Introduction

Osteoarthritis (OA) of the knee is very common and is a leading cause of disability worldwide. It results from the loss of cartilage at the knee joint and is often accompanied by degeneration of the underlying bone. Inflammation is not usually involved.

Epidemiology

  • Incidence: 750.00 cases per 100,000 person-years
  • Peak incidence: 70+ years
  • Sex ratio: more common in females 1:1
Condition Relative
incidence
Osteoarthritis of the knee1
Septic arthritis in adults0.02
Pseudogout0.01
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Risk factors:
  • Female
  • Obesity
  • Previous trauma to the knee e.g. meniscal and ligament damage
  • Polyarticular hand OA

Clinical features

Features:
  • Knee pain: this is exacerbated when walking up inclines or when standing from a sitting position
  • Varus deformity (valgus deformity is rare with knee OA)
  • Joint line tenderness
  • Joint line bony swelling (osteophytes)
  • Crepitus
  • Quadricep wasting due to reduced muscle activity
  • Fixed flexion deformities

Investigations

Investigations:
  • X-ray of the knee: signs include joint space narrowing and osteophyte formation. There is a wide variability in the correlation between radiological signs and clinical features.
  • Arthroscopy: useful for evaluating early cartilage changes e.g. fissuring, surface erosion