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Knee Arthritis

  • Osteoarthritis (OA) of the knee (gonarthrosis) is a degenerative joint disease
  • Leads to progressive loss of articular cartilage

Epidemiology

  • Knee is the most common joint affected in OA

Etiology/Risk factors

  • Increasing age
  • Female sex
  • Obesity
  • Occupational knee stress
  • Metabolic syndrome – central obesity, dysplipidemia, hypertension

Pathoanatomy

  • Abnormalities in the articular cartilage
    • Increased water content
    • Decreased level of proteoglycans
    • Loss in collagen organisation
  • Synovium and capsule
    • Early phase of OA – mild inflammation in the synovium
    • Intermediate phase of OA – moderate inflammation and hypervascularity of the synovium
    • Late phase of OA – increased thickness and vascularity of synovium
  • Bone              
    • Remodelling of subchondral bone – forms lytic lesions with sclerotic edges
    • Bone cysts

Pathophysiology

  • Basic mechanism – imbalance between matrix metalloproteases (MMPs) and tissue inhibitors of MMPs (TIMPs)
  • MMPs are proteolytic enzymes – responsible for degradation of extracellular matrix proteins
    • Examples of MMPs – stromelysin, plasmin, aggrecanase-1
    • MMP synthesis is stimulated by cytokines released by the synovium – IL-1, IL-6, TNF-alpha
  • TIMPs inhibit MMP activity and prevent excessive degradation

Classification – Kellgren and Lawrence Classification

  • Grade 0 – no joint space narrowing or reactive changes
  • Grade 1 – possible osteophytic lipping, doubtful joint space narrowing
  • Grade 2 – definite osteophytes, possible joint space narrowing
  • Grade 3 – moderate osteophytes, definite joint space narrowing, some sclerosis and bone deformity
  • Grade 4 – large osteophytes , marked joint space narrowing, severe sclerosis and bone deformity

Clinical features

  • Knee pain – causes functional limitations to the patient
  • Knee stiffness
  • Sensation of locking and/or crunching of joint
  • Antalgic gait – knee is maintained in flexion
  • Baker’s cyst
  • Decreased range of motion
  • Malalignment of the knee  – can be varus (bow-legged) or valgus (knock-kneed) depending on whether the medial or lateral compartment are affected

Diagnosis

X-ray
  • Joint space narrowing
  • Osteophytes
  • Eburnation
  • Subchondral sclerosis and cysts

Treatment

  • NSAIDs – first line
  • Lifestyle modifications – weight loss, physiotherapy

Operative

  • High-tibial osteotomy – for younger patients with medial OA
  • Unicompartmental knee replacement – if OA affects just one compartment
  • Total knee replacement – can be cruciate retaining or cruciate sacrificing
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