Lower Hounsfield units on CT are associated with cage subsidence after anterior cervical discectomy and fusion

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  • 1 Department of Neurological Surgery, University of California, San Francisco, California; and
  • 2 Department of Neurosurgery, First Affiliated Hospital of China Medical University, Shenyang, China
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OBJECTIVE

A consequence of anterior cervical discectomy and fusion (ACDF) is graft subsidence, potentially leading to kyphosis, nonunion, foraminal stenosis, and recurrent pain. Bone density, as measured in Hounsfield units (HUs) on CT, may be associated with subsidence. The authors evaluated the association between HUs and subsidence rates after ACDF.

METHODS

A retrospective study of patients treated with single-level ACDF at the University of California, San Francisco, from 2008 to 2017 was performed. HU values were measured according to previously published methods. Only patients with preoperative CT, minimum 1-year follow-up, and single-level ACDF were included. Patients with posterior surgery, tumor, infection, trauma, deformity, or osteoporosis treatment were excluded. Changes in segmental height were measured at 1-year follow-up compared with immediate postoperative radiographs. Subsidence was defined as segmental height loss of more than 2 mm.

RESULTS

A total of 91 patients met inclusion criteria. There was no significant difference in age or sex between the subsidence and nonsubsidence groups. Mean HU values in the subsidence group (320.8 ± 23.9, n = 8) were significantly lower than those of the nonsubsidence group (389.1 ± 53.7, n = 83, p < 0.01, t-test). There was a negative correlation between the HU values and segmental height loss (Pearson’s coefficient −0.735, p = 0.01). Using receiver operating characteristic curves, the area under the curve was 0.89, and the most appropriate threshold of HU value was 343.7 (sensitivity 77.1%, specificity 87.5%). A preoperative lower HU is a risk factor for postoperative subsidence (binary logistic regression, p < 0.05). The subsidence rate and distance between allograft and polyetheretherketone (PEEK) materials were not significantly different (PEEK 0.9 ± 0.7 mm, allograft 1.0 ± 0.7 mm; p > 0.05).

CONCLUSIONS

Lower preoperative CT HU values are associated with cage subsidence in single-level ACDF. Preoperative measurement of HUs may be useful in predicting outcomes after ACDF.

ABBREVIATIONS ACDF = anterior cervical discectomy and fusion; AUC = area under the ROC curve; BMD = bone mineral density; DEXA = dual-energy x-ray absorptiometry; HU = Hounsfield unit; PEEK = polyetheretherketone; ROC = receiver operating characteristic; ROI = region of interest.

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Contributor Notes

Correspondence Minghao Wang: First Affiliated Hospital of China Medical University, Shenyang, China. wisewangmh@hotmail.com.

INCLUDE WHEN CITING Published online June 5, 2020; DOI: 10.3171/2020.3.SPINE2035.

Disclosures Dr. Mummaneni reports being a consultant to DePuy Synthes, Globus, and Stryker; having direct stock ownership in Spinicity/ISD; receiving support of non–study-related clinical or research effort from NREF, ISSG, and AO Spine; and receiving royalties from DePuy Synthes, Thieme Publishers, and Springer Publishers. Dr. Chou reports being a consultant to Medtronic and Globus, and receiving royalties from Globus.

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