J Korean Neurosurg Soc.  2022 Jan;65(1):96-106. 10.3340/jkns.2021.0131.

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

• Lee JS
• Son DW
• Lee SH
• Ki SS
• Lee SW
• Song GS
• Woo JB
• Kim YH

• KMID: 2523917
• DOI: http://doi.org/10.3340/jkns.2021.0131

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.

Keyword

Cervical vertebrae; Prosthesis failure; Risk assessment; Osteoporosis; Computed tomography

Figure

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  Fig. 1. Measurement of the preoperative radiologic parameters. TIH : total intervertebral height, SA : segmental angle, CA : C2-7 cobb angle, SVA : sagittal vertical axis.

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  Fig. 2. A and b : Definition of intraoperative distraction, [(post disc H – pre disc H) / pre disc H] × 100.0 (%)]. H : height ant mid portion of disc space.

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  Fig. 3. Measurement of Hounsfield units. A : Axial image of preoperative computed tomography (CT) image. Red line : Region of interest (ROI) area including cortical bone and cancellous bone, blue line : ROI area including cancellous bone. b : Sagittal section of preoperative CT image. SD : standard deviation.

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  Fig. 4. The flow for each of the two risk factors of the cage decrement. HU : Hounsfield unit.

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  Fig. 5. Change of the mean value of total intervertebral height according to the risk factors from preoperative to follow up period. A : Risk factor : HU value <530 (upper vertebral, cortical + cancellous). b : Risk factor : intraoperative distraction <22.41. C : Change of average total intervertebral height at cage decrement group and control group. HU : Hounsfield unit, FU : follow up, TIH : total intevertebral height.

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  Fig. 6. A 59-year old man patient presented with tingling sensation of both arm, C6/7 ACDF. A : Preoperative TIH : 35.34 mm. b : Postoperative TIH : 39.21 mm. C : F/U TIH : 35.44 mm. This case belonged to cage subsidence group, but it did not belong to cage decrement group (pre TIH : 35.34 mm

Reference

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