The importance of stabilisation in enabling bone fusion demonstrated by successful revision of failed occipitocervical fusion using patient-specific atlantoaxial joint spacers: a case report

Introduction

Background

The surgical management of occipitocervical junction (OCJ) pathologies is challenging due to the unique anatomy and biomechanics (1,2).

Pathologies of the OCJ, and the resulting cervical medullary syndrome, are frequently observed in conditions that cause ligamentous laxity, such as Down syndrome, Goldenhar syndrome, osteogenesis imperfecta, Marfan syndrome, Morquio syndrome, Stickler syndrome, and Ehlers-Danlos syndrome (EDS), which are classified as hereditary disorders of connective tissue (HDCTs) (3-6).

EDS is a heterogeneous group of rare HDCTs resulting from mutations in collagen genes. It is characterized by skin hyperextensibility, tissue fragility, and joint instability (7). According to the new international classification established in 2017, 13 EDS variants have been identified (8). Of these 13 variants, five are associated with spinal involvement. The spinal manifestations of EDS include OCJ instability, atlantoaxial subluxation, basilar invagination, and spinal deformities (6,9). In the EDS literature, it has been shown that these pathologies in the OCJ can affect cerebrospinal fluid and vascular flow, leading to a wide range of symptoms such as headaches, long tract findings, dyspraxia, gait abnormalities, and autonomic dysfunctions (6).

In OCJ pathologies related to EDS, occipitocervical fusion (OCF) is preferred when conservative treatment proves insufficient (10). The goals of surgery are to manage the deformity, control neurological symptoms, and achieve mechanical stability that promotes a conducive environment for fusion (2).

Studies examining the spinal effects of EDS are generally comprised of fusion series performed due to thoracic or lumbar spinal deformities. The literature assessing cervical issues and cervical fusion is limited (11).

The management of failure in OCF surgery is particularly challenging. Repeat surgeries in this region can lead to wound infections and problems with wound healing. Additionally, achieving sufficient stability for fusion is difficult due to the limited bone stock in the OCJ area (12).

Rationale and knowledge gap

The literature indicates that complications associated with OCF are more common in patients with EDS and other HDCTs. However, these studies offer limited data on fusion rates and implant failure (11,13-17).

The number of studies in the literature concerning complications of OCF and revision surgery is quite limited (12). Tang et al., in their case report, reported that at 31 months postoperatively, rod breakage in a patient who underwent OCF resulted in an increase in deformity. They achieved solid fusion through rod revision, deformity correction, and bone grafting (18). Okamoto et al., in their case series of 142 patients who underwent posterior OCF and cervicothoracic fusion, reported an implant failure rate of 4.2% (19). Ahmed et al. reported the complications in their case series of 8 patients who underwent OCF (2).

Objective

In this case report, we describe a patient with EDS who underwent OCF and experienced complete reabsorption of the bone graft and nonunion. The condition was then successfully treated using custom-made, anatomically conforming 3D-printed (3DP) titanium alloy (Ti-6Al-4V) facet joint devices (3DMorphic Pty Ltd., Sydney, NSW, Australia). Regrafting included a bioactive glass (GlassBone^TM, Noraker, Lyon-Villeurbanne, France).

As a manufacturing method, 3D printing works by adding material layer-by-layer to build a 3D structure, enabling the manufacturing of complex geometries. The surface roughness of 3DP titanium can be tailored to enhance osseointegration. The irregularity of 3DP titanium increases the surface area at the device-anatomy interface, enhancing osseointegration (20). This ability to manipulate surface topology offers advantages in additive manufacturing over subtractive methods, such as Computer Numerical Control (CNC) machining (21,22). Additionally, titanium’s enhanced osseointegration, when compared with bioinert materials like polyether ether ketone (PEEK), makes it ideal for orthopaedic applications (20,23,24). We present this case in accordance with the CARE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-24-157/rc).

Case presentation

A 19-year-old male with a history of EDS was initially diagnosed with Chiari malformation type-1 (Chiari I) following investigations for recurrent occipital headaches. In the same year, he underwent posterior fossa decompression surgery for Chiari I. One year after surgery, the patient sustained a head injury while playing soccer, leading to a recurrence of Chiari I-related symptoms.

An initial flexion-extension computed tomography (CT) scan revealed a clival-axial angle of 117.8 degrees in flexion and 150.8 degrees in extension, leading to a diagnosis of atlantoaxial instability (Figure 1). Typically, the clival-axial angle ranges from 150 degrees in flexion to 180 degrees in extension. There is conjecture that correcting the clival-axial angle may be correlated with improvements in neurological deficits (25). Halo-vest fixation was performed prior to OCF, with significant symptom improvement leading to the decision for OCF (26).

Figure 1 Measurement of clivo-axial angle. (A) Pre-operative flexion; (B) pre-operative extension; (C) post-op initial surgery; (D) post-op revision surgery.

The fusion was performed using an occipital plate, navigated (Medtronic Stealth System, Medtronic, Louisville, CO, USA) C1 screws with a transarch technique, and C2 pars screws (Infinity OCT system, Medtronic). Large amounts of allograft were packed in the surgical site.

Post-OCF surgery, the patient showed symptom improvement. However, a CT scan 6 months post-operatively demonstrated remarkable resorption of bone graft around the original construct and no significant new fusion bone growth was evident without implant failure (Figure 2).

Figure 2 Computed tomography slices demonstrating the progression of bone fusion at time points (A) immediately after first surgery, (B) 6 months post first surgery, (C) 5 months following the revision surgery with 3D-printed custom-made implants, and (D) coronal slices of pre- and post-revision surgery demonstrating solid arthrodesis at the craniocervical junction.

The patient was conservatively followed, but 15 months later, his preoperative symptoms, including increased neck pain and occipital headaches, returned. A CT scan showed erosion and non-union in the C1–2 region with evidence of screw loosening. Clivo-axial angle remained unchanged between the first operation and revision surgery (<1°).

After continued conservative management, the patient underwent revision surgery 30 months after the initial fusion. During the revision surgery, almost no graft or fusion was identified at the C1–2 level. The C1–2 joints were entered and curetted, with the C2 nerve roots protected and mobilized.

Patient-specific 3DP titanium cages (2.9-mm tall, 8-mm wide, and approximately 12.5-mm long) were placed in the joint spaces, and a loose C2 screw (2.5-mm diameter) was revised with a 1-mm thicker screw. An anatomical biomodel and Virtual Surgery Planning were used to aid with planning and navigation intra-operatively (Figure 3). All planning, device design, and manufacturing were done by 3DMorphic Pty Ltd. (Sydney, Australia). The surgical site was packed with iliac crest autograft, and the cages were packed with a bioactive glass (GlassBone^TM, Noraker, Lyon-Villeurbanne, France).

Figure 3 Virtual surgery planning demonstrating (A) planned correction and 3D modelling in Materialise MIMICS (version 21.0), (B) anatomical biomodel with cage insertion, and (C) removal of inserter. Note that a thinner inserter was used intraoperatively due to neurovascular access constraints. Numbers indicate slice position within the CT volume, and coloured lines are a crosshair indicating position within the three planes (A). CT, computed tomography.

After securing the system, the final occipitocervical angle was confirmed using an O-arm, showing slight extension and ideal implant positioning. Flexion was increased, and the system was locked again. Total blood loss was 500 mL. Post-revision CT showed adequate bony fusion at the C1–2 level (Figure 2), and all symptoms resolved.

The patient was braced, undertook physical therapy, and was advised of ‘red flag’ symptomology in the recovery period. There were no adverse events following the revision surgery. At 8 months postoperatively, X-rays demonstrated no change in alignment (Figure 4). At the 15-month follow-up, the patient reported no symptoms except for morning muscle spasms. The patient reported Neck Disability Index (NDI) scores of 56% before the revision surgery and 30% 6 months post-operatively (27). A timeline of this case is presented in Figure 5.

Figure 4 Eight-month post-operative X-ray.

Figure 5 Timeline of the patient’s history. Images: Flaticon.com. CT, computed tomography.

All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Discussion

Although an extensive body of literature studies the effects of EDS on connective tissue and its clinical manifestations, studies investigating its impact on bone biology and bone fusion are limited. Most of the spinal fusion studies involve small case series or expert opinions, and these studies primarily focus on the thoracic and lumbar vertebrae, with only limited discussion of fusion rates (28).

Wu et al. evaluated the effect of EDS on adjacent segment disease (ASD) in patients who underwent transforaminal interbody fusion (TLIF). In this study, 85 patients with EDS were compared to a matched cohort of 85 individuals without EDS. The findings indicated a higher incidence of ASD in patients with EDS; however, no significant difference was observed between the EDS and non-EDS groups regarding the rate of pseudoarthrosis (13).

In their published series of six cases of posterior spine fusion, Robenhorst et al. reported one case of death due to hemoperitoneum, one case of symptomatic implant and hook dislodgement, and one case of recurrent implant failure requiring repeated surgery. However, three patients achieved a fusion without complications (14).

In a series of five pediatric spine deformity cases, McMaster et al. reported issues such as excessive blood loss, hematoma, and wound dehiscence. Despite these complications, solid fusion was achieved in all patients (15).

In another series of five patients with spinal deformity undergoing thoracolumbar fusion, Akpinar et al. reported the development of vascular injuries during the anterior approach and iliac wing graft harvest. However, solid fusion was achieved in all patients at the four-year follow-up (16).

In their case series examining neurological and vascular complications in four patients undergoing thoracic and lumbar fusion surgery for deformity, Vogel et al. reported no cases of nonunion (17).

One of the few studies on cervical fusion in the literature was performed by Chi et al., who in 2024 compared 533 patients with EDS to a matched control group of 2,634 individuals undergoing anterior cervical discectomy and fusion (ACDF). The study demonstrated that patients with EDS experienced a significantly higher incidence of complications such as wound complications, surgical site infections, pseudoarthrosis, and implant failure (11).

The C1–2 level is the most susceptible to nonunion and implant failure in OCF procedures. In the case we present, nonunion and implant failure occurred specifically at this level. This is due to the extensive mobility of the C1–2 joint, which is involved not only in axial rotation but also in flexion-extension and lateral bending. Achieving adequate stability at this level to promote successful fusion is particularly challenging (29-31).

In cases of nonunion at this site, various methods have been attempted to enhance stability and promote fusion. One option is to increase stability through external means such as a collar or halo vest fixation without performing revision surgery, although the efficacy of these approaches remains controversial. For patients undergoing revision surgery, extending the fusion level distally in addition to addressing the C1–2 region and augmenting grafting may be considered as a strategy to enhance stability. However, this approach carries the potential for additional complications due to the increased surgical field (12,29).

Additionally, in the initial surgery, stability and fusion rates may be improved by using a transoral anterior approach to achieve a better C1–2 stabilization. However, this technique is associated with a high risk of complications inherent to transoral surgery (32).

One of the significant advancements in C1–2 fusion in recent years is the technique described by Goel in 2004, particularly for basilar invagination and atlantoaxial dislocation. This method involves C1–2 facet distraction using intraarticular spacers and bone grafts (33). This technique not only increases the fusion area but also helps restore OCJ alignment through distraction.

Exposure of the atlantoaxial joint is challenging, often requiring longer surgical time and potentially causing more bleeding compared to the C1–2 fusion technique described by Goel et al. and Harms et al. (34,35). In the present case, no distraction was applied, which differs from Goel’s [2004] distraction method (33).

A posterior approach, beneath the C2 nerve root, is most effective for accessing the C1/2 facet joint space. While transection of the C2 nerve root has been routinely described, the senior author prefers to preserve and work around the nerve (33). For the placement of the C1 screws, the C2 nerve root was carefully distracted distally, allowing the screws to be implanted over the C2 nerve. The joint is most easily accessed from the C2 side, beneath the C2 nerve root. To control bleeding, one can apply hemostatic agents and pressure with a swab. This allows the surgeon to alternate to the contralateral side, allowing for a side-to-side dissection. Bone surfaces in the areas targeted for fusion were decorticated, and large amounts of graft were packed next to all decorticated surfaces.

In the revision surgery for our patient, intraoperative O-arm scans showed an increase in the occipitocervical angle following cage insertion. This increase suggests that C1–2 spacers can be useful in correcting deformities. However, since there was no alignment issue in our patient, the excessive occipitocervical angle increase was slightly reduced. In another study, Goel demonstrated the efficacy of this method across different patient groups (32).

Conclusions

In this case report, the 2004 technique developed by Goel was modified to use patient-specific 3DP titanium cages in the C1–2 joint space. We think that the addition of the patient-specific titanium cages aided physiological realignment and led to greater stability than screw fixation alone and most importantly a solid fusion in an obviously difficult fusion environment. Although this is a case study of a relatively rare condition, the senior author considers this successful modification of the Goel et al. technique worth reporting as it may aid in similar “difficult fusion” cases.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the CARE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-24-157/rc

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-24-157/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-24-157/coif). W.C.H.P. is a founder and director of 3DMorphic. W.C.H.P. is the inventor of the following patents which are assigned to 3DMorphic Pty Ltd. AUS: 2017212147 granted, USA: 11,331,205B2 granted, JPN: 2018-557165 granted, CAN: 3.012.390 granted, EPO 3407817 granted. J.C.H. is an employee at 3DMorphic. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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