The association between lower Hounsfield units on computed tomography and cage subsidence after lateral lumbar interbody fusion

Abstract

OBJECTIVEOne vexing problem after lateral lumbar interbody fusion (LLIF) surgery is cage subsidence. Low bone mineral density (BMD) may contribute to subsidence, and BMD is correlated with Hounsfield units (HUs) on CT. The authors investigated if lower HU values correlated with subsidence after LLIF.METHODSA retrospective study of patients undergoing single-level LLIF with pedicle screw fixation for degenerative conditions at the University of California, San Francisco, by 6 spine surgeons was performed. Data on demographics, cage parameters, preoperative HUs on CT, and postoperative subsidence were collected. Thirty-six–inch standing radiographs were used to measure segmental lordosis, disc space height, and subsidence; data were collected immediately postoperatively and at 1 year. Subsidence was graded using a published grade of disc height loss: grade 0, 0%–24%; grade I, 25%–49%; grade II, 50%–74%; and grade III, 75%–100%. HU values were measured on preoperative CT from L1 to L5, and each lumbar vertebral body HU was measured 4 separate times.RESULTSAfter identifying 138 patients who underwent LLIF, 68 met the study inclusion criteria. All patients had single-level LLIF with pedicle screw fixation. The mean follow-up duration was 25.3 ± 10.4 months. There were 40 patients who had grade 0 subsidence, 15 grade I, 9 grade II, and 4 grade III. There were no significant differences in age, sex, BMI, or smoking. There were no significant differences in cage sizes, cage lordosis, and preoperative disc height. The mean segmental HU (the average HU value of the two vertebrae above and below the LLIF) was 169.5 ± 45 for grade 0, 130.3 ± 56.2 for grade I, 100.7 ± 30.2 for grade II, and 119.9 ± 52.9 for grade III (p < 0.001). After using a receiver operating characteristic curve to establish separation criteria between mild and severe subsidence, the most appropriate threshold of HU value was 135.02 between mild and severe subsidence (sensitivity 60%, specificity 92.3%). After univariate and multivariate analysis, preoperative segmental HU value was an independent risk factor for severe cage subsidence (p = 0.017, OR 15.694, 95% CI 1.621–151.961).CONCLUSIONSLower HU values on preoperative CT are associated with cage subsidence after LLIF. Measurement of preoperative HU values on CT may be useful when planning LLIF surgery.

Biomechanical Effects of Pedicle Screw Positioning on the Surgical Segment in Models After Oblique Lumbar Interbody Fusion: An in-silico Study

“…Biomechanical deteriorations initially trigger surgical segment complications. [6][7][8] Relations between screw positions and biomechanical environments have been widely reported. [9][10][11] This study has numerically investigated the effects of screw insertional position changes, and biomechanical indicators related to surgical segment complications (ie, cage subsidence, non-union, segmental instability, and fixation failure) have been computed and recorded.…”

“…2,5 Biomechanical deteriorations initially trigger these complications. [6][7][8] Studies reported that screw insertional positions and trajectories would affect the local biomechanical environment. [9][10][11] radiography guidance.…”

Comparative Study of Cage Subsidence in Single-Level Lateral Lumbar Interbody Fusion

“…Some groups have reported that HU values may serve as an assessment of osteoporosis, given the moderate correlation between HU values and osteoporosis [ 37 , 38 , 39 ]. HU values have also evaluated studies of LLIF cage subsidence [ 40 , 41 ]. It was shown that the decrease in the HU value of preoperative CT correlates with the severity of cage subsidence after LLIF.…”

Bone Phenotyping Approaches in Human, Mice and Zebrafish – Expert Overview of the EU Cost Action GEMSTONE (“GEnomics of MusculoSkeletal traits TranslatiOnal NEtwork”)

“…In clinical settings, aBMD is compared to a young reference cohort of the same ethnic background and sex, generating a T-score. The International Society of Clinical densitometry (ISCD) defines osteoporosis in adults as a T score ≤2.5, representing 2.5 standard deviations below the young reference mean value ( 69 ). Another score reported from DXA measurements is the Z-score.…”