12.3 Arthritides

12.3 Arthritides

Quick Answer: Arthritic disorders are the highest-volume imaging pathology tested across NBCE exams. On Part II, you must match a radiographic pattern to the correct arthropathy and state the clinical impression — including whether chiropractic management is appropriate, co-management is needed, or rheumatology/orthopedic referral is indicated. Use ABCS, then classify: degenerative (proliferative bone) versus inflammatory (erosive, osteopenic) versus seronegative spondyloarthropathy (SI joints + spine) versus crystal disease (chondrocalcinosis, overhanging erosions).

Roughly half of Diagnostic Imaging items require linking film findings to a working diagnosis, not merely naming a sign. Arthritis vignettes often include age, joint distribution, morning stiffness duration, skin findings, and HLA-B27 history — the film confirms the pattern your clinical reasoning already suspects.

ABCS Applied to Arthritic Films

1. Alignment — subluxation (RA), ankylosis (AS), varus/valgus (advanced OA), ulnar drift
2. Bone — osteophytes and sclerosis (OA) vs. erosions and osteopenia (RA) vs. proliferation/periostitis (psoriatic)
3. Cartilage/joint spaces — asymmetric vs. uniform narrowing; which compartments (medial tibiofemoral in knee OA)
4. Soft tissues — tophaceous swelling (gout), synovial proliferation (inflammatory), calcification in soft tissues (CPPD)

Osteoarthritis (Degenerative Joint Disease)

The most common arthropathy; wear-and-tear with mechanical distribution.

Radiographic Hallmarks (Four Classic Signs)

1. Joint-space narrowing — asymmetric, typically maximal in weight-bearing compartments (medial knee, superior hip)
2. Osteophytes — marginal bony spurs at joint margins
3. Subchondral sclerosis — increased radiodensity beneath articular cartilage
4. Subchondral cysts — lucent geodes in sclerotic bone

Common Sites and Part II Patterns

• Hands: DIP and PIP involvement (Heberden and Bouchard nodes clinically); sparing of MCPs (unlike RA); mucinous cysts at DIP
• Knee: Medial compartment narrowing, osteophytes, varus alignment in advanced disease
• Hip: Superior joint-space loss, subchondral cysts, sclerosis; protrusio in advanced OA
• Spine: Disc-space narrowing, endplate sclerosis, osteophytes, vacuum phenomenon in discs; facet arthropathy — distinguish from inflammatory spine disease (AS has SI fusion and syndesmophytes bridging vertically)

Clinical Impression and Referral

OA is appropriate for chiropractic co-management in many cases when no acute inflammatory flare, instability, or severe structural loss contraindicates care. Refer for rapidly progressive joint destruction, locked knee with mechanical block, or failed conservative trial before joint replacement discussion.

Rheumatoid Arthritis

Systemic autoimmune synovitis; symmetric small-joint polyarthritis.

Radiographic Progression

1. Periarticular osteopenia (earliest sign)
2. Soft-tissue swelling from synovitis
3. Marginal erosions at bare areas (uncovered bone)
4. Uniform joint-space narrowing from pannus destruction
5. Subaxial subluxations — ulnar deviation at MCPs, swan-neck/boutonnière deformities clinically

Distribution Clues

• MCPs, PIPs, wrists, MTPs — classic
• DIPs spared — key discriminator from OA and psoriatic arthritis
• Cervical spine: C1-C2 subluxation (odontoid erosion) — high-yield referral concern before manipulation

Clinical Impression

RA is not a primary chiropractic-only condition. Co-manage with rheumatology; do not perform high-velocity cervical manipulation with atlantoaxial instability. Urgent referral for acute hot monoarthritis to rule out septic joint.

Seronegative Spondyloarthropathies

Group includes ankylosing spondylitis, psoriatic arthritis, reactive arthritis, and enteropathic arthritis. Shared features: enthesitis, asymmetric oligoarthritis, spine/SI involvement, HLA-B27 association.

Ankylosing Spondylitis

• Sacroiliac joints: Erosions → sclerosis → bilateral fusion ("shiny corner" sign early)
• Spine: Syndesmophytes (thin vertical ossification of outer annulus) → bamboo spine with ankylosis
• Disc spaces: Relatively preserved height compared to degenerative disc disease
• Hip: Concentric joint-space loss, protrusio acetabuli
• Referral: Rheumatology for biologic/DMARD therapy; fracture risk in fused spine ("chalk stick fracture") — even minor trauma needs evaluation

Psoriatic Arthritis

• Asymmetric joint involvement; DIP predilection (unlike RA)
• Erosions + bone proliferation — "pencil-in-cup" deformity at IP joints
• Fluffy periostitis along shaft of phalanges
• Skin/nail psoriasis in stem — clinical correlation
• Arthritis mutilans: Severe osteolysis — urgent rheumatology

Reactive Arthritis

• Asymmetric lower-extremity oligoarthritis (knees, ankles, MTPs)
• Enthesopathy (Achilles, plantar fascia)
• Periosteal reaction in acute phase
• Classic triad (urethritis, conjunctivitis, arthritis) may appear in stem

Gout and Calcium Pyrophosphate Deposition (CPPD)

Gout (Monosodium Urate)

• Early: Soft-tissue tophus (dense nodular swelling) without bony erosion
• Chronic: Punched-out erosions with serrated margins and characteristic overhanging edges (preserved cartilage overhangs erosion)
• Distribution: First MTP (podagra) classic; also tarsal, ankle, knee
• Joint space: May be preserved until late
• Clinical impression: Acute hot monoarthritis = septic joint until proven otherwise — refer for aspiration; chronic tophaceous gout → rheumatology/co-management

CPPD (Pseudogout)

• Chondrocalcinosis: Linear calcification in hyaline/fibrocartilage (knee menisci, symphysis pubis, triangular fibrocartilage)
• Joint changes: resemble OA with unusual compartments (patellofemoral, radiocarpal)
• Clinical: Acute knee inflammation in elderly; differentiate infection

Less Common but Testable Patterns

Side-by-Side Pattern Recognition (Part II High-Yield)

Referral and Management Implications

• Rheumatology referral: RA, AS, psoriatic, uncontrolled inflammatory disease, any suspected autoimmune flare
• Urgent referral: Acute hot swollen joint (septic vs. crystal), rapidly destructive arthritis, neurologic deficit from C1-C2 subluxation
• Orthopedic referral: End-stage OA with mechanical symptoms, locked joint, Charcot with instability
• Chiropractic role: OA and stable spondyloarthropathy co-management with medical oversight; modify techniques when ankylosis, osteoporosis, or instability present

Part II Strategy for Arthritis Items

1. Identify distribution in the stem before the film (symmetric hands vs. first MTP vs. spine)
2. ABCS — look for erosion vs. osteophyte as the primary fork
3. Match four OA signs or RA erosive pattern as the two most common distractors
4. Answer the question asked: sometimes it is the diagnosis, sometimes the next referral step, sometimes the feature that rules out a mimic

Arthritis imaging mastery on Part II is pattern classification under time pressure — proliferative degenerative, erosive inflammatory, axial seronegative, or crystal — each with distinct clinical implications for patient safety and referral.