Only prolonged time from abstraction found to affect viable nucleated cell concentrations in vertebral body bone marrow aspirate

Background context: Vertebral body-derived bone marrow aspirate (BMA, with an appropriate carrier) is a potential alternative to traditional iliac crest bone graft for use in spinal fusion surgery. No studies have looked at the effect of different temporary handling/storage conditions on the osteoprogenitor potential of BMA. This is especially important because aspirate, as with cancellous and/or cortical grafts, may be extracted some time before actual implementation in regular clinical use.

Purpose: To characterize factors that affect BMA cell concentration during routine spinal instrumentation, this study examined whether cell counts change significantly between the second pedicle aspirated and the first pedicle harvested at the same vertebral level. This study also aims to examine the optimal perioperative storage conditions for BMA obtained from the vertebral body.

Study design: In vitro concentrations of viable cells were determined in BMA harvested from the first and second pedicles on every vertebral level, and after 1 hour of storage in different perioperative conditions.

Patient sample: BMA was harvested from 28 pedicles from seven patients undergoing lumbar instrumented fusion surgeries.

Outcome measures: The outcome measure included viable nucleated cell concentrations in BMA.

Methods: After obtaining HIC approval from our institution, 28 vertebral marrow aspirates (obtained from seven patients) were evaluated. Based on prior work, 4-mL aspirates from each pedicle were evaluated. BMA was aspirated from both pedicles of two vertebral levels per patient. Samples were divided and placed in different storage conditions to examine the effect of laterality (first versus second pedicle aspirated per level), temperature, media, and time, on nucleated cell counts. No funding was received for this study, and the authors disclose no study specific conflicts of interest.

Results: Cell count was not significantly different between the first or second side aspirated for each vertebral level. Similarly, no significant differences were found for samples after 1 hour of storage at different temperatures (0 °C, room temperature, or 37 °C) or media (none, saline, essential media). Of the conditions examined, time from aspiration was the only variable found to have an impact on nucleated cell counts (p=.003). The viable cell count decreased to less than half by 4 hours.

Conclusion: As vertebral BMA is increasingly considered as a bone grafting option, the field would be remiss not to consider factors that could affect cell viability after abstraction and before implementation. We expected a greater effect of perioperative storage conditions than was observed. Although the variables evaluated might show small effects on cell viability in a larger study, this would not be expected to be significant. In the current study, only prolonged time from abstraction could be shown to have a significant effect on cell viability.