Modern ESF Pin Terminology
by IMEX Veterinary
For many years, external fixation pin use centered around the Kirschner-Ehmer (KE) external fixation device and newer modifications of it. This resulted in potentially confusing pin terminology that is poorly suited to the use of improved external fixation devices such as the IMEX SK external fixator. Modern, accurate terminology will clear up potential ordering errors and provide educators with a consistent vocabulary to train students, residents and practitioners. These changes will greatly simplify future pin discussion as well.
Using the medium KE clamp and a 3.2 mm (1/8”) smooth pin as a common example, note that the term “medium” continues to be used for smooth pins, negative-profile pins and positive-profile pins, regardless of the fact that each creates a significantly different size and shape of pin tract in the patient’s bone. Since veterinarians were forced into using Kirschner terminology, a 3.2 mm shaft positive-profile pin continued to be called a 3.2 mm (1/8”) pin even though the thread diameter engaging the bone is actually 4.0 mm.
Bone screw diameters are defined by the thread diameter of the screw regardless of the screw head diameter and it is logical to use the same terminology with external fixation pins. In other words, the portion of the implant that limits diameter choice is the portion that is implanted into bone, not the portion outside of the bone.
An example of a customer order using historic terminology for a positive-profile ESF pin might be:
“I want to order a 3.2 mm (1/8”) Interface pin” or “I used a 3.2 mm (1/8”), medium, positive-profile pin.” This pin has a 3.2 mm (1/8”) shaft and 4.0 mm thread diameter. The word “medium” is often associated with either description.
An example of a representative customer order or inquiry for a 3.2 mm (1/8”) Interface positive-profile, medium pin, based on modern terminology would be:
“I want to order a 3.2/4. 0 mm Interface pin” or “I used a 3.2/4.0 mm positive-profile pin.” The term medium could be included with either description but is not necessary as mentioning both the shaft and thread diameters eliminates any potential for error while accurately providing both the shaft diameter, and more importantly, the thread diameter.
A likely ordering conversation using proper modern terminology for a “medium” Duraface pin might be:
“I want a 4.0 mm Duraface pin” or “I need a medium, 4.0 mm Duraface pin.” Since the shaft and thread diameters of Duraface pins are the same, it is not necessary to discuss the pin as a 4.0/4.0 mm Duraface pin.
FIGURE 1 | Images depict identical thread diameters while illustrating different shaft diameters
Note both the medium, 3.2/4.0 mm Interface and the medium, 4.0 mm Duraface pin both have the same thread diameter engaging the bone and utilize the same 3.1 mm drill bit for predrilling. Discussing shaft diameters only, the term “medium” can be confusing.