Comparative Features of Osteoarthritis and Rheumatoid Arthritis

Slide 1 · Comparative Features of

Osteoarthritis and Rheumatoid Arthritis

Pathogenesis • Morphology • Clinical discrimination

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

By the end of this lecture, distinguish OA from RA by:

Identifying the primary tissue and mechanism injured in each disorder.

Relating cellular mechanisms to joint morphology and progression.

Recognizing characteristic joint distribution, symptoms, and imaging.

Explaining the value and limitations of RA serology and extra-articular disease.

Slide 3 · The core differential: Six domains

Domain

Osteoarthritis

Rheumatoid arthritis

Primary driver

Biomechanical cartilage injury

Autoimmunity

Inflammation

Secondary / low grade

Primary / chronic synovitis

Pathology

Cartilage loss, osteophytes, cysts

Pannus, erosions, possible fusion

Serology

No characteristic autoantibodies

ACPA / rheumatoid factor

Extra-articular

Absent as an OA feature

May involve several organs

Slide 4 · Different starting points converge on joint damage

Cartilage matrix injury

Chondrocyte response

Net matrix loss

OA: Wear-related stress and disordered repair initiate the process.

Slide 5 · Autoimmune synovitis follows a different route

CD4+ T-cell response

Cytokine-driven synovitis

Pannus and erosions

RA: Immune inflammation is the primary engine of articular destruction.

Slide 6 · What normally protects an articular surface?

Hyaline cartilage

Type II collagen network resists tensile stress.

Proteoglycans and water resist compression.

Chondrocytes

Produce and renew cartilage matrix.

Secrete remodeling enzymes and inhibitors.

Synovial environment

Supports a mobile joint surface.

Persistent synovial inflammation can destroy cartilage.

Slide 7 · The primary lesion determines secondary changes

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

First major lesion: Articular cartilage matrix degeneration.

Chondrocytes attempt repair, but matrix degradation exceeds synthesis.

Subchondral bone responds to cartilage loss.

First major lesion: Persistent autoimmune synovitis.

Hyperplastic synovium generates invasive pannus.

Bone erosion follows inflammation and osteoclast activation.

Slide 8 · Osteoarthritis is not primarily an autoimmune synovitis

Degeneration dominates even though inflammation is present.

OA causes structural and functional failure of synovial joints.

Biomechanical stress is the principal pathogenic mechanism.

Inflammatory mediators can accelerate, but do not define, the primary lesion.

Disease often develops insidiously as age-associated primary OA.

Slide 9 · Primary and secondary osteoarthritis

Primary OA

Usually insidious without an identifiable initiating cause.

Common after midlife; May affect few joints or be generalized.

Secondary OA

Associated with predisposing joint deformity or earlier injury.

Systemic factors named include diabetes, obesity, and ochronosis.

Slide 10 · How cartilage injury becomes a persistent lesion

Biomechanical / genetic susceptibility

Chondrocyte injury

Matrix degradation > repair

Surface fissures

Cartilage loss is a failure of both extracellular matrix integrity and compensatory repair.

Slide 11 · Early OA: Chondrocytes attempt repair

The early cellular response is active, not simply passive wear.

Chondrocytes proliferate and form small clusters.

Proteoglycan synthesis continues despite matrix damage.

Cartilage water content increases.

Catabolic degradation continues to exceed anabolic replacement.

Slide 12 · OA matrix breakdown: Collagen and proteoglycans

Chondrocyte stress

Matrix metalloproteinases

Type II collagen disruption

Fissures and clefts

Loss of the collagen network disrupts tensile integrity; Proteoglycan depletion contributes to surface failure.

Slide 13 · Inflammation in OA: Contributor, not initiator

Synovial / chondrocyte signals

IL-1, IL-6 and prostaglandins contribute to low-grade inflammation.

Nitric oxide participates in tissue signaling.

Repair-associated signals

TGF-β and bone morphogenetic proteins contribute to osteophyte development.

TGF-β is also implicated in matrix metalloproteinase production.

Slide 14 · OA morphology: A progressive sequence

Cartilage softening

Fissures / fragmentation

Full-thickness loss

Subchondral change

Loose bodies, eburnation, cyst formation, and marginal osteophytes appear with progression.

Slide 15 · OA: Superficial cartilage fibrillation

Histologic change reflects cleavage of the surface matrix.

Fissures and clefts create a granular, softened articular surface.

Chondrocyte clustering accompanies early cartilage degeneration.

Progressive disruption ultimately removes full-thickness cartilage.

The lesion begins in cartilage rather than invasive synovial pannus.

Slide 16 · OA loose bodies arise from sloughed cartilage

Advanced articular cartilage may detach into the joint cavity.

Disrupted cartilage can separate as full-thickness fragments.

Dislodged fragments become intra-articular loose bodies (“joint mice”).

This finding belongs to advanced surface degeneration.

It should not be mistaken for the immune pannus of RA.

Slide 17 · OA eburnation is exposed, polished bone

Cartilage loss transfers friction to the subchondral surface.

After total local cartilage loss, subchondral bone becomes the articular surface.

Friction smooths and polishes exposed bone, yielding ivory-like eburnation.

Subchondral sclerosis accompanies established radiographic OA.

Eburnation is a bone response to absent cartilage, not synovial invasion.

Slide 18 · How subchondral cysts form in OA

Subarticular microfractures

Small gaps in bone

Synovial-fluid entry

Fibrous-walled cyst

Fluid is forced into subchondral bone through a valve-like mechanism.

Slide 19 · Osteophytes are marginal bony outgrowths

They represent a repair-associated response at joint margins.

Mushroom-shaped bone projections form near articular edges.

Initially capped by fibrocartilage and hyaline cartilage.

Cartilage caps progressively ossify.

TGF-β and bone morphogenetic proteins are implicated in their formation.

Slide 20 · OA synovium is relatively quiet

Mild secondary inflammation contrasts with RA pannus.

Usually only mild synovial congestion and fibrosis.

Few infiltrating inflammatory cells are typical.

Destructive lymphoplasmacytic synovitis is not the defining lesion.

Absence of aggressive pannus helps explain why ankylosis is not characteristic.

Slide 21 · Joint morphology: Two distinct mechanisms

OSTEOARTHRITIS

Osteophytes

Cartilage loss / cyst

RHEUMATOID ARTHRITIS

Pannus

Bone erosion

Slide 22 · Osteoarthritis: Structural changes and why they arise

Finding

Immediate lesion

Pathogenic explanation

Fibrillation

Surface clefts

Type II collagen / proteoglycan breakdown

Loose bodies

Detached cartilage

Full-thickness fragmentation

Eburnation

Polished subchondral bone

Cartilage loss exposes bone

Subchondral cysts

Fibrous-walled cavities

Fluid forced through bony defects

Osteophytes

Marginal bony projections

Abnormal reparative bone formation

Slide 23 · OA radiographs show a characteristic bone–cartilage response

The advanced structural pattern often establishes the diagnosis.

Joint-space narrowing reflects articular cartilage loss.

Subchondral sclerosis marks a bone response to load.

Osteophytes appear as peripheral bony projections.

Subchondral cysts may accompany the typical pattern.

Slide 24 · OA distribution: Load and local mechanics matter

Weight-bearing joints

Knees and hips are common sites.

Lower cervical and lumbar spinal levels may be affected.

Hand and foot joints

Distal and proximal interphalangeal joints.

First carpometacarpal and first tarsometatarsal joints.

Slide 25 · Symptoms: OA pain differs from RA inflammation

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

Deep pain typically becomes worse during joint use.

Stiffness on awakening usually improves with activity.

Crepitus and limitation of motion may develop.

Pain and stiffness are often worse on waking or after inactivity.

Swelling, warmth, and inflammatory discomfort predominate.

A chronic waxing-and-waning course may cause progressive limitation.

Slide 26 · Rheumatoid arthritis is systemic autoimmunity

The primary lesion is a chronic nonsuppurative synovitis.

RA produces proliferative inflammatory synovitis.

Synovial inflammation destroys cartilage and periarticular bone.

Progressive disease can produce fibrous and then bony ankylosis.

Extra-articular lesions are possible in skin, lung, heart, and vessels.

Slide 27 · RA pathogenesis: Adaptive immunity to synovial injury

CD4+ T-cell activation

Macrophage / synovial activation

Proinflammatory mediators

Pannus formation

The identity of the initiating joint antigen is not firmly established account.

Slide 28 · RA effector mediators and their targets

TNF, IL-1, IL-6

Macrophage-derived cytokines recruit and activate leukocytes.

They promote synovial protease release and cartilage injury.

IL-17 and IFN-γ

Th17-derived IL-17 recruits neutrophils / monocytes.

Th1-derived IFN-γ activates macrophages and synovial cells.

Slide 29 · RANKL explains inflammatory bone erosion

Activated T cells

RANKL expression

Osteoclast activation

Bone resorption

RA marginal erosions are immunologically driven; OA osteophytes reflect abnormal repair.

Slide 30 · Citrullination creates important RA autoantigens

Post-translational protein modification can generate recognized epitopes.

Arginine residues are converted to citrulline in certain proteins.

Joint-associated targets include fibrinogen, type II collagen, α-enolase, and vimentin.

Anti–citrullinated peptide antibodies (ACPA) recognize modified epitopes.

Antibody responses complement, rather than replace, T-cell-driven inflammation.

Slide 31 · ACPA is diagnostically useful, not universal

A positive result adds evidence for RA in the proper clinical setting.

ACPA is detected in serum in up to about 70% of cases.

ACPA can coexist with synovial lymphoid follicles and plasma cells.

Absence of ACPA does not exclude RA.

The initiating pathogenic antigen(s) remain incompletely defined.

Slide 32 · Rheumatoid factor identifies a distinct autoantibody response

Rheumatoid factor is not synonymous with ACPA.

Rheumatoid factor refers to autoantibodies directed against the Fc region of IgG.

IgM and IgA rheumatoid factors in many RA patients.

Rheumatoid factor is neither obligatory nor completely disease-specific.

Autoantibody results should be interpreted with the joint phenotype.

Slide 33 · Why genetic and environmental factors matter in RA

Inherited susceptibility

HLA-DR4 is associated particularly with ACPA-positive RA.

Genetic predisposition influences disease development and persistence.

Potential triggers

Smoking and infection, including periodontitis, are proposed contributors.

They may facilitate citrullination; Precise triggers are uncertain.

Slide 34 · RA synovium changes its gross architecture

Inflamed synovium no longer remains thin and smooth.

Synovium becomes edematous, thickened, and hyperplastic.

Delicate and bulbous villous projections emerge.

Increased vascularity develops with angiogenesis.

The expanding tissue forms the substrate for invasive pannus.

Slide 35 · RA synovitis contains an organized immune infiltrate

Histology demonstrates chronic immune-mediated inflammation.

Synoviocyte proliferation and hyperplasia.

CD4+ helper T cells, B cells, plasma cells, dendritic cells, and macrophages.

Lymphoid follicles may form within the synovium.

Fibrin-rich surface exudates may contain neutrophils.

Slide 36 · RA: Pannus is an invasive lesion, not just swelling

Components

Edematous hyperplastic synovium and inflammatory cells.

Granulation tissue and proliferating fibroblasts.

Destructive effects

Spreads onto the cartilage surface.

Erodes cartilage and allows inflammatory tissue to extend toward bone.

Slide 37 · From proliferative synovitis to joint destruction

Synovial hyperplasia

Inflammatory pannus

Cartilage erosion

Joint-space loss

Persistent inflammatory granulation tissue invades cartilage rather than merely responding to its disappearance.

Slide 38 · RA progression: Erosion to ankylosis

Periarticular bone erosion

Loss of cartilage barrier

Fibrous bridge

Bony ankylosis

Fibrous fusion may eventually ossify; OA does not typically produce joint fusion.

Slide 39 · Subchondral pathology in OA and RA

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

Eburnation and sclerosis are consequences of cartilage loss.

Subchondral cysts arise through bony gaps and fluid entry.

Marginal osteophytes add bone.

Osteoclast-driven resorption produces erosions.

Pannus directly penetrates cartilage and bone.

Ankylosis may ultimately fuse joint surfaces.

Slide 40 · Rheumatoid nodules show a necrobiotic architecture

These extra-articular lesions are a pathologic clue to RA.

Usually firm, nontender subcutaneous masses at pressure sites.

Central fibrinoid necrosis is a defining microscopic feature.

A rim of activated macrophages surrounds the necrotic center.

Lymphocytes and plasma cells populate the surrounding tissue.

Slide 41 · Extra-articular RA can involve several organ systems

RA is not confined to synovial joints.

Skin: Rheumatoid nodules.

Blood vessels: Leukocytoclastic vasculitis in severe disease.

Pleura, lung, and pericardium may be affected.

Ocular disease can include uveitis and keratoconjunctivitis.

Slide 42 · Joint distribution provides an early diagnostic clue

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

Knees, hips, spine, DIP / PIP, and thumb-base joints are common.

Often one or a few joints, although generalized OA occurs.

Prominent distal interphalangeal osteophytes can form Heberden nodes.

Usually begins in small joints of hands and feet.

Often symmetric and eventually polyarticular.

MCP and PIP involvement is characteristic in the hands.

Slide 43 · Joint symptoms reflect the underlying lesion

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

Mechanical pain with joint use.

Brief stiffness that tends to improve after movement.

Crepitus / restricted range of motion with degeneration.

Significant systemic autoimmune manifestations are not typical.

Morning / post-rest inflammatory stiffness.

Swollen, warm, painful joints.

Fatigue and malaise may precede arthritis.

Chronic relapsing inflammation can produce deformities.

Slide 44 · The hand is a high-yield OA–RA discriminator

Specific joint groups matter more than a generic “hand arthritis” label.

OA frequently affects distal interphalangeal joints and first carpometacarpal joints.

Heberden nodes reflect distal interphalangeal osteophytes.

RA typically involves metacarpophalangeal and proximal interphalangeal joints.

RA hand deformities may include ulnar deviation and flexion–hyperextension.

Slide 45 · Comparison of imaging patterns

Domain

Osteoarthritis

Rheumatoid arthritis

Joint space

Narrowing from cartilage loss

Narrowing after cartilage destruction

Bone margin

Marginal osteophytes

Periarticular erosions

Bone density

Subchondral sclerosis

Juxta-articular osteopenia

Other signs

Subchondral cysts / eburnation

Deformity and possible ankylosis

Slide 46 · A radiograph measures structure, not symptom severity

OA structural severity is not a direct pain scale.

Radiographic OA can be diagnostic when characteristic advanced changes are present.

The extent of radiographic OA does not correlate tightly with pain and disability.

Clinical limitation still requires direct functional assessment.

For inflammatory RA, erosions and osteopenia indicate a different mechanism.

Slide 47 · Serologic evaluation separates immune disease from degeneration

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

There is no characteristic OA autoantibody panel.

Laboratory serology is not the defining basis of OA diagnosis.

Typical advanced imaging may obviate biopsy.

ACPA and rheumatoid factor support RA diagnosis.

Seronegativity is possible; Roughly one-fifth.

Clinical pattern and radiography remain important; Biopsy is rarely required.

Slide 48 · Why similar-looking symptoms may have different causes

Finding

OA interpretation

RA interpretation

Joint pain

Articular cartilage loss / altered load

Active synovial inflammation

Stiffness

Mechanical stiffness, improves with activity

Inflammatory stiffness after rest

Swelling

Bony enlargement / secondary changes

Synovial thickening and inflammation

Reduced motion

Cartilage depletion / osteophytes

Pannus, erosions, eventual fusion

Slide 49 · A defensible clinical comparison workflow

Distribution & symmetry

Pain / stiffness pattern

Imaging features

Autoantibody context

Interpret these domains together; No isolated symptom or serologic test should replace clinicopathologic correlation.

Slide 50 · When the pattern is atypical, reconsider the differential

The textbook contrasts OA and RA; Not all arthritis is either one.

Young-onset OA merits assessment for a predisposing abnormality.

RA may lack rheumatoid factor and ACPA.

Joint distribution and inflammatory signs may overlap in practice.

Crystal, infectious, and other immune-mediated arthritides form separate categories.

Slide 51 · Therapeutic goals follow the pathogenesis

OSTEOARTHRITIS

RHEUMATOID ARTHRITIS

Reduce pain and preserve joint function.

Modify mechanical load and activities.

In severe structural disease, arthroplasty may be considered.

Anti-inflammatory approaches can be used for symptoms.

Suppress immune inflammation and prevent progressive destruction.

Methotrexate and other immunosuppressants.

TNF antagonists and other immune-targeting biologics are described.

Disease control may require sustained therapy.

Slide 52 · Immunosuppression adds a risk absent from mechanical OA care

Pathway-directed RA treatment has clinically relevant tradeoffs.

TNF plays a central role in sustained synovial inflammation.

Anti-TNF treatment reduces inflammation but is not curative.

Long-term anti-TNF therapy predisposes to opportunistic infections.

Robbins specifically highlights reactivation or infection involving Mycobacterium tuberculosis.

Slide 53 · Case A: Activity-related knee pain

A 68-year-old has slowly progressive knee discomfort worsened by walking, crepitus, and radiographs showing osteophytes with subchondral sclerosis.

Which process best explains the radiographic pattern?

OA — cartilage loss with load-related subchondral bone remodeling.

Slide 54 · Case B: Inflammatory small-joint arthritis

A patient has symmetric painful swelling of metacarpophalangeal and proximal interphalangeal joints, marked stiffness on waking, and periarticular erosions.

What lesion principally drives the cartilage destruction?

RA — inflammatory synovial pannus invading the articular surface.

Slide 55 · Case C: Negative serology does not close the diagnosis

A patient has symmetric warm small-joint swelling and erosive inflammatory changes, but both rheumatoid factor and ACPA tests are negative.

Does negative serology exclude rheumatoid arthritis?

No — seronegative RA exists; Interpret clinical and imaging evidence.

Slide 56 · High-yield final comparison

Diagnostic axis

Osteoarthritis

Rheumatoid arthritis

Pathogenesis

Cartilage degeneration / failed repair

Autoimmune inflammatory synovitis

Inflammation

Secondary, usually limited

Primary and prominent

Tissue result

Fissures, eburnation, osteophytes

Pannus, erosions, ankylosis

Distribution

Weight-bearing, DIP / thumb base

Symmetric small joints, MCP / PIP

Clinical timing

Use-related pain

Morning or post-rest symptoms

Serology / systemic

No characteristic autoantibodies

ACPA / RF; extra-articular lesions

Slide 57 · Morphology explains the entire differential

Use causal reasoning rather than memorizing disconnected features.

OA: Matrix failure → fissures → cartilage loss → sclerosis, cysts, and osteophytes.

RA: Autoimmunity → chronic synovitis → pannus → cartilage and bone erosion.

OA is predominantly a degenerative joint disease; RA is systemic immune-mediated disease.

Distribution, inflammatory symptoms, radiology, and serology form a coherent diagnostic pattern.

Slide 58 · Sources and source-fidelity boundaries

Primary source

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th ed. (2026), Chapter 26 — Joints: Osteoarthritis and Rheumatoid Arthritis.

Comparative source

Table 26.5: primary lesion, inflammation, distribution, pathology, antibodies, and organ involvement. Figure 26.37: morphology labels.

Original teaching schematics are not photomicrographs or reproduced textbook figures.