Plasma 25-hydroxyvitamin D concentrations and bone histomorphometry were investigated in 24 grossly obese subjects. The mean plasma 25OHD concentration was significantly lower in the obese group than in age-matched, healthy controls. Subnormal values were found in four obese subjects and in a further two subjects, who were investigated at the end of the summer, plasma 25-hydroxyvitamin D levels were at the lower end of the normal winter range. Bone histology was abnormal in two patients. In one, mild osteomalacia and secondary hyperparathyroidism were present while in the other patient the appearance suggested increased bone turnover, possibly as a result of healing osteomalacia. We conclude that gross obesity is associated with an increased risk of vitamin D deficiency, probably because of reduced exposure to uv radiation. Histological evidence of metabolic bone disease may also occur. Preoperative vitamin D deficiency may contribute in some patients to the development of metabolic bone disease after intestinal bypass.

It was hypothesised that subchondral bone thickness, hardness and remodelling are influenced by exercise intensity, and by location within a joint. Dorsal carpal osteochondral injury is a major cause of lameness in horses undergoing high intensity training. This project aimed to determine the subchondral bone thickness, formation, resorption and hardness at sites with high and low incidence of pathology in 2 year-old horses undergoing 19 weeks high intensity treadmill training or low intensity exercise, and to compare these factors between exercise groups. Dorsal and palmar test sites were identified on radial, intermediate and third carpal articular surfaces after euthanasia. Adjacent osteochondral samples from each test site underwent histomorphometric analysis (for subchondral bone thickness, osteoid perimeter, osteoid seam width, eroded cavity area and eroded cement line surface length) and microhardness testing. Bone from horses undergoing high intensity training was thicker with a greater osteoid perimeter, and at individual sites had a smaller osteoid seam width and eroded cavity. Exercise-related differences were most marked at dorsal locations. Maximal differences in bone formation indices were observed at dorsal radial and medial third carpal locations. Overall subchondral bone from dorsal sites was thicker with a greater osteoid perimeter. Subchondral bone from dorsal sites was approximately 35% harder than bone from palmar sites. These results show topographical variations in subchondral bone structure, formation, resorption and material properties and a site-specific response to exercise. The maximal response to exercise was at high load sites with a clinical predisposition to injury. These findings indicate that the combined effect of exercise and local load variations within a joint may lead to maxiinal adaptive responses or overload of these responses at sites predisposed to injury. 0 3001

Both ulnas of skeletally mature roosters (Gallus domesticus) were deprived of functional load bearing by proximal and distal submetaphyseal osteotomies. Twenty-four hours later the animals were injected with 1.5 mCi of 3H-uridine and the ulna on one side was subjected to a single period of a cyclical load engendering physiological strain levels at 1 Hz for 6 min. Twenty-four hours after loading the animals were killed. Autoradiographic examination of comparable regions of cortex in sections from the bone's midshafts showed that in the loaded bones, 72 +/- 2.7% of osteocytes were labeled compared with 12 +/- 3.5% in the corresponding areas of their contralateral nonloaded pair (P less than 0.001). The number of grains per labeled osteocyte was also higher in the loaded side (6 +/- 0.5 compared with 4 +/- 0.5, P less than 0.01). There was no obvious correlation between the longitudinal strain distribution during artificial loading and the distribution of labeled osteocytes throughout the bone cross-section. However, previous long-term experiments using a similar loading preparation had consistently shown the site of most periosteal new bone formation to also not be directly related to the local strain magnitude. Perhaps it is significant that the greatest percentage of labeled cells were found in the cortex where the long-term experiments had shown most new bone formation to subsequently occur.

No abstract