Osteoarthritis -

Degenerative, chronic arthropathy characterized by cartilage loss, new bone formation at joint margins & capsular fibrosis

Aetiology

1. Abnormal forces on normal cartilage
2. Normal forces on abnormal cartilage
- Ie. the cartilage fatigue threshold is overcome
Abnormal Forces
- Force = Load/ Unit area
- Increased Load
  - Both magnitude & frequency
  - Eg. Obese
- Decreased Contact Area
Stress exceeds local threshold
- Age
  - More stiff & less strong & elastic
  - Difference from Osteoarthritis poorly defined
    - Hypocellular
    - Decreased water (cf. Osteoarthritis with damaged cartilage imbibing water)
    - Increased Stiffness
- CPP & HA deposition
  - Increased Softness
  - Chronic Inflammation

Obesity
- Especially Knee > Hip > Hand
- 7x risk
- Reason
  - Animal studies high fat diet » Osteoarthritis
  - ? Metabolic & mechanical reason
Heredity
- Increased polyarthritic Osteoarthritis in families
- ? Mutation Type II procollagen
Trauma
- Cartilage injury at time of trauma
- Malunion resulting in abnormal force vectors
Occupational
- ? Repetitive use
Sport
- Throwing athletes – elbow

Cardinal features are
- Cartilage disintegration
- Subchondral sclerosis
- Subchondral cysts
- Osteophyte formation
- Capsular fibrosis
Cartilage Destruction
- Macroscopic
  - At most heavily loaded part
  - Softened & fibrillated
  - Fibrillation propagated as fissures to subchondral bone
  - Fragments separate
  - Become loose bodies which can ↑ in size
  - Digested
  - Cartilage lost
  - Bone exposed & eburnated
- Microscopic
  - Vertical clefts in surface
  - Superficial chondrocyte loss
  - Increased cellularity with clusters of chondrocytes
  - Duplication & irregularity of tidemark
  - Subchondral Plate Sclerosis
  - Dense & thickened
  - Marked osteoblastic activity
  - Increased vascularity
Subchondral Cyst Formation
- Usually near maximum cartilage loss
- May extend into metaphysis
- Margins sclerotic
- Filled with thick gelatinous material
Osteophyte formation
- Bone at margins of joint
- Cortex thickened & sclerotic
- Prominent cement lines
- Parallel to joint surface
- Covered in hyaline cartilage
Capsular Fibrosis
- Capsule markedly thickened
- May be adherent
- Hyalinization & amyloid
- Synovial Thickening
- Debris in synovial fluid incites phagocytosis by synovial cells
- Breakdown products evoke mild inflammatory response
- Slightly thick membrane

Pain
- Usual presentation
- Insidious onset
- Slow worsening
- May be ill-defined or referred
- Initially mechanical
- Graduate to constant
- Then night pain develops
- Often worst 1st few steps
Stiffness
- Occurs after inactivity
- Becomes constant
- AM stiffness not as prominent as RA
Swelling
- Intermittent from effusion
- Continuous due to capsular thickening or osteophytes
Deformity
- From joint instability
Disability
- Inability to perform ADL

Grade	Description
I	softening & swelling of cartilage
II	fragmentation & fissuring in area > 1.3cm
III	as grade 2 but area > 1.3cm
IV	erosion of cartilage down to bone

Outerbridge Classification

Usually middle-aged woman
Pain, swelling & stiffness in fingers
Characteristic knobbly appearance of IPJ
- From osteophytes & soft tissue swelling
  - Heberden’s Nodes – DIP joints
  - Bouchard’s Nodes – PIP joints
Often affects knees
- Medial & PFJ compartments
May also affect
- Base of thumb
- MTPJ of hallux
- Facet Joints

Early
- Pain relief
- Analgesics
- NSAID
- Local heat
- Rest
- Modify activities
- Rest during flares
- Physiotherapy
  - Maintain ROM
  - Maintain power
  - Load reduction
- Weight loss
- Walking stick
- Avoid of unnecessary stress
- Brace
Intermediate
- Realignment osteotomy
- A/S washout
- SynVisc (hyaluronic acid) ?
Late
- Arthrodesis
- Arthroplasty