Definition of Union after Acute Fracture and Surgery for Fracture Nonunion of the Scaphoid

The carpal scaphoid is a challenging bone, which has intrigued generations of hand surgeons. Its shape, alignment and size render it difficult to image. In most fractures of the skeleton two radiographic images taken in perpendicular planes are all that are required to define its anatomical attributes such as the line of the fracture, comminution and displacement. Furthermore, most fractures heal with external callus formation, and its presence assists in the diagnosis of union. Finally, malalignment or loss of position can be identified. In fractures near joints the surgeon relies on the fact that the fracture position has not altered significantly since the previous assessment in order to infer the state of union as it is uncommon to see callus formation on radiographs. For these fractures, such as those at the distal radius, in the early stages after the injury no surgeon could categorically state that the fracture had ‘united’. The scaphoid bone presents additional problems in that, as most of it is intraarticular, no external callus is expected or seen, nor is any obvious evidence of remodeling anticipated. Furthermore, because of its small size and oblique orientation, assessment of any displacement at the fracture site during treatment is extremely difficult to identify. It is therefore almost impossible to state, in the early period, whether the break across the scaphoid has joined. The term ‘‘union’’ is intriguing as in most studies on fracture union, particularly the scaphoid, it is used as if the state is clearly defined and can be easily identified. This is far from the truth. The term ‘‘union’’ is used as if the fracture has two states: it has either healed or not healed. The only other state is ‘‘delayed union’’ which is a diagnosis that can only be made in retrospect after union is certain. Union, the restoration of bony architecture across the fracture site, is a physiologic process, which occurs continuously from the instant that the fracture occurs till the end of bone remodeling. At this stage the structure has resumed its previous function, as far as it is likely to. The stiffness of the ‘‘uniting bone’’ is a function of time and the adequacy of the healing process. In this process the structure, at some stage, has healed to an extent that most of the previous function can be performed within the physiological limits of the new bone. This state, when some function can be resumed with little risk of adversely influencing healing, is judged as ‘‘clinical union’’. The state of ‘‘clinical union’’ is altered by any intervention to stabilize the bone, such that function of the part is