Background Superior-level facet joint violation by pedicle screws may result in increased stress to the level above the instrumentation and may contribute to adjacent segment disease (ASD). Previous studies have evaluated facet joint violations in open or percutaneous screw cases, but there are no reports describing a direct institutional comparison. Objective To compare the incidence of superior-level facet violation for open versus percutaneous pedicle screws, and evaluate patient and surgical factors that impact this outcome. Methods We reviewed 279 consecutive patients who underwent an index instrumented lumbar fusion from 2007 to 2011 for degenerative spine disease with stenosis with or without spondylolisthesis. We used a CT grading system which represents progressively increasing grades of facet joint violation. Patient and surgical factors were evaluated to determine their impact on facet violation. Results Our cohort consisted of 126 open and 153 percutaneous cases. Percutaneous procedures had a higher overall violation grade (p=0.018) and greater incidence of high-grade violations (p=0.0059) compared to open procedures. Bivariate analysis showed significantly greater violations in percutaneous cases for age<65, obesity, pedicle screws at L4, and 1- and 2-level surgeries. Multivariate analysis showed the percutaneous approach and depth of the spine to be independent risk factors for high-grade violations. Conclusion This study demonstrates greater facet violations for percutaneously placed pedicle screws compared to open.

Duane retraction syndrome (DRS) is a congenital eye-movement disorder defined by limited outward gaze and retraction of the eye on attempted inward gaze. Here, we report on three heterozygous loss-of-function MAFB mutations causing DRS and a dominant-negative MAFB mutation causing DRS and deafness. Using genotype-phenotype correlations in humans and Mafb-knockout mice, we propose a threshold model for variable loss of MAFB function. Postmortem studies of DRS have reported abducens nerve hypoplasia and aberrant innervation of the lateral rectus muscle by the oculomotor nerve. Our studies in mice now confirm this human DRS pathology. Moreover, we demonstrate that selectively disrupting abducens nerve development is sufficient to cause secondary innervation of the lateral rectus muscle by aberrant oculomotor nerve branches, which form at developmental decision regions close to target extraocular muscles. Thus, we present evidence that the primary cause of DRS is failure of the abducens nerve to fully innervate the lateral rectus muscle in early development.

Object Low-grade astrocytomas are slow-growing, infiltrative gliomas that over time may progress into more malignant tumors. Various factors have been shown to affect the time to progression and overall survival including age, performance status, tumor size, and the extent of resection. However, more recently it has been suggested that histological subtypes (fibrillary, protoplasmic, and gemistocytic) may impact patient outcome. In this study the authors have performed a large comparative population-based analysis to examine the characteristics and survival of patients with the various subtypes of WHO Grade II astrocytomas. Methods Patients diagnosed with fibrillary, protoplasmic, and gemistocytic astrocytomas were identified through the Surveillance, Epidemiology, and End Results (SEER) database. The chi-square test and Student t-test were used to evaluate differences in patient and treatment characteristics between astrocytoma subtypes. Kaplan-Meier analysis was used to assess overall survival, and the log-rank test was used to evaluate the differences between survival curves. Univariate and multivariate analyses were also performed to determine the effect of various patient, tumor, and treatment variables on overall survival. Results A total of 500 cases were included in the analysis, consisting of 326 fibrillary (65.2%), 29 protoplasmic (5.8%), and 145 gemistocytic (29%) variants. Gemistocytic astrocytomas presented at a significantly older age than the fibrillary variant (46.8 vs 37.7 years, p < 0.0001), with protoplasmic and fibrillary subtypes having a similar age. Although protoplasmic and fibrillary variants underwent radiotherapy at similar rates, gemistocytic tumors more frequently received radiotherapy (p = 0.0001). Univariate analysis revealed older age, larger tumor size, and the use of radiotherapy to be poor prognostic factors, with resection being associated with improved survival. The gemistocytic subtype (hazard ratio [HR] 1.62 [95% CI 1.27–2.07], p = 0.0001) also resulted in significantly worse survival than fibrillary tumors. Bivariate analyses demonstrated that older age, the use of radiotherapy, and resection significantly influenced median survival. Tumor subtype also affected median survival; patients who harbored gemistocytic tumors experienced less than half the median survival of fibrillary and protoplasmic tumors (38 vs 82 months, p = 0.0003). Multivariate analysis revealed increasing age (HR 1.05 [95% CI 1.04–1.05], p < 0.0001), larger tumor size (HR 1.02 [95% CI 1.01–1.03], p = 0.0002), and the use of resection (HR 0.70 [95% CI 0.52–0.94], p = 0.018) to be independent predictors of survival. Examination of tumor subtype revealed that the gemistocytic variant (HR 1.30 [95% CI 0.98–1.74], p = 0.074) was associated with worse patient survival than fibrillary tumors, although this only approached significance. The protoplasmic subtype did not affect overall survival (p = 0.33). Conclusions Gemistocytic tumor histology was associated with worse survival than fibrillary and protoplasmic astrocytomas. As protoplasmic astrocytomas have a survival similar to fibrillary tumors, there may be limited utility to the identification of this rare variant. However, increased attention should be paid to the presence of gemistocytes in low-grade gliomas as this is associated with shorter time to progression, increased malignant transformation, and reduced overall survival.

Duane retraction syndrome (DRS) is the most common form of congenital paralytic strabismus in humans and can result from α2-chimaerin (CHN1) missense mutations. We report a knockin α2-chimaerin mouse (Chn1 abducens neurons use bidirectional ephrin signaling via mutant α2-chimaerin to direct growth, while cervical spinal neurons use only ephrin forward signaling, and trochlear neurons do not use ephrin signaling. These findings reveal a role for ephrin bidirectional signaling upstream of mutant α2-chimaerin in DRS, which may contribute to the selective vulnerability of abducens motor neurons in this disorder.

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