Titanium Plate-Endplate Space in Zero-Profile Cages May Speed Fusion but Impact Cervical Structure in ACDF Surgery

If you or someone you know has faced severe neck pain, numbness, or weakness from cervical spondylosis—where degenerated discs press on nerves or the spinal cord—anterior cervical discectomy and fusion (ACDF) is likely a familiar solution. As the “gold standard” surgery for these cases, ACDF removes damaged discs, relieves pressure, and fuses vertebrae to stabilize the neck. But a 2020 study from West China Hospital, Sichuan University, highlights a tiny detail in one popular implant that could shift how surgeons balance healing speed and long-term neck health.

The implant in question? The Zero-P zero-profile cage, made by Synthes GmbH. Unlike traditional ACDF setups (which use separate plates and cages), the Zero-P combines a titanium plate with a polyetheretherketone (PEEK) cage into one device. It’s designed to sit flush with the vertebrae, reducing risks like swallowing problems or implant visibility. But surgeons often notice a gap—called a titanium plate-endplate (TPE) space—between the Zero-P’s titanium plate and the vertebral endplate on X-rays. This space forms when doctors overpolish the endplates (the flat surfaces of vertebrae) to help the PEEK cage make better contact with the bone—a step meant to speed up fusion. For patients with less severe degeneration, the implant fits perfectly, no TPE space needed.

Curious if this gap affected outcomes, researchers Yi-Fei Deng, Yang Meng, Hao Liu, and colleagues analyzed 80 patients who had single-level ACDF with the Zero-P between 2011 and 2018. They split patients into two groups: 41 with TPE space (Group A) and 39 without (Group B). All surgeries were done by the same surgeon using the classic Cloward approach—Group A’s endplates were overpolished to create TPE space, while Group B’s implants fit flush with untouched endplates.

Patients were followed for at least 12 months (median 15 months) to track three key areas:

Clinical outcomes: Japanese Orthopedic Association (JOA) scores (nerve function), Neck Disability Index (NDI) (daily life impact), and Visual Analog Scale (VAS) (pain intensity).
Structural integrity: Cobb C (overall cervical curvature), Cobb S (angle at the fused level), and intervertebral disc height (IDH).
Fusion progress: X-rays and CT scans to check if vertebrae had fused solidly.

The results were surprising—and balanced:

No difference in how patients felt: Both groups saw big improvements in JOA (nerve function), VAS (pain), and NDI (disability) after surgery. At every follow-up (3 months, 6 months, 1 year, and beyond), there were no meaningful differences between Group A and Group B. In short: the space didn’t change how well patients recovered clinically.
Faster fusion with TPE space: Group A (with the gap) fused much faster than Group B. At 3 months, 11 Group A patients had fused compared to just 3 in Group B. By 6 months, 25 Group A patients had fused vs. 18 in Group B. This makes sense: overpolishing endplates let the PEEK cage press more firmly against the bone—one of the biggest drivers of fusion.
Less structural stability with TPE space: While Group A fused faster, they lost more of their cervical shape over time. At the final follow-up, Group A had significantly lower Cobb C (overall cervical curvature) and IDH (disc height) than Group B. Cobb S (segmental angle) was also lower in Group A, though the difference wasn’t statistically significant. The reason? TPE space meant the titanium plate—designed to support the neck—didn’t contact the vertebrae. Without that support, the neck gradually lost some of its restored alignment.

Importantly, the overall fusion rate at the end of follow-up was nearly identical: 97.6% for Group A vs. 94.9% for Group B. The real trade-off was between how quickly fusion happened and how well the neck retained its structure.

Why does this matter for patients and surgeons? For surgeons, it’s a new factor to consider: creating TPE space might help patients fuse faster, but it could mean less long-term stability in cervical alignment. For patients, the takeaway is reassuring: regardless of whether the gap exists, you’re still likely to get the same pain relief and functional improvement.

The study builds on earlier research about implant placement—like a 2017 World Neurosurgery study that linked Zero-P insertion points to maintaining anterior disc height. It also aligns with a 2009 Spine study showing that cage-endplate contact boosts fusion, even if it means less plate support.

While the findings don’t rewrite the rulebook for ACDF, they add nuance to how surgeons use zero-profile cages. Every patient is different, and the best approach depends on balancing individual needs—whether prioritizing faster fusion (for someone with high activity levels) or long-term structural integrity (for someone at risk of alignment issues).

The study was conducted by Yi-Fei Deng, Yang Meng, Hao Liu, Xing Rong, Ying Hong, Bei-Yu Wang, Chen Ding, and Yi Yang at the Department of Orthopedic Surgery and Department of Anesthesia and Operation Center/West China School of Nursing, West China Hospital, Sichuan University, Chengdu, China.

Original study: Deng YF, Meng Y, Liu H, et al. 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. Chinese Medical Journal 2020;133(21):2641–2643. doi.org/10.1097/CM9.0000000000001129

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