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Differential Effects of Culture-expanded Bone Marrow Cells on the Regeneration of Bone Between the Femoral and the Tibial Lengthenings

Background Transplantation of culture-expanded bone marrow cells (BMC) and platelet-rich plasma (PRP) during limb lengthening shorten the treatment period by accelerating callus formation, but the direct effects of BMC and PRP on the regeneration of the bone have not been determined. Methods Fifty-one bones (23 femora, 28 tibiae) in 28 patients (17 males, 11 females), with an average age of 15.0±3.21 years, were lengthened by treatment with BMC and PRP. Clinical outcome was compared between the 51 bones with BMC and PRP treatment and the 60 bones without cell therapy. The parameters including age at surgery, length gained, healing index (HI), number of BMC, bone-specific alkaline phosphatase (BAP) activity of BMC, and PRP concentration, were compared between the femur and the tibia treated with BMC and PRP. Linear regression analysis was then performed to correlate the HI and other variables. Results The HI of the BMC and PRP groups was significantly lower than that of the control group. Average HI, amount of lengthening, number of BMC, BAP activity, and PRP concentration were 30.0±6.72 days/cm, 8.10±2.90 cm, 1.35±0.56×107, 9.02±3.98 U/L, and 2.4±0.7×106 /UL, respectively. There were no significant differences in the length gained, the number and BAP activity of BMC, and the PRP concentration between the femur and the tibia. Femoral lengthening showed significantly faster healing than tibial lengthening, although the age at surgery was significantly older in femoral lengthening. A negative relationship between the HI and the length gained was observed in the tibia. In the femur, there was a negative linear relationship between the HI and the number and BAP activity of BMC, whereas no significant correlations were detected in the tibia. Conclusions In femoral lengthening, decrease in the HI was remarkable by BMC and PRP transplantation, and there was a progressive increase in bone healing as the number and the osteoblastic differentiation of transplanted BMC increased. Our results suggested that regionally varying bone-forming processes by cell transplantation might be related to local blood supply and soft tissue covering. Level of Evidence Therapeutic retrospective study, level III.