Relationship between toluidine blue-stained calcification fronts and tetracycline-labeled surfaces in normal human iliac crest biopsies

Interest of Bone Histomorphometry in Bone Pathophysiology Investigation: Foundation, Present, and Future

Despite the development of non-invasive methods, bone histomorphometry remains the only method to analyze bone at the tissue and cell levels. Quantitative analysis of transiliac bone sections requires strict methodologic conditions but since its foundation more 60 years ago, this methodology has progressed. Our purpose was to review the evolution of bone histomorphometry over the years and its contribution to the knowledge of bone tissue metabolism under normal and pathological conditions and the understanding of the action mechanisms of therapeutic drugs in humans. The two main applications of bone histomorphometry are the diagnosis of bone diseases and research. It is warranted for the diagnosis of mineralization defects as in osteomalacia, of other causes of osteoporosis as bone mastocytosis, or the classification of renal osteodystrophy. Bone biopsies are required in clinical trials to evaluate the safety and mechanism of action of new therapeutic agents and were applied to anti-osteoporotic agents such as bisphosphonates and denosumab, an anti-RANKL, which induces a marked reduction of the bone turnover with a consequent elongation of the mineralization period. In contrast, an increased bone turnover with an extension of the formation site is observed with teriparatide. Romosozumab, an anti-sclerostin, has a dual effect with an early increased formation and reduced resorption. Bone histomorphometric studies allow us to understand the mechanism of coupling between formation and resorption and to evaluate the respective role of bone modeling and remodeling. The adaptation of new image analysis techniques will help bone biopsy analysis in the future.

Impaired bone mineralization accompanied by low vitamin D and secondary hyperparathyroidism in patients with femoral neck fracture

SUMMARY

Although it is well established that a decrease in bone mass increases the risk of osteoporotic fractures, the proportion of fractures attributable to areal bone mineral density (BMD) is rather low. Here, we have identified bone mineralization defects together with low serum 25-hydroxyvitamin D (25-(OH) D) levels as additional factors associated with femoral neck fractures.

INTRODUCTION

Osteoporotic fractures of the femoral neck are associated with increased morbidity and mortality. Although it is well established that a decrease in bone mass increases the risk of osteoporotic fractures, the proportion of fractures attributable to areal BMD is rather low. To identify possible additional factors influencing femur neck fragility, we analyzed patients with femoral neck fracture.

METHODS

We performed a detailed clinical and histomorphometrical evaluation on 103 patients with femoral neck fracture including dual-energy X-ray absorptiometry, laboratory parameters, and histomorphometric and bone mineral density distribution (BMDD) analyses of undecalcified processed biopsies of the femoral head and set them in direct comparison to skeletal healthy control individuals.

RESULTS

Patients with femoral neck fracture displayed significantly lower serum 25-(OH) D levels and increased serum parathyroid hormone (PTH) compared to controls. Histomorphometric analysis revealed not only a decreased bone volume and trabecular thickness in the biopsies of the patients, but also a significant increase of osteoid indices. BMDD analysis showed increased heterogeneity of mineralization in patients with femoral neck fracture. Moreover, patients with femoral neck fracture and serum 25-(OH) D levels below 12 μg/l displayed significantly thinner trabecular bone.

CONCLUSION

Taken together, our data suggest that impaired bone mineralization accompanied by low serum 25-(OH) D levels is of major importance in the etiology of femoral neck fractures. Therefore, balancing serum 25-(OH) D levels and thereby normalizing PTH serum levels may counteract pronounced mineralization defects and might decrease the incidence of femoral neck fractures.

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)

Relationship between the location of osteoblastic alkaline phosphatase activity and bone formation in human iliac crest bone

It is not feasible to use in vivo tetracycline double labeling to study bone formation in biopsies taken during the emergency fixation of fractures. We therefore compared the trabecular localization and extent of osteoblastic alkaline phosphatase (AP) perimeters with tetracycline and osteoid perimeters in iliac crest biopsies from 7 women with postmenopausal osteoporosis and 13 women without metabolic bone disease. Fresh biopsies were chilled to -70 degrees C, and triplicate serial unfixed undecalcified cryostat sections were cut and reacted for AP, stained for osteoid, or mounted unstained. At individual remodeling sites, the mineralizing perimeter (M.Pm) was measured as the extent of a double or single label accompanied by greater than or equal to 1 lamella of osteoid and greater than or equal to 1 lamella of mineralized matrix between the mineralization front and the adjacent label. Osteoid perimeters (O.Pm) and AP perimeters (AP.Pm) were also measured. In each biopsy there was good agreement between the location of AP and bone formation (kappa statistic, range 0.71-1.0). The overall sensitivity and specificity of AP as an indicator of the location of bone formation were 0.963 and 0.902, respectively. At the level of the basic multicellular unit, in those samples in which greater than 3 active BMUs were found, there was (1) significant positive correlation between the M.Pm and both AP.Pm and AP-positive O.Pm (except 1 patient) and (2) no significant difference between the M.Pm and AP-positive O.Pm (17 of 18 patients and 18 of 18 patients at the tissue level).(ABSTRACT TRUNCATED AT 250 WORDS)

Osteomalacia and osteoporosis in femoral neck fracture

Iliac crest bone histomorphometry, plasma and urine biochemistry and clinical history were examined in 78 unselected patients (68 women, 10 men) at the time of femoral fracture. Histological abnormalities occurred in 56 of the 78 biopsies. The commonest of these was a low bone volume of less than 15% which, irrespective of other abnormal histological features, was present in 37 of the biopsies. On the basis of the histomorphometry, patients could be classified into four main groups. Normal histomorphometry (bone volume greater than 15%, osteoid surfaces less than 24%, mineralising surface greater than 60%) was present in 22 patients, 23 had osteoporosis as the only abnormality (bone volume less than 15%, osteoid surface less than 24%, mineralising surface greater than 60%), nine had osteomalacia (osteoid surfaces greater than 24%, mineralising surface less than 60%, osteoid width greater than 13 microns) and 13 had decreased mineralising surfaces. Of the remainder, five had increased osteoid surface and six had insufficient osteoid to assess mineralising surface. Plasma and urine biochemistry in the four groups showed that, compared to age-matched controls, all groups had reduced plasma albumin. In comparison to the group with normal histomorphometry, patients with osteoporosis had a higher plasma calcium (P less than 0.01), tubular reabsorption of calcium (P less than 0.05) and plasma vitamin D binding protein (P less than 0.01); patients with osteomalacia had a higher plasma creatinine (P less than 0.02) and parathyroid hormone (P less than 0.02) and lower plasma 24,25-dihydroxyvitamin D (P less than 0.02), urinary calcium/creatinine ratio (P less than 0.02) and tubular reabsorption of phosphate (P less than 0.02). The biochemistry in patients with decreased mineralising surface was no different from patients with a normal biopsy. The prevalence of both osteoporosis and osteomalacia increased with age and, in subjects over the age of 90, osteoporosis occurred in 71% of patients and osteomalacia occurred in 29% of patients. The osteomalacic group were significantly older than the other three groups (P less than 0.05). The histomorphometry did not relate to the site of fracture (subcapital or intertrochanteric). A history of stroke, gastrectomy, rheumatoid arthritis, steroid treatment, thyroid disease, alcohol abuse and anti-convulsant therapy was present in patients with femoral fracture but did not relate to any particular histomorphometric classification.

Bone histomorphometric reference values in 88 normal Italian subjects

The study deals with bone histomorphometric results obtained from 88 normal subjects (38 women and 50 men; range: 20-89 years), in order to establish control values in an Italian population. Bone specimens were obtained at autopsy from a standardized area of the iliac crest. The following indicators were measured: bone volume (BV/TV), osteoid volume, osteoid surface, osteoblast surface, eroded surface, osteoclast surface, osteoid thickness. Dependence of histomorphometric indicators on sex and age was evaluated by multiple regression analysis, including sex, age, and also a quadratic term (age2) and two interaction terms (sex x age, sex x age2). BV/TV was mainly affected by age. In fact, a decrease in the amount of bone was found with increasing age in both males and females. The reduction appeared rather regular, with negligible differences between males and females. The other indicators were found to be age- and sex-independent. As a consequence, they did not give information on the possible changes of bone apposition and resorption processes due to aging. On the whole, histomorphometric indicators of trabecular bone of the normal Italian population do not greatly differ from those reported for most other caucasian people.

Effects of cyclical therapy for osteoporosis using an oral regimen of inorganic phosphate and sodium etidronate: a clinical and bone histomorphometric study

Cyclical therapy for osteoporosis has been proposed as a means to induce a coherently structured improvement in bone remodelling dynamics. This pilot study involved 37 osteoporotic patients with symptomatic vertebral compression fractures, treated with an oral protocol designed to activate endogenous bone turnover and selectively depress osteoclastic bone resorption, utilizing inorganic phosphate and sodium etidronate respectively in sequential 3 monthly cycles. Biochemical parameters were recorded during the first cycle, and quantitative bone histomorphometry was obtained from iliac crest biopsies before and after 23.4 +/- 8.5 (SEM) months of treatment. In addition, fracture rates (expressed as new vertebral fractures/1000 patient years) were studied by sequential lateral spinal radiographs. Lumbar bone mineral density (BMD) was assessed by sequential dual-beam photon densitometry. The results demonstrated equivocal biochemical evidence of 2 degrees hyperparathyroidism during the initial cycle of therapy with inorganic phosphate. However, fracture rates declined significantly from 640/1000 patient years during the first 15 months therapy to 242/1000 patient years during a further 20 months follow-up (P less than 0.01). Lumbar BMD increased over baseline by 8.38 +/- 2.87% after 12 months treatment (P less than 0.01). Bone histomorphometric analysis disclosed a modest increment in bone volume from 16.0 to 17.4% tissue volume, and a significant increase in eroded surface from 4.2 +/- 0.6 to 6.0 +/- 0.9% cancellous surface (P less than 0.05). However, histomorphometric parameters of bone formation deteriorated. It is concluded that this cyclical protocol resulted in short-term improvement in trabecular bone mass, but there is no evidence at a cellular level that long-term improvements in bone remodelling occurred.

Uses and limitations of bone biopsy in management of metabolic bone disease

Bone biopsy is now an established diagnostic and investigative procedure which is widely used in the management of metabolic bone diseases. Its unique feature is that it facilitates direct visualization of bone cells and bone structure and, through double tetracycline labelling, allows the indirect measurement of bone turnover. Its main diagnostic contribution has been in unravelling the complexities of renal osteodystrophy, which consequently is now much better understood. However, it has also uncovered a variety of mineralization defects caused by agents such as fluoride, diphosphonates and aluminum that might otherwise have bone unsuspected clinically. Its main investigative roles have been to provide unique insight into the mechanisms of bone loss with age and in osteoporosis, and to assess the effects on bone and bone cells of potential therapeutic agents in established osteoporosis. This has been possible through the use of histomorphometry, which is used to quantify changes in bone volume and turnover as well as alterations in the microanatomical structure of bone that can reduce bone strength and increase the risk of fracture. Although most biopsies will continue to be taken for histomorphometry, recent studies have shown that specimens may be used to provide additional information such as quantitation and localization of elements within bone, and to provide bone cells for in vitro culture. It is likely that, in future, specimens will be taken from patients with various disorders so that the techniques of cell and molecular biology can be applied to harvested bone cells and thus provide a new dimension to our understanding of metabolic bone disease.