Biological and biomechanical basis of long-bone diaphyseal fractures: from fracture to non-union

Bone healing of diaphyseal fractures is a complex biological process that can often be adversely affected by patient-related and fracture-related factors and eventually end in delayed union and non-union. Surgical and non-surgical approaches have been widely applied, according to the fracture pattern and patient characteristics. For humeral diaphyseal fractures, plate fixation provided excellent results in terms of healing rate and time to union. For femoral and tibial shaft fractures, locked intramedullary nailing is considered the technique of choice. If impaired, the reparative process after intramedullary nailing can be enhanced through different surgical techniques, such as dynamization or exchange nailing. Moreover, the mechanical stability of the fracture site can be improved through augmentation plating, bone grafting or external fixation techniques, with satisfactory results. This article aims to review the biomechanical principles of reparative osteogenesis in long bone fractures after conservative and surgical treatment. Moreover, the evidence on the current options for bone healing enhancement, and treatment and prevention of delayed union and non-union will be discussed.