Depending on the breed, dogs reach skeletal maturity between 5 months (toy breeds) and 18 months (giant breeds) through a very rapid, biphasic growth rate. During the initial growth phase, both structural and material properties of immature bone are considerably different from those of adult bone and are characterized by lower strength and stiffness, as well as lower yield stress and elastic modulus. In addition, the diaphyseal cortices are considerably thinner in young dogs compared to adults. As a result, immature canine bone is highly susceptible to implant failure via screw pullout. In addition, due to the rapid initial growth phase and the natural flexion angle of the elbow and knee, postoperative immobilization of these joints in young dogs will ineluctably result in ankylosis secondary to adhesion formation and muscle contracture. For the hind limb, it has been documented that this so-called "fracture disease" leads to irreversible loss of function even after a few days of immobilization. To prevent this debilitating complication, early controlled postoperative mobilization is essential, which in itself represents a real challenge in hyperactive, non-leash-trained puppies.

Surgical Options

External Fixation

The use of external fixation is poorly suited for the treatment of humeral or femoral shaft fractures in young dogs for several mechanical and biological reasons. The remote position of the external fixator frame away from the neutral axis of the bone accentuates the bending stresses at the pin/bone interface, which becomes an even greater stress riser. This poor biomechanical configuration promotes early failure via implant pullout even with use of positive cancellous profile transosseous pins. From a biological standpoint, the transfixation of the thigh or arm musculature generates postoperative pain, precludes free range of motion (ROM) at the knee or elbow, and routinely results in loss of ROM.

Intramedullary Nailing

Regardless of the osteosynthesis technique chosen, physes must be preserved at all cost. This absolute requirement renders the use of normograde intramedullary devices, such as pins or interlocking nails, ill-advised during the first, rapid growing phase. As an example, classic intramedullary nailing via the intertrochanteric fossa has been associated with dramatic alterations of the femoral head and neck anatomy including coxa valga, hyper-anteversion, small malformed femoral head, short thin femoral neck and coxofemoral subluxation.

Plate Osteosynthesis

Due to the shortcomings of intramedullary nailing and external fixation techniques, plate osteosynthesis remains the treatment of choice for diaphyseal fractures in juvenile dogs. However, the strict adherence to the classic AO principles of anatomical reduction and rigid internal fixation during the early growth phase routinely results in catastrophic implant failure via screw pullout. The critical evaluation of these failures has led to the development of a new biological, elastic plate osteosynthesis technique (EPO) better suited for the treatment of diaphyseal fractures in puppies. The technique relies on the increased overall compliance of the bone/plate construct to reduce the risk of focal failure of the screw/bone interface. We have been using EPO in conjunction with minimally invasive surgical strategies (MIS) such as restoration of alignment rather than anatomical reconstruction and percutaneous sliding plate techniques to further decrease postoperative morbidity and optimize functional recovery.

Elastic Plate Osteosynthesis

Fractures are repaired with Veterinary Cuttable Plates (VCP - Synthes) applied via a routine approach specific to the bone being treated. The fracture hematoma is not removed because of its favorable effects on healing. The plate is applied according to the principles of bridge plating (use of longer plate and fewer screws). Indirect fracture reduction is accomplished by traction on the distal fragment with small fragment forceps and/or by means of the plate. Sometimes the tip of a small forceps is used to realign a large fragment or an oblique fracture, but without attempting a precise reduction. Since anatomical reduction is not attempted, restoration of the bone length is achieved by determining the appropriate plate length from radiographic views of the contralateral intact bone. The plate is cut to the desired length according to the anticipated position of the screws in relation to the growth plates. The screws are placed in the two most proximal and the two most distal holes of the plates. Cortical 2.0-mm or 2.7-mm screws are inserted without tapping. Two adjacent screws should always be oriented in diverging planes in order to increase resistance to pullout. Closure is routine.

With this technique, the preservation of the strong periosteal sleeve, in conjunction with the use of an undersized implant (VCP), allows controlled motion at the fracture site, which in turn promotes rapid bone healing via callus formation. The flexural deformation of the bone/plate construct is achieved, in part, by controlling the working length of the implant (i.e., the central section of the plate devoid of bone screws). The central plate span without screws should be as long as possible and include no less than 3 consecutive empty screw holes. This screw distribution increases the working length of the plate and therefore its compliance. As a result, it decreases the stress riser effect of a single empty screw hole, thus reducing the risk of implant fatigue failure. Similarly, the overall increase in compliance of the repaired bone/plate construct reduces bone/screw interface stresses, which limits the risk of implant failure via screw pullout.

The outcome of elastic fixation using 2.0 and 2.7 Synthes VCPs has been evaluated by Cabassu (VCOT 2001) in a series of 24 consecutive juvenile femoral fractures. The working length of the plates encompassed from 7 to 20 adjacent empty holes. All plates were secured via two proximal and two distal cortical screws inserted without tapping. Clinical union occurred as early as two weeks and was achieved in all cases by four weeks postoperatively. Implant failure, whether from screw loosening or plate plastic deformation or fracture, was not found. In most cases, callus remodeling could be observed after two months, and bony union was achieved by four months. Diaphyseal growth was undisturbed and consistently occurred without loss of alignment or anatomical deformation of either epiphysis.

Minimally Invasive Techniques

Minimally invasive [percutaneous] plate osteosynthesis (MI[P]PO) was recently combined with elastic fixation in an effort to further reduce postoperative morbidity. As with traditional "open but do not touch" approaches, restoration of alignment is achieved via small bone forceps. Using the craniocaudal radiograph of the contralateral bone, the VCP is cut to length, then bent proximally to follow the bone contour. The contoured plate is then slid epiperiosteally from either direction and secured to the proximal and distal metaphyses. Since the fracture site is not exposed, it is beneficial to verify proper alignment via intraoperative fluoroscopy. By virtually eliminating exposure of the fracture site, this approach helps preserve the fracture hematoma, a critical step in enhancing bone healing. In addition, it minimizes damage to the soft tissues (muscles, fascia, and periarticular retinaculum), thus reducing scar tissue formation and promoting early use of the fractured limb. Both factors have been shown to be greatly beneficial in children and are likely to show similar advantages in young dogs.

Postoperative Care

Although weightbearing and ROM are recommended immediately after surgery, high-impact activities (jumping, rough play), while difficult to truly control, should be avoided. In contrast, physical activities such as leash walking, trotting, and swimming or wading are beneficial. Professional physical rehabilitation using an underwater treadmill is rarely needed in puppies that are naturally active.

One must keep in mind that the single most important factor contributing to the success of this new surgical approach (EPO) to diaphyseal fractures in immature dogs is the higher construct compliance, which reduces the risk of screw pullout. Second, by promoting rapid bone healing and by minimizing iatrogenic soft tissue injuries, the use of minimally invasive techniques (MIPPO) optimizes early functional recovery.