Space Between the Titanium Plate of Zero-Profile Cage and Endplate of the Vertebral Body Might Affect the Fusion Process in Anterior Cervical Discectomy and Fusion
Anterior cervical discectomy and fusion (ACDF) is widely regarded as the “gold standard” surgical treatment for patients with spondylotic myelopathy when conservative treatments fail. Among the various devices used in ACDF, the zero-profile, standalone device (Zero-P; Synthes GmbH, Zuchwil, Switzerland) has gained popularity over traditional plate and cage systems. However, the insertion point of the Zero-P device in the intervertebral disc space and its relationship with the endplate of the vertebral body remain critical factors influencing clinical and radiological outcomes. This study investigates the impact of the space between the titanium plate of the Zero-P device and the endplate of the vertebral body (TPE space) on the fusion process and the maintenance of cervical alignment.
The zero-profile device is designed to eliminate the need for an additional anterior plate, thereby reducing the risk of complications such as dysphagia and soft tissue irritation. However, the presence of TPE space, which is often observed on lateral X-rays, has been hypothesized to affect the fusion process and cervical alignment. In clinical practice, the endplate is sometimes polished to facilitate the insertion of the Zero-P device, especially in cases with large anterior osteophytes. This preparation ensures better contact between the posterior polyetheretherketone (PEEK) cage and the superior and inferior endplates, potentially accelerating the fusion process. However, this also creates a TPE space, which may compromise the support provided by the titanium plate to the cervical spine.
The study retrospectively reviewed 80 patients who underwent single-level ACDF using zero-profile devices between January 2011 and December 2018. The patients were divided into two groups based on the presence or absence of TPE space on post-operative radiographs. Group A consisted of 41 patients with TPE space, while Group B included 39 patients without TPE space. All surgeries were performed by the same surgeon using the classical Cloward approach. In Group A, the endplates were overpolished to facilitate the insertion of the Zero-P device, resulting in TPE space. In Group B, the endplates were not overpolished, and the implant was perfectly matched with the endplates, eliminating the TPE space.
Post-operative follow-up was conducted at 3, 6 months, 1 year, and annually thereafter. Clinical outcomes were assessed using the Japanese Orthopedic Association (JOA) score, neck disability index (NDI), and visual analog scale (VAS) score. Radiographic outcomes, including the overall cervical angle (Cobb C), segmental cervical angle (Cobb S), and intervertebral disc height (IDH), were measured using radiographs. Fusion status was determined using radiographs and computed tomography.
The results showed significant improvement in JOA scores and reductions in VAS and NDI scores post-operatively in both groups. However, there were no significant differences in JOA, NDI, and VAS scores between the two groups at any follow-up point. Pre-operative and immediate post-operative Cobb C, Cobb S, and IDH measurements also showed no significant differences between the groups. However, at the last follow-up, Cobb C and IDH were significantly lower in Group A compared to Group B (P = 0.042 and P < 0.0001, respectively). Cobb S was also lower in Group A, but the difference was not statistically significant (P = 0.101).
The fusion process was faster in Group A, with a significant difference observed (P < 0.0001). This is attributed to the increased contact and compression between the posterior PEEK cage and the endplates in Group A, which facilitated the fusion process. However, the maintenance of Cobb C, Cobb S, and IDH was inferior in Group A, indicating that the TPE space weakened the support provided by the titanium plate. The overall fusion rate at the last follow-up showed no significant difference between the groups (P = 0.965), with one patient in Group A and two patients in Group B failing to achieve solid fusion.
The insertion point and composition of the zero-profile device play a crucial role in maintaining cervical alignment. Proper positioning of the titanium plate along the anterior vertebral line is essential for maintaining Cobb C, Cobb S, and IDH. The anterior cortical corner of the endplate may provide greater strength compared to other parts of the endplate. In Group A, the absence of contact between the titanium plate and the endplate resulted in reduced support, leading to a greater decrease in Cobb C, Cobb S, and IDH compared to Group B, where the titanium plate was perfectly matched with the endplate.
In conclusion, the presence of TPE space can facilitate the fusion process by increasing contact between the posterior PEEK cage and the endplates. However, this comes at the cost of reduced maintenance of Cobb C, Cobb S, and IDH. The small differences in clinical outcomes between the two groups suggest that the presence of TPE space does not significantly affect the overall clinical prognosis. Surgeons should consider the trade-offs between faster fusion and reduced cervical alignment when deciding whether to create TPE space during ACDF using zero-profile devices.
doi.org/10.1097/CM9.0000000000001129
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