Reverse Total Shoulder Arthroplasty

Reverse total shoulder arthroplasty (RTSA) has revolutionized the management of complex shoulder conditions, particularly rotator cuff arthropathy. By reversing the ball-and-socket anatomy, placing a convex glenosphere on the glenoid and a concave socket on the humerus, RTSA converts the deltoid muscle into the primary arm elevator.

Epidemiology:

• Exponential growth in utilization over the past decade (over 300 percent increase)
• Now represents over 60 percent of all shoulder arthroplasties in some series
• Mean patient age 65-75 years, though indications expanding to younger patients
• Female predominance (60-65 percent) reflecting rotator cuff arthropathy demographics

Historical Development:

• Professor Paul Grammont (Lyon, France) developed the modern design in 1985
• Key innovation was the Grammont principle: medialization of center of rotation
• Earlier designs (Neer Mark I, II) failed due to glenoid loosening from eccentric loading
• Modern semi-constrained designs achieve over 90 percent 10-year survivorship

Rotator Cuff Tear Arthropathy (CTA):

Cuff tear arthropathy represents the end-stage of massive rotator cuff tear with secondary degenerative changes. It is the most common indication for RTSA.

Pathophysiological Cascade:

1. Massive rotator cuff tear: Usually supraspinatus and infraspinatus
2. Loss of force couple: Deltoid pulls humeral head superiorly unopposed
3. Superior migration: Humeral head articulates with undersurface of acromion
4. Mechanical changes: Increased joint reaction forces, synovial fluid changes
5. Cartilage destruction: Both glenoid and humeral head articular surfaces
6. Bony remodeling: Femoralization of humeral head, acetabularization of glenoid

Grammont Biomechanical Principles:

The Grammont design addressed the failures of earlier reverse designs through key biomechanical innovations:

Functional Outcomes Explained by Biomechanics:

• Forward elevation: Typically restored to 120-140 degrees (deltoid-powered)
• External rotation: Often limited (0-30 degrees) due to posterior cuff deficiency
• Internal rotation: Variable, often limited to buttock level
• Strength: Improved compared to preoperative pseudoparalysis

Instability Patterns:

• Anterior: Most common, excessive retroversion, subscapularis failure
• Posterior: Rare, excessive anteversion
• Superior: Very rare, deltoid dysfunction

Activity Restrictions (Long-term):

• Avoid lifting greater than 10-15kg (risk of acromial stress fracture, instability)
• No contact sports or high-impact activities
• Swimming, golf, and tennis often possible with low demand

The topic repeatedly notes that RTSA restores elevation but rarely restores active external rotation, and the Exam Warning hints that "latissimus dorsi transfer can improve ER in select cases" - this section develops that under-stated point. When the posterior cuff (infraspinatus and teres minor) is absent or fatty-infiltrated, a reverse alone leaves the patient with a combined loss of active elevation and external rotation (CLEER): pseudoparalysis plus a positive Hornblower sign and external-rotation lag, so the forearm swings uncontrollably into the trunk when they try to reach forward or hold an object away from the body.

The established solution is to combine the reverse with a modified L'Episcopo transfer - detaching the latissimus dorsi and teres major, rerouting them around the humerus and reattaching them posterolaterally so that these internal rotators are converted into active external rotators. Boileau popularised performing both the reverse and the transfer through a single deltopectoral approach in the beach-chair position, avoiding the classic two-incision posterior dissection.

Key selection points:

• CLEER (irreparable postero-superior cuff plus teres minor loss, in cuff tear arthropathy or tumour reconstruction) is the indication for the combined reverse plus transfer.
• Isolated loss of external rotation (ILER) with preserved elevation can be treated by the transfer alone, without a reverse.
• The transfer restores the ability to control the spatial position of the arm (external rotation with the arm at the side), which is the main driver of patient satisfaction, rather than adding elevation.

The NOTCH mnemonic and the Sirveaux and Simovitch data tell you to give the baseplate "inferior tilt" and to implant the glenosphere low, but examiners expect you to know how that tilt is measured and why it matters - a point the topic names (the Simovitch card cites the "prosthesis-scapular neck angle" and glenosphere height) but does not define. Two radiographic parameters quantify it:

• RSA angle (Boileau): the inclination of the glenoid baseplate relative to the floor of the supraspinatus fossa (the scapular reference line). Cuff tear arthropathy glenoids are frequently superiorly inclined, and leaving that superior tilt is a leading driver of notching. The target is a neutral inclination - an RSA angle under 5 degrees - obtained by inferior reaming, an inferiorly-tilted or augmented baseplate, and lowering the baseplate on the glenoid.
• Prosthesis-scapular neck angle (PSNA) (Simovitch): the angle between the glenosphere and the scapular neck. Together with the height of glenosphere implantation it predicts inferior notching, and glenosphere height carries roughly eight times more influence than the neck angle - so implant the sphere low.

Combine neutral or inferior inclination with inferior glenosphere overhang of more than 5 mm and a low baseplate position. Persistent superior inclination and a high or flush glenosphere are the malpositions most strongly linked to notching in long-term data.

Global Epidemiology and Utilization:

• RTSA utilization has grown several-fold over the past two decades and is now the most common shoulder arthroplasty in many high-income health systems
• It overtook anatomic TSA in the US around the late 2010s and continues to expand into fracture and revision indications
• Mean age at surgery is typically 70-75 years with a female predominance (around 60-65 percent), mirroring cuff tear arthropathy demographics

RTSA is a young procedure with rapidly evolving design philosophy. Examiners reward candidates who can discuss genuine controversy rather than recite dogma.