VetFix System (Clamp-Rod Internal Fixator)
State of the art treatment of long bone fractures in animals mandatesas in human medicinethat a wide variety of implants are available around the clock. Therefore, a versatile system, requiring only a minimum of instruments and implants, has been desperately sought. In the late nineties, the AO Development Institute in Davos in conjunction with the Expert Group of AO VET (VEEG), the veterinary section of the AO Foundation, initiated the development of the VetFix System. The following requirements for the new system were set by the VEEG: simple in its design, user friendly, costs within an acceptable range, and available in different sizes. The VetFix system consists of a round, roughened stainless steel rod with a longitudinal laseredged line. The rod accepts special symmetrical clamps that slide onto it to any desired position. The clamps can be rotated to either side of the rod to accept cortex screws of the desired length (Fig 1). The VetFix System, manufactured from the same implant quality stainless steel as used for the Dynamic Compression Plates, was developed in the following four sizes (named after the cortex screws that they accept): 4.5/5.5, 3.5, 2.7, and 2.0 mm (Fig 2). End clamps were developed to prevent the bar moving within the clamps (Fig 3). At the moment, only the 3.5, 2.7, and 2.0 mm systems exist for small animals.
Discussion
The VetFix provides a free arrangement of clamps that enables the surgeon to choose the screw position according to the fracture configuration and the bony contours. A recent comparison of two 4.5/5.5 mm VetFix systems using six and ten clamps respectively on a rod of the length of the broad 10 -hole DCP revealed no significant differences in stiffness and strength. This range allows the surgeon to concentrate on the fracture situation and choose the clamp setup that is the most appropriate for the situation.
The clamps were tested in a separate mechanical test setup comparing smooth and roughened (sand blasted) rod surfaces under dry and moistened conditions. Their holding power was tested in rod rotation and pull out and compared to each other. On the basis of these results, the best combinations were chosen for serial production. The VetFix System may be contoured to the surface of the bone in all directions at the same time.
The VetFix System allows compression between fragments only by using lag screw technique. Direct axial compression of the fracture cannot be achieved with the VetFix System. It is used as a neutralization fixation. The VetFix is similar to a so-called biological fracture fixation system, which represents state of the art fracture treatment in humans and is also widely accepted in small animal trauma surgery. The VetFix is a low contact internal fixation system that is thought to maintain superior blood supply to the periosteum underneath the implant.
Using a rod in connection with the clamps makes the VetFix a more voluminous implant than any of the corresponding DCP implants. The diameter reaches its maximum over the clamps, which may increase soft tissue irritation. Preliminary observations in this respect based on fascia and skin closure, showed no strenuous skin tension when the humerus, radius, femur, or tibia were treated. In the metacarpal/metatarsal area, skin closure may lead to moderate tension.
The AO Veterinary Expert Group decided on the name VetFix: Clamp-Rod Internal Fixator (CRIF).
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