Reverse total shoulder arthroplasties (RTSA) or replacements (RTSR) are a variant on the standard total shoulder replacement (TSR). It is often the preferred method when there has been advanced damage to the rotator cuff as seen in rotator cuff tear arthropathy.
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Prosthetic components
Humeral components
proximal cup-shaped portion is a radiolucent polyethylene 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 specially coated metal plate that is attached to the native glenoid fossa with bicortical screws
Procedure
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.
Advantages and disadvantages
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 adduction for the upper extremity after the surgery. Internal and external rotation are more limited in this arrangement, however.
The indications for reverse total shoulder replacement are expanding and include
osteoarthritis in patients with a degenerate rotator cuff
irreparable massive cuff tear
replacement after tumor surgery
complex fractures in elderly patients where the greater and lesser tuberosity fragments are involved
failed standard total shoulder replacement
Axillary nerve dysfunction is a contraindication for reverse total shoulder replacement.
The design is thought 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.
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%. Complications include:
aseptic loosening of the glenoid component: most common complication (~30% of all shoulder replacements, but decreased with reverse total shoulder replacements 5)
aseptic loosening of the humeral component
dislocation
periprosthetic fractures
acromial/scapular spine fracture, most commonly a stress fracture 6
hardware failure
axillary nerve palsy
infection (uncommon)
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.
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