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 25-28 September, 2018 | Singapore
diameter compared to a similar diameter screw, thus are less likely to break. Bolts also provide superior mechanical behavior compared to screws.
The interlocking nail is placed along the mechanical
axis of the bone. The interlocking nail neutralizes bending, rotational and axial compressive forces due
to incorporation of transfixation bolts or screws which pass through the pin and lock into the bone. This is in contrast to a single intramedullary Steinmann pin which
is only effective in neutralization of bending forces. The interlocking nail has a similar bending strength compared to bone plates, but is slightly weaker in neutralization of torsional forces. The screws also prevent pin migration, a common complication seen with Steinmann pins.
When using an interlocking nail, the largest diameter nail should be selected that can be accommodated by the medullary cavity at the fracture site. In most large dogs, an 8 mm nail and either 3.5 or 4.5mm screws or bolts can be used in the femur and humerus. In medium- sized dogs, the 6 mm nail and either 2.7 or 3.5 mm screws or bolts are typically used. In small dogs and cats, the 4.7 mm nail and 2.0 mm screws are typically used. The tibia of medium and large - sized dogs will usually accommodate a 6 mm nail, but some large dogs will accept an 8 mm nail. Small dogs and some cats
will accept a 4.0 mm nail for repair of tibial fractures. Dejardin et. al. have developed a novel interlocking
nail that provides an angle stable locking mechanism. The advantage of angle stable locking is the elimination of torsional and bending slack, resulting in reduced interfragmentary motion. This interlocking nail system provided comparable mechanical performance to a plate system. Dejardin’s nail is currently available.
Surgical Approach
Bone Grafts
Numerous sites for harvest of cancellous bone graft have been described in the dog, but the most practical are the greater tubercle of the humerus, wing of the ilium and the medial, proximal tibia. The humerus provides the greatest amount of cancellous bone, but the ilium and tibia provide sufficient amounts for most applications. All of these
sites are readily accessible, have easily recognizable landmarks, have little soft tissue covering, and provide relatively large amounts of cancellous bone. The greater trochanter can also be used if other sites are not available; however, the yield of cancellous bone is markedly
less. Occasionally multiple sites are required to harvest sufficient quantities of bone to fill large bone defects or during arthrodesis.
Minimal instrumentation is required for harvest of cancellous bone graft. Basic surgical instruments are used to approach the site selected for harvest. A hole is drilled through the near cortex using either a drill bit, trephine
or trocar-pointed pin. A curette is used to scoop the graft out of the metaphyseal cancellous bone. The cancellous bone should be scooped out in large clumps if possible. Use a curette that can be comfortably manipulated in the medullary cavity; I prefer to use a relatively large curette as this speeds harvest and reduces trauma to the graft. Closure is performed routinely in 2-3 layers. Recently, a technique was described using an acetabular reamer to harvest large amounts of cortico-cancellous bone graft from the lateral surface of the wing of the ilium.
The graft collected should be handled gently. It is desirable to collect the graft immediately prior to usage. This increases the osteogenic properties of the graft.
As graft is harvested, it should be placed on a blood- soaked gauze until transfer to the recipient site. Extreme care should be taken to store the graft properly; do not accidentally discard the graft due to misidentification of the gauze as being used. The graft should be
atraumatically packed into the recipient site. Lavage of the site should be avoided after the graft is placed.
Acknowledgements to Dr B. Beale
Cheal EJ, Mansmann KA, Digioia III AM, Hayes WC, Perren SM. Role of interfrag- mentary strain in fracture healing: ovine model of a healing osteotomy. J Orthop Res 1991; 9: 131-142.
Hulse D, Hyman W, Nori M, Slater M. Reduction in plate strain by addition of an intramedullary pin. Vet Surg 1997; 26: 451-459.
Hulse D, Ferry K, Fawcett A, Gentry D, Hyman W, Geller S, Slater M. Effect of in- tramedullary pin size on reducing bone plate strain. Vet Comp Orthop Traumatol 2000; 13:185-90.
Johnson AL, Egger EL Eurell JC, Losonsky JM. Biomechanics and biology of fracture healing with external skeletal fixation. Compend Contin Educ Prac Vet 1998; 20 (4): 487-502.
Johnson AL, Seitz SE, Smith CW, Johnson JM, Schaeffer DJ. Closed reduction and type-II external fixation of comminuted fractures of the radius and tibia in dogs: 23 cases (1990-1994). JAVMA 1996; 209 (8): 1445-1448.
Palmer, RH. Biological Osteosynthesis. Veterinary Clinics of North America: Small Animal Practice 1999; 29 (5): 1171-1185.
Palmer, RH. Fracture-patient assessment score (FPAS): a new decision-making
tool for orthopedists and teachers. 6 Annual American College of Veterinary
Surgeons Symposium, San Francisco, 1996: 155-157
Closed reduction and stabilization is the optimal method of treatment when possible. Unfortunately, this method
is rarely possible in the senior patient due to the severity of fractures seen, long time until bony union, and the tendency for patients to develop bandage sores. Open surgical approaches can be either traditional or minimally invasive. The minimally invasive approach has also been described as an “open but don’t touch” approach. The acronym, OBDT, is used to describe this technique. The advantages to using an OBDT technique is preservation of vascular supply to the fracture site and thus quicker healing, shorter intraoperative time, less postoperative pain and early return to function. Methods of stabilization that work well with an OBDT approach include the interlocking nail, plate-rod hybrid and external fixation. The key feature of a minimally-invasive approach is the preservation of the soft tissue envelope at the fracture site. Small comminuted fragments will become quickly incorporated into the bony callus if left with a vascular pedicle. Anatomic reduction of small fragments is
difficult if vascular supply to the fragment is to remain uncompromised.

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