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. 2022 Jun;16(3):512-520.
doi: 10.14444/8258. Epub 2022 May 19.

Sacral Prosthesis Substitution as a System of Spinopelvic Reconstruction After Total Sacrectomy: Assessment Using the Finite Element Method

Morales-Codina Ana María  1 , Martín-Benlloch Juan Antonio  2
Affiliations

Sacral Prosthesis Substitution as a System of Spinopelvic Reconstruction After Total Sacrectomy: Assessment Using the Finite Element Method

Morales-Codina Ana María et al. Int J Spine Surg. 2022 Jun.

Abstract

Background: 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. Reconstructing spinopelvic stability after a total sacrectomy is a challenge that has not yet been overcome. Thus, the objectives of the present study are as follows:Establish a new system of reconstructing the spinopelvic region after a total sacrectomy using a rapid prototyping technique to design the sacral replacement pieces.Evaluate the biomechanical properties of this system.Study a new reconstruction system for the spinopelvic joint that reduces reconstruction failures after total sacrectomy, reducing postoperative complications and allowing early sitting and standing of these patients.

Methods: A sacral replacement implant was designed according to an authentic clinical case of a patient who had undergone a total sacrectomy. Using the finite element method, a biomechanical study was carried of 2 reconstructions that had been performed using the new prosthetic. The results of the study were compared with 4 other reconstruction models.

Results: A maximum von Mises stress of 112 MPa and a vertical displacement of -0.13 mm in L5 were observed in the models of the sacral implant that had been generated. A maximum rigidity of 861.5 Nm/mm was observed in the models when assuming a reduction in rigidity of more than 85% with respect to the other models assessed. In all models, maximum tension was concentrated in the rods joining L5 with the screws anchored to the pelvis.

Conclusions: The sacral prosthesis substitution after a total sacrectomy produced a profound reduction in stress in the instrumentation and the bone structure as well as smaller vertical displacement, the lowest values ever reported. These results indicated that the assembly was rigid and stable and would prevent the collapse of the spine in the pelvis. According to stress values, the replacement piece was not likely to rupture as a consequence of static load or implant fatigue.

Keywords: biomechanics; finite element analysis; spinopelvic reconstruction; spinopelvic stabilization; total sacrectomy; tumors of the sacrum.

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Conflict of interest statement

Declaration of Conflicting Interests: The authors report no conflicts of interest in this work.

Figures

Figure 1
Figure 1
Clinical case. During the initial surgery, reconstruction was performed according to model 2 (A). After 5 mo, the rods broke at the fusion site of the L5 pedicle screws and the proximal iliacs (B). A second reconstruction was subsequently performed on the basis of model 4 (C).
Figure 2
Figure 2
Sacral prosthesis substitution.
Figure 3
Figure 3
Finite element models.
Figure 4
Figure 4
Stress distributions resulting from application of loads in the finite element models.
See this image and copyright information in PMC

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