Zero-P: a new zero-profile cage-plate device for single and multilevel ACDF. A single institution series with four years maximum follow-up and review of the literature on zero-profile devices

Abstract

Purpose: To analyze the prospectively collected data in a series of patients treated with single- or multilevel ACDF with a stand-alone, zero-profile device, focusing on clinico-radiological outcome, complications and technical hints, and to review the literature on such new devices.

Methods: Eighty-five patients harboring symptomatic DDD underwent ACDF with the Zero-P cage-plate: 29 at 1-level and 56 at 2-4 levels (total 162 devices). In the multilevel group, 9 patients received a combination of Zero-P and stand-alone cages (hybrid implants). This study focuses on 32 patients with follow-up ranging from 20 to 48 months. NDI, SF-36 and arm pain VAS scores were registered preoperatively and at follow-up visits. Dysphagia was assessed using the Bazaz score. Imaging included X-rays, CT and MRI, also to assess the presence of vertebral body fractures in multilevel cases. Paired Student t test was used for statistical analysis.

Results: SF-36 and NDI showed a statistically significant improvement (p < 0.01) and mean arm pain VAS score decreased from 79 to 41. X-rays and CT demonstrated, respectively, a 94.5 % and a 92 % fusion rate. Three patients complained of moderate and two of mild transient dysphagia (15.5 %). No device-related complications occurred and no fractures, secondary to four screws insertion in one vertebral body (i.e., swiss cheese effect), were detected in multilevel cases. In patients with extensive anterior osteophytes only a "focal spondylectomy" was required.

Conclusion: The Zero-P device is safe and efficient, even in multilevel cases. Dysphagia is minimal, extensive anterior osteophytectomy is unnecessary and technical hints may ease the surgical workflow. This is the largest series, with the longest follow-up, reported.

Figures

Fig. 1

a Sagittal, T2-weighted MRI scan showing degenerative disc disease and spinal cord compression at C4–C5 and C5–C6; signs of instability at C4–C5 are also seen. b Lateral flexion–extension X-ray confirming instability at C4–C5. c Postoperative X-ray showing a hybrid construct with a Zero-P device at C4–C5 (the unstable level) and a stand-alone CFRP cage at C–C6 level

Fig. 2

a Sagittal, T2-weighted MRI scan showing degenerative disc disease and spinal cord compression at C3–C4, C4–C5 and C5–C6. Axial MRI (b) and CT (c) scans demonstrating degenerative changes and neural structures compression, respectively, at C3–C4, C4–C5 and C5–C6. d Postoperative AP and lateral X-ray showing a 3-level implant, with good sagittal alignment and satisfactory stability on flexion–extension views (e, f)

Fig. 3

a Zero-P cage-plate device, filled with bone substitute, hold by the aiming device instrument

Fig. 4

a Comparison between pre- and postoperative (last follow-up) SF-36 mean score. b Comparison between pre- and postoperative (last follow-up) NDI mean score

Fig. 5

Postoperative, sagittal T2-weighted MRI showing the lack of artefacts and a nice view of the spinal cord with a CSF film around it

Fig. 6

An off-side positioned Zero-P device, with one screw encroaching the foramen transversarium

Fig. 7

Extensive anterior osteophytes are present at all spinal levels on lateral X-ray (a), mostly at C4–C5, C5–C6 and C6–C7. The Zero-P device allows a “focal spondylectomy” (b), which is required to enter the disc level and also to insert screws through the Zero-P plate using dedicated instruments with the right angulation (cranial arrow). Sagittal, reconstructed CT scan (c, d) demonstrate the resected osteophyte (cranial arrow) and the remaining anterior osteophyte (caudal arrow), which would prevent the implantation of an anterior cervical plate

Fig. 8

a Fluoroscopic picture showing a conflict between the vertebral body distractor’s pin and the screwdriver inserted through the aiming device instrument. This is shown also with an intraoperative picture (b); a custom-made aiming device, with a smaller “nose” (c) can be helpful to reduce such technical problem

Fig. 9

a Flexion–extension lateral X-ray showing a C4–C5 instability in a patient with DISH. b A Zero-P device has been used to fix the unstable segment

Fig. 10

a Lateral X-ray highlighting a 3-level fixation. 2-year follow-up X-ray. b Showing a solid fusion through the Zero-P cages, as also seen on reconstructed coronal (c) and sagittal (d) CT scan