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 patient's 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.

Assessment of creatinine clearance in healthy subjects over 65 years of age.

Eighteen healthy people over 65 years of age were studied to compare the 99mTC-diethylenetriamine pentaacetic acid (DTPA) clearance, the measured 24-hour creatinine clearance and the assessed creatinine clearance using the Cockcroft and Gault (C-G) formula to measure their glomerular filtration rate. Significant correlations were found between the isotopic method and the measured creatinine clearance (r = 0.71; p less than 0.001); the measured creatinine clearance and the C-G formula (r = 0.81; p less than 0.001), and the isotopic method and the C-G formula (r = 0.70; p less than 0.001). The C-G formula correlated better with both the 99mTc-DTPA clearance and the measured creatinine clearance when the female correction factor was used. This study has shown that in healthy, elderly people, the C-G formula for assessing the creatinine clearance correlated extremely well with the standard clinical tests for measuring the glomerular filtration rate. Whilst the formula has clinical value and allows rapid and accurate assessment of renal function in the elderly, the clinician must be aware that the formula relatively underestimates the true renal clearance.