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).

The Definition promises that inflammatory arthritis "encompasses... Rheumatoid Arthritis, Psoriatic Arthritis, Ankylosing Spondylitis", and the differential lists a "Psoriatic / seronegative" pattern — but the rest of the topic develops only RA. The seronegative spondyloarthropathies (psoriatic arthritis, ankylosing spondylitis, reactive and enteropathic arthritis) behave differently in ways examiners probe.

• They are RF- and anti-CCP-negative and HLA-B27-associated, and the primary lesion is enthesitis (inflammation where tendon/ligament/capsule insert into bone) rather than the synovial pannus that drives RA — although a secondary synovitis also occurs.
• The radiographic signature is mixed erosive and proliferative, not purely erosive. Alongside erosions there is new bone formation — enthesophytes, periostitis, and a tendency to ankylosis (bony fusion). Psoriatic arthritis classically produces the "pencil-in-cup" deformity and can swing between an erosive-mutilating form (arthritis mutilans) and a bone-forming one; ankylosing spondylitis tends toward a stiff, ankylosed glenohumeral joint, often with supero-lateral humeral-head erosion (the "hatchet" head), and is accompanied by sacroiliitis and spinal disease.

Surgical implications: the arthroplasty decision still hinges on cuff integrity and glenoid bone stock, as in RA, and the perioperative principles are shared (infection risk, osteopenia, hold biologics). But ankylosing spondylitis adds its own hazards — a stiff, ankylosed shoulder that is harder to mobilise, a rigid kyphotic cervical spine that is brittle and difficult to intubate (a high fracture risk on positioning), and a higher rate of heterotopic ossification after arthroplasty. Medical control also differs: TNF and IL-17 inhibitors are central for axial spondyloarthritis and psoriatic disease, whereas methotrexate (a mainstay in RA) is less effective for axial AS.

Synovial Fluid Analysis:

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

The radiograph in the Classification section comes from a reported case of rice-body arthropathy, but the entity is never explained — and it carries an important "do not miss".

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.

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.

• 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.