Endoscopic instrumented posterolateral lumbar fusion with Healos and recombinant human growth/differentiation factor-5

Abstract

Daniel Kim, MD, Stanford, CA, USA; Tsai-Sheng Fu, Taoyuan, Republic of China; Tae-Ahn Jahng, MD, Chonbuk, South KoreaBackground context: Autogenous bone is considered the most effective bone graft material for posterolateral lumbar fusion, yet nonunions occur in up to 35% of patients. The donor site complications may occur in 25% to 30% of patients. In addition, many surgeries are lengthy procedures, which involve a relative large surgical field, and are associated with a great deal of morbidity and a long hospital stay.Purpose: The primary goal of this study is to use the minimal invasive surgical technique and to evaluate the efficacy of a novel osteoinductive growth factor and osteoconductive matrix formulation (recombinant human growth/differentiation factor [rhGDF-5] and Healos) at inducing and facilitating bone formation in a lumbar spinal posterolateral fusion sheep model.Materials and methods: Twelve skeletally mature sheep underwent bilateral posterolateral spinal fusion at the L4–L5 level. All surgeries were performed using a posterolateral endoscopic approach and transpedicle screw fixation. The animals were randomized in two groups based on the side and material applied. Autogenous iliac crest bone graft or bone graft substitute (rhGDF-5 and Healos) was used either on the right or the left side alternatively. Every animal had both the materials. Three groups were formed on the basis of the survival time: 60 days, 120 days and 180 days. All animals were euthanized after survival time for manual, radiographic, histologic and dual-energy X-ray absorptiometry (DEXA) evaluation.Results: There were no neurologic impairments, infections nor other complications. All four sheep had partial fusion on both sides at 60 days, but greater bone growth was found in the side of rhGDF-5 and Healos by radiograph and DEXA. In the eight animals that survived after 120 days, the manual palpation, radiograph and computed tomography scans determined that fusion rate for rhGDF-5 and Healos was 100% (eight of eight fusion sites), compared with 88% (seven of eight fusion sites) using autogenous iliac bone graft. There was no abnormal overgrowth of new bone by these two materials.Conclusion: These results show that endoscopic posterolateral spinal arthrodesis and instrumentation is a feasible, effective and safe method in the sheep model. Minimal invasive endoscopic surgery will minimize the morbidity of paraspinal muscle denervation and devascularization seen with open techniques. Healos (osteoconductive matrix) can be a useful carrier in the biologic and mechanical environment of a posterolateral intertransverse fusion site. In combination with rhGDF-5 (osteoinductive material), it produces fusion rates that are compatible with those of autologous bone graft. Use of the minimal invasive technique and the bone graft substitutes will eliminate the problem of graft donor site morbidity and possibly increase the chances for successful fusion.