Biomechanical analysis of fixation methods for bone flap repositioning after lateral orbitotomy approach: A finite element analysis.

OBJECTIVE: In ophthalmic surgery, different materials and fixation methods are employed for bone flap repositioning after lateral orbitotomy approach (LOA), yet there is no unified standard. This study aims to investigate the impact of different fixation strategies on orbital stability through Finite Element Analysis (FEA) simulations of the biomechanical environment for orbital rim fixation in LOA. METHODS: A Finite Element Model (FEM) was established and validated to simulate the mechanical responses under various loads in conventional lateral orbitotomy approach (CLOA) and deep lateral orbital decompression (DLOD) using single titanium plate, double titanium plates, and double absorbable plates fixation methods. The simulations were then validated against clinical cases. RESULTS: Under similar conditions, the maximum equivalent stress (MES) on titanium alloy fixations was greater than that on absorbable plate materials. Both under static and physiological conditions, all FEM groups ensured structural stability of the system, with material stresses remaining within safe ranges. Compared to CLOA, DLOD, which involves the removal of the lateral orbital wall, altered stress conduction, resulting in an increase of MES and maximum total deformation (MTD) by 1.96 and 2.62 times, respectively. Under a horizontal load of 50 N, the MES in FEM/DLOD exceeded the material's own strength, with an increase in MES and MTD by 3.18 and 6.64 times, respectively, compared to FEM/CLOA. Under a vertical force of 50 N, the MES sustained by each FEM was within safe limits. Bone flap rotation angles remained minimally varied across scenarios. During follow-up, the 12 patients validated in this study did not experience complications related to the internal fixation devices. CONCLUSION: Under static or physiological conditions, various fixation methods can effectively maintain stability at the orbitotomy site, and absorbable materials, with their smoother stress transmission properties, are more suited for application in CLOA. Among titanium plate fixations, single titanium plates can better withstand vertical stress, while double titanium plates are more capable of handling horizontal stress. Given the change in the orbital mechanical behavior due to DLOD, enhanced fixation strength should be considered for bone flap repositioning.

Initial implementation of surgical guide design utilizing digital medicine for lateral orbital decompression surgery.

This study aimed to assess the feasibility of utilizing a surgical guide, designed through digital medical technology, in lateral orbital decompression surgery. METHODS: In total, 18 patients with thyroid-associated ophthalmopathy (TAO), who underwent orbital balance decompression surgery at the Affiliated Eye Hospital of Nanchang University between September 2018 and August 2022, were included. Orbital CT scanning was performed on all patients with TAO, and Mimics 21.0 software was used to reconstruct a three-dimensional model of the orbit based on the CT data. The osteotomy guide plate for lateral orbital decompression surgery was designed using 3-matic 13.0 software, adhering to the criteria of surgical effectiveness and safety. The surgical positioning guide was designed using Geomagic Wrap 21.0. Once printed, the surgical guide was sterilized with low-temperature plasma and applied during surgery. Of the nine patients treated using a surgical navigation system, three cases experienced cerebrospinal fluid leakage complications during the procedure, and two exhibited inadequate bone removal along the lateral wall. In contrast, among the nine patients treated with surgical guides, no intraoperative cerebrospinal fluid leakage or evidence of insufficient lateral wall bone removal was observed, highlighting a statistically significant distinction between the two cohorts (p = 0.046). Postoperative improvements were notable in best-corrected visual acuity (BCVA) and exophthalmos for patients afflicted with extremely severe TAO. The surgical guide, designed with digital medical technology, has been shown to be an effective and secure auxiliary tool in lateral orbital decompression surgery. It not only aids in reducing the incidence of intraoperative complications, but also enhances the accuracy and safety of surgery. These improvements offer robust support for continued exploration in this field within clinical practice.