The spinal osteoporoses. Mechanisms of pathogenesis and pathophysiology

Morphobiochemical diagnosis of acute trabecular microfractures using gamma correction Tc-99m HDP pinhole bone scan with histopathological verification

We prospectively performed gamma correction pinhole bone scan (GCPBS) and histopathologic verification study to make simultaneous morphobiochemical diagnosis of trabecular microfractures (TMF) occurred in the femoral head as a part of femoral neck fracture.Materials consisted of surgical specimens of the femoral head in 6 consecutive patients. The specimens were imaged using Tc-99m hydroxymethylene diphosphonate (HDP) pinhole scan and processed by the gamma correction. After cleansing with 10% formalin solution, injured specimen surface was observed using a surgical microscope to record TMF. Morphological findings shown in the photograph, naive pinhole bone scan, GCPBS, and hematoxylin-eosin (H&E) stain of the specimen were reciprocally correlated for histological verification and the usefulness of suppression and enhancement of Tc-99m HDP uptake was biochemically investigated in TMF and edema and hemorrhage using gamma correction.On the one hand, GCPBS was able to depict the calcifying calluses in TMF with enhanced Tc-99m HDP uptake. They were pinpointed, speckled, round, ovoid, rod-like, geographic, and crushed in shape. The smallest callus measured was 0.23 mm in this series. On the other hand, GCPBS biochemically was able to discern the calluses with enhanced high Tc-99m HDP uptake from the normal and edema dipped and hemorrhage irritated trabeculae with washed out uptake.Morphobiochemically, GCPBS can clearly depict microfractures in the femoral head produced by femoral neck fracture. It discerns the microcalluses with enhanced Tc-99m HDP uptake from the intact and edema dipped and hemorrhage irritated trabeculae with suppressed washed out Tc-99m HDP uptake. Both conventional pinhole bone scan and gamma correction are useful imaging means to specifically diagnose the microcalluses naturally formed in TMF.

A prospective cohort analysis of adjacent vertebral body bone mineral density in lumbar surgery patients with or without instrumented posterolateral fusion: a 9- to 12-year follow-up

STUDY DESIGN

A prospective, cohort study of 11 patients who underwent either a posterior lumbar spinal fusion with instrumentation (n = 7) or a lumbar laminotomy and discectomy alone (n = 4) and who were evaluated by dual energy radiograph absorptiometry (DEXA) to determine bone mineral density (BMD) at the adjacent three cephalad vertebral levels.

OBJECTIVES

To determine long-term BMD changes that occur at the adjacent three levels above an instrumented posterolateral lumbar fusion or an isolated laminotomy and lumbar discectomy.

SUMMARY OF BACKGROUND DATA

No long-term prospective study has evaluated the affects of instrumented lumbar fusions on bone remodeling at adjacent vertebral levels. Several studies in animals and humans have reported a decrease in BMD at the adjacent level during the first 6 months after spinal fusion with a return to baseline at 1-year follow-up in up to 60% of patients.

METHODS

DEXA was performed initially at a mean postoperative follow-up of 4 years (range, 2.3-5.5 years) and again at a mean of 10.8 years (range, 9.1-2.4 years). Eleven patients were divided into two groups: laminotomy and discectomy (n = 4) and instrumented posterior spinal fusion (n = 7). All patients underwent surgical procedures at the L4-L5 or L5-S1 levels with DEXA analysis being performed on the adjacent three cephalad levels. The discectomy group (mean age, 57.8 years) underwent lumbar hemilaminotomy without fusion whereas the other group (mean age, 60 years) underwent pedicle-screw instrumentation and posterolateral lumbar fusion. Peripheral sites, including the femoral neck, were included in the DEXA analysis to normalize for individual differences in bone mineral metabolism.

RESULTS

At the mean 10.8-year follow-up, the fusion group was noted to have at the adjacent level, two levels cephalad, and three levels cephalad normalized BMDs of 1.47, 1.39, and 1.27, respectively. A 14.8%, 10.8%, and 9.5% increase respectively in normalized BMD was observed when compared with the mean 4-year fusion values (P < 0.05). This increase was also noted on comparative T-score, Z-score, and absolute BMD values (P < 0.05). The discectomy group when evaluated revealed no statistically significant change from the mean 4 to 10.8-year follow-up (BMD, normalized BMD, T-score, Z-score). No statistically significant difference was noted in hip BMD at the mean 4-year and 10.8-year follow-up (1.05 versus 1.03), suggesting that the effects were local.

CONCLUSIONS

The local BMD adjacent to an instrumented lumbar fusion is increased at a mean of 10.8-years after surgery. There is a gradual decrease in BMD changes with increasing distance from the fusion level. Alterations in fusion site biomechanics and modulus mismatch between the host bone and the spinal instrumentation most likely result in chronic, localized bone remodeling with an increased BMD that decreases the greater the distance from the fusion mass.

Trabecular microfracture

Healing trabecular microfractures are a common feature in cancellous bone. These lesions, when observed in macerated cancellous bone slices, measure about 500 microns in diameter and surround fractures in trabeculae with microcallus. Whether microcallus is a structure acting primarily as a transient brace, preventing relative movement of the fragmented segments and enabling the trabecula to heal, or whether it is a permanent buttress reducing the stress on the fractured strut, preventing the healing process, is not known. Microfractures are the result of normal physical activity. Hence, the widespread occurrence of trabecular microfracture in cancellous bone implies that a reasonable rate of microfracture is physiologically tolerable. There are three putative effects for trabecular microfracture. One is that, in response to impulse loading, cancellous subchondral bone increases its rigidity due to osteosclerosis resulting from bone formed around microfractures. Another hypothesis is that, if sufficient trabecular microfractures occur, they will compromise the trabecular structure of the vertebra and the proximal femur leading to osteoporotic fracture. By inducing remodeling changes, microfractures have an effect on the maintenance of joint structure. There are two histological patterns for microfractures: an early stage, when actively forming woven bone is bridging the fracture; and a more common late stage, when woven bone is inactive. Femoral studies fail to demonstrate that an increasing number of healed or healing microfractures in osteoarthrosis causes the increase of bone in the head of femur. Only one study has reported a significant increase in the number of trabecular microfractures in osteoarthritic femoral heads compared with normal controls. This significant increase was in patients taking antiinflammatory drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

"Physiological osteoporosis" and "osteoblast insufficiency" in old age. Comparative radiological-morphometric and statistical studies on the spongy bone of lumbar and cervical vertebral bodies

To investigate the expectation of general insufficiency of osteoblasts with increasing age, we studied autotopsy material from 105 deceased persons of both sexes who had died between 16 and 91 years and in whom clinically manifest diseases of the bone had been excluded. Quantitative morphometric examination of the structure of the spongy bone of the 3rd-5th lumbar vertebral bodies (LVBs) and of the 5th-7th cervical vertebral bodies (CVBs) was carried out in frontal and sagittal planes, the parameters analysed being volumetric density (Vv), surface density (Sv) and specific surface area (S/V), and the results were subjected to statistical evaluation. The results showed that in the three LVBs, Vv, Sv and S/V behave in a similar manner, Vv and Sv decreasing after the age of 50 years by more than one-third while S/V remains constant throughout life. The three lower CVBs had higher values than the LVBs for all three structural parameters. In the 7th CVB somewhat lower Vv and Sv values and higher S/V values were found than in the 5th and 6th. The age-related changes, by contrast, were very small. This differing behavior of the spongy bone in the two regions of the spinal column is an expression of the different characteristic loading forces in each regions: LVB loading is predominantly static, CVB loading mainly dynamic. Thus, from the functional point of view, what is known as "physiological osteoporosis due to ageing" is nothing more than adaptation by an ageing bone to physical activity, reflecting--like the bone of the young adult--the current loading of the cancellous bone by the actions of the musculoskeletal system. Since such physical activity is often age-related, the performance of the osteoblasts does not depend upon age per se, but merely on the remaining functional adaptive capacities of the ageing organism as whole.

Poor growth prior to early childhood: decreased health and life-span in the adult

Previous studies in animal populations have shown that stunted neural and thymolymphatic growth early in development may result in permanently impaired neural and immune function, decreased body growth, vertebral wedging, and decreased life-span. In the human adult, small vertebral neural canal (VNC) diameters may reflect early stunted neural and immune development and impaired function that leads to decreased health (inferred by greater vertebral wedging) and life-span in the adult. VNC, which complete their growth by early childhood (age 4), are markers of early development in adults. On the other hand, features following general body growth, such as height, weight (represented here by vertebral body height) continues to grow until young adulthood. They are less reliable, because they readily experience catch-up growth (even in chronically stressed populations) and, unlike VNC, may mask poor early growth. To test associations between early growth and adult health and life-span in humans, we measured 2,060 VNC, vertebral heights, vertebral wedging, nerve-root tunnel lengths, severity of vertebral osteophytosis, and ages at death in 90 adult (aged 15-55 years) prehistoric skeletons (950-1300 A.D.). Tibial lengths were also measured in a subsample (n = 30). Multivariate, bivariate, and nonparametric analyses showed that small VNC are significantly associated with greater vertebral wedging and decreased life-span (P less than 0.05-0.00001). VNC are independent of vertebral body heights and tibial lengths (general body growth). VNC, but not statural components, are useful in predicting adult health, presumably because they reflect neural and immune development and do not readily experience catch-up growth. Thus, longitudinal retrospective measures of early growth and adult health were systematically linked within individuals regardless of confounding factors operating over the 350-year time period. Since this research was completed, this model has repeatedly been independently confirmed in four living urban industrial populations. Longitudinal retrospective analysis was employed together with direct measures of VNC, neural and immune function. Together these results suggested that it may be essential to improve growth prior to early childhood in order to maximize adult health and life-span.

Age changes in the bone mineral of the lumbar spine in normal women

The bone mineral content (BMC) and the bone mineral areal content (BMAC) were determined with dual-photon absorptiometry in the third lumbar vertebra in a random sample of 214 women between 35 and 80 years of age in the city of Göteborg, Sweden. A continuous aging decrease (1%/year) of both the BMC and the BMAC was noted after age 35. The rate at which bone loss occurred was similar for all age groups when analyzed by 5 year intervals. No clear acceleration of bone loss was noted around the usual time of the menopause.

Impaired osteoblast function in osteoporosis: comparison between calcium balance and dynamic histomorphometry

Osteoblast function was investigated in 27 patients with idiopathic osteoporosis. Transiliac bone biopsy specimens were taken after double labelling with tetracycline, and metabolic calcium balance was studied almost simultaneously. Many of the patients showed poor double labelling of their otherwise unremarkable trabecular osteoid, suggesting impaired formation of bone at many of these surfaces. This phenomenon was not accompanied by increased width of osteoid seams (as seen in osteomalacia), indicating that formation of the matrix and its mineralisation were in equilibrium. For the first time, highly significant positive correlations (p less than 0.01) were found between indices of bone formation, determined by labelling with tetracycline, and calcium balance. Thus some patients with osteoporosis who are rapidly losing bone have low rates of formation of trabecular bone both by individual osteoblasts and in relation to available bone surfaces. As histological indices of bone resorption also independently correlated strongly and inversely (p less than 0.01) with calcium balance the rate of initiation of new basic multicellular units by osteoclastic resorption of trabecular surfaces (or the depth of resorption at these surfaces) also appears to be an important determinant of mineral balance. The mechanisms that regulate the effective life span of mature osteoblasts require further investigation, particularly as some promising treatments that can increase trabecular bone volume in osteoporosis, such as parathyroid peptide hPTH (1-34) and sodium fluoride, must work through a reversal of osteoblastic depression.

Thiazide for the postponement of postmenopausal bone loss

The effect of thiazide on bone mineral loss in normal postmenopausal women was examined during a 3 yr placebo-controlled clinical trial. Sixty-three healthy women in their early menopause were randomized to treatment with bendroflumethiazide 5 mg/day or placebo for 2 yr, while both groups received placebo for the third year of the trial. Calcium supplement 0.5 g/day was given throughout the 36 mo to all participants. Bone mineral content (BMC) determined by 125I-photon absorptiometry of the forearms decreased 2% per year in the placebo group (p less than 0.001). In the thiazide group no fall in BMC was seen during the first 6 mo. whereafter BMC declined with the same rats as in the placebo group. At the end of the 3 yr trial BMC averaged 94.1% in the placebo group and 95.2% in the thiazide group (p greater than 0.05). Despite a daily supplement of 0.5 g calcium, thiazide induced a persistent fall in the urinary calcium excretion of 25% (p less than 0.001), whereas the calcium supplement in the placebo group caused a significant increase in mean urine calcium of 10%-20% (p less than .001). At stop of thiazide medication a rebound effect caused a marked rise in urine calcium. One month after withdrawal of the calcium supplement the urinary calcium excretion had returned to the initial level in both groups. It is concluded that despite a sustained urine calcium lowering action the effect of thiazide upon postmenopausal bone loss is shortlived.

[Primary hyperparathyroidism--bone turnover and osteitis fibrosa assessed by x-ray (author's transl)]

1. In primary hyperparathyroidism an increased bone turnover is seen, accompanied by osteitis fibrosa (= fibroosteoclasia, FO) in severe forms of the disease. Both types of bone reaction may be detected by microradioscopy X-rays of the hand, extensive striation of metacarpal cortical bone indicating increased bone turnover and subperiosteal resorption of phalanges pointing to FO. 2. In the present study 65 patients with proven PHPT were evaluated before and 39 after operation. Microradioscopy was combined with biochemical assessment of hyperparathyroidism including alkaline serum phosphatase (aPh) as an index of osteoblastic activity, hydroxyprolin excretion (HyPro) reflecting bone turnover, immunoreactive parathyroid hormone levels (PTH), serum calcium (SCa), urinary calcium (UCa), serum inorganic phosphorus (SP) and clearance of phosphate (Cp). A comparison was made with the incidence of renal stone disease and the degrees of metacarpal striation (StG) and subperiosteal resorption (UG) were followed after operation. 3. Preoperative X-rays of 60% of the PHPT subjects showed increased StG and/or UG, and in 41,5% the diagnosis of PHPT was possible from the X-ray findings only. There existed a significant correlation between StG and UG on one hand and aPh, HyPro and PTH on the other. No correlation, either positive or negative, was seen between FO and the incidence of renal stones. After surgery, subperiosteal bone lesions disappeared in all patients, while intracortical striations persisted in half of the subjects despite the normalised bone turnover. Thus, primary hyperparathyroidism may not only lead to endosteal bone loss but to an irreversible intracortical bone deficit as well.