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Thomas J. Buell, Davis G. Taylor, Ching-Jen Chen, and Bhiken I. Naik

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Davis G. Taylor, Thomas J. Buell, Tony R. Wang, Matthew J. Shepard, Dominic Maggio, Ching-Jen Chen, Min S. Park, and Mark E. Shaffrey

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Davis G. Taylor, Ching-Jen Chen, Thomas J. Buell, Min S. Park, J. Javier Provencio, and M. Yashar S. Kalani

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Thomas J. Buell, Shay Bess, Ming Xu, Frank J. Schwab, Virginie Lafage, Christopher P. Ames, Christopher I. Shaffrey, and Justin S. Smith

OBJECTIVE

Proximal junctional kyphosis (PJK) is, in part, due to altered segmental biomechanics at the junction of rigid instrumented spine and relatively hypermobile non-instrumented adjacent segments. Proper application of posteriorly anchored polyethylene tethers (i.e., optimal configuration and tension) may mitigate adjacent-segment stress and help prevent PJK. The purpose of this study was to investigate the impact of different tether configurations and tensioning (preloading) on junctional range-of-motion (ROM) and other biomechanical indices for PJK in long instrumented spine constructs.

METHODS

Using a validated finite element model of a T7–L5 spine segment, testing was performed on intact spine, a multilevel posterior screw-rod construct (PS construct; T11–L5) without tether, and 15 PS constructs with different tether configurations that varied according to 1) proximal tether fixation of upper instrumented vertebra +1 (UIV+1) and/or UIV+2; 2) distal tether fixation to UIV, to UIV−1, or to rods; and 3) use of a loop (single proximal fixation) or weave (UIV and/or UIV+1 fixation in addition to UIV+1 and/or UIV+2 proximal attachment) of the tether. Segmental ROM, intradiscal pressure (IDP), inter- and supraspinous ligament (ISL/SSL) forces, and screw loads were assessed under variable tether preload.

RESULTS

PS construct junctional ROM increased abruptly from 10% (T11–12) to 99% (T10–11) of baseline. After tethers were grouped by most cranial proximal fixation (UIV+1 vs UIV+2) and use of loop versus weave, UIV+2 Loop and/or Weave most effectively dampened junctional ROM and adjacent-segment stress. Different distal fixation and use of loop versus weave had minimal effect. The mean segmental ROM at T11–12, T10–11, and T9–10, respectively, was 6%, 40%, and 99% for UIV+1 Loop; 6%, 44%, and 99% for UIV+1 Weave; 5%, 23%, and 26% for UIV+2 Loop; and 5%, 24%, and 31% for UIV+2 Weave.

Tethers shared loads with posterior ligaments; consequently, increasing tether preload tension reduced ISL/SSL forces, but screw loads increased. Further attenuation of junctional ROM and IDP reversed above approximately 100 N tether preload, suggesting diminished benefit for biomechanical PJK prophylaxis at higher preload tensioning.

CONCLUSIONS

In this study, finite element analysis demonstrated UIV+2 Loop and/or Weave tether configurations most effectively mitigated adjacent-segment stress in long instrumented spine constructs. Tether preload dampened ligament forces at the expense of screw loads, and an inflection point (approximately 100 N) was demonstrated above which junctional ROM and IDP worsened (i.e., avoid over-tightening tethers). Results suggest tether configuration and tension influence PJK biomechanics and further clinical research is warranted.

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Thomas J. Buell, James H. Nguyen, Marcus D. Mazur, Jeffrey P. Mullin, Juanita Garces, Davis G. Taylor, Chun-Po Yen, Mark E. Shaffrey, Christopher I. Shaffrey, and Justin S. Smith

OBJECTIVE

Fixed sagittal spinal malalignment is a common problem in adult spinal deformity (ASD). Various three-column osteotomy techniques, including the extended pedicle subtraction osteotomy (ePSO), may correct global and regional malalignment in this patient population. In contrast to the number of reports on traditional PSO (Schwab grade 3 osteotomy), there is limited literature on the outcomes of ePSO (Schwab grade 4 osteotomy) in ASD surgery. The objective of this retrospective study was to provide focused investigation of radiographic outcomes and complications of single-level lumbar ePSO for ASD patients with fixed sagittal malalignment.

METHODS

Consecutive ASD patients in whom sagittal malalignment had been treated with single-level lumbar ePSO at the authors’ institution between 2010 and 2015 were analyzed, and those with a minimum 2-year follow-up were included in the study. Radiographic analyses included assessments of segmental lordosis through the ePSO site (sagittal Cobb angle measured from the superior endplate of the vertebra above and inferior endplate of the vertebra below the ePSO), lumbar lordosis (LL), pelvic tilt (PT), pelvic incidence and LL mismatch, thoracic kyphosis (TK), and sagittal vertical axis (SVA) on standing long-cassette radiographs. Complications were analyzed for the entire group.

RESULTS

Among 71 potentially eligible patients, 55 (77%) had a minimum 2-year follow-up and were included in the study. Overall, the average postoperative increases in ePSO segmental lordosis and overall LL were 41° ± 14° (range 7°–69°, p < 0.001) and 38° ± 11° (range 9°–58°, p < 0.001), respectively. The average SVA improvement was 13 ± 7 cm (range of correction: −33.6 to 3.4 cm, p < 0.001). These measurements were maintained when comparing early postoperative to last follow-up values, respectively (mean follow-up 52 months, range 26–97 months): ePSO segmental lordosis, 34° vs 33°, p = 0.270; LL, 47.3° vs 46.7°, p = 0.339; and SVA, 4 vs 5 cm, p = 0.330. Rod fracture (RF) at the ePSO site occurred in 18.2% (10/55) of patients, and pseudarthrosis (PA) at the ePSO site was confirmed by CT imaging or during rod revision surgery in 14.5% (8/55) of patients. Accessory supplemental rods across the ePSO site, a more recently employed technique, significantly reduced the occurrence of RF or PA on univariate (p = 0.004) and multivariable (OR 0.062, 95% CI 0.007–0.553, p = 0.013) analyses; this effect approached statistical significance on Kaplan-Meier analysis (p = 0.053, log-rank test). Interbody cage placement at the ePSO site resulted in greater ePSO segmental lordosis correction (45° vs 35°, p = 0.007) without significant change in RF or PA (p = 0.304). Transient and persistent motor deficits occurred in 14.5% (8/55) and 1.8% (1/55) of patients, respectively.

CONCLUSIONS

Extended PSO is an effective technique to correct fixed sagittal malalignment for ASD. In comparison to traditional PSO techniques, ePSO may allow greater focal correction with comparable complication rates, especially with interbody cage placement at the ePSO site and the use of accessory supplemental rods.

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Thomas J. Buell, Daniel M. S. Raper, I. Jonathan Pomeraniec, Dale Ding, Ching-Jen Chen, Davis G. Taylor, and Kenneth C. Liu

Stenosis of the transverse sinus (TS) and sigmoid sinus (SS), with a trans-stenosis pressure gradient, has been implicated in the pathophysiology of idiopathic intracranial hypertension (IIH). MRI has shown improvement in TS and SS stenosis after high-volume lumbar puncture (HVLP) in a subset of patients with IIH. The authors present the first report of an IIH patient with immediate post-HVLP TS and SS trans-stenosis pressure gradient reduction and an attendant increase in TS and SS cross-sectional area confirmed using intravascular ultrasonography (IVUS). Recurrence of the patient’s TS-SS stenosis coincided with elevated HVLP opening pressure, and venous sinus stent placement resulted in clinical improvement. This report suggests that TS and SS stenosis may be a downstream effect of elevated intracranial pressure in IIH, rather than its principal etiological mechanism. However, the authors hypothesize that endovascular stenting may obliterate a positive feedback loop involving trans-stenosis pressure gradients, and still benefit appropriately selected patients.

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Thomas J. Buell, Davis G. Taylor, Ching-Jen Chen, Christopher I. Shaffrey, Justin S. Smith, and Shay Bess

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Davis G. Taylor, Ajay Chatrath, Panagiotis Mastorakos, Gabriella Paisan, Ching-Jen Chen, Thomas J. Buell, and John A. Jane Jr.

OBJECTIVE

Syringogenesis in Chiari malformation type I (CM-I) is thought to occur secondary to impaction of the cerebellar tonsils within the foramen magnum (FM). However, the correlation between the CSF area and syringogenesis has yet to be elucidated. The authors sought to determine whether the diminution in subarachnoid space is associated with syringogenesis. Further, the authors sought to determine if syrinx resolution was associated with the degree of expansion of subarachnoid spaces after surgery.

METHODS

The authors performed a retrospective review of all patients undergoing posterior fossa decompression for CM-I from 2004 to 2016 at the University of Virginia Health System. The subarachnoid spaces at the FM and at the level of the most severe stenosis were measured before and after surgery by manual delineation of the canal and neural tissue area on MRI and verified through automated CSF intensity measurements. Imaging and clinical outcomes were then compared.

RESULTS

Of 68 patients, 26 had a syrinx at presentation. Syrinx patients had significantly less subarachnoid space at the FM (13% vs 19%, p = 0.0070) compared to those without syrinx. Following matching based on degree of tonsillar herniation and age, the subarachnoid space was significantly smaller in patients with a syrinx (12% vs 19%, p = 0.0015). Syrinx resolution was associated with an increase in patients’ subarachnoid space after surgery compared with those patients without resolution (23% vs 10%, p = 0.0323).

CONCLUSIONS

Syrinx development in CM-I patients is correlated with the degree to which the subarachnoid CSF spaces are diminished at the cranial outlet. Successful syrinx reduction is associated with the degree to which the subarachnoid spaces are increased following surgery.

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Rebecca M. Burke, Thomas J. Buell, Dominic M. Maggio, Ulas Yener, Chun-Po Yen, Christopher I. Shaffrey, and Justin S. Smith

Adolescent idiopathic scoliosis patients treated with spinal fusion may develop adjacent segment disease and curve progression into adulthood. Revision operations can be challenging, especially for adult patients treated with outdated instrumentation such as sublaminar hooks and/or wires. The authors demonstrate revision lumbar spine surgery in a 38-year-old female with scoliosis progression from junctional degeneration below a prior T5–L3 posterior instrumented arthrodesis with a hook-and-rod wire system. They also demonstrate safe application of an ultrasonic bone scalpel for completion of a Smith-Petersen osteotomy. The patient provided written, informed consent for all material presented in this case demonstration.

The video can be found here: https://youtu.be/3PmaFtNcqKc.