Qiang Jian and Zhenlei Liu contributed equally to this study as co-first authors.
This study aimed to investigate the outcome of using 3-dimensional (3D)-printed prostheses to reconstruct a cervical lateral mass to maintain cervical stability.
We retrospectively analyzed data of 7 patients who underwent cervical lateral mass reconstruction using a 3D-printed prosthesis, comprising axial and subaxial lateral mass reconstruction in 2 and 5 patients, respectively. Bilateral mass was reconstructed in 1 patient and unilateral mass in the remaining 6 patients.
Using a 3D-printed lateral mass prosthesis, internal fixation was stable for all 7 patients postoperatively. No implant-related complications such as prosthesis loosening, displacement, and compression were observed at the last follow-up.
Reconstruction of the lateral mass structure is beneficial in restoring load transfer in the cervical spine under physiological conditions. A 3D-printed prosthesis can be considered a good option for reconstruction of the lateral mass as fusion was achieved, with no subsequent complications observed.
The cervical lateral mass is composed of a superior and inferior zygopophysis of the same segment and the isthmus between them. The superior and inferior facets and capsule of the 2 adjacent segments constitute the facet joints of the cervical spine. In Louis’s 3-column spine concept, bilateral facet joints have an important role in axial stability structure, which consists of 2 columns (bilateral facet joints) at the C1–2 level and 3 columns (the anterior vertebral bodies and discs, together with the 2 posterior facet joints) from C2 to the sacrum [
Cervical spine damage and loss of stability may be due to tumor, infection, trauma, or surgery. In particular, posterior surgery for cervical vertebral tumors or dumbbell tumors often involves total or partial resection of the lateral mass, resulting in a loss of the cervical spine’s load-bearing structure [
Three-dimensional (3D)-printing, an additive manufacturing method, is a process in which 3D models are created through successive layers based on a computer-aided design [
Clinical data of patients who had undergone an implant using a 3D-printed lateral mass prosthesis for reconstruction of the cervical lateral mass structure at Department of Neurosurgery, Xuanwu Hospital were retrospectively analyzed. Due to its retrospective design, the requirement of written informed consent was waived.
From December 2018 to January 2021, 7 patients received a lateral mass prosthetic implant at Department of Neurosurgery, Xuanwu Hospital, including 2 patients with axial tumors and 5 patients with dumbbell tumors of the subaxial cervical spine, one of whom had vertebral body involvement. Unilateral prothesis was implanted in 6 patients and bilateral protheses in 1 patient.
Prior to the first operation, all patients had undergone preoperative plain radiographic, computed tomography (CT), and magnetic resonance imaging (MRI) examinations. For patients with vertebral tumors, a preoperative puncture biopsy was performed to determine the nature of the vertebral tumor. Based on preoperative imaging data evaluation, the range of bone structures to be excised (lateral mass resection or total
Patients’ CT data were obtained, and Mimics software (ver. 21.0, Materialize HQ Technologielaan, Leuven, Belgium) was used for modeling to generate
The prosthesis was designed to be in direct contact with both the endplate of the C3 vertebral body and the articular surface of the inferior facet of C1. The superior bilateral articular surface of the axial anterior column was designed to occupy the anterior two-thirds of the articular surface of the inferior facet of the atlas. The prosthesis was designed to form a self-stabilizing structure through fixing 4 screws to the superior and inferior vertebral bodies. Two screws fixed to C1 were tilted backward and upward to fix onto the lateral mass of the atlas, and 2 screws fixed to C3 were tilted backward and downward to fix onto C3’s vertebral body.
The superior facet articular surface of the axial prosthesis was designed to occupy the posterior one-third of the atlas’s inferior facet articular surface, and the inferior facet articular surface of the prosthesis was matched to the C3 superior zygopophysis. The screw attached to C3 was tilted inward and attached to the C3 lateral mass.
In the early stage, we expected to achieve a more stable prosthetic combination with fewer fixed levels. Therefore, bilateral screw trajectories were designed for the body part of the anterior column and lateral mass prosthesis, with the expectation of achieving a 3-column stable structure through fixing the anterior column and bilateral lateral mass prostheses together using 2 anterior screws.
At a later stage, the lateral mass prosthesis was designed to form a self-stabilizing structure with 2 screws attached to the adjacent lateral masses without a common screw trajectory on the body part of both anterior column and lateral mass prosthesis.
A subaxial cervical lateral mass prosthesis directly matched the facet articular surface of the adjacent lateral masses, thus avoiding invasion of the vertebral artery. The prosthesis was fixed with 2 screws to form a self-stable structure. The pedicle screws fixed to C2 and T1 were inclined inward, with the remainder being lateral mass screws.
Prostheses were made using a porous structure consisting of regular dodecahedral units (porosity range, 60%–80%; pore size range, 400–600 μm). The 3D data file of the designed prosthesis was printed by ARCAM EBM Q10 printer, and the printing powder used was Ti6A14VELI, in accordance with the ASTM F300L standard. Postprocessing, the printed prosthesis was placed into the patient and fixed [
Patients’ imaging and clinical effect data were retrospectively analyzed. Imaging data included tumor location, postoperative recurrence, and prosthesis stability. An absence of instrumentation failure or loosening and subsidence of the caudal end of the lateral mass prosthesis was considered evidence of fusion. Clinical effects were evaluated using the 17-point scoring system of the Japanese Orthopedic Association (JOA).
CT 3D reconstruction and MRI scans were reexamined prior to discharge and postoperatively at 3, 6, and 12 months. JOA scores and complications were recorded at the last follow-up.
Demographic data concerning the 7 study patients are summarized in
A 63-year-old man was admitted to our hospital with right shoulder pain. Preoperative CT and MRI scans showed an axial tumor (
Posterior cervical surgery was first performed to completely remove the posterior column structure of the axis, including the spinous process, lamina, inferior articular process and posterior wall of the axial transverse process foramen, to expose and dissociate the bilateral V3 segment of the vertebral arteries and C3 nerve roots, remove the anterior axis transverse process nodules in front of the vertebral artery, and remove the posterior 1/3 of the superior axis articular process above the V3 segment of the bilateral vertebral arteries. Finally, bilateral axial lateral mass prostheses were placed and fixed using a posterior screw rod system (
After complete disinfection of the oral and nasal cavities with iodophor, in a supine position, the patient's mouth was opened with a mouth opener, and the mucosa and muscle of the posterior pharyngeal wall were cut open. The tumor was visible on the axial surface, and part of the tumor was removed to fully expose the anatomical structure. The anterior atlas arch and axial odontoid process were removed, the C2/3 disc was removed, then the axial vertebral body was resected with the tumor. The dural sac was explored, and the tumor on the dural surface was completely removed. A 3D-printed axial prosthesis was placed, the lateral mass of the atlas was fixed cephalally with screws, and the upper margin of the C3 vertebral body was fixed caudally with screws. The anterior column prosthesis and the posterior lateral mass prostheses were fixed with a single screw, as the shared trajectory of the screw secured the 3-column fixed structure. The muscles and mucosa of the larynx wall were sutured in layers, and a nasal feeding tube was placed.
Wound healing of the posterior pharyngeal wall was determined using television fibrolaryngoscopy on day 7 postoperatively. Wound healing was satisfactory. The gastric tube was removed and a fluid diet was provided. Postoperative imaging showed a satisfactory match (
A 15-year-old male patient presented to our hospital with neck and upper limb pain and weakness in both lower limbs. Physical examination showed 4+ muscle strength grading of both lower extremities and knee reflex grading +++. MRI showed right C5/6 and C6/7 dumbbell-shaped tumors, involving C6–7 vertebral bodies (
In the first stage, resection of the intraspinal tumor and reconstruction of the lateral mass were performed via the posterior approach. We removed the cervical 6/7 spinous process, and the right semilamina and lateral masses to expose the epidural tumor invading along the foramina. The tumor had destroyed the transverse process and pedicle, and there was an abundant blood supply surrounding the vertebral artery. Intralesional excision of the intraspinal and partial paravertebral tumors was performed under microscopy. The right spinal nerves of C7–8 appeared to be well protected. An intraoperative rapid frozen section revealed a chordoma. A 3D-printed lateral mass prosthesis was implanted on the right side (
Seven days later, a secondary anterior paravertebral and vertebral tumor resection and an anterior column prosthesis reconstruction were performed. An anterior oblique incision was made to expose the anterior vertebral body. The tumor was visible on the spine surface. After part of the tumor was removed, C-arm x-ray fluoroscopy was used to determine the C5/6 and C6/7 intervertebral disc and related vertebral bodies. After the intervertebral discs and posterior longitudinal ligament were resected, the tumor together with the C6 and C7 vertebral bodies were then removed. An anterior vertebral body prosthesis of an appropriate size was placed between C5 and T1, and an anterior titanium plate was fixed with 4 screws. The internal fixation position of the C-arm was confirmed to be satisfactory, and a drainage tube was placed paraspinally.
The drainage tube was removed on postoperative day 1. Postdischarge, the patient did not receive proton beam radiation. Six-month follow-up imaging examinations indicated that the implant was in a good position (
A 62-year-old woman presented with pain and weakness in her left arm. MRI revealed a left C5–7 dumbbell-shaped tumor (
A posterior cervical approach was undertaken to expose the bilateral C5/T1 lamina and to excise the left lamina, the lateral mass, and the C6/7 pedicle. The tumor was attached to the dural surface and spinal nerve roots were involved. After resection, the spinal nerve root was swollen (
Postoperatively, this patient reported no further pain in the left arm, and radiographic examinations taken prior to discharge showed that the prosthesis remained in a good position (
In spinal cord tumors, the incidence rate of spinal dumbbell tumors is reported to be approximately 18%, and is mainly located in the cervical segment [
Each vertebra of the upper cervical spine has particular morphological and biomechanical characteristics. The bilateral lateral mass of the atlas bears the entire weight of the head and, for this reason, reconstruction of the lateral mass structure is more common in cases of atlas lesions than in cases of axial lesions. Furthermore, the axial vertebra plays a unique role in the distribution of axial loads, transferring the weight carried through the bilateral superior facets to the 3 columns, namely, the anterior vertebral body and bilateral lateral mass joints [
The vertebrae of the subaxial cervical spine are ordinary and morphologically similar to one another. Unlike the facet joints of the lumbar spine, the posterior subaxial cervical facet carries 64% of the cervical axial load [
For resolving such challenges, 3D printing is a promising solution. The advantages of individualized 3D-printed prostheses are as follows. First, the design of the 3D-printed prosthesis is flexible and more individualized. These prostheses can completely reconstruct the multi-column mechanical support structure of the upper and subaxial cervical spine, in a manner that conforms more closely to the biomechanical characteristics of the normal human body, which theoretically avoid the shift in load above the bone defect to the screw and rod system. In addition, for cases involving a combined approach, the shared screw trajectory of the anterior column and lateral mass prosthesis can also be designed. These devices further improve the immediate stability of the prosthesis. Second, through the use of computer-aided design, 3D-printed prostheses possess high accuracy to precisely match the bone structure [
This study was limited in that there was an absence of biomechanical evaluations and a numeric value concerning axial load sharing was not determined. Future research is required to verify this understanding of load sharing using finite element analysis.
Reconstruction of the lateral mass structure is beneficial for restoring load transfer in the cervical spine under physiological conditions. A 3D-printed prosthesis is a good choice for reconstruction of the lateral mass to achieve fusion.
The authors have nothing to disclose.
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Conceptualization: ZC; Data curation: QJ, WD, JG; Writing - original draft: QJ; Writing - review & editing: Zu, FJ
Imaging findings for case number 1. Sagittal contrast-enhanced magnetic resonance imaging (MRI) (A) and axial T2-weighted MRI (B) showing an axial tumor (Enneking stage IIB). The Weinstein-Boriani-Biagini stages were 5–10, A–D. Preoperative puncture pathology indicated chordoma. (C) A preoperative design of the 3-dimensional-printed axial lateral mass (LM) prosthesis. (D) An intraoperative image shows the implantation of the posterior LM prosthesis. (E) A postoperative sagittal computed tomography scan of the reconstruction shows that the LM prosthesis is in a good position and that the anterior screw was inserted into the anterior column and LM prostheses. (F) Postoperative sagittal T2-weighted MRI indicates good spinal canal volume. Postoperative lateral (G) and anteroposterior (H) radiographs of the cervical spine show that the LM prosthesis is well positioned.
Imaging findings for case number 3. (A, B) Preoperative contrast-enhanced sagittal and axial T2-weighted magnetic resonance imaging shows a dumbbell tumor with C6/7 vertebral body involvement. Preoperative biopsy pathology indicated chordoma. (C) The lateral mass (LM) prosthesis was preoperatively designed based on the patient’s computed tomography (CT) data, and (D) the 3D-printed LM prosthesis was manufactured. (E) The first-stage posterior approach was used to remove the intraspinal tumor and reconstruct the LM structure. (F) A coronal CT scan of the reconstruction at 6 postoperative months shows that the LM prosthesis is in a good position. Dynamic radiographs taken in extension (G) and flexion (H) showed the stability of the implant.
Imaging findings for case number 4. Enhanced sagittal (A) and axial T2-weighted (B) magnetic resonance imaging findings indicate left dumbbell tumors at C6/7 and C7/T1. (C) Tumor infiltration of the nerve root was observed intraoperatively, and (D) a lateral mass prosthesis was implanted following tumor resection. Postoperative lateral cervical radiograph (E) and sagittal computed tomography scan images of the reconstruction (F) show that the prosthesis was well positioned and that it was highly matched with the surrounding structures.
Seven patients with lateral mass reconstruction
Case No. | Age (yr)/sex | Lesion | Lateral mass span | Reconstruction material | Clinical manifestation | Preoperative JOA score | Follow-up (mo) | Adjuvant therapy | Complication | JOA score at final follow-up |
---|---|---|---|---|---|---|---|---|---|---|
1 | 63/M | C2 chordoma | Bilateral C2 | 3D-printed titanium alloy prosthesis | Neck pain, shoulder pain, dysphagia | 15 | 32 | Radiation therapy | Dysphagia after radiotherapy | 17 |
2 | 73/M | C2 chordoma | Right C2 |
3D-printed titanium alloy prosthesis | Neck pain, dysphagia | 15 | 9 | None | None | 17 |
3 | 16/M | C6-7 chordoma | Right C6–7 | 3D-printed titanium alloy prosthesis | Upper limb pain | 14 | 14 | None | Recurrence | 16 |
4 | 62/F | C6-7 metastasis | Left C6–7 | 3D-printed titanium alloy prosthesis | Upper limb pain and weakness | 15 | 5 | Chemotherapy | None | 16 |
5 | 49/M | C3/4 dumbbell schwannoma | Right C3–4 | 3D-printed titanium alloy prosthesis | Upper limb numbness | 16 | 6 | None | None | 17 |
6 | 28/M | C6-7 dumbbell schwannoma | Right C6–7 | 3D-printed titanium alloy prosthesis | Upper limb pain | 15 | 4 | None | None | 17 |
7 | 42/F | C6-7 schwannoma | Left C6–7 | 3D-printed titanium alloy prosthesis | Limb numbness | 14 | 3 | None | None | 16 |
JOA, Japanese Orthopedic Association; 3D, 3-dimensional.
Matching error.
Literature review concerning lateral mass reconstruction
Study | Age (yr)/sex | Pathology | Lateral mass span | Reconstruction material |
---|---|---|---|---|
Bongioanni et al., [ |
36/M | Aneurysmal bone cyst | C1 | An iliac-crest bone graft |
Suchomel et al., [ |
62/M | Chordoma | Bilateral C2 | Harms mesh cage |
Wang et al., [ |
12/F | Aneurysmal bone cyst | Bilateral C1 | Titanium mesh cage, rib graft |
Chung et al., [ |
48/M | Osteosarcoma | C1 | Titanium mesh cage |
Jandial et al., [ |
27/M | Metastatic Ewing sarcoma | Bilateral C1 | Expandable cages |
Winking, [ |
54/F | Nodular plasmocytoma | C1 | Harms cage |
Bobinski et al., [ |
48/F | Angiosarcoma | C1 | 2 Titanium cages |
54/M | Multiple myeloma | C1 | Titanium cage | |
Clarke et al., [ |
35/M | Chordoma | Oc–C3 | Titanium mesh cage |
60/F | Chondrosarcoma | C1–6 | Titanium mesh cage | |
50/M | Epithelioid schwannoma | Oc–C3 | Titanium mesh cage | |
61/F | Dumbbell schwannoma | C3–5 | Titanium mesh cage | |
77/F | Chordoma | Left, Oc–C4; Right, Oc–C3 | Titanium mesh cage | |
16/M | Schwannoma | C6–T1 | Fibular strut | |
25/M | Osteochondroma | C3–6 | Fibular strut | |
Clarke et al., [ |
8/F | Osteosarcoma | Bilateral C1 | Allograft fibular strut |
Peciu-Florianu et al., [ |
12/M | Osteoblastoma | Bilateral C1 | Titanium cages |
Stephens and Wright, [ |
27/M | Eosinophilic granuloma | C1 | A titanium expandable cage |
Neva et al., [ |
18/F | Aneurysmal bone cyst | C1 | Static titanium cage |
Ji et al., [ |
50/F | Schwannoma | C3–4 | A strip of shaped allograft bone |