The occipitocervical (OC) junction, one of the most complex and mobile regions of the spine, consists of two important joints: the occipitocervical (OC) joint and the atlantoaxial (AA) joint [1]. Flexion, extension, and rotation are significant at these joints: primarily, at the C0–C1 level, angles of flexion and extension average 23°–25°, and in the atlantoaxial joint, the average rotation is approximately 23°–39°, and angles of flexion and extension average 10°–20° [2]. These joints are prone to injury, degenerative changes, and instability as a result of various causes, such as trauma (e.g., Jefferson’s and hangman’s fracture), infection, tumors, congenital anomalies, and inflammatory diseases (e.g., rheumatoid arthritis and osteoarthritis) [3]. Instability usually results in axial pain, with or without radiculopathy, and in focal sensorimotor deficit, respiratory disturbances, and myelopathy [4,5].

OC and AA fusion are established techniques for treating upper cervical instability [5,6]. Cervical instability has a bimodal distribution, affecting young and elderly patients. Each patient’s clinical and radiological findings should be evaluated individually to alleviate the symptoms and determine the best surgical treatment with the lowest risk of complications. Surgical management with OC fusion or AA fusion has been shown to yield better results than do conservative treatment options [7–9]; however, even with the proper understanding of the pathological process and detailed knowledge of anatomy, these operations may lead to undesired and serious complications [10,11]. According to previous reports, patients who underwent OC fusion are prone to a more significant number of complications and more need for revision surgery than patients who underwent AA fusion [12]. In this retrospective study, we compared surgical outcomes of OC and AA fusion with regard to operative time, average amount of blood loss, postoperative complications, and rate of revision surgery.

This research was approved by the ethics committee of Okayama Rosai Hospital (approval no., 421). The necessary informed consent forms were duly signed and obtained from all the patients involved in the study. The cohort of this multicenter retrospective analysis consisted of patients who underwent OC and AA fusion for mechanical in stability of various causes at Okayama Rosai Hospital and Okayama University Hospital between 2011 and 2023. The operations were performed by three surgeons in two hospitals. We included patients with (1) severe mechanical instability of the upper cervical spine; (2) severe myelopathy and axial neck pain, with or without radiculopathy, confirmed by radiological findings; and (3) failure of more than 3 months’ worth of conservative treatment or recurrent symptoms. We excluded patients with less than 1 year of follow-up and those lacking postoperative computed tomographic and magnetic resonance imaging studies. Surgical time, intraoperative blood loss, and postoperative complications were documented to assess surgical outcomes. Radiographs were obtained to identify screw malposition, rod breakage, and nonunion.

To analyze ordinal scale data, we used the Mann-Whitney U test, and to evaluate data for continuous variables, we used the independent-samples t-test. To determine the presence of nonrandom associations between the two categorical variables, we used the chi-square or Fisher’s exact test to compare nominal scale data. In addition, we documented Frankel grades (regarding neurological outcomes) before and after both procedures. We meticulously performed all statistical calculations by using GraphPad Prism ver. 6.0 (GraphPad Software, Boston, MA, USA). A p-value of <0.05 indicated statistical significance; this threshold guided the identification of meaningful differences and associations within the study findings.

Occipitocervical fixation has evolved significantly, with advancements in surgical techniques aimed at improving stability at the craniocervical junction while reducing complications and enhancing outcomes [13]. Initially, surgical interventions at the craniocervical junction were limited by the anatomical complexities and significant risks involved. In the early 20th century, Foerster introduced the concept of fusion with grafts [14], but patients required a minimum of 12 weeks of traction; this led to early investigations into techniques involving wires and bone grafts to stabilize the craniocervical region [14]. These early materials, although semirigid, were often plagued by complications such as nonunion and hardware failure.

The advent of modern internal fixation systems, particularly the introduction of occipital plates and screw–rod systems, provided more rigid stabilization, resulting in better outcomes and reduced complications. In the first significant advancement in AA fixation, Gallie in 1939 introduced a sublaminar wire fixation method, which remained a standard approach for decades. As biomechanical understanding improved, with Goel’s pioneering and with Magerl’s introduction of transarticular screw fixation in 1987, stability and outcomes of AA fusion procedures were enhanced [15,16]. Although underlying pathological conditions often dictate the surgical approach, a critical decision is whether to perform OC fusion or AA fusion [3]. Comparing the outcomes of these procedures is crucial [17] because both aim to treat cervical instability that results from changes related to rheumatoid arthritis, basilar invagination, trauma, degenerative disorders, tumors, and infection [18,19] (Table 4).

Our results indicate that OC fusion is associated with longer operative times than AA fusion (p=0.0203), probably because it is more invasive. The complication rate was also higher after OC fusion than after AA fusion, as was the reoperation rate (p<0.0001). These findings are consistent with those of Tian et al. [20], who reported a higher revision rate after OC fusion (11.3%) than after AA fusion (5.2%) in a retrospective cohort study. Zileli and Akınturk [19] reported similar findings in 67 (52%) of 128 patients who underwent OC fusion.

According to the literature, the rate of reoperations after OC fixation is high because of implant-related complications, craniocervical malalignment, or infection. In addition, the anatomical complexity of the craniocervical junction and the presence of comorbid conditions, such as rheumatoid arthritis or cerebral palsy, may contribute to the significantly higher rates of screw loosening and infection after OC fusion than after AA fusion (p=0.00073). In our study, revision surgeries were indicated for deep SSI and rod breakage/screw loosening after AA fusion and for deep SSI and rod breakage and screw loosening/pullout after OC fusion (Fig. 2).

With regard to patients’ quality of life, the most prevalent complication reported to be associated with OC fusion is dysphagia. In our sample, only one patient had dysphagia (Fig. 3). This proportion was not statistically significant (p=0.409); according to the literature, however, such incidence have ranged from 10% to 25% during long-term follow-up. The incidence of dysphagia was recently reviewed by Singh et al. [21], who also studied the health-related quality of life after OC fusion and return to work and who found that on average, 26% of patients had long-term dysphagia.

Of the implant-related complications, which usually occur in the middle to late postoperative period, the most common is distal screw loosening. Our results indicated that the incidence of implant failure, including screw loosening and rod breakage, was higher after OC fusion than after AA fusion (p=0.154). Some authors have also proposed ending OC fusion at the level of C3 or even C4 to prevent a higher load on the C2 screw [13]. However, this increases the risk of blood loss, exposure, and longer operation time, which can potentially result in undesirable events such as infection. The results by Wenning and Hoffmann [22] were completely different from ours because the two groups did not differ with regard to revision or infection. Furthermore, in a retrospective study of 799 patients, Winegar et al. [16] noted that the incidence of infection was 30.9% and that of hardware-related failure was 22.3% among those who underwent OC fusion. In another study, Choi et al. [23], who used OC fusion to treat 16 patients with cervicocranial instability that resulted from different pathologic causes, noted a high incidence of infection (13.3%) and hardware-related failure (12.6%).

Despite these risks, OC fusion remains essential for significant OC instability, especially in cases involving congenital malformations or tumor resections. In contrast, AA fusion generally results in fewer complications, is less invasive, and improves clinical outcomes and patient satisfaction. Hu et al. [24] noted that whereas all patients undergoing OC fusion complained of reduced neck mobility, only 4.2% of those undergoing AA fusion reported such issues. Our findings also indicated that AA fusion was a shorter procedure, the risk of SSI was lower, and mobility was better preserved, which reduced the overall surgical burden on patients. These findings are consistent with those of Yang et al. [12], who retrospectively evaluated 483 OC and 737 AA fusions recorded in a patient database and found that complications such as rod breakage, screw loosening, infection, and revision surgery were also less frequent after AA fusion (26.3%) than after OC fusion (40.9%), which highlights the safety and effectiveness of AA fusion [15]. However, the findings by Yang et al. [12] involved data collected within only 30 days after surgery (a very short follow-up period), and their source, the PearlDiver Database (which is publicly available and is a Health Insurance Portability and Accountability Act–compliant database), contained no information about surgical time or intraoperative blood loss.

The decision-making process remains complex; one of the important goal is the preservation of movement along side stable fixation. Surgeons must carefully evaluate each patient’s condition individually to determine the most appropriate surgical approach. OC fusion should be reserved for cases in which AA fusion would not provide sufficient stability, such as when the OC joint is or will become unstable after the patient’s underlying pathological processes are addressed.

Limitations of this study included a small sample size, short follow-up periods, and a heterogeneous diagnostic distribution. Further research with larger patient cohorts and extended observation periods is required. In addition, we did not evaluate quality of life, which may significantly affect patient satisfaction and recovery outcomes.

Although OC fusion is indispensable for certain conditions, particularly basilar invagination, it entails more risk of complications and more need for revision surgery than AA fusion. Surgeons must balance the need for OC fusion against these risks to ensure that the chosen surgical intervention aligns with the patient’s needs and conditions.