Qualitative bone defect in uremic osteosclerosis

Fractal geometry and vertebral compression fractures

Cancellous bone in postmenopausal osteoporosis is characterized by widely spaced and disconnected trabeculae. These architectural changes may disproportionately increase bone fragility compared with the decrease in bone mass alone. To determine whether there is an independent architectural contribution to fracture risk, we applied fractal geometry to the cancellous bone in osteoporosis. Fractal objects have recurrent, branching patterns that are quantified by a fractal dimension D, that describes how the object fills space. Photomicrographs of transiliac bone biopsy specimens were digitized, and D was calculated from the negative of the straight portion of the slope of the log of the number of pixels containing boundary points versus the log of the pixel size over a range of pixel sizes. The results were compared with the cancellous bone histomorphometry in 31 individuals, aged 19-80 years, who were healthy before sudden death. D was inversely related to age (r = -0.72, p < 0.0001) and trabecular spacing (r = -0.87; p < 0.0001) and directly related to bone area (r = 0.86, p < 0.0001) and trabecular number (r = 0.83, p < 0.0001). We then examined 12 healthy volunteers and 12 patients with vertebral compression fractures as a result of osteoporosis who were matched for age and cancellous bone area. The patients with fractures had a 7.9% lower mean value for D (1.224 +/- 0.085 SD versus 1.329 +/- 0.125, p < 0.026). Other markers of the cancellous architecture, such as trabecular width, separation, and number, were not different between the matched groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypercalcemic hyperparathyroidism and hypophosphatemic osteomalacia complicating neurofibromatosis

Neurofibromatosis is sometimes complicated by impaired renal tubular reabsorption of phosphate, hypophosphatemia, and osteomalacia. Hyperparathyroidism has also been reported in patients with neurofibromatosis. When hypercalcemia and elevated levels of parathyroid hormone are found in osteomalacia, however, it may be difficult to determine if the hyperparathyroidism was primary or tertiary. We describe a patient with neurofibromatosis, hypercalcemic hyperparathyroidism, hypophosphatemic osteomalacia, vitamin D deficiency, and clear-cell hyperplasia of all four parathyroid glands. Serial biomechanical, bone biopsy, and densitometric studies confirmed that treatment with ergocalciferol, calcium, and phosphate supplements significantly improved the osteomalacia but caused increased parathyroid overactivity. After subtotal parathyroidectomy, the parathyroid hormone concentration became normal and the bone mineral content increased at the spine and hip, but inappropriate phosphaturia persisted. The findings indicate that hyperparathyroidism, osteomalacia, and vitamin D deficiency adversely affect each other.

In vitro initial fixation of porous-coated acetabular total hip components. A biomechanical comparative study

Two-phase in vitro testing was performed to determine the initial mechanical stability of uncemented but fixed porous coated acetabular components. Six each of three-screw fixation, two-peg fixation, and three-spike fixation porous acetabular components were implanted into fresh and embalmed human cadaver acetabula. Measurement of prosthesis-bone displacement at a load of 100 kg did not show a significant difference among the three methods of fixation. However, torque testing showed that three-screw fixation failed at significantly higher loads (46 N-m) than two-peg fixation (32 N-m) or three-spike fixation (32 N-m).

Diminished rates of bone formation in normal black adults

Blacks have a greater bone mass and a lower incidence of osteoporosis and hip fractures than whites. We performed biopsies of the iliac crest in 12 blacks (6 men and 6 women) and 13 whites (8 men and 5 women) who were matched for age (range, 19 to 46 years) and weight, to determine whether histomorphometric differences between blacks and whites could be identified. The static measurements of cortical and cancellous bone architecture were not significantly different in the two groups. In contrast, the dynamic measurements, determined with tetracycline markers, showed that the mean rate of bone formation in the blacks was only 35 percent of that in the whites (P less than 0.001). We conclude that the rate of bone turnover is lower in blacks than in whites, since bone resorption and bone formation are closely coupled in the steady state. If reconstitution of previously resorbed cavities at remodeling sites is incomplete in osteoporosis, a reduction in the rate of skeletal remodeling could provide a means for maintaining and preserving bone mass in blacks.

Bone histomorphometry in vitamin D-deficient rats infused with calcium and phosphorus

Defective mineralization of bone and cartilage is the classical histological finding in vitamin D deficiency. Whether this represents a direct effect on mineral deposition or is a consequence of the decreased calcium and phosphorus levels that result from impaired intestinal absorption is not clear. A method has been developed in which vitamin D-deficient rats have plasma calcium and phosphorus levels maintained in the normal range by continuous infusion. Histomorphometric analysis of undecalcified tibiae from these animals was compared with that of rats given vitamin D. Epiphyseal growth plate thickness, trabecular osteoid volume, and mean osteoid seam width were not increased. Moreover, the administration of two time-spaced courses of tetracycline revealed that the mineralization rate and the time interval between apposition and subsequent mineralization of osteoid (mineralization lag time) were identical to those in rats treated with vitamin D. Trabecular bone volume was increased (osteosclerosis) in the vitamin D-deficient rats. In vitamin D-deficient controls without infusions, the osteosclerosis was mostly osteoid, whereas the excess bone was well mineralized in the vitamin D-deficient rats infused with calcium and phosphorus. Osteosclerosis in vitamin D-deficient animals may result from both decreased bone resorption and increased osteoid apposition. This study provides firm evidence that vitamin D is not essential for mineralization in young growing rats. Decreased availability of calcium and phosphorus thus may be the sole basis of the mineralization defect seen in vitamin D deficiency.

Adult osteosclerosis

Quantitative bone histology was carried out in five osteosclerotic adults. The bone was extremely hard in all patients, and open biopsy was usually required. One patient, aged 18 years, presented with hypoplastic anemia, and the most probable explanation for the osteosclerosis is a marrow stem cell defect leading to defective osteoclasts. Another had the dominant form of osteopetrosis. Her bone contained cartilage remnants, and there were many large, morphologically abnormal osteoclasts, which lacked normal cytoplasmic acid phosphatase activity. The third patient had chronic renal failure and osteomalacia; here the increased bone mass might have resulted from an inability of normal osteoclasts to resorb bone, due to the surface coating of osteoid, though an earlier increase of bone formation cannot be excluded. The fourth patient, who suffered from systemic mastocytosis, had high turnover bone, with greatly increased bone formation. The fifth patient, with fluorosis of bone, also had increased bone formation and resorption, the process being much more pronounced in the head of her pathologically fractured femur than it was in the iliac crest. In this patient some osteoclasts had reduced acid phosphatase activity and long cytoplasmic extensions, both changes similar to those observed in diphosphonate-treated animals. Very diverse processes can result in the increased cancellous bone mass producing the radiographic appearance of diffuse osteosclerosis.