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Zhuo Xi, Shane Burch, Praveen V. Mummaneni, Rory Richard Mayer, Charles Eichler and Dean Chou

OBJECTIVE

Obese patients have been shown to have longer operative times and more complications from surgery. However, for obese patients undergoing minimally invasive surgery, these differences may not be as significant. In the lateral position, it is thought that obesity is less of an issue because gravity pulls the visceral fat away from the spine; however, this observation is primarily anecdotal and based on expert opinion. The authors performed oblique lumbar interbody fusion (OLIF) and they report on the perioperative morbidity in obese and nonobese patients.

METHODS

The authors conducted a retrospective review of patients who underwent OLIF performed by 3 spine surgeons and 1 vascular surgeon at the University of California, San Francisco, from 2013 to 2018. Data collected included demographic variables; approach-related factors such as operative time, blood loss, and expected temporary approach-related sequelae; and overall complications. Patients were categorized according to their body mass index (BMI). Obesity was defined as a BMI ≥ 30 kg/m2, and severe obesity was defined as a BMI ≥ 35 kg/m2.

RESULTS

There were 238 patients (95 males and 143 females). There were no significant differences between the obese and nonobese groups in terms of sex, levels fused, or smoking status. For the entire cohort, there was no difference in operative time, blood loss, or complications when comparing obese and nonobese patients. However, a subset analysis of the 77 multilevel OLIFs that included L5–S1 demonstrated that the operative times for the nonobese group was 223.55 ± 57.93 minutes, whereas it was 273.75 ± 90.07 minutes for the obese group (p = 0.004). In this subset, the expected approach-related sequela rate was 13.2% for the nonobese group, whereas it was 33.3% for the obese group (p = 0.039). However, the two groups had similar blood loss (p = 0.476) and complication rates (p = 0.876).

CONCLUSIONS

Obesity and morbid obesity generally do not increase the operative time, blood loss, approach-related sequelae, or complications following OLIF. However, obese patients who undergo multilevel OLIF that includes the L5–S1 level do have longer operative times or a higher rate of expected approach-related sequelae. Obesity should not be considered a contraindication to multilevel OLIF, but patients should be informed of potentially increased morbidity if the L5–S1 level is to be included.

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Minghao Wang, Praveen V. Mummaneni, Zhuo Xi, Chih-Chang Chang, Joshua Rivera, Jeremy Guinn, Rory Mayer and Dean Chou

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.

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Zhuo Xi, Dean Chou, Praveen V. Mummaneni, Huibing Ruan, Charles Eichler, Chih-Chang Chang and Shane Burch

OBJECTIVE

In adult spinal deformity and degenerative conditions of the spine, interbody fusion to the sacrum often is performed to enhance arthrodesis, induce lordosis, and alleviate stenosis. Anterior lumbar interbody fusion (ALIF) has traditionally been performed, but minimally invasive oblique lumbar interbody fusion (OLIF) may or may not cause less morbidity because less retraction of the abdominal viscera is required. The authors evaluated whether there was a difference between the results of ALIF and OLIF in multilevel anterior or lateral interbody fusion to the sacrum.

METHODS

Patients from 2013 to 2018 who underwent multilevel ALIF or OLIF to the sacrum were retrospectively studied. Inclusion criteria were adult spinal deformity or degenerative pathology and multilevel ALIF or OLIF to the sacrum. Demographic, implant, perioperative, and radiographic variables were collected. Statistical calculations were performed for significant differences.

RESULTS

Data from a total of 127 patients were analyzed (66 OLIF patients and 61 ALIF patients). The mean follow-up times were 27.21 (ALIF) and 24.11 (OLIF) months. The mean surgical time was 251.48 minutes for ALIF patients and 234.48 minutes for OLIF patients (p = 0.154). The mean hospital stay was 7.79 days for ALIF patients and 7.02 days for OLIF patients (p = 0.159). The mean time to being able to eat solid food was 4.03 days for ALIF patients and 1.30 days for OLIF patients (p < 0.001). After excluding patients who had undergone L5–S1 posterior column osteotomy, 54 ALIF patients and 41 OLIF patients were analyzed for L5–S1 radiographic changes. The mean cage height was 14.94 mm for ALIF patients and 13.56 mm for OLIF patients (p = 0.001), and the mean cage lordosis was 15.87° in the ALIF group and 16.81° in the OLIF group (p = 0.278). The mean increases in anterior disc height were 7.34 mm and 4.72 mm for the ALIF and OLIF groups, respectively (p = 0.001), and the mean increases in posterior disc height were 3.35 mm and 1.24 mm (p < 0.001), respectively. The mean change in L5–S1 lordosis was 4.33° for ALIF patients and 4.59° for OLIF patients (p = 0.829).

CONCLUSIONS

Patients who underwent multilevel OLIF and ALIF to the sacrum had comparable operative times. OLIF was associated with a quicker ileus recovery and less blood loss. At L5–S1, ALIF allowed larger cages to be placed, resulting in a greater disc height change, but there was no significant difference in L5–S1 segmental lordosis.

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Ping-Guo Duan, Praveen V. Mummaneni, Joshua Rivera, Jeremy M. V. Guinn, Minghao Wang, Zhuo Xi, Bo Li, Hao-Hua Wu, Christopher P. Ames, Shane Burch, Sigurd H. Berven and Dean Chou

OBJECTIVE

Patients undergoing long-segment fusions from the lower thoracic (LT) spine to the sacrum for adult spinal deformity (ASD) correction are at risk for proximal junctional kyphosis (PJK). One mechanism of PJK is fracture of the upper instrumented vertebra (UIV) or higher (UIV+1), which may be related to bone mineral density (BMD). Because Hounsfield units (HUs) on CT correlate with BMD, the authors evaluated whether HU values were correlated with PJK after long fusions for ASD.

METHODS

The authors performed a retrospective study of patients older than 50 years who had undergone ASD correction from the LT spine to the sacrum in the period from October 2007 to January 2018 and had a minimum 2-year follow-up. Demographic and spinopelvic parameters were measured. HU values were measured on preoperative CT at the UIV, UIV+1, and UIV+2 (2 levels above the UIV) levels and were assessed for correlations with PJK.

RESULTS

The records of 127 patients were reviewed. Fifty-four patients (19 males and 35 females) with a mean age of 64.91 years and mean follow-up of 3.19 years met the study inclusion criteria; there were 29 patients with PJK and 25 patients without. There was no statistically significant difference in demographics or follow-up between these two groups. Neither was there a difference between the groups with regard to postoperative pelvic incidence (PI), sacral slope (SS), lumbar lordosis (LL), PI minus LL (PI-LL), thoracic kyphosis (TK), or sagittal vertical axis (SVA; all p > 0.05). Postoperative pelvic tilt (p = 0.003) and T1 pelvic angle (p = 0.014) were significantly higher in patients with PJK than in those without. Preoperative HUs at UIV, UIV+1, and UIV+2 were 120.41, 124.52, and 129.28 in the patients with PJK, respectively, and 152.80, 155.96, and 160.00 in the patients without PJK, respectively (p = 0.011, 0.02, and 0.018). Three receiver operating characteristic (ROC) curves for preoperative HU values at the UIV, UIV+1, and UIV+2 as a predictor for PJK were established, with areas under the ROC curve of 0.710 (95% CI 0.574–0.847), 0.679 (95% CI 0.536–0.821), and 0.681 (95% CI 0.539–0.824), respectively. The optimal HU value by Youden index was 104 HU at the UIV (sensitivity 0.840, specificity 0.517), 113 HU at the UIV+1 (sensitivity 0.720, specificity 0.517), and 110 HU at the UIV+2 (sensitivity 0.880, specificity 0.448).

CONCLUSIONS

In patients undergoing long-segment fusions from the LT spine to the sacrum for ASD, PJK was associated with lower HU values on CT at the UIV, UIV+1, and UIV+2. The measurement of HU values on preoperative CTs may be a useful adjunct for ASD surgery planning.

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Zhuo Xi, Praveen V. Mummaneni, Minghao Wang, Huibing Ruan, Shane Burch, Vedat Deviren, Aaron J. Clark, Sigurd H. Berven and Dean Chou

OBJECTIVE

One 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.

METHODS

A 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.

RESULTS

After 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).

CONCLUSIONS

Lower 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.