A spine frame for intra-operative fixation to increase accuracy in spinal navigation and robotics.

OBJECTIVE: Intra-operative movements due to mechanical ventilation or manipulations are a limiting factor for accurate spinal navigation or robotic-assisted spinal surgery. The purpose of this study was to assess the accuracy of an intra-operative spinal fixation device in an experimental setup. MATERIALS AND METHODS: We developed a fixation device, attached to the operating table, that combines soft tissue retraction with spinal process fixation. Using a lumbar spine cadaver, tightness of fixation was evaluated using two measurement systems. Accuracy measurements using changes in spatial co-ordinates of implanted reference markers were performed in three segments, following different manipulations of the spine. In addition, for intra-operative movements of the spine during mechanical ventilation, the range of motion was determined in 10 patients during lumbar interbody fusion. RESULTS: The spine frame was easy to use and did not restrict screw insertion. Mean deviations of the markers' in all segments were measured at between 0.35 and 0.8 mm, following pedicle screw insertion and lateral traction. Intra-operative range of motion of the spine was measured with a mean value of 8.7 +/- 3.3 mm. CONCLUSION: Using our spine frame, a rigid fixation following manipulation of the spine was demonstrated. By overcoming the intra-operative movement-dependent inaccuracy, safety in navigated spine surgery and robotic-assisted procedures might be improved.     

The influence of cage positioning and cage type on cage migration and fusion rates in patients with monosegmental posterior lumbar interbody fusion and posterior fixation

In posterior lumbar interbody fusion, cage migrations and lower fusion rates compared to autologous bone graft used in the anterior lumbar interbody fusion procedure are documented. Anatomical and biomechanical data have shown that the cage positioning and cage type seem to play an important role. Therefore, the aim of the present study was to evaluate the impact of cage positioning and cage type on cage migration and fusion. We created a grid system for the endplates to analyze different cage positions. To analyze the influence of the cage type, we compared “closed” box titanium cages with “open” box titanium cages. This study included 40 patients with 80 implanted cages. After pedicle screw fixation, 23 patients were treated with a “closed box” cage and 17 patients with an “open box” cage. The follow-up period averaged 25 months. Twenty cages (25%) showed a migration into one vertebral endplate of <3 mm and four cages (5%) showed a migration of ≥3 mm. Cage migration was highest in the medio-medial position (84.6%), followed by the postero-lateral (42.9%), and the postero-medial (16%) cage position. Closed box cages had a significantly higher migration rate than open box cages, but fusion rates did not differ. In conclusion, cage positioning and cage type influence cage migration. The medio-medial cage position showed the highest migration rate. Regarding the cage type, open box cages seem to be associated with lower migration rates compared to closed box cages. However, the cage type did not influence bone fusion.     

Acquisition of resistance to 1-(4-amino-2-methyl-5-pyrimidinyl) methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride in V79 cells through increased removal of O6-alkylguanine

The molecular mechanism of acquisition of resistance to 1-(4-amino-2-methyl-5-pyrimidinyl)-methyl-3-(2-chloroethyl)-3-nitroso ure a hydrochloride (ACNU) was investigated using ACNU-resistant clones (ACNUr-1-4) isolated from the V79 cell line. The binding level of alkyl cyanate, a decomposition product of ACNU, to protein in ACNUr-1 cells was not less than that in the parental V79 cells, indicating that the acquired resistance was not due to a reduced intracellular concentration of ACNU. Because O6-chloroethylguanine, an intermediate in cytotoxic interstrand cross-link formation by ACNU, is known to be repaired by the same mechanism as O6-ethyldeoxyguanosine (O6-EtdGuo), we quantitated O6-EtdGuo by radioimmunoassay at various times after exposure of cells to 100 micrograms/ml N-ethyl-N-nitrosourea for 20 min. In V79 cells, elimination of O6-EtdGuo was negligible, but in all four resistant clones, 30 to 59% of the O6-EtdGuo was removed within 24 hr after exposure. This increased removal of O6-EtdGuo among the resistant clones was associated with the activity of O6-alkylguanine DNA alkyltransferase (O6-AGT) determined using cell extracts. The present results indicate that increased removal of O6-chloroethylguanine in ACNU-resistant clones by O6-AGT is mechanistically linked to the acquisition of resistance to ACNU.     

Neuroprotective Effect of Melatonin on Cortical Impact Injury in the Rat

Summary  The pineal hormone melatonin is a highly efficient physiological scavenger of free radicals involved in secondary brain damage. A variety of experimental studies have demonstrated a neuroprotective effect for melatonin, based on its antioxidant activity. The purpose of the present study was to investigate the time-dependency and a possible protective effect of exogenous melatonin in the cortical impact model in rats. The protective effect was quantified determining contusion volume, brain edema and brain water content.  45 anesthetized male Sprague-Dawley rats (250–350 mg) were subjected to cortical impact injury of moderate severity (7 m/s, deformation 2 mm). Melatonin (100 mg/kg bw i.p.), or a vehicle was injected 20 min before trauma, immediately after, and 1 and 2 hours after trauma during daytime and nighttime. Posttraumatic lesion volume using hematoxylin-eosin staining, hemispheric swelling, brain water content, cerebral perfusion pressure and intracranial pressure 24 hours after injury were investigated.  Melatonin, given during nighttime, significantly reduced contusion volume corresponding to a mean reduction of contusion volume of 27% (placebo, n=7: 41.9±5.2 mm³, melatonin, n=8: 30.5±4.2 mm³, p<0.05). Given during daytime, the reduction in contusion volume was not significant (placebo, n=8: 42.1±5.1 mm³, melatonin, n=8: 35.9±2.2 mm³, reduction of 15%, p=0.08, n.s.). Hemispheric swelling was unchanged by melatonin treatment. Mean arterial blood pressure and rectal temperature remained stable before and after the cortical impact injury and injection of melatonin. This study shows that melatonin significantly reduces contusion volume with major effects during night.     

Reciprocal relationship between O6-methylguanine-DNA methyltransferase P140K expression level and chemoprotection of hematopoietic stem cells

Retroviral-mediated delivery of the P140K mutant O(6)-methylguanine-DNA methyltransferase (MGMT(P140K)) into hematopoietic stem cells (HSC) has been proposed as a means to protect against dose-limiting myelosuppressive toxicity ensuing from chemotherapy combining O(6)-alkylating agents (e.g., temozolomide) with pseudosubstrate inhibitors (such as O(6)-benzylguanine) of endogenous MGMT. Because detoxification of O(6)-alkylguanine adducts by MGMT is stoichiometric, it has been suggested that higher levels of MGMT will afford better protection to gene-modified HSC. However, accomplishing this goal would potentially be in conflict with current efforts in the gene therapy field, which aim to incorporate weaker enhancer elements to avoid insertional mutagenesis. Using a panel of self-inactivating gamma-retroviral vectors that express a range of MGMT(P140K) activity, we show that MGMT(P140K) expression by weaker cellular promoter/enhancers is sufficient for in vivo protection/selection following treatment with O(6)-benzylguanine/temozolomide. Conversely, the highest level of MGMT(P140K) activity did not promote efficient in vivo protection despite mediating detoxification of O(6)-alkylguanine adducts. Moreover, very high expression of MGMT(P140K) was associated with a competitive repopulation defect in HSC. Mechanistically, we show a defect in cellular proliferation associated with elevated expression of MGMT(P140K), but not wild-type MGMT. This proliferation defect correlated with increased localization of MGMT(P140K) to the nucleus/chromatin. These data show that very high expression of MGMT(P140K) has a deleterious effect on cellular proliferation, engraftment, and chemoprotection. These studies have direct translational relevance to ongoing clinical gene therapy studies using MGMT(P140K), whereas the novel mechanistic findings are relevant to the basic understanding of DNA repair by MGMT.     

Favorable prognosis in pediatric brainstem low-grade glioma: Report from the German SIOP-LGG 2004 cohort

Reports on pediatric low-grade glioma (LGG) of the caudal brainstem are retrospective with heterogeneous cohorts, variable treatments and inconsistent outcome data. We analyzed their natural history and asked whether brainstem location proved unfavorable for survival within the framework of the comprehensive SIOP-LGG 2004 management strategy. Within the prospectively registered, population-based German SIOP-LGG 2004 cohort 116 patients (age 0.2–16.5 years, 10% Neurofibromatosis NF1) were diagnosed with LGG of the pons (27%) and medulla oblongata (73%). After biopsy (23%), variable resection (63%) or radiologic diagnosis only (14%), 59 patients received no adjuvant treatment. Radiologic progression or severe neurologic symptoms prompted chemo- (n = 39) or radiotherapy (n = 18). After further progression (28/57), salvage treatments included multiple treatment lines for 12/28 patients. Five-years event-free survival dropped to 0.40, while 5-years overall survival was 0.95 (median observation time 6.8 years). Higher extent of resection yielded lower progression rate (p = 0.001), but at a cost of 21/100 patients suffering from new postsurgical complications including respiratory insufficiency. Central review confirmed pilocytic astrocytoma (56%), diffuse astrocytoma (8%) or glioneuronal histology (16%) (others 4%, no histology 17%). Malignant evolution was documented in five patients associated with Histone3 mutation in 2/5. Our treatment algorithm conveyed high overall survival for pediatric brainstem LGG. Extensive neurosurgical resection did increase additional postoperative neurologic deficits but not overall survival in this often-chronic disease. More than half of all patients can be safely followed by observation, while multimodal adjuvant treatment can control progressive tumors. Molecular assessment should confirm low-grade diagnosis and may detect patterns prognostic for malignant evolution.