Robin Richards

A prospective study of computer-aided design and manufacture of titanium plate for cranioplasty and its clinical outcome

The use of computerized three dimensional imaging and automated milling of models to produce accurate titanium plates for the reconstruction of craniofacial defects is described. A total of 148 patients have had extensive calvarial defects repaired using this (computer aided design and manufacture) technique developed in our unit. Of these, 141 were repaired secondarily (delayed cranioplasty), whilst seven were repaired immediately following craniectomy (single stage cranioplasty). All cases were assessed for accuracy of fit, restoration of natural skull contour and aesthetics. Seventy-two patients were reviewed after 1 year to determine the effect on adverse preoperative symptoms. Of the plates 97% had an excellent or good intraoperative fit. The modal insertion time was only 15 minutes. Postoperatively 98% resulted in the restoration of natural skull shape and symmetry. After 1 year, 82% of patients had complete resolution or diminution in severity of the adverse symptoms. A staphylococcus infection necessitated the temporary removal of one plate.

Three-dimensional CT analysis to determine acetabular retroversion and the implications for the management of femoro-acetabular impingement

This study examined the relationship between the cross-over sign and the true three-dimensional anatomical version of the acetabulum. We also investigated whether in true retroversion there is excessive femoral head cover anteriorly. Radiographs of 64 hips in patients being investigated for symptoms of femoro-acetabular impingement were analysed and the presence of a cross-over sign was documented. CT scans of the same hips were analysed to determine anatomical version and femoral head cover in relation to the anterior pelvic plane after correcting for pelvic tilt. The sensitivity and specificity of the cross-over sign were 92% and 55%, respectively for identifying true acetabular retroversion. There was no significant difference in total cover between normal and retroverted cases. Anterior and posterior cover were, however, significantly different (p < 0.001 and 0.002). The cross-over sign was found to be sensitive but not specific. The results for femoral head cover suggest that retroversion is characterised by posterior deficiency but increased cover anteriorly.

Analysis of cover of the femoral head in normal and dysplastic hips: NEW CT-BASED TECHNIQUE

We present a new CT-based method which measures cover of the femoral head in both normal and dysplastic hips and allows assessment of acetabular inclination and anteversion. A clear topographical image of the head with its covered area is generated. We studied 36 normal and 39 dysplastic hips. In the normal hips the mean cover was 73% (66% to 81%), whereas in the dysplastic group it was 51% (38% to 64%). The significant advantage of this technique is that it allows the measurements to be standardised with reference to a specific anatomical plane. When this is applied to assessing cover in surgery for dysplasia of the hip it gives a clearer understanding of where the corrected hip stands in relation to normal and allows accurate assessment of inclination and anteversion.

The use of computer-generated three-dimensional models in orbital reconstruction

In this paper we describe the application of three-dimensional (3D) imaging and computer-generated models in the management of orbital deformity. The technique was found to be particularly useful in posttraumatic deformity and fibrous dysplasia involving the orbit. Further application was found in cases of radiation hypoplasia, high facial cleft, and facial atrophy. Funding restrictions necessitate appropriate selection of cases when using new and expensive 3D imaging rather than traditional and less expensive methods. To remain within a realistic budget only those patients who will clearly benefit from the third dimension compared with traditional methods of assessment and management should be selected. These include patients requiring precise reduction or secondary reconstruction in which there is a matched normal anatomical component for comparison. This application is also only beneficial where the planned reconstruction is dimensionally stable.

Validation of computer-assisted manufacture of titanium plates for cranioplasty

We have constructed 300 titanium cranioplasty plates, over 150 cases using a computerised technique, the remainder by external impression. The clinical follow-up of these cases over 8 years has shown consistently good results that justify our simple low-cost method of manufacturing these plates. Both techniques require the provision of a model on which to construct the plate. In the traditional technique, an approximate model is derived from the resected bone or a direct impression of the defect over the patients scalp. Using the computerised technique, a more accurate model of the defect and the surrounding bone is milled in polyurethane foam from cross-sectional computerised tomographic (CT) scans. Sheet titanium is pressed to shape from a design outlined on a counterdie. The subsequent stages of the plate construction are then the same for both methods. This study describes the stages of the model manufacture, the validation of its accuracy and the plate construction that follows. Use of the computerised method has resulted in a reduction of errors, enabling the manufacture of a smaller plate than was possible previously. It has also enabled design changes through the achievement of greater accuracy in fit.

The influence of pelvic tilt on acetabular orientation and cover: a three-dimensional computerised tomography analysis.

The orientation of the pelvis influences that of the acetabulum. In particular, pelvic tilt in the sagittal plane may lead to inaccurate interpretation of plain pelvic radiographs. We therefore quantified the relationship between this pelvic tilt and acetabular orientation in native hips, and determined whether pelvic tilt affects femoral head cover. We analysed computed tomography scans of 93 hips (36 normal, 31 dysplastic, 26 with acetabular retroversion) and measured acetabular anteversion, inclination, and femoral head cover at pelvic tilt angles ranging from −20° to 20° in relation to the anterior pelvic plane using 5° increments. Pelvic tilt changed acetabular version with a decrease in anteversion ranging from 2.5° to 5° for every 5° of forward tilt. The effect on inclination was less marked and varied. In normal and dysplastic hips pelvic tilt increased apparent femoral head cover. A greater understanding of the influence of pelvic tilt may allow improvements in the radiological diagnosis and surgical treatment of acetabular abnormalities, particularly in relation to acetabular reorientation procedures and femoroacetabular impingement.

Describing the shapes of faces using surface primitives

Abstract Humans are poor at recognizing faces from images that convey the spatial layout of major features but that omit information (e.g. simple line drawings) or invert information (photographic negatives) about the image intensity. The role played by the image intensity may be to convey useful information about surface pigmentation and/or 3D shape. To investigate the role played by the latter, in this paper we describe the development of a method for describing the 3D surface shape of individual faces explicitly, and consider some initial results which suggest that this method does capture some psychologically relevant dimensions of facial variation. Implications for machine recognition and other practical computer applications are discussed.

Laser scanning of the ear identifying the shape and position in subjects with normal facial symmetry.

The objective of the present study was to discover if dimensional measurements of the ear could be determined with a laser scanning technique and whether or not the location of landmarks of the ear could be reliably measured with respect to those on the midline of the face. Computer-generated images were created from laser scans of 20 subjects. Dimensional measurements were made between landmarks on the ear and face. Differences between repeated dimensional measurements of the ear were very small, as were those measurements made between landmarks on the ear to the midline of the face. Differences between dimensions of the left and right ears were observed, but were of a small magnitude. The results suggest that the dimensions of the ear and its position with respect to landmarks in the midline of the face can be reliably measured on normal subjects and that laser scanning is a useful technique for planning and monitoring facial reconstruction of the ear.

Non-Axisymmetrical (Life-Like) Abdominal Aortic Aneurysm Models: A Do-It-Yourself Approach

Purpose: To construct life-like non-axisymmetrical abdominal aortic aneurysm models from latex. Technique: A computed tomographic 3-dimensional reconstruction of an actual abdominal aortic aneurysm was cast in plastic to provide a core for a “chemical metal” mould. The mould was then coated with nonadhesive prevulcanized dipping latex and cured to provide an idealized hollow reconstruction of the aneurysm. Conclusions: Chemical metal can be manipulated quite easily to make a mould of any required size or surface character, which then allows the manufacture of a well-matched latex model for biophysical studies of non-axisymmetrical abdominal aortic aneurysms.

Method for the analysis of the 3-D shape of the face and changes in the shape brought about by facial surgery

A method based on differential geometry is presented for quantitatively measuring facial (or body) surfaces and the amount of change produced in them by facial surgery. Facial shape is described mathematically in terms of 8 fundamental surface types. Changes produced in the shape of the face are described in terms of changes in these constituent surfaces. The method is illustrated using examples of faces changed by reconstructive surgery and its relationship to clinical observation explained.