A Novel Three-Dimensional Computational Method to Assess Rod Contour Deformation and to Map Bony Fusion in a Lumbopelvic Reconstruction After En-Bloc Sacrectomy

Introduction: En-bloc resection of a primary malignant sacral tumor with wide oncological margins impacts the biomechanics of the spinopelvic complex, deteriorating postoperative function. The closed-loop technique (CLT) for spinopelvic fixation (SPF) uses a single U-shaped rod to restore the spinopelvic biomechanical integrity. The CLT method was designed to provide a non-rigid fixation, however this hypothesis has not been previously tested. Here, we establish a computational method to measure the deformation of the implant and characterize the bony fusion process based on the 6-year follow-up (FU) data.Materials and Methods: Post-operative CT scans were collected of a male patient who underwent total sacrectomy at the age of 42 due to a chordoma. CLT was used to reconstruct the spinopelvic junction. We defined the 3D geometry of the implant construct. Using rigid registration algorithms, a common coordinate system was created for the CLT to measure and visualize the deformation of the construct during the FU. In order to demonstrate the cyclical loading of the construct, the patient underwent gait analysis at the 6th year FU. First, a region of interest (ROI) was selected at the proximal level of the construct, then the deformation was determined during the follow-up period. In order to investigate the fusion process, a single axial slice-based voxel finite element (FE) mesh was created. The Hounsfield values (HU) were determined, then using an empirical linear equation, bone mineral density (BMD) values were assigned for every mesh element, out of 10 color-coded categories (1st category = 0 g/cm3, 10th category 1.12 g/cm3).Results: Significant correlation was found between the number of days postoperatively and deformation in the sagittal plane, resulting in a forward bending tendency of the construct. Volume distributions were determined and visualized over time for the different BMD categories and it was found that the total volume of the elements in the highest BMD category in the first postoperative CT was 0.04 cm3, at the 2nd year, FU was 0.98 cm3, and after 6 years, it was 2.30 cm3.Conclusion: The CLT provides a non-rigid fixation. The quantification of implant deformation and bony fusion may help understate the complex lumbopelvic biomechanics after sacrectomy.

Use of a 3D-Printed Patient-Specific Surgical Jig and Ready-Made Total Sacral Endoprosthesis for Total Sacrectomy and Reconstruction

Objective. In the present study, the authors aimed to optimize the workflow of utilizing a 3D printing technique during surgical treatment for malignant sacral tumors, mainly on preparation of patient-specific surgical jigs and ready-made 3D-printed total sacral endoprosthesis. Methods. Three patients with a malignant sacral tumor received total sacrectomy with preoperative design of a patient-specific 3D-printed cutting jig and endoprosthetic reconstruction. Size of ready-made 3D-printed endoprosthesis was determined based on preoperative images, planned surgical margin, and size of the endoprosthesis. A patient-specific cutting jig was designed with a bilateral cutting slot matching the bilateral planes of the implant precisely. The tumor was removed en bloc through a single posterior approach only, being followed by reconstruction with ready-made total sacral endoprosthesis. Results. The mean time for preoperative design and manufacture of the surgical jig was 6.3 days. Surgical jigs were successfully used during surgery and facilitated the osteotomy. The mean operation time was 177 minutes (range 150-190 minutes). The mean blood loss was 3733 ml (range 3600-4000 ml). R0 resections were achieved in all the three cases proven by pathology. Evaluation of osteotomy accuracy was conducted by comparing preoperative plans and postoperative CT scans. The mean osteotomy deviation was 2.1 mm (range 0-4 mm), and mean angle deviation of osteotomy was 3.2° (range 0-10°). At a mean follow-up of 18.7 months, no local recurrence was observed. One patient had lung metastasis 15 months after surgery. Two patients were alive with no evidence of the disease. Conclusions. The patient-specific surgical jig and ready-made 3D-printed total sacral endoprosthesis can shorten the surgical preparation time preoperatively, facilitating accurate osteotomy and efficient reconstruction intraoperatively. The workflow seems to be feasible and practical.

Nerve Root Sparing En Bloc Resection of Sacral Chondrosarcoma: Technical Note and Review of the Literature

BACKGROUND Total en bloc sacrectomy provides the best long-term local control for large primary bony sacral tumors, but often requires lumbosacral nerve root sacrifice leading to loss of ambulation and/or bowel, bladder, and/or sexual dysfunction. Nerve-sparing techniques may be an option for some patients that avoid these outcomes and accordingly improve postoperative quality of life. OBJECTIVE To describe the technique for a posterior-only en bloc hemisacrectomy with maximal nerve root preservation and to summarize the available literature. METHODS A 38-yr-old woman with a 7.7 × 5.4 × 4.5 cm biopsy-proven grade 2 chondrosarcoma involving the left L5-S2 posterior elements underwent a posterior-only left hemisacrectomy tri-rod L3-pelvis fusion. A systematic review of the English literature was also conducted to identify other descriptions of high sacrectomy with distal sacral nerve root preservation. RESULTS Computer-aided navigation facilitated an extracapsular resection that allowed preservation of the left-sided L5 and S3-Co roots. Negative margins were achieved and postoperatively the patient retained ambulation and good bowel/bladder function. Imaging at 9-mo follow-up showed no evidence of recurrence. The systematic review identified 4 prior publications describing 6 total patients who underwent nerve-sparing sacral resection. Enneking-appropriate resection was only obtained in 1 case though. CONCLUSION Here we describe a technique for distal sacral nerve root preservation during en bloc hemisacrectomy for a primary sacral tumor. Few prior descriptions exist, and the present technique may help to reduce the neurological morbidity of sacral tumor surgery.

Radiomics Models for the Preoperative Prediction of Pelvic and Sacral Tumor Types: A Single-Center Retrospective Study of 795 Cases

PurposeTo assess the performance of random forest (RF)-based radiomics approaches based on 3D computed tomography (CT) and clinical features to predict the types of pelvic and sacral tumors.Materials and MethodsA total of 795 patients with pathologically confirmed pelvic and sacral tumors were analyzed, including metastatic tumors (n = 181), chordomas (n = 85), giant cell tumors (n =120), chondrosarcoma (n = 127), osteosarcoma (n = 106), neurogenic tumors (n = 95), and Ewing’s sarcoma (n = 81). After semi-automatic segmentation, 1316 hand-crafted radiomics features of each patient were extracted. Four radiomics models (RMs) and four clinical-RMs were built to identify these seven types of tumors. The area under the receiver operating characteristic curve (AUC) and accuracy (ACC) were used to evaluate different models.ResultsIn total, 795 patients (432 males, 363 females; mean age of 42.1 ± 17.8 years) were consisted of 215 benign tumors and 580 malignant tumors. The sex, age, history of malignancy and tumor location had significant differences between benign and malignant tumors (P < 0.05). For the two-class models, clinical-RM2 (AUC = 0.928, ACC = 0.877) performed better than clinical-RM1 (AUC = 0.899, ACC = 0.854). For the three-class models, the proposed clinical-RM3 achieved AUCs between 0.923 (for chordoma) and 0.964 (for sarcoma), while the AUCs of the clinical-RM4 ranged from 0.799 (for osteosarcoma) to 0.869 (for chondrosarcoma) in the validation set.ConclusionsThe RF-based clinical-radiomics models provided high discriminatory performance in predicting pelvic and sacral tumor types, which could be used for clinical decision-making.

Reconstruction after Subtotal Sacrectomy for Sacral Ewing’s Sarcoma Using Tibial Allograft Strut Grafting: A Case Report

We present the case of a 15-year-old girl. Two months after becoming aware of pain, she was diagnosed with a sacral tumor and referred to our department. She was diagnosed with a sacral Ewing’s sarcoma; after chemotherapy, it was determined that the tumor could be resected, so surgical treatment was performed. The sacrum and ilium were partially resected at the lower end of S1, and the lumbar vertebrae and pelvis were fixed with a pedicle screw and two iliac screws on each side of L3, and the sacral resection was reconstructed with a tibial strut allograft. No tumor recurrence or metastasis has been observed 1 year postoperatively. She developed bladder and rectal dysfunction, but she remained independent in activities of daily living and her daily life was not limited. The bone fusion in the reconstructed area confirmed the lack of instrumentation looseness. Surgical treatment for sacral Ewing’s sarcoma was performed to cure the patient. We believe that the tibial allograft contributed to the patient’s ability to walk on her own due to its high mechanical stability. Postoperative bone healing was observed with the same material, suggesting that the tibial allograft is useful for similar procedures.