Craniosynostosis is the premature fusion of the cranial sutures early in development. If left untreated, craniosynostosis can lead to complications resulting from cranial deformities or increased intracranial pressure. The standard treatment involves calvarial reconstruction, which in many cases undergoes rapid re-synostosis. This requires additional surgical intervention that is associated with a high incidence of life threatening complications. To better understand this rapid healing, a pediatric mouse model of re-synostosis was developed and characterized. Defects (1.5. mm by 2.5. mm) over the posterior frontal suture were created surgically in weanling (21. days post-natal) and adolescent (50. days post-natal) C57Bl/6J mice. In addition, defects were created in the frontal bone lateral to the posterior frontal suture. The regeneration of bone in the defect was assessed using advanced image processing algorithms on micro-computed tomography scans. The genes associated with defect healing were assessed by real-time PCR of mRNA isolated from the tissue present in the defect. The results showed that the weanling mouse healed in a biphasic process with bone bridging the defect by post-operative (post-op) day 3 followed by an increase in the bone volume on day 14. In adolescent mice, there was a delay in bone bridging across the defect, and no subsequent increase in bone volume. No bridging of the defect by 14. days post-op was seen in identically sized defects placed lateral to the suture in both weanling and adolescent animals. This study demonstrates that bone regeneration in the cranium is both age and location dependent. Rapid and robust bone regeneration only occurred when the defect was created over the posterior frontal suture in immature weanling mice.
Age is a well-known influential factor in bone healing, with younger patients generally healing bone fractures more rapidly and suffering fewer complications compared with older patients. Yet the impact age has on the response to current bone healing treatments, such as delivery of bone morphogenetic protein 2 (BMP-2), remains poorly characterized. It remains unclear how or if therapeutic dosing of BMP-2 should be modified to account for age-related differences in order to minimize potential adverse effects and consequently improve patient bone-healing outcomes. For this study, we sought to address this issue by using a preclinical critically sized segmental bone defect model in rats to investigate age-related differences in bone repair after delivery of BMP-2 in a collagen sponge, the current clinical standard. Femoral defects were created in young (7-week-old) and adult (8-month-old) rats, and healing was assessed using gene expression analyses, longitudinal radiography, ex vivo micro-computed tomography (µCT), as well as torsional testing. We found that young rats demonstrated elevated expression of genes related to osteogenesis, chondrogenesis, and matrix remodeling at the early 1-week time point compared with adult rats. These early gene expression differences may have impacted long-term healing as the regenerated bones of young rats exhibited higher bone mineral densities compared with those of adult rats after 12 weeks. Furthermore, the young rats demonstrated significantly more bone formation and increased mechanical strength when BMP-2 dose was increased from 1 µg to 10 µg, a finding not observed in adult rats. Overall, these results indicate there are age-related differences in BMP-2-mediated bone regeneration, including relative dose sensitivity, suggesting that age is an important consideration when implementing a BMP-2 treatment strategy.
Alginate calcification has been previously reported clinically and during animal implantation; however no study has investigated the mechanism, extensively characterized the mineral, or evaluated multiple methods to regulate or eliminate mineralization. In the present study, alginate calcification was first studied in vitro: calcium-crosslinked alginate beads sequestered surrounding phosphate while forming traces of hydroxyapatite. Calcification in vivo was then examined in nude mice using alginate microbeads with and without adipose stem cells (ASCs). Variables included the delivery method, site of delivery, sex of the animal, time in vivo, crosslinking solution, and method of storage prior to delivery. Calcium-crosslinked alginate microbeads mineralized when injected subcutaneously or implanted intramuscularly after 1-6 months. More extensive analysis with histology, microCT, FTIR, XRD, and EDS showed calcium phosphate deposits throughout the microbeads with surface mineralization that closely matched hydroxyapatite found in bone. Incorporating 25 m. m bisphosphonate reduced alginate calcification whereas using barium chloride eliminated mineralization. Buffering the crosslinking solution with HEPES at pH 7.3 while washing and storing samples in basal media prior to implantation also eliminated calcification in vivo. This study shows that alginate processing prior to implantation can significantly influence bulk hydroxyapatite formation and presents a method to regulate alginate calcification.
BACKGROUND AND PURPOSE: Mandibular distraction osteogenesis is the preferred treatment at many centers for micrognathic patients with recalcitrant upper airway obstruction. Timing of extubation after placement of mandibular distractors is the subject of ongoing debate. Maintaining intubation allows for the airway size to be increased through gradual mandibular distraction, thus decreasing the impact of airway edema, which may occur after extubation. However, prolonged intubation has risks including subglottic stenosis, ventilator-associated pneumonia, and accidental extubation. In this retrospective chart review, our experience with mandibular distraction followed by immediate extubation is examined.
METHODS: A 4-year retrospective review of patients diagnosed with Pierre Robin Sequence who underwent mandibular distraction within the first 3 months of life was performed. All patients were treated at a tertiary children’s hospital and had failed preoperative positioning and airway adjuncts. Patients who were intubated preoperatively were excluded. Analytic endpoints included patient demographics, comorbidities, preoperative and postoperative respiratory support, rates of immediate extubation, need for reintubation, progression to tracheostomy, correlative polysomnography, direct laryngoscopic grade view, and functional nasoendoscopy.
RESULTS: A total of 52 (29 males, 23 females) patients met inclusion criteria. The mean follow-up interval was 18 months. Six patients (12%) progressed to tracheostomy in long-term follow-up. There was 1 mortality (2%), which was remote from surgical intervention. Seventy-three percent of patients undergoing distraction were extubated immediately in the operating room. In those who remained intubated (27%), the mean intubation interval was 7.2 days (range, 1–14 days). No significant differences were found in associated comorbidities, syndromic status, cleft pathology, preoperative respiratory support, or grade of view on direct laryngoscopy between the extubated and intubated groups. Case duration >120 minutes and the subjective designation of a difficult airway by the anesthesiologist were associated with maintaining intubation (P <0.05). Twenty-one percent of patients in the extubated group experienced a respiratory event before discharge, and 11% (4 patients) required reintubation. Respiratory events were significantly more likely in patients with other congenital anomalies, a syndromic diagnosis, cardiac anomalies, gastroesophageal reflux disease, and in those who required respiratory support greater than low-flow nasal cannula before distraction (P < 0.05). Secondary airway anomalies and cleft palate were not associated with respiratory events or reintubation.
CONCLUSION: Our data suggest that immediate extubation after placement of mandibular distractors is feasible in patients who are not intubated preoperatively. Extra caution should be exercised in patients who required significant respiratory support before distraction and in those with certain comorbidities, as these patients were more likely to experience respiratory events and reintubation.