Reverse Shoulder Arthroplasty

Reverse total shoulder arthroplasty (RSA) is a biomechanically ingenious prosthesis that inverts the normal ball-and-socket anatomy of the shoulder — placing a hemispherical ball (glenosphere) on the glenoid and a cup on the humerus. This reversal mediates and inferiorises the centre of rotation, dramatically increasing the mechanical advantage of the deltoid muscle, which then acts as the primary elevator of the arm in the absence of a functioning rotator cuff. RSA has revolutionised the treatment of rotator cuff deficiency with arthritis and is now the most rapidly growing shoulder arthroplasty procedure worldwide.

• Designed by Paul Grammont in 1985 (Grammont prosthesis); FDA approval in the USA in 2003; now accounts for approximately 50% of all shoulder arthroplasty procedures in the USA and UK
• Grammont design principles: (1) glenosphere fixed to glenoid (metaglene baseplate); (2) centre of rotation mediased to the glenoid face (eliminating the rotator cuff moment arm problem); (3) inferior tilt of glenosphere (10° inferior) to reduce notching; (4) deltoid lever arm increased by medialisation and distalisation of the humerus
• The key insight: in a cuff-deficient shoulder, the standard ball-and-socket allows the humeral head to migrate superiorly when the deltoid fires — RSA prevents this escape and converts deltoid contraction into glenohumeral elevation
• Indications now extending beyond classic cuff tear arthropathy to include complex fractures, failed previous arthroplasty, inflammatory arthritis with cuff deficiency, severe instability, and tumour reconstruction

• Pseudoparalysis: inability to actively elevate the arm beyond 90° despite passive range of motion being preserved — indicates functional loss of the rotator cuff (particularly supraspinatus and infraspinatus); RSA reliably restores active elevation through deltoid recruitment in pseudoparalysis
• Age threshold: RSA traditionally reserved for patients over 70 — implant survivorship concerns in younger, more active patients; evidence now supports RSA in patients over 60 in appropriate settings; younger patients require careful counselling

• Mediased centre of rotation (COR): Grammont design places COR at the glenoid surface (not lateral to it as in normal anatomy) — eliminates torque on the metaglene-glenoid interface, reducing loosening risk
• Deltoid tensioning: distalisation of the humerus (lengthening the arm by approximately 2–3 cm) pre-tensions the deltoid — essential for RSA function; insufficient tension = poor elevation; excessive tension = acromial stress fracture or neurological injury
• Deltoid wrapping: mediased COR increases the arc of deltoid muscle that is in contact with the prosthesis during elevation — "wrapping effect" increases mechanical advantage; anterior and posterior deltoid recruited for rotation
• Internal and external rotation after RSA: consistently poor — RSA reliably restores forward elevation (typically to 130–150°) and abduction, but internal and external rotation depend on intact teres minor and remaining posterior cuff fibres; loss of ER is a significant limitation particularly for activities of daily living behind the back
• Bony Increased Offset RSA (BIO-RSA): lateralised glenosphere design increases moment arm for external rotators — improves ER compared to original Grammont design; reduces scapular notching; increasingly used

• Approach: deltopectoral (most common) or superior deltoid-splitting; subscapularis may be tenotomised and repaired or partially released depending on design
• Metaglene positioning: central screw placement in strongest glenoid bone (subchondral); inferior tilt of glenosphere 10–15° (reduces scapular notching); inferior positioning of baseplate at inferior glenoid rim — inferior overhang of glenosphere prevents scapular notching during adduction; the inferior screw is the most critical fixation element
• Humeral component version: approximately 20–30° of retroversion; some surgeons use 0° anteversion in RSA to improve internal rotation
• Intraoperative deltoid tension assessment: elbow should flex passively but with resistance when traction applied in axial direction; trial reduction confirms appropriate stability and tension
• Tuberosity management in fracture RSA: anatomical tuberosity repair (subscapularis anteriorly, infraspinatus/teres minor posteriorly) improves external rotation outcomes — meticulous repair and bone grafting of tuberosity fragments critical; failure of tuberosity healing significantly worsens outcomes

• Scapular notching: most common specific complication of RSA; inferior scapular neck erosion from humeral cup during adduction; reduces with inferior positioning of glenosphere overlapping inferior glenoid rim; lateralised (BIO-RSA) design further reduces notching by moving COR laterally
• Acromial fracture: must be identified promptly — if suspected, CT scan; undisplaced fractures may be managed conservatively with sling immobilisation; displaced fractures require ORIF; failure to diagnose leads to progressive deltoid dysfunction and devastating loss of elevation

• Forward elevation: reliably restored to 130–150° in most patients — the primary functional goal of RSA
• External rotation: limited improvement; typically 20–40° post-operatively depending on teres minor and posterior cuff integrity
• Pain relief: excellent — comparable to anatomical TSA in appropriately selected patients
• 10-year survivorship: approximately 85–90% in primary RSA for CTA; revision rates increasing with longer follow-up; NJR (UK) 10-year survivorship for primary RSA approximately 88%; highest revision rates in younger patients and fracture indications
• Fracture RSA: more variable outcomes than primary CTA; tuberosity healing critical for external rotation; overall good pain relief and elevation in elderly

• Mediased vs lateralised RSA designs: original Grammont = fully mediased COR; benefits — reduced metaglene torque (lower loosening); limitations — higher notching, poor ER, higher instability; lateralised designs (BIO-RSA, lateralised glenospheres or humeral offset) reduce notching, improve ER, and reduce instability; current consensus favours a balance of lateralisation for most primary RSA cases
• Latissimus dorsi ± teres major transfer with RSA: for patients with pseudoparalysis AND significant loss of external rotation (particularly after brachial plexus injury, severe infraspinatus atrophy, or failed massive cuff repairs); improves ER from near-zero to approximately 30–40°; technically demanding; performed simultaneously with RSA or as staged procedure
• RSA in the setting of significant glenoid bone loss: from prior arthroplasty, fracture, or erosion — iliac crest bone graft or allograft used to reconstruct glenoid before metaglene placement; structural graft incorporation essential; alternative is augmented/angled baseplates for specific defects
• Inferior component positioning: placing the baseplate inferior on the glenoid (overhang at inferior glenoid rim) is the single most reliable technique to prevent scapular notching — the inferior screw is the most critical for primary fixation; failure to achieve inferior positioning is the most common technical error leading to notching
• RSA in young patients (<60): growing literature supports acceptable outcomes and survivorship in younger patients with no other reconstructive option; detailed counselling about activity modification, revision risk, and functional limitations essential; restricted activity recommendations post-operatively

• RSA indication: irreparable rotator cuff + arthritis (CTA); pseudoparalysis; failed TSA; complex fracture elderly; deltoid must be intact and innervated
• Grammont principles: glenosphere on glenoid; COR mediased to glenoid face; humerus distalised; deltoid pre-tensioned
• Pseudoparalysis: active elevation <90° with preserved passive ROM; indicates rotator cuff functional loss; RSA reliably restores elevation
• RSA reliably restores elevation to 130–150°; external rotation limited — teres minor and posterior cuff critical for ER
• Scapular notching: most common RSA-specific complication; prevent with inferior glenosphere positioning + inferior overhang; lateralised designs further reduce notching
• Acromial fracture: stress fracture from excessive deltoid tension; diagnose promptly; ORIF if displaced; missed diagnosis = loss of deltoid function = loss of elevation
• Axillary nerve: must be intact for RSA to function; deltoid denervation = catastrophic RSA failure
• Cutibacterium acnes: most common shoulder PJI organism; cultures 14 days; often normal serology
• BIO-RSA (lateralised): reduces notching, improves ER, reduces instability vs original Grammont mediased design
• Latissimus dorsi transfer + RSA: for severe ER deficit; improves ER from near-zero to 30–40°