Biomechanical stability of magnesium plate and screw fixation systems in LeFort I osteotomy: a three-dimensional finite element analysis.

Background: Titanium (Ti-6Al-4 V) is used for fixation in LeFort I osteotomy, a procedure for treating midface deformities. This study assessed the biomechanical stabilities of two Mg alloys (WE43 and ZK60) as biodegradable alternatives and compared them against Ti using finite element analyses. The LeFort I osteotomy procedure was simulated, and various plate and screw configurations were tested. The maximum principal and peak von Mises stresses in the metal plates and bone screws were measured under four load conditions, and the stability was evaluated.

Results: The holes in the Mg screws, as compared with the Ti counterparts, exhibited higher and lower stress levels in the cortical and cancellous bones, respectively. The Mg screws also exhibited a higher fracture risk. The ZK60 plate, as compared with the Ti and WE43 plates, exhibited a lower fracture risk under all load conditions. ZK60 exhibited higher biomechanical stability in terms of maintaining the gap between osteotomy surfaces and lower fracture risk; the osteotomy surfaces with Ti im-plants underwent bone impaction, resulting in gap closure.

Conclusions: Although the Mg implants exhibited better stress distribution, their screw strength requires improvement. Appropriate improvements can promote the use of Mg alloys in bone fixation applications.