Knee Osteoarthritis - Recon

Introduction

Definition degenerative disease of synovial joints that causes progressive loss of articular cartilage
Epidemiology
- incidence
  - hip OA (symptomatic)
    - 88 per 100,000 per year
  - knee OA (symptomatic)
    - 240 per 100,000 per year
Risk factors
- modifiable
  - articular trauma
  - occupation, repetitive knee bending
  - muscle weakness
  - large body mass
  - metabolic syndrome
    - central (abdominal) obesity, dyslipidemia (high triglycerides and low-density lipoproteins), high blood pressure, and elevated fasting glucose levels.
- non-modifiable
  - gender
    - females >males
  - increased age
  - genetics
  - race
    - African American males are the least likely to receive total joint replacement when compared to whites and Hispanics
Pathophysiology
- pathoanatomy
  - articular cartilage
    - increased water content
    - alterations in proteoglycans
      - eventual decrease in amount of proteoglycans
    - collagen abnormalities
      - organization and orientation are lost
    - binding of proteoglycans to hyaluronic acid
  - synovium and capsule
    - early phase of OA
      - mild inflammatory changes in synovium
    - middle phase of OA
      - moderate inflammatory changes of synovium
      - synovium becomes hypervascular
    - late phases of OA
      - synovium becomes increasingly thick and vascular
  - bone
    - subchondral bone attempts to remodel
      - forming lytic lesion with sclerotic edges (different than bone cysts in RA)
    - bone cysts form in late stages
    - osteophytes form through the pathologic activation of endochondral ossification mediated by the Indian hedgehog (Ihh) signaling molecule
Cell biology
- proteolytic enzymes
  - matrix metalloproteases (MMPs)
    - responsible for cartilage matrix digestion
      - examples
        
        stromelysin
        
        plasmin
        
        aggrecanase-1 (ADAMTS-4)
  - tissue inhibitors of MMPS (TIMPs)
    - control MMP activity preventing excessive degradation
    - imbalance between MMPs and TIMPs has been demonstrated in OA tissues
  - inflammatory cytokines
    - secreted by synoviocytes and increase MMP synthesis
      - examples
        
        IL-1
        
        IL-6
        
        TNF-alpha
Genetics
- inheritance
  - non-mendilian
- genes potentially linked to OA
  - vitamin D receptor
  - estrogen receptor 1
  - inflammatory cytokines
    - IL-1
      - leads to catabolic effect
    - IL-4
    - matrilin-3
    - BMP-2, BMP-5

Classification

Kellgren & Lawrence (based on AP weightbearing XRs)
Grade 0	• no joint space narrowing (JSN) or reactive changes
Grade 1	• possible osteophytic lipping + doubtful JSN
Grade 2	• definite osteophytes + possible JSN
Grade 3	• moderate osteophytes + definite JSN + some sclerosis + possible bone end deformity
Grade 4	• large osteophytes + marked JSN + severe sclerosis + definite bone end deformity

Presentation

History
- identify age, functional activity, pattern of arthritic involvement, overall health and duration of symptoms
Symptoms
- function-limiting knee pain
  - effect on walking distances
- pain at night or rest
- activity induced swelling
- knee stiffness
- mechanical
  - instability, locking, catching sensation
Physical exam
- inspection
  - body habitus
  - gait
    - often an increased adductor moment to the limb during gait
  - limb alignment
  - effusion
  - skin (e.g. scars)
- range of motion
  - lack of full extension (>5 degrees flexion contracture)
  - lack of full flexion (flexion <110 degrees)
- ligament integrity

Imaging

Radiographs
- recommended views
  - weight-bearing views of affected joint
- optional views
  - knee
    - sunrise view
    - PA view in 30 degrees of flexion
- findings
  - pattern of arthritic involvement
    - medial and/or lateral tibiofemoral, and/or patellofemoral
  - characteristics
    - joint space narrowing
    - osteophytes
    - eburnation of bone
    - subchondral sclerosis
    - subchondral cysts

Studies

Histology
- loss of superficial chondrocytes
- replication and breakdown of the tidemark
- fissuring
- cartilage destruction with eburnation of subchondral bone

Treatment

Nonoperative
- non-steroidal anti-inflammatory drugs
  - indications
    - first line treatment for all patients with symptomatic arthritis
  - technique
    - Non-steroidal anti-inflammatory drugs (first choice)
      - selection should be based on physician preference, patient acceptability and cost
      - duration of treatment based on effectiveness, side-effects and past medical history
  - outcomes
    - AAOS guidelines: strong evidence for
- tramadol
  - indications
    - treatment option for patients with symptomatic arthritis
  - technique
    - weak opioid mu receptor agonist
      - good evidence for mid term (8-13 weeks) improvement in pain and stiffness over placebo
  - outcomes
    - AAOS guidelines: strong evidence for
- rehabilitation, education and wellness activity
  - indications
    - first line treatment for all patients with symptomatic arthritis
  - technique
    - self-management and education programs
    - combination of supervised exercises and home program have shown the best results
      - these benefits lost after 6 months if exercises are stopped
  - outcomes
    - AAOS guidelines strong evidence for
- weight loss programs
  - indications
    - patients with symptomatic arthritis and BMI > 25
  - technique
    - diet and low-impact aerobic exercise
  - outcomes
    - AAOS guidelines: moderate evidence for
- controversial treatments
  - acupuncture
    - AAOS guidelines: strong evidence against
  - viscoelastic joint injections
    - AAOS guidelines: strong evidence against
  - glucosamine and chondroitin
    - AAOS guidelines: strong evidence against
  - needle lavage
    - AAOS guidelines: moderate evidence againnst
  - lateral wedge insoles
    - AAOS guidelines: moderate evidence against
Operative
- high-tibial osteotomy
  - indications
    - younger patients with medial unicompartmental OA
  - technique
    - valgus producing proximal tibial oseotomy
  - outcomes
    - AAOS guidelines: limited evidence for
- unicompartmental arthroplasty (knee)
  - indications
    - isolated unicompartmental disease
  - outcomes
    - TKA have lower revision rates than UKA in the setting of unicompartmental OA
- total knee arthroplasty
  - indications
    - symptomatic knee osteoarthritis
    - failed non-operative treatments
  - techniques
    - cruciate retaining vs. crucitate sacrificing implants show no difference in outcomes
    - patellar resurfacing
      - no difference in pain or function with or without patella resurfacing
      - lower reoperation rates with resurfacing
    - drains are not recommended