Reconstruction With A Novel Suspended,Modular,and 3D-Printed Total Sacral Implant After Resection Of Sacral Giant Cell Tumor

ObjectiveTo investigate the efficacy and safety of spinopelvic reconstruction based on a novel suspended,modular,and 3D-printed total sacral implant after total piecemeal resection of a sacral giant cell tumor with the preservation of bilateral S1-3 nerve roots via a posterior-only approach.MethodsFive patients who had undergone total piecemeal resection of SGCT involving upper sacral segments(S1 and S2)and the midline with the preservation of bilateral S1-3 nerve roots via a posterior-only approach between September 2017 and July 2018 were retrospectively reviewed.A novel suspended,modular,and the 3D-printed total sacral implant had been used for reconstruction.This series included two female and three male patients,with a mean age of 42.2 years(range,31-53 years).All patients came to our hospital because of persistent pain in the low back or sacrococcygeal region.Two cases had radioactive pain in the buttocks,perineum,or unilateral or bilateral lower extremities.One patient had unilateral lower limb weakness.One patient had hypoesthesia in the sellar region.The sacrococcygeal masses could be palpable in 4 cases.The masses could be palpated in the anterior sacral region by digital rectal examination in 4 cases.One case had progressive sacral nerve compression.One patient had difficulty in urinating and defecating.All patients underwent plain radiography,CT,and MRI to identify the form,location,and size of the tumor and its relationship with surrounding structures.All tumors were located in the S1 vertebrae and below.S1-4 were involved in two patients;S1-3 were involved in three patients;The largest tumor volume is 10.0cm*8.0cm*6.0cm,the smallest one is 6.0cm*4.0cm*3.0cm.MRI revealed presacral soft tissue masses in four patients.There is no obvious calcification in the soft tissue mass.The tumor did not cross the sacroiliac joint and invade the ilium.The tumors all showed osteolytic destruction.All patients who underwent CT-guided needle biopsy and histologic examination showed giant cell tumors of the bone.Denosumab was administered subcutaneously at a dose of 120 mg twice a month before surgery.The sacral implant was designed as a patient-specific structure.CT images were exported to the software to reconstruct a 3D rendering.After osteotomy planes were determined,the customized implant was designed using 3D design software according to the shape of the bone defect.The implant consisted of two modules that are connected by a sleeve device with serrated teeth locked by a screw.The ends of the two wing-parts form inverted U-shaped structures hooking the bilateral iliac crest which are fixed by two cancellous bone screws through two nail paths.There are two multiaxial screw heads situated on the back of the implant for connection to lumbar vertebrae with titanium rods.The implant consisted of three bone-implant junctions,including the proximal surface of the center part fitting to the inferior endplate of L5 vertebrae and the surfaces on both sides of the implant matched to the osteotomy planes of the bilateral iliac and iliac crest.Bone-implant junctions were of the porous structure to facilitate ingrowth and were firmly fixed with bone using lock screws and/or cancellous bone screws through nail paths.The small holes on the backside of the implant are designed for soft tissue suture fixation.A metal 3D printer system was used to print the implant.Selective laser melting was used in fabrication by successive layering of melted titanium alloy according to a computer-aided design model.The osteotomy guide plates,accurately indicating the range of osteotomy required for resection of tumors,were designed using 3D design software.They were prepared based on the patient's anatomy of the ilium and were highly conformed to the surface morphology of bone and had positioning holes for Kirschner wire drilling.Polylactic acid was used as a raw material.An abdominal aorta balloon implantation was performed on the day of operation.Surgical time,blood loss,complications,preoperative and postoperative neurological function,instrumentation failure,and local control were presented and analyzed.ResultsAll patients underwent the operation without death or serious complications.The implant was installed on the defect,connecting the ilium and lumbar vertebrae,and fixed with a screw-rod system up to the level of L3-4 or L4-5.The mean operative time was 502 min(range,360-640 min)and the mean operative blood loss 4400 mL(range,3000-7000 mL).The mean follows up was 24.8 months.Wound healing was poor in one patient.After the operation,the pain was significantly relieved,and the patients resumed walking as early as 4 weeks later.Patients recovered well without evidence of local recurrence.The patients showed no neurogenic bladder dysfunction and no fecal incontinence or gait disturbance.No implant failures or related clinical symptoms were detected during follow up.Satisfactory bone ingrowth and osseointegration at the bone-implant junctions were found in follow-up CT.No lung metastasis occurred in 5 patients.ConclusionAlthough technically challenging,it is feasible and safe to use a suspended,modular,and 3D-printed implant for reconstruction after total piecemeal resection with the preservation of bilateral S1-3 nerve roots in patients with SGCT.We believe that this implant can be applied to sacral reconstruction in a wide variety of diseases.Considering the complexity of the operation,rich experience,multidisciplinary cooperation,and careful preoperative planning are the keys to the success of the operation.