Risk Factors of Allogenous Bone Graft Collapse in Two-Level Anterior Cervical Discectomy and Fusion

Abstract

Objective Anterior cervical discectomy and fusion (ACDF) is commonly used surgical procedure for cervical degenerative disease. Among the various intervertebral spacers, the use of allografts is increasing due to its advantages such as no harvest site complications and low rate of subsidence. Although subsidence is a rare complication, graft collapse is often observed in the follow-up period. Graft collapse is defined as a significant graft height loss without subsidence, which can lead to clinical deterioration due to foraminal re-stenosis or segmental kyphosis. However, studies about the collapse of allografts are very limited. In this study, we evaluated risk factors associated with graft collapse. Methods We retrospectively reviewed 33 patients who underwent two level ACDF with anterior plating using allogenous bone graft from January 2013 to June 2017. Various factors related to cervical sagittal alignment were measured preoperatively (PRE), postoperatively (POST), and last follow-up. The collapse was defined as the ratio of decrement from POST disc height to follow-up disc height. We also defined significant collapses as disc heights that were decreased by 30% or more after surgery. The intraoperative distraction was defined as the ratio of increment from PRE disc height to POST disc height. Results The subsidence rate was 4.5% and graft collapse rate was 28.8%. The pseudarthrosis rate was 16.7% and there was no association between pseudarthrosis and graft collapse. Among the collapse-related risk factors, pre-operative segmental angle ( p =0.047) and intra-operative distraction ( p =0.003) were significantly related to allograft collapse. The cut-off value of intraoperative distraction ≥37.3% was significantly associated with collapse ( p =0.009; odds ratio, 4.622; 95% confidence interval, 1.470-14.531). The average time of events were as follows: collapse, 5.8±5.7 months; subsidence, 0.99±0.50 months; and instrument failure, 9.13±0.50 months. Conclusion We experienced a higher frequency rate of collapse than subsidence in ACDF using an allograft. Of the various preoperative factors, intra-operative distraction was the most predictable factor of the allograft collapse. This was especially true when the intraoperative distraction was more than 37%, in which case the occurrence of graft collapse increased 4.6 times. We also found that instrument failure occurs only after the allograft collapse.

Morphologic Change of Cortico-Cancellous Allograft used for Anterior Cervical Discectomy and Fusion

“…16 Furthermore, Woo et al reported that the graft collapse rate of cortico-cancellous allograft reached 28.8% when significant collapse was assessed by a decrease in disc height of > 30%. 12 However, these reports did not demonstrate whether graft failure, including resorption or fracture, can affect bone union, subsidence, and lordosis restoration.…”

“…In their retrospective study, Woo et al showed that intraoperative distraction of > 37% from the preoperative disc height increases the chance of allograft failure. 12 Moreover, increased interbody spacer height has been reported as a risk factor for subsidence. 26 Finally, since logistic regression analysis in the present study showed that an increased number of surgical levels are risk factors for allograft failure, special care while applying anterior plating or bone graft would be needed for multilevel surgeries.…”

“…9,11,12 Although previous studies have reported the incidence of morphologic changes, including resorption and fracture of the corticocancellous allograft, the clinical impact of such complications is still unclear. 12 Understanding the incidence and clinical significance of graft resorption and fracture associated with corticocancellous allograft would be helpful to physicians for selecting interbody devices and also aid surgeons cope with such complications appropriately. Therefore, the present study aimed to evaluate the incidence of graft morphologic changes in corticocancellous allografts, such as graft resorption or fracture, and clarify the clinical impact of graft morphologic changes on radiological and clinical outcomes of ACDF in terms of fusion rate, subsidence, sagittal alignment, and patient-reported outcome measures.…”

“…9,11 However, corticocancellous allografts are not associated with graft-related complications, such as graft resorption and fracture. 9,11,12 Although previous studies have reported the incidence of morphologic changes, including resorption and fracture of the corticocancellous allograft, the clinical impact of such complications is still unclear. 12 Understanding the incidence and clinical significance of graft resorption and fracture associated with corticocancellous allograft would be helpful to physicians for selecting interbody devices and also aid surgeons cope with such complications appropriately.…”

Short Plate with Screw Angle over 20 Degrees Improves the Radiologic Outcome in ACDF: Clinical Study

“…Implant-related complications, such as graft failure, subsidence and screw pullout are major concerns in ACDF-only surgeries. Graft collapse has been reported to occur at 28.8% [ 18 , 19 ]. The risk of subsidence with stand-alone cage or allospacer still remain as one of the main complications with this technique.…”