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

Abstract

ObjectiveSubsidence 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.MethodsWe 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).ResultsSubsidence 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).ConclusionThe UPR measurement method confirmed that UPR was correlated with subsidence. Particularly when the sum of pUPR is ≥38%, the possibility of subsidence increased.

The Effect of Bi-Cortical Screw Fixation for Subsidence and Cervical Alignment in Patients Undergoing Single-Level Anterior Cervical Discectomy and Fusion

“…Graft subsidence is one of the major complications of ACDF, which can result in foraminal stenosis, segmental kyphosis, pseudarthrosis, and adjacent segment disease 12) . The known risk factors of subsidence after ACDF are age, BMI, smoking history, low BMD 2)…”

“…, end plate preparation 15) , cage type 1,7,22) , location 21) , cervical alignment 13,14) , and a small degree of segmental instability 10,12,19,25) . Furthermore, Lee et al 14) suggested that the main surgical and patient factors affecting subsidence are cervical alignment, age, and use of plates system.…”

“…there was scarce evidence that subtle difference in subsidence contributes to directly favorable patient outcomes. However, considering the fact that severe complications can result from severe subsidence such as foraminal stenosis 12) or adjacent segment disease 1,7,22,26) . Surgeons should not neglect the subsidence.…”

“…The known risk factors for subsidence are age, body mass index (BMI), smoking history, low bone mineral density (BMD) 2) , end plate preparation 15) , cage type 1,7,22,26) , and location 21) . Furthermore, in a recent clinical study, cervical alignment 13,14) and even a small degree of segmental instability 10,12,19,25) have been suggested as risk factors for subsidence.…”

Influence of complete uncinate process removal on 2-year assessment of radiologic outcomes: subsidence and sagittal balance in patients receiving one-level anterior cervical discectomy and fusion

“…Although most anterior cervical discectomy and fusion procedures include cervical uncosectomy or uncoforaminotomy to decompress nerve roots in patients with cervical radiculopathy, Lee DH et al reported that complete uncinate process resection (UPR) during ACDF improves pain in a patient's arm more rapidly than conventional ACDF without UPR and provides similar fusion rates [3,5]. Meanwhile, SH Lee et al reported that complete UPR over 38% during ACDF increases the risk of subsidence during follow up [4].…”