The Kirschner Ehmer apparatus is most commonly used as a type-I or type-II fixator. A type-I fixator engages the two cortices of one mandibular branch and a type-II fixator engages both branches. Fixation with a type-II fixator provides for better stability and should be used whenever possible.
Fixation pins come in several different varieties and lengths.
Smooth transfixation pins (a)
Threaded negative profile transfixation pins (b)
Threaded positive profile transfixation pins (c)
Positive-profile threaded pins have higher strength and better pin-bone interface stability; pins with a diameter of approximately 4 mm are used in the horse. Partially threaded pins are preferred in type-I fixators.
Fractures of the interdental space and horizontal ramus are almost always open fractures. Wound debridement and flushing is extremely important. Nevertheless, infections of soft tissues as well as the bone are common. Therefore, establishment of ventral drainage is important.
In older or infected fractures, wound débridement is important. All infected bone must be removed with a curette or rongeur. Additional flushing is indicated.
4. Surgical technique
The fracture is reduced manually. Once the pins are placed, they aid in reduction.
A small stab incision is made at the intended pin location and the holes for the pins are predrilled.
Note: Care must be taken to continuously cool the drill bits to prevent thermal tissue damage.
If possible, two pins are used on each side of the fracture.
Application of clamps and connecting bar
Pins are connected by clamps to an external connecting bar. The use of clamps and the connecting bar helps in the reduction of the fragments until proper alignment is reached.
Once alignment is achieved, the clamps are tightened to the pin and the connecting bar.
All pins as well as external bars are shortened and padded to prevent them from getting caught on objects in the horse’s environment.
Alternatively, a tension band wire is applied around the pins and tightened to achieve interfragmentary compression of the fracture. A piece of plastic or rubber hose material can be placed over the protruding ends of the fixation pins and filled with polymethylmethracylate to maintain the relationship of the transfixation pins.
During the post-surgical period, the horse is confined to stall rest for one week. They should be housed in smooth walled stalls. Mangers, grates and gate latches represent hazards to the horse fitted with an external fixator. The horse should be fed from the floor with soft fiber feed stuff; firm feed such as hay cubes, apples or carrots should not be fed. Crossbars may be bandaged or the horse fitted with a padded recovery hood to protect the fixator from entrapment and disruption. Antibiotics and anti-inflammatory drugs are given for 3 to 5 days or longer, if required, especially in open fractures. Daily pin track care is recommend to prevent infection. Follow up radiographs are taken at about 8 weeks after surgery. Once the fracture is healed, the fixator is removed with the horse under slight sedation.