Biomechanical analysis of reduction malarplasty with L-shaped osteotomy

Reduction malarplasty with L-shaped osteotomy is widely used for surgical correction of prominent zygoma and bilateral zygomatic asymmetry. One of the keys to this surgery is the formation of the greenstick fracture on the root of the zygomatic arch. However, the greenstick fracture cannot be seen directly both in the postoperative x-ray films and three-dimensional computed tomography images, and it is unknown how the greenstick fracture forms biomechanically. So it is of great concern to both the doctors and patients whether the greenstick fracture can really take place on the root of the zygomatic arch. This study focused on the biomechanism and deformation effects of the surgery by using the method of finite element (FE) analysis.

Computed tomography data of 2 patients with prominent malar complex were obtained for three-dimensional reconstruction. The FE models of the zygomatic complex with L-shaped osteotomy were established by using Mimics via thresholding, segmentation techniques, and material properties assignment with gray value conversion. Then simulations including the boundary conditions and the forces of the surgery were performed in ABAQUS.

The FE models have fine quality; the first one contains 63,053 units and 100,995 nodes, and the other one contains 70,238 units and 136,219 nodes. Under the loading of pressures, the zygoma and the zygomatic arch inward have deformation displacement. Maximum stress concentration was found just at the root of the zygomatic arch.

A appropriate zygomatic pressure will generate a stress concentration to form the greenstick on the root of the zygomatic arch. This study can help surgeons understand and conduct the reduction malarplasty with L-shaped osteotomy from a biomechanical insight.