136. Biomechanical study of the sacral replacement part as a model for spinopelvic reconstruction following total sacrectomy

Abstract

BACKGROUND CONTEXT Total sacrectomy is usually performed when a sacral tumor involves high-level sacral vertebra. Following total sacrectomy, the continuity between the spine and pelvis is necessary for ambulation, and to enable patients to resume daily living activities sooner during rehabilitation. PURPOSE The aim of this study is to assess the biomechanical properties of a novel spinopelvic reconstruction system following total sacrectomy: a sacral solid porous titanium replacement part manufactured through a rapid prototyping technique (EBM, electron beam melting). STUDY DESIGN/SETTING Biomechanic study. METHODS Three studies were carried out: with finite element methods (FEM), fatigue with a polyamide model, and in cadaver. The following models were compared in the FEM study: (1) two connected rods in L, L3-L5 pedicle screws, and two bilateral iliac screws; (2) Model 1 with no L3 fixation; (3) two connected rods in L, two screws to the L5 body and L3-L5 pedicle screws; (4) Model 3 with no L3 fixation; (5) sacral replacement part connected to the L5 body with two screws and two bilateral iliac screws, pedicle screws in L4-L5, and two vertical rods that connect them to the part; (6) Model 5 with a trans-iliac fixation rod. The L5 (mm) vertical drop, the Von Mises stress (Nm), and stress distribution were assessed. In the other studies, Model 5 was evaluated, checking the existence of errors in the instrumentation. RESULTS The areas of maximum stress were located in the connection between L5 and the pelvis in all the models. No errors were detected in the fatigue with a polyamide model studies nor in cadaver. CONCLUSIONS Significant reductions of tension and vertical displacements were achieved with the sacral replacement part as well as the lowest values published to date; this indicates that the assembly is rigid and stable, preventing the collapse of the spine on the pelvis. With the tensions obtained with the replacement part–112 MPa there is no risk of breaking when exposed to static loads nor fatigue behavior of the implants, as opposed to the other assessed and published models. Once implanted, the replacement part could show good behavior by reconstructing the anterior spine, preventing overloads in the spine or pelvis, increasing fusion rates, potentially reducing the number of check-up surgeries due to instrumental breaking down, and allowing early mobilization of the patient. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.