Diagnosis of Recurrent Fracture in a Pediatric Cohort.

Significant fracture history in children is defined as having at least one vertebral fracture, at least 2 fractures by age 10, or at least 3 fractures by age 19. Between September 2011 and December 2014, clinical data were collected on children with a significant fracture history that attended a major Australian children's hospital. Fifty-six patients were identified as having 305 fractures in total, including 44 vertebral fractures. 18% of patients (10/56) were diagnosed with osteogenesis imperfecta (OI) by a bone health expert, molecular testing or both, and they sustained 23% of all fractures (71/305). Analysis of serum bone biochemistry showed all median values to be within a normal range and no clinically significant differences between patients with and without OI. The DXA and pQCT derived bone mineral density (BMD) and bone mineral content (BMC) Z scores were reduced overall. DXA derived total body and lumbar spine areal BMD-for-age and BMC-for-age Z scores were significantly lower in children who had vertebral fractures or who were later diagnosed with OI. Similarly, pQCT performed on radii and tibiae showed Z scores significantly less than zero. pQCT-derived limb muscle cross sectional area Z scores were significantly lower in the OI subgroup. In conclusion, this study describes the bone phenotype of children referred to a tertiary hospital clinic for recurrent fractures and highlights a subset of children with previously undiagnosed OI, but a larger cohort without classic OI. Thus it can be clinically challenging to differentiate between children with OI type 1 (mild phenotype) and non-OI children without bone densitometry and genetic testing. We conclude that recurrent fractures in children should prompt a comprehensive bone and systemic health assessment to eliminate an underlying pathology.

Skeletal muscle and motor deficits in Neurofibromatosis Type 1.

Neurofibromatosis Type 1 (NF1) is a genetic neurocutaneous disorder with multisystem manifestations, including a predisposition to tumor formation and bone dysplasias. Studies over the last decade have shown that NF1 can also be associated with significant motor deficits, such as poor coordination, low muscle tone, and easy fatigability. These have traditionally been ascribed to developmental central nervous system and cognitive deficits. However, recent preclinical studies have also illustrated a primary role for the NF1 gene product in muscle growth and metabolism; these findings are consistent with clinical studies demonstrating reduced muscle size and muscle weakness in individuals with NF1. Currently there is no evidence-based intervention for NF1 muscle and motor deficiencies; this review identifies key research areas where improved mechanistic understanding could unlock new therapeutic options.

Spatial control of bone formation using a porous polymer scaffold co-delivering anabolic rhBMP-2 and anti-resorptive agents.

Current clinical delivery of recombinant human bone morphogenetic proteins (rhBMPs) utilises freeze-dried collagen. Despite effective new bone generation, rhBMP via collagen can be limited by significant complications due to inflammation and uncontrolled bone formation. This study aimed to produce an alternative rhBMP local delivery system to permit more controllable and superior rhBMP-induced bone formation. Cylindrical porous poly(lactic-co-glycolic acid) (PLGA) scaffolds were manufactured by thermally-induced phase separation. Scaffolds were encapsulated with anabolic rhBMP-2 (20 µg) ± anti-resorptive agents: zoledronic acid (5 µg ZA), ZA pre-adsorbed onto hydroxyapatite microparticles, (5 µg ZA/2% HA) or IkappaB kinase (IKK) inhibitor (10 µg PS-1145). Scaffolds were inserted in a 6-mm critical-sized femoral defect in Wistar rats, and compared against rhBMP-2 via collagen. The regenerate region was examined at 6 weeks by 3D microCT and descriptive histology. MicroCT and histology revealed rhBMP-induced bone was more restricted in the PLGA scaffolds than collagen scaffolds (-92.3% TV, p < 0.01). The regenerate formed by PLGA + rhBMP-2/ZA/HA showed comparable bone volume to rhBMP-2 via collagen, and bone mineral density was +9.1% higher (p < 0.01). Local adjunct ZA/HA or PS-1145 significantly enhanced PLGA + rhBMP-induced bone formation by +78.2% and +52.0%, respectively (p ≤ 0.01). Mechanistically, MG-63 human osteoblast-like cells showed cellular invasion and proliferation within PLGA scaffolds. In conclusion, PLGA scaffolds enabled superior spatial control of rhBMP-induced bone formation over clinically-used collagen. The PLGA scaffold has the potential to avoid uncontrollable bone formation-related safety issues and to customise bone shape by scaffold design. Moreover, local treatment with anti-resorptive agents incorporated within the scaffold further augmented rhBMP-induced bone formation.

A sugar-based phase-transitioning delivery system for bone tissue engineering.

Bone tissue engineering approaches commonly involve the delivery of recombinant human bone morphogenetic proteins (rhBMPs). However, there are limitations associated with the currently used carriers, including the need for surgical implantation and the associated increase in infection risk. As an alternative to traditional porous collagen sponge, we have adopted a solution of the injectable sucrose acetate isobutyrate (SAIB) as a carrier for rhBMP-2. The ability to deliver rhBMP-2 and other agents by injection reduces the infection risk and lesion size whilst in surgery, with the potential to avoid open surgery altogether in some indications. The primary methodology used for this in vivo study was a C57BL6/J mouse ectopic bone formation model. Specimens were examined by x-ray, microCT, and histology at 3 weeks. SAIB was delivered non-invasively and produced up to 3-fold greater bone volume compared to collagen. To further refine and improve upon the formulation, SAIB containing rhBMP-2 was admixed with candidate compounds including ceramic microparticles, anti-resorptives, and cell signalling inhibitors and further tested in vivo. The formulation combining SAIB/rhBMP-2, the bisphosphonate zoledronic acid (ZA), and hydroxyapatite (HA) microparticles yielded a 10-fold greater bone volume than SAIB/rhBMP-2 alone. To investigate the mechanism underlying the synergy between ZA and HA, we used in vitro binding assays and in vivo fluorescent biodistribution studies to demonstrate that ceramic particles could bind and sequester the bisphosphonate. These data show the utility of SAIB as a non-invasive rhBMP delivery system as well as describing an optimised formulation for bone tissue engineering.

The potential role of muscle in bone repair.

Bone repair is a complex phenomenon involving many cell types and signaling factors. Substantial evidence exists to suggest that stem cells originating from local osseous tissues, particularly the periosteum, can contribute to bone repair. However, there are situations where injury or post-surgical management can deplete the amount of, and/or access to these crucial progenitors. The fact that bone repair can still occur in these circumstances implicitly reflects the existence of compensatory secondary systems. One potential alternate source of osteoprogenitors is muscle, which is closely associated with bone and typically suffers trauma during an orthopedic insult. While muscle access is known to be beneficial to bone repair, this is conventionally credited to its high vascularity, and thus its contribution to the local blood supply. However, there is emerging evidence to suggest that progenitors from muscle may directly contribute to bone healing. Defining the role of muscle in bone formation and repair has significant clinical implications, particularly where promoting access to this tissue may enhance the repair outcome.

Induction of periosteal bone formation by intraosseous BMP-2 injection in a mouse model of osteogenesis imperfecta.

PURPOSE: Surgical interventions are routinely performed on children with osteogenesis imperfecta (OI) to stabilize long bones, often post fracture. We speculated that a combination of intramedullary reaming and intraosseous injection of recombinant bone morphogenetic protein-2 (BMP-2) could enhance periosteal ossification and ultimately cortical thickness and strength. This approach was conceptually tested in a preclinical model of genetic bone fragility. METHODS: Six experimental groups were tested including no treatment, intramedullary reaming, and reaming with 5 µg BMP-2 injection performed in the tibiae of both wild type (WT) and Col1a2 G610C/+ (OI, Amish mutation) mice. Bone formation was examined at a two-week time point in ex vivo specimens by micro-computed tomography (microCT) analysis and histomorphometry with a dynamic bone label. RESULTS: MicroCT data illustrated increases in tibial cortical thickness with intramedullary reaming alone (Saline) and reaming plus BMP-2 injection (BMP-2) compared to no intervention controls. In the OI mice, the periosteal bone increase was not statistically significant with Saline but there was an increase of +192% (p = 0.053) with BMP-2 injection. Dynamic histomorphometry on calcein label was used to quantify new woven bone formation; while BMP-2 induced greater bone formation than Saline, the anabolic response was blunted overall in the OI groups. CONCLUSIONS: These data indicate that targeting the intramedullary compartment via reaming and intraosseous BMP-2 delivery can lead to gains in cortical bone parameters. It is suggested that the next step is to validate safety and functional improvements in a clinical OI setting.

A comparison of subtraction MRI with the standard contrast-enhanced imaging in Perthes' disease.

PURPOSE: Perthes' disease (PD) results from loss of blood supply to the hip and can progress to femoral head deformity. MRI in the early course of the disease can provide data on the initial extent of infarct. Vascularity of the femoral head is assessed by gadolinium-enhanced MRI (contrast MRI), which may be improved by the digital subtraction technique (subtraction MRI). We hypothesized that gadolinium-enhanced MRI without subtraction was comparable with subtraction MRI in depicting the femoral head perfusion. METHODS: In all, 34 patients (34 hips) with unilateral PD had gadolinium-enhanced MRI as part of a prospectively randomized study. Nine patients had three MRIs, 15 had two and ten had a single MRI. Measurement of perfusion of the femoral head (MRI perfusion index) was obtained using digital image analysis on all the MRIs, including both before and after subtraction. A paired sample t-test was performed to compare the measurements. RESULTS: The mean age of the patients was 8.9 years (sd 1.6). At the time of diagnosis, the subtraction MRI did not elicit a statistically significant difference in MRI perfusion index measurements when compared with the contrast MRI (p = 0.19). The same findings were found when including all patients at various stages of the disease (p = 0.30). Qualitatively, although some subtraction MRI images showed superior delineation of epiphysis, there are no significant differences throughout the whole series. CONCLUSION: Although the current literature supports the increasing role of the subtraction MRI for PD management, our study proposed that the contrast MRI without subtraction technique appears adequate in assessing femoral head perfusion. LEVEL OF EVIDENCE: Level I - Diagnostic study.

Cannulated screw versus Kirschner-wire fixation for Milch II lateral condyle fractures in a paediatric sawbone model: a biomechanical comparison.

PURPOSE: Lateral condyle fractures of the humerus are common in the paediatric population, accounting for up to 20% of elbow fractures. Traditional management involves internal fixation with Kirschner (K)-wires, however, this has been associated with complications and insufficiently rigid fixation. Recently, cannulated screws have been proposed as a more stable method of fixation. While cannulated screws have been thought to allow earlier range of movement and shorten time to union, data regarding the biomechanical performance and optimal screw placement is scarce. We hypothesize that cannulated screw fixation is superior to K-wire fixation and screw placement can enhance the stability of the construct. METHODS: Paediatric humerus sawbones with Milch II fractures were fixed with one of three methods. Fractures were reduced with either a single cannulated screw either through the centre of the capitellum (oblique), or placed up the lateral column across the growth plate (lateral), or fixed with two K-wires. Fixed sawbone fractures were then mechanically tested in two directions simulating in vivo forces. RESULTS: The lateral screw construct had a higher maximum force to failure, higher stiffness and absorbed higher energy as compared with the K-wire fixation and oblique screw under an anterior force. When loaded from the posterior direction, only the lateral column screw was better than K-wire fixation. CONCLUSIONS: Screw fixation is a biomechanically effective alternative to K-wire fixation, especially when placed up the lateral column of the distal humerus. Further clinical studies are required before transcapitellar screw fixation can be adopted.

The anabolic and catabolic responses in bone repair.

The literature on fracture repair has been reviewed. The traditional concepts of delayed and nonunion have been examined in terms of the phased and balanced anabolic and catabolic responses in bone repair. The role of medical manipulation of these inter-related responses in the fracture healing have been considered.

The deformity index as a predictor of final radiological outcome in Perthes' disease.

The deformity index is a new radiological measurement of the degree of deformity of the femoral head in unilateral Perthes' disease. Its values represent a continuous outcome measure of deformity incorporating changes in femoral epiphyseal height and width compared with the unaffected side. The sphericity of the femoral head in 30 radiographs (ten normal and 20 from patients with Perthes' disease) were rated blindly as normal, mild, moderate or severe by three observers. Further blinded measurements of the deformity index were made on two further occasions with intervals of one month. There was good agreement between the deformity index score and the subjective grading of deformity. Intra- and interobserver agreement for the deformity index was high. The intraobserver intraclass correlation coefficient for each observer was 0.98, 0.99 and 0.97, respectively, while the interobserver intraclass correlation coefficient was 0.98 for the first and 0.97 for the second set of calculations. We also reviewed retrospectively 96 radiographs of children with Perthes' disease, who were part of a multicentre trial which followed them to skeletal maturity. We found that the deformity index at two years correlated well with the Stulberg grading at skeletal maturity. A deformity index value above 0.3 was associated with the development of an aspherical femoral head. Using a deformity index value of 0.3 to divide groups for risk gives a sensitivity of 80% and specificity of 81% for predicting a Stulberg grade of III or IV. We conclude that the deformity index at two years is a valid and reliable radiological outcome measure in unilateral Perthes' disease.

Biomechanical considerations in slipped capital femoral epiphysis and insights into prophylactic fixation.

PURPOSE: Slipped capital femoral epiphysis (SCFE) is a deformity of the proximal femur secondary to widened and unstable physis. In stabilising the slip, gold standard treatments stop growth and involve premature physeal closure, which prevents the remodelling of the acquired deformity and creates a leg length discrepancy that may be significant in younger patients. METHODS: We measured the impact of placing threaded screws across the proximal femoral physis by measuring the centre-trochanteric distance (CTD) and articulo-trochanteric distance (ATD) in participants with or without prophylactic fixation. We then compared the mechanical performance of static (stainless and titanium cannulated Synthes screws) and potentially growing implants (Synthes SCFE screw and Pega Medical Free Gliding screw) in a validated synthetic bone model. RESULTS: In the review of 30 non-fixed and 60 fixated hips over a mean follow-up of 1.9 years, we have noted a significant difference in pre/post CTD and ATD, as well as the change in CTD and ATD over time. In the biomechanical study, the newer implants allowing growth (Synthes SCFE screw and Pega Medical Free Gliding screw) were both shown to be at least non-inferior. CONCLUSIONS: The primary deformity of a SCFE in itself alters hip mechanics. Also, as confirmed in this study, there is a secondary deformity that is created by static fixation and relative trochanteric overgrowth. To help remodel mild deformities and prevent secondary trochanteric overgrowth, growing implants seem to be non-inferior to the more standard means of fixation in static testing.

Zoledronic acid causes enhancement of bone growth into porous implants.

The effect of zoledronic acid on bone ingrowth was examined in an animal model in which porous tantalum implants were placed bilaterally within the ulnae of seven dogs. Zoledronic acid in saline was administered via a single post-operative intravenous injection at a dose of 0.1 mg/kg. The ulnae were harvested six weeks after surgery. Undecalcified transverse histological sections of the implant-bone interfaces were imaged with backscattered scanning electron microscopy and the percentage of available pore space that was filled with new bone was calculated. The mean extent of bone ingrowth was 6.6% for the control implants and 12.2% for the zoledronic acid-treated implants, an absolute difference of 5.6% (95% confidence interval, 1.2 to 10.1) and a relative difference of 85% which was statistically significant. Individual islands of new bone formation within the implant pores were similar in number in both groups but were 69% larger in the zoledronic acid-treated group. The bisphosphonate zoledronic acid should be further investigated for use in accelerating or enhancing the biological fixation of implants to bone.

Endochondral fracture healing with external fixation in the Sost knockout mouse results in earlier fibrocartilage callus removal and increased bone volume fraction and strength.

Sclerostin deficiency, via genetic knockout or anti-Sclerostin antibody treatment, has been shown to cause increased bone volume, density and strength of calluses following endochondral bone healing. However, there is limited data on the effect of Sclerostin deficiency on the formative early stage of fibrocartilage (non-bony tissue) formation and removal. In this study we extensively investigate the early fibrocartilage callus. Closed tibial fractures were performed on Sost(-/-) mice and age-matched wild type (C57Bl/6J) controls and assessed at multiple early time points (7, 10 and 14days), as well as at 28days post-fracture after bony union. External fixation was utilized, avoiding internal pinning and minimizing differences in stability stiffness, a variable that has confounded previous research in this area. Normal endochondral ossification progressed in wild type and Sost(-/-) mice with equivalent volumes of fibrocartilage formed at early day 7 and day 10 time points, and bony union in both genotypes by day 28. There were no significant differences in rate of bony union; however there were significant increases in fibrocartilage removal from the Sost(-/-) fracture calluses at day 14 suggesting earlier progression of endochondral healing. Earlier bone formation was seen in Sost(-/-) calluses over wild type with greater bone volume at day 10 (221%, p<0.01). The resultant Sost(-/-) united bony calluses at day 28 had increased bone volume fraction compared to wild type calluses (24%, p<0.05), and the strength of the fractured Sost(-/-) tibiae was greater than that that of wild type fractured tibiae. In summary, bony union was not altered by Sclerostin deficiency in externally-fixed closed tibial fractures, but fibrocartilage removal was enhanced and the resultant united bony calluses had increased bone fraction and increased strength.

The effect of limb-length discrepancy on gait.

We evaluated the gait of thirty-five neurologically normal children who had a limb-length discrepancy of the lower extremities that ranged from 0.8 to 15.8 per cent of the length of the long extremity (0.6 to 11.1 centimeters). The twenty-two boys and thirteen girls had an average age of thirteen years (range, eight to seventeen years). No patient had a substantial angular or rotational deformity of the lower extremities. We found no correlation between the actual discrepancy or the per cent discrepancy and any of the dependent kinematic or kinetic variables, including pelvic obliquity. Discrepancies of less than 3 per cent of the length of the long extremity were not associated with compensatory strategies. When a discrepancy was 5.5 per cent or more, more mechanical work was performed by the long extremity and there was a greater vertical displacement of the center of body mass. Clinically, this degree of discrepancy was manifested by the use of toe-walking as a compensatory strategy. Children who had less of a discrepancy were able to use a combination of compensatory strategies to normalize the mechanical work performed by the lower extremities.

Relationship of peak height velocity to other maturity indicators in idiopathic scoliosis in girls.

BACKGROUND: Our aim was to compare height velocity data, obtained from clinical height measurements, for girls who had idiopathic scoliosis with the data for adolescents who did not have scoliosis. We also compared the growth data with chronological age, menarchal age, and Risser sign in terms of their accuracy in the prediction of growth and progression of the scoliosis. METHODS: One hundred and twenty of 371 patients in a database of girls managed with a brace for the treatment of idiopathic scoliosis had sufficient height data for us to quantify their growth peak. Height velocity data was generated from standing-height measurements obtained, in a scoliosis clinic, with a minimum six-month interval between measurements, and the timing of peak height velocity was calculated. The age at menarche was recorded from the patients' records. The Risser sign and Cobb angle were determined by a single observer. Progression of the scoliosis was defined as an increase in the Cobb angle of at least 10 degrees, compared with the curve magnitude at the time of the initial evaluation, after a minimum of six months. Progression to a magnitude requiring surgery was defined as progression of at least 10 degrees to a magnitude of 45 degrees or more. RESULTS: The height velocity plot grouped by peak height velocity showed a high peak and a sharp decline with values similar to those in normal populations. Extrapolating from percentile charts, 90 percent of our patients ceased growing by 3.6 years after peak height velocity. The growth peak was blunted (averaged over too long a period such that the data for the period of most rapid growth was averaged in with that for a period of slower growth) when chronological age, menarchal age, and Risser sign were used to predict growth; this indicated that these maturity scales grouped the patients poorly in terms of growth. The primary curve was progressive in eighty-eight of the 120 patients. Sixty of these patients had a curve of more than 30 degrees at peak height velocity, and in fifty (83 percent) of the sixty the curve progressed to 45 degrees or more. The remaining twenty-eight patients had a curve of 30 degrees or less at peak height velocity, with only one curve (4 percent) progressing to 45 degrees or more. Peak height velocity also grouped patients for maximal progression of the curve more accurately than did the other maturity scales, as most of the curves progressed maximally at peak height velocity. There was a wider spread of timing of maximal progression when chronological age, menarchal age, and Risser sign were used to predict progression. CONCLUSIONS: Height velocities generated from clinical height measurements for patients with idiopathic scoliosis document the growth peak and predict cessation of growth reliably. Knowing the timing of the growth peak provides valuable information on the likelihood of progression to a magnitude requiring spinal arthrodesis.

The use of the percentage change in Oswestry Disability Index score as an outcome measure in lumbar spinal surgery.

STUDY DESIGN: A retrospective analysis of the change in the Oswestry Low Back Pain Disability Questionnaire in a heterogeneous group of 144 operatively managed patients was undertaken to examine the change in disability index as an outcome measure. OBJECTIVES: To establish the percent change in disability index as an outcome measure able to identify risk factors for poor results in lumbar spinal surgery. METHODS: Epidemiologic, diagnostic, and surgical variables were examined as risk factors using step-wise multiple linear regression analysis at both follow-up times (6 months and 2 years), with percent change in disability index used as the outcome measure. RESULTS: At 6-months follow-up, previous surgery, female gender, workers' compensation, a lower initial disability index score, increasing age, and spinal fusion alone as an operative procedure were independently and significantly negatively correlated with outcome. Further analysis revealed that for patients with spinal canal stenosis, the magnitude of the initial disability index did not correlate with outcome, whereas patients with low back pain or a prolapsed intervertebral disc fared better if they had high initial disability scores. Data at 2-years follow-up were less adequate. However, previous surgery on the spine and low initial disability score were significant negative predictors of outcome at 6-month and 2-year follow-up. CONCLUSIONS: The findings indicate that the absolute value and change in these scores after surgery vary from patient to patient, but that their percentage change is likely to be the best marker of outcome when such subjective scoring systems are used.

Prediction of the crankshaft phenomenon by peak height velocity.

STUDY DESIGN: Retrospective review. OBJECTIVES: To evaluate the relation of the peak height velocity with the occurrence of the crankshaft phenomenon after posterior arthrodesis and instrumentation in idiopathic scoliosis. SUMMARY OF BACKGROUND DATA: Although patients with closed triradiate cartilages are unlikely to exhibit the crankshaft phenomenon after a posterior spinal fusion and instrumentation, open triradiate cartilages do not necessitate that crankshafting will occur. Less than half of patients with idiopathic scoliosis and open triradiate cartilages will exhibit the crankshaft phenomenon. METHODS: The authors reviewed 43 patients with idiopathic scoliosis who were Risser 0 at the time of posterior spinal fusion. Twenty-three patients had open triradiate cartilages and twenty had closed. The timing of peak height velocity was identified. RESULTS: All patients with closed triradiate cartilages were beyond their peak height velocity at the time of surgery. Among those with open triradiate cartilages, 8 were operated on before or during their peak and 15 were operated on afterward. All patients fused before or during the peak crankshafted. Two of the fifteen patients fused after the peak crankshafted. In one, it was low grade. In the other, it appears that the fusion blunted the peak height velocity to a point at which it was unidentifiable. CONCLUSIONS: In patients with open triradiate cartilages, surgery performed before or during the peak height velocity is a strong predictor of the crankshaft phenomenon, and later surgery is a strong negative predictor of the crankshafting (P = 0.000009). Isolated posterior fusion before the height velocity decelerates results in the crankshaft phenomenon, whereas fusion during the deceleration phase does not.

Intravenous pamidronate reduces osteoporosis and improves formation of the regenerate during distraction osteogenesis. A study in immature rabbits.

We examined the effect on bone mineral density (BMD) of a single dose of 3 mg/kg of the bisphosphonate, pamidronate (Novartis) in distraction osteogenesis in immature rabbits. Seventeen rabbits (9 control, 8 given pamidronate) were examined by dual-energy x-ray absorptiometry. There was a significant increase in the BMD in the pamidronate group compared with the control animals. The mean areal BMD (g/cm2) in the bone proximal and distal to the regenerate was increased by 40% and 39%, respectively, compared with the control group (p < 0.05). The BMD of the regenerate bone was increased by a mean of 43% (p < 0.05). There was an increase of 22% in the mean area of regenerate formed in the pamidronate group (p < 0.05). Histological examination of bone in nine rabbits (5 control, 4 pamidronate) showed an increase in osteoblastic rimming and mineralisation of the regenerate, increased formation of bone around the pin sites and an increase in the cortical width of the bone adjacent to the regenerate in the rabbits given pamidronate. Pamidronate had a markedly positive effect. It reduced the disuse osteoporosis normally associated with lengthening using an external fixator and increased the amount and density of the regenerate bone. Further study is required to examine the mechanical properties of the regenerate after the administration of pamidronate.

Zoledronic acid improves the mechanical properties of normal and healing bone.

OBJECTIVE: To determine the effects of the bisphosphonate zoledronic acid on the mechanical properties of normal and regenerating bone in a rabbit model of distraction osteogenesis. BACKGROUND: Bisphosphonate therapy is used for treating osteoporosis and, more recently, to enhance bone healing and reduce stress-shielding osteoporosis in distraction osteogenesis. METHODS: Thirty eight rabbits underwent 14 days of distraction osteogenesis on the right rear limb. They received either zero, one or two doses of intravenous zoledronic acid. Four point bending tests were performed to collect mechanical data. RESULTS: The peak load capacity of the regenerating bone was significantly increased by bisphosphonate therapy, but a similar trend in normal bone was not significant. The energy absorbed to failure did not vary significantly in either group. CONCLUSIONS: These data suggest that bisphosphonate therapy has a beneficial effect on the load capacity of regenerating bone, without increasing the brittleness of either new or existing bone. RELEVANCE: Zoledronic acid administration may be a potentially valuable adjunct to distraction osteogenesis treatment, to enhance bone strength, thus reducing refracture complications.

Modulation of endochondral ossification by MEK inhibitors PD0325901 and AZD6244 (Selumetinib).

MEK inhibitors (MEKi) PD0325901 and AZD6244 (Selumetinib) are drugs currently under clinical investigation for cancer treatment, however the Ras-MAPK pathway is also an important mediator of normal bone cell differentiation and function. In this study we examined the effects of these compounds on endochondral processes using both in vitro and in vivo models. Treatment with PD0325901 or AZD6244 significantly increased Runx2 and Alkaline phosphate gene expression in calvarial osteoblasts and decreased TRAP+ cells in induced osteoclast cultures. To test the effects of these drugs on bone healing, C57/Bl6 mice underwent a closed tibial fracture and were treated with PD0325901 or AZD6244 at 10mg/kg/day. Animals were culled at day 10 and at day 21 post-fracture for analysis of the fracture callus and the femoral growth plate in the contralateral leg. MEKi treatment markedly increased cartilage volume in the soft callus at day 10 post-fracture (+60% PD0325901, +20% AZD6244) and continued treatment led to a delay in cartilage remodeling. At the growth plate, we observed an increase in the height of the hypertrophic zone relative to the proliferative zone of +78% in PD0325901 treated mice. Osteoclast surface was significantly decreased both at the terminal end of the growth plate and within the fracture calluses of MEKi treated animals. The mechanistic effects of MEKi on genes encoding cartilage matrix proteins and catabolic enzymes were examined in articular chondrocyte cultures. PD0325901 or AZD6244 led to increased matrix protein expression (Col2a1 and Acan) and decreased expression of catabolic factors (Mmp13 and Adamts-5). Taken together, these data support the hypothesis that MEKi treatment can impact chondrocyte hypertrophy, matrix resorption, and fracture healing. These compounds can also affect bone architecture by expanding the hypertrophic zone of the growth plate and reducing osteoclast surface systemically.