The goal of any fracture treatment is rapid and complete restoration of limb function. Stable realignment of bones and restoration of a full range of motion in the joint are necessary for complete limb function. Osteosynthesis attempts to achieve this goal by open reduction and internal fixation using implants. For many years surgeons were fascinated by impressive pictures of direct bone healing. Too often, this was accomplished at the expense of extensive surgical tissue trauma by forcing precise reduction. Perfect anatomical reduction, however, is not necessary in diaphyseal fractures. This knowledge, which was available to our surgical forefathers, underwent a renaissance in the 1990s when radiographic monitoring of perfectly reduced diaphyseal fractures revealed an increased frequency of complications, including infection, delayed union and implant failure.

Some bacterial contamination occurs during any type of surgery. The fate of this contamination depends largely on the viability of the tissues. With the aim of placing as little stress as possible on fracture healing, diaphyseal fragments need not be replaced precisely, but rather can be reduced indirectly with distraction of the main fragments, which are then held in place by muscle tension. In this manner, the fracture zone remains untouched within the soft tissue envelope.

Fixation may be limited to splinting the bone. Interfragmentary compression is not mandatory in diaphyseal fractures. The main fragments are stabilized by a buttress plate, an internal fixator, an interlocking nail, intramedullary pinning and/or external skeletal fixation.

Buttress Plate

As few screws as possible are placed close to the fracture. Larger fragments are incorporated into the repair site by means of lag screws only in cases in which this can be done without detaching the bone pieces from surrounding muscles. A long plate, extending to the joint, is employed and attached peripherally to the main fragments using two or, preferably, three or four screws. Unused screw holes remaining in the middle of the plate are not deleterious to the implant construct. They distribute bending forces and allow slight movement in the fracture zone, which is a good stimulus for callus formation. However, the plate must be sufficiently strong because it has a weight-bearing role until the callus is adequately developed. In cats and small dogs, plates of 2.4 or 2.7 mm screw size have proven successful, while 3.5 mm plates are good for medium-sized dogs and 4.5 mm plates are used for larger breeds. For very large heavy dogs, 4.5 lengthening plates without screw holes in the middle section provide adequate stability. When it is anticipated that the available plate may not resist expected high stress levels, a plate/rod combination can be used to bear the load. In order to minimize perfusion interference of the bone under the plate, narrow or special plates with limited bone contact are preferred.

The Association for the Study of Internal Fixation developed the dynamic compression plate (DCP) further to create the low-contact dynamic compression plate (LC-DCP), which took into consideration vascularization and even distribution of the stiffness of the implant. This established a trend, in which the prototype, the point contact fixator (PC-Fix), was used to develop plate systems with angular stability, referred to as internal fixator. Screws with threaded heads placed at right angles into threaded holes allow placement of the plate such that a small gap is maintained between it and the periosteum, preserving periosteal perfusion. The advantage of locked screws, which have been used for some time in Unilock implants for jaw fracture repair, is high pull-out resistance. In the most recent generation of plates, the locking compression plates (LCPs), the screw holes accept conventional screws in the normal fashion, or locking screws. Evidence-based studies are necessary to determine whether the advantages of angle-stable fixation systems are worth the high price in veterinary patients.

Clamp Rod Internal Fixator

The Clamp Rod Internal Fixator (CRIF) is a system similar to an internal fixator but is more feasible financially. Originally designed for biological osteosynthesis of long bone fractures in animals, it has since been used for other indications in osteosynthesis. The CRIF system consists of round stainless steel bars, which are contoured and screwed to the bone using special clamps that are slid onto the rod to any desired position. By tightening the screws, the clamps become compressed, fixing them firmly to the bar, and the entire system to the bone. Clamp sizes fit 2.0, 2.7, and 3.5 mm AO standard screws, and available rod diameters are 2, 3, and 5 mm. The CRIF is a simplified version of a similar system used in human spine surgery and offers variability in the length of the implant, similar to cuttable veterinary plates and also to reconstruction plates. In contrast to other systems, the superior stiffness characteristics of the CRIF ensure good support even in comminuted long bone fractures. The CRIF system offers outstanding contouring properties which makes it suitable for curved bones. Furthermore, it does not need to be contoured perfectly to the bone because the clamps, which can be diverted freely, usually compensate for insufficient contouring. This feature permits minimally invasive treatment of long bone fractures via short incisions at the proximal and distal ends. The reduced contact area, limited only to the clamp surfaces, enables the maintenance of good blood supply to the periosteum, which makes this implant particularly useful for infected fractures or revisions of non-unions or mal-unions.

Interlocking Nail

As an alternative to plate or CRIF reconstruction, the medullary cavity may be splinted by a pin. Here, the biological principle is maintained because the medullary cavity is not reamed and a small-diameter pin is used. Interlocking nails prevent rotation, changes in the axis and bone shortening. Callus formation is more pronounced than after plate fixation.

If open reduction is required in this procedure, the fragments must be left in the envelope of soft tissue. The pin is usually locked distally and proximally with two transverse screws or bolts on either side. For dynamization, the locking implants are removed on one side.

Intramedullary Pin

When Steinmann pins are used, support and rotational stability can be achieved by also using an external skeletal fixator. For this, a threaded Kirschner wire is placed peripherally in each main fragment and then fastened to a connecting bar with clamps. Dynamization is produced by removing the external fixation device before the fracture callus has consolidated to bone.

External Skeletal Fixation

Fractures distal to the elbow and stifle joints with multiple fragments are also suitable for external skeletal fixation. External fixators may also be used for segment displacement when dealing with major bone deficits. In this technique, the bone is transected at a distance from the defect, and the callus forming at this location is distracted until the bone ends make contact. Unlike conventional techniques, which sometimes require multiple bone transplantations, bone shortening and large deficits can be remedied by callus distraction in one operation. The rate of distraction is crucial and must not exceed 1 mm per day. It should be continuous (0.017 mm/24 min) or distributed over four extensions of 0.25 mm each. To conserve the medullary vasculature, a corticotomy is carried out, although an intact nutrient artery is not an absolute prerequisite for the development of distraction callus regeneration.

Many of the described aspects in this paper apply mainly to diaphyseal fractures. Anatomically precise reconstruction is still mandatory for joint fractures.

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