A relationship between the composition of the urine and that of urinary tract calculi in spinal patients.

Chemical analysis was carried out on 42 urinary phosphatic calculi obtained from 14 spinal cord patients (two to seven stones per patient) and on small samples taken from different sites in a further 17 large phosphatic calculi. In 'early' stones (removed up to 30 months after onset of the cord lesion) the ratio of calcium to magnesium was significantly higher than in 'late' stones. Samples taken from sites nearer to the centres of calculi contained more calcium and less magnesium than did those from more peripheral sites. This change in the composition of urinary calculi with time corresponds with the known alterations in urinary calcium and magnesium following spinal cord injury.