Bone transport over an intramedullary nail. A case report with histologic examination of the regenerated segment.

Bone transport is useful for the treatment of segmental defects, non-union and osteomyelitis. Bone transport has been compared to conventional techniques for the treatment of segmental defects and infection and found to provide better restoration of leg length, to need less cancellous grafting, to have fewer graft fractures and to require less operating time and hospital stay and to have a lower disability [1±3]. When comparing bone transport with cancellous grafting rates of union and infection have been found to be similar [1±3]. Bone transport over an intramedullary nail has been reported in animal studies [4,5] and in small clinical trials [6±9]. There are clear advantages to intramedullary ®xation during bone transport, including improved rigidity of the ®xation construct [8,10]. This has been suggested to be an important mechanical factor for optimal regeneration; other advantages include maintenance of anatomic length and alignment and early removal of the external ®xation system, permitting improved patient mobilisation and muscle function [11]. However, bone transport over an intramedullary nail undermines two of Ilizarov's principles for optimising osteogenesis: preservation of blood supply and preservation of medullary osteogenic tissue, thereby possible compromising the viability of the regenerating segment [12]. Yet, studies using sheep and goat models of distraction osteogenesis over an intramedullary nail do not demonstrate compromise of the regenerating segment [4,10]. Important questions remain regarding viability of the transport segment, the healing pattern of the regenerating segment in humans, the capacity of the endosteum to contribute to primary healing [6] and the observed asymmetry in healing between posterolateral and anteromedial regions of the tibia [4,10]. In this paper a case of intercalary segment bone transport performed over an intramedullary nail for the treatment of a tibial non-union with large segmental bone loss is reported. The radiographic and histologic features of the regenerating segment in a human are described and the in ̄uence of an intramedullary device on distraction osteogenesis during bone transport is discussed.