Biomechanical Consequences of High Transverse Hemi-Sacrectomy

Principal Investigator: Michael J. Yaszemski, M.D.
Project Coordinator: Qingshan Chen — chen.qingshan@mayo.edu

Transverse hemi-sacrectomy is sometimes necessary as a curative procedure when dealing with aggressive lesions of the caudal sacrum. The purpose of this study was to determine the biomechanical consequences of transverse hemi-sacrectomy at various levels in a cadaveric model to determine whether complex reconstruction is necessary. Ten cadaveric pelves were placed randomly into 3 groups. Group I (3 pelves) served as a control group, with the sacrum left entirely intact. In Group II (4 pelves), transverse hemi-sacrectomy was performed just caudal to the S1 neural foramina. In Group III (3 pelves), transverse hemi-sacrectomy was performed just cephalad to the level of the S1 neural foramina. Morphometric data was recorded for each of the pelves. The specimens were then tested under compressive loading on a specially designed testing apparatus, which simulates in vivo loading conditions and minimally restricts the bony elements of the pelvis. Video-based motion analysis was used to track the displacement of the iliac wings and sacrum during loading as well. There were no significant differences between the morphometric dimensions of the pelves prior to testing. The average load to failure was 3014N in Group I, 2166 N in Group II and 1045 N in Group III. The average stiffness of the specimens was 353 N/mm in Group I, 222 N/mm in Group II, and 100 N/mm in Group III. All specimens failed due to fractures that occurred along the medial sacral ala. There were no differences between sacro-iliac diastasis, or iliac wing angulation during loading among the three groups. According to our weight bearing criteria, Groups I and II would be able to mobilize postoperatively, while Group III would not.