Transpedicular aspiration of osteoprogenitor cells from the vertebral body: progenitor cell concentrations affected by serial aspiration

Abstract

Background context: Spinal fusion is facilitated when the fusion site is augmented with autograft bone. Iliac crest, long the preferred source of autograft material, is the site of frequent complications and pain. Connective tissue progenitor cells (CTPs) aspirated from marrow provide a promising alternative to traditional autograft harvest. The vertebral body represents an even larger potential reservoir of progenitor cells than the ilium.

Purpose: To test the hypothesis that a suitable concentration of osteoprogenitor cells can be aspirated from different depths of the vertebral body, maintaining progenitor cell concentrations comparable to the "gold standard," the iliac crest, even after sequential aspirations along the same transpedicular axis.

Study design: Prospective clinical investigation quantifying CTP concentrations within the vertebral body relative to depth of sequential aspirations.

Patient sample: Adult men and women undergoing elective posterior lumbar fusion and pedicle screw instrumentation (six men and seven women, mean age 56 years [range 40-74 years]).

Outcome measures: Cell count, CTP concentration (CTPs/cc marrow), and CTP prevalence (CTPs/million cells) were calculated for both individual and pooled aspirate samples.

Methods: Thirteen patients were enrolled into an institutional review board-approved protocol studying transpedicular aspiration of marrow progenitor cells. Connective tissue progenitor cells were aspirated from four depths along the transpedicular axis of the vertebral body and quantified according to cell concentration and CTP prevalence. Histochemical analysis of alkaline phosphatase-positive colony-forming units (CFUs) provided the prevalence of vertebral CTPs relative to depth of aspiration, vertebral level, age, and gender.

Results: Four 2.0cc aspirations were obtained from each pedicle of lumbar vertebrae selected for pedicle screw fixation (four 2.0cc aspirates from each of four pedicles). Aspirates of vertebral marrow demonstrated comparable or greater concentrations of CFUs compared with standards previously established for the iliac crest. Overall, the 208 aspirations from 26 vertebral bodies provided a mean CTP concentration of 741.5+/-976.2 CTPs per cubic centimeter of marrow, ranging from a mean concentration of 1316+/-1473 CTPs per cubic centimeter of marrow at superficial (30mm) aspirations to 439+/-557 CTPs per cubic centimeter marrow at deepest (45mm) aspiration depths (p<.00002). There were no significant differences relative to vertebral body level, side aspirated, or gender. An age-related decline in cellularity was suggested for vertebral body aspirates.

Conclusions: The vertebral body is a potential marrow reservoir for aspiration of autograft osteogenic CTPs that can be used to augment spinal fusion. The cancellous bone within that portion of the vertebral body routinely cannulated during pedicle screw placement allows serial aspirations with only modest depletion of progenitor cell concentrations or dilution with peripheral blood. Connective tissue progenitor cell concentrations from all depths were comparable to the mean levels previously established for the iliac crest. The ability to simultaneously harvest progenitor cells for graft augmentation while preparing the pilot hole for pedicle screw fixation will expand the potential for cell harvest techniques for fusion augmentation and reduce the need for iliac crest harvest.