[Bone histology in postmenopausal osteoporosis--variations in cellular activity]

Modern understanding of the etiology of postmenopausal osteoporosis is based on the imbalance between bone resorption and formation due to estrogen deficiency, which may take several forms and combinations of decreased and/or increased activity of both or one cell type. Studies of postmenopausal osteoporosis have pointed to the existence of heterogeneity in the remodeling imbalance. Bone histology analyzed in a group of women with established postmenopausal osteoporosis undergoing bone biopsy is part of the diagnostic procedure. Data were compared and grouped according to the published histomorphometric classification of postmenopausal osteoporosis.

The study included 43 postmenopausal women aged 44-71 years with osteoporosis established by densitometry of the lumbar spine and hip. Secondary causes of osteoporosis were ruled out. Full thickness transiliacai bone biopsy specimens were obtained after double labeling regime with oxytetracycline (Geomycin, Pliva). Biopsy specimens were processed for undecalcified embedding in resin and sections stained by Goldner trichrome and toluidine blue, or used for fluorescence microscopy. A grid attached to the microscope eyepiece was used for histomorphometry. The following parameters were assessed according to the recommendations of the American Society for Bone and Mineral Research: bone volume (BV/TV, %), osteoid surface (OS/BS, %), osteoblast surface (Ob. S/BS, %), osteoid volume (OV/BV, %), osteoid thickness (O. Th, m), osteoclast surface (Oc. S/BS, %), mineral apposition rate (MAR, m/day). Thus obtained data were compared to published reference data for normal healthy population and also expressed as z-scores (the number of standard deviations by which the value differs from the mean of the normal age and sex matched controls). The study was approved by the hospital ethics committee. All patients signed an informed consent to take part in the clinical study.

Histomorphometric analysis of bone biopsy demonstrated that on an average bone resorption, i.e. osteoclast surface, was considerably increased and osteoid volume moderately increased. The remaining histomorphometric parameters studied were generally normal for age and sex as compared to the published reference data. Increased osteoclast surface in 65% of patients indicated that bone loss was an active and prevailing process in these postmenopausal women, which was considerably more pronounced than in the normal age-matched population. Results of the histomorphometric analysis were categorized according to the published classification of postmenopausal osteoporosis. The percentage of patients in each group differed from literature data, most probably due to the sample size and choice. None of the patients had histomorphometric features of reduced osteoblastic and osteoclastic activity, but in 37% of postmenopausal women osteoclastic activity was increased while osteoblastic activity was normal, a feature not described in the original histomorphometric classification of postmenopausal osteoporosis.

Histomorphometric analysis of bone biopsy in women with postmenopausal osteoporosis revealed bone resorption as a predominant finding. Different groups were recognized based on the diversity of bone cell activity. The difference in the frequencies in study groups, and observation of a distinct group not included in the histomorphometric classification of postmenopausal osteoporosis probably resulted from sample size and nonspecific population traits. Histomorphometric analysis of bone in postmenopausal osteoporosis is an important contribution to better understanding of this most common bone disorder.