Inflammatory Arthritis of the Shoulder

Epidemiology:

• Prevalence: 90% of RA patients develop shoulder symptoms.
• Gender: Female predominance (approximately 3:1).
• Trend: Surgical incidence declining due to effective biologic therapies.
• Bilateral: Commonly bilateral involvement.

The disease is synovium-driven, distinguishing it from cartilage-first osteoarthritis:

1. Synovitis: Hypertrophic inflamed synovium forms a destructive pannus.
2. Marginal Erosions: Begin at the "bare area" where cartilage does not protect bone.
3. Cartilage Destruction: Proteolytic enzymes (collagenase, metalloproteinases) released by pannus.
4. Cuff Attrition: Pannus invades rotator cuff tendons from the undersurface, causing thinning and rupture.
5. Central Migration: The humeral head erodes centrally into the glenoid vault (acetabularisation).

Synovial Fluid Analysis:

• If diagnosis unclear or infection suspected (septic arthritis).
• RA Fluid: WBC 2,000-50,000 (inflammatory), Cloudy, Low viscosity, Glucose low.

Rehabilitation Protocol:

• Phase 1 (0-6 weeks): Sling. Passive ROM only (protect Subscap repair). Pendulums.
• Phase 2 (6-12 weeks): Active assistive ROM. AAROM pulleys.
• Phase 3 (3-6 months): Active ROM. Gentle strengthening.
• Phase 4 (6+ months): Full activity.

Specific Considerations in RA:

• Slower healing: Soft tissue repairs (subscap) take longer.
• Osteopenia: Avoid aggressive passive stretching (fracture risk).
• Skin: Care with dressings/tape (tears).

Pain Relief:

• Arthroplasty (TSA or Reverse) provides excellent pain relief (over 90%) in RA.
• Function is less predictable than in OA, due to muscles/cuff.

Implant Survival:

• Anatomic TSA: 90% at 10 years, but accelerated glenoid loosening (radiographic lucency common).
• Reverse TSA: 85-90% at 10 years. Complication rate slightly higher.
• Hemi: Lower satisfaction, ongoing glenoid pain.

Summary: Surgery significantly improves Quality of Life, but complication rates (infection, fracture) are higher than in OA.

• Anatomic TSA vs reverse in the cuff-intact RA shoulder. With an intact cuff, anatomic TSA gives better rotation and preserves bone, but progressive cuff attrition is intrinsic to RA and may cause later glenoid loosening ("rocking horse"). Some surgeons favour primary reverse arthroplasty in older RA patients to pre-empt this, accepting reduced rotation and notching. No high-level trial resolves the trade-off.
• Holding biologics. The optimal hold interval is extrapolated from low-grade, mostly retrospective data; recommendations are consensus (Guideline-level), and the magnitude of infection reduction is uncertain. Over-holding risks a disabling flare.
• Continuing vs stopping methotrexate. Continuing is now standard, but practice still varies in patients with renal impairment or concurrent high-dose steroids.
• Role of synovectomy. Arthroscopic synovectomy gives short-term pain relief but does not alter long-term joint destruction; its value in the biologic era is debated and increasingly limited to medically refractory synovitis with preserved cartilage.
• Glenoid component in soft bone. Whether to implant a glenoid (better pain relief) or accept hemiarthroplasty/ream-and-run (lower loosening risk) in severely osteopenic, eroded glenoids remains individualised.
• Cervical spine clearance. Routine flexion/extension films before every RA arthroplasty are traditional teaching, but selective imaging guided by symptoms and examination is increasingly advocated.

Global epidemiology:

• RA affects roughly 0.5–1% of adults worldwide; shoulder symptoms develop in the majority over the disease course and involvement is frequently bilateral.
• Female-to-male ratio approximately 3:1; peak onset in the fourth-to-sixth decades.
• Widespread early use of methotrexate and biologic DMARDs has reduced the incidence of end-stage erosive shoulder disease and of synovectomy/early arthroplasty compared with historical cohorts — a trend seen across high-income health systems.

Registry and outcome signals:

• Major arthroplasty registries (AOANJRR, NJR for England/Wales, the Nordic registries) show reverse arthroplasty use rising steeply, including for inflammatory arthritis with cuff or glenoid compromise.
• Revision rates for arthroplasty in RA run slightly higher than in OA, driven chiefly by infection and soft-tissue (cuff/subscapularis) failure rather than by polyethylene wear.

High- vs limited-resource practice variation:

• Where biologics and early rheumatology access are routine, surgeons increasingly see "burned-out" dry-stage disease rather than florid synovitis.
• In limited-resource settings, patients more often present with advanced erosive ("resorptive") disease, severe glenoid bone loss and massive cuff deficiency — shifting practice toward reverse arthroplasty or, where implants/expertise are unavailable, hemiarthroplasty or arthrodesis.
• Combined rheumatology–orthopaedic clinics improve perioperative optimisation and are an aspirational model regardless of setting.