Bone remodeling in predialysis chronic renal failure: how does the choice of index for mineralizing surface influence the interpretation?

Missing observations in bone histomorphometry on osteoporosis: implications and suggestions for an approach

Crucial bone histomorphometric indices, i.e., turnover-related indices, are based on tetracycline double labeling. However, these indices are particularly exposed to loss of information because of missing readings on double labels. If the failure to make the observation is related to its magnitude, then selection bias may invalidate the conclusions. Therefore, ignoring missing double labels may lead to a selection of high-turnover patients. The aim of this study was to analyze the dimension and the impact of excluding iliac crest bone biopsies with missing readings in women with spinal crush fracture osteoporosis (n = 158, median 68 years, range 49-80 years). Furthermore, two different lower limits of the mineral apposition rate (MAR) were examined to explore their usefulness as a biological minimum that can be used for cases with missing readings, i.e., recoding of missing values. The average MAR (calculated as the mean of all interlabel widths measured in each individual) shows a lower limit of 0.3 microm/day, suggesting an apparent minimum for the interlabel width (Ir.L.Wi) of 3-4 microm. Identifying the smallest interlabel width measured in each individual and calculating the minimal MAR shows that 77% of the minimal MAR values are below 0.3 microm/day and reach a minimum of 0.1 microm/day, corresponding to an interlabel width of about 1 microm. Therefore, the minimal MAR presents a biological minimum of 0.1 microm/day. This value is used for our recoding: if no labels are sampled (2% of our population), Ir.L.Wi is assigned the value 0; if none or an insufficient number of double labels are sampled (29% of our population), then Ir.L.Wi is assigned the value 1 microm. Excluding cases with missing readings on any dependent variable increases the mineralizing surface (MS/BS) by 60% (2p < 0.01); other indices show no significant change. The suggested recoding decreases the average MAR by 4% (2p < 0.01), prolongs the remodeling period by 19% (2p < 0.01), and tends to decrease the activation frequency (2p = 0.09). Furthermore, the number of excluded biopsies tends to be larger among the older (2p = 0.09) and more severely osteopenic individuals (2p = 0.09). We conclude that ignoring missing double labels leads to selection bias; therefore, specific measures such as recoding procedures are needed to allow proper representation of low turnover patients. There is also a risk of bias caused by the exclusion of the older, osteopenic patients in bone histomorphometric osteoporosis trials.

Quantitative computed tomography for spinal bone mineral measurements in chronic renal failure

The aim of this study was to assess non-invasively the status of spinal trabecular bone in patients with chronic renal failure and the influence of the disease stage. Single energy quantitative computed tomography (CT) was used in 89 patients with chronic renal failure to measure spinal trabecular bone equivalent density. 23 patients were independent of dialysis and 66 were receiving long-term haemodialysis. Spinal trabecular bone density of the patients was compared with locally determined normal ranges. Although trabecular bone mineral density (BMD) was lower (9% on average) in the patients who were not dependent on dialysis compared with the predicted mean normal values (BMDp) for age- and sex-matched normal subjects, the difference was not statistically significant. A statistically significant reduction was found in patients on dialysis (BMD/BMDp 0.75 +/- 0.16, Z-score -1.3). Osteosclerosis was found in 11 patients and they were excluded from the study. Longitudinal measurements in 42 patients on dialysis without osteosclerosis showed a 2.9% mean reduction in BMD/BMDp over a period of 8 months. All but one of the 16 haemodialysis patients with osteopenic spinal fractures had trabecular BMD values lower than the fracture threshold determined by our technique. In conclusion, end-stage chronic renal failure was associated with reduction in the spinal trabecular bone density.

Extent of alkaline phosphatase cytochemistry vs. extent of tetracycline fluorescence in the evaluation of histodynamic variables of bone formation

Alkaline phosphatase (ALP) activity is a new histomorphometric index of the extent of osteoblastic surfaces involved in mineralization. To assess its validity in the evaluation of bone formation, we carried out a comparative study between histomorphometric values obtained on the basis of the extent of tetracycline labeling and of the length of ALP-positive endosteal surfaces. The following variables were compared (indicated by ALP when based on the extent of ALP positivity): trabecular mineralizing surface (MS/BS vs. ALP.S/BS); osteoid mineralizing surface (MS/OS vs. ALP.S/OS); bone formation rate (BFR/BS vs. ALP.BFR/BS); and adjusted appositional rate (Aj.AR vs. ALP.Aj.AR). Bone biopsies from 39 patients with chronic renal failure and different types of renal osteodystrophy were considered (48 +/- 12 years of age; 19 men and 20 women). Patients were double labeled with tetracycline and biopsies were embedded in glycol-methacrylate at +4 degrees C. Patients showed various types of renal osteodystrophy and were assigned to different groups of pathologies. Although it differed in incidence according to the different groups, ALP activity was found in typical plump osteoblasts bordering osteoid seams and in flat cells, either in contact with osteoid or along the quiescent surfaces of bone in continuity with it. Tetracycline codistributed with all these features to variable extents, according to groups. In all patients, however, ALP.S/BS and ALP.S/OS respectively exceeded MS/BS and MS/OS. In consequence of this, ALP.BFR/BS and ALP.Aj.AR were greater than BFR/BS and Aj.AR, respectively. For each of the variable considered, differences among groups of patients with different types of renal osteodystrophy were highly significant. Good correlations were found between the variables measured with the two methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Pretransplant parathyroidectomy in renal failure: effects on bone histology and aluminum deposits during dialysis and after kidney transplantation

Using repeat bone biopsies, we studied whether 1) subtotal parathyroidectomy (PTX) enhances aluminum (Al) deposition in bone and 2) whether pretransplant PTX affects Al removal from bone after kidney transplantation. Twenty-four kidney graft recipients, 10 subjected to PTX 9-44 months prior to transplantation and 14 controls matched for dialysis duration, had bone biopsies taken at transplantation. Serum calcium and parathyroid hormone levels had decreased after PTX in all 10. At transplantation, eroded bone surface was lower in PTX-recipients, while extent of Al-stained bone surface and prevalence of symptomatic Al-related bone disease were similar in both groups (PTX: 2/10; non-PTX: 4/14). Hence, PTX did not enhance accumulation of stainable bone Al nor increase prevalence of clinical bone disease during dialysis. Fourteen (7 PTX) recipients with functioning grafts had a second biopsy 12 months after transplantation. Symptomatic Al-related bone disease was cured regardless of pretransplant PTX, and Al-stained surface had decreased in all but one (PTX) recipient.

Depression of osteoblastic activity in immobilized limbs of suckling rats

Recently we characterized the immobilization-related osteopenia in adult rats and showed that it is caused by increased bone resorption and decreased bone formation (Weinreb et al. 1989 Bone 10:187). To assess the effect of age on disuse osteopenia, this study investigated the effects of immobilization on bone turnover in very young, suckling rats. The 15-day-old rats underwent unilateral hind limb immobilization by sciatic neurectomy; the contralateral limb was left intact and served as control. Experimental or sham-operated animals were killed after 0, 2, 4, or 12 days postsurgery. Dry, fat-free weight and ash weight were determined in both femora, and both tibiae were subjected to static and dynamic histomorphometry. Immobilization caused a progressive deficit in bone mass in the immobilized limb compared to the contralateral intact limb but did not affect femoral longitudinal growth. The total mineral content in the immobilized femora was 13.6% less than that in the intact limb by day 12. Concomitantly, tibial cancellous bone area and perimeter declined in the immobilized limb by 37.3 and 32.2%, respectively. This reduction in bone mass in the tibiae of immobilized limbs was associated with increased bone resorption, expressed as osteoclast perimeter, number of osteoclasts per mm surface, and number of osteoclasts per mm2 tissue area. Bone formation was reduced as a result of impaired osteoblast activity as evidenced by (1) decreased endocortical and trabecular mineral apposition rate; (2) reduced trabecular mineral formation rate; (3) decreased percentage of ash of the femoral dry weight; and (4) increased volume of unmineralized osteoid in the tibial metaphysis.(ABSTRACT TRUNCATED AT 250 WORDS)