Joachim Mühling

Intraoperative navigation in oral and maxillofacial surgery

Surgical procedures in the oral and maxillofacial region may be difficult in areas of complex anatomy. Up to now, surgical planning has been based almost exclusively on the surgeons experience and on the interpretation of 2-dimensional (2D) radiologic information. Our experiences with a commercially available 3D navigation system (Viewing Wand, ISG, Mississauga, Ontario, Canada) is reported upon. The system consists of a mechanical operating arm with 6 joints and 6 degrees of freedom working as a 3D digitizer and is interfaced to a computer graphics workstation. After registration of the position of the patients head in relation to the tip of the instrument on the navigation arm, the surgeon can observe the 3D position and direction of the instrument in use on the monitor, i.e. on the computed tomography and/or magnetic resonance tomography images of the patient taken before. In 40 interventions performed so far, the accuracy was 2 mm and better. 3 cases are presented in this paper. The system facilitates surgery especially in anatomically complicated situations without the risk of damaging neighbouring structures. Planning of surgical interventions is much easier. By using computer assisted simulation and navigation systems, we expect an improvement in quality and a reduction in surgical risks. Thus, looking ahead surgery has become possible. More extensive and more radical interventions are likely to be performed in the near future. Responsibility for the surgical intervention, however, remains exclusively with the surgeon.

Comparative examination of the accuracy of a mechanical and an optical system in CT and MRT based instrument navigation

The aim of an intraoperative instrument navigation system is to support the surgeon in the localization of anatomical regions and to guide the use of surgical instruments. An overview of technical principles and literature reports on various navigation systems is provided here. The navigation accuracy (tested on a plastic phantom under simulated operating room conditions) of the mechanical Viewing Wand system and the optical SPOCS system amounts to 1 to 3 mm for computerized tomography (CT) data, with a significant inverse dependence on the layer thickness. The values for magnetic resonance tomography (MRT) data are significantly higher. In regard to the choice of registration points, a statistically inverse dependence exists between the number of points and the distance between the points. During the time period between autumn 1993 and mid-1999, more than 120 clinical applications were performed. The intraoperative accuracy was in the range of < or = 3 mm. Registering the patient position with preoperatively inserted screw markers achieved accuracy values of < or = 2 mm. The instrument navigation technique has proved to be very advantageous for the spatial orientation of the surgeons. The possibility of checking resection borders has opened up new perspectives in tumor surgery. A quality improvement and a reduction of the operational risks as well as a considerable decline in the stress placed on the patient can be expected in the near future due the techniques of computer-assisted surgery.

Trigonocephaly: Results after surgical correction of nonsyndromatic isolated metopic suture synostosis in 54 cases

Children with nonsyndromatic isolated metopic suture synostosis suffer from a significant deformity of the supraorbital ridges, the temporal regions and hypotelorism. We retrospectively analyzed 54 consecutive cases of isolated nonsyndromatic metopic synostosis treated over a 14-year-period. The data were evaluated using patients clinical records, skull radiographs in two planes, CT-scans, MRI scans and pre-/post-operative photographs. Surgery with standardized fronto-orbital advancement was performed at a median age of 11.5 months. Follow-up ranged from 4.5 months to 177.4 months, with an average of 51.9 months. The average blood loss was less than 255ml and the average post-operative length of stay was 5 days. Not a single major complication was observed except for uncomplicated dural tears in six cases. According to the classification of Whitaker, results were considered good to excellent (Category I and II) in all except one case (Category IV). As the current techniques have been standardized for routine use, surgical risks are reasonably low with no mortality or permanent morbidity. We think that the treatment of single metopic synostosis is safe with very low reoperation rates and short length of hospital stay. Overall, our results showed acceptable minor complication rates and generally satisfactory aesthetic outcomes.

The accuracy of image guided surgery based on cone beam computer tomography image data

OBJECTIVEnThe objective of this study was to verify if accurate patient-to-image registration for precision navigation in maxillofacial surgery is possible based on cone beam computed tomography (CBCT) image data.nnnSTUDY DESIGNnA maxillary registration template was placed on a standard plastic skull phantom that was equipped with a custom made model of the maxilla and with target markers. Imaging was performed with a CBCT device (Newtom 9000 Digital Volume Tomograph (DVT), QR s.r.l., Verona, Italy) and a computed tomography (CT) scanner (Somatom 4, Siemens, Forchheim, Germany). Using an infrared navigation system (Polaris, NDI, Waterloo, Ontario), multiple pair-point registration of both image data sets and the phantom were performed. The target registration error (TRE) was evaluated.nnnRESULTSnA total of 243 registrations were performed for either image data set. The spatial distribution of TRE on the skull showed increasing inaccuracy with growing distance from the registration markers. The average target registration error was 1.50 +/- 0.82 mm with CBCT and 1.57 +/- 0.84 mm with CT image data and did not differ significantly. Error distribution correlated strongly between CT- and CBCT-based registration.nnnCONCLUSIONSnThe overall registration accuracy based on CBCT image data was similar to CT. The strong correlation of the geometric distribution of TRE between CT- and CBCT-based measurements proves that CBCT can be equivalent to CT in image-guided maxillofacial surgery.

Template-based registration for image-guided skull base surgery

Objectives To evaluate whether patient-to-image registration with the use of a maxillary template is sufficiently accurate for image guided skull base surgery. Study Design and Setting In an experimental phantom study, pair-point registration of a skull phantom to its CT image data was performed with 243 different configurations of a maxillary template with markers. Then artificial skull mounted target markers were located with an infrared tracking device as used in navigation systems. Results The average target registration error was 1.57 mm in the anterior skull base (95% confidence interval, 1.53 to 1.61 mm), but 3.31 mm in the lateral skull base (95% confidence interval, 3.26 to 3.37 mm). Conclusions Fiducial marker registration based on a maxillary template is sufficiently accurate for image-guided surgery in the anterior skull base, but not for the lateral skull base. Significance Template-based registration is an accurate yet noninvasive registration method for frontal skull base surgery.

Intraoperative computed tomography and automated registration for image-guided cranial surgery

OBJECTIVESnTwo key problems for the use of navigation systems in image-guided surgery are accurate patient-to-image registration and the fact that with ongoing surgery the patients anatomy is altered while the image data remains unchanged. A system for intraoperative CT imaging and fully automated registration of this image addresses both problems. It had been evaluated successfully in phantom studies. In this clinical study, we assessed the impact of the system on intraoperative workflow and registration accuracy in everyday patient care.nnnMETHODSnIn ten patients who underwent image-guided surgery, CT image data were acquired intraoperatively and were automatically registered in the navigation system. Registration accuracy and surgical outcome were assessed clinically. In six of these patients, a maxillary splint with markers had been inserted to cross-check registration accuracy. The target registration error of these markers was measured.nnnRESULTSnIn all cases, registration accuracy was clinically sufficient and the surgical task could be performed successfully. In those cases where a maxillary template with target markers was attached for additional control of the registration accuracy, the target registration error was always better than 2 mm. Automated registration reduced the intraoperative registration time considerably and partially compensated for the time needed to perform the image data acquisition.nnnCONCLUSIONSnIntraoperative CT imaging and automated registration successfully address the two key problems of image-guided surgery. The method is robust and accurate and proved its usability in everyday patient care.

Long-term results in nonsyndromatic unilateral coronal synostosis treated with fronto-orbital advancement.

Children with unilateral isolated coronal suture synostosis suffer from frontal plagiocephaly. In this retrospective study we analyzed 21 patients who were treated with an identical and standardized surgical technique of fronto-orbital advancement with hypercorrection with an average follow-up of 57.5 months. The median age at surgery was 12.1 months. The median average amount of blood loss during the operation was less than 188xa0ml. Not a single major complication was observed. According to the classification of Whitaker, 15 patients had a Class 1 outcome, with excellent surgical results. Three patients were defined as Class 2 outcome. One of our patients was Class 3 and two patients were Class 4 because of severe forehead retrusion and temporal hollowing. Re-operation rate was 14.3%. 67% of our patients showed a correction or an improvement of the typical C-shaped deformity in their follow-up examination. Aesthetic outcomes were excellent in 13, good in 5, and poor in 3 of cases, as judged by their families and the craniofacial team. Unilateral coronal synostosis can be successfully treated by fronto-orbital advancement with a low complication rate and an excellent clinical outcome. To minimize the need of re-operations, fronto-orbital advancement should be performed with an overcorrection on the affected side.

Surgical outcome after using a modified technique of the pi-procedure for posterior sagittal suture closure

Fusion of the sagittal suture is the most prevalent form of craniosynostosis. Due to the variety of deformities of scaphocephaly depending on the location of the fused sagittal suture, the surgical procedure has to be adjusted to the individual case. In this study, 38 patients with a predominantly posterior sagittal suture closure were treated with a modified technique of the pi-procedure and the surgical outcome has been evaluated with respect to complications, morphological and aesthetic outcome. The improvement of the cephalic index in our series in the follow-up examination (mean 60.1 months) after surgery was significant (p<0.0001). According to the classification of Whitaker, 31 patients had a Class 1 outcome, with excellent surgical results. Aesthetic outcomes were excellent in 29, good in 5, and poor in 4 of cases, as judged by both the families and the craniofacial team. No severe complications have been observed. Posterior sagittal suture with marked occipital bulging can be successfully treated with this modified posterior procedure with a low complication rate, significant improvement of the cephalic index and a good aesthetic outcome. In all cases of sagittal synostosis, the operative procedure should be tailored to the nature and severity of the deformity.

Computer-assisted three-dimensional surgical planning: 3D virtual articulator: technical note

This study presents a computer-assisted planning system for dysgnathia treatment. It describes the process of information gathering using a virtual articulator and how the splints are constructed for orthognathic surgery. The deviation of the virtually planned splints is shown in six cases on the basis of conventionally planned cases. In all cases the plaster models were prepared and scanned using a 3D laser scanner. Successive lateral and posterior-anterior cephalometric images were used for reconstruction before surgery. By identifying specific points on the X-rays and marking them on the virtual models, it was possible to enhance the 2D images to create a realistic 3D environment and to perform virtual repositioning of the jaw. A hexapod was used to transfer the virtual planning to the real splints. Preliminary results showed that conventional repositioning could be replicated using the virtual articulator.

Subtotal cranial vault remodelling in anterior sagittal suture closure: impact of age on surgical outcome

Isolated fusion of the sagittal suture is usually treated before 1 year of age, but some patients present at a later age. The aim of this study was to evaluate the impact of childrens age on the surgical outcome. The authors investigated 46 patients with isolated nonsyndromic sagittal craniosynostosis limited to the anterior two-thirds of the cranial vault. All patients underwent subtotal cranial vault remodelling, 36 patients (78.3%) before the age of 12 months (mean 8.92 months) and 10 patients after the age of 12 months (mean 15.77 months). Perioperative parameters and measurements of the cephalic index, preoperatively and postoperatively, were evaluated. All 46 patients showed improved head shape independent of their age. In patients younger than 12 months, mean cephalic indices improved from 65.99 to 74.49 (p<0.0001) and in patients older than 12 months from 66.38 to 74.38 (p<0.0004). There were no statistical differences in perioperative parameters including length of surgery, intraoperative blood loss and duration of hospital stay. In this study, patients showed no significant differences in surgical outcome that could have been related to the age at surgery. Surgical treatment should be performed early enough to benefit from the remodelling potential of the skull.