Reverse Shoulder Arthroplasty: Complications, Scapular Notching, and Prevention

What is the most common complication of reverse shoulder?

The most common complication following reverse shoulder arthroplasty (RSA) is scapular notching, characterized by erosion of the inferior scapular neck by the humeral component, which can impact range of motion and, in severe cases, lead to pain or implant loosening.

Understanding Reverse Shoulder Arthroplasty (RSA)

Reverse shoulder arthroplasty is a highly effective surgical procedure for individuals suffering from severe shoulder conditions, particularly those involving irreparable rotator cuff tears with associated arthritis (rotator cuff tear arthropathy), complex fractures, or failed conventional shoulder replacements. Unlike traditional shoulder replacement, where a prosthetic ball is placed on the humerus and a socket on the scapula, RSA reverses this anatomy. A prosthetic ball (glenosphere) is fixed to the scapula, and a socket (humeral cup) is attached to the humerus. This design allows the deltoid muscle to become the primary elevator of the arm, compensating for a non-functional rotator cuff.

The Most Common Complication: Scapular Notching

Scapular notching stands out as the most frequently observed radiographic complication following RSA. It refers to the mechanical impingement and subsequent erosion of the inferior aspect of the scapular neck by the medial rim of the humeral polyethylene liner during adduction and internal rotation of the arm.

• Definition: This erosion creates a characteristic "notch" or indentation in the bone of the scapula, visible on X-rays.
• Incidence: Its reported incidence varies widely in literature, ranging from 10% to over 90% in some series, depending on follow-up duration, imaging techniques, and criteria for grading. While common, its clinical significance is not always proportional to its radiographic presence.
• Mechanism: The reversed anatomy of RSA inherently places the humeral component in close proximity to the scapular neck. During certain movements, particularly when the arm is brought towards the body (adduction) or rotated inward, the polyethylene liner of the humeral component can rub against the scapula, causing wear and bone loss over time.

Contributing Factors to Scapular Notching:

Several factors can increase the risk and severity of scapular notching:

• Surgical Technique and Implant Positioning:
  • Glenoid Component Inferior Tilt: If the glenosphere is not sufficiently tilted inferiorly, it can reduce the space between the humeral component and the scapula.
  • Glenoid Lateralization: Insufficient lateralization of the glenosphere (i.e., not extending the center of rotation far enough from the scapula) can increase impingement.
  • Humeral Component Design: Designs with a larger medial offset or a more prominent medial rim on the polyethylene insert can be more prone to notching.
• Patient Anatomy: Individual variations in scapular morphology and the patient's pre-operative range of motion can play a role.
• Post-operative Rehabilitation: Certain movements, particularly excessive adduction and internal rotation, if not appropriately managed during recovery, can exacerbate notching.

Clinical Significance and Symptoms of Scapular Notching

While scapular notching is very common radiographically, it's crucial to understand that it is often asymptomatic. Many patients with visible notching experience no pain or functional limitations directly attributable to it. However, in some cases, notching can progress and become clinically significant.

Potential Symptoms and Consequences:

• Pain: As the notching deepens, it can lead to localized pain around the shoulder.
• Decreased Range of Motion: Severe notching can mechanically limit shoulder movement, particularly adduction and internal rotation, and sometimes abduction and external rotation if the notching compromises the deltoid's lever arm or causes tendon irritation.
• Weakness: In advanced stages, notching can impinge on the deltoid muscle or its attachments, potentially leading to weakness.
• Glenoid Loosening: The most serious, albeit less common, consequence is the progressive erosion leading to aseptic loosening of the glenoid component, which may necessitate revision surgery. This occurs when the notching compromises the integrity of the bone-implant interface.

Prevention and Management Strategies

Efforts to prevent and manage scapular notching are a significant focus in RSA.

Surgical Prevention Strategies:

• Inferior Glenoid Tilt: Placing the glenosphere with a slight inferior tilt can move the center of rotation away from the inferior scapular neck.
• Glenoid Lateralization: Using lateralizing glenosphere designs or bone grafting to lateralize the glenoid component creates more space between the humeral component and the scapula.
• Humeral Component Design: Implants with a reduced medial offset or specific designs that minimize impingement are continuously being developed.
• Soft Tissue Management: Careful soft tissue release and balancing during surgery can optimize joint mechanics.

Rehabilitation Considerations:

Post-operative rehabilitation plays a role in minimizing impingement. Therapists guide patients through exercises that restore functional range of motion while initially avoiding extreme positions of adduction and internal rotation that could exacerbate notching. Strengthening the deltoid and periscapular muscles is crucial for optimal function and stability.

Other Potential Complications of Reverse Shoulder Arthroplasty

While scapular notching is the most common, RSA, like any major surgery, carries risks of other complications that fitness professionals and patients should be aware of:

• Infection: A serious complication that can require further surgery and prolonged antibiotic treatment.
• Glenoid Loosening/Failure: Aseptic loosening of the glenoid component, distinct from notching-related loosening, due to poor bone integration or mechanical failure.
• Humeral Fracture: Periprosthetic fractures can occur during or after surgery.
• Dislocation: Although less common with RSA than traditional TSA, dislocation of the humeral cup from the glenosphere can occur.
• Nerve Injury: Damage to nerves around the shoulder (e.g., axillary nerve) can lead to weakness or numbness.
• Deltoid Dysfunction: Impingement, injury, or disuse of the deltoid muscle can compromise the primary function of the RSA.

Conclusion

Scapular notching is undeniably the most common radiographic complication associated with reverse shoulder arthroplasty. While frequently asymptomatic, understanding its mechanism, contributing factors, and potential clinical implications is vital for both surgeons and rehabilitation specialists. Advances in surgical techniques, implant design, and post-operative management continue to aim at minimizing its incidence and progression, ultimately enhancing patient outcomes and the longevity of this transformative procedure. For fitness professionals, recognizing the potential for notching and its impact on movement patterns is crucial for safely and effectively guiding clients through post-surgical rehabilitation and long-term exercise.