Positioning and clinical application of the inflection point of the uncinate process in anterior cervical discectomy and fusion (ACDF): a retrospective study

Abstract

Objective: We propose a novel intraoperative landmark for decompression during anterior cervical discectomy and fusion (ACDF), referred to as the inflection point of the uncinate process (IPUP). Its safety and efficacy were systematically assessed through comprehensive radiographic analyses and clinical investigations during ACDF.

Methods: Computed tomography (CT) scan data from 135 patients were analyzed retrospectively. Eight imaging parameters were evaluated: inflection point of uncinate process (IPUP) distance, medial wall of the transverse foramen (MTF)-IPUP distance, anterior wall of the transverse foramen (ATF)-IPUP distance, posterior wall of the transverse foramen (PTF)-IPUP distance, the intervertebral foraminal decompression line(IFDL)-MTF distance, the intervertebral foraminal decompression (IFD) distance, the intervertebral foraminal decompression (IFD) angle, and the maximum decompression angle. A retrospective analysis was conducted on the radiographic data of 87 patients with cervical spondylosis who underwent ACDF between January 2020 and January 2023. Patients were divided into two groups: the IPUP group and the non-IPUP group. Three postoperative radiographic parameters were evaluated: the decompression width, the effective rate of intervertebral foraminal decompression, and the transverse diameter of the spinal cord at the surgical level.

Results: The IPUP distance gradually increased from C3 to C6. The minimal MTF-IPUP distance and PTF-IPUP distance were observed at C5, while the minimal ATF-IPUP distance occurred at C4. The shortest MTF-IFDL distance was observed at C5, while it exceeded 2 mm across all cervical levels. The IFD distance and IFD angle both decreased from C3 to C6, whereas the maximum decompression angle increased. Postoperatively, the decompression width in the IPUP group exceeded the transverse diameter of the spinal cord in all patients and was significantly greater than that in the non-IPUP group at all levels except C3.

Conclusion: Using the IPUP as an intraoperative decompression landmark during ACDF can safely achieve broader spinal cord and nerve root decompression. Vertical decompression confined within the medial borders of the bilateral IPUPs is generally sufficient in most cases. In patients with foraminal stenosis, additional safe neural decompression can be accomplished either by oblique decompression at an 11° lateral deviation from the IPUP or by extending 3 mm laterally at the base of the intervertebral foramen.

Keywords: ACDF; Foraminal decompression; Imaging study; Inflection point of uncinate process.