Effect of risedronate on bone resorption during consolidation phase of distraction osteogenesis: a rabbit model.

PURPOSE: To evaluate the effects of continuous local injection of risedronate in the prevention of bone resorption in a lengthened segment. METHODS: 11 male rabbits underwent subperiosteal osteotomy of the left tibia and an external fixator was applied anteromedially. After a lag phase of one week, a 2-week distraction phase and a 5-week consolidation phase followed. Risedronate was continuously injected into the centre of the distracted segment at a rate of 10 micro g/kg/day during the first 14 days of consolidation by a subcutaneously implanted osmotic pump. A control group received purified buffer solution (PBS) using the same protocol. The lengthened bone segments were evaluated using radiography, quantitative computed tomography, and 3-point bending mechanical test. RESULTS: Risedronate injection prevented osteopenia as compared to PBS injection. The mean bone mineral content, volumetric density and cross-sectional area of the lengthened segments were significantly higher in the risedronate group than in controls (as much as 65%, 30%, and 25%, respectively). There was no significant difference between the 2 groups regarding the ultimate load to failure. CONCLUSION: Continuous local injection of risedronate into the lengthened segment can prevent osteopenia during distraction osteogenesis but fails to enhance mechanical strength of newly distracted segments.

Optimal increase in bone mass by continuous local infusion of alendronate during distraction osteogenesis in rabbits.

Several methods have been used to increase bone mass in distraction osteogenesis. Since bone resorption as well as regeneration is stimulated in the distracted segment, bisphosphonate can be a beneficial agent for distraction osteogenesis. Here, we examined the effects of bisphosphonate injected continuously into the regenerate on bone volume, and architectural and mechanical properties of distraction osteogenesis. The left tibia of Japanese White rabbits (n=66) was subjected to slow distraction using an external fixator. At the beginning of the consolidation phase, alendronate (7 microg/kg/day) was infused directly into the lengthened segment for 14 days using an osmotic pump. Control rabbits were infused with phosphate buffered saline (PBS). The tibiae were monitored weekly by soft X-ray and dual-energy X-ray absorptiometry (DXA). The animals were sacrificed at 4, 6, and 8 weeks after operation to examine bone mineral density (BMD) and cortical bone thickness (CBT) by peripheral quantitative computerized tomography (pQCT), while the mechanical property of the lengthened tibia was measured by three-point bending test. In PBS-infused control animals, bone mineral content around the lengthened segment began to decrease after the first week of consolidation phase, forming a tubular bone structure with thin cortex. Infusion of alendronate increased peak bone mineral content around the lengthened segment. At the end of the experiment, volumetric BMD, CBT and mechanical strength of the lengthened segment of the treatment group were approximately twice those of the control animals. Alendronate infused in this manner significantly prevented the osteopenia that critically began early in the consolidation phase, though the dose used in this study was relatively low and no adverse events were noted.

Continuous local infusion of fibroblast growth factor-2 enhances consolidation of the bone segment lengthened by distraction osteogenesis in rabbit experiment.

Experimental tibial lengthening was achieved in 61 rabbits to examine the effect of continuous local infusion of recombinant human fibroblast growth factor-2 (rhFGF-2) on bone healing of the lengthened segment. The tibial diaphysis was separated by osteotomy and was subjected to slow progressive distraction (rate: 0.35 mm/12 h) using a monolateral external fixator. There were a lag phase for 1 week, a distraction phase for 2 weeks, and a consolidation phase for 5 weeks in this experiment. At various stages of distraction, rhFGF-2 was infused continuously for 2 weeks into the lengthened segment (rate: 14.28 microg/60 microl/day) using an osmotic pump implanted under the skin. Bone healing was significantly accelerated when rhFGF-2 was infused in the beginning of consolidation phase, but not in the distraction phase or in the lag phase. Infusion of normal saline (N/S) using the same osmotic pump had no effect. Dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computerized tomography (pQCT) studies demonstrated that rhFGF-2-treated tibia had increased bone mineral density (BMD), bone mineral content (BMC) and cortical bone thickness (CBT) when compared with N/S-treated tibia. Three-point bending test demonstrated that rhFGF-2-treated bone had significantly stronger mechanical properties than N/S-treated bone. Finally, distribution of the infused materials was checked by using Indian ink or radio-opaque. The dyes distributed widely but exclusively in the lengthened segment. Based on these results, we conclude that direct delivery of rhFGF-2 into the lengthened segment can shorten the consolidation phase of limb lengthening and the method is applicable to the clinical treatment.

Continuous infusion of insulin-like growth factor-I into the epiphysis of the tibia.

We have developed a method to promote longitudinal bone growth at the level of a specific growth-plate (GP) in young rabbits. Insulin-like growth factor-I (IGF-I) was continuously infused by means of an osmotic pump into the bone marrow cavity of the proximal epiphysis of the tibia. Radiological measurement showed a 2-mm overgrowth of the tibia after 4 weeks of treatment, while histological analysis demonstrated a 15% increase in the thickness of the selected GP. The local infusion of IGF-I increased the numbers of both proliferative and hypertrophic chondrocytes and promoted hyperplasia of bony trabeculae within the epiphysis. The distribution of material infused locally into the epiphysis was simulated by the infusion of Indian ink using the same methodology (osmotic pump) as that for IGF-I. Most of the dye remained within the bone marrow cavity of the epiphysis, but a portion infiltrated into the GP, reaching the deep layer of the physeal chondrocytes and primary spongiosa of the metaphysis. These results suggest that the method reported here is a valid one for delivering cytokines or growth factors to the selected GP and for controlling the growth and differentiation of physeal chondrocytes.

Unilateral chronic insufficiency of anterior cruciate ligament decreases bone mineral content and lean mass of the injured lower extremity.

We studied the effects of unilateral chronic anterior cruciate ligament (ACL) injury on bone size, bone mineral content (BMC), bone mineral density (BMD), soft tissue composition and muscle strength of the injured lower extremity in Japanese 21 men and 12 women aged 15 to 39 years. Bone area, BMD, BMC, lean mass and fat mass of lower extremity were measured using dual energy X-ray absorptiometry. The isometric and isokinetic muscle strength was assessed by an isokinetic machine.BMC, lean mass, circumference of the thigh and circumference of the lower leg of the injured lower extremity were significantly smaller than those of the intact lower extremity (p=0.0002, p<0.0001, p<0.0001, p=0.0131). In contrast, fat mass and %Fat of the injured lower extremity was significantly greater than that of the intact lower extremity (p=0.0301, p<0.0001). Bone area and BMD did not produce significant difference. These findings suggest that chronic insufficiency of ACL decreases BMC and lean mass of the injured lower extremity.

Differences of therapeutic effects on regional bone mineral density and markers of bone mineral metabolism between alendronate and alfacalcidol in Japanese osteoporotic women.

We studied the differences of therapeutic effects on regional bone mineral density (BMD) and markers of bone mineral metabolism between alendronate and alfacalcidol in Japanese osteoporotic women. Ninety-two Japanese women suffering from primary osteoporosis without osteoporotic fractures, aged 55 to 81 years, were divided into two groups: women treated orally with alendronate for one-year (5mg/day) (alendronate group, n=35) and women treated orally with alfacalcidol for one year (0.5 microg/day) (alfacalcidol group, n=57). The mean BMD of the 2nd to 4th lumbar vertebrae (L2-4BMD) and regional BMD were measured using dual energy X-ray absorptiometry. In the alendronate group, the percentage changes of L2-4BMD, lumbar spine BMD, thoracic spine BMD, pelvis BMD in the alendronate group were 106.3+/-4.6%, 104.2+/-6.6%, 107.1+/-10.4%, 107.1+/-10.5%, respectively. The percentage changes of L2-4BMD and regional BMD except for head BMD in the alendronate group were significantly greater than those in the alfacalcidol group. In the alfacalcidol group, L2-4BMD, thoracic spine BMD and lumbar spine BMD were maintained at respective pretreatment levels, whereas other regional BMD were decreased. Both serum bone-specific alkaline phosphatase and urinary type I collagen cross-linked N-telopeptide of the alendronate group were decreased, whereas these markers of bone mineral metabolism of alfacalcidol group were increased compared with the respective pre-treatment levels. The results suggest that one-year treatment with alendronate increased L2-4BMD, lumbar spine BMD, thoracic spine BMD and pelvis BMD, and that markers of both bone formation and bone resorption were decreased following one-year treatment with alendronate.

Bisphosphonate modulates morphological and mechanical properties in distraction osteogenesis through inhibition of bone resorption.

Despite the general clinical acceptance of distraction osteogenesis and much attention to bone formation in this method, little is recognized about activated bone resorption in the regenerated bone. The purpose of this study was to demonstrate the simultaneously activated bone resorption with activated bone formation and to investigate the role and efficacy of bisphosphonate in distraction osteogenesis. Left tibiae of 54 immature rabbits were lengthened for 3 weeks at a rate of 0.7 mm/day after a 1-week lag. Regenerated bone was quantitatively investigated by radiographic bone density, bone histomorphometry, and three-point bending testing. Animals received either vehicle or nitrogen-containing bisphosphonate (N-BP), YM529/ONO5920 at doses of 0.4 mg/kg/w or 0.004 mg/kg/w for 6 weeks. Regenerated bone of the vehicle group showed a radiologically characteristic zone structure containing the osteopenic zones adjacent to the sclerotic zones. The regenerated bone of the 0.4-mg/kg/w group showed no osteopenic zones during the course and eventually became homogeneously radiodense. The bone volume corresponding to the osteopenic zone of this group was 5.6-fold greater compared with that of the vehicle group. The lengthened bone strength of this group was 3.3-fold greater in ultimate force than that of the vehicle group and equivalent to the contralateral tibia. The 0.004-mg/kg/w group had no substantial differences compared with the vehicle group, despite radiological enhancement of the mineralized front as well as somewhat delayed bone resorption. These results demonstrate that not only bone formation but also bone resorption is highly activated in the regenerated bone, implying high bone turnover. Sufficient N-BP caused a notable modulation in morphological properties of the regenerated bone through inhibition of highly activated bone resorption and eventually increased mechanical properties.

Biophysic evaluation of bone quality-application of Fourier transform infrared spectroscopy and phosphorus-31 solid-state nuclear magnetic resonance spectroscopy.

In this review, we focus on findings obtained with biophysic techniques, Fourier transformed infrared (FTIR) spectroscopy and phosphorus-31 solid-state nuclear magnetic resonance (31P solid-state NMR) spectroscopy, which may allow us to evaluate bone quality and to predict bone strength. FTIR measures the absorption energy that produces an increase in the vibrational or rotational energy of atoms or groups of atoms within the molecule. FTIR spectroscopy allows us to examine the relative amount of minerals and matrix content and the arrangement of apatite and organic matrix. FTIR spectroscopy should become an important tool, because the relative amount of minerals and the arrangement of apatite and organic matrix could be a measure for evaluating bone quality. 31P solid-state NMR spectroscopy is useful for evaluating the quality of bone and predicting bone strength by calculating the spine-lattice relaxation time (T1) of bone. 31P solid-state NMR imaging can be used to measure quantitatively the mass of hydroxyapatite. The T1 relaxation time of both bone and deficient hydroxyapatite was much longer than that of pure hydroxyapatite. T1 relaxation time is one of the promising indices of bone quality.