Does the Angulation of the Screws in the Zero‐P Implant Affect the Clinical and Radiological Outcomes of Patients?

Abstract

Objective When implanting the Zero‐P device, the screws of Zero‐P form a bone wedge with a 40 ± 5° cranial and caudal angle (CCA). However, no study has been performed in the optimal CCA of the Zero‐P implant. To investigate whether the cranial/caudal angles (CCA) of the screws affect the clinical and radiological outcomes in patients undergoing ACDF with the Zero‐P implant. Methods From January 2016 to December 2023, we retrospectively analyzed 186 patients who underwent 1‐level ACDF with the Zero‐P device. The patients were divided into four groups: group A (cranial angle ≤40°, caudal angle ≤40°); group B (cranial angle ≤40°, caudal angle >40°); group C (cranial angle >40°, caudal angle ≤40°); and group D (cranial angle >40°, caudal angle >40°). The clinical outcomes, including Japanese Orthopaedic Association (JOA), neck disability index (NDI), and visual analogue scale (VAS) scores, the radiological parameters, including cervical lordosis (CL), cervical lordosis of operated segments (OPCL), intervertebral space height (ISH) and fusion rate (FR), and the complications, were evaluated and compared. Parametric tests, non‐parametric tests, and chi‐square tests were conducted to analyze the data. Results The OPCL of group A was significantly less than that of the other groups at the final follow‐up (p 0.05). Conclusion A larger CCA of the screws (cranial angle >40°, caudal angle >40°) was better for maintaining OPCL and reducing the incidence of ASD. A smaller CCA of the screws (cranial angle ≤40°, caudal angle ≤40°) was better for maintaining ISH and reducing the rate of subsidence.

Keywords

• ACDF
• Cervical degenerative disc disease
• Cranial/caudal angles
• Zero‐P