Bone Abstracts

A first twin born at 28 weeks gestation weighing 630 g underwent an end-to-end anastamosis for colonic stricture on day 92 of life. He collapsed with severe Escherichia coli sepsis post-operatively and became anuric. Veno–veno haemofiltration (CVVH) was instituted as a life-preserving measure, continuing for 3 days.

On day 119, osteopaenia and rachitic changes were noted on a chest X-ray. Review of his prior biochemistry showed a precipitous fall in serum phosphate, as well as alkaline phosphatase, followed by a rapid rise in serum alkaline phosphatase activity dating to the period of haemofiltration. The filtrate solution contained no phosphate; phosphate supplementation (1 mmol/kg per day) had been discontinued prior to his end-to-end anastamosis and not recommenced.

His skeletal survey showed multiple fractures including both femurs, both lower legs, the small bones of the feet, left distal ulna and left distal humerus and vertebral crush fractures. The fractures had not been suspected clinically. X-rays prior to his operation showed thin cortices but no rickets or fractures.

Fractures have been previously reported in the context of metabolic bone disease of prematurity (preterm MBD) in association with prolonged intravenous feeding, physiotherapy, diuretic and steroid use and with conjugated hyperbilirubinaemia. The profound loss of phosphate during hemofiltration likely resulted in severe bone disease with substantial increase in bone fragility. Loss of alkaline phosphatase activity may have allowed a transient increase in mineralisation inhibitors, contributing to the problem. To our knowledge vertebral crush fractures have not been reported previously in preterm MBD. Care should be taken to ensure adequate provision of mineral substrate in infants undergoing even brief periods of CVVH.