Orthopaedic surgeons have long attempted to obtain the maximal stability of their osteosynthesis repair while preserving the soft-tissue environment of the fracture site. As an example, this philosophy has been the basis of the use of compression plating techniques after anatomical reduction and has proven clinically successful for decades. Starting in the mid-80s, a better understanding of the crucial importance of gentle manipulation of soft tissues progressively led surgeons to increasingly rely on indirect reduction techniques during fracture treatment. The acceptance of these new techniques resulted in a paradigm shift, which became the foundation of a new concept known as "biological osteosynthesis." Significant modifications compared to traditional fixation include gentle manipulation of bone fragments using small fragment reduction forceps, no attempt at anatomical reduction, and, last but not least, increasingly limited use of autogenous cancellous bone grafts. The advantages of biological osteosynthesis have been experimentally demonstrated and validated in the dog and include faster bone healing and a decreased number of complications and failures when compared to traditional techniques.

This next step in the evolution of the biological osteosynthesis philosophy led to the development of techniques that could avoid any manipulation of the fracture hematoma. In some instances, only limited "keyhole" incisions, remote to the fracture site, are used to slide a bone plate over the fracture. This sliding plate technique relies on the use of longer bone plates only anchored to the bone via a limited number of screws at each extremity. While this technique heavily relies on minimal disturbance of the biological environment to optimize bone healing, it results in mechanically weaker constructs and should only be used after careful case evaluation. Although clinically rewarding, this technique is technically more challenging. In addition, because the fracture site cannot be visually controlled, a clear appreciation of the 3-dimensional bone geometry as well as spatial limb alignment is indispensable.

While the concept of minimally invasive osteosynthesis (MIO) initially evolved from traditional plating techniques, other implants such as external skeletal fixators and interlocking nails are particularly well suited for this new therapeutic approach. Similarly, the use of MIO techniques in the treatment of diaphyseal fractures has been successfully expanded to the treatment of articular and periarticular fractures. In such cases, however, the orthopaedic surgeon's reliance on intraoperative fluoroscopy becomes even more critical than it is in the treatment of diaphyseal fractures.

Due to the lack of intraoperative visualization associated with closed reduction and fixation techniques, preoperative planning is critical in minimally invasive osteosynthesis (MIO). It begins with the acquisition and interpretation of high-quality orthogonal radiographs of the affected segment, plus in some cases, additional projections such as oblique or stress views to obviate subtle lesions. The main limitation associated with standard radiography is the inability to reproduce the 3-D configuration of structures examined. It is, however, a relatively cost-effective modality that addresses pre- and intraoperative needs in most instances. Advanced imaging is indicated in cases with comminuted fractures involving the periarticular regions or for the assessment of complex structures such as the sacroiliac region in the pelvis. A CT scan is best suited in such cases and provides 2D transverse images and 3-D reconstruction of the affected bone.

To facilitate the osteosynthesis, patient positioning on the surgery table is essential to the smooth execution of the surgical procedure, from fracture reduction, to restoration of alignment, to proper implant position. In each case, the patient position should be evaluated by both the anesthesiologist and the surgeon to prevent anesthetic complications while facilitating the surgical procedure. From a surgical standpoint, the patient should be positioned so as to facilitate all surgical phases including approach and reduction maneuvers, as well as implant insertion and fixation. It must also permit unrestricted C-arm mobility around the patient so that intraoperative views of adjacent joints, in both sagittal and frontal planes, can be easily obtained throughout the surgical procedure. One should bear in mind that poor positioning will impair image accuracy, which in turn may lead to inadequate restoration of alignment and/or improper fracture fixation. Following completion of patient positioning, C-arm mobility is reassessed to ensure that orthogonal views of the joints proximal and distal to the fracture can be obtained. This ultimate preoperative assessment is made before final preparation to allow modification of the position if necessary.

To facilitate reduction, forces may be applied to 1) segments adjacent to or 2) epi/metaphyseal regions of the affected bone. Traction tables and hanging leg techniques are examples of the former and use ligamentotaxis for reduction. Bone reduction forceps applied through small incisions, normograde insertion of an intramedullary rod and application of toothed reduction handles (joysticks) are examples of the latter. The main inconvenience associated with bone reduction forceps is their inability to maintain reduction passively, and the surgeon or an assistant is required to maintain them in position until implant fixation is completed. Conversely, all the other techniques allow continuous traction of the fracture and maintain reduction passively, facilitating implant insertion and fixation. The choice of a particular method is based on fracture location and configuration, and is somewhat surgeon dependent. As a general rule, ligamentotaxis techniques achieve better results in lower (antebrachium and crus) rather than upper (brachium and thigh) segments, while manipulation of the fractured bone is often preferred in fractures involving the humerus and femur. In all cases, the primary goal is restoration of alignment in the sagittal, frontal, and transverse planes including pro-recurvatum, varus-valgus, rotation, and length - all of which may be verified during surgery using intraoperative imaging to minimize unsuccessful attempts at reduction, as they may induce severe iatrogenic trauma. Conversion to an open approach should be considered in cases where adequate, atraumatic restoration of alignment cannot be completed using MIO techniques.

Although biological osteosynthesis techniques do not seek anatomical reduction of the fracture, restoration of limb segment length and alignment in both frontal and sagittal planes, as well as in rotation, are crucial to functional recovery. Simple techniques such as plate pre-contouring using dry bones or contralateral radiographs are strongly recommended, as is multiple, continuous intraoperative assessment of limb alignment whether using intraoperative imaging or locoregional landmarks. While the latter may be feasible for diaphyseal fractures, the former is essential for joint osteosyntheses. Finally, one must keep in mind that while striking a balance between biological and mechanical constraints is the basic principle governing biological synthesis, minimally invasive techniques are not applicable in all cases and are not meant as a substitute to more traditional fixation techniques with visual control of the fracture site and limb alignment.