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Use of Hounsfield units of S1 body to diagnose osteoporosis in patients with lumbar degenerative diseases

Da Zou, Weishi Li, Fei Xu, and Guohong Du

OBJECTIVE

The aim of this study was to evaluate the use of Hounsfield unit (HU) values of the S1 body to diagnose osteoporosis in patients with lumbar degenerative diseases.

METHODS

The records of 316 patients of ages ≥ 50 years and requiring surgery for lumbar degenerative diseases were reviewed. The bone mineral density (BMD) of the S1 body and L1 was measured in HU with preoperative lumbar CT. Circular regions of interest (ROIs) were placed on midaxial and midsagittal images of the S1 body. Dual-energy x-ray absorptiometry (DXA) and the criterion of L1 HU ≤ 110 HU were used to diagnose osteoporosis. The area under the receiver operating characteristic curve (AUC) was calculated to assess the use of HUs of the S1 body to diagnose osteoporosis.

RESULTS

The interobserver and intraobserver reliability of measuring HU of the S1 body was excellent with intraclass correlation coefficients over 0.8 (p < 0.001). The correlation between HUs of the S1 body and average T-score of L1–4 was significant with Pearson correlation coefficients ≥ 0.60 (p < 0.001). The AUCs for using HUs of the S1 body to diagnose osteoporosis were 0.86 and 0.88 for axial HU and sagittal HU, respectively (p < 0.001). The HU thresholds with balanced sensitivity and specificity for diagnosing osteoporosis were 202 HU for axial HU (sensitivity: 76%; specificity: 76%) and 185 HU for sagittal HU (sensitivity: 80%; specificity: 80%).

CONCLUSIONS

Both sagittal and axial HUs of the S1 body are useful tools for assessing BMD and diagnosing osteoporosis. Measuring HUs of the S1 body preoperatively from lumbar CT may help with surgical planning for patients with lumbar degenerative diseases.

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Computed tomography Hounsfield unit–based prediction of pedicle screw loosening after surgery for degenerative lumbar spine disease

Da Zou, Aikeremujiang Muheremu, Zhuoran Sun, Woquan Zhong, Shuai Jiang, and Weishi Li

OBJECTIVE

The authors investigated the relation between Hounsfield unit (HU) values measured on CT and the risk of pedicle screw loosening in patients who underwent lumbar pedicle screw fixation for degenerative lumbar spine disease.

METHODS

Patients who were treated with lumbar pedicle screw fixation between July 2011 and December 2015 at the authors’ department were reviewed. Age, sex, BMI, smoking and diabetes histories, range of fixation, and fusion method were recorded as the basic patient information. The HU values for lumbar bone mineral density (BMD) for the L1, L2, L3, and L4 vertebra were measured on CT scans. Logistic regression analysis was used to identify the independent influencing factors of pedicle screw loosening.

RESULTS

A total of 503 patients were included in the final analysis. The pedicle screw loosening rate at the 12-month follow-up was 30.0% (151 of 503 patients). There were no significant differences in sex, BMI, or histories of smoking and diabetes between the patients with (loosening group) and those without (nonloosening group) screw loosening (p > 0.05). The mean HU value of L1–4 was lower in the loosening group than the nonloosening group (106.3 ± 33.9 vs 132.6 ± 42.9, p < 0.001). In logistic regression analysis, being male (OR 2.065; 95% CI 1.242–3.433), HU value (OR 0.977; 95% CI 0.970–0.985), length of fixation (OR 3.616; 95% CI 2.617–4.996), and fixation to S1 (OR 1.699; 95% CI 1.039–2.777) were the independent influencing factors for screw loosening.

CONCLUSIONS

HU value measured on CT was an independent predictor for pedicle screw loosening, and lower HU value was significantly correlated with higher risk of screw loosening.

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Hounsfield units of the vertebral body and pedicle as predictors of pedicle screw loosening after degenerative lumbar spine surgery

Fei Xu, Da Zou, Weishi Li, Zhuoran Sun, Shuai Jiang, Siyu Zhou, and Zhuofu Li

OBJECTIVE

The authors aimed to compare the efficacy of lumbar vertebral body Hounsfield units (HUs) and pedicle HUs at predicting pedicle screw loosening.

METHODS

The authors retrospectively assessed 143 patients with L3–5 instrumentation. The patients were classified into one of two groups based on the status of their L3 screws (a screw loosening group or a control group). The pedicle HUs and vertebral HUs of L3 were measured using preoperative lumbar CT scans, and the pedicle HUs were measured in two ways: by excluding or by including cortical bone.

RESULTS

The screw loosening rate was 20.3% (n = 29/143) at the 12-month follow-up. The vertebral body HUs and pedicle HUs in the screw loosening group were lower than those in the control group (vertebral body group: 98.6 HUs vs 121.4 HUs, p < 0.001; pedicle excluding cortical bone: 208.9 HUs vs 290.5 HUs, p = 0.002; pedicle including cortical bone: 249.4 HUs vs 337.5 HUs, p < 0.001). The pedicle HUs tended to have a higher area under the receiver operating characteristic curve value in predicting screw loosening, compared with that of vertebral body HUs, but the difference was not statistically significant (p > 0.05). Among patients with low vertebral body HUs of ≤ 130, the loosening rate was much lower in patients with pedicle HUs of ≤ 340 than in those with pedicle HUs of > 340 (31.0% vs 13.0%, respectively; p < 0.05).

CONCLUSIONS

Vertebral body HUs alone are insufficient to accurately evaluate the risk of pedicle screw loosening. Therefore, it is important to collect both the pedicle HU and vertebral body HU measurements for surgical planning.

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Collaborative spinal robot system for laminectomy: a preliminary study

Zhuofu Li, Shuai Jiang, Xiongkang Song, Shanshan Liu, Chengxia Wang, Lei Hu, and Weishi Li

OBJECTIVE

The application of robots in the field of pedicle screw placement has achieved great success. However, decompressive laminectomy, a step that is just as critical as pedicle screw placement, does not have a mature robot-assisted system. To address this lack, the authors designed a collaborative spine robot system to assist with laminectomy. In this study, they aimed to investigate the reliability of this novel collaborative spinal robot system and compare it with manual laminectomy (ML).

METHODS

Thirty in vitro porcine lumbar vertebral specimens were obtained as experimental bone specimens. Robot-assisted laminectomy (RAL) was performed on the left side of the lamina (n = 30) and ML was performed on the right side (n = 30). The time required for laminectomy on one side, whether the lamina was penetrated, and the remaining thickness of the lamina were compared between the two groups.

RESULTS

The time required for laminectomy on one side was longer in the RAL group than in the ML group (median 326 seconds [IQR 133 seconds] vs 108.5 seconds [IQR 43 seconds], p < 0.001). In the RAL group, complete lamina penetration occurred twice (6.7%), while in the ML group, it occurred 9 times (30%); the difference was statistically significant (p = 0.045). There was no statistically significant difference in the remaining lamina thickness between the two groups (median 1.035 mm [IQR 0.419 mm] vs 1.084 mm [IQR 0.383 mm], p = 0.842).

CONCLUSIONS

The results of this study confirm the safety of this novel spinal robot system for laminectomy. However, its efficiency requires further improvement.

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Apical segmental resection osteotomy with dual axial rotation corrective technique for severe focal kyphosis of the thoracolumbar spine

Clinical article

Zhongqiang Chen, Yan Zeng, Weishi Li, Zhaoqing Guo, Qiang Qi, and Chuiguo Sun

Object

In this paper, the authors' goal was to evaluate the feasibility, safety, and efficacy of apical segment resection osteotomy with dual axial rotation correction for severe focal kyphosis by examining outcomes.

Methods

Between May 2004 and December 2006, the authors treated 23 patients with severe focal kyphosis (average Cobb angle 86.9°, range 50°–130°) using apical segmental resection osteotomy with dual axial rotation correction and instrumented anterior column reconstruction and fusion. Radiographic assessment of sagittal plane balance and kyphotic Cobb angle (including a scoliosis Cobb angle in 9 cases) was performed in each patient before and immediately after surgery and at the last follow-up (minimum 2 years). The Frankel grading system for neurological function and Oswestry Disability Index for quality of life were evaluated before surgery and at the last follow-up. The patient satisfaction index was also used for clinical evaluation at the last follow-up.

Results

The mean surgical time was 6.7 hours. The average blood loss was 2960 ml. All patients underwent follow-up for 2 or more years after surgery. The fusion rate was 95.65%. The average kyphotic angle improved from 86.9° preoperatively to 25.6° immediately postoperatively, with an average correction rate of 72.17%. At the last follow-up, the average kyphotic angle was 27.4°, making the final correction rate 69.87%. The sagittal plane balance was significantly improved at the last follow-up. Preoperatively, 15 patients had neurological deficits, and the Frankel grade was E in 8 cases, D in 8 cases, C in 6 cases, and B in 1 case. At the last follow-up, 15 cases were Grade E, 5 were Grade D, and 3 were Grade C. The average improvement in the Oswestry Disability Index score was 43.30%. The patient satisfaction index result showed a total satisfaction rate of 91.30%. Complications included 1 case of late neurological deficit due to shifting of an expandable artificial vertebra, 5 cases of nerve root injury, 3 cases of dural tear, and 1 case of transient lower-extremity weakness due to insufficient blood supply to the spinal cord during surgery.

Conclusions

Apical segmental resection osteotomy with dual axial rotation correction and instrumented fusion is an effective and safe way to treat severe focal kyphosis of the thoracolumbar spine.

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Clinical and radiographic evaluation of posterior surgical correction for the treatment of moderate to severe post-tuberculosis kyphosis in 36 cases with a minimum 2-year follow-up

Clinical article

Yan Zeng, Zhongqiang Chen, Qiang Qi, Zhaoqing Guo, Weishi Li, Chuiguo Sun, and Andrew P. White

Object

The object of this study was to compare the clinical and radiographic outcomes of 36 patients with posttuberculosis kyphosis who underwent one of two types of osteotomy.

Methods

Each patient underwent single-stage correction via a posterior surgical approach. A modified pedicle subtraction osteotomy (mPSO) was performed when the kyphotic deformity was less than 70° (7 cases), whereas a posterior vertebral column resection (VCR) was performed when the kyphotic deformity exceeded 70° (29 cases). Full-length standing radiographs were obtained before surgery and at follow-up visits. These images were used to measure the kyphosis angle; sagittal alignment of the lumbar, thoracic, and cervical regions; and sagittal balance of the spine. Back pain was rated using the visual analog scale (VAS), and neurological function was classified based on the American Spinal Injury Association (ASIA) grading system. Each patient's overall satisfaction with surgical treatment was measured with the Patient Satisfaction Index. For purposes of comparison, patients were studied in 2 groups based on the region of their kyphotic apex. Half of the cohort had apical kyphosis in the lower thoracic spine or thoracolumbar junction (TL group). Using both radiographic and clinical assessments, the authors compared this group with the other half of the patients who had apical kyphosis in the upper to mid thoracic spine (MT group).

Results

The cohort included 15 males and 21 females, with an average age of 34 years at the time of surgery. The minimum follow-up was 24 months, and the mean follow-up was 31 months. Following surgery, kyphosis across the treated segments was reduced by an average of 60°. Lumbar lordosis also improved by an average of 24°, and thoracic kyphosis improved by an average of 20°. Both back pain and neurological function improved after surgical treatment. There was a 67% improvement in VAS scores, and 13 of the 36 patients had improvement in their ASIA grade. The 2 surgical procedures used for deformity correction (mPSO and VCR) demonstrated comparable radiographic and clinical results. Note, however, that differences were found in both radiographic and clinical outcomes in comparing patients who had lower thoracic or thoracolumbar (TL group) versus upper to midthoracic (MT group) apical kyphosis.

Conclusions

Posterior tubercular kyphosis can be effectively improved through corrective surgery, and deformity correction can be accompanied by improvement in clinical symptoms. When appropriately selected, both the mPSO and the VCR can be expected to yield satisfactory reduction of post-tuberculosis kyphotic deformities. Differences in radiographic and clinical outcomes should be anticipated, however, when treating such deformities in different regions of the spine.

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Diagnosis and treatment of ossification of the ligamentum flavum associated with dural ossification

Clinical article

Xin-Zhi Sun, Zhong-Qiang Chen, Qiang Qi, Zhao-Qing Guo, Chui-Guo Sun, Wei-Shi Li, and Yan Zeng

Object

In this paper, the authors aimed to summarize the clinical characteristics of ossification of the ligamentum flavum (OLF) associated with dural ossification (DO) and to identify improved methods for preoperative diagnosis.

Methods

Thirty-six patients who had undergone OLF surgery between February 2005 and September 2009 were included in this retrospective study. The patients were divided into 2 groups: one that included patients with intraoperative evidence of DO and a second group that included patients without DO. The clinical features of DO were summarized and the neurological status of the patients was evaluated pre- and postoperatively.

Results

The incidence rate of DO associated with OLF was 39% (14/36). The sensitivity and specificity of the tram track sign were found to be 93% and 59%, respectively. Dural ossification was found among 86% of the patients with tuberous type Sato classification. The postoperative neurological status of patients was generally improved relative to that observed prior to surgery, although neurological recovery did not differ between the 2 groups. Cerebrospinal fluid leakage was the main complication, occurring predominantly in the patients with DO, and all leaks resolved in all patients after comprehensive treatments.

Conclusions

The tram track sign and Sato classification were found to be useful for preoperative diagnosis of DO and for determining the surgical procedure to be performed. Dural ossification had no effect on postoperative neurological recovery.

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Incidence and risk factors of dural ossification in patients with thoracic ossification of the ligamentum flavum

Yongzhao Zhao, Qian Xiang, Shuai Jiang, Jialiang Lin, Longjie Wang, Chuiguo Sun, and Weishi Li

OBJECTIVE

Dural ossification (DO) is a common clinical feature in patients with thoracic ossification of the ligamentum flavum (OLF) and associated with the increased risk of perioperative complications. However, few studies have been conducted to determine the incidence and independent risk factors of DO in patients with thoracic OLF. The aim of this retrospective study was to determine the incidence and independent risk factors of DO in patients with thoracic OLF.

METHODS

A total of 107 patients with thoracic OLF who were admitted to the authors’ hospital from December 2020 to December 2021 were included in this study. The independent risk factors of DO in patients with thoracic OLF were determined through univariate analysis followed by multivariate logistic regression analysis with p < 0.05. The diagnostic efficacy of the DO in OLF (DO-OLF) risk classification model was determined on the basis of independent risk factors and evaluated on the basis of sensitivity, specificity, and agreement rate.

RESULTS

The incidence of DO in patients with thoracic OLF was 35% (37/107 patients). The tuberous type according to the Sato classification (OR 9.75, p < 0.01) and larger (≥ 9°) supine local kyphosis angle (LKA) (OR 8.13, p < 0.01) were two independent risk factors of DO in thoracic OLF. The DO-OLF risk classification, a novel approach for the diagnosis of DO in patients with thoracic OLF, was established on the basis of the combination of the tuberous type according to the Sato classification and larger supine LKA. The sensitivity, specificity, and agreement rate of this approach for distinguishing between patients with thoracic OLF at high and low risk of DO were 87%, 93%, and 91%, respectively.

CONCLUSIONS

The incidence of DO in patients with thoracic OLF was 35%. The tuberous type according to the Sato classification and larger supine LKA (≥ 9°) were independent risk factors of DO in patients with thoracic OLF. The novel DO-OLF risk classification approach could serve as an efficient method for predicting DO in patients with thoracic OLF.

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Relationship between the postoperative variations of paraspinal muscles and adjacent-segment degeneration in patients with degenerative lumbar spinal stenosis after posterior instrumented lumbar fusion

Fei Xu, Siyu Zhou, Zhuoran Sun, Shuai Jiang, Gengyu Han, and Weishi Li

OBJECTIVE

This study aimed to quantify pre- and postoperative paraspinal muscular variation following posterior lumbar interbody fusion (PLIF) in patients with degenerative lumbar spinal stenosis (DLSS) and measure the association of this variation with adjacent-segment degeneration (ASD).

METHODS

Data from 149 patients who underwent L4–S1 PLIF for DLSS were collected. Patients were divided into radiologically confirmed ASD and control groups according to follow-up radiological findings. MRI was performed before surgery and at the last follow-up. Muscular parameters including the relative cross-sectional area (rCSA), relative functional cross-sectional area (rFCSA), relative total cross-sectional area (rTCSA), and fatty infiltration (FI) of the multifidus (MF), erector spinae (ES), and psoas major (PM) muscles were measured on preoperative and follow-up L2–S1 MR images. Logistic regression was used to investigate risk factors for ASD.

RESULTS

The rate of radiological ASD was 42.3% at the final follow-up (mean 25.71 ± 8.35 months). At surgical levels, the rFCSA and rTCSA of the MF and ES muscles decreased. The FI of the MF from L2–3 to L5–S1 and ES muscles at L5–S1 significantly increased after surgery, while the rFCSA and rTCSA of the PM muscle increased and its FI decreased. At adjacent levels, the rFCSA and rTCSA of the MF muscle and rTCSA of the ES muscle decreased and the FI of the MF muscle increased postoperatively (p < 0.05), but the rFCSA and rTCSA of the PM muscle increased and its FI decreased (p < 0.05). The FIs of the MF, ES, and PM muscles at adjacent levels significantly differed between the ASD and control groups. Logistic regression analysis indicated that higher BMI (p = 0.002) and FI of the PM muscle at adjacent levels (p = 0.025) were significant risk factors for ASD.

CONCLUSIONS

The functional area decreased in the MF and ES muscles and increased in the PM muscle after L4–S1 PLIF. A compensatory postoperative decrease in FI of the PM muscle at the adjacent level was a protective factor for ASD in DLSS patients after PLIF.

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A novel surgical planning system using an AI model to optimize planning of pedicle screw trajectories with highest bone mineral density and strongest pull-out force

Chi Ma, Da Zou, Huan Qi, Chentian Li, Cheng Zhang, Kedi Yang, Feng Zhu, Weishi Li, and William W. Lu

OBJECTIVE

The purpose of this study was to evaluate the ability of a novel artificial intelligence (AI) model in identifying optimized transpedicular screw trajectories with higher bone mineral density (BMD) as well as higher pull-out force (POF) in osteoporotic patients.

METHODS

An innovative pedicle screw trajectory planning system called Bone’s Trajectory was developed using a 3D graphic search and an AI-based finite element analysis model. The preoperative CT scans of 21 elderly osteoporotic patients were analyzed retrospectively. The AI model automatically calculated the number of alternative transpedicular trajectories, the trajectory BMD, and the estimated POF of L3–5. The highest BMD and highest POF of optimized trajectories were recorded and compared with AO standard trajectories.

RESULTS

The average patient age and average BMD of the vertebral bodies were 69.6 ± 7.8 years and 55.9 ± 17.1 mg/ml, respectively. On both sides of L3–5, the optimized trajectories showed significantly higher BMD and POF than the AO standard trajectories (p < 0.05). On average, the POF of optimized trajectory screws showed at least a 2.0-fold increase compared with AO trajectory screws.

CONCLUSIONS

The novel AI model performs well in enabling the selection of optimized transpedicular trajectories with higher BMD and POF than the AO standard trajectories.