The development of a dynamic,six-axis spine simulator

Background contextAlthough a great deal of research has been completed to characterize the stiffness of spinal specimens, there remains a limited understanding of the spine in 6 df and there is a lack of data from dynamic testing in six axes.PurposeThis study details the development and validation of a dynamic six-axis spine simulator.Study designBiomechanical study.MethodsA synthetic spinal specimen was used for the purpose of tuning the simulator, completing positional accuracy tests, and measuring frequency response under physiological conditions. The spine simulator was used to complete stiffness matrix tests of an L3–L4 lumbar porcine functional spinal unit. Five testing frequencies were used, ranging from quasistatic (0.00575 Hz) to dynamic (0.5 Hz). Tests were performed without an axial preload and with an axial preload of 500 N.ResultsThe validation tests demonstrated that the simulator is capable of producing accurate positioning under loading at frequencies up to 0.5 Hz using both sine and triangle waveforms. The porcine stiffness matrix tests demonstrated that the stiffness matrix is not symmetrical about the principal stiffness diagonal. It was also shown that while an increase in test frequency generally increased the principal stiffness terms, axial preload had a much greater effect.ConclusionsThe spine simulator is capable of characterizing the dynamic biomechanics of the spine in six axes and provides a means to better understand the complex behavior of the spine under physiological conditions.     

Cool Mist Irrigation Improves Heat Dissipation during Surgical Bone Drilling

Objective High-speed drilling generates heat in small cavities and may pose a risk for neurovascular tissues. We hypothesize that a continuous pressurized cold mist could be an alternative approach for better cooling during drilling of bone to access cranial lesions. This study aims to examine this idea experimentally. Design Ex-vivo drilling tests with controlled speed, feed, and depth were performed on cortical bone samples. Thermocouples were embedded underneath the drilling path to compare the temperature rises under mist cooling (at 3°C, < 300 mL/h) and flood irrigation (at 22°C, > 800 mL/h). Results A significant difference exists between these two systems (p value < 0.05). The measured temperature was ∼ 4°C lower for mist cooling than for flood irrigation, even with less than a third of the flow rate. Conclusion Experimental data indicate the capability of mist cooling to reduce heat generation while simultaneously enabling flow reduction and targeted cooling. An improved field of view in an extremely narrow access corridor may be achieved with this technology.     

Single institutional experience using biological mesh for abdominal wall reconstruction

Background

Complex ventral hernias remain a challenge. We present a study evaluating outcomes of complex ventral hernia repair using human-derived acellular dermal matrix (AlloDerm) and porcine-derived acellular dermal sheet (Permacol).

Methods

A retrospective review of 251 patients undergoing complex hernia repair was performed. Primary outcome was hernia recurrence; and secondary outcomes included early and late complications and mortality.

Results

Recurrence for Permacol versus AlloDerm was 32% versus 47% (P = .02). There was a difference in early complications (48% vs 30%, P = .007) and also late complications (30% vs 21%, P = .16) of Permacol versus AlloDerm. Overall survival was 85% for the Permacol group versus 78% for the AlloDerm group (P = .23). Recurrence for Permacol versus AlloDerm for underlay technique was 19% versus 22% and that for bridging technique was 44% versus 57%.

Conclusion

There exists a high complication rate from both Permacol and AlloDerm in complex ventral hernia repair especially when used as a fascial bridge.     

Simpson grade: an opportunity to reassess the need for complete resection of meningiomas

Background

The relevance of the Simpson grading system as a predictor of meningioma progression or recurrence in modern neurosurgical practice has recently been called into question. The aim of our study was to compare the risk of progression/recurrence of tumours that had been treated with different Simpson grade resections in a contemporary population of benign (WHO grade I) meningioma patients.

Method

One hundred eighty-three patients with histologically confirmed WHO grade I meningioma were retrospectively analysed. All patients underwent first-time craniotomy as their initial therapy between 2004 and 2012. Univariate analysis was performed using log-rank testing and Kaplan-Meier analysis for progression/recurrence-free survival. Multivariate analysis was performed using Cox proportional hazards regression modelling.

Results

The three-year progression/recurrence-free survival rates for patients receiving Simpson grade 1, 2 or 4 resections were 95 %, 87 % and 67 %, respectively. Simpson grade 4 resections progressed/recurred at a significantly greater rate than Simpson grade 1 resections (hazard ratio [HR]?=?3.26, P?=?0.04), whereas Simpson grade 2 resections did not progress/recur at a significantly greater rate than Simpson grade 1 resections (HR?=?1.78, P?=?0.29). Subtotal resections progressed/recurred at a significantly greater rate than gross-total resections (HR?=?2.47, P?=?0.03).

Conclusions

Tumours that undergo subtotal resection are at a significantly greater risk of progression/recurrence than tumours that undergo gross-total resection. Gross-total resection should therefore be the aim of surgery. However, given modern access to follow-up imaging and stereotactic radiosurgery, these results should not be used to justify overly ‘heroic’ tumour resection.     

Monocyte activity is linked with abdominal aortic aneurysm diameter

Background

Systemic inflammation and increased matrix metalloproteinase (MMP) cause elastin degradation leading to abdominal aortic aneurysm (AAA) expansion. Several prospective studies report that statin therapy can reduce AAA expansion through anti-inflammation. We hypothesize that monocyte activity plays a pivotal role in this AAA development and this study examines patient peripheral blood monocyte cell adhesion, transendothelial migration, and MMP concentrations between AAA and non-AAA patients.

Materials and methods

Peripheral blood was collected and monocytes isolated from control (n = 15) and AAA (n = 13) patients. Monocyte adhesion, transmigration, and permeability assays were assessed. Luminex assays determined MMP-9 and tissue inhibitor of metalloproteinase-4 (TIMP-4) concentrations from cell culture supernatant and patient serum.

Results

AAA patient monocytes showed increased adhesion to the endothelium relative fluorescence units (RFU, 0.33 ± 0.17) versus controls (RFU, 0.13 ± 0.04; P = 0.005). Monocyte transmigration was also increased in AAA patients (RFU, 0.33 ± 0.11) compared with controls (RFU, 0.25 ± 0.04, P = 0.01). Greater numbers of adhesive (R² = 0.66) and transmigratory (R² = 0.86) monocytes were directly proportional to the AAA diameter. Significantly higher serum levels of MMP-9 (2149.14 ± 947 pg/mL) were found in AAA patients compared with controls (1189.2 ± 293; P = 0.01). TIMP-4 concentrations were significantly lower in AAA patients (826.7 ± 100 pg/mL) compared with controls (1233 ± 222 pg/mL; P = 0.02). Cell culture supernatant concentrations of MMP and TIMP from cocultures were higher than monocyte-only cultures.

Conclusions

Monocytes from AAA patients have greater adhesion and transmigration through the endothelium in vitro, leading to elevated MMP-9 levels and the appropriate decrease in TIMP-4 levels. The ability to modulate monocyte activity may lead to novel medical therapies to decrease AAA expansion.