Usually, internal fixation is applied under general anesthesia with the horse in lateral recumbency with the fractured splint bone up.
In cases where fissure fractures of the third metacarpal/metatarsal bone are expected or diagnosed the plate can be applied in standing position with the horse under deep sedation and regional anesthesia.
A longitudinal skin incision of 8-10 cm length is performed directly over the lateral/medial aspect of the proximal splint bone.
Further information on approaches to the splint bones can be found here.
The fibers of the collateral ligament, which inserts on the proximal splint bone need to be split to allow plate and/or screw placement to the abaxial or palmar/plantar surface of the proximal splint bone. Dissection has to be extended to free up the palmaro/plantaro-lateral/medial aspect of the splint bone respectively.
AO Teaching videos
Proximal Fracture of MC IV - 6-hole 3.5 one-third Tubular Plate
2. Plate selection and preparation
A 3.5 mm (narrow) DCP, LC-DCP or LCP, third-tubular plate or reconstruction plate (LCP/DCP) is appropriate in most cases. Usually a 5-hole plate can be used. The distal part of the splint bone becomes very thin, which prevents the use of a longer plate in most horses.
The plate is positioned on the palmaro/plantaro-latero/medial side of the splint bone. Special care must be taken to the orientation and location of the plate, so that at least two screws can be inserted on each side of the fractured zone. In the distal part, the screws need to be very short to avoid protrusion into the third metacarpal/-tarsal bone.
Minimal contouring of the plate is necessary to match the contours of the proximal splint bone. No torsional adjustments of the plate are required. The plate can be bent with either the bending pliers or the bending press.
3. Considerations about screw positioning
Screws may engage only the splint bone (left) or include the near cortex of the third metacarpal/metatarsal bone (right). The fusion of the splint bone with the third metacarpal/metatarsal bone results in joint stability; however, this is not ideal from a physiological standpoint because it eliminates normal micro-movement within the joint and between the splint bone and the third metacarpal/metatarsal bone. Therefore, whenever possible the screws should only engage the fractured bone.
4. Reduction and fixation
Normally, the first reduction can be achieved by digital pressure on the fragments.
Application of the plate
The plate is then applied to the proximal fragment with one screw applying routine technique.
Insertion of the second screw
Before the second screw is inserted correct positioning of the plate is assured. Plate orientation cannot be changed after insertion of the second screw. The plate is fixed to the distal fragment with the help of another screw inserted, in load position, if deemed necessary. Thereby, the fracture is reduced into its anatomical position.
The remaining plate holes are subsequently filled with screws inserted in neutral position. If a plate hole is positioned over the fracture line, the hole is left empty or the screw is inserted at an angle avoiding the fracture plane.
5. Plate fixation with fusion to the third metacarpal/metatarsal bone
Occasionally, one cannot achieve sufficient stability with screws placed in the splint bones only. In such cases inclusion of the palmaro/plantaro-lateral/medial cortex of the third metacarpal/metatarsal bone in the fixation should be considered. It must be kept in mind, that this eliminates normal micro movement within the joint and between the splint bone and the third metacarpal/metatarsal bone.
Dislocation of proximal stump
If the proximal part of the splint bone is not firmly attached to the third metacarpal/metatarsal bone and/or is very short, there is a high risk of dislocation. In such cases, fixation of the proximal stump to the third metacarpal/metatarsal bone can represent a good option to achieve a stable fixation.
6. Alternative: Screw fixation for simple oblique fractures
Screws can only be used in simple oblique and minimally displaced splint bone fractures, because screw fixation alone is generally associated with a relatively high rate of technical failure. The application of a plate is the preferred treatment, however, because it serves as a tension band when fixed also to the distal fragment.
In Warmblood-, Thoroughbred-, Arabian- and American Quarter horses 3.5 mm screws should be used. In small Islandic horses, ponies or foals 2.7 mm screws can be used.
Usually, two screws can be used. If possible, a third screw should be introduced to improve the stability of the fixation.
Example of a postoperative complication with fixation failure. In this case, screws were also inserted into the third metacarpal/-tarsal bone. Screws without a plate are too fractious to achieve stable fixation of the splint bone to the third metacarpal/-tarsal bone.
A bandage is applied for two weeks. Perioperative antibiotics are administered for 3 days postoperatively. The sutures are removed after 10 days.
The horse is kept in a stall for 4 weeks before hand-walking exercises are initiated for another 8 weeks.
Follow-up x-rays are taken 4 and 12 weeks after surgery to evaluate fracture healing. If all looks good, the horse can go back to its intended work.