The Effect of Hounsfield Unit Value with Conventional Computed Tomography and Intraoperative Distraction on Postoperative Intervertebral Height Reduction in Patients Following Stand-Alone Anterior Cervical Discectomy and Fusion

Abstract

Objective : The most common complication of anterior cervical discectomy and fusion (ACDF) is cage subsidence and maintenance of disc height affects postoperative clinical outcomes. We considered cage subsidence as an inappropriate indicator for evaluating preservation of disc height. Thus, this study aimed to consider patients with complications such as reduced total disc height compared to that before surgery and evaluate the relevance of several factors before ACDF.Methods : We retrospectively reviewed the medical records of 40 patients who underwent stand-alone single-level ACDF using a polyetheretherketone (PEEK) cage at our institution between January 2012 and December 2018. Our study population comprised 19 male and 21 female patients aged 24–70 years. The minimum follow-up period was 1 year. Twenty-seven patients had preoperative bone mineral density (BMD) data on dual-energy X-ray absorptiometry. Clinical parameters included sex, age, body mass index, smoking history, and prior medical history. Radiologic parameters included the C2-7 cobb angle, segmental angle, sagittal vertical axis, disc height, and total intervertebral height (TIH) at the preoperative and postoperative periods. Cage decrement was defined as the reduction in TIH at the 6-month follow-up compared to preoperative TIH. To evaluate the bone quality, Hounsfield unit (HU) value was calculated in the axial and sagittal images of conventional computed tomography.Results : Lumbar BMD values and cervical HU values were significantly correlated (r=0.733, p<0.001). We divided the patients into two groups based on cage decrement, and 47.5% of the total patients were regarded as cage decrement. There were statistically significant differences in the parameters of measuring the HU value of the vertebra and intraoperative distraction between the two groups. Using these identified factors, we performed a receiver operating characteristic (ROC) curve analysis. Based on the ROC curve, the cut-off point was 530 at the HU value of the upper cortical and cancellous vertebrae (p=0.014; area under the curve [AUC], 0.727; sensitivity, 94.7%; specificity, 42.9%) and 22.41 at intraoperative distraction (p=0.017; AUC, 0.722; sensitivity, 85.7%; specificity, 57.9%). Using this value, we converted these parameters into a bifurcated variable and assessed the multinomial regression analysis to evaluate the risk factors for cage decrement in ACDF. Intraoperative distraction and HU value of the upper vertebral body were independent factors of postoperative subsidence.Conclusion : Insufficient intraoperative distraction and low HU value showed a strong relationship with postoperative intervertebral height reduction following single stand-alone PEEK cage ACDF.

Low cervical vertebral CT value increased early subsidence of titanium mesh cage after anterior cervical corpectomy and fusion

“…Wang et al [ 29 ] reported that lower preoperative HU values of the vertebral are associated with cage subsidence in single-level ACDF. Another study reported that lumbar BMD values were significantly correlated with cervical HU values; moreover, low HU values may lead to postoperative intervertebral height reduction [ 20 ].…”

“…Several reports have shown that the HU value of the vertebral was closely related to BMD and could evaluate the risk of pedicle screw loosening and cage subsidence in lumbar spine surgery [ 15 – 18 ]. A few studies have evaluated the association between vertebral body HU value and cage subsidence after anterior cervical discectomy and fusion (ACDF) [ 19 , 20 ]. However, the relationship between the HU value of the vertebral body and TMC subsidence in ACCF remains unclear.…”

Systematic Review and Meta-Analysis of the Effect of Osteoporosis on Fusion Rates and Complications Following Surgery for Degenerative Cervical Spine Pathology

“…Nine of these were retrospective cohort or database studies, and 2 were prospective cohort studies. [6][7][8][9][10][11][12][13][14][15][16] Of the 8 studies that assessed cage migration, 5 found that poor bone stock was associated with the development of this complication. 7,9,10,14, 15 Lee et al calculated Hounsfield units (HUs) based on 6 regions of the cervical spine in a cohort of 40 patients who underwent anterior cervical discectomy and fusion (ACDF) with stand-alone polyether-ether-ketone (PEEK) cages.…”

“…The literature currently presents conflicting evidence for many postoperative complications, including rates of cage subsidence, pseudarthrosis, readmission, and reoperation in osteoporotic patients following surgery for cervical spine pathology. [6][7][8][9][10][11][12][13][14][15][16] Thus, the purpose of this review is to systematically gather and analyze current data to create a more comprehensive understanding of how osteoporosis potentially impacts outcomes following surgery for degenerative cervical conditions.…”

A Novel Cervical Vertebral Bone Quality Score Independently Predicts Cage Subsidence After Anterior Cervical Diskectomy and Fusion

“…16 In the current study, cage subsidence was calculated using a well-validated method of total loss of segmental height as the difference from the postoperative X-ray taken within 1 week after surgery to the most recent follow-up X-ray. 10,[17][18][19][20] The segmental height was calculated on lateral X-ray as the distance from the inferior endplate of the inferior fused vertebral body to the superior endplate of the superior fused vertebral body. Cage subsidence was defined as ≥3 mm loss of segmental height of the fusion, which has been demonstrated as a well validated threshold in previous literature.…”