A biography of the point contact fixator (PC-Fix).

Starting in the mid-eighties, the AO (from the German "Arbeitsgemeinschaft für Osteosynthesefragen") Research Institute (ARI), Davos, Switzerland together with the commercial partners of the AO Foundation embarked on a decade-long project to design, develop, test in experimental animals and human clinical trials as well as bring to clinical use a new system for surgical osteosynthesis. The new plating system, what became known as the Point Contact Fixator (PC-Fix), addressed the shortcomings of the conventional plating by Dynamic Compression Plate (DCP) discovered either by careful examination of the clinical complications or by chance observation and informed inquiry in experimental animals. The focus was on avoiding iatrogenic damage to bone vascularisation caused by the implant design and mechanical function and, thus, aiding efforts of surgeons to preserve vital bone tissue needed for healing. Infections have been and will remain a great concern in all surgery. Preservation of blood perfusion of traumatised bone is of paramount importance to reduce the risk of infection, especially in view of the emergence and the accelerated spread of bacterial resistance to antibiotics. Prof. Stephan Perren led this project in all its stages with his unique insight and wisdom. Unfortunately, due to the complex interplay of factors guiding the interests of the AO Foundation and its commercial partners, the findings of the PC-Fix project became watered down with implant systems that followed the DCP. The message of "keep the perfusion" faded into "lock the screws". The potential benefits of PC-Fix have been lost for millions of trauma patients.

Regional myocardial stress distribution from magnetic resonance image-based mathematical models.

The instantaneous regional stress distribution within the myocardium, which cannot be directly measured, has been estimated using improved numerical methods and nonaxisymmetric biventricular geometry. To do this, we have employed computer-aided solid mathematical modeling to generate a three-dimensional representation for an ex vivo canine biventricular unit using magnetic resonance imaging. A two-dimensional transverse section was isolated from the solid mathematical model for regional stress analysis using p-version finite element analysis. Loading conditions and material property descriptions were taken from published reports. Analyses showed the maximum principal stresses to range from -1.76 X 10(5) to 8.52 X 10(5) dynes/cm2 during systolic loading, and from -3.85 X 10(4) to 1.13 X 10(5) dynes/cm2 during diastolic loading. This study demonstrates that magnetic resonance image-based solid mathematical biventricular models are suitable for regional stress analysis using p-version finite element analysis. p-Version finite element analysis using magnetic resonance image-based cardiac representations facilitates in vivo stress-strain analyses and may allow the clinical estimation of regional myocardial stress.

Applications of computer graphics in craniofacial surgery.

Three-dimensional surface images can be reconstructed from CT scans. These are particularly useful in the study and management of patients with congenital and acquired craniofacial deformities. The principles of 3-D reformation, the production of the surface images, and recent advances in modification of these images for specific clinical needs are presented.

Three-dimensional wrist imaging: evaluation of functional and pathologic anatomy by computer.

The wrist has been studied morphologically and functionally using advanced technology. The osseous morphology of the wrist was investigated by computed tomography and surface reconstruction software. The functional behavior of the wrist in motion was studied using electromagnetic tracker technology. Three-dimensional imaging from CT scans is emerging as a research tool for the study of gross surface morphology, especially for osseous structures. One of the most demanding applications of this technology lies in the human wrist, because of its small size and inherent complexity. We have demonstrated some of the potential of computer graphics and three-dimensional surface reconstructions in the wrist for patients with osseous abnormalities. Acquisition of six-degree-of-freedom kinematic data to describe carpal motion has been made possible by new electromagnetic tracker technology. Analysis of these data in human wrist experiments revealed that the instantaneous center of rotation was not fixed in the head of the capitate, as was previously thought.

Internal fixation of malar fractures: an experimental biophysical study.

Open reduction and internal fixation of displaced zygoma fractures are necessary to avoid immediate and delayed facial disfigurement. Interosseous wires, Kirschner wires, and more recently, rigid metallic miniplates have been recommended for fixation of these and other midfacial fractures. However, the precise physical stability of the zygoma with respect to wire versus miniplate fixation methods and with respect to the number and location of miniplates applied is not known. Noncomminuted zygoma fractures were simulated by saw osteotomy in eight fresh human cadaver heads (16 zygoma "fractures"). Each zygoma was sequentially fixated with three miniplates, two miniplates, one miniplate, and three interosseous wires across the orbital rim and arch "fractures". Static and oscillating loads simulating maximal physiologic masticatory stresses were applied to the fixated zygoma along the lines of action of the masseter muscle by means of a tensometer. The stability and adequacy of each pattern of fixation were recorded. Double-miniplate fixation across the orbital rim of simulated noncomminuted zygoma "fractures" is sufficient to withstand static and oscillating loading similar to physiologic masticatory forces. Neither single-miniplate fixation nor triple-wire fixation are sufficient to stabilize the zygoma against similar forces.

Use of general purpose mechanical computer assisted engineering software in orthopaedic surgical planning: advantages and limitations.

Two surgical plans were developed for an appropriately complex reconstructive orthopaedic surgery case. One plan was developed with customary methods using two-dimensional (2D) radiographs. The second plan was developed with general purpose mechanical computer assisted engineering (MCAE) software using x-ray computed tomography (CT) data. The limitations of each method are identified. To create a surgical plan using three-dimensional (3D) medical datasets and MCAE software, five necessary steps were identified: (a) data reduction; (b) contour extraction; (c) 3D model creation; (d) extraction of mass properties; (e) model idealization. The principal limitation of general purpose MCAE software is the lack of pre-processing modules with which to address the unique requirements of medical image datasets.

Measurement of acetabular component migration using two-dimensional radiography.

The relationships between apparent acetabular component migration, choice of anatomic landmarks, and changes in rotation of the pelvis were determined by examining radiographs of a pelvic model in multiple projections. The minimum apparent migration associated with transverse and longitudinal rotation of 5 degrees from neutral was 2 mm. The least apparent migration was noted when the teardrop was used as the principal anatomic landmark. Determination of component migration in clinical studies from serial radiographs involves a minimum projection and magnification error of 2 mm.

Automated solid models from serial section images.

A new method for creating unambiguous and complete boundary representation solid models with a hybrid polygonal/nonuniform rational B spline representation was developed and tested using computed tomography scans of the wrist. Polygon surface approximation was applied to a sequence of parallel planar outlines of individual bone elements in the wrist. An automated technique for the transformation of edge contours into solid models was implemented. This was performed using a custom batch file command sequence generator coupled to a commercially available mechanical computer-aided design and engineering software system known as I-DEAS (Structural Dynamics Research Corporation, Milford, OH). This transformation software allows the use of biomedical scan slice data with a solid modeler.

Mathematical three-dimensional solid modeling of biventricular geometry.

The characterization of regional myocardial stress distribution has been limited by the use of idealized mathematical representations of biventricular geometry. State-of-the-art computer-aided design and engineering (CAD/CAE) techniques can be used to create complete, unambiguous mathematical representations (solid models) of complex object geometry that are suitable for a variety of applications, including stress-strain analyses. We have used advanced CAD/CAE software to create a 3-D solid model of the biventricular unit using planar geometric data extracted from an ex vivo canine heart. Volumetric analysis revealed global volume errors of 4.7%, -1.3%, -1.6%, and -1.1% for the left ventricular cavity, right ventricular cavity, myocardial wall, and total enclosed volumes, respectively. Model errors for 34 in-plane area and circumference determinations (mean +/- SD) were 5.3 +/- 6.7% and 3.8 +/- 2.7%. Error analysis suggested that model volume errors may be due to operator variability. These results demonstrate that solid modeling of the ex vivo biventricular unit yields an accurate mathematical representation of myocardial geometry which is suitable for meshing and subsequent finite element analysis. The use of CAD/CAE solid modeling in the representation of biventricular geometry may thereby facilitate the characterization of regional myocardial stress distribution.

Quantitative 3D maxillary arch evaluation of two different infant managements for unilateral cleft lip and palate.

OBJECTIVE: A two-institution retrospective study was undertaken to determine whether two different prepalatoplasty protocols quantitatively affect maxillary arch morphology in infants with complete unilateral cleft lip and palate (UCLP). DESIGN: Serial maxillary dental casts, obtained at regular intervals through the first 18 months of life from preintervention until palatoplasty were evaluated quantitatively using computer-assisted three-dimensional digitization and analysis for three populations: institution 1 (protocol 1), institution 2 (protocol 2), and unaffected individuals (neither cleft nor treatment). Sequential UCLP patients from institution 1 were matched for age and initial alveolar cleft width, sex and cleft side having been demonstrated to be nonsignificant, with UCLP patients from institution 2 and to unaffected individuals for age for the analysis. SETTING: Both treatment institutions are well-established regional interdisciplinary cleft centers. Institution 1 is located in a tertiary, academic children's hospital in a metropolis within a primarily agrarian region of the Midwest; institution 2 is a freestanding private clinic located in a small city within a primarily agrarian region of an eastern state; the unaffected population is a historic archive acquired in the 1930s. Data acquisition (model digitization) and computer processing were performed at institution 1. PATIENTS: Eighty-five casts of 28 infants from institution 1, 106 casts of 31 infants from institution 2, and 68 casts of 29 unaffected infants were analyzed. All infants had alginate impressions taken prior to intervention and at several additional 6-month intervals after that, consistent with each institution's treatment protocol. INTERVENTIONS: At institution 1, patients with UCLP underwent lip adhesion and placement of a passive alveolar molding plate at 7 weeks of age, definitive cheiloplasty at 7 months of age, and one-stage palatoplasty at 14 months of age. At institution 2, patients with UCLP underwent definitive cheiloplasty at 3 months of age, had no maxillary orthopedics, and had vomer flap hard palate repair at 12 months of age and soft palate repair at 18 months of age. MAIN OUTCOME MEASURES: The outcome measures included directly digitized (cleft segment and hemialveolar ridge lengths) and derived (alveolar base width, alveolar cleft gap, maxillary frenum-alveolar base perpendicular angle, and rates of change over time of digitized cleft segment and hemialveolar ridge lengths) features. The data were assessed by comparing simple linear regression lines and an unpaired, two-tailed t test. RESULTS: Prior to initiating therapy, there were no statistically significant differences between the two populations with clefts. However, both populations with clefts differed significantly from unaffected individuals (p < .001), with increased maxillary base widths and larger perpendicular/frenum angles. At the time of palatoplasty, the two populations with clefts had statistically significant differences between them in the maxillary base width (p < .01) and the cleft gap distance (p < .05). The base width of institution 1 did not differ significantly from that of widths of unaffected children, and that of institution 2 was significantly less, although the latter had already received first-stage palate repair. Alveolar segment growth rates were similar for the greater and lesser segments, respectively, and the left side hemialveolus of both groups. The growth rate for the noncleft side hemialveolus of institution 2 exceeded (p < .05) that of both institution 1 and unaffected patients. CONCLUSION: Two different regimens for the initial management of UCLP can significantly affect maxillary alveolar arch growth with respect to the treatment used and in comparison with unaffected controls.