J Korean Neurosurg Soc.  2017 Sep;60(5):550-559. 10.3340/jkns.2017.0202.014.

The Effect of Uncinate Process Resection on Subsidence Following Anterior Cervical Discectomy and Fusion

• Lee SH
• Lee JS
• Sung SK
• Son DW
• Lee SW
• Song GS

• KMID: 2457962
• DOI: http://doi.org/10.3340/jkns.2017.0202.014

Abstract

OBJECTIVE
Subsidence is a frequent complication of anterior cervical discectomy and fusion. Postoperative segmental micro-motion, thought to be a causative factor of subsidence, has been speculated to increase with uncinate process resection area (UPR). To evaluate the effect of UPR on micro-motion, we designed a method to measure UPR area based on pre- and postoperative computed tomography images and analyzed the relationship between UPR and subsidence as a proxy of micro-motion.
METHODS
We retrospectively collected clinical and radiological data from January 2011 to June 2016. A total of 38 patients (53 segments) were included. All procedures included bilateral UPR and anterior plate fixation. UPR area was evaluated with reformatted coronal computer tomography images. To reduce level-related bias, we converted UPR area to the proportion of UPR to the pre-operative UP area (pUPR).
RESULTS
Subsidence occurred in 18 segments (34%) and positively correlated with right-side pUPR, left-side pUPR, and the sum of bilateral pUPR (sum pUPR) (R=0.310, 301, 364; p=0.024, 0.029, 0.007, respectively). Multiple linear regression analysis revealed that subsidence could be estimated with the following formula: subsidence=1.522+2.7×sum pUPR (R2=0.133, p=0.007). Receiver-operating characteristic analysis determined that sum pUPR≥0.38 could serve as a threshold for significantly increased risk of subsidence (p=0.005, area under curve=0.737, sensitivity=94%, specificity=51%). This threshold was confirmed by logistic regression analysis for subsidence (p=0.009, odds ratio=8.471).
CONCLUSION
The UPR measurement method confirmed that UPR was correlated with subsidence. Particularly when the sum of pUPR is ≥38%, the possibility of subsidence increased.

Keyword

Spondylosis; Prosthesis failure; Zygapophyseal joint; Spinal fusion; Complication

MeSH Terms

Bias (Epidemiology)
Diskectomy*
Humans
Linear Models
Logistic Models
Methods
Prosthesis Failure
Proxy
Retrospective Studies
Spinal Fusion
Spondylosis
Zygapophyseal Joint

Figure

• 

  Fig. 1 Scheme illustrating the proposed relationship between uncinated process resection (UPR) and subsidence during anterior cervical discectomy and fusion (ACDF). The upper line demonstrates ACDF without UPR. Because of the intact uncovertebral joint, the segment achieves rigid stability. The lower line demonstrates ACDF with UPR. Through the disruption of bony structures and ligaments, UPR causes more micro-motion, which leads to the increase of subsidence. UP: uncinated process, VB: vertebral body, Lig.: ligaments surrounding uncovertebral joints.

• 

  Fig. 2 Flow diagram depicting the patient inclusion process. ACDF: anterior cervical discectomy and fusion, CT: computed tomography, UPR: uncinated process resection area, SA: stand-alone cage, TDR: total disc replacement.

• 

  Fig. 3 Three sequential sections were obtained from the most posterior vertebral body toward the anterior direction. A: Pre-operative axial image at C6–7. B: postoperative axial image at the same level. A1–3: Pre-operative coronal images. B1–3: postoperative coronal images, with the number corresponding to the axial image (A and B).

• 

  Fig. 4 Area measurements (uncinate process and vertebral body). A: Pre-operative (op), B: post-op coronal reformatted CT image at C5/6. C and D: The images are inverted. The base of the post-op UP was defined as a line connecting two points at the pre-op UP height. E and F: Measurements of bilateral UPs and VB. G and H: Schema of the UP and VB. I=pre-op right (Rt.) UP, J=pre-op left (Lt.) UP, K=pre-op VB, L=post-op Rt. UP, M=post-op Rt. UP, N=post-op VB. Rt. pUPR=1−L/I, the difference in VB=K−N. CT: computed tomography, UP: uncinate process, VB: vertebral body, pUPR: proportion of UPR to pre-UP.

• 

  Fig. 5 Simple scatter graph and regression analysis between subsidence and the sum of bilateral pUPR (p=0.007; R2=0.133; adjusted R2=0.116). pUPR: proportion of uncinate process resection to pre-uncinate process area.

• 

  Fig. 6 Receiver operating characteristic (ROC) analysis was performed to determine the cut-off value of sum pUPR that induced significant subsidence. Sum pUPR above 0.38 could serve as a threshold for significantly increased risk of subsidence (p=0.005, AUC=0.737, sensitivity=94%, specificity=51%). pUPR: proportion of uncinate process resection (UPR) to pre-uncinate process (UP) area.

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  Fig. 7 Simple scatter plot: linear regression line with 95% confidence interval between subsidence and the sum of bilateral pUPR in ACDF with stand-alone PEEK cage (R=0.139, p=0.595). The dashed line represents the expected subsidence calculated by formula 2: subsidence=1.522+2.7×sum pUPR. pUPR: proportion of uncinate process resection to pre-uncinate process area, ACDF: anterior cervical discectomy and fusion, PEEK: polyether-ether-ketone.

Reference

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