Cheng Liming

Finite Element Analysis of Pelvic Reconstruction Using Fibular Transplantation Fixed with Rod-Screw System After Type I Resection

The purpose of this study is to investigate the stability and the stress distribution of pelvic reconstruction using fibular transplantation combined with rod-screw system fixation after type I resection. A total pelvic finite-element model including the lumbar-sacral spine, proximal femur was constructed. Three- dimensional finite element models of different implants including fibula, rod and screw were constructed using ways of solid modeling. Then various reconstructed finite element models were assembled with different finite element implant model and type I resected pelvic finite element model. The load of 500 N was imposed vertically onto the superior surface of L3 vertebra body, and the pelvis was fixed in bilateral leg standing positions. Finite- element analysis was performed to account for the stress distribution on the bones and implants. The pelvis displacement of the different rod-screw fixation methods and the maximum equivalent stress (max EQV) on all nodes and element were figured out to evaluate the advantages and disadvantages of different reconstructive methods. Stress concentration was found in the fibula after force loading if the internal fixation were not used. After the internal fixation was implanted, stress concentration in the fibula was decreased. Stress concentration was also found in the implants, especially in the connection sites between screw and rod. The best stable fixation method after fibula transplantation is L5S1HR (the double rods plus L5-S1 pedicle screws and ilium screws fixation). According to the stability and stress concentration, the method of L5-S1HR fixation combined with fibula transplantation is better than other fixation methods in pelvic reconstruction after type I resection.

Vasculogenic Mimicry in Osteosarcoma : Histomorphologic Studies in Vivo and in Vitro

This study was to examine whether there is evidence for vasculogenic mimicry in osteosarcoma. In vivo and in vitro studies were conducted. Studies using hematoxylin and eosin (HE) stain and CD31 immunohistochemical stain to observe the micro vascular channels in human osteosarcoma specimens were performed. Osteosarcoma cell lines (U-20S) were also tested in vitro for their ability to form tubular networks in three- dimensional culture containing type I collagen. The structures of the tubular networks were observed with phase contrast microscope and transmission electron microscope (TEM). Morphometric observation using HE stain and CD31 immunohistochemical stain showed that tumor cell-lined channels were detected in vivo in osteosarcoma; By comparison, all vascular areas in the pedicel of osteochondroma or outside osteochondroma were endothelial-lined. Morphometric Observation with light microscope and TEM showed that highly aggressive osteosarcoma cell lines (U-20S) formed networks containing channels when grown in three-dimensional culture containing type I collagen, in the absence of endothelial cells or fibroblasts. These observations strongly suggest that aggressive osteosarcoma cells may generate vascular channels that facilitate tumor perfusion independent of tumor angiogenesis and have the ability of vasculogenic mimicry.