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What is congenital knee fusion?

The knee joint is sometimes found to be fused at birth due to a developmental disorder. Congenital knee fusion, also called congenital synostosis of the knee, is a very rare condition that alters the structure of the limb and affects function.


Babies with knee fusion are unable to bend the knee (fixed flexion deformity) which may cause difficulties with normal delivery. There is a shortening of the limb as the growth plates at the ends of the bones are absent. Muscular degeneration is usually present. Later in life children have difficulty learning to walk. They may also have associated abnormalities such as fused fingers (syndactyly) or other joint problems.


Limb deficiencies usually develop in the 5th or 6th week after fertilization. In congenital knee fusion, the joint cavity does not form and the thighbone and shinbone fuse together as they develop.

Congenital knee fusion may be associated with:

  • Hereditary factors
  • Viral infection
  • Trauma
  • Exposure to radiation
  • Chemical exposure
  • Deficient blood supply to the area

Poor movement of the joint also interferes with joint development.


Your doctor will review your child’s medical and family history and perform a physical examination of the limb and the rest of the skeletal system. X-rays, MRI and ultrasound studies may be obtained to visualize the knee and other structures. Electrophysiological studies and muscle testing is performed to assess neuromuscular function. Your child will also need evaluation by other specialists. Genetic studies may be recommended.


To treat congenital knee fusion your doctor will initially recommend observation to see how your child grows. Surgery may be performed when your child is 5-6 years of age. This includes limb reconstruction surgery which involves disarticulation of the fused knee, osteotomy (making precise cuts in the bone) and realignment of the bones.