The Fixin Implant System

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The Fixin Implant System

Kevin P. Benjamino and Massimo Petazzoni

The Fixin system differs from other locking systems because it is a locking screw‐insert (bushing)‐plate construct [14]. Locking is achieved between the screwhead and the bushing by a conical coupling locking mechanism. The bushing is an intermediary insert that screws into the plate and couples with the screwhead (Figure 8.1). Fixin screws have a 1.0° and 1.5° (large and mini system, respectively) conical head that will lock into a corresponding tapered cone within the bushing [24]. The screw‐bushing coupling is achieved by friction, micro‐welding, and elastic deformation between the screwhead and the bushing insert [1, 2] (Figure 8.2). An advantage of the screw‐bushing‐plate construct is that it allows for an easier option if the implant needs to be removed, as opposed to both nonlocking and locking screw to plate interfaces. In other systems, if the screw has deformed (cold welding) to the screw hole or the screwhead does not engage the screwdriver, many times the screw cannot be removed without cumbersome methods such as burring the screwhead. If the screwhead is no longer able to engage the screwdriver the bushing‐screw complex can be removed with the bushing extractor. The bushing construct also allows for even force distribution over the screwhead. If the screw hole is not filled with a screw, the bushing still maintains even force distribution, decreasing the risk of plate failure over this site, in comparison to previous plate designs (dynamic compression plates, combination locking compression plates, etc.). The addition of the bushing increases the screws resistance to shear forces and also allows for a thinner plate design overall. With the bushing–plate construct, the bushings allow for the plate design to be decreased in thickness and of comparable strength to other, thicker locking plate systems. Due to the decreased thickness, the plate allows for more elasticity (elastic deformation), which promotes earlier callous formation around the fracture or osteotomy and earlier clinical and radiographic union. Also, a thinner plate design allows for less irritation and impingement on surrounding soft tissue structures (proximal tibia, distal tibia, carpus, tarsus, and other distal extremities) [24].

3D Illustration of a plate, a conical-shaped head with bushing, a transverse section of bushing revealing conical-shaped head, transverse-section of plate revealing head of screws, and plate with screws (left–right).

Figure 8.1 Note the conical‐shaped head within the bushing that is threaded into the plate. The coupling/locking mechanism is engaged via divergent angles.

(Source: Courtesy of Massimo Petazzoni.)

3D Illustration with a plus sign between (a) a plate lacking with one bushing and (b) a bushing with an equal sign of (c) a plate composed of 6 bushing. (d) A plate with a bushing extractor and has a clockwise direction.

Figure 8.2 This demonstrates the plate and bushing combination. D refers to the designated bushing extractor for ease of replacing or removing the bushings.

(Source: Courtesy of Massimo Petazzoni.)

8.1 Fixin Implants and Instrumentation

8.1.1 Standard and Mini Fixin Systems

The plates are constructed of AISI 316LVM stainless steel, the bushing inserts and screws are composed of titanium alloy Ti‐6Al‐4 V, and the screws are self‐tapping. As noted, the Fixin system combines two different metals, providing a titanium‐to‐stainless‐steel interface. While historically there has been concern for the occurrence of galvanic corrosion when two different types of metal are combined, recent studies have demonstrated that this does not occur between titanium and stainless steel. In one study, which evaluated galvanic corrosion in different interfaces (stainless steel to stainless steel, stainless steel to titanium, and titanium to titanium) during cyclic loading in saline, it was shown that the stainless‐steel‐to‐titanium interface had less evidence of corrosion than the other interfaces [5]. In another study evaluating cyclic loading in serum, the mixture of metal implants did not cause metal release or loss when compared to a single metal construct, further demonstrating the safety of titanium‐to‐stainless‐steel interface [6].

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Jun 13, 2021 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on The Fixin Implant System
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