Keep skin incisions away from the intended location(s) of plate(s).
1.3 Precise anatomic reconstruction
Interfragmentary compression creates large “normal” (rectangular) forces.
Axial and rotational alignment must be preserved at the time of fracture reduction.
Interfragmentary compression occurs whenever two fracture surfaces are pressed tightly together.
Use bone grafts as a replacement for early bridging callus.
Normal function in the horse depends upon anatomic reconstruction of fractures and joint surfaces. Slight malalignments in the reconstruction of a fractured bone can lead to significant deviations in foot position and leg conformation in this long-legged species. It is important that axial and rotational alignment are preserved at the time of fracture reduction.
Comminuted fractures may make anatomic reconstruction more difficult since many small fragments may no longer be salvageable. Length, axial, and rotational alignment can be maintained using interfragmentary screws. Voids in the bony cortex are filled with a cancellous bone graft. The grafts are used wherever possible because they cause formation of an early structural bridge. This can be important in preserving the integrity of the internal fixation.
Cancellous bone grafts can be used as a kind of callus replacement over potentially weak areas of the reconstruction; stable internal fixation may limit natural callus formation.
Nowhere is anatomic reconstruction more important than in the case of a fractured joint. Here, even a small step or incongruity in the surface may lead to degenerative joint disease and associated loss of function. When dealing with displaced fractures, direct visualization is essential for adequate reduction. Intraoperative image intensification or radiographic monitoring can help ensure reduction but the images obtained can be misleading.
1.4 Stable fixation
Interfragmentary compression is at the heart of internal fixation using screws and plates.
Fig. F1A: Creating large “normal forces” upon the fracture plane is the main objective of interfragmentary compression.
Interfragmentary compression creates large normal forces (forces perpendicular to the fracture planes) that prevent movement of the individual bone fragments (Fig. F1A). These large normal forces in turn create large frictional forces that prevent sliding of the fracture fragments over each other. Although usually thought of as being achieved only with the use of lag screws, interfragmentary compression occurs whenever two fracture surfaces are pressed tightly together. For instance, it occurs when plates are used to compress the surfaces of a transverse fracture or osteotomy (Fig. F1B). This axial compression is often combined with interfragmentary compression produced by individual lag screws in fractures that have transverse and oblique components (Fig. F1C). When fractures are treated with casts or splints, healing occurs with motion and callus formation. Relative motion between individual fragments fixed with screws or with screws and a plate may be detrimental to fracture healing.
Fig. F1B: A plate applied to the reduced fracture provides axial compression.
Fig. F1C: A combination of plate axial compression and interfragmentary screw compression in a comminuted fracture.
Large gaps seem less sensitive to small amounts of motion than small gaps. This observation can be explained by the fact that equal amounts of motion in small gaps and large gaps represent a different percentage of that gap. Healing tissues can only stretch so far before they rupture. As healing progresses and motion decreases the tissue's ability to stretch diminishes as well, i.e. from granulation tissue to cartilage to bone. Theoretical and experimental studies have explored this phenomenon which has been termed interfragmentary strain [5, 6].
Since interfragmentary strain may influence fracture healing, relative motion should be controlled by the internal fixation and special attention must be given to small gaps that may be subject to delayed healing or non union due to micromotion. These small gaps may also increase the risk of implant failure through the cyclic loading that occurs during weight bearing.
Combine axial compression produced by a plate with interfragmentary compression produced by a lag screw.
Interfragmentary strain may influence fracture healing.
Small gaps may also increase the risk of implant failure through cyclic loading.
1.5 Soft tissue considerations
Adequate vascularity of soft tissues and bone is very important.
Nutrient vessels and periosteal soft tissues provide a blood supply to the bone.
Adequate vascularity of soft tissues and bone is important if fracture healing is to occur. Most equine fractures are high energy events with bone literally exploding into the surrounding soft tissues. This initial trauma may devitalize the soft tissues as well as the bone. Bone receives its blood supply by way of its nutrient vessel and periosteal soft tissue attachments. Much of this blood supply may be interrupted at the time of the fracture. While the nutrient vessel is almost always compromised, the integrity of the periosteal blood supply can be difficult to assess prior to surgical intervention. This makes open reduction and internal fixation a risky technique since avascular tissue will be at a higher risk for necrosis and infection. Further loss of blood supply to the bone may occur due to the exposure necessary for open reduction and implant placement. Proper evaluation of soft tissue viability will influence the outcome of postoperative complications, such as infection and wound dehiscence. Adequate first aid and preoperative care are essential for the preservation of the remaining blood supply following injury.
Whenever possible, internal fixation using lag screws should be accomplished under radiographic control through stab incisions to minimize additional soft tissue compromise. This is usually performed for nondisplaced fractures. Sometimes additional stab incisions can be used for the insertion of screws even when open approaches are used for visualization and reduction. As an alternative to expansion of the primary incision, this technique serves to limit the necessary exposure. Soft tissues should always be protected during drilling and tapping by the use of drill guides and tap sleeves.
The need for open reduction and internal fixation must be balanced by its risks. Experience with this paradox in the horse will help define each surgeon's abilities and limitations.
Avascular tissue will be at a higher risk for necrosis and infection.
Anesthetic recovery can be a critical time.
The need for open reduction and internal fixation must be balanced by its risks.
1.6 Functional rehabilitation
As stressed