What is the difference between a regular shoulder replacement and a reverse shoulder replacement?

Difference Between Regular and Reverse Shoulder Replacement

A regular (total) shoulder replacement maintains the normal anatomy with a ball on the humerus and socket on the glenoid, while a reverse shoulder replacement inverts this design—placing a metal ball (glenosphere) on the glenoid and a cup on the humerus—to compensate for a deficient or absent rotator cuff by allowing the deltoid muscle to power shoulder movement. 1

Anatomical Design Differences

Regular Total Shoulder Arthroplasty (TSR)

• Preserves normal shoulder anatomy: The humeral component has a ball-shaped head that articulates with a plastic socket component fixed to the glenoid 1
• Requires intact rotator cuff: The rotator cuff tendons must be functional to stabilize the joint and provide active motion 1
• Normal center of rotation: Maintains the anatomical center of rotation at the humeral head 1

Reverse Shoulder Arthroplasty (RSA)

• Inverted anatomy: The glenoid component is a round metal ball (glenosphere) attached to a baseplate on the glenoid surface, while the humeral component has a cup-shaped articular margin 1
• Altered biomechanics: Moves the center of rotation medial (toward the body) and distal (downward), which fundamentally changes how the shoulder functions 1
• Deltoid-powered motion: This design allows the deltoid muscle to serve as the main stabilizer and power source for the shoulder, compensating for the absent or deficient rotator cuff 1
• Reduced glenoid stress: The more medial and distal center of rotation decreases the risk of glenoid loosening compared to conventional designs 1

Clinical Indications

Regular TSR Indications

• Advanced glenohumeral osteoarthritis with intact rotator cuff tendons 1
• Superior clinical outcomes compared to hemiarthroplasty for advanced shoulder osteoarthritis 1
• Patients must have functional rotator cuff to achieve good results 2

Reverse TSR Indications

• Massive, unrepairable rotator cuff tears with pseudoparalysis (preserved deltoid contraction but loss of active elevation) who have failed other treatments 1
• Rotator cuff tear arthropathy (combination of massive rotator cuff tear and glenohumeral arthritis) 1
• Irreparable rotator cuff tears without arthritis when non-arthroplasty options have failed or have low likelihood of success 3, 4
• Failed total shoulder arthroplasty as a salvage procedure 1
• Originally introduced in 1987 specifically for patients with deficient rotator cuff 1

Functional Outcomes

Regular TSR Outcomes

• Low-quality evidence suggests TSR may provide small improvements over hemiarthroplasty in pain (1.49 points lower on 0-10 scale) and function (10.57 points higher on 0-100 scale) at 2 years 2
• Quality of life differences are uncertain between TSR and hemiarthroplasty 2

Reverse TSR Outcomes

• Reliable pain relief and functional restoration in properly selected patients with rotator cuff deficiency 3, 4
• At mean 52-month follow-up, patients showed significant improvements: pain scores improved from 6.3 to 1.9, forward flexion from 53° to 134°, and function scores from 33.3 to 75.4 3
• 90.7% survivorship at mean 52 months for irreparable rotator cuff tears without arthritis 3
• Patients with prior failed rotator cuff repair have comparable functional outcomes to primary RSA but face higher complication risk (RR 6.26) and revision rates (RR 3.91) 5

Complications

Regular TSR Complications

• Glenoid loosening is the most common complication (14.3%) 1
• Rotator cuff tears can occur postoperatively 1
• Polyethylene wear and osteolysis 1

Reverse TSR Complications

• Scapular notching (most common) 1
• Dislocation 1
• Periprosthetic fractures 1
• Acromial fractures 1, 5
• Glenoid baseplate failure 1
• Overall complication prevalence of 20% with revision rates up to 11% 1, 3

Critical Contraindications for Reverse TSR

Severely impaired deltoid function is an absolute contraindication to RSA since the deltoid must power shoulder motion 4

Additional contraindications include:

• Isolated supraspinatus tear (rotator cuff is too intact) 4
• Full active shoulder elevation with massive rotator cuff tear and arthritis (shoulder is still functional) 4

Special Considerations

• Age concerns: The American Academy of Orthopaedic Surgeons notes concerns about performing shoulder arthroplasty in patients <50 years due to potential risks of increased prosthetic loosening and decreased survivorship 6
• Expansion of indications: While RSA was originally designed for older adults with rotator cuff deficiency, its use has expanded to younger populations with severe shoulder pathology 6
• No high-quality comparative data: Despite being established procedures, no high-quality randomized trials compare shoulder replacement to non-surgical treatments or compare reverse TSR to other treatment options 2