Congenital pseudoarthrosis of the tibia, or anterolateral bowing of the tibia with congenital dysplasia, describes abnormal bowing that can progress to a segment of bone loss simulating the appearance of a joint. The condition is usually apparent shortly after birth and rarely diagnosed after age two.

Terminology

The recommended term is anterolateral bowing of the tibia with congenital dysplasia (c. 2025). While the term congenital pseudoarthrosis is widely spread, true pseudoarthrosis is rarely present at birth. Instead, the patient is born with tibial dysplasia and deformity, which will eventually fracture and develop the pseudoarthrosis ⁶.

Pathology

The aetiology is unclear, however, up to 80% ^4,5 of cases are associated with neurofibromatosis type 1 (NF1), in which there is a loss of activity of the protein neurofibromin causing defective differentiation of osteoblasts ⁵. Overall, 10% of patients with NF1 are diagnosed with tibial pseudoarthrosis.

Fibular, ulnar, and radial pseudoarthroses can also occur, but much less frequently, and usually only in patients with NF1.

The Crawford and Schorry classification system is commonly used to describe this condition.

Radiographic features

• progressive bowing (usually anterolateral in the tibia)

• resorption of a short segment of bone

  • usually at the site of maximal bowing

  • usually between mid and distal one-third of the shaft

• angulation at the site of absent bone segment

• often mimics the appearance of a joint

  • cupping of the bone proximal to the absent section

  • sharpened narrow appearance of the distal bone

• often fracture or bowing of accompanying bone (fibula with tibia, radius with ulna)