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Study design:Review article on bone metabolism and therapeutic approach on bone loss in patients with spinal cord injury (SCI).Objective:The first part aims to describe the process of bone demineralization and its effects on bone mass in patients with SCI. The second part describes and discusses the therapeutic approaches to limiting the alteration in bone metabolism related to neurological lesions.Setting:Propara Rehabilitation Center, Montpellier, France.Results:During the first 24 months postinjury, demineralization occurs exclusively in the sublesional areas and predominantly in weight-bearing skeletal sites such as the distal femur and proximal tibia, both of which are trabecular-rich sites. Reduced bone mass, in association with a modified bone matrix property and composition, is very likely at the origin of pathological fractures after minor trauma to which these patients are frequently exposed. Since these fractures may be asymptomatic yet may lead to complications, preventing and managing ‘neurological osteoporosis’ remains a considerable challenge. Two main approaches are considered: the first consists in applying a mechanical stimulus to the bone tissue by standing, orthotically aided walking or functional electrical stimulation (FES). The second uses medications, particularly antiresorptive drugs such as calcitonin or diphosphonates.Conclusion:To develop well-adapted treatments, a more precise understanding of bone loss etiology is needed. The current rehabilitation programs are based on the idea that the bone physiological changes observed in patients with SCI are due to immobility, but results indicate that alterations inherent to neurological damage may play an even greater role in inducing osteoporosis.Spinal Cord (2006) 44, 203–210. doi:10.1038/sj.sc.3101832; published online 13 September 2005 [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of strenuous exercise on bone metabolism and related hormones in elderly subjects. Methods: Twenty one active elderly subjects (11 men and 10 women; mean age 73.3 years) showing a mean theoretical Vo2max of 151.4% participated. Concentrations of plasma ionised calcium (iCa), serum intact parathyroid hormone (iPTH), 25-hydroxyvitamin D (25(OH)D), and 1 .25-dihydroxy-vitamin D3 (1.25(OH)₂D3), as well as the bone biochemical markers type l collagen C-telopeptide for bone resorption and osteocalcin and bone alkaline phosphatase for bone formation, were analysed before and after a maximal incremental exercise test. Results: At basal level, iPTH was positively correlated with age (r =0.56, p<0.01) and negatively correlated with 25(OH)D (r= -0.50; p<0.01) and 1.25(OH)₂D3 (r= -0.47; p<0.05). Moreover, 25(OH)D and 1.25(OH)₂D3 levels were negatively correlated with age (r = -0.50, p<0.01 and r = -0.53, pc<.01, respectively). After exercise, iCa and 25(OH)D decreased (p<0.001 and p = 0.01, respectively) while iPTH increased (p<0.00l). The levels of 1.25(OH)₂D3, bone biochemical markers, haematocrit, and haemoglobin were unchanged. The variations in iCa and 25(OH)D were not related to age and/or sex. The iPTH variation was directly related to basal iPTH levels (p<0.01) and indirectly related to age. Conclusions: In active elderly subjects, strenuous exercise disturbed calcium homeostasis and bone related hormones without immediate measurable effect on bone turnover. Although an increase in iPTH could have an anabolic action on bone tissue, our findings from our short term study did not allow us to conclude that such action occurred. [ABSTRACT FROM AUTHOR]

We examined the effects of antioxidant supplementation in association with progressive aerobic training on the bone metabolism of healthy elderly individuals. For 8 weeks, 13 participants (mean age 74 years) received vitamin C (500 mg) and vitamin E (100 mg) daily and participated in a supervised progressive aerobic training programme. After the 8 weeks, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D concentrations were increased significantly by 42.8% (P < 0.001) and 26.8% (P < 0.01) respectively, while parathyroid hormone concentration was decreased by 17.5% (p < 0.05). Of the bone markers, only bone alkaline phosphatase decreased, by 14.6% (P < 0.05). No variation was observed for ionized calcium, insulin-like growth factor-1 or insulin-like growth factor binding protein-3. Our findings suggest that 8 weeks of combined antioxidant supplementation and aerobic training modified vitamin D metabolism and parathyroid hormone concentration. These adaptations might counterbalance the unfavourable hormonal profile frequently observed in the elderly that predisposes them to accentuated age-related bone loss.

This study investigated the effect of intense physical activities that generate high mechanical constraints on bone metabolism and serum leptin concentrations and the potential relationships among bone mineral density (BMD), bone biochemical markers and leptin variation. Thirteen male decathletes (mean age 22.4 +/- 2.9 years), nationally or internationally ranked (15.5 h/week of training), were compared with 13 healthy sedentary subjects (mean age 25.9 +/- 3.3 years). BMD was measured by DEXA and bone turnover was evaluated by specific markers. Leptin and calciotropic hormones levels were analysed in parallel. BMDs were higher in athletes than in controls at total body (13.9%), lumbar spine (17%), femoral neck (25%) and radius (9%), but not at the head. Athletes presented higher concentrations of osteocalcin (59.8%), cross-linked C-telopeptide of type-I collagen (41.1%) and 1,25-dihydroxyvitamin-D (37.1%). Basal leptin concentration was lower in athletes (0.94 +/- 0.54 vs. 5.07 +/- 1.1 ng ml(-1)), and this difference persisted when leptin levels were adjusted for whole body fat mass (WBFM). No difference was observed for bone-specific alkaline phosphatase or intact parathyroid hormone. Serum leptin levels were negatively correlated with various BMD values only when both the groups were pooled (n = 26). This relationship did not persist when leptin levels were adjusted for WBFM. Male athletes, who practise sports generating high mechanical constraints on the body, present a specific bone metabolism that includes high BMD, as well as high bone turnover. The blunted leptin secretion did not seem to have deleterious effect on the process of bone adaptation to high mechanical constraints.

This longitudinal study evaluated the effects of a triathlon season on bone metabolism and hormonal status. Seven male competitive triathletes (mean age 19.3 years, range 18 - 20) with 5.0 +/- 0.3 years of competition experience were tested twice during the season: at the beginning of training and 32 weeks later. Total and regional bone mineral density (BMD) was determined by dual-energy X-ray absorptiometry, while bone turnover was evaluated by specific biochemical markers: bone-specific alkaline phosphatase (B-ALP), osteocalcin, and urinary type I collagen C-telopeptide. In addition, sexual, calciotropic and somatotropic hormones were also analyzed. After 32 weeks, a BMD increase was found at the lumbar spine (1.9 %; p = 0.031) and skull (3.1 %; p = 0.048), while no variation was observed for total body or at the proximal femur. The B-ALP level decreased (-23.2 %; p = 0.031), but no variation was found for the other bone markers. 1.25 (OH) (2)D3, IGF-1 and the bioavailability IGF-1 index (IGF-1/IGFBP-3) increased by 18.3 % (p = 0.047), 29 % (p = 0.048), 33 % (p = 0.011), respectively, while PTH, testosterone, IGFBP-3 and cortisol concentrations were unchanged. In conclusion, the triathlon season had a moderately favourable effect on BMD, although a slowing down of bone formation activity was observed. No variation in hormonal levels was observed that could have limited the effects of exercise on bone tissue.

Our cross-sectional study aimed at the early determination of changes in bone metabolism in terms of bone mineral density (BMD) and bone turnover in persons with complete spinal cord injury (SCI) during the acute phase of paraplegia. Combined dual-energy x-ray absorptiometry (DXA) and specific biochemical markers of bone turnover were used to determine bone metabolism. Seven persons with SCI (age, 31.3 +/- 9.5 years) who had sustained injury an average of 3 months earlier (103 +/- 10.8 days) were compared with 10 able-bodied controls (27.5 +/- 4.3 years). Four paraplegics and 3 quadriplegics composed the SCI group. BMD was measured by DXA, while bone turnover was evaluated by serum osteocalcin (OC), bone alkaline phosphatase (B-ALP), and serum and urinary type I collagen C-telopeptide (CTXs and CTXu). Regional BMD (proximal femur, lumbar spine, radius, lower limb) was similar in the 2 groups except in the upper limb (P <.05). CTXs and CTXu were significantly higher in SCI (P <.01 and P <.001, respectively), whereas among the bone formation markers used, only serum OC was affected by immobilization (P <.05). The SCI group developed hypercalciuria (0.76 +/- 0.37 v 0.35 +/- 0.14), whereas calcemia was normal (2.42 +/- 0.09 v 2.31 +/- 0.10). Intact parathyroid hormone (iPTH) and 1.25 (OH)(2) vitamin D levels were suppressed in persons with SCI (P <.001) by 80.6% and 66%, respectively. In conclusion, it was not possible to detect any variation in BMD from the DXA technique at this early stage of demineralization, but the sensitivity and early response of the biochemical markers strongly suggested their usefulness for the early identification of persons with SCI at risk of severe osteoporosis., (Copyright 2002, Elsevier Science (USA). All rights reserved.)

The orientation of paraplegic athletes toward adapted sport activities required good knowledge of their functional characteristics. Wheelchair locomotion, especially for highly dynamic situations, poses the problem of trunk equilibrium management and head stabilization. The study aimed at designing a quantitative method to assess the ability of paraplegics to obtain trunk balance under dynamic stresses, and to analyze the various balance strategies, according to the spinal lesion level of the subjects. High (HPA) and low (LPA) paraplegic athletes were subjected to four series of antero-posterior stresses of increasing intensity, generated by an oscillating platform. By means of a computerized video-based movement analyzer, acceleration in the saggittal plane was measured at four different spinal level and, for each one, a damping factor was determined. This factor, computed at the head level, appeared to be representative of the subjects' ability to maintain balance. We attempted to differentiate balance strategies in the LPA and HPA groups through analysis of the relative contributions to damping of the thoracic and cervical spinal segments. The first results show an increasing tendency of neck reflex stiffening according to the neurological level.

The authors, using external fixators, have applied measured compression forces through the growth plate of the lower end of the femur in rabbits. They have calculated the degree of compression necessary to slow down or to stop growth. It was shown that growth may become normal following release of the compression provided that the compression was not excessive. An histological study was conducted with showed lesions varying from a simple diminution in the height of the cellular columns to the development of bony bridges depending on the intensity of the compression.