In some old fractures, cartilaginous tissue forms over the fractured bone end with a cavity in between containing clear fluid. This condition is called as -
Pseudarthrosis develop after a fracture that has not united due to inadequate immobilization, i.e. Pseudarthrosis is a type of nonunion.
Inadequate immobilization permits constant movement at the fracture site which hampers the formation of normal callus, and fibroblast forms excessive fibrous tissue in this situation which results in non-union.
If the movement continues to occur at the non-union site, the fracture site develops features of a joint,i.e. Pseudarthrosis:-
Covered by a cartilage (fibrocartilage)
There is synovial lining
Space is filled with synovial fluid like clear fluid
Mobility
Delayed union
Slow union
Nonunion
Pseudoarthrosis