The medially displaced and potentially scarred-down labrum in an ALPSA lesion may require more extensive mobilization and release from the underlying periosteum before it can be adequately reattached to the glenoid rim.
• Rehabilitation: Post-surgical rehabilitation for both involves a structured program to restore range of motion, strength, and proprioception, gradually progressing to sport-specific activities.

Why MRI is Crucial for Diagnosis

MRI plays an indispensable role in diagnosing and differentiating these labral lesions due to its excellent soft tissue contrast.

• Detailed Visualization: MRI allows for detailed visualization of the labrum, joint capsule, ligaments, and surrounding soft tissues, which are not visible on conventional X-rays.
• Lesion Characterization: It can accurately characterize the type of labral tear (Bankart vs. ALPSA), the presence of bone loss (bony Bankart), and other associated injuries (e.g., Hill-Sachs lesion on the humeral head).
• Surgical Planning: The precise information obtained from MRI guides the orthopedic surgeon in planning the most appropriate surgical approach and technique, accounting for the specific characteristics of the lesion.

Conclusion

While both Bankart and ALPSA lesions represent injuries to the anterior-inferior glenoid labrum resulting from shoulder dislocation, their distinction lies in the integrity of the periosteum and the resulting configuration of the torn labrum. A Bankart lesion involves a complete avulsion and often retraction of the labrum, potentially with bone. An ALPSA lesion involves medial displacement of the labrum, which remains attached to an intact periosteal sleeve. Understanding these nuanced differences, particularly through accurate MRI interpretation, is paramount for healthcare professionals to effectively diagnose, treat, and manage shoulder instability, ensuring optimal outcomes for affected individuals. If you suspect a shoulder injury, always consult with a qualified medical professional for accurate diagnosis and personalized treatment recommendations.