Reconstruction after total sacrectomy using a new instrumentation technique - A biomechanical comparison

Study Design. The stresses exerted on the instrumentation and adjacent bone were evaluated for three reconstruction methods after a total sacrectomy: a modified Galveston reconstruction (MGR), a triangular frame reconstruction (TFR), and a novel reconstruction (NR). Objective. To perform finite-element analysis of reconstruction methods used after a total sacrectomy. Summary of Background Data. When a sacral tumor involves the first sacral vertebra, a total sacrectomy is necessary. It is mandatory to reconstruct the continuity between the spine and the pelves after a total sacrectomy. However, no previous reports have described a biomechanical study of the reconstructed lumbosacral spine. Methods. A finite-element model of the lumbar spine and pelvis was constructed. Then three-dimensional MGR, TFR, and NR models were reconstructed, and a finite-element analysis was performed to account for the stresses on the bones and instrumentation. Results. With excessive stress concentrated at the spinal rod in MGR, there is a strong possibility that the rod between the spine and the pelvis may fail. Although there was no stress concentration on the instruments in TFR, excessive stress on the iliac bones around the sacral rod was above the yield stress of the iliac bone. Such stress may cause a loosening of the sacral rod from the iliac bone. In NR, excessive stress concentration was not detected in the rod or the bones. This reconstruction has a low risk of instrument failure and loosening. Conclusions. If the patient were to stand or sit immediately after MGR or TFR instrumentation, failure or loosening may occur. The NR has a low risk of instrument failure and loosening after a total sacrectomy.