servation of joint function. To accomplish these goals, external casts or splints must sometimes be used in the postoperative period or at least during recovery from anesthesia. Anesthetic recovery can be a critical time in the early treatment of a horse with a fracture, and protection of the animal and the reconstructed fracture is of paramount importance. Casts are often used to help ensure a safe recovery. Concern for preservation of the animal and its operated extremity has resulted in specialized recovery techniques such as the raft/pool recovery system.
Healing of bone itself does not ensure full functional rehabilitation. Failure of bone healing, however, does ensure failure of functional rehabilitation. Therefore, healing of bone is the first criterion for the rehabilitation of an afflicted animal.
Success in fracture treatment is measured according to expectations. Some injuries are so severe that they are lifethreatening. In such cases, just saving an animal's life to allow it to be pasture sound may be a success. In other cases, the animal will be expected to perform at levels equal to or surpassing those of its former status. Here, fracture fixation and bone healing constitute only a small part of the total rehabilitation process. Further efforts will be required to bring the horse back to its former athletic prowess. Truly successful fracture treatment must involve the whole animal and reach beyond the gains made in the operating theatre.
Success in fracture treatment is measured against preoperative expectations.
1.7 References
1. Nunamaker DM, Richardson DW, Butterweck DM (1991) Mechanical and biological effects of plate luting. J Orthop Trauma; 5:138–145.
2. Young DR, Richardson DW, Nunamaker DM, et al. (1989) Use of dynamic compression plates for treatment of tibia diaphyseal fractures in foals: Nine cases (1980–1987). J Am Vet Med Assoc; 194:1755.
3. Nunamaker DM, Richardson DW, Butterweck DM, et al. (1986) A new external skeletal fixation device that allows immediate full weightbearing: Application in the horse. Vet Surg; 15:345.
4. Nunamaker DM, Richardson DW (1992) External skeletal fixation in the horse. Proc 37th Annual Convention of Am Assoc Equine Pract; 549.
5. Perren SM (1979) Physical and biological aspects of fracture healing with special reference to internal fixation. Clinical Orthop; 138:175.
6. Cheal EJ, Mansmann KA, DiGioia III AM, et al. (1991) Role of interfragmentary strain in fracture healing: ovine model of a healing osteotomy. J Orthop Res; 9:131–142.
1.7.1 Online references
See online references on the PEOS internet home page for this chapter: http://www.aopublishing.org/PEOS/01.htm
David M. Nunamaker
2.1.1 Drilling and tapping holes in bone
2.5 Mechanics of plate fixation
2.5.1 Contouring and prebending
2.1 Screw fixation
Screw fixation is a technique that is at the heart of internal fixation using AO techniques. Screws can be used in a variety of ways to stabilize bone fragments and to secure plates to bone.
2.1.1 Drilling and tapping holes in bone
Screws are inserted into bone through drill holes. Drilling is an important process since it helps determine the nature of the bone-screw interface. Use of a hand brace or drill may cause the operator to drill oval holes due to drill bit wobble. Power drilling is recommended and combined with the use of appropriately sized drill guides, will help prevent the drilling of oval holes.
Drill hole quality is also dependent on the drill bit itself. A good sharp drill bit that is designed for use in bone should drill at a rate of 1 mm/s. Sharp drill bits are necessary for drilling in bone. Drilling rates slower than 1 mm/s may be related to a dull bit or the accumulation of swath material in the drill bit's flutes that prevent further penetration and increase heat production. Drill bits may become dull instantly when they strike a metal surface as can occur when drilling into a previously placed screw. A sharp bit can drill through more than 1 meter of bone before it becomes dull. Dull bits should be discarded. Resharpening is not recommended for large animal surgeries because the drill bit accumulates cyclic fatigue in rotational bending as it is being used. Older drill bits are therefore more easily broken than new ones.
Older drill bits break more easily due to fatigue accumulated in rotational bending.
Increased pressure on the drill bit improves efficiency, but can cause bending.
Power drilling results in a round, symmetric hole.
Use a sharp drill bit, and drill at a rate of 1mm/s.
Periodically