Shoulder Arthroplasty — Indications

Shoulder arthroplasty encompasses a spectrum of procedures from hemiarthroplasty (humeral head replacement only) to total shoulder arthroplasty (TSA, both humeral and glenoid replacement) and reverse total shoulder arthroplasty (RSA). Correct patient selection — matching the right procedure to the right diagnosis — is the most critical determinant of outcome. An intact or repairable rotator cuff is a prerequisite for anatomical shoulder arthroplasty.

• The glenohumeral joint is the most mobile joint in the body — a shallow glenoid socket on a mobile scapula; stability provided predominantly by the rotator cuff, capsulo-labral complex, and negative intra-articular pressure rather than bony congruity
• Normal glenohumeral anatomy: glenoid retroverts approximately 7° relative to the scapular plane; humeral head retroversion approximately 20–30°; neck-shaft angle approximately 130–135°; these parameters guide component positioning in anatomical TSA
• Rotator cuff assessment is the pivotal examination step: an intact or reconstructable rotator cuff (particularly supraspinatus and subscapularis) is required for anatomical shoulder arthroplasty to function; irreparable rotator cuff tear mandates reverse shoulder arthroplasty
• Subscapularis: most critical muscle for anterior stability and internal rotation; divided as part of the deltopectoral approach; must be repaired meticulously; failure leads to anterior instability and progressive glenoid loosening

• Total shoulder arthroplasty: gold standard for glenohumeral OA with intact rotator cuff; superior pain relief and function compared to hemiarthroplasty for primary OA; the glenoid component is the weak link — glenoid loosening is the most common cause of revision
• Hemiarthroplasty vs TSA in OA: multiple RCTs and meta-analyses show TSA provides superior pain relief, range of motion, and patient satisfaction compared to HA for primary OA — TSA preferred when glenoid is arthritic and cuff is intact

The Walch classification (1999) describes glenoid morphology in primary glenohumeral OA and guides component selection and surgical technique.

• Walch B2: most common complex glenoid variant in primary OA; posterior glenoid erosion creates biconcave glenoid; requires either eccentric anterior reaming (risks anterior perforation) or augmented posterior glenoid component to correct retroversion and restore neutral version
• Glenoid retroversion correction: for every 1 mm of eccentric reaming, approximately 3° of retroversion is corrected; maximum safe eccentric reaming approximately 10–12 mm before risk of anterior perforation

• Deltopectoral approach: standard for all anatomical shoulder arthroplasty and most RSA; internervous plane between deltoid (axillary nerve) and pectoralis major (medial/lateral pectoral nerves); cephalic vein retracted medially or laterally
• Subscapularis management: three options — tenotomy (cut and repair), peel (osteotomy of lesser tuberosity), or subscapularis-sparing (SST) — subscapularis-sparing approach avoids the risk of subscapularis failure but limits glenoid exposure
• Subscapularis failure after TSA: catastrophic complication — leads to anterior instability, progressive posterior glenoid wear (rockwood sign — superior migration + glenoid destruction), and rapid implant failure; subscapularis repair integrity must be confirmed at 6 weeks post-operatively; protect repair in rehabilitation
• Superior approach: used for some RSA configurations (superolateral deltoid split) — avoids subscapularis but limited glenoid exposure; suits RSA where glenoid access via deltopectoral approach is adequate

• All-polyethylene cemented glenoid: traditional design; excellent long-term data; keel or pegged fixation; cement provides immediate fixation; 10-year survivorship approximately 90%
• Metal-backed glenoid: allows cementless fixation; modular PE exchange; early results disappointing due to backside wear and early loosening — largely abandoned for anatomical TSA but used in RSA baseplate
• Glenoid loosening (rocking horse phenomenon): the most common cause of revision in anatomical TSA; eccentric loading from malpositioning or edge loading causes cyclic micromotion at cement-bone interface → peripheral scalloping (rocking horse radiograph sign) → progressive loosening; meticulous glenoid preparation and component positioning are essential to prevent this
• Pegged vs keeled glenoid: multiple RCTs show no significant difference in survivorship; pegged glenoid associated with lower radiolucent line rates in some series; surgeon preference

• Pre-operative CT planning with 3D reconstruction: mandatory for complex glenoid deformity (Walch B2, B3, C); allows measurement of retroversion, bone stock, and planning of reaming depth and component size; 3D printing of patient-specific guides now available for augmented glenoid placement
• Humeral head version: target 20–30° of retroversion at implantation; over-retroverted humeral component increases posterior instability; under-retroverted increases anterior instability and subscapularis tension; intraoperative assessment using forearm as reference (20–30° ER with elbow at 90° = correct version)
• Periprosthetic joint infection in shoulder arthroplasty: Cutibacterium acnes (formerly Propionibacterium acnes) most common pathogen in shoulder — slow-growing anaerobe; cultures must be held for 14 days; serology (CRP, ESR) often normal; high index of suspicion for unexplained pain, stiffness, or loosening after shoulder arthroplasty; two-stage revision protocol
• Axillary nerve protection: lies 5–7 mm distal to the inferior glenoid rim; at risk during inferior capsular release and anterior glenoid preparation; always identify and protect before inferior capsule release
• Young patients and shoulder arthroplasty: avoid glenoid component in patients under 50 with intact glenoid cartilage if possible — hemiarthroplasty or resurfacing preserves glenoid for future TSA; glenoid bone loss from repeated revision makes late TSA difficult

• TSA = gold standard for glenohumeral OA with intact rotator cuff; superior to HA in all outcome measures for primary OA
• Rotator cuff integrity is the pivotal decision — intact cuff = anatomical TSA; irreparable cuff = RSA
• Walch B2: biconcave glenoid + posterior subluxation = most complex OA glenoid variant; eccentric reaming vs augmented component
• Glenoid loosening = most common TSA revision cause; rocking horse sign on X-ray; cemented all-poly glenoid is standard
• Subscapularis failure = catastrophic; anterior instability + rapid glenoid destruction; protect repair to 6 weeks minimum
• Cuff tear arthropathy: RSA; do NOT perform anatomical TSA without functioning cuff
• 4-part fracture in elderly (>75): RSA preferred over HA — more predictable function; tuberosity healing unreliable with HA
• Cutibacterium acnes: most common shoulder PJI organism; anaerobe; cultures held 14 days; serology often normal
• Axillary nerve: 5–7 mm below inferior glenoid rim; protect during inferior capsule release
• Pre-op CT planning: mandatory for Walch B2/B3/C glenoids; 3D reconstruction guides reaming and augment selection