Introduction: In the attempt to improve fusion rates in spondylodesis surgery, focus has been applied on numerous factors, including surgical strategies, instrumentation-devices and –material, technical preparation of the fusion bed, stringency of radiological outcome criteria, patient-related factors such as age, sex, tobacco consumption, and severity of underlying pathology. In recent years the development of new techniques for exploring mechanisms in cellular and molecular biology have further directed focus toward more advanced biological techniques and considerations. To the authors’ knowledge, little or no attention has been focused on one of the basic and important factors in the attempt to achieve fusion, ie the impact of bone graft quantity placed at the fusion bed.

The aim of this study was to investigate the influence of autologous bone graft quantity in posterolateral instrumented spinal fusion (PLF) in respect to fusion rates.

Methods and results: A prospective clinical study in 76 patients, in which CD-instrumented posterolateral lumbar or lumbosacral spine fusion surgery was performed. The quantity of autologous bone graft applied at the fusion bed was recorded peroperatively. Spinal fusion rates were assessed by AP/lateral radiographs at one-year follow-up by two independent observers, according to our strict classification system. The impact of bone graft quantity, tobacco consumption, age and sex of the patients were analysed in respect to fusion-rates by logistic regression.

According to our classification “fusion” was seen in 76% of the patients, “non-union” in 12.7% and “doubtful”fusion in 11.3%. In “fusion” segments, the median amount of bone used was 24.4 (13–53) g and 14.7 (12.5–23.4) g in “non-union” segments. The “non-union” rate was 7.1% for non-smokers in contrast to 21.4% for patients who smoked during the first six post-operative months. The impact on fusion rates by graft quantity and cigarette smoking were significant, p< 0.006 respectively 0.035. Age and gender did not influence fusion rates. Thirty-three percent of patients with “non-union” had a corresponding failure of the implant.

Conclusions: The quantity of graft used at the fusion bed is critical for successful fusion. Based on the results presented here, we recommend a minimum of 24 g of autogenous bone graft at each intervention segment in auto-grafted posterolateral spinal spondylodesis surgery. In addition, this study underlines the importance of tobacco arrest, in at least the first six post-operative months. The data presented here strongly support the importance of quantifying or optimally standardising the amount of graft placed at each intervention segment.