Reverse total shoulder arthroplasties (RTSA) or replacements (RTSR) are a variant of the standard total shoulder replacement (TSR). It is often the preferred method when there has been advanced damage to the rotator cuff, as it increases the range of motion by medialising the center of rotation and increasing the deltoid muscle's lever action.

Indications

• rotator cuff tear arthropathy ¹²

• massive cuff tear ¹²

• glenohumeral osteoarthritis ¹²

• rheumatoid arthritis ¹²

• replacement after tumor surgery

• complex fractures in elderly patients where the greater and lesser tuberosity fragments are involved 

• failed standard total shoulder replacement

Contraindications

• axillary nerve dysfunction

Technique

Device structure

The reverse total shoulder arthroplasty flips the normal mechanical arrangement of the shoulder's ball-and-socket joint. Instead of the humeral head fitting into the glenoid, a rounded hemispheric glenoid prosthesis articulates with a socket on the humeral head prosthesis:

• humeral components

  • proximal cup-shaped portion is a radiolucent polyethene insert that articulates with the glenosphere

  • metal stem in the proximal humeral shaft

• glenoid components

  • glenosphere is the rounded metal ball of the prosthesis that attaches to a baseplate (metaglene)

  • baseplate (metaglene) is a specially coated metal plate that is attached to the native glenoid fossa with bicortical screws

Implant design has been classified into three types ^12,13:

• medial glenoid/medial humerus (MGMH): original Grammont prosthesis design

  • medialises the center of rotation to the scapula with no lateral offset of the glenosphere

  • 2x increased risk of scapular notching ¹²

• medial glenoid/lateral humerus (MGLH): lateral positioning of the humeral component

• lateral glenoid/medial humerus (LGMH):

  • increased arc of rotation through lateral positioning of the glenoid component through thickened glenosphere, spacers, bone graft, etc

  • possible increased risk of baseplate failure and glenoid loosening ¹²

No significant difference post-operative range of motion differences, early complication rates, or revision rates have been established between the three design types with ¹².

Radiographic features

Plain radiograph

• neutral AP view (Grashey view) and axillary views obtained

• >2 mm of lucency around the prosthetic component is concerning for loosening

• scapular notching (erosion of the inferior scapular neck) is suggestive of glenoid component failure

• acromial and scapular spine fractures after reverse total shoulder arthroplasty are more common

CT

• better for evaluation if there is a suboptimal radiograph

• as on conventional radiography, >2 mm of lucency around the prosthetic component is concerning for loosening

MRI

• metal artifact reduction techniques have improved the ability to image prostheses on MRI

Ultrasound

• useful for imaging the rotator cuff musculature, evaluating the prosthesis dynamically, and evaluating for joint effusion

• cannot be used to evaluate for component loosening

Complications

The overall complication rate for all forms of total shoulder arthroplasty is ~15% ^ref. Complications for reverse TSA specifically include:

• scapular notching: most common complication ~10-50% depending on prosthesis design; may not be clinically significant ¹²

• infection: ~2.5% (range 0.7-5.2%) ¹²

• dislocation: ~1% ¹²

• axillary nerve injury: ~1.5% (range 0.5-2.3%) ¹²

• aseptic loosening

  • glenoid component: most common complication affecting ~30% of all shoulder replacements ⁵, but decreased (~5%; range 3-10% ¹²) with reverse total shoulder replacements ⁵

  • humeral component: less common (~4%; range 1.2-10% ¹²)

• proximal humeral stress shielding ¹²

• hardware failure ¹²

  • glenosphere dissociation (rare) ¹⁴

• periprosthetic fractures

  • intra-operative glenoid fracture ¹²

  • acromial/scapular spine fracture, most commonly a stress fracture ^6,12

• heterotopic ossification ^11,12

• scapular spur ¹²

• failed bone graft incorporation ¹²

Outcomes

Reversing the ball and socket arrangement, the point of rotation is moved more medially, aiding the deltoid muscle which, without an intact rotator cuff, will provide most of the early abduction for the upper extremity through a level action ¹². However, internal and external rotation are more limited in this arrangement.

The design is reported to have relatively good short and medium-term outcomes compared with other types of total shoulder replacements, with improved recovery time and pain scores ³. Long-term outcomes remain poorly defined.

History and etymology

French surgeon Paul-Marie Grammont (1940-2013) designs a clinically successful reverse prosthesis (where other reverse designs have failed) for arthritic shoulders with massive rotator cuff tear in 1985, in which normal anatomical prostheses could not solve the problem of restoring both joint stability and mobility ^7,8.

The idea of reverse total shoulder arthroplasty thought by Grammont was an important step forward in the field of shoulder arthroplasty in fact the previous constrained prostheses (spherical or inverted spherical designs) all failed because their center of rotation remained lateral to the scapula, limiting movement and producing excessive torque at the prosthesis-bone interface of the glenoid component, thus leading to premature loosening ^7,8.