Intermittent parathyroid hormone (1-34) treatment increases callus formation and mechanical strength of healing rat fractures

Teriparatide Therapy as an Adjuvant for Tissue Engineering and Integration of Biomaterials

Critically sized large bone defects commonly result from trauma, radical tumor resections or infections. Currently, massive allografting remain as the clinical standard to treat these critical defects. Unfortunately, allograft healing is limited by the lack of osteogenesis and bio-integration of the graft to the host bone. Based on its widely studied anabolic effects on the bone, we have proposed that teriparatide [recombinant parathyroid hormone (PTH(1-34))] could be an effective adjuvant for massive allograft healing. In support of this theory, here we review studies that have demonstrated that intermittent PTH(1-34) treatment enhances and accelerates the skeletal repair process via a number of mechanisms including: effects on mesenchymal stem cells (MSC), angiogenesis, chondrogenesis, bone formation and remodeling. We also review the current literature on the effects of PTH(1-34) therapy on bone healing, and discuss this drug's long term potential as an adjuvant for endogenous tissue engineering.

Systemic administration of pharmacological agents and bone repair: what can we expect

Pharmacologic agents that modulate bone formation and bone remodelling are in broad use and development for the treatment of osteoporosis and other disorders of bone fragility. There is significant interest into the effect these agents may have on bone repair and fracture healing and whether these agents may be beneficial or detrimental to bone repair. Bisphosphonates delay callus remodelling, but increased callus volume seen during endochondral bone repair with bisphosphonate use allows for equivalent biomechanical properties for the fractured bone. Teripartide stimulates bone formation and in bone repair appears to have the potential to accelerate fracture callus formation and remodelling, potentially accelerating fracture healing. Animal models of fracture healing have demonstrated accelerated healing with larger callus volume, more rapid remodelling to mature bone, and improved biomechanical properties of the fractured bone. Clinical data with teriparatide has shown mixed results for its ability to stimulate fracture healing. Wnt signalling is one of the major pathways through which cartilage and bone formation is regulated during development. This same pathway has been identified as one of the ways that teriparatide stimulates bone formation. Antibodies to downstream proteins in this pathway, Dkk-1 and sclerostin, show significant promise of accelerating even normal fracture healing in preclinical animal models.

Short-term teriparatide delivery and osseointegration: a clinical feasibility study

Teriparatide is an anabolic osteoporosis therapeutic agent that can improve healing after fractures and periodontal surgeries. Clinical studies investigating the effects of teriparatide on the osseointegration of titanium implants have not been performed. We conducted an open-label randomized controlled feasibility study and included 24 individuals with edentulous lower jaws. The participants received 2 study implants in the mandible during interforaminal dental implant surgery. They were randomly assigned to receive either 20 µg of teriparatide once daily for 28 days or no treatment. Study implants were retrieved from 23 participants after 9 weeks and were subjected to histomorphometric analyses. Endpoints were new bone-volume-per-tissue-volume (NBV/TV) and new bone-to-implant-contact (NBIC). We report here that median values of NBV/TV in the control and the teriparatide groups were 15.4% vs. 17.6% in the periosteal compartment, 11.3% vs. 16.5% in the cortical compartment, and 7.3% vs. 12.0% in the medullary compartment, respectively. NBIC median values in the control and the teriparatide groups were 3.3% vs. 4.1% in the periosteal compartment, 5.0% vs. 4.4% in the cortical compartment, and 0.3% vs. 1.4% in the medullary compartment, respectively. The results provide the first histological data on the osseointegration of titanium study implants in individuals treated with teriparatide. ClinicalTrials.gov number, NCT00089674.

Parathyroid hormone treatment increases fixation of orthopedic implants with gap healing: a biomechanical and histomorphometric canine study of porous coated titanium alloy implants in cancellous bone

Parathyroid hormone (PTH) administered intermittently is a bone-building peptide. In joint replacements, implants are unavoidably surrounded by gaps despite meticulous surgical technique and osseointegration is challenging. We examined the effect of human PTH(1-34) on implant fixation in an experimental gap model. We inserted cylindrical (10 × 6 mm) porous coated titanium alloy implants in a concentric 1-mm gap in normal cancellous bone of proximal tibia in 20 canines. Animals were randomized to treatment with PTH(1-34) 5 μg/kg daily. After 4 weeks, fixation was evaluated by histomorphometry and push-out test. Bone volume was increased significantly in the gap. In the outer gap (500 μm), the bone volume fraction median (interquartile range) was 27% (20-37%) for PTH and 10% (6-14%) for control. In the inner gap, the bone volume fraction was 33% (26-36%) for PTH and 13% (11-18%) for control. At the implant interface, the bone fraction improved with 16% (11-20%) for PTH and 10% (7-12%) (P = 0.07) for control. Mechanical implant fixation was improved for implants exposed to PTH. For PTH, median (interquartile range) shear stiffness was significantly higher (PTH 17.4 [12.7-39.7] MPa/mm and control 8.8 [3.3-12.4] MPa/mm) (P < 0.05). Energy absorption was significantly enhanced for PTH (PTH 781 [595-1,198.5] J/m(2) and control 470 [189-596] J/m(2)). Increased shear strength was observed but was not significant (PTH 3.0 [2.6-4.9] and control 2.0 [0.9-3.0] MPa) (P = 0.08). Results show that PTH has a positive effect on implant fixation in regions where gaps exist in the surrounding bone. With further studies, PTH may potentially be used clinically to enhance tissue integration in these challenging environments.

Preparation and evaluation of parathyroid hormone incorporated CaP coating via a biomimetic method

Parathyroid hormone (PTH) is a potent bone growth stimulator used for osteoporosis treatment. However, the inconvenience of daily administration and side effect of systemic exposure severely limit its use in clinical applications. Local, controlled delivery is a promising approach which can maintain therapeutic concentration locally for a long period. In this study, PTH was incorporated into a biomimetic calcium phosphate (CaP) coating via a coprecipitation process in a modified simulated body fluid (m-SBF). It was found that PTH was successfully incorporated into biomimetic CaP coating on titanium surface with a high incorporation efficiency. The incorporation of PTH into coatings had significantly changed the coating morphology, but the composition of the coating remained unchanged. Localized release of PTH had occurred in vitro, and was accompanied with partial dissolution of CaP coatings. Cell culture study demonstrated that the PTH released from CaP coatings fully retained its bioactivity. It had improved substantially MC3T3-E1 cell proliferation but slightly delayed the expression of alkaline phosphatase (ALP) of the cells. In summary, our results have shown that CaP coatings incorporated with PTH may be a promising approach for osteoporosis and other bone-related disease treatment in the future.

The combined effect of parathyroid hormone and bone graft on implant fixation

Impaction allograft is an established method of securing initial stability of an implant in arthroplasty. Subsequent bone integration can be prolonged, and the volume of allograft may not be maintained. Intermittent administration of parathyroid hormone has an anabolic effect on bone and may therefore improve integration of an implant. Using a canine implant model we tested the hypothesis that administration of parathyroid hormone may improve osseointegration of implants surrounded by bone graft. In 20 dogs a cylindrical porous-coated titanium alloy implant was inserted into normal cancellous bone in the proximal humerus and surrounded by a circumferential gap of 2.5 mm. Morsellised allograft was impacted around the implant. Half of the animals were given daily injections of human parathyroid hormone (1-34) 5 μg/kg for four weeks and half received control injections. The two groups were compared by mechanical testing and histomorphometry. We observed a significant increase in new bone formation within the bone graft in the parathyroid hormone group. There were no significant differences in the volume of allograft, bone-implant contact or in the mechanical parameters. These findings suggest that parathyroid hormone improves new bone formation in impacted morsellised allograft around an implant and retains the graft volume without significant resorption. Fixation of the implant was neither improved nor compromised at the final follow-up of four weeks.

Strontium is incorporated into the fracture callus but does not influence the mechanical strength of healing rat fractures

Strontium ranelate (SrR) is a new agent used in the treatment of osteoporosis and is suggested to reduce bone resorption and increase bone formation. We investigated whether SrR influences the macro- and nanomechnical properties of healing fractures in rats. A closed tibia fracture model was used to study fracture healing in rats after 3 and 8 weeks of healing. Two groups of rats were treated with SrR (900 mg/kg/day) mixed into the food, while two groups served as control animals. The healing fractures were investigated by three-point bending, dual energy X-ray absorptiometry, energy-dispersive X-ray spectroscopy (EDX), and nanoindentation. There was a 100-fold increase (P < 0.001) in serum Sr after 3 and 8 weeks of SrR treatment. The callus volume was significantly higher in the SrR-treated group than in control animals (P < 0.01) after 3 weeks of healing. This was accompanied by a significant increase in callus bone mineral content (P < 0.05). However, after 8 weeks of healing, no difference was found in either callus volume or bone mineral content. SrR did not influence maximum load or stiffness of the fractures after either 3 or 8 weeks of healing. EDX showed that Sr was incorporated into the callus; however, this did not influence the nanomechanical properties. In conclusion, SrR stimulates callus formation but has no effect on callus remodeling. Sr is incorporated into the newly formed callus tissue, but this has no deteriorating effect on the mechanical properties of rat tibial fractures at either the macroscopic or nanoscopic level after 3 or 8 weeks of healing.

Effects of zoledronic acid on healing of mandibular fractures: an experimental study in rabbits

PURPOSE

The purpose of the present study was to evaluate the effects of systemically administered zoledronic acid (ZA) on mandibular fracture healing in a rabbit model using radiodensitometric, biomechanical, histologic, and histomorphometric methods.

MATERIALS AND METHODS

A total of 36 skeletally mature male New Zealand white rabbits were used. The rabbits were randomly divided into 2 groups. A mandibular corpus fracture was created experimentally in all 36 rabbits. The experimental group was administered an intravenous, single dose of 0.1 mg/kg ZA, and the control group was administered only saline infusion during the procedure. All rabbits were sacrificed on the 21st postoperative day. Digital radiodensitometric analysis, a 3-point bending test, and histologic and histomorphometric examinations were performed on the harvested hemimandibles. The data were analyzed statistically.

RESULTS

Biomechanical testing data showed that ZA treatment resulted in a significant increase in the healed bone strength. This result was supported by the radiologic, histologic, and histomorphometric findings.

CONCLUSIONS

The results of the present study have revealed that systemic administration of ZA accelerates and improves the bone healing of mandibular fractures.

Intermittent parathyroid hormone fails to stimulate osseointegration in diabetic rats

OBJECTIVES

Diabetes is considered a risk factor in the osseointegration of dental implants, which suggests that these patients might benefit from anabolic therapies. Preclinical studies, including investigations by this research group, revealed that intermittent administration of parathyroid hormone (PTH) stimulates bone formation on the surface of titanium implants under physiological conditions. However, the anabolic effect of PTH on osseointegration under the hyperglycemic condition of diabetes is unknown.

METHODS

The ability of PTH to stimulate osseointegration was investigated in 40 female Wistar rats that were randomly divided into the following treatment groups: diabetes, diabetes plus PTH, control, and control plus PTH. Diabetes was induced by intraperitoneal injection of streptozotocin (45 mg/kg) at 1 week before implantation. Rats received PTH at a dose of 60 μg/kg or a vehicle by subcutaneous injection starting at the day of implant insertion into the tibia. Histomorphometric analysis was performed after 4 weeks.

RESULTS

The medullary peri-implant bone area significantly increased in rats receiving PTH in comparison with the control group (41±12% to 20±12%; P<0.01). Moreover, there was an increased bone-to-implant contact (BIC) area in animals treated with PTH (47±18% to 27±16%; P<0.05). In contrast, diabetic rats failed to benefit from the anabolic treatment. A similar peri-implant bone area occurred in the diabetes group, independent of treatment with PTH (13±9% to 15±6%; P>0.05). Moreover, PTH did not affect the BIC area under hyperglycemic conditions (16±12% to 16±8%; P>0.05). No significant changes were observed in the cortical compartment of all groups.

CONCLUSION

These results demonstrate that the metabolic characteristics of the diabetic rats produced a condition that was unable to respond to PTH treatment. These findings led us to hypothesize that metabolic control of diabetes might be a critical determinant when diabetic patients are undergoing anabolic therapy to enhance osseointegration.

Osteoporosis update from the 2010 santa fe bone symposium

The 11th Santa Fe Bone Symposium was held in Santa Fe, NM, USA, on August 6-7, 2010. This annual event addresses clinically relevant advances in the fields of osteoporosis and metabolic bone disease. The venue includes plenary presentations by internationally recognized experts, oral presentations of abstracts, and interactive panel discussions of challenging cases and controversial issues. Attendees are active participants throughout the symposium program. Topics for the 2010 symposium included potential applications of novel technologies for the assessment of skeletal health for research and clinical practice; new and emerging treatments for osteoporosis; appropriate use of pharmacological agents to prevent osteoporosis; controversies with bisphosphonate therapy; practical applications of the World Health Organization fracture risk assessment tool (FRAX; World Health Organization Collaborating Centre for Metabolic Bone Diseases, University of Sheffield, UK); insights into the use of osteoanabolic agents to enhance fracture healing; and challenges in laboratory testing in the assessment of factors contributing to skeletal fragility. Concurrent sessions focused on critical thinking for technologists in the acquisition and analysis of data with dual-energy X-ray absorptiometry. The key messages from each presentation, including the best available medical evidence and potential current and future clinical applications, are provided here.

Management of osteoporosis in patients hospitalized for hip fractures

Hip fracture is associated with high morbidity, mortality, and economic burden worldwide. It is also a major risk factor for a subsequent fracture. A literature search on the management of osteoporosis in patients with hip fracture was performed on the Medline database. Only one clinical drug trial was conducted in patients with a recent hip fracture. Further studies that specifically address post-fracture management of hip fracture are needed. The efficacy of anti-osteoporosis medication in older individuals and those at high risk of fall is reviewed in this paper. Adequate nutrition is vital for bone health and to prevent falls, especially in malnourished patients. Protein, calcium, and vitamin D supplementation is associated with increased hip BMD and a reduction in falls. Fall prevention, exercise, and balance training incorporated in a comprehensive rehabilitation program are essential to improve functional disability and survival. Exclusion of secondary causes of osteoporosis and treatment of coexistent medical conditions are also vital. Such a multidisciplinary team approach to the management of hip fracture patients is associated with a better clinical outcome. Although hip fracture is the most serious of all fractures, osteoporosis management should be prioritized to prevent deterioration of health and occurrence of further fracture.

Intermittent weekly administration of human parathyroid hormone (1-34) improves bone-hydroxyapatite block bonding in ovariectomized rats

Hydroxyapatite (HA) blocks have been widely used for the reconstruction of bone defects and as a bone substitute. Bone-implant bonding depends on both implant-related factors and patient variables. Intermittent human parathyroid hormone (h-PTH) has a strong anabolic effect on bone formation. The purpose of the present study is to evaluate whether intermittent h-PTH administration enhances bone-HA block bonding in normal versus ovariectomized (OVX) rats. Cancellous bone osteotomy and HA-block implantation were performed on the proximal left tibia in both OVX and sham-operated 7-month-old female Sprague-Dawley rats. Newly formed cancellous bone around the HA block and bone-HA block bonding were evaluated by bone histomorphometry at 8 weeks after the administration of h-PTH (100 μg/kg/week) or its vehicle. The administration of h-PTH significantly increased cancellous bone volume by stimulating bone formation in OVX rats (p < 0.01). Although bone-HA block bonding was significantly decreased in OVX rats compared to that of sham-operated rats (p < 0.01), h-PTH improved the bone-HA block bonding in OVX rats (p < 0.01). These results suggest that intermittent h-PTH treatment may improve bone-HA bonding in osteoporosis by restoring cancellous bone volume and enhancing cancellous bone formation around the HA block.

Teriparatide therapy and beta-tricalcium phosphate enhance scaffold reconstruction of mouse femoral defects

To investigate the efficacy of endocrine parathyroid hormone treatment on tissue-engineered bone regeneration, massive femoral defects in C57Bl/6 mice were reconstructed with either 100:0 or 85:15 poly-lactic acid (PLA)/beta-tricalcium phosphate (β-TCP) scaffolds (hereafter PLA or PLA/βTCP, respectively), which were fabricated with low porosity (<30%) to improve their structural rigidity. Experimental mice were treated starting at 1 week postop with daily subcutaneous injections of 40 μg/kg teriparatide until sacrifice at 9 weeks, whereas control mice underwent the same procedure but were injected with sterile saline. Bone regeneration was assessed longitudinally using planar X-ray and quantitative microcomputed tomography, and the reconstructed femurs were evaluated at 9 weeks either histologically or biomechanically to determine their torsional strength and rigidity. Teriparatide treatment increased bone volume and bone mineral content significantly at 6 weeks and led to enhanced trabeculated bone callus formation that appeared to surround and integrate with the scaffold, thereby establishing union by bridging bone regeneration across the segmental defect in 30% of the reconstructed femurs, regardless of the scaffold type. However, the bone volume and mineral content in the PLA reconstructed femurs treated with teriparatide was reduced at 9 weeks to control levels, but remained significantly increased in the PLA/βTCP scaffolds. Further, bridged teriparatide-treated femurs demonstrated a prototypical brittle bone torsion behavior, and were significantly stronger and stiffer than control specimens or treated specimens that failed to form bridging bone union. Taken together, these observations suggest that intermittent, systemic parathyroid hormone treatment can enhance bone regeneration in scaffold-reconstructed femoral defects, which can be further enhanced by mineralized (βTCP) particles within the scaffold.

Glucocorticoid attenuates the anabolic effects of parathyroid hormone on fracture repair

Long-term use of glucocorticoid (GC) not only reduces bone mass and strength, which leads to a greater risk of fracture, but also hinders fracture repair. In this study, we produced open fractures in GC-treated mice and investigated the effects of human parathyroid hormone 1-34 (hPTH) on fracture repair. Swiss-Webster mice were randomly divided into five groups. Three groups of GC-treated mice were given prednisolone, which was slowly released from subcutaneously implanted pellets at the rate of 1.4 mg/kg/day. Placebo pellets were implanted into the animals in two placebo groups. Three weeks later, osteotomies at the midshaft femora were performed and intramedullary pins were inserted to stabilize the fracture site under general anesthesia. Following fracture surgery, three GC groups were treated subcutaneously with vehicle, PTH at a low dose (40 ug/kg/day), and PTH at a high dose (80 ug/kg/day), respectively. Two placebo groups were given vehicle and PTH at a dose of 40 ug/kg/day, respectively. Radiographs, dual-energy X-ray absorptiometry, and mechanical testing (four-point bending) were used to evaluate fracture repair at 4 weeks after fracture surgery. Callus development, endochondral ossification, and recovery of mechanical strength at the fracture sites in GC animals treated with vehicle were significantly suppressed compared to placebo animals. Normally, PTH accelerates fracture repair. In GC-treated mice, PTH fails to improve endochondral ossification and mechanical properties compared to vehicle treatment, suggesting that the anabolic effect of PTH on fracture healing can be attenuated by GC administration in mice.

Parathyroid hormone and bone healing

Fracture healing is a complex process, and a significant number of fractures are complicated by impaired healing and non-union. Impaired healing is prevalent in certain risk groups, such as the elderly, osteoporotics, people with malnutrition, and women after menopause. Currently, no pharmacological treatments are available. There is therefore an unmet need for medications that can stimulate bone healing. Parathyroid hormone (PTH) is the first bone anabolic drug approved for the treatment of osteoporosis, and intriguingly a number of animal studies suggest that PTH could be beneficial in the treatment of fractures and could thus be a potentially new treatment option for induction of fracture healing in humans. Furthermore, fractures in animals with experimental conditions of impaired healing such as aging, estrogen withdrawal, and malnutrition can heal in an expedited manner after PTH treatment. Interestingly, fractures occurring at both cancellous and cortical sites can be treated successfully, indicating that both osteoporotic and nonosteoporotic fractures can be the target of PTH-induced healing. Finally, the data suggest that PTH partly prevents the delay in fracture healing caused by aging. Recently, the first randomized, controlled clinical trial investigating the effect of PTH on fracture healing was published, indicating a possible clinical benefit of PTH treatment in inducing fracture healing. The aim of this article is therefore to review the evidence for the potential of PTH in bone healing, including the underlying mechanisms for this, and to provide recommendations for the clinical testing and use of PTH in the treatment of impaired fracture healing in humans.

Parathyroid hormone: is there a role in fracture healing?

Parathyroid hormone is a well-known regulator of calcium metabolism in the body. It binds to osteoblasts and assists in the regulation of bone turnover. Changes in parathyroid hormone levels have been documented in pathologic states such as osteoporosis, and fluxes are also noted during healing of fractures. Because fracture healing requires time and is sometimes unreliable, a search for fracture-healing adjuvants that accelerate the healing rate and improve reliability of healing is compelling. Parathyroid hormone, as a systemic mediator of calcium and bone metabolism, is a good candidate. Much research has been accomplished in animal models examining the role of parathyroid hormone in fracture healing. Although further research is required, especially in human fracture patients, early indicators are that parathyroid hormone may play a role in accelerating fracture healing in healthy patients and in reducing rates of fracture nonunion in compromised patients or tissue beds.

Intermittent PTH(1-34) does not increase union rates in open rat femoral fractures and exhibits attenuated anabolic effects compared to closed fractures

Intermittent Parathyroid Hormone (PTH)((1-34)) has an established place in osteoporosis treatment, but also shows promising results in models of bone repair. Previous studies have been dominated by closed fracture models, where union is certain. One of the major clinical needs for anabolic therapies is the treatment of open and high energy fractures at risk of non-union. In the present study we therefore compared PTH((1-34)) treatment in models of both open and closed fractures. 108 male Wistar rats were randomly assigned to undergo standardized closed fractures or open osteotomies with periosteal stripping. 27 rats in each group were treated s.c. with PTH((1-34)) at a dose of 50 mug/kg 5 days a week, the other 27 receiving saline. Specimens were harvested at 6 weeks for mechanical testing (n=17) or histological analysis (n=10). In closed fractures, union by any definition was 100% in both PTH((1-34)) and saline groups at 6 weeks. In open fractures, the union rate was significantly lower (p<0.05), regardless of treatment. In open fractures the mechanically defined union rate was 10/16 (63%) in saline and 11/17 (65%) in PTH((1-34)) treated fractures. By histology, the union rate was 3/9 (33%) with saline and 5/10 (50%) with PTH((1-34)). Radiological union was seen in 13/25 (52%) for saline and 15/26 (58%) with PTH((1-34)). Open fractures were associated with decreases in bone mineral content (BMC) and volumetric bone mineral density (vBMD) on quantitative computerized tomography (QCT) analysis compared to closed fractures. PTH((1-34)) treatment in both models led to significant increases in callus BMC and volume as well as trabecular bone volume/total volume (BV/TV), as assessed histologically (p<0.01). In closed fractures, PTH((1-34)) had a robust effect on callus size and strength, with a 60% increase in peak torque (p<0.05). In the open fractures that united and could be tested, PTH((1-34)) treatment also increased peak torque by 49% compared to saline (p<0.05). In conclusion, intermittent PTH((1-34)) produced significant increases in callus size and strength in closed fractures, but failed to increase the rate of union in an open fracture model. In the open fractures that did unite, a muted response to PTH was seen compared to closed fractures. Further research is required to determine if PTH((1-34)) is an appropriate anabolic treatment for open fractures.

Orthopedic uses of teriparatide

Teriparatide is a drug currently approved for treating patients with osteoporosis who are at high risk for future fracture. In the treatment of osteoporosis, teriparatide works as an anabolic agent stimulating bone formation throughout the skeleton by principally enhancing osteoblast-derived bone formation relative to osteoclast-derived bone resorption. The net effect is increased bone mass. For patients with a fracture, a similar process of increased bone formation is required transiently at the fracture site for repair. Teriparatide has been investigated in animal models and in patients as a potential agent to enhance fracture repair. In addition, evidence that teriparatide enhances chondrogenesis has generated interest in using the agent for articular cartilage repair. Research is currently underway to understand the effects teriparatide may have on mesenchymal stem cells, and on other effects that have been reported anecdotally in patients using the drug for osteoporosis care, including the healing of fracture nonunions and a decreased incidence of back pain. We review the current animal and human reports available on the uses of teriparatide in musculoskeletal diseases beyond osteoporosis.

Effect of intermittent systemic administration of recombinant parathyroid hormone (1-34) on mandibular fracture healing in rats

PURPOSE

To establish a rat mandibular fracture model and investigate the short- and long-term effects of recombinant parathyroid hormone (PTH 1-34) on mandibular fracture healing in rats.

MATERIALS AND METHODS

A controlled unilateral mandibular fracture was created surgically in 29 male Sprague-Dawley rats and then stabilized using an external fixation device. The rats were divided into 2 groups: 1 group received daily subcutaneous injections of 10 microg/kg of PTH(1-34) and 1 group served as the vehicle control. The rats were killed on postoperative days 7 and 21, and radiographic densitometry and histologic evaluation of new bone formation were performed.

RESULTS

A novel unilateral mandibular fracture model was established that has significant differences from previously published models, both in the location of the osteotomy site and in the rigid external stabilization device. The PTH(1-34) treated rats showed a statistically significant difference (P < .05) in callous formation compared with the control animals. Radiographic densitometry evaluation of the injury site revealed an increase in bone density, apparent at day 7 in the experimental group. Visual inspection of the histologic sections stained with Masson's trichrome blue showed an apparent increase in new bone formation at 21 days in the PTH-treated group compared with the control group.

CONCLUSIONS

Intermittent systemic administration of PTH(1-34) might enhance the healing of mandibular fractures in the early phase (7-day period). Long-term administration (21-day period) showed no statistically significant differences between the control and experimental group by radiographic densitometry.

Evidence for anti-osteoporosis therapy in acute fracture situations--recommendations of a multidisciplinary workshop of the International Society for Fracture Repair

The International Society for Fracture Repair convened a multidisciplinary workshop to assess the current evidence around the interaction between anti-osteoporosis drugs and the healing of incident fractures, with a view to making recommendations for clinical practice. The consensus was that there is no evidence-based reason to withhold anti-resorptive therapy while a fracture heals, whether or not the patient was taking such therapy when the fracture occurred. The workshop also considered existing models of service provision for secondary prevention and concluded that the essential ingredient for reliable delivery is the inclusion of a dedicated coordinator role. Several unresolved issues were defined as subjects for further research, including the question of whether continuous long-term administration of anti-resorptives may impair bone quality. The rapidly changing area requires re-assessment of drugs and their interaction with fracture healing in the near future.

Teriparatide for acceleration of fracture repair in humans: a prospective, randomized, double-blind study of 102 postmenopausal women with distal radial fractures

Animal experiments show a dramatic improvement in skeletal repair by teriparatide. We tested the hypothesis that recombinant teriparatide, at the 20 microg dose normally used for osteoporosis treatment or higher, would accelerate fracture repair in humans. Postmenopausal women (45 to 85 years of age) who had sustained a dorsally angulated distal radial fracture in need of closed reduction but no surgery were randomly assigned to 8 weeks of once-daily injections of placebo (n = 34) or teriparatide 20 microg (n = 34) or teriparatide 40 microg (n = 34) within 10 days of fracture. Hypotheses were tested sequentially, beginning with the teriparatide 40 microg versus placebo comparison, using a gatekeeping strategy. The estimated median time from fracture to first radiographic evidence of complete cortical bridging in three of four cortices was 9.1, 7.4, and 8.8 weeks for placebo and teriparatide 20 microg and 40 microg, respectively (overall p = .015). There was no significant difference between the teriparatide 40 microg versus placebo groups (p = .523). In post hoc analyses, there was no significant difference between teriparatide 40 microg versus 20 microg (p = .053); however, the time to healing was shorter in teriparatide 20 microg than placebo (p = .006). The primary hypothesis that teriparatide 40 microg would shorten the time to cortical bridging was not supported. The shortened time to healing for teriparatide 20 microg compared with placebo still may suggest that fracture repair can be accelerated by teriparatide, but this result should be interpreted with caution and warrants further study.

Strontium ranelate enhances callus strength more than PTH 1-34 in an osteoporotic rat model of fracture healing

Treatment of an underlying disease is often initiated after the occurrence of an osteoporotic fracture. Our aim was to investigate whether teriparatide (PTH 1-34) and strontium ranelate affect fracture healing in ovariectomized (OVX) rats when provided for the first time after the occurrence of an osteoporotic fracture. We combined the model of an OVX rat with a closed diaphyseal fracture. Sixty Sprague Dawley rats were randomly assigned to four groups. Fracture healing in OVX rats after treatment with pharmacological doses of strontium ranelate and PTH 1-34 was compared with OVX and sham-treated control groups. After 28 days, the femur was excised and scanned by micro computed tomography and the callus evaluated, after which biomechanical torsional testing was performed and torque and toughness until reaching the yield point were analyzed. Only treatment with strontium ranelate led to a significant increase in callus resistance compared to the OVX control rats, whereas both PTH 1-34 and strontium ranelate increased the bone volume/tissue volume ratio of the callus. The PTH 1-34-increased trabecular bone volume within the callus was even higher compared to sham. As for the callus tissue volume, the increase induced by strontium ranelate was significant, contrary to the changes induced by PTH. Callus in strontium ranelate-treated animals is more resistant to torsion compared with OVX control rats. To our knowledge, this is the first report of the enhancement of fracture healing by strontium ranelate. Because both treatments enhance bone and tissue volume within the callus, there may be a qualitative difference between the calluses of PTH 1-34- and strontium ranelate-treated OVX rats. The superior results obtained with strontium ranelate compared to PTH in terms of callus resistance could be the consequence of a better quality of the new bone formed within the callus.

Parathyroid hormone PTH(1-34) increases the volume, mineral content, and mechanical properties of regenerated mineralizing tissue after distraction osteogenesis in rabbits

BACKGROUND AND PURPOSE

Parathyroid hormone (PTH) has attracted considerable interest as a bone anabolic agent. Recently, it has been suggested that PTH can also enhance bone repair after fracture and distraction osteogenesis. We analyzed bone density and strength of the newly regenerated mineralized tissue after intermittent treatment with PTH in rabbits, which undergo Haversian bone remodeling similar to that in humans.

METHODS

72 New Zealand White rabbits underwent tibial mid-diaphyseal osteotomy and the callus was distracted 1 mm/day for 10 days. The rabbits were divided into 3 groups, which received injections of PTH 25 microg/kg/day for 30 days, saline for 10 days and PTH 25 microg/kg/day for 20 days, or saline for 30 days. At the end of the study, the rabbits were killed and the bone density was evaluated with DEXA. The mechanical bone strength was determined by use of a 3-point bending test.

RESULTS

In the 2 PTH-treated groups the regenerate callus ultimate load was 33% and 30% higher, absorbed energy was 100% and 65% higher, BMC was 61% and 60% higher, and callus tissue volume was 179% and 197% higher than for the control group.

INTERPRETATION

We found that treatment with PTH during distraction osteogenesis resulted in substantially higher mineralized tissue volume, mineral content, and bending strength. This suggests that treatment with PTH may benefit new bone formation during distraction osteogenesis and could form a basis for clinical application of this therapy in humans.

Is there a role for bone morphogenetic proteins in osteoporotic fractures?

The central role of bone morphogenetic proteins (BMPs) in the remodelling process of the human skeleton has been identified in numerous experimental and clinical studies. BMPs appear to be key agents in the osteoblastic differentiation of mesenchymal stem cells, and more recent evidence implicates them with the cells of the osteoclastic lineage. BMP-2, BMP-4, BMP-6 and BMP-7 have been studied in the context of osteoporosis and have been associated with its pathophysiological pathways. The theoretical advantages of local or systemic treatment of osteoporotic fractures with BMPs include the potential of inducing a rapid increase in bone strength locally at the fractured area and systemically in the entire skeleton, as well as accelerating the bone-healing period. Animal models of osteoporotic fractures suggested that the induction of new bone by local or systemic use of BMP-7 should be investigated as potential bone augmentation therapy to improve bone quality in symptomatic spinal osteoporosis. As our knowledge expands, new innovations may provide clinicians with advanced biologically-based therapies for the successful treatment of osteoporotic fractures.

Recent advances toward the clinical application of PTH (1-34) in fracture healing

PTH 1-34, an active form of parathyroid hormone, has been shown to enhance osteoblastic bone formation when administered as a daily subcutaneous injection. The effect of the intermittent administration of PTH (1-34) is an uncoupling of bone turnover with an increase in bone mass and density and decrease in risk of vertebral and nonvertebral fractures. While PTH (1-34) has been used clinically to increase bone mass and reduce fracture risk in postmenopausal women with osteoporosis, there is increasing evidence that PTH (1-34) may promote fracture healing. Animal studies have demonstrated accelerated callus formation with enhanced remodeling and biomechanical properties of the healing fracture. Given these effects, PTH (1-34) will likely be used clinically to enhance fracture union in poor healing situations such as osteoporosis and recalcitrant nonunions.

Modulation of the inflammatory response for enhanced bone tissue regeneration

Proinflammatory cytokines are infamous for their catabolic effects on tissues and joints in both inflammatory diseases and following the implantation of biomedical devices. However, recent studies indicate that many of these same molecules are critical for triggering tissue regeneration following injury. This review will discuss the role of inflammatory signals in regulating bone regeneration and the impact of both immunomodulatory and antiinflammatory pharmacologic agents on fracture healing, to demonstrate the importance of incorporating rational control of inflammation into the design of tissue engineering strategies.

Can we improve fixation and outcomes in the treatment of femoral neck fractures? The use of pharmaceuticals

Femoral neck fracture rates are on the rise with an estimated 500,000 occurring annually by 2040. Despite the mainstay of open reduction and internal fixation, nonunion rates of up to 33% have been reported for displaced femoral neck fractures. Recently, increasing attention has been focused upon the role of osteobiologics to stimulate fracture repair. This article looks at the role of these anabolic compounds and discusses their potential future roles in augmenting the treatment of this condition.

Survey of spine surgeons on attitudes regarding osteoporosis and osteomalacia screening and treatment for fractures, fusion surgery, and pseudoarthrosis

BACKGROUND CONTEXT

Osteoporosis and osteomalacia are significant risk factors for fracture and spine instrumentation failure. Low-energy fractures are becoming increasingly more common because of an increase in life expectancy and age of the population. Decreased bone density is an independent risk factor for instrumentation failure in spinal fusion operations.

PURPOSE

To assess the awareness and practice patterns of spine surgeons regarding metabolic bone disorders and osteoporosis with emphasis on fracture care and arthrodesis.

STUDY DESIGN/SETTING

Questionnaire study.

PATIENT SAMPLE

Spine surgeons attending the "Disorders of the Spine" conference (January 2007, Whistler, British Columbia, Canada).

OUTCOME MEASURES

Respondent reported frequencies of diagnostics, screening, and treatment methods for patients with low-energy spine fractures, pseudoarthrosis, and those undergoing spinal arthrodesis.

METHODS

A ten-question survey was administered to orthopedic surgeons and neurosurgeons who treated spine fractures and degenerative spine conditions in their practice. The survey was given to those who were attending a continuing medical education spinal disorders conference. The survey asked about treatment patterns with respect to osteoporosis and osteomalacia workup and treatment for patients with low-energy spine fractures, pseudoarthrosis, and those undergoing spinal arthrodesis.

RESULTS

Of the 133 surgeons to whom the questionnaire was distributed at this meeting, 114 questionnaires were returned that corresponds to a response rate of 86%. Twenty-one surveys were excluded because of incomplete biographical information, resulting in a total of 93 completed questionnaires that were available for analysis. When treating patients with low-energy spine fractures, 60% checked dual-energy X-ray absorptiometry (DEXA) and 39% checked metabolic laboratories (of those who did not order laboratories and DEXA about 63% refer for treatment). Before instrumented fusion, 44% of those queried checked DEXA and 12% checked metabolic laboratories (vitamin D, parathyroid hormone [PTH], and calcium [Ca]). Before noninstrumented fusion, 22% checked DEXA and 11% checked metabolic laboratories. Before addressing pseudoarthrosis, 19% checked DEXA and 20% checked metabolic laboratories.

CONCLUSIONS

Despite of the large number of elderly patients undergoing spine care and the high incidence of osteoporosis and/or osteomalacia in this population, a large portion of the spine surgeons who responded to the survey reported that they do not perform routine osteoporosis/osteomalacia workups. Of those who do perform workups, some commented that it will change their surgical plan or preoperative treatment. It appears that there is a need for increased awareness among spine specialists regarding osteoporosis screening and treatment. Osteoporosis practice patterns may also be affected with newly evolving government quality reporting regulations.

The influence of osteoporosis in femoral fracture healing time

AIM

In order to assess the effect of osteoporosis on healing time, the files of 165 patients with femoral shaft fractures that were treated in our institution with locked-reamed intramedullary nailing were retrospectively reviewed.

PATIENTS AND METHODS

Patients with open fractures, pathological fractures, revision surgery, severe brain injuries and prolonged ITU stay were excluded. In all patients the Singh-index score for osteoporosis and the canal bone ratio (CBR) were assigned. Sixty-six patients fulfilled the inclusion criteria. Patients were divided into two groups; group A (29 patients) consisted of patients over 65 years old with radiological evidence of osteoporosis and group B (37 patients) of patients between 18 and 40 years old with no signs of osteoporosis.

RESULTS

In all group A patients Singh score < or =4 and CBR>0.50 were assigned, suggesting the presence of osteoporosis, whereas all group B patients were assigned with Singh score > or =5 and CBR<0.48. Fractures of group A healed in 19.38+/-5.9 weeks (12-30) and in group B 16.19+/-5.07 weeks (10-28), P=0.02.

CONCLUSIONS

Fracture healing of nailed femoral diaphyseal fractures is significantly delayed in older osteoporotic patients. Further studies are required to clarify the exact impact of osteoporosis in the whole healing process.

Micro-CT analysis with multiple thresholds allows detection of bone formation and resorption during ultrasound-treated fracture healing

Multiple threshold algorithms applied to microcomputed tomography analysis were used to probe the effects of low-intensity pulsed ultrasound on fracture healing. Rat femurs were fractured in accordance with IACUC guidelines. Ultrasound treatment was administered daily to one femur; the contralateral bone was treated with a sham transducer. Each week for 3 weeks healing fractures were harvested and scanned by micro-CT. Remodeling activity was confirmed by evaluation of TRAP activity. Using thresholds of 331-700 and 225-330, area of cortical bone, and new bone formation, respectively, were identified, and by inference, regions of bone resorption. The increased sensitivity of this multithresholding procedure revealed that ultrasound treatment significantly increased the rate of fracture healing in vivo by activating both new bone formation and by increasing the removal of cortical bone in a time- and site-specific manner. At week 1, compared to the proximal side, there was a significant increase in new bone formation distal to the fracture site. Removal of the existing cortical bone followed the same pattern at week 2. Results of the study indicate that at sites of bone turnover, this multithresholding analytical technique can be used to provide quantitative information on bone formation, as well as resorption.

Longitudinal in vivo analysis of the region-specific efficacy of parathyroid hormone in a rat cortical defect model

PTH has been shown to enhance fracture repair; however, exactly when and where PTH acts in this process remains to be elucidated. Therefore, we conducted a longitudinal, region-specific analysis of bone regeneration in mature, osteopenic rats using a cortical defect model. Six-month-old rats were ovariectomized, and allowed to lose bone for 2 months, before being subjected to bilateral 2-mm circular defects in their femoral diaphyses. They were then treated for 5 wk with hPTH1-38 at doses of 0, 3, 10, or 30 microg/kg . d and scanned weekly by in vivo quantitative computed tomography. Quantitative computed tomography analyses showed temporal, dose-dependent increases in mineralization in the defects, intramedullary (IM) spaces, and whole diaphyses at the defect sites. Histomorphometry confirmed PTH stimulation of primarily woven bone in the defects and IM spaces, but not the periosteum. After necropsy, biomechanical testing identified an increase in strength at the highest PTH dose. Serum procollagen type I N-terminal propeptide concentration showed a transient increase due to drilling, but procollagen type I N-terminal propeptide also increased with PTH treatment, whereas tartrate-resistant acid phosphatase unexpectedly decreased. Analyses of lumber vertebra confirmed systemic efficacy of PTH at a nonfracture site. In summary, PTH dose dependently induced new bone formation within defects, at endocortical surfaces, and in IM spaces, resulting in faster and greater bone healing, as well as efficacy at other skeletal sites. The effects of PTH were kinetic, region specific, and most apparent at high doses that may not be entirely clinically relevant; therefore, clinical studies are necessary to clarify the therapeutic utility of PTH in bone healing.

Recombinant human parathyroid hormone (PTH 1-34) and low-intensity pulsed ultrasound have contrasting additive effects during fracture healing

Fracture healing is thought to be naturally optimized; however, recent evidence indicates that it may be manipulated to occur at a faster rate. This has implications for the duration of morbidity associated with bone injuries. Two interventions found to accelerate fracture healing processes are recombinant human parathyroid hormone [1-34] (PTH) and low-intensity pulsed ultrasound (LIPUS). This study aimed to investigate the individual and combined effects of PTH and LIPUS on fracture healing. Bilateral midshaft femur fractures were created in Sprague-Dawley rats, and the animals treated 7 days/week with PTH (10 microg/kg) or a vehicle solution. Each animal also had one fracture treated for 20 min/day with active-LIPUS (spatial-averaged, temporal-averaged intensity [I(SATA)]=100 mW/cm(2)) and the contralateral fracture treated with inactive-LIPUS (placebo). Femurs were harvested 35 days following injury to permit micro-computed tomography, mechanical property and histological assessments of the fracture calluses. There were no interactions between PTH and LIPUS indicating that their effects were additive rather than synergistic. These additive effects were contrasting with LIPUS primarily increasing total callus volume (TV) without influencing bone mineral content (BMC), and PTH having the opposite effect of increasing BMC without influencing TV. As a consequence of the effect of LIPUS on TV but not BMC, it decreased volumetric bone mineral density (vBMD) resulting in a less mature callus. The decreased maturity and persistence of cartilage at the fracture site when harvested offset any beneficial mechanical effects of the increased callus size with LIPUS. In contrast, the effect of PTH on callus BMC but not TV resulted in increased callus vBMD and a more mature callus. This resulted in PTH increasing fracture site mechanical strength and stiffness. These data suggest that PTH may have utility in the treatment of acute bone fractures, whereas LIPUS at an I(SATA) of 100 mW/cm(2) does not appear to be indicated in the management of closed, diaphyseal fractures.

Effect of alendronate and intermittent parathyroid hormone on implant fixation in ovariectomized rats

BACKGROUND

Intermittent administration of parathyroid hormone (PTH) leads to bone formation by increasing osteoblast numbers and activity levels. Animal studies have shown that intermittent PTH administration increases implant fixation in normal rats. The purpose of this study was to analyze the osseous incorporation of an implant in osteoporotic rats while treating them with intermittent PTH (1-34) or alendronate.

METHODS

A total of 36 ovariectomized (OVX) Wistar rats were randomized into three groups. Polymethylmethacrylate cement rods were implanted in one tibia in each rat. The three groups received daily PTH (60 mug/kg body weight [BW]), alendronate (200 mug/kg BW), or saline (0.5 ml/kg BW). A sham-ovariectomized group (n = 12) was treated with saline. After 2 weeks, the area around the implants was analyzed by histomorphometry for bone volume density (BVD) and implant bone contact. Bone mineral density (BMD) was evaluated by dual-energy X-ray absorptiometry.

RESULTS

The BVD was higher in the specimens treated with PTH than in the other groups. PTH improved the BVD, BMD, and implant bone contact. Alendronate doubled the implant bone contact compared to the OVX and sham groups but did not improve BVD or BMD.

CONCLUSIONS

These findings confirm that intermittent PTH enhances implant fixation in osteoporotic bone. The clinical significance of these findings is that application of intermittent PTH may be beneficial for early implant fixation in fractures, nonunions, and prosthetic replacements when bone density is decreased.

Micro-computed tomography assessment of fracture healing: relationships among callus structure, composition, and mechanical function

Non-invasive characterization of fracture callus structure and composition may facilitate development of surrogate measures of the regain of mechanical function. As such, quantitative computed tomography- (CT-) based analyses of fracture calluses could enable more reliable clinical assessments of bone healing. Although previous studies have used CT to quantify and predict fracture healing, it is unclear which of the many CT-derived metrics of callus structure and composition are the most predictive of callus mechanical properties. The goal of this study was to identify the changes in fracture callus structure and composition that occur over time and that are most closely related to the regain of mechanical function. Micro-computed tomography (microCT) imaging and torsion testing were performed on murine fracture calluses (n=188) at multiple post-fracture timepoints and under different experimental conditions that alter fracture healing. Total callus volume (TV), mineralized callus volume (BV), callus mineralized volume fraction (BV/TV), bone mineral content (BMC), tissue mineral density (TMD), standard deviation of mineral density (sigma(TMD)), effective polar moment of inertia (J(eff)), torsional strength, and torsional rigidity were quantified. Multivariate statistical analyses, including multivariate analysis of variance, principal components analysis, and stepwise regression were used to identify differences in callus structure and composition among experimental groups and to determine which of the microCT outcome measures were the strongest predictors of mechanical properties. Although calluses varied greatly in the absolute and relative amounts of mineralized tissue (BV, BMC, and BV/TV), differences among timepoints were most strongly associated with changes in tissue mineral density. Torsional strength and rigidity were dependent on mineral density as well as the amount of mineralized tissue: TMD, BV, and sigma(TMD) explained 62% of the variation in torsional strength (p<0.001); and TMD, BMC, BV/TV, and sigma(TMD) explained 70% of the variation in torsional rigidity (p<0.001). These results indicate that fracture callus mechanical properties can be predicted by several microCT-derived measures of callus structure and composition. These findings form the basis for developing non-invasive assessments of fracture healing and for identifying biological and biomechanical mechanisms that lead to impaired or enhanced healing.

Parathyroid hormone (1-34) augments spinal fusion, fusion mass volume, and fusion mass quality in a rabbit spinal fusion model

STUDY DESIGN

The posterolateral rabbit spinal fusion model was used to assess the effect of intermittent parathyroid hormone on spinal fusion outcomes.

OBJECTIVE

To test the hypothesis that intermittent parathyroid hormone (PTH) improves spinal fusion outcomes in the rabbit posterolateral spinal fusion model.

SUMMARY OF BACKGROUND DATA

Spinal fusion is the definitive management for spinal deformity or instability, yet despite current technology, 5% to 40% of lumbar fusions result in pseudarthrosis. Animal studies have demonstrated enhanced fracture healing with the use of PTH, but the effect of PTH on spinal fusion is poorly described.

METHODS

Forty-four male New Zealand white rabbits underwent bilateral posterolateral spine fusion (L5-L6 level). Twenty-two rabbits received daily subcutaneous injections of PTH (1-34) (10 microg/kg) and 22 received an injection of saline fluid. All were killed 6 weeks after surgery. L5-L6 vertebral segments were removed and analyzed with manual bending, faxitron radiography, microCT, and histomorphometry.

RESULTS

Manual bending identified fusion in 30% (control) versus 81% (PTH) animals (P < 0.001). A radiographic scoring system ("0" = no bone formation, "5" = full fusion) resulted in an average score of 3.36 (control) versus 4.51 (PTH) (P < 0.001). MicroCT analysis demonstrated a median mass of 3.5 cc (control) (range, 2.25-5.40 cc) versus 6.03 cc (PTH) (range, 4.34-10.58 cc) (P < 0.001). Histology showed a median percentage bone area of 14.3% (control) (n = 12) versus 29.9% (PTH) (n = 15) (P < 0.001). The median percentage cartilage was 2.7% (control) (n = 5) versus 26.6% (PTH) (n = 5) (P < 0.01). Osteoclast quantification revealed median values of 140.5 (control) (n = 6) and 345.0 (PTH) (n = 8) (P < 0.001) respectively, and the percentage of osteoblasts revealed a median value of 31.4% (control) (n = 6) versus 64.4% (PTH) (n = 8) (P < 0.001).

CONCLUSION

Intermittent PTH administration increased posterolateral fusion success in rabbits. Fusion bone mass and histologic determinants were also improved with PTH treatment. PTH has promise for use as an adjunctive agent to improve spinal fusion in clinical medicine.

Combined effects of recombinant human BMP-7 (rhBMP-7) and parathyroid hormone (1-34) in metaphyseal bone healing

Fracture healing involves multiple stages of repair and coordinated actions of multiple cell types. Consequently, it may be possible to enhance healing through treatment strategies that target more than one repair process or cell type. The goal of this study was to determine the combined effects of recombinant human bone morphogenetic protein 7 (rhBMP-7) and parathyroid hormone (PTH(1-34)) on metaphyseal bone healing. A wedge-shaped defect was created in the lateral aspect of the distal tibia in female New Zealand white rabbits (n=64) and was filled with tricalcium phosphate (TCP). Animals were assigned to four groups: 1) BMP-7 and PTH; 2) BMP-7; 3) PTH; and 4) control (TCP alone). In groups 1 and 2, 200 microg rhBMP-7 was incorporated into the TCP. Animals received daily subcutaneous injections of 10 microg/kg PTH(1-34) (groups 1 and 3) or saline (groups 2 and 4). Healing at 4 weeks was assessed using micro-computed tomography, histology, immunohistochemistry, and mechanical testing. Combined treatment with rhBMP-7 and PTH resulted in increased callus total volume (TV), mineralized volume (BV), average cross-sectional area, and bone mineral content (BMC) as compared to the control group (p<0.02). BV and BMC were also higher in the combined treatment group as compared to the BMP-7 group (p<0.02); however, tissue mineral density was highest in the BMP-7 group (p=0.002). New bone formation in the BMP-7 group was largely restricted to the defect site, while PTH promoted bone formation throughout the defect and surrounding regions. Combined treatment led to greater quantities of woven trabecular bone, increased trabecular thickness, decreased trabecular separation (p<0.04), and a trend towards increased numbers of osteoclasts (p=0.09). Combined treatment also resulted in increased torsional rigidity and compressive strength as compared to the control and BMP-7 groups (p<0.001). These results suggest that the improvements in mechanical function obtained with the combined treatment resulted from differing biological activities of rhBMP-7 and PTH. While the activities of rhBMP-7 appeared to be strictly anabolic, those of PTH appeared to work in the context of coupled remodeling. The combination of both agents led to greater bone volume as well as better microstructural organization and integration of this bone with the surrounding tissues.

Intermittent administration of human parathyroid hormone (1-34) increases new bone formation on the interface of hydroxyapatitecoated titanium rods implanted into ovariectomized rat femora

BACKGROUND

As hydroxyapatite (HA) has good osteoconductive properties, HA is used as coating material for the implants in cementless arthroplasty. However, its effect is not sufficient for osteoporotic bone. Parathyroid hormone (PTH) is known to have anabolic effects on bone formation. Intermittent administration of PTH increases both cancellous and cortical bone mass. The aim of this study was to confirm the effect of the fixation strength of HA-coated implants in the osteoporotic condition with a mechanical test and a bone histomorphometric method.

METHODS

Female Sprague-Dawley rats were used for this study. Four weeks after ovariectomy (OVX) or sham surgery, HA-coated titanium rods were inserted into the distal femoral canal (Sham+HA group and OVX+HA group). PTH was administered immediately after the implantation of the HAcoated rods (OVX+HA+P group). We measured the shear strength at the bone-implant interface by a push-out test and the newly formed bone volume on the implant (BV.Im) by bone histomorphometry at 2 and 4 weeks after implantation.

RESULTS

The bone-implant shear strength in the OVX+HA group was significantly lower than that in the Sham+HA group at 2 weeks after implantation of the rods. In the OVX+HA+P group, the strength was significantly higher than that in the other groups. Similarly, at 4 weeks, statistically significant differences were confirmed in the bone-implant shear strength among the Sham+HA group, the OVX+HA group, and the OVX+HA+P group. BV.Im in the OVX+HA group was significantly lower than that in the Sham+HA group at 2 weeks after implantation. BV.Im was significantly higher in the OVX+HA+P group than that in the OVX+HA group. However, there was no difference in BV.Im between the Sham+HA group and the OVX+HA+P group. At 4 weeks after implantation, BV.Im was significantly lower in the OVX+HA group than that in the other groups, but no difference was found between the Sham+HA group and the OVX+HA+P group.

CONCLUSIONS

Intermittent administration of PTH has an effect to increase new bone formation on the surface of HA-coated implants in the osteoporotic condition. This finding suggests that PTH administration is useful to improve the initial fixation of HA-coated implants even in osteoporotic patients.

Teriparatide (1-34 human PTH) regulation of osterix during fracture repair

Based on remarkable success of PTH as an anabolic drug for osteoporosis, case reports of off-label use of teriparatide (1-34 PTH) in patients with complicated fractures and non-unions are emerging. We investigated the mechanisms underlying PTH accelerated fracture repair. Bone marrow cells from 7 days 40 microg/kg of teriparatide treated or saline control mice were cultured and Osx and osteoblast phenotypic gene expression assessed by real-time RT-PCR in these cells. Fractured animals injected daily with either saline or 40 microg/kg of teriparatide for up to 21 days were X-rayed and histological assessment performed, as well as immunohistochemical analyses of the Osx expression in the fracture callus. Osx, Runx2 and osteoblast or chondrocyte phenotypic gene expression was also assessed in fracture calluses. Our data shows that Osx and Runx2 are up-regulated in marrow-derived MSCs isolated from mice systemically treated with teriparatide. Furthermore, these MSCs undergo accelerated osteoblast maturation compared to saline injected controls. Systemic teriparatide treatments also accelerated fracture healing in these mice concomitantly with increased Osx expression in the PTH treated fracture calluses compared to controls. Collectively, these data suggest a mechanism for teriparatide mediated fracture healing possibly via Osx induction in MSCs.

A perspective: engineering periosteum for structural bone graft healing

Autograft is superior to both allograft and synthetic bone graft in repair of large structural bone defect largely due to the presence of multipotent mesenchymal stem cells in periosteum. Recent studies have provided further evidence that activation, expansion and differentiation of the donor periosteal progenitor cells are essential for the initiation of osteogenesis and angiogenesis of donor bone graft healing. The formation of donor cell-derived periosteal callus enables efficient host-dependent graft repair and remodeling at the later stage of healing. Removal of periosteum from bone autograft markedly impairs healing whereas engraftment of multipotent mesenchymal stem cells on bone allograft improves healing and graft incorporation. These studies provide rationale for fabrication of a biomimetic periosteum substitute that could fit bone of any size and shape for enhanced allograft healing and repair. The success of such an approach will depend on further understanding of the molecular signals that control inflammation, cellular recruitment as well as mesenchymal stem cell differentiation and expansion during the early phase of the repair process. It will also depend on multidisciplinary collaborations between biologists, material scientists and bioengineers to address issues of material selection and modification, biological and biomechanical parameters for functional evaluation of bone allograft healing.

Bisphosphonates can block the deterioration in implant fixation after withdrawal of intermittent doses of parathyroid hormone

We have examined the deterioration of implant fixation after withdrawal of parathyroid hormone (PTH) in rats. First, the pull-out force for stainless-steel screws in the proximal tibia was measured at different times after withdrawal. The stimulatory effect of PTH on fixation was lost after 16 days. We then studied whether bisphosphonates could block this withdrawal effect. Mechanical and histomorphometric measurements were conducted for five weeks after implantation. Subcutaneous injections were given daily. Specimens treated with either PTH or saline during the first two weeks showed no difference in the mechanical or histological results (pull-out force 76 N vs 81 N; bone volume density 19% vs 20%). Treatment with PTH for two weeks followed by pamidronate almost doubled the pull-out force (152 N; p < 0.001) and the bone volume density (37%; ANOVA, p < 0.001). Pamidronate alone did not have this effect (89 N and 25%, respectively). Thus, the deterioration can be blocked by bisphosphonates. The clinical implications are discussed.

Stimulation of fracture-healing with systemic intermittent parathyroid hormone treatment

Over the past several years, there has been an increasing interest in the biology of bone repair and potential technologies for enhancing fracture-healing. Part of this interest is derived from the growing age of the population and the recognition that increased age carries an increased risk of complications after fracture. Although use of locally implanted or injected growth factors has received the most attention, systemic treatments for the enhancement of bone repair, especially for situations in which bone repair may be diminished or delayed, are now under investigation. Since the approval of parathyroid hormone (PTH) as an anabolic treatment for osteoporosis, there has been an increasing interest in other potential clinical uses for this compound in musculoskeletal conditions. It is now widely recognized that PTH administration is an effective therapy to increase bone mineral density and prevent fractures in patients with osteoporosis. More recently, a growing body of evidence has supported the conclusion that PTH will also be an effective anabolic therapy for the enhancement of bone repair after fracture. This review focuses on the recent research demonstrating the potential of PTH in the management of bone repair in a number of fracture models and also highlights the ongoing studies into the mechanisms of PTH actions on endochondral bone repair.

Critical issues in translational and clinical research for the study of new technologies to enhance bone repair

Osteoporosis increases fracture risk, especially in metaphyseal bone. Fractures seriously impair function and quality of life and incur large direct and indirect costs. Although the prevention of fractures is certainly the option, a fast and uneventful healing process is optimal when fractures do occur. Many new therapeutic strategies have been developed to accelerate fracture-healing or to diminish the complication rate during the course of fracture-healing. However, widely accepted guidelines are needed to demonstrate the positive or negative interactions of bioactive substances, drugs, and other agents that are being used to promote fracture-healing. For each study design, the primary study goal should be indicated. Outcome variables should include both objective and subjective parameters. The guidelines should be harmonized between European and American regulatory authorities to ensure comparability of results of studies and to foster global harmonization of regulatory requirements.

Ossicle and vossicle implant model systems

Bone regeneration and repair is a goal of many skeletal therapies and numerous agents positively or negatively impact these processes. New therapeutic agents and effective model systems are continually sought to identify agents and characterize their mechanisms of action are in constant demand. In addition, investigations of tumor cell-bone interaction in the skeletal metastatic microenvironment require well-defined and readily orchestrated models. This chapter describes a novel ectopic ossicle model and a vossicle modification that can be used to provide focused and rapid feedback of bone growth and bone-cellular interactions. The ossicle model is a bone marrow stromal cell (BMSC)-based model and the vossicle model is a neonatal vertebral bone transplant model. These models offer opportunities to mix and compare mesenchymal (donor derived) and hematopoietic elements (host derived). Multiple implants can be placed in one mouse to facilitate various outcome analyses, such as histomorphometry, micro-CT, gene expression studies, and cell tracking using markers such as luciferase, in response to pharma cological or genetic manipulation. Implants can also be combined with other cell types, such as cancer cells to evaluate the bone-tumor microenvironment.

Enhanced chondrogenesis and Wnt signaling in PTH-treated fractures

Studies have shown that systemic PTH treatment enhanced the rate of bone repair in rodent models. However, the mechanisms through which PTH affects bone repair have not been elucidated. In these studies we show that PTH primarily enhanced the earliest stages of endochondral bone repair by increasing chondrocyte recruitment and rate of differentiation. In coordination with these cellular events, we observed an increased level of canonical Wnt-signaling in PTH-treated bones at multiple time-points across the time-course of fracture repair, supporting the conclusion that PTH responses are at least in part mediated through Wnt signaling.

INTRODUCTION

Since FDA approval of PTH [PTH(1-34); Forteo] as a treatment for osteoporosis, there has been interest in its use in other musculoskeletal conditions. Fracture repair is one area in which PTH may have a significant clinical impact. Multiple animal studies have shown that systemic PTH treatment of healing fractures increased both callus volume and return of mechanical competence in models of fracture healing. Whereas the potential for PTH has been established, the mechanism(s) by which PTH produces these effects remain elusive.

MATERIALS AND METHODS

Closed femoral fractures were generated in 8-wk-old male C57Bl/6 mice followed by daily systemic injections of either saline (control) or 30 microg/kg PTH(1-34) for 14 days after fracture. Bones were harvested at days 2, 3, 5, 7, 10, 14, 21, and 28 after fracture and analyzed at the tissue level by radiography and histomorphometry and at the molecular and biochemical levels level by RNase protection assay (RPA), real-time PCR, and Western blot analysis.

RESULTS

Quantitative muCT analysis showed that PTH treatment induced a larger callus cross-sectional area, length, and total volume compared with controls. Molecular analysis of the expression of extracellular matrix genes associated with chondrogenesis and osteogenesis showed that PTH treated fractures displayed a 3-fold greater increase in chondrogenesis relative to osteogenesis over the course of the repair process. In addition, chondrocyte hypertrophy occurred earlier in the PTH-treated callus tissues. Analysis of the expression of potential mediators of PTH actions showed that PTH treatment significantly induced the expression of Wnts 4, 5a, 5b, and 10b and increased levels of unphosphorylated, nuclear localized beta-catenin protein, a central feature of canonical Wnt signaling.

CONCLUSIONS

These results showed that the PTH-mediated enhancement of fracture repair is primarily associated with an amplification of chondrocyte recruitment and maturation in the early fracture callus. Associated with these cellular effects, we observed an increase in canonical Wnt signaling supporting the conclusion that PTH effects on bone repair are mediated at least in part through the activation of Wnt-signaling pathways.