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Continued Evolution of ESF Pins 

by IMEX Veterinary

The mainstay of external fixation in North America and much of the world for many years was the Kirschner-Ehmer (KE) device, and because of its long history, fixation pin development and terminology were centered on pins for use with that clamp.

Fixation pins evolved from smooth pin, to negative-thread, to single cortex negative-thread, to positive-profile threaded fixation pins. IMEX was the first company to market positive-profile pins sized to all three KE clamps and has developed many additional diameter and length choices since.

As positive-profile pins such as the Interface and Centerface became routinely utilized, increased pin longevity and decreased patient morbidity were attributed to these modern pins. However, difficulty using positive-profile pins when combined with the KE clamp led to development of new external fixation devices to simplify their use. Unfortunately, the historical dominance of the KE clamp and pins developed for it inhibited development of even better fixation pins and related devices. Four historical errors associated with positive-profile pins developed for the KE device that inhibited improvements in ESF technology include:

  • Allowing positive-profile pins to dictate future pin development
  • Allowing positive-profile pins to define ESF pin terminology
  • Assuming that positive-profile pins are inherently superior to other thread profiles
  • Allowing positive-profile pin dimensions to dictate future clamp design

The SK ESF device overcame these mistakes by supporting both positive and negative thread profiles while allowing a variety of pin diameters to function with each clamp size. Ultimately, breaking free of these historical assumptions led to the development of Duraface ESF pin technology. Although a negative-profile pin, the Duraface pin achieves mechanical improvements when compared to positive-profile pins of the same thread size by increasing shaft diameter and attenuating the thread/non-thread junction with a tapered thread-run-out feature (U.S. Patent #8,282,676). These changes in pin geometry result in increased mechanical performance outlined below.

Bending Stiffness Comparison of External Rods Chart

FIGURE 1 – Duraface Mechanical Attributes | Duraface fixation half-pins contrasted to our legendary Interface® half-pins demonstrate:

Griffin H, Toombs JP, Bronson DG, et al. Mechanical evaluation of a tapered thread-run-out half-pin designed for external skeletal fixation in small animals. Vet Comp Orthop Traumatol 2011; 4: 257-261.