Mikula, Anthony L.

Study design. Retrospective observational study of consecutive patients. Objective. The purpose of the study is to determine if a surgeon’s qualitative assessment of bone intraoperatively correlates with radiologic parameters of bone strength. Summary of Background Data. Preoperative radiologic assessment of bone can include modalities such as computed tomography (CT) Hounsfield units (HUs), dual-energy x-ray absorptiometry (DXA) bone mineral density with trabecular bone score (TBS) and magnetic resonance imaging vertebral bone quality (VBQ). Quantitative analysis of bone with screw insertional torque and pull-out strength measurement has been performed in cadaveric models and has been correlated to these radiologic parameters. However, these quantitative measurements are not routinely available for use in surgery. Surgeons anecdotally judge bone strength, but the fidelity of the intraoperative judgment has not been investigated. Methods. All adult patients undergoing instrumented posterior thoracolumbar spine fusion by one of seven surgeons at a single center over a 3-month period were included. Surgeons evaluated the strength of bone based on intraoperative feedback and graded each patient’s bone on a 5-point Likert scale. Two independent reviewers measured preoperative CT HUs and magnetic resonance imaging VBQ. Bone mineral density, lowest T-score, and TBS were extracted from DXA within 2 years of surgery. Results. Eighty-nine patients were enrolled and 16, 28, 31, 13, and 1 patients had Likert grade 1 (strongest bone), 2, 3, 4, and 5 (weakest bone), respectively. The surgeon assessment of bone correlated with VBQ (τ=0.15, P=0.07), CT HU (τ=−0.31, P<0.01), lowest DXA T-score (τ=−0.47, P<0.01), and TBS (τ=−0.23, P=0.06). Conclusion. Spine surgeons’ qualitative intraoperative assessment of bone correlates with preoperative radiologic parameters, particularly in posterior thoracolumbar surgeries. This information is valuable to surgeons as this supports the idea that decisions based on feel in surgery have a statistical foundation.

OBJECTIVE Spine metastases are commonly treated with radiotherapy for local tumor control; pathologic fracture is a potential complication of spinal radiotherapy. Both Hounsfield units (HUs) on CT and vertebral bone quality (VBQ) on MRI have been argued to predict stability as measured by odds of pathologic fracture, although it is unclear if there is a difference in the predictive power between the two methodologies. The objective of the present study was to examine whether one methodology is a better predictor of pathologic fracture following radiotherapy for mobile spine metastases. METHODS Patients who underwent radiotherapy (conventional external-beam radiation therapy, stereotactic body radiation therapy, or intensity-modulated radiation therapy) for mobile spine (C1–L5) metastases at a tertiary care center were retrospectively identified. Details regarding underlying pathology, patient demographics, and tumor morphology were collected. Vertebral involvement was assessed using the Weinstein-Boriani-Biagini (WBB) system. Bone quality of the non–tumor-involved bone was assessed on both pretreatment CT and MRI. Univariable analyses were conducted to identify independent predictors of fracture, and Kaplan-Meier analyses were used to identify significant predictors of time to pathologic fracture. Stepwise Cox regression analysis was used to determine independent predictors of time to fracture. RESULTS One hundred patients were included (mean age 62.7 ± 11.9 years; 61% male), of whom 35 experienced postradiotherapy pathologic fractures. The most common histologies were lung (22%), prostate (21%), breast (14%), and renal cell (13%). On univariable analysis, the mean HUs of the vertebrae adjacent to the fractured vertebra were significantly lower among those experiencing fracture; VBQ was not significantly associated with fracture odds. Survival analysis showed that average HUs ≤ 132, nonprostate pathology, involvement of ≥ 3 vertebral body segments on the WBB system, Spine Instability Neoplastic Score (SINS) ≥ 7, and the presence of axial pain all predicted increased odds of fracture (all p < 0.001). Cox regression found that HUs ≤ 132 (OR 2.533, 95% CI 1.257–5.103; p = 0.009), ≥ 3 WBB vertebral body segments involved (OR 2.376, 95% CI 1.132–4.987; p = 0.022), and axial pain (OR 2.036, 95% CI 0.916–4.526; p = 0.081) predicted increased fracture odds, while prostate pathology predicted decreased odds (OR 0.076, 95% CI 0.009–0.613; p = 0.016). Sensitivity analysis suggested that an HU threshold of ≤ 132 and a SINS of ≥ 7 identified patients at increased risk of fracture. CONCLUSIONS The present results suggest that bone density surrogates as measured on CT, but not MRI, can be used to predict the risk of pathologic fracture following radiotherapy for mobile spine metastases. More extensive vertebral body involvement and the presence of mechanical axial pain additionally predict increased fracture odds.

Study Design. Retrospective cohort study. Objective. Hounsfield units (HUs) are known to correlate with clinical outcomes, but no study has evaluated how they correlate with biomechanical computed tomography (BCT) and dual-energy x-ray absorptiometry (DXA) measurements. Summary of Background. Low bone mineral density (BMD) represents a major risk factor for fracture and poor outcomes following spine surgery. DXA can provide regional BMD measurements but has limitations. Opportunistic HUs provide targeted BMD estimates; however, they are not formally accepted for diagnosing osteoporosis in current guidelines. More recently, BCT analysis has emerged as a new modality endorsed by the International Society for Clinical Densitometry for assessing bone strength. Methods. Consecutive cases from 2017 to 2022 at a single institution were reviewed for patients who underwent BCT in the thoracolumbar spine. BCT-measured vertebral strength, trabecular BMD, and the corresponding American College of Radiology Classification were recorded. DXA studies within three months of the BCT were reviewed. Pearson Correlation Coefficients were calculated, and receiver-operating characteristic curves were constructed to assess the predictive capacity of HUs. Threshold analysis was performed to identify optimal HU values for identifying osteoporosis and low BMD. Results. Correlation analysis of 114 cases revealed a strong relationship between HUs and BCT vertebral strength (r=0.69; P<0.0001; R 2=0.47) and trabecular BMD (r=0.76; P<0.0001; R 2=0.58). However, DXA poorly correlated with opportunistic HUs and BCT measurements. HUs accurately predicted osteoporosis and low BMD (Osteoporosis: C=0.95, 95% CI 0.89–1.00; Low BMD: C=0.87, 95% CI 0.79–0.96). Threshold analysis revealed that 106 and 122 HUs represent optimal thresholds for detecting osteoporosis and low BMD. Conclusion. Opportunistic HUs strongly correlated with BCT-based measures, while neither correlated strongly with DXA-based BMD measures in the thoracolumbar spine. HUs are easy to perform at no additional cost and provide accurate BMD estimates at noninstrumented vertebral levels across all American College of Radiology-designated BMD categories.

OBJECTIVE The purpose of this study was to analyze risk factors for sacral fracture following noninstrumented partial sacral amputation for en bloc chordoma resection. METHODS A multicenter retrospective chart review identified patients who underwent noninstrumented partial sacral amputation for en bloc chordoma resection with pre- and postoperative imaging. Hounsfield units (HU) were measured in the S1 level. Sacral amputation level nomenclature was based on the highest sacral level with bone removed (e.g., S1 foramen amputation at the S1–2 vestigial disc is an S2 sacral amputation). Variables collected included basic demographics, patient comorbidities, surgical approach, preoperative radiographic details, neoadjuvant and adjuvant radiation therapy, and postoperative sacral fracture data. RESULTS A total of 101 patients (60 men, 41 women) were included; they had an average age of 69 years, BMI of 29 kg/m2, and follow-up of 60 months. The sacral amputation level was S1 (2%), S2 (37%), S3 (44%), S4 (9%), and S5 (9%). Patients had a posterior-only approach (77%) or a combined anterior–posterior approach (23%), with 10 patients (10%) having partial sacroiliac (SI) joint resection. Twenty-seven patients (27%) suffered a postoperative sacral fracture, all occurring between 1 and 7 months after the index surgery. Multivariable logistic regression analysis demonstrated S1 or S2 sacral amputation level (p = 0.001), combined anterior–posterior approach (p = 0.0064), and low superior S1 HU (p = 0.027) to be independent predictors of sacral fracture. The fracture rate for patients with superior S1 HU < 225, 225–300, and > 300 was 38%, 15%, and 9%, respectively. An optimal superior S1 HU cutoff of 300 was found to maximize sensitivity (89%) and specificity (42%) in predicting postamputation sacral fracture. In addition, the fracture rate for patients who underwent partial SI joint resection was 100%. CONCLUSIONS Patients with S1 or S2 partial sacral amputations, a combined anterior–posterior surgical approach, low superior S1 HU, and partial SI joint resection are at higher risk for postoperative sacral fracture following en bloc chordoma resection and should be considered for spinopelvic instrumentation at the index procedure.

OBJECTIVE Proximal junctional kyphosis (PJK) is a complication of surgical management for adult spinal deformity (ASD) with a multifactorial etiology. Many risk factors are controversial, and their relative importance is not fully understood. The authors aimed to elucidate the association between bone mineral density (BMD) and PJK. METHODS A systematic literature search was performed using PubMed and Web of Science keywords of "Proximal Junctional Kyphosis [MeSH] OR Proximal Junctional Failure [MeSH]" AND "Bone Mineral Density [MeSH] OR Hounsfield Units [MeSH] OR DEXA [MeSH]" set to the date range of January 2002 to July 2022. Studies required a minimum of 10 patients and 12 months of follow-up. Articles were included if they were in the English language and presented a primary retrospective cohort that included a comparison of patients with and without PJK, as well as a radiographic biomarker for BMD, such as Hounsfield units (HU) or T-score. RESULTS A total of 18 unique studies with 2185 patients who underwent ASD surgery were identified. Of these, 537 patients (24.6%) developed PJK. Eight studies provided T-scores that were amenable to comparison, which found that patients who developed PJK were found to have lower BMD T-scores by a mean of −0.69 (95% CI −0.88 to −0.50; I 2 = 63.9%, p < 0.001). The HU at the UIV among patients with the PJK group (n = 101) compared with the non-PJK group (n = 156) was found to be significantly lower (mean difference −32.35, 95% CI −46.05 to −18.65; I 2 = 28.7%, p < 0.001). CONCLUSIONS This meta-analysis suggests that low preoperative BMD as measured by T-score and a diagnosis of osteoporosis were associated with higher postoperative PJK. Additionally, lower HU on CT at the UIV were found to be significant risk factors for postoperative PJK as well. These findings suggest that more attention to preoperative BMD is a risk factor for PJK among ASD patients is warranted.

Study Design. Retrospective cohort study. Objective. The present study is the first to assess the impact of paraspinal sarcopenia on patient-reported outcome measures (PROMs) following cervical laminoplasty. Background. While the impact of sarcopenia on PROMs following lumbar spine surgery is well-established, the impact of sarcopenia on PROMs following laminoplasty has not been investigated. Methods. We performed a retrospective review of patients undergoing laminoplasty from C4-6 at a single institution between 2010 and 2021. Two independent reviewers utilized axial cuts of T2-weighted magnetic resonance imaging sequences to assess fatty infiltration of the bilateral transversospinales muscle group at the C5-6 level and classify patients according to the Fuchs Modification of the Goutalier grading system. PROMs were then compared between subgroups. Results. We identified 114 patients for inclusion in this study, including 35 patients with mild sarcopenia, 49 patients with moderate sarcopenia, and 30 patients with severe sarcopenia. There were no differences in preoperative PROMs between subgroups. Mean postoperative neck disability index scores were lower in the mild and moderate sarcopenia subgroups (6.2 and 9.1, respectively) than in the severe sarcopenia subgroup (12.9, P=0.01). Patients with mild sarcopenia were nearly twice as likely to achieve minimal clinically important difference (88.6 vs. 53.5%; P<0.001) and six times as likely to achieve SCB (82.9 vs. 13.3%; P=0.006) compared with patients with severe sarcopenia. A higher percentage of patients with severe sarcopenia reported postoperative worsening of their neck disability index (13 patients, 43.3%; P=0.002) and Visual Analog Scale Arm scores (10 patients, 33.3%; P=0.03). Conclusion. Patients with severe paraspinal sarcopenia demonstrate less improvement in neck disability and pain postoperatively and are more likely to report worsening PROMs following laminoplasty. Level of Evidence. 3

Study Design: Retrospective review. Objective: The purpose of this study was to investigate the surgical outcomes in a cohort of patients with severe preoperative axial neck pain undergoing laminoplasty for cervical spondylotic myelopathy (CSM). Summary of Background Data: No study has investigated whether patients with severe axial symptoms may achieve satisfactory neck pain and disability outcomes after laminoplasty. Methods: We performed a retrospective review of 91 patients undergoing C4-6 laminoplasty for CSM at a single academic institution between 2010 and 2021. Patient-reported outcome measures (PROMs), including Neck Disability Index (NDI), visual analog scale (VAS) Neck, and VAS Arm, were recorded preoperatively and at 6 months and 1 year postoperatively. Patients were stratified as having mild pain if VAS neck was 0–3, moderate pain if 4–6, and severe pain if 7–10. PROMs were then compared between subgroups at all the perioperative time points. Results: Both the moderate and severe neck pain subgroups demonstrated a substantial improvement in VAS neck from preoperative to 6 months postoperatively (−3.1±2.2 vs. −5.6±2.8, respectively; P<0.001), and these improvements were maintained at 1 year postoperatively. There was no difference in VAS neck between subgroups at either the 6-month or 1-year postoperative time points. Despite the substantially higher mean NDI in the moderate and severe neck pain subgroups preoperatively, there was no difference in NDI at 6 months or 1 year postoperatively (P=0.99). There were no differences between subgroups in the degree of cord compression, severity of multifidus sarcopenia, sagittal alignment, or complications. Conclusions: Patients with moderate and severe preoperative neck pain undergoing laminoplasty achieved equivalent PROMs at 6 months and 1 year as patients with mild preoperative neck pain. The results of this study highlight the multifactorial nature of neck pain in these patients and indicate that severe axial symptoms are not an absolute contraindication to performing laminoplasty in well-aligned patients with CSM.

Study Design. Retrospective cohort study. Objective. The purpose of the present study was to assess the impact of sarcopenia on the development of proximal junctional kyphosis (PJK) and proximal junctional failure (PJF) following thoracolumbar spine fusion surgery using opportunistic evaluation of paraspinal fatty degeneration on preoperative magnetic resonance imaging. Summary of Background Data. While paraspinal sarcopenia has been shown to have detrimental consequences following posterior cervicothoracic fusions, the impact of paraspinal sarcopenia on PJK and PJF following thoracolumbar spine fusion surgery remains unknown. Materials and Methods. We performed a retrospective review of patients who underwent posterior spine fusion surgery that extended caudally to the pelvis and terminated cranially between T10 and L2 between 2010 and 2017. The cohort was divided into three groups: (1) patients without PJK or PJF, (2) patients with PJK but no PJF, and (3) patients with PJF. Univariate and multivariate analyses were performed to determine risk factors for the development of proximal junctional complications. Results. We identified 150 patients for inclusion in this study. Mean Hounsfield Units at the upper instrumented vertebra (UIV) was 148.3±34.5 in the cohort of patients without PJK or PJF, which was substantially higher than values recorded in the PJK (117.8±41.9) and PJF (118.8±41.8) subgroups ( P <0.001). Severe multifidus sarcopenia was identified at a much higher rate in the subgroups of patients who developed PJK (76.0%) and PJF (78.9%) than in the subgroup of patients who developed neither PJK nor PJF (34.0%; P <0.001). Multivariate analysis demonstrated both low HU at the UIV and moderate-severe multifidus sarcopenia to be risk factors for the development of PJK and PJF. Conclusion. The results of this study suggest severe paraspinal sarcopenia and diminished bone density at the UIV impart an increased risk of developing PJK and PJF, while markers of systemic frailty such as modified Frailty Index and Charlson Comorbidity Index are not associated with an increased risk of these complications. Level of Evidence. III.

OBJECTIVE There are few prior reports of acute pelvic instrumentation failure in spinal deformity surgery. The objective of this study was to determine if a previously identified mechanism and rate of pelvic fixation failure were present across multiple institutions, and to determine risk factors for these types of failures. METHODS Thirteen academic medical centers performed a retrospective review of 18 months of consecutive adult spinal fusions extending 3 or more levels, which included new pelvic screws at the time of surgery. Acute pelvic fixation failure was defined as occurring within 6 months of the index surgery and requiring surgical revision. RESULTS Failure occurred in 37 (5%) of 779 cases and consisted of either slippage of the rods or displacement of the set screws from the screw tulip head (17 cases), screw shaft fracture (9 cases), screw loosening (9 cases), and/or resultant kyphotic fracture of the sacrum (6 cases). Revision strategies involved new pelvic fixation and/or multiple rod constructs. Six patients (16%) who underwent revision with fewer than 4 rods to the pelvis sustained a second acute failure, but no secondary failures occurred when at least 4 rods were used. In the univariate analysis, the magnitude of surgical correction was higher in the failure cohort (higher preoperative T1-pelvic angle [T1PA], presence of a 3-column osteotomy; p < 0.05). Uncorrected postoperative deformity increased failure risk (pelvic incidence–lumbar lordosis mismatch > 10°, higher postoperative T1PA; p < 0.05). Use of pelvic screws less than 8.5 mm in diameter also increased the likelihood of failure (p < 0.05). In the multivariate analysis, a larger preoperative global deformity as measured by T1PA was associated with failure, male patients were more likely to experience failure than female patients, and there was a strong association with implant manufacturer (p < 0.05). Anterior column support with an L5–S1 interbody fusion was protective against failure (p < 0.05). CONCLUSIONS Acute catastrophic failures involved large-magnitude surgical corrections and likely resulted from high mechanical strain on the pelvic instrumentation. Patients with large corrections may benefit from anterior structural support placed at the most caudal motion segment and multiple rods connecting to more than 2 pelvic fixation points. If failure occurs, salvage with a minimum of 4 rods and 4 pelvic fixation points can be successful.