Dogs reach skeletal maturity between 5 to 18 months depending on the breed. During this period, all bones exhibit a two-phase growth cycle, an initial rapid phase (20 wk) followed by a substantially slower growth to maturation (48 wk). During the initial part of this biphasic developmental process, both structural and material properties of the immature bone are very different from those of adult bone. Major characteristics are a lower strength and stiffness, lower yield stress and elastic modulus. If we also consider that the diaphyseal cortices in the young dogs are considerably thinner than in the adult, it is intuitive that immature canine bone is potentially susceptible to implant failure due to screw pull out.

Diaphyseal fractures in immature dogs are usually simple low-energy fractures, often incomplete and can be associated with intact paired bones.

Greenstick fractures of the cortex are very common; they are incomplete fractures where only one side of the cortex is fractured while the opposite cortex is bent due to the elasticity and plasticity of the juvenile bone. The intact cortex is along the compression aspect of the fracture. The thick periosteum of immature animals can act as a restraint and stabilizer of the fracture preventing full displacement of the segments. The periosteum also aids in focal hematoma formation, subsequent callus formation and fracture healing. These fractures tend to heal very rapidly due to their strong and very active periosteum.

Clinical Examination

The puppy may be presented with a history of non-weight-bearing or partial weight-bearing lameness. The affected area can show various degrees of deformity, swelling and local pain. Palpable crepitus is usually absent. Careful physical and radiographic examination (orthogonal X-ray views of the affected and contralateral limb) is necessary to complete the diagnosis.

Treatment Options

External Coaptation

In case of minimal deformity and minimal or no displacement, treatment consists of a combination of some form of external immobilization, rest and exercise restriction by cage confinement for 3 to 5 weeks.

Coaptation after traction and reduction can yield good results for suitable diaphyseal fractures.

Cast or splinted bandages require a diligent management to decrease the potential for complications. Depending on the stage and speed of growth of the patient, the cast or splint will require frequent checks and revisions, up to once a week in a very young animal.

Unfortunately, the indications for external coaptation are limited to fractures below the elbow and stifle.

Inappropriate application and incorrect management of external coaptation can lead to a very high rate of complications.

Complete immobilization of the knee in young dogs can result in stiffening of the joint secondary to adhesion formation and quadriceps contracture.

Fracture disease is a syndrome characterized by joint stiffness or laxity, periarticular fibrosis, degeneration of the joint cartilage, osteopenia and muscle atrophy.

Other adverse effects of improperly placed limb splintage are valgus and rotational deformity. Immobilization of the stifle joint should be avoided, particularly in cases of distal femoral fractures to avoid the risk of devastating complications like quadriceps contracture and genu recurvatum. Prolonged immobilization of the hind limb in a non-weight-bearing position causes coxa valga and increased anteversion. Unfortunately, the last two conditions are not reversible.

Coaptation of the antebrachiocarpal joint typically causes palmar carpal ligament laxity and consequent carpal hyperextension. This problem is commonly seen in large breeds and usually resolves spontaneously with controlled exercise. The application of any form of supporting bandages, in the attempt of correcting the hyperextension are inappropriate and should be avoided.

Frequent radiographic monitoring of the healing process is advisable. As soon as radiographic signs of clinical union are visible, coaptation should be removed.

Surgical Options

Early recognition of fracture is essential for a successful treatment of these injuries. Delayed repair will necessitate reduction manoeuvres that can damage the blood supply and disrupt the early callus. The goal of the repair of diaphyseal fractures is normal alignment, whereas anatomic apposition is not a priority because of the potential for compensatory remodelling.

Although fractures in immature skeleton can be treated for the most part as fractures in adults, it is mandatory to bear in mind the associated effects on further growth. Intramedullary pins, cross pins, Rush pins, plates, screws or external skeletal fixation, should be applied as to not interfere or restrict the normal growth at the physes.

Intramedullary Pin (IM Pins)

The use of intramedullary pins is generally limited to femoral, humeral and tibia fractures.

IM nailing in immature animals is favored by the high proportion of cancellous bone present in the medullary cavity. IM pins should be smooth and relatively smaller in diameter than those used in adults. They should not occupy more than 25% of the physeal cross-sectional area and should be inserted perpendicular to the physis to not disturb the growth potential.

Classic IM pinning of the femur through the intertrochanteric fossa has been associated with serious alterations as malformations of the femoral head and neck, coxa valga, hyper-anteversion and coxofemoral subluxation.

External Fixator (ESF)

The principles of application of external skeletal fixation in immature animals follow the same general principles as in the adults. However, the intrinsic stability and rapid healing of the fractures of immature animals favour the use of fixators with a low stiffness configuration.

The thin and relatively soft cortices of immature animals compromise the bone-implant interface for the fixation pins. Fortunately, this does not generally represent a concern as clinical union usually occurs before the ESF failure. Major recommendations in the insertion of the fixator pins are never bridge a physis, avoid thermal necrosis during insertion, avoid insertion into fissures along the bone. For mechanical and biological reasons, the use of external fixation is poorly suited for the treatment of femoral shaft fractures. Due to the anatomical characteristics of the region, the external fixator frame will result in a position, far from the neutral axis of the femur. This remote position will accentuate the bending stresses at the pin-bone interface. The biological consideration is that the transfixion of the muscle groups of the lateral aspect of the thigh generate pain, decrease the range of motion and can result in quadriceps contracture.

Plates

Although fractures of humerus, radius and ulna, and tibia can be successfully treated either with external or internal fixation, plate osteosynthesis remains the treatment of choice for femoral diaphyseal fractures in juvenile dogs, particularly in large and athletic breeds.

In spite of the strict adherence to the classic AO principles, catastrophic implant failure due to screw pull out during the early growth phase has been a commonly reported complication.

The critical evaluation of these failures contributed to the evolution of internal fixation of fractures with a change of emphasis from mechanical to biological priorities. A more flexible fixation encourages the formation of callus while less precise, indirect reduction and minimally invasive techniques reduce the operative trauma.

A biological internal fixation avoids the need for precise reduction, especially of the intermediate fragments, and takes advantage of indirect reduction; it also involves the use of long-span bridging plates (locking or non) and fewer screws for fixation in order to achieve a “flexible fixation.”

The two techniques that suit this requisite are the elastic plate osteosynthesis (EPO) and plate and rod osteosynthesis. Both techniques can be combined either with an “Open But Do Not Touch” approach, in order to preserve the hematoma and decrease the surgical trauma or with minimally invasive percutaneous plate application (MIPO) in an effort to further decrease the postoperative morbidity.

References

1.  Torzilli PA, Takebe K, Burstein AH, Zika JM, Heiple KG. The material properties of immature bone. J Biomech Eng. 1982;104(1):12–20.

2.  Torzilli PA, Takebe K, Burstein AH, Heiple KG. Structural properties of immature canine bone. J Biomech Eng. 1981;103(4):232–8.

3.  Cabassu JP. Elastic plate osteosynthesis of femoral shaft fractures in young dogs. Vet Comp Orthop Traumatol. 2001;14:40–45.

4.  Perren SM. Evolution of the internal fixation of long bones fractures. J Bone Joint Surg (Br). 2002;84(8):1093–1110.

5.  Déjardin LM, Cabassu JP. Femoral fractures in young dogs. AO Dialogue. 2008;3:39–43.