Posterior fusion for fragility type 2 odontoid fractures

OBJECTIVE The purpose of this study was to evaluate the outcomes of elderly patients with type 2 odontoid fractures treated with an instrumented posterior fusion. METHODS Ninety-three consecutive patients older than 65 years of age in whom a type 2 odontoid fracture had been treated with a variety of C1–2 posterior screw fixation techniques were retrospectively reviewed. RESULTS The average age was 78 years (range 65–95 years). Thirty-seven patients had an additional fracture, 30 of which involved C1. Three patients had cervical spinal cord dysfunction due to their injury. All patients had comorbidities. The average total hospitalization was 9.6 days (range 2–37 days). There were 3 deaths and 19 major complications, the most common of which was pneumonia. No patient suffered a vertebral artery injury. Imaging studies were obtained in 64 patients at least 12 months postsurgery (mean 19 months). Fusion was assessed by dynamic radiographs in all cases and with a CT scan in 80% of the cases. Four of the 64 patients did not achieve fusion (6.25% overall). All patients in whom fusion failed had undergone C1 lateral mass fixation and C2 pars (1/29, 3.4%) or laminar (3/9, 33.3%) fixation. CONCLUSIONS Instrumented posterior cervical fusions may be performed in elderly patients with acceptable morbidity and mortality. The fusion rate is excellent except when bilateral C2 translaminar screws are used for axis fixation.

Axis screws: results and complications of a large case series

SUMMARY OBJECTIVE: To present the surgical results of patients who underwent axis screw instrumentation, discussing surgical nuances and complications of the techniques used. METHODS: Retrospective case-series evaluation of patients who underwent spinal surgery with axis instrumentation using screws. RESULTS: Sixty-five patients were included in this study. The most common cause of mechanical instability was spinal cord trauma involving the axis (36 patients – 55.4%), followed by congenital craniocervical malformation (12 patients – 18.5%). Thirty-seven (57%) patients required concomitant C1 fusion. Bilateral axis fixation was performed in almost all cases. Twenty-three patients (35.4%) underwent bilateral laminar screws fixation; pars screws were used in twenty-two patients (33.8%), and pedicular screws were used isolated in only three patients (4.6%). In fourteen patients (21.5%), we performed a hybrid construction. There was no neurological worsening nor vertebral artery injury in this series. CONCLUSION: Axis screw instrumentation proved to be a safe and efficient method for cervical stabilization. Laminar and pars screws were the most commonly used

Axis instrumentation: surgical results

OBJECTIVE: Evaluate the surgical results of axis screw instrumentation. METHODS: Retrospective evaluation of the clinical and radiological data of patients submitted to axis fixation using screws. RESULTS: Seventeen patients were surgically treated. The mean age was 41.8 years (range: 12-73). Spinal cord trauma was the most common cause of instability (8 patients - 47%). Bilateral axis fixation was performed in all cases, except one, with laminar screw (total of 33 axis screws). Seven patients (41.1%) underwent bilateral pars screws; laminar screws were used in six cases and pedicular screws were used in two. In two cases, we performed a hybrid construction (laminar + pars and pedicle + pars). There was no neurological worsening or death, nor complications directly related to use axis screws. CONCLUSION: Axis instrumentation was effective and safe, regardless of the technique used for stabilization. Based on our learnt experience, we proposed an algorithm to choose the best technique for axis screw fixation.

The role of targeted secretion in the establishment of cell polarity and the orientation of the division plane in Fucus zygotes

In this study, we investigate the role of polar secretion and the resulting asymmetry in the cell wall in establishing polarity in Fucus zygotes. We have utilized brefeldin-A to selectively interrupt secretion of Golgi-derived material into the cell wall as assayed by toluidine blue O staining of sulfated fucoidin. We show that the polar secretion of Golgi-derived material is targeted to a cortical site of the zygote identified by the localization of actin filaments and dihydropyridine receptors. The deposition of Golgi-derived material into the cell wall at this target site is temporally coincident with and required for polar axis fixation. We propose that local secretion of Golgi-derived material into the cell wall transforms the target site into the fixed site of polar growth. We also found that polar secretion of Golgi-derived material at the fixed site is essential for growth and differentiation of the rhizoid, as well as for the proper positioning of the first plane of cell division. We propose that the resulting asymmetry in the cell wall serves as positional information for the underlying cortex to initiate these polar events. Our data supports the hypothesis that cell wall factors in embryos, previously shown to be responsible for induction of rhizoid cell differentiation, are deposited simultaneously with and are responsible for polar axis fixation. Furthermore, the pattern of polar growth is attributable to a positional signal at the fixed site and appears to be independent of the orientation of the first cell division plane. Thus, the establishment of zygotic cell polarity and not the position of the first division plane, is critical for the formation of the initial embryonic pattern in Fucus.

Polar localization of a dihydropyridine receptor on living Fucus zygotes

We have used a fluorescently-labeled dihydropyridine (FL-DHP) to vitally stain living Fucus zygotes during the establishment of cell polarity. Localization of FL-DHP is primarily at the plasma membrane and FL-DHP binding is competitively blocked by an unlabeled dihydropyridine. Distribution of FL-DHP is initially symmetrical before fixation of the polar axis, but becomes asymmetrical in response to a unilateral light gradient. The distribution of FL-DHP receptors can be relocalized when the direction of the photopolarizing stimulus is changed. Treatment of cells with cytochalasin B prior to axis fixation reversibly prevents localization of FL-DHP receptors. Observation of FL-DHP labeling by time-lapse fluorescence microscopy indicates that the existing receptors are redistributed during polar axis formation. The asymmetric distribution of FL-DHP receptors coincides temporally and spatially with increased local intracellular calcium ion concentrations, as measured by calcium green dextran. Based on the site, timing, photo-reversibility, and actin dependence of the asymmetric localization of FL-DHP receptors, we conclude that FL-DHP is a vital probe for the later stage of polar axis formation in Fucus zygotes. Furthermore, we propose that FL-DHP receptors correspond to ion channels that are transported to the future site of polar growth to create the changes in local calcium concentration required for polarity establishment.

Calcium and related channels in fertilization and early development of Fucus

Unfertilized eggs of Fucus serratus are primed to respond rapidly to the fertilizing sperm. The unfertilized egg plasma membrane is excitable due to the presence of voltage-regulated Ca 2+ and K + channels. Sperm-egg interaction elicits a fertilization potential as the first observable fertilization event. It is speculated that sperm-gated Na + channels are responsible for the initial depolarization phase, leading to opening of Ca 2+ channels, allowing Ca 2+ influx and further depolarizing the membrane to the threshold for outward K + channels. K + efflux repolarizes the membrane and the zygote plasmalemma quickly becomes dominated by a large K + conductance. The involvement of Ca 2+ in axis formation and fixation is not clear. Ca 2+ carries a proportion of the inward current at the future rhizoid pole and asymmetric 45 Ca influx has been detected in polarizing zygotes. However, there is no requirement for external Ca 2+ in axis fixation. In contrast, Ca 2+ influx is required for expression of polarity and rhizoid growth. New developments in patch clamping can now enable localized areas of the plasma membrane in polarized cells to be studied. So far, both inward and outward single channel currents have been observed in the growing rhizoid tip, most probably carrying Cl - and K + respectively. These channels can be related to the currents identified by previous studies using the extracellular vibrating probe.