Fig. 10.

Classifications scheme for tibial tuberosity fractures.^12,18–21 The Watson-Jones classification groups tibial tuberosity fractures into three types: type I, a small fragment with superior displacement; type II, a larger fragment involving the secondary centre of ossification and the proximal tibial epiphysis; type III, a fracture that passes proximally and posteriorly across the epiphyseal plate and proximal articular surface of the tibia (Salter–Harris type III). Ogden provided two further sub-classifications: type I, when only the distal portion of the tuberosity is injured; while type IA is a fracture through the tuberosity ossification centre with mild anterior displacement of the fragment, in type IB the fragment is separated from the metaphysis and may or may not also be separated from the rest of the secondary ossification centre. Type II injury involves the cartilaginous junction between two secondary ossification centres and usually leads to avulsion of the tuberosity ossification centre with variable involvement of the proximal tibial ossification centre. In type IIA, the tuberosity segment may fracture (usually a compression–impaction mechanism) at the juncture of the main tibial and tuberosity ossification centres. In type IIB, the fracture line propagates through a variably sized anterior portion of the proximal tibial ossification centre. Type III injuries involve significant separation of the fragments and propagation of the fracture line into the articular surface. Type IIIA is a unitary fracture while type IIIB is a comminuted fracture. Type IV is an avulsion of the entire tuberosity and proximal tibia epiphysis. Type V, as described by Mackoy, is an Ogden type III fracture associated with a Salter–Harris type IV fracture of the proximal tibia.