Felix Matthews

Comparison of different registration methods for surgical navigation in cranio-maxillofacial surgery

BACKGROUND Surgical navigation requires registration of the pre-operative image dataset with the patient in the operation theatre. Various marker and marker-free registration techniques are available, each bearing an individual level of precision and clinical practicability. In this study the precision of four different registration methods in a maxillofacial surgical setting is analyzed. MATERIALS AND METHODS A synthetic full size human skull model was registered with its computer tomography-dataset using (a) a dentally mounted occlusal splint, (b) the laser surface scanning, (c) five facial bone implants and (d) a combination of dental splint and two orbital bone implants. The target registration error was computed for 170 landmarks spread over the entire viscero- and neurocranium in 10 repeats using the VectorVision2 (BrainLAB AG, Heimstetten, Germany) navigation system. Statistical and graphical analyses were performed by anatomical region. RESULTS An average precision of 1mm was found for the periorbital region irrespective of registration method (range 0.6-1.1mm). Beyond the mid-face, precision linearly decreases with the distance from the reference markers. The combination of splint with two orbital bone markers significantly improved precision from 1.3 to 0.8mm (p<0.001) on the viscerocranium and 2.3-1.2mm (p<0.001) on the neurocranium. CONCLUSIONS An occlusal splint alone yields poor precision for navigation beyond the mid-face. The precision can be increased by combining an occlusal splint with just two bone implants inserted percutaneously on the lateral orbital rim of each side.

Precision and accuracy of the 3dMD photogrammetric system in craniomaxillofacial application.

Background: In modern anthropometry of such complex structures as the face, three-dimensional scanning techniques have become more and more common. Before establishing them as a criterion standard, however, meticulous evaluation of their precision and accuracy under both ideal and clinical circumstances is essential. Potential sources of error need to be identified and addressed. Materials and Methods: Under ideal circumstances, a phantom is used to examine the precision and accuracy of the 3dMD system. A clinical setting is simulated by varying different parameters such as angle, distance, and system reregistration, as well as data evaluation under different levels of magnification. Results: The handling of the system was unproblematic in matters of data acquisition and data analysis. It was very reliable, with a mean global error of 0.2 mm (range, 0.1-0.5 mm) for mannequin head measurements. Neither the position of the head nor that of the camera influenced these parameters. New referencing of the system did not influence precision and accuracy. Conclusions: The precision and accuracy of the tested system are more than sufficient for clinical needs and greater than those of other methods, such as direct anthropometry and two-dimensional photography. The evaluated system can be recommended for evaluation and documentation of the facial surface and could offer new opportunities in reconstructive, orthognathic, and craniofacial surgery.

Gender, Age, and Body Surface Area are the Major Determinants of Ascending Aorta Dimensions in Subjects With Apparently Normal Echocardiograms

BACKGROUND Limited data have been published on the normal size of the ascending aorta (AA) measured using transthoracic echocardiography (TTE). METHODS AA diameters were measured in 1799 patients with normal cardiac findings on TTE and compared with the diameters of the sinus of Valsalva (SoV). RESULTS Mean diameters in men and women, respectively, were 3.4 and 3.1 cm for the SoV and 3.2 and 3.0 cm for the AA. The sizes of the SoV and the AA showed strong correlations with age, age squared, and body surface area. The 5th and 95th percentile curves for the SoV and AA showed faster growth of diameters in early adulthood compared with old age. The dimensions of the SoV were larger than those of the AA (mean differences, 0.19 cm in men and 0.08 cm in women), and the difference between the SoV and AA was negatively correlated with age. CONCLUSION The findings of this study stress the importance of indexing dimensions of the SoV and the AA to age and body surface area separately for men and women.

Surgical Navigation in Craniomaxillofacial Surgery: Expensive Toy or Useful Tool? A Classification of Different Indications

The complex 3-dimensional (3D) anatomy and geometry of the human skull and face combined with the need for precise symmetry poses challenges for reconstructive surgery of the region. Therefore, and with the technical improvements during the past 10 years or so, surgical navigation has become an established technique in craniomaxillofacial surgery. 1-4 Many technical problems have been solved, and the accuracy of multiple strategies of imaging and registration has been proved. 5 However, the procedure of preparing a patient for navigation is still linked to extra effort for the patient and surgeon. Even noninvasive registration procedures, such as a splint fixed to the upper jaw, as described by Schramm et al, 6 require dental impressions and additional imaging with the splint in situ. Insecurity surrounds surgical navigation of the lower jaw with different techniques available, such as mounting a dynamic reference frame to the mandible 7-9 or retaining the mandible in a defined position against the maxilla. 7,10-15 Thus, the state of surgical navigation of the mandible has been deemed unsatisfactory to date. 16 The aim of the present study was to evaluate the feasibility and limitations of surgical navigation. In addition, we determined the time and effort of the surgical team in relation to the benefit.

A CT Database for Research, Development and Education: Concept and Potential

Both in radiology and in surgery, numerous applications are emerging that enable 3D visualization of data from various imaging modalities. In clinical practice, the patients images are analyzed on work stations in the Radiology Department. For specific preclinical and educational applications, however, data from single patients are insufficient. Instead, similar scans from a number of individuals within a collective must be compiled. The definition of standardized acquisition procedures and archiving formats are prerequisite for subsequent analysis of multiple data sets.Focusing on bone morphology, we describe our concept of a computer database of 3D human bone models obtained from computed tomography (CT) scans. We further discuss and illustrate deployment areas ranging from prosthesis design, over virtual operation simulation up to 3D anatomy atlases. The database of 3D bone models described in this work, created and maintained by the AO Development Institute, may be accessible to research institutes on request.

Point-to-point registration with mandibulo-maxillary splint in open and closed jaw position. Evaluation of registration accuracy for computer-aided surgery of the mandible

INTRODUCTION Computer navigation plays an increasingly important role in craniomaxillofacial surgery. The difficulties in computer navigation at the craniomaxillofacial site lie in the accurate transmission of the dataset to the operating room. This study investigates the accuracy of the dental-splint registration method for the skull, midface, and mandible. MATERIAL AND METHODS A synthetic human skull model was prepared with landmarks and scanned with cone beam computer tomography (CBCT). Two registration splints fixed the mandible against the viscerocranium in two different positions (closed vs. open). The target registration error was computed in all 278 landmarks spread over the entire skull and mandible in 10 repeated measurements using the VectorVision(2) (BrainLAB Inc., Feldkirchen, Germany) navigation system. RESULTS If registered in the closed position an average precision of 2.07 mm with a standard deviation (SD) of 0.78 mm was computed for all landmarks distributed over the whole skull. Registration in the open position resulted in an average precision of 1.53 mm (SD=0.55 mm). For single landmarks the precision decreases linearly with distance from the reference markers. The longer the three-dimensional distance between the registration points, the more precise the computer navigation is, mainly in the most posterior area of the cranium. CONCLUSION Our findings in the cranium are comparable with those of other studies. Artificial fixation of the lower jaw via splint seems to introduce no additional error. The registration points should be as far apart from each other as possible during navigation with the splint.

3-Dimensional Imaging for Lower Third Molars: Is There an Implication for Surgical Removal?

PURPOSE Surgical removal of impacted third molars may be the most frequent procedure in oral surgery. Damage to the inferior alveolar nerve (IAN) is a typical complication of the procedure, with incidence rates reported at 1% to 22%. The aim of this study was to identify factors that lead to a higher risk of IAN impairment after surgery. MATERIALS AND METHODS In total 515 surgical third molar removals with 3-dimensional (3D) imaging before surgical removal were retrospectively evaluated for IAN impairment, in addition to 3D imaging signs that were supposed predictors for postoperative IAN disturbance. Influence of each predictor was evaluated in univariate and multivariate analyses and reported as odds ratio (OR) and 95% confidence interval (CI). RESULTS The overall IAN impairment rate in this study was 9.4%. Univariate analysis showed narrowing of the IAN canal (OR, 4.95; P < .0001), direct contact between the IAN and the root (OR, 5.05; P = .0008), fully formed roots (OR, 4.36; P = .045), an IAN lingual course with (OR, 6.64; P = .0013) and without (OR, 2.72; P = .007) perforation of the cortical plate, and an intraroot (OR, 9.96; P = .003) position of the IAN as predictors of postoperative IAN impairment. Multivariate analysis showed narrowing of the IAN canal (adjusted OR, 3.69; 95% CI, 1.88 to 7.22; P = .0001) and direct contact (adjusted OR, 3.10; 95% CI, 1.15 to 8.33; P = .025) to be the strongest independent predictors. CONCLUSION Three-dimensional imaging is useful for predicting the risk of postoperative IAN impairment before surgical removal of impacted lower third molars. The low IAN impairment rate seen in this study-compared with similar selected study groups in the literature of the era before 3D imaging-indicates that the availability of 3D information is actually decreasing the risk for IAN impairment after lower third molar removal.

Protrusion of hardware impairs forearm rotation after olecranon fixation. A report of two cases.

Tension-band wire fixation is a common surgical technique that is used in the treatment of olecranon fractures and during osteotomies1-3. A number of problems that are specifically related to the use of Kirschner wires have been identified, including wire migration, skin ulceration, and the need for hardware removal4-6. We found only one published article that described diminished forearm rotation following the use of the tension-band technique7. Fig. 1 A patient with impaired forearm rotation after tension-band wire fixation of an olecranon osteotomy. A: The true lateral radiograph shows no evidence of undue penetration of the Kirschner wires into the soft tissues (arrow). B: Kirschner-wire protrusion (arrow) as seen in the three-dimensional model derived from the computed tomography scan. Impingement of the wires with the soft tissues is highly probable. We observed several instances of limitation of forearm rotation following tension-band wire fixation of the olecranon at our medical center (Division of Trauma Surgery, University Hospital of Zurich). Hence, we evaluated computed tomography scans of these patients and developed a computational simulation model with use of three-dimensional computed tomography reconstruction of the elbow. Unlike other authors who studied cadaver elbows3,6-9, we employed a virtual three-dimensional bone model to demonstrate the anatomy of the proximal aspect of the ulna and to simulate Kirschner-wire placement. One hundred and seventeen consecutive patients (seventy-one men and forty-six women) who had undergone internal fixation of the olecranon between April 2003 and November 2004 were retrospectively analyzed. The average age of the patients was 52.1 years (range, twenty-five to eighty-eight years). Of the 117 patients, forty-one underwent osteotomy of the olecranon for exposure of an intra-articular fracture of the distal aspect of the humerus and seventy-six had fixation of an olecranon fracture. The …

Anatomy of impacted lower third molars evaluated by computerized tomography: is there an indication for 3-dimensional imaging?

OBJECTIVE Surgical removal of impacted third molar is one of the most frequent procedures in oral surgery. Today 3-dimensional (3D) imaging is occasionally used. The aim of this study was to describe and estimate the frequencies of anatomic variations of lower third molars in patients with panoramic findings at high risk for inferior alveolar nerve (IAN) injury. STUDY DESIGN The investigators designed and implemented a retrospective cases series study with a study population composed of patients presenting with an impacted lower third molar with projection of the tooth over the full width of the IAN in panoramic radiograph and, therefore, 3D imaging before a planned surgical removal. Spatial relationship to the IAN, type of angulation, root configuration and maturation were primary study variables. Descriptive statistics were computed for all variables. RESULTS A total of 707 wisdom teeth in 472 patients (54% female, 46% male) were evaluated. A close relationship to the IAN was seen in 69.7%, and in 45.1% the diameter of the mandibular canal was reduced. In 52.8% the IAN was vestibular and in 37.3% lingual to the roots; there were 9.9% with an inter- or intraroot course. Most teeth had 1 or 2 roots (86.7%), but 13.3% had ≥3 roots. Mesial angulation was the main type (40.2%), followed by vertical (29%), horizontal (13.9%), distal (10.2%), and transverse (6.8%) positions. CONCLUSION Based on the range of variations in the course of the nerve and the number of roots the authors recommend 3D imaging before surgical removal of a lower third molar that shows signs of a close relationship to the IAN.

Image Fusion for Intraoperative Control of Axis in Long Bone Fracture Treatment

Background:The incidence of malalignment after long bone fracture fixation is reported to be between 0 and 37%. Modern fracture treatment strives towards closed reduction and minimally invasive fracture fixation, thus not exposing the fracture itself. Hence, the occurrence of malalignment might even be higher than previously reported and quite frequently even necessitate secondary operations. Minimally invasive techniques rely heavily on intraoperative fluoroscopy. However, fluoroscopic images have small cross-sections and consequently limit intraoperative visualization of the limb to individual segments only. Under these circumstances, correct alignment of fragments in long bone fractures is often compromised.Methods:We present a new software prototype using an absolute reference panel to concatenate two or more discontinuous fluoroscopic images into one single panoramic picture. The reference panel is placed on the operating table under the limb to be examined. Prior to digital picture fusion, the software applies non-linear distortion, picture scaling and de-rotation algorithms to the fluoroscopic images.Results:The presented software runs on a notebook and processes images generated by a commercially available mobile C-arm within seconds. The reliability of alignment in the panorama picture is found to be numerically adequate and the technique appropriate for clinical use.Conclusion:This method aims to improve the intraoperative visualization in minimally invasive osteosynthesis and therefore diminish malalignments in long bone fracture treatment.