EFFECTS OF VERTICAL-BANDED GASTROPLASTY ON BONE AND MINERAL METABOLISM IN OBESE PATIENTS

The surgical treatment of obesity can have adverse effects on bone, bu t there are few published data on the effects of vertical-banded gastr oplasty. Serial measurements of bone mineral density at the lumbar spi ne and three upper femoral sites, using dual-energy X-ray absorptiomet ry, and also of biochemical indices of bone and mineral metabolism at intervals up to 2 years after operation were performed in 18 patients with morbid obesity who had vertical-banded gastroplasty. Bone mineral density measurements were also made in age- and sex-matched non-obese controls. Bone density before operation was significantly greater in the obese than in the controls (P <0.02 at all sites). The obese patie nts lost weight rapidly after vertical-banded gastroplasty (mean weigh t loss 29 kg at 1 year, P <0.001). This was accompanied by a measurabl e loss of bone density from the trochanter and Ward's triangle sites i n the upper femur (P <0.05), but not from the lumbar spine. Bone densi ty values remained stable over 14 months in the controls. Hydroxyproli ne excretion increased significantly (P <0.005), indicating an increas e in bone resorption. Alkaline phosphatase levels decreased significan tly (P <0.001), but this probably represents the reversal of hepatic s teatosis. There was no evidence of hyperparathyroidism or vitamin D de ficiency. In conclusion, vertical-banded gastroplasty causes modest bo ne density loss from femoral sites, but not the lumbar spine. The diff iculties of assessing bone density changes in the obese are discussed.