Comparison of bone morphogenetic protein-2 and osteoactivin for mesenchymal cell differentiation: effects of bolus and continuous administration.

Current osteoinductive protein therapy utilizes bolus administration of large doses of bone morphogenetic proteins (BMPs), which is costly, and may not replicate normal bone healing. The limited in vivo biologic activity of BMPs requires the investigation of growth factors that may enhance this activity. In this study, we utilized the C3H10T1/2 murine mesenchymal stem cell line to test the hypotheses that osteoactivin (OA) has comparable osteoinductive effects to bone morphogenetic protein-2 (BMP-2), and that sustained administration of either growth factor would result in increased osteoblastic differentiation as compared to bolus administration. Sustained release biodegradable hydrogels were designed, and C3H10T1/2 cells were grown on hydrogels loaded with BMP-2 or OA. Controls were grown on unloaded hydrogels, and positive controls were exposed to bolus growth factor administration. Cells were harvested at several time points to assess osteoblastic differentiation. Alkaline phosphatase (ALP) staining and activity, and gene expression of ALP and osteocalcin were assessed. Treatment with OA or BMP-2 resulted in comparable effects on osteoblastic marker expression. However, cells grown on hydrogels demonstrated osteoblastic differentiation that was not as robust as cells treated with bolus administration. This study shows that OA has comparable effects to BMP-2 on osteoblastic differentiation using both bolus administration and continuous release, and that bolus administration of OA has a more profound effect than administration using hydrogels for sustained release. This study will lead to a better understanding of appropriate delivery methods of osteogenic growth factors like OA for repair of fractures and segmental bone defects.

Outcomes of lumbopelvic fixation in the treatment of complex sacral fractures using minimally invasive surgical techniques.

BACKGROUND CONTEXT: Complex sacral fractures with vertical and anterior pelvic ring instability treated with traditional fixation methods are associated with high rates of failure and poor clinical outcomes. Supplemental lumbopelvic fixation (LPF) has been applied for additional stability to help with fracture union. PURPOSE: The study aimed to determine whether minimally invasive LPF provides reliable fracture stability and acceptable complication rates in cases of complex sacral fractures. STUDY DESIGN/SETTING: This is a retrospective cohort study at a single level I trauma center. PATIENT SAMPLE: The sample includes 24 patients who underwent minimally invasive LPF for complex sacral fracture with or without associated pelvic ring injury. OUTCOME MEASURES: Reoperation for all causes, loss of fixation, surgical time, transfusion requirements, length of hospital stay, postoperative day at mobilization, and mortality were evaluated. METHODS: Patient charts from 2008 to 2014 were reviewed. Of the 32 patients who underwent minimally invasive LPF for complex sacral fractures, 24 (12 male, 12 female) met all inclusion and exclusion criteria. Outcome measures were assessed with a retrospective chart review and radiographic review. The authors did not receive external funding for this study. RESULTS: Acute reoperation was 12%, and elective reoperation was 29%. Two (8%) patients returned to the operating room for infection, one (4.2%) required revision for instrumentation malposition, and seven (29%) underwent elective removal of instrumentation. No patient experienced failure of instrumentation or loss of correction. Average surgical time was 3.6 hours, blood loss was 180 mL, transfusion requirement was 2.1 units of packed red blood cells, and postoperative mobilization was on postoperative day 5. No mortalities occurred as a result of the minimally invasive LPF procedure. CONCLUSIONS: Compared with historic reports of open LPF, our results demonstrate reliable maintenance of reduction and acceptable complication rates with minimally invasive LPF for complexsacral fractures. The benefits of minimally invasive LPF may be offset with increased elective reoperations for removal of instrumentation.