History of External Skeletal Fixation Pins
Veterinary external skeletal fixation developed around the Kirschner-Ehmer ESF clamp and began with the use of smooth fixation pins typically fashioned from trocar pointed Steinmann pins. Veterinary surgeons quickly discovered the necessity of threaded ESF pins and began to utilize partially threaded Steinmann pins as ESF pins. However, these pins often broke at the thread/non-thread junction and they were not considered to have adequate fatigue strength for veterinary patients. Fully threaded IM pins were then tried in an effort to eliminate the stress riser between the threaded and smooth portions of Steinmann pins, but were deemed not to be of adequate bending strength.
Kirschner Medical then provided the veterinary surgeon with the Ellis™ pin (Kirschner Medical, Timonium, MD). The Ellis™ pin was basically a partially threaded IM pin with a very short length of thread. Theoretically, the short thread length would result in the thread/non-thread junction being placed in the medullary cavity and would thus be shielded from cyclic loading and fatigue failure. The resulting application would result in only the far cortex being engaged with threads and the near cortex being engaged by the smooth portion of the pin. Reports of fatigue failure were reduced but not eliminated. The near cortex was potentially stripped as the threaded/non-threaded junction passed through the wall of the bone, and potential for premature pin loosening was considerable.
Veterinary surgeons then began to search human orthopaedic catalogs for strong pins of appropriate diameter to function with the Kirschner-Ehmer clamp used in many veterinary practices. The Turner Hip Pin (Zimmer) and the Centrally Threaded Traction Pin (Synthes) were two human pins that made their way into veterinary literature. A unique feature of these two human threaded pins is the presence of raised (“positive” or “rolled on”) threads. Clinical performance of these pins was considered excellent, and the “positive thread” design was considered responsible for good fatigue performance combined with adequate bending strength. These pins also provided threaded engagement for both bone cortices. Drilling of a pilot hole for placement of an ESF pin (pre-drilling) then became recognized as highly beneficial in veterinary patients.
The reported performance of these human pins (two cortex, positive thread ESF pins) led to their popularity in veterinary referral centers, but limited size availability and the high cost of human implants limited widespread use of these pins in veterinary patients. IMEX™ Veterinary, Inc. was founded to produce these pins in a variety of sizes appropriate to existing veterinary fixation devices. The resulting INTERFACE™ fixation half-pins and CENTERFACE™ fixation full-pins became available; sized for the small, medium, and large KE clamps at a cost only slightly more than that of single cortex, negative threaded pins. To complement the full versatility of SK™ ESF clamps, INTERFACE™ and CENTERFACE™ pins of intermediate sizes (2.0mm, small-plus, 3.0mm and medium-plus) are now available as well. IMEX™ offers more pin diameters, lengths, and thread choices than any other veterinary orthopaedic company.
Due to the popularity of these threaded pins, IMEX™ now has a selection of more than sixty ESF pins available to the veterinary surgeon, and remains the world leader in veterinary ESF pin technology. Due to the long history of the KE clamp, the terms “small, medium, and large” typically refer to pin shanks of 3/32”, 1/8” and 5/32” respectively.
IMEX™ INTERFACE™ and CENTERFACE™ fixation pins do not feature the thread profile of a bone screw but are designed with the unique environmental and mechanical differences between a bone screw and ESF pin being taken into design consideration. This design stresses long-term performance of the pin-bone interface over acute performance.
All IMEX™ ESF pins are produced from the highest quality, human implant
grade 316LVM material.
