Introduction: Adipose-derived stem cells (ADSCs) have been demonstrated to form vascularized bone in various animal and pre-clinical models. While bone marrow-derived stem cells (BMSCs) have been widely used in spinal fusion studies, adipose offers a number of advantages as an alternative clinical cell source, including a larger available tissue volume, higher stem cell concentration, and reduced donor site morbidity. In this study we compared the efficacy of ADSCs vs. BMSCs in achieving successful spinal fusion when combined with a clinical-grade bone graft substitute in a rat model.
Methods: ADSCs and BMSCs were isolated from the inguinal fat pads and long bones, respectively, of female Lewis rats (6-10 wk old) and cultured in vitro until passage 2 (P2) for subsequent transplantation. The frequency of colony forming unit fibroblast (CFU-F) colonies was also assessed in vitro for both ADSCs and BMSCs. Posterolateral spinal fusion surgery at L4-5 was performed on 36 female Lewis rats (6-10 wk old) divided into 3 experimental groups:  Vitoss (Stryker) clinical-grade bone graft substitute only (n=12);  Vitoss + 2.5 x 10^6 P2 ADSCs /side (n=12); and  Vitoss + 2.5 x 10^6 P2 BMSCs /side (n=12). Fusion was assessed at postoperative week 8 via micro-computed tomography (MicroCT) analysis and manual palpation.
Results: ADSCs exhibited a faster proliferative rate and a higher frequency of CFU-F colonies in vitro than BMSCs. The mean fusion volume in the ADSC group was significantly larger than the BMSC and vitoss groups (44.3 mm^3 vs. 27.6 and 30.0 mm^3, respectively, p<0.01). The mean manual palpation score was the highest in the ADSC group compared with the BMSC and VO groups (1.5 versus 0.7 versus 0.8 p=0.03).
Conclusions: When combined with a bone graft substitute in a rat model, ADSCs yielded increased fusion mass volume and more robust fusion than BMSCs.
Patient Care: Investigated the potential role of adipose-derived stem cells, which may represent a better source of cells for osteogenesis in humans if the results are translatable.
Learning Objectives: To discuss the outcomes of adipose-derived stem cells versus bone-marrow derived stem cells in a rat model