Neurophysiological and paraspinal oximetry monitoring to detect spinal cord ischemia in patients during and after descending aortic repair: An international multicenter explorative study.

BACKGROUND: During descending aortic repair, critically decreased blood flow to the myelum can result in ischemic spinal cord injury and transient or permanent paraplegia. Assessment of motor evoked potentials (MEPs) has been shown to be a valuable tool which allows to detect spinal cord ischemia (SCI) intraoperatively within a therapeutic window suitable to prevent progression to paraparesis or paraplegia. MEP monitoring is not feasible during postoperative care in the awakening patient. Therefore, ancillary techniques to monitor integrity of spinal cord function are needed to detect delayed spinal cord ischemia. OBJECTIVE: The purpose of this study is to evaluate whether assessment of long loop reflexes (LLR; F-waves) and paraspinal muscle oximetry using Near-Infrared Spectroscopy (NIRS) are feasible and valid in detecting delayed SCI. METHODS: We aim to include patients from three tertiary referral centers undergoing aortic repair with MEP monitoring in this study.F-wave measurements and paraspinal NIRS oximetry will be operated intra- and postoperatively. Measurement characteristics and feasibility will be assessed in the first 25 patients. Subsequently, a second cohort of 75 patients will be investigated to determine the sensitivity and specificity of F-waves and NIRS in detecting perioperative SCI. In this context for the MEP group SCI is defined intraoperatively as significant MEP changes and postoperatively as newly developed paraplegia. CONCLUSIONS: A clinical study design and protocol is proposed to assess if F-waves and/or NIRS-based paraspinal oximetry are feasible and valid in detecting and monitoring for occurrences of delayed SCI.

Evaluation of an improved orthognathic articulator system. 2. Accuracy of occlusal wafers.

The errors produced by occlusal wafers constructed on casts of the teeth mounted on a standard articulator and an improved orthognathic articulator were investigated by carrying out simulated orthognathic surgery on plastic skulls. The wafers were used to relocate the position of the maxillae of the skulls. The vertical and horizontal displacements of the maxillae were determined from measurements of the positions of markers on the skull and teeth. Comparison of the magnitudes of the actual and intended movements showed that wafers constructed on the standard articulator had systematic prediction errors of up to 5mm, but the improved orthognathic articulator showed much smaller random errors. There was a statistically significant improvement in overall accuracy in predicting maxillary Le Fort I position with the use of the improved orthognathic articulator which the authors recommend for clinical use.

Evaluation of an improved orthognathic articulator system: 1. Accuracy of cast orientation.

A systematic study was carried out using plastic model skulls to quantify the accuracy of the transfer of face bow registration to the articulator. A standard Dentatus semi-adjustable articulator system was compared to a purpose built orthognathic articulator system by measuring the maxillary occlusal plane angles of plastic model skulls and of dental casts mounted on the two different types of articulators. There was a statistically significant difference between the two systems; the orthognathic system showed small random errors, but the standard system showed systematic errors of up to 28°.

Errors in orthognathic surgery planning: the effect of inaccurate study model orientation.

The results of orthognathic surgery may differ significantly from the planned outcome using dental models. The orientation of dental models mounted on articulators using conventional face bows does not accurately replicate the orientation of the patients' teeth and jaws, but introduces a systematic error. A mathematical analysis showed that the misalignment of the maxillary model introduces errors in the perioperative wafers, which may lead to the incorrect surgical positioning of the maxilla reported in the literature. The results of the mathematical analysis were validated by image analysis of photographs of mounted maxillary models, used to simulate five orthognathic procedures. No significant difference between the experimental results and the theoretical predictions from the mathematical equations was noted. Planning for maxillary forward and upward movement produced more advancement and only 50% of maxillary impaction. Planning for maxillary forward and downward movement produced less advancement and more inferior displacement in relation to horizontal and vertical reference planes.