Overview & Anatomy
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
Types of Shoulder Arthroplasty
| Procedure | Components Replaced | Rotator Cuff Requirement | Primary Indication |
|---|---|---|---|
| Hemiarthroplasty (HA) | Humeral head only | Intact cuff required | 4-part proximal humerus fracture; AVN humeral head; young patients preserving glenoid |
| Total shoulder arthroplasty (TSA) | Humeral head + glenoid component | Intact cuff — mandatory | Glenohumeral OA with intact cuff; primary arthritis; post-traumatic OA with intact cuff |
| Reverse total shoulder arthroplasty (RSA) | Reversed ball-and-socket — glenosphere on glenoid; cup on humerus | Rotator cuff IRREPARABLE — relies on deltoid | Cuff tear arthropathy; irreparable rotator cuff tear; failed anatomical TSA; complex fracture in elderly |
| Resurfacing arthroplasty | Humeral head cap — bone-conserving | Intact cuff | Young active patients with OA; preserves bone stock; no intramedullary canal instrumentation |
- 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
Indications by Diagnosis
| Diagnosis | Preferred Procedure | Notes |
|---|---|---|
| Primary glenohumeral OA + intact cuff | TSA | Gold standard; superior to HA in OA; address glenoid retroversion (>15° — augmented glenoid or eccentric reaming) |
| Rheumatoid arthritis (RA) | TSA or RSA depending on cuff status | Rotator cuff commonly involved in RA; assess carefully; bone quality poor; cement fixation often needed |
| Cuff tear arthropathy | Reverse shoulder arthroplasty (RSA) | Irreparable cuff + arthritis; RSA replaces cuff function with deltoid leverage; do NOT perform anatomical TSA |
| 4-part proximal humerus fracture (acute) | RSA (increasingly) or HA | RSA preferred in elderly (>75) — more predictable function than HA; HA needs tuberosity healing which often fails |
| AVN humeral head (early stages) | HA or resurfacing | Preserve glenoid if not arthritic; TSA if glenoid involved; core decompression for Stages I–II |
| Failed previous shoulder arthroplasty | RSA (most revisions) | Glenoid loosening most common failure; subscapularis insufficiency; RSA handles cuff deficiency and instability |
Glenohumeral Arthritis — Classification (Walch)
The Walch classification (1999) describes glenoid morphology in primary glenohumeral OA and guides component selection and surgical technique.
| Walch Type | Glenoid Morphology | Surgical Implication |
|---|---|---|
| A1 | Central wear; concentric glenoid; minimal retroversion | Standard glenoid component; straightforward |
| A2 | Central wear with medialisation; deep central erosion | Risk of perforation; careful reaming; augment if necessary |
| B1 | Posterior wear; subchondral sclerosis posteriorly; no subluxation | Eccentric anterior reaming to correct retroversion |
| B2 | Posterior wear + biconcave glenoid; posterior subluxation of humeral head | Most complex anatomical TSA glenoid; eccentric reaming vs augmented/asymmetric glenoid component |
| B3 | Monoconcave glenoid with >15° retroversion; posterior subluxation >80% | Consider RSA or augmented glenoid; very difficult to correct with standard component |
| C | Dysplastic retroversion (>25°) regardless of wear; developmental origin | Augmented glenoid or consider RSA; challenging anatomy |
- 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
Surgical Approach
- 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
Glenoid Component — Design & Fixation
- 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
Consultant-Level Considerations
- 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
Exam Pearls
- 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