Surgeon-Specific Treatment Selection Bias and Heterogeneous Perioperative Practices in an Observational Spine Surgery Study. A Statistical Tutorial with Implications for Analysis of Observational Studies of Perioperative Interventions.

BACKGROUND: It is essential that treatment effects reported from retrospective observational studies are as reliable as possible. In a retrospective analysis of spine surgery patients, we obtained a spurious result: tranexamic acid (TXA) had no effect on intraoperative blood loss. This statistical tutorial explains how this result occurred and why statistical analyses of observational studies must consider the effects of individual surgeons. METHODS: We used an observational database of 580 elective adult spine surgery patients, supplemented with a review of perioperative medication records. We tested whether common statistical methods (multivariable regression or propensity score-based methods) could adjust for surgeons' selection bias in TXA administration. RESULTS: Because TXA administration (frequency, timing, and dose) and surgeon were linked (collinear), estimating and testing the independent effect of TXA on outcome using multivariable regression without including surgeon as a variable would provide biased (spurious) results. Likewise, because of surgeon/TXA linkage, assumptions of propensity score-based analysis were violated, statistical methods to improve comparability between groups failed, and spurious blood loss results were worsened. Others numerous differences among surgeons existed in intraoperative and postoperative practices and outcomes. CONCLUSIONS: In observational studies in which individual surgeons determine whether their patients receive the treatment of interest, consideration must be given to inclusion of surgeon as an independent variable in all analyses. Failure to include the surgeon in an analysis of observational data carries a substantial risk of obtaining spurious results, either creating a spurious treatment effect or failing to detect a true treatment effect.

Postoperative Use of the Muscle Relaxants Baclofen and/or Cyclobenzaprine Associated With an Increased Risk of Delirium Following Lumbar Fusion.

STUDY DESIGN: Retrospective, single-center, cohort study. OBJECTIVE: Investigate whether the incidence of postoperative delirium in older adults undergoing spinal fusion surgery is associated with postoperative muscle relaxant administration. SUMMARY OF BACKGROUND DATA: Baclofen and cyclobenzaprine are muscle relaxants frequently used for pain management following spine surgery. Muscle relaxants are known to cause central nervous system side effects in the outpatient setting and are relatively contraindicated in individuals at high risk for delirium. However, there are no known studies investigating their side effects in the postoperative setting. METHODS: Patients over 65 years of age who underwent elective posterior lumbar fusion for degenerative spine disease were stratified into two treatment groups based on whether postoperative muscle relaxants were administered on postoperative day one as part of a multimodal analgesia regimen. Doubly robust inverse probability weighting with cox regression for time-dependent covariates was used to examine the association between postoperative muscle relaxant use and the risk of delirium while controlling for variation in baseline characteristics. RESULTS: The incidence of delirium was 17.6% in the 250 patients who received postoperative muscle relaxants compared with 7.9% in the 280 patients who did not receive muscle relaxants ( P=0.001 ). Multivariate analysis to control for variation in baseline characteristics between treatment groups found that patients who received muscle relaxants had a 2.00 (95% CI: 1.14-3.49) times higher risk of delirium compared with controls ( P=0.015 ). CONCLUSION: Postoperative use of muscle relaxants as part of a multimodal analgesia regimen was associated with an increased risk of delirium in older adults after lumber fusion surgery. Although muscle relaxants may be beneficial in select patients, they should be used with caution in individuals at high risk for postoperative delirium.

Biomechanical assessment of the effect of sublaminar band tensioning on lumbar motion.

OBJECTIVE: Adjacent-segment disease (ASD) proximal to lumbosacral fusion is assumed to result from increased stress and motion that extends above or below the fusion construct. Sublaminar bands (SBs) have been shown to potentially mitigate stresses in deformity constructs. A similar application of SBs in lumbar fusions is not well described yet may potentially mitigate against ASD. METHODS: Eight fresh-frozen human cadaveric spine specimens were instrumented with transforaminal lumbar interbody fusion (TLIF) cages at L3-4 and L4-5, and pedicle screws from L3 to S1. Bilateral SBs were applied at L2 and tightened around the rods extending above the L3 pedicle screws. After being mounted on a testing frame, the spines were loaded at L1 to 6 Nm in all 3 planes, i.e., flexion/extension, right and left lateral bending, and right and left axial rotation. Motion and intradiscal pressures (IDPs) at L2-3 were measured for 5 conditions: intact, instrumentation (L3-S1), band tension (BT) 30%, BT 50%, and BT 100%. RESULTS: There was significant increase in motion at L2-3 with L3-S1 instrumentation compared with the intact spine in flexion/extension (median 8.78°, range 4.07°-10.81°, vs median 7.27°, range 1.63°-9.66°; p = 0.016). When compared with instrumentation, BT 100% reduced motion at L2-3 in flexion/extension (median 8.78°, range 4.07°-10.81°, vs median 3.61°, range 1.11°-9.39°; p < 0.001) and lateral bending (median 6.58°, range 3.67°-8.59°, vs median 5.62°, range 3.28°-6.74°; p = 0.001). BT 50% reduced motion at L2-3 only in flexion/extension when compared with instrumentation (median 8.78°, range 4.07°-10.81°, vs median 5.91°, range 2.54°-10.59°; p = 0.027). There was no significant increase of motion at L1-2 with banding when compared with instrumentation, although an increase was seen from the intact spine with BT 100% in flexion/extension (median 5.14°, range 2.47°-9.73°, vs median 7.34°, range 4.22°-9.89°; p = 0.005). BT 100% significantly reduced IDP at L2-3 from 25.07 psi (range 2.41-48.08 psi) before tensioning to 19.46 psi (range -2.35 to 29.55 psi) after tensioning (p = 0.016). CONCLUSIONS: In this model, the addition of L2 SBs reduced motion and IDP at L2-3 after the L3-S1 instrumentation. There was no significant increase in motion at L1-2 in response to band tensioning compared with instrumentation alone. The application of SBs may have a clinical application in reducing the incidence of ASD.

Spinal Meningioma in Adults: Imaging Characteristics, Surgical Outcomes, and Risk Factors for Recurrence.

OBJECTIVE: Although spinal meningiomas (SMs) are associated with overall long tumor-free survival, SMs can recur. This study analyzed factors associated with complications, misdiagnosis, and recurrence of SMs. METHODS: We reviewed patient demographics; radiographic characteristics of patients with SMs, including level, location within the canal, and size; surgical resection; pathology; and recurrence. RESULTS: The study included 64 women and 10 men (74 SMs). Of patients, 64 showed no recurrence after surgery with a median (range) follow-up of 17 (1-99) months. Recurrence was identified in 10 patients (13.5%) during a median (range) follow-up of 66 (25-230) months. There was no significant difference in sex between the recurrence and no recurrence cohorts. Patients in the recurrence cohort were significantly younger (median [range] age 58 [35-70] years) than patients in the no recurrence cohort (median [range] age 69 [18-93] years; P = 0.0091). There was significant predilection for foraminal locations in the recurrence cohort (P < 0.001) compared with the no recurrence cohort. SM was correctly identified on preoperative magnetic resonance imaging or computed tomography myelography in 62 of 64 tumors (96.9%) in the no recurrence cohort, but in only 6 of 10 tumors (60%) in the recurrence cohort (P < 0.001). CONCLUSIONS: In 74 patients with SMs, a preponderance of female patients and a predilection of tumors for the thoracic spine were shown. Recurrence was significantly more common in younger than older patients. Risk factors for recurrence included larger tumors, foraminal location, and en plaque lesions. Patients who developed recurrence were significantly more likely to have been misdiagnosed on preoperative imaging with nerve sheath tumors or lymphoma.

Use of a Smartphone Leveling Application to Optimize Cervical Thoracic Alignment Before Posterior Instrumentation.

OBJECTIVE: Posterior cervical decompression and instrumentation (PCDI) often is associated with increase in sagittal balance and loss of lordosis. Here, we propose a simple method of surgical positioning using a readily available smartphone application to optimize cervical thoracic alignment in PCDI. The intent of this optimization is to minimize losses in lordosis and increases in sagittal balance. METHODS: For patients since 2019, the position of the head was adjusted so that the occiput to thoracic spine was aligned and the chin brow angle was parallel to the rails of the surgical table using a leveling smart application (RIDGID level). Patients before 2019 who were not optimized were compared. RESULTS: There were 13 patients in the nonoptimized cohort (NOC) and 20 in the optimized cohort (OC). In the NOC, the change in lordosis was -7° (P = 0.016) and change in C2-sagittal vertical axis was 7 mm (P < 0.001) from preoperative to postoperative values. In the OC, the change in lordosis was 2° (P = 0.104) and change in C2-SVA was 2 mm (P = 0.592) from preoperative to postoperative values. Between the NOC and OC cohorts, the changes in lordosis and sagittal balance between cohorts were significant (P = 0.002 and P = 0.001, respectively). There was no significant difference in clinical outcomes as measured by Japanese Orthopaedic Association or complication rates. CONCLUSIONS: Positioning of the patient in preparation for PCDI can influence postoperative lordosis and sagittal balance. Using the leveling application on the smartphone (RIDGID level), is a rapid and free alternative for the maintenance of lordosis and sagittal balance during instrumentation in the operating room.

What is the most accurate substitute for an invisible T1 slope in cervical radiographs? A comparative study of a novel method with previously reported substitutes.

OBJECTIVE: The ability to utilize the T1 slope is often limited by poor visibility on cervical radiographs. The C7 slope has been proposed as a reliable substitute but may have similar limitations of visibility. Herein, the authors propose a novel method that takes advantage of the superior visibility on CT to accurately substitute for the radiographic T1 slope and compare the accuracy of this method with previously reported substitutes. METHODS: Lateral neutral standing cervical radiographs and cervical CT scans were examined. When the T1 slope was clearly visible on radiographs, the C3-7 slopes and T1 slope were measured. In CT method 1, a direct method, the T1 slope was measured from the upper endplate of T1 to the bottom edge of the CT image, assuming the edge was parallel to the horizontal plane. In CT method 2, an overlaying method, the T1 slope was calculated by superimposing the C7 slope angle measured on a radiograph onto the CT scan and measuring the angle formed by the upper endplate of T1 and the superimposed horizontal line of the C7 slope. A Pearson correlation with linear regression modeling was performed for potential substitutes for the actual T1 slope. RESULTS: Among 160 patients with available noninstrumented lateral neutral cervical radiographs, the T1 slope was visible in only 54 patients (33.8%). A total of 52 patients met the inclusion criteria for final analysis. The Pearson correlation coefficients between the T1 slope and the C3-7 slopes, CT method 1, and CT method 2 were 0.243 (p = 0.083), 0.292 (p = 0.035), 0.609 (p < 0.001), 0.806 (p < 0.001), 0.898 (p < 0.001), 0.426 (p = 0.002), and 0.942 (p < 0.001), respectively. Linear regression modeling showed R2 = 0.807 for the correlation between C7 slope and T1 slope and R2 = 0.888 for the correlation between T1 slope with the CT method 2 and actual T1 slope. CONCLUSIONS: The C7 slope can be a reliable predictor of the T1 slope and is more accurate than more rostral cervical slopes. However, this study disclosed that the novel CT method 2, an overlaying method, was the most reliable estimate of true T1 slope with a greater positive correlation than C7 slope. When CT studies are available in patients with an invisible T1 slope on cervical radiographs, CT method 2 should be used as a substitute for the T1 slope.

Outcomes and complications of surgical treatment of anterior osteophytes causing dysphagia: Single center experience.

STUDY DESIGN: Retrospective case series. OBJECTIVE: To better understand the functional swallow outcomes, cervical balance, and surgical complications, we examined patients with anterior osteophytes and dysphagia who were treated operatively. SUMMARY OF BACKGROUND DATA: Anterior osteophytes from diffuse idiopathic skeletal hyperostosis (DISH) or degenerative etiology of the cervical spine can cause dysphagia from mechanical compression of the esophagus. Osteophytectomy is generally accepted as a safe surgical treatment, but the risk of instability is unclear. The potential for associated complications must be considered. METHODS: Patients who had anterior osteophytes and dysphagia from 2005 to 2020 were reviewed retrospectively. Demographics, radiographic parameters, functional swallow outcome, and complications were examined. RESULTS: There were 15 patients identified treated surgically. Increased osteophyte height positively correlated with severity of dysphagia with Pearson coefficient of 0.53 (p = 0.042). Functional Outcome Swallowing Scale (FOSS) scores improved after surgical treatment from median of 2 to 0 (p = 0.002). C2-7 SVA did increase by 8 mm (p = 0.007) but was generally well tolerated. There was a 27% complication rate including a case of C5 lateral mass fracture with central cord syndrome after a fall 4 days following osteophytectomy. There was one patient who was preoperatively dependent on gastrostomy tube who required a tracheostomy and had continued reliance on the gastrostomy tube. CONCLUSION: Surgical treatment of anterior osteophytes causing dysphagia with osteophytectomy can lead to overall improved FOSS scores for most patients. However, a high preoperative FOSS score may be a prognostic indicator of poor postoperative functional swallow outcome. It is important to consider the potential for instability when osteophytectomy is performed at 3 or more spinal segments.