Rate of fusion using novel synthetic bone graft mixed with allograft stem cell product in lumbar fusions

Over 400,000 spine fusions are performed in the United States annually with 75% involving the lumbar region. It is the indicated treatment of many chronic orthopedic conditions that fail conservative management. There are numerous surgical approaches; however, common to all is the removal of the intervertebral disc and the insertion of a bone graft which promotes arthrodesis. Iliac crest autografts are regarded as the "gold standard" bone graft material for lumbar fusions; however, they come with a significant complication rate. Recently developed biologic mixtures, such as the one used in this study, have illustrated similar qualities to autograft material. This study aims to observe how the mixture of a cellular allograft with a fully synthetic bone graft will affect the rate of arthrodesis in patients undergoing lumbar fusions. A retrospective chart review on patients who received a lumbar interbody fusion using a combination of Vimax® and Osteoflo® between May 26, 2021, to December 31, 2022, was performed. Demographic information was obtained. Pre-operative radiographs were measured in addition to 2-week, 6-week, 3-month, 6-month, and 1-year post-operative radiographs. Post-operative radiographs were examined to assign a Bridwell fusion grade to interbody and lateral mass fusions. A total of 129 patients receiving 211 lateral mass fusions and 199 interbody fusions were studied. A proportion of 3.3% of lateral mass fusions recorded a Bridwell Grade I (complete fusion) at 3 months post-operative and 77.8% at 1 year post-operative. Among interbody fusions, 14.1% were assigned a Bridwell Grade I at 3-month post-operative and 92.0% at the 1-year post-operative timepoint. Non-modifiable risk factors such as age and sex at birth had no impact on arthrodesis rate at 1 year for lateral mass or interbody fusions. Additionally, there was no significant difference in long-term fusions rates at the 1-year post-operative mark between obese and non-obese groups. Comorbidities did not affect the rate of arthrodesis 1-year post-operative apart from depression and hypertension. Patients with depression, and those without hypertension, exhibited significantly reduced lateral mass fusion rates with no difference in interbody fusion rates. While significant variations in rates of fusion were noted amongst surgical approaches at intermediate time points, no difference was observed 1 year post-operatively. Significant improvements in spondylolisthesis, anterior disc height, posterior disc height, and foraminal height were observed at each post-operative period. The cellular allograft and synthetic mixture demonstrated significant arthrodesis rate at 92%, which trends higher than historically reported results for iliac crest autograft. Important to note, the absence of reduced arthrodesis rate in particular at-risk groups, such as the elderly, obese, and those with osteoporosis, suggests this mixture can be used in an extensive patient population and can overcome historically challenging arthrodesis patient cohorts.