Friedrich R. Carls

Simulating facial surgery using finite element models

This paper describes a prototype system for surgical planning and prediction of human facial shape after craniofacial and maxillofacial surgery for patients with facial deformities. For this purpose it combines, unifies, and extends various methods from geometric modeling, finite element analysis, and image processing to render highly realistic 3D images of the post surgical situation. The basic concept of the system is to join advanced geometric modeling and animation systems such as Alias with a special purpose finite element model of the human face developed under AVS. In contrast to existing facial models we acquire facial surface and soft tissue data both from photogrammetric and CT scans of the individual. After initial data preprocessing, reconstruction, and registration, a finite element model of the facial surface and soft tissue is provided which is based on triangular finite elements. Stiffness parameters of the soft tissue are computed using segmentations of the underlying CT data. All interactive procedures such as bone and soft tissue repositioning are performed under the guidance of the modeling system which feeds the processed geometry into the FEM solver. The resulting shape is generated from minimizing the global energy of the surface under the presence of external forces. Photorealistic pictures are obtained from rendering the facial surface with the advanced animation system on which this prototype is built. Although we do not claim any of the presented algorithms themselves to be new, the synthesis of several methods offers a new facial model quality. Our concept is a significant extension to existing ones and, due to its versatility, can be employed in different applications such as facial animation, facial reconstruction, or the simulation of aging. We illustrate features of our system with some examples from the Visible Human Data Set.TM CR Descriptors: I.3.5 [Computational Geometry and Object Modeling]: Physically Based Modeling; I.3.7 [Three-Dimensional Graphics and Realism]; I.4.6 [Segmentation]: Edge and Feature Detection Pixel Classification; I.6.3 [Applications]; Additional

Seven years clinical experience with mandibular distraction in children

Mandibular distraction was performed on 14 children, between September 1991 and December 1997. Their average age was 6.9 years, ranging from 1.5 to 13.5 years. All patients had severe hypoplastic mandibles with retromandibulism. Seven of the children (50%) had respiratory distress due to obstruction of the upper airway before distraction. This resolved in every case. Five patients underwent unilateral and nine bilateral distraction. A total of 23 distractors were used, 15 were applied extraorally and 8 endorally. The average latency time after operation was 2.8 days, but for the past 2 years, distraction was started beginning with the operation. The distraction was increased twice daily for an average of 5.5 weeks, by 0.4 or 0.5 mm each time, depending on the distractor. Computed tomography and ultrasound were used to follow the ossification process in the distraction gap and to measure the lengthening achieved. Subsequent retention time averaged 2.4 weeks. The mandibles were elongated by up to 18 mm (average 9.3 mm) and the respiratory distress symptoms resolved in all patients. Several minor complications which are reported occurred. Six patients were followed up for periods between 3 and 7 years. During this time further growth of the distracted mandibles was recorded.

A Bernstein-Bézier Based Approach to Soft Tissue Simulation

This paper discusses a Finite Element approach for volumetric soft tissue modeling in the context of facial surgery simulation. We elaborate on the underlying physics and address some computational aspects of the finite element discretization.

Complications following arthroscopy of the temporomandibular joint: analysis covering a 10-year period (451 arthroscopies)

451 arthroscopies of the temporomandibular joint (TMJ) have been performed on 373 patients during 10 years of clinical experience. The complication rate was low (1.77%). Most complications were transient, consisting mainly of temporary deficits of the 5th and 7th cranial nerves. No patient required arthrotomy because of complications, but one patient had to undergo angiography and embolization of a traumatic aneurysm of the superficial temporal artery secondary to arthroscopy.

Mandibular osteomyelitis: evaluation and staging in 18 patients, using magnetic resonance imaging, computed tomography and conventional radiographs.

Over a period of 3 years, 18 patients with mandibular osteomyelitis were prospectively investigated by conventional radiograph, computed tomography (CT) and in 6 cases by magnetic resonance imaging (MRI). The diagnosis was based on histology in 17 patients operated upon.

Loose bodies in the temporomandibular joint: The advantages of arthroscopy

Loose bodies are a rare cause of temporomandibular joint symptoms. Their main source is synovial chondromatosis. We report on clinical findings, diagnostic methods, treatment choices and outcome following the removal of loose bodies in 10 patients. Seven patients were evaluated and treated by means of arthroscopy, while in three patients open arthrotomy was performed. In five patients, no diagnostic imaging technique had demonstrated the presence of loose bodies prior to arthroscopy. In six patients, histology revealed synovial chondromatosis. In four patients, osteochondral fragments alone were found. Until now, the recommended treatment of choice for the removal of all loose bodies and of affected synovial tissue required open arthrotomy. We conclude that the advantages of arthroscopy consist in locating loose bodies that are not detectable radiologically and in reducing operative trauma.

Value of three-dimensional computed tomography in craniomaxillofacial surgery.

Three-dimensional (3-D) computed tomographic (CT) scans of 72 adult patients were evaluated by two observers in a blinded fashion by comparing the 3-D images with the two-dimensional (axial and coronal) CT scans. With 3-D CT, the observers found improved visualization of facial anatomy in certain patients (i.e., asymmetries of the whole face and skull, large defects of the midface and skull vault, and fractures with major dislocation). In these defects, the information can be assimilated more rapidly. The documentation of effects of cranial surgery on craniofacial growth and resorption after reconstruction with autologous material can also be evaluated more accurately. Because higher levels of radiation are used, 3-D CT protocols are less indicated in patients with minor dislocation of fractures, tumors, and inflammations. Three-dimensional CT images in these patients are of little help and can mislead the surgeon. Further improvements in hardware and software will allow more accurate surgical planning by performing interactive surgery or by producing precise models.

A new method for assessing the temporomandibular joint quantitatively by dental scan.

The objective of this study was to assess the applicability of a multiplanar reformatting program (dental scan) for delineation and quantitative evaluation of the temporomandibular joint (TMJ) in the sagittal and coronal planes using the data of axial computed tomography. The resulting images were compared with standardized linear tomograms and direct sagittal and frontal computed tomography. Standardized linear tomograms and computed tomography of the TMJ in axial, frontal and sagittal planes were obtained in 11 patients. The axial computed tomography slices were then reconstructed in oblique frontal and sagittal planes according to the horizontal condylar angle of the TMJ by dental scan software. For each patient and each of the three imaging methods, 14 measurements were undertaken and 24 qualitative characterizations were assessed. Axial computed tomograms in combination with their corresponding coronal and sagittal reconstructions were more accurate than conventional tomograms. Direct coronal and sagittal scans gave the most detailed images, but required additional radiation dose, time and cost. Reconstructions of axial computed tomography slices of the TMJ using the dental scan software show several advantages over linear tomograms. They allow qualitative as well as quantitative evaluation of the TMJ.

Development of the frontal sinus following bilateral fronto-orbital osteotomies

The presence of frontal sinuses following bilateral fronto-orbital advancement is discussed controversially in the literature. In a retrospective study, 33 patients (18 male and 15 female) were operated on between 1982 and 1993, with at least one year postoperative follow-up and with a minimum age of 6 years at the end of the follow-up period following bilateral fronto-orbital remodelling, were included. The average age at which the procedure was performed was 29 months with a minimum of 3 months and a maximum of 7.8 years. The study presented shows a pneumatization of the frontal sinus in 72.7% of 33 patients following bilateral fronto-orbital advancement. The first radiographic signs of sinus development were detected between the ages of 4 and 11, average 8.3 years. There were no statistically proven correlations between frontal sinus pneumatization and age at operation or the amount of advancement or sex of the patients. Surgical enlargement of the cranium by frontal advancement with adequate stabilization results in an enlargement of the neurocranium, thereby decreasing pressure on the inner frontal cortex and allowing frontal sinus pneumatization to proceed normally. Hence, the development of a frontal sinus may be a reflection of the effectiveness of the surgical therapy.

Development of the Frontal Sinus Following Bilateral Pronto-orbital Osteotomies

The presence of frontal sinuses following bilateral fronto-orbital advancement is discussed controversially in the literature. In a retrospective study, 33 patients (18 male and 15 female) were operated on between 1982 and 1993, with at least one year postoperative follow-up and with a minimum age of 6 years at the end of the follow-up period following bilateral fronto-orbital remodelling, were included. The average age at which the procedure was performed was 29 months with a minimum of 3 months and a maximum of 7.8 years. The study presented shows a pneumatization of the frontal sinus in 72.7% of 33 patients following bilateral fronto-orbital advancement. The first radiographic signs of sinus development were detected between the ages of 4 and 11, average 8.3 years. There were no statistically proven correlations between frontal sinus pneumatization and age at operation or the amount of advancement or sex of the patients. Surgical enlargement of the cranium by frontal advancement with adequate stabilization results in an enlargement of the neurocranium, thereby decreasing pressure on the inner frontal cortex and allowing frontal sinus pneumatization to proceed normally. Hence, the development of a frontal sinus may be a reflection of the effectiveness of the surgical therapy.