Infectious Arthritis

Slide 1 · Infectious Arthritis

Mechanisms, morphology, clinicopathologic patterns

Suppurative · Mycobacterial · Viral · Lyme

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Trace how microorganisms reach synovial joints and explain the significance of cartilage injury.

Distinguish acute suppurative, mycobacterial, viral, and Lyme patterns using source-supported features.

Interpret the diagnostic value of joint aspirate, infection context, and characteristic histopathology.

Slide 3 · Infectious arthritis: The central definition

Infection involving articular structures

Infectious agents can reach the joint through blood, direct introduction, or spread from adjacent infected tissues.

Slide 4 · One parent category, four major patterns

Suppurative

Acute bacterial

Often rapid, painful monoarthritis

Mycobacterial

Chronic tuberculosis

Granulomas, pannus, eventual fusion

Viral / Lyme

Viral: Acute to subacute

Lyme: Episodic large-joint arthritis

Slide 5 · Three routes by which joints become infected

Hematogenous

Dissemination

Direct

Inoculation

Contiguous spread

From nearby infection

Different routes converge on infection of articular structures.

Slide 6 · Hematogenous route: Conceptual sequence

Microbe reaches

Bloodstream

Dissemination through

Circulation

Joint seeding

Articular

Infection

The diagram illustrates route of entry, not a molecular-level mechanism.

Slide 7 · Direct inoculation versus contiguous spread

Direct inoculation

Organism is introduced directly into articular structures

Route defined by local entry

Contiguous spread

An infected nearby site involves the joint

Soft-tissue abscess or osteomyelitis

Slide 8 · Neighboring osteomyelitis can involve the joint

Infection

In bone

Contiguous extension

Joint involvement

Articular injury

Slide 9 · Why articular cartilage is vulnerable

Bone

Articular cartilage

Joint cavity

Synovial lining (schematic)

Schematic. Cartilage has limited regenerative capacity compared with bone.

Slide 10 · Joint infection can create lasting disability

Microbial

Infection

Articular injury

Rapid tissue

Destruction

Permanent

Deformity

The ultimate outcome depends on course and effective recognition/treatment.

Slide 11 · Clinical tempo helps organize the differential

Abrupt

Suppurative bacterial arthritis

Acute pain, swelling, immobility

Insidious

Tuberculous arthritis

Gradually progressive joint pain

Variable / Episodic

Viral: Acute/subacute

Lyme: Migratory or recurring

Slide 12 · The infectious arthritis evaluation framework

Determine onset: Sudden acute, insidious progressive, or intermittent episodes.

Identify joint pattern: Single joint versus limited or migratory large-joint involvement.

Integrate exposure, immune status, and evidence of a causative organism.

Slide 13 · Suppurative arthritis: An acute bacterial process

Rapid, destructive infection of a synovial joint

The etiologic organism varies with age, underlying disease, exposure, and anatomic site.

Slide 14 · Bacteremia is the usual route in acute suppuration

Infection at

Distant focus

Hematogenous

Spread

Joint seeding

Acute suppurative

Arthritis

Slide 15 · The organism depends on clinical setting

The anatomic site and patient context influence the responsible bacterium.

Neonatal infections have distinctive routes and organisms.

Host defense defects and medical conditions create pathogen-specific susceptibility.

Slide 16 · Changing pathogen distribution after vaccination

Earlier burden

Haemophilus influenzae was historically an important cause

After effective vaccination

The incidence of H. Influenzae arthritis has declined

Current U.S. Setting

Staphylococcus aureus is most common

Slide 17 · A neonatal pathway: Adjacent bone infection

Epiphyseal

Osteomyelitis

Contiguous extension

Articular infection

Suppurative

Arthritis

This contiguous route in neonates.

Slide 18 · Illustrative age- and host-linked pathogen clues

All age groups (U.S.)

Staphylococcus aureus

Leading bacterial cause

Neonates

Group B Streptococcus

May accompany adjacent epiphyseal infection

Sickle cell disease

Salmonella

Heightened infection susceptibility

Slide 19 · Terminal complement deficiency and gonococcal spread

C5–C9 deficiency

Impaired membrane

Attack complex

Susceptibility to disseminated gonococcal infection

Possible

Arthritis

Slide 20 · Additional predisposing conditions

Congenital or acquired immunodeficiencies.

Debilitating illnesses and preexisting chronic arthritis.

Trauma involving the joint and intravenous substance use.

Slide 21 · Risk factor and pathogen clues

Clinical setting

Source-linked organism or pattern

General U.S. bacterial arthritis

Staphylococcus aureus most common

Neonatal infection

Group B Streptococcus; possible osteomyelitis spread

Sickle cell disease

Salmonella susceptibility

Complement C5–C9 deficiency

Disseminated gonococcal infection / arthritis

Intravenous substance use

Greater axial joint involvement

Slide 22 · Classic acute presentation

Sudden pain, swelling, and limited joint motion

The rapid clinical onset is a major distinction from insidious tuberculous arthritis.

Slide 23 · Suppuration within the joint cavity

Bone

Articular cartilage

Purulent joint fluid

Synovial lining (schematic)

Conceptual purulent effusion. Not a clinical or histologic specimen.

Slide 24 · Inflammation explains the acute syndrome

Articular

Infection

Purulent

Effusion

Pain and swelling

Restricted

Joint motion

Clinical sequence is a mechanistic teaching synthesis, not a source-derived quantitative pathway.

Slide 25 · Systemic inflammatory signs are common

Fever is a frequent accompanying feature.

Leukocytosis is often observed.

C-reactive protein is commonly elevated.

Slide 26 · Typical appendicular joint involvement

Lower extremity

Knee

Hip

Upper extremity

Shoulder

Elbow and wrist

Other listed site

Sternoclavicular joint

An important possible location

Slide 27 · The diagnostic hinge: Aspiration of an affected joint

Acute clinical

Suspicion

Joint

Aspiration

Purulent

Fluid

Identify the

Organism

Source states joint aspiration is diagnostic if purulent fluid yields an identifiable organism.

Slide 28 · Microbiologic attribution matters

A purulent aspirate provides evidence of suppuration.

Identifying the infectious organism establishes the etiologic diagnosis in the setting described.

Neither leukocytosis nor raised CRP substitutes for joint-level organism identification.

Slide 29 · Why early diagnosis changes the outcome

Recognize the

Acute pattern

Establish

Infection

Effective antimicrobial

Therapy

Avoid joint

Destruction

Robbins specifically states prompt recognition and effective antimicrobial treatment can prevent destruction.

Slide 30 · Abrupt versus indolent joint infection

Suppurative

Sudden painful swollen joint

Restricted motion; Acute inflammation

Mycobacterial

Insidious, progressively painful joint

Granulomas; Pannus; Late joint-space loss

Slide 31 · Tuberculous arthritis: The chronic pattern

Progressive joint infection caused by Mycobacterium tuberculosis

It primarily in adults.

Slide 32 · Tuberculous organisms reach joints in two ways

Pulmonary or

Other visceral source

Hematogenous dissemination

Joint infection

An alternative route is direct extension from adjacent osteomyelitis.

Slide 33 · Contiguous tuberculosis route

Adjacent tuberculous

Osteomyelitis

Spread into joint

Chronic granulomatous

Arthritis

Slide 34 · Mycobacterial arthritis: Cumulative tissue damage

Insidious

Onset

Caseating

Granulomas

Synovial

Pannus

Fibrous

Ankylosis

Slide 35 · Mycobacterial articular damage

Bone

Articular cartilage

Granulomatous tissue

Synovial lining (schematic)

Schematic representation of granulomatous tissue, not an H&E photomicrograph.

Slide 36 · Synovial pannus can advance over cartilage

Tuberculous joint

Infection

Synovial pannus

Formation

Pannus extends

Over cartilage

Marginal bone

Erosion

Slide 37 · Late tuberculosis can obliterate the joint space

Chronic

Granulomatous injury

Persistent structural

Destruction

Fibrous

Ankylosis

Obliterated

Joint space

Slide 38 · Weight-bearing joints in mycobacterial arthritis

Most frequent

Hip

Weight-bearing joint

Next

Knee

Weight-bearing joint

Then

Ankle

Weight-bearing joint

Slide 39 · Distinguishing bacterial and tuberculous morphology

Acute bacterial

Purulent joint aspirate

Acute inflammation and rapid clinical onset

Tuberculous

Confluent caseating granulomas

Pannus, bone erosion and fibrous ankylosis

Slide 40 · Viral arthritis spans more than one mechanism

Direct viral joint infection or infection-triggered autoimmunity

The arthritis may be acute or subacute.

Slide 41 · Viral causes named by Robbins

Viral group / agent

Alphaviruses

Parvovirus B19

Other agents

Rubella

Epstein–Barr virus

Hepatitis viruses

Hepatitis B virus

Hepatitis C virus

Slide 42 · Two explanations for viral joint symptoms

Direct involvement

The virus infects the joint

Examples: Rubella and some alphaviruses

Immune-mediated response

Viral infection triggers an autoimmune reaction

Joint symptoms need not imply direct viral invasion

Slide 43 · Lyme arthritis: A spirochetal joint infection

Borrelia burgdorferi transmitted by Ixodes ticks

Lyme disease follows a multiorgan course and may later involve joints.

Slide 44 · The geographic context

United States

New England

Mid-Atlantic states

Additional region

Upper Midwest

Range described as expanding

Slide 45 · Lyme disease: Multisystem sequence

Initial skin

Infection

Dissemination to

Other organs

Subsequent

Articular episodes

Slide 46 · Early-treated versus untreated Lyme disease

With timely treatment

Arthritis now affects fewer than 10% of infected patients

Textbook reports many infections are treated earlier

Without timely treatment

Up to 80% may develop migratory arthritis

Episodes can persist for weeks or months

Slide 47 · Lyme arthritis: Characteristic distribution

Most characteristic

Knee

Large joint

Other common sites

Shoulder and elbow

Large joints

Additional site

Ankle

Large joint

Slide 48 · Lyme arthritis can recur at new sites

Initial episode

1–2 joints

Symptoms for weeks

To months

New joint

Episodes later

Slide 49 · Diagnostic evidence in Lyme arthritis

Anti-Borrelia antibodies are the usual basis of diagnosis.

Borrelia DNA may be detected using PCR on synovial fluid.

The reported approximate synovial-fluid PCR detection rate is 70% in patients with Lyme arthritis.

Slide 50 · Antibiotic therapy changes Lyme outcome

Cure in approximately 90%

This statement concerns therapy active against Borrelia; This pathology lecture does not prescribe regimens.

Slide 51 · Persistent arthritis need not imply ongoing detectable infection

Postinfectious / antibiotic-refractory Lyme arthritis

The organism may not be detected in joint fluid, even by PCR, in such cases.

Slide 52 · Proposed immune mechanism after Borrelia clearance

Prior Borrelia

Infection

Cross-reactive immune

Response proposed

Potential self-antigen

Recognition

Persistent

Synovitis

This is a proposed explanatory mechanism, not established in every patient.

Slide 53 · Histology of Lyme-associated synovitis

Synoviocyte hyperplasia and fibrin deposition are described.

Mononuclear inflammation includes a prominent CD4⁺ T-cell population.

Arterioles may exhibit concentric “onion-skin” wall thickening (obliterative endarteritis).

Slide 54 · Why chronic Lyme synovitis can mimic rheumatoid arthritis

Synovial

Hyperplasia

Dense mononuclear

Infiltration

Chronic destructive

Synovitis

Rheumatoid-like

Histology

Severe Lyme synovitis can resemble rheumatoid arthritis histologically.

Slide 55 · Infectious arthritis: Organizing clinical patterns

Syndrome

Tempo

Distinguishing clue

Acute suppurative

Sudden

Purulent aspirate with identifiable organism

Mycobacterial

Insidious

Caseating granulomas; pannus; ankylosis

Viral

Acute / subacute

Direct viral infection or triggered immunity

Lyme

Episodic / migratory

Large joints; anti-Borrelia antibodies

Slide 56 · Infectious versus reactive arthritis

Infectious arthritis

Infectious agent may seed articular tissues

Suppurative, mycobacterial, viral, Lyme are considered here

Reactive arthritis

Arthritis follows genitourinary or gastrointestinal infection

The associated postinfectious syndrome is a separate Robbins topic

Slide 57 · Infectious versus crystal-induced arthritis

Infectious

Microorganisms involve the joint

Organism-directed diagnosis is important

Crystal-induced

Deposition of urate, calcium pyrophosphate, or other crystals

Crystal-driven inflammation can damage cartilage

Slide 58 · Case discussion: Sudden monoarthritis

A patient develops abrupt severe knee pain, swelling and restricted motion, accompanied by fever and a raised inflammatory response.

Which finding would make the suppurative diagnosis etiologically specific?

Slide 59 · Case reasoning: Acute suppurative pattern

The critical source-supported diagnostic step

Aspiration yielding purulent articular fluid strongly supports acute suppuration.

Identifying the organism in the aspirate establishes the infectious etiology in the Robbins description.

Rapid recognition and effective antimicrobial treatment can avert destructive outcomes.

Slide 60 · Case discussion: Indolent hip disease

An adult with gradually progressive hip pain develops chronic joint damage. Synovial tissue demonstrates confluent caseating granulomas.

Which infectious arthritis pattern explains the combination?

Slide 61 · Case reasoning: Mycobacterial arthritis

How morphology and tempo align

Tuberculosis can reach the joint from a visceral source or adjacent osteomyelitis.

Caseating granulomas with pannus and marginal erosion are characteristic source findings.

Long-standing disease may produce fibrous ankylosis and joint-space obliteration.

Slide 62 · Case discussion: Episodic large-joint synovitis

A patient from a region associated with Lyme disease develops recurrent episodes involving one or two large joints. Synovium shows chronic inflammation.

Which source-based evidence supports a Borrelia-associated explanation?

Slide 63 · Case reasoning: Lyme arthritis

Combine history with joint-specific tests

Anti-Borrelia antibody testing is the usual diagnostic basis.

Synovial-fluid PCR can detect Borrelia DNA, but a negative result does not by itself resolve persistent post-treatment disease.

Chronic synovitis can resemble rheumatoid arthritis; Morphology alone may be insufficient.

Slide 64 · Morphologic pattern and likely infectious category

Morphologic or clinical finding

Category to consider

Purulent aspirate; abrupt swollen monoarthritis

Acute suppurative arthritis

Caseating granulomas and synovial pannus

Mycobacterial arthritis

Acute or subacute viral-associated symptoms

Viral arthritis

Chronic CD4⁺-rich synovitis with obliterative endarteritis

Lyme arthritis (compatible, not exclusive)

Slide 65 · Clinicopathologic synthesis

Onset and joint

Distribution

Host factors and

Route of infection

Articular or serologic

Organism evidence

Morphologic and

Clinical classification

Teaching synthesis; No single universal test or cutoff is implied.

Slide 66 · Essential conclusions

All three entry routes may seed joints; Cartilage destruction can leave permanent disability.

Acute purulent arthritis requires prompt recognition and etiologic identification.

Tuberculosis, viral infection, and Lyme disease produce distinctive chronicity, mechanisms, and diagnostic clues.

Slide 67 · Primary reference and lecture scope

Robbins, Cotran & Kumar: Pathologic Basis of Disease

11th edition (2026) · Chapter 26: Bones, Joints, and Soft Tissue Tumors

Infectious Arthritis; Suppurative Arthritis; Mycobacterial Arthritis; Viral Arthritis; Lyme Arthritis

Comparative context: Reactive Arthritis and Crystal-Induced Arthritis