Evolution of the internal fixation of long bone fractures: The scientific basis of biological internal fixation: choosing a new balance between stability and biology

Abstract

The advent of 'biological internal fixation' is an important development in the surgical management of fractures. Locked nailing has demonstrated that flexible fixation without precise reduction results in reliable healing. While external fixators are mainly used today to provide temporary fixation in fractures after severe injury, the internal fixator offers flexible fixation, maintaining the advantages of the external fixator but allowing long-term treatment. The internal fixator resembles a plate but functions differently. It is based on pure splinting rather than compression. The resulting flexible stabilisation induces the formation of callus. With the use of locked threaded bolts, the application of the internal fixator foregoes the need of adaptation of the shape of the splint to that of the bone during surgery. Thus, it is possible to apply the internal fixator as a minimally invasive percutaneous osteosynthesis (MIPO). Minimal surgical trauma and flexible fixation allow prompt healing when the blood supply to bone is maintained or can be restored early. The scientific basis of the fixation and function of these new implants has been reviewed. The biomechanical aspects principally address the degree of instability which may be tolerated by fracture healing under different biological conditions. Fractures may heal spontaneously in spite of gross instability while minimal, even non-visible, instability may be deleterious for rigidly fixed small fracture gaps. The theory of strain offers an explanation for the maximum instability which will be tolerated and the minimal degree required for induction of callus formation. The biological aspects of damage to the blood supply, necrosis and temporary porosity explain the importance of avoiding extensive contact of the implant with bone. The phenomenon of bone loss and stress protection has a biological rather than a mechanical explanation. The same mechanism of necrosis-induced internal remodelling may explain the basic process of direct healing.

Temporal Variation in Fixation Stiffness Affects Healing by Differential Cartilage Formation in a Rat Osteotomy Model

“…High IFS as estimated in the F and D1 groups with contact of the bony fragments causes bone resorption, which is known from earlier studies on larger animals [31]. As mentioned previously, this might be different when the dynamization is performed late and the already existing callus is reducing the IFM and IFS to uncritical values.…”

“…Histologically, larger IFM leads to the predominance of endochondral ossification with a prolonged chondral phase and later bone formation [16,22,23,25,36,43] and may cause bone resorption at the fragment ends [31]. The bridging of the periosteal and intracortical fracture gaps Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.…”

“…However, these observations did not document how the tissue differentiation in the healing callus is affected by the time of dynamization. In particular, the tissue composition of fibrous tissue and cartilage, as well as possible bone resorption processes due to high interfragmentary strain (IFS) [31], could not be described so far. However, the knowledge of tissue composition would allow a better insight into the process of bone healing.…”

The influence of cyclic compression and distraction on the healing of experimental tibial fractures

“…In general, elastic fixation systems like intramedullary nailing or transcutaneously implanted plates are used to stabilize the main fragments and to regain the anatomical axes of the joint [2,10,15,17]. Early, sufficient callus generation is required to regain stiffness and to prevent fatigue failure of the implants [11,22]. Often, free fragments were left untouched in order to prevent additional vascular damage [17].…”

Infection resistance of unreamed solid, hollow slotted and cannulated intramedullary nails: An in‐vivo experimental comparison

“…Although internal fixation of fractures has evolved in recent years with a change of emphasis from mechanical to biological priorities [24], infection remains an important factor in the long term outcome of fracture treatment, particularly in severe open fractures. The consequences for the patients in case of a postoperative osteomylitis are catastrophic, leading to implant removal, prolonged hospitalization, failure of the implant, possible amputation or even death [12,14].…”