No. Duraface® half-pins are intelligently designed negative-profile pins. However, based on mechanical testing they outperform currently marketed positive-profile ESF pins of comparable size.
Pin ultimate strength and deflection under load are two key factors involved in determining a pin’s fatigue life. By starting with the geometry of a positive-profile pin and adding shaft diameter while at the same time blending and minimizing the stress riser effect; pin ultimate strength, deformation under load, and fatigue life are all improved. The patented tapered TRO (thread-run-out) technology from IMEX® mitigates the stress riser effect and contributes to the mechanical performance of Duraface® half-pins.
No. A key design feature of these pins was to increase stiffness without changing the pin tract diameter in the bone. As such, the same drill bits used to pre-drill IMEX® Interface® and Centerface® fixation pins are compatible with Duraface® half-pins.
There is no reason not to make the switch. The only negative is past history and experience. For example, technicians and nurses preparing surgery packs, without training on “new” pins may continue to consider shaft diameter as the “pin” size and not look at actual bone engagement diameters. This may lead to pack or ordering errors. It may be best to make a clean switch and not mingle Interface® and Duraface® pins in the same pack.
Bone size is the first consideration when choosing the appropriate fixation pin diameter. If a pin diameter is selected that is too large compared to the corresponding bone, the risk of iatrogenic fracture increases. In cases where increased pin stiffness is desired, the usual approach is to use a larger pin, but again, bone diameter often limits selection of larger ESF pins. So to compare stiffness and fatigue life of pins, it is appropriate to focus on pins that create the same “hole size” in the patient bone. Bone screws have always been defined by thread diameter and ESF pins should as well.
The SK® ESF clamp from IMEX® was designed to function over a greater range of pin diameters than other ESF clamps. The SK® ESF clamp was also designed to grip any pin style (smooth, positive-profile, and negative-profile) effectively. Most other ESF clamps have a much smaller range of pin choices. Clamps that have pin diameter ranges compatible with certain Duraface® half-pins will hold these pins; however, it is likely the surgeon using non-SK® clamps will not have as great a pin diameter choice as with the SK® ESF clamp by IMEX®. This is also true when standard positive-profile pins are used.
Work through the problem just like an Interface® pin. Use a pin gauge and a complimentary wall chart from IMEX®. As discussed in pin history, it is best to consider the thread diameter to determine a pin’s size. Develop a habit of determining Duraface® pins, and for that matter Interface® pins, based on thread diameter. Then compare pin length and thread length on the wall chart as a secondary verification. If you do not have a complimentary IMEX® pin wall chart, please contact us today to obtain one.
When converting to Duraface® pins, the best way to avoid ordering errors is to order by part number. Duraface® part numbers are the same as the corresponding Interface® part numbers except the first two digits are 17 instead of 15. For example, a 3.2/4.0mm Interface® pin is part number 15180 and a 4.0mm Duraface® pin is part number 17180. Both pins have a 4.0mm thread diameter and use a 3.1mm drill bit for pre-drilling. Both can be used in the small or the large SK® clamp.
The patented technology behind the Duraface® pin is quite simple. Most importantly, the Duraface® pin supports simple frames based on half-pin use which is a philosophy that separates IMEX® from other ESF companies. All of this can be achieved without added cost or instrumentation.
Excess frame stiffness is possible with any ESF pin. However, the major cause of excess frame stiffness is the use of multiple full-pins. Full-pins are considered very stiff and with older devices were actually necessary to yield adequate frame stiffness when using weak external bars. IMEX®, with release of the SK® ESF device, was the first to pioneer the concept of simple ESF frames built primarily with half-pins. Use of these half-pin frames creates excess frame strength much less often than constructs containing multiple full-pins. High frame strength is considered appropriate early in fracture repair. Appropriately constructed frames predominately using half-pins are easier to destabilize while allowing the surgeon to place pins in safe corridors more consistently than those based on full-pins. If you have been hesitant to reduce full-pin use, the Duraface® half-pin may be what you have been waiting for.
There are many clinical scenarios where increased pin stiffness and cyclic fatigue life would potentially benefit patient management. Some examples include: short fracture fragments, fractures of the humerus and femur, highly comminuted fractures, transverse fractures, overly active or obese patients, or multiple limb injuries.