This study focuses on the safety and efficacy of an available DBM bone graft material used as a graft extender in multi-segment posterolateral instrumented lumbar fusion. Overall, the successful fusion rate was documented with an average of 80.8 %, which is comparable to the results with an autogenous iliac bone graft. The results demonstrate the benefits of composite DBM and osteoconductive material with a lamina local bone graft for multi-segment lumbar spine fusion. DBM could be successfully used as a bone graft extender for multi-segment posterolateral fusion success. Through the combination of DBM, autogenous laminectomy bone chips, and synthetic osteoconductive materials, the custom bone graft composites can provide all three components: osteogenesis, osteoinduction and osteoconduction, for bone formation. It can be used as an effect bone graft substitute for multi-segment posterolateral lumbar fusion and may decrease morbidities associated with autogenous iliac bone graft harvest.
AIBG remains the gold standard for successful spine fusion. However, it should be recognized as having associated complications such as donor site morbidity, postoperative pain, added blood loss, and increased surgical time [1, 2]. The current study demonstrated the same findings that the operative time, blood loss and hospital stay duration being higher in the autologous iliac bone graft group.
Autologous laminectomy bone is harvested from the lamina, spinous process, and facet during the decompression procedures. For single-level posterolateral fusion, ALB has similar successful fusion rates as AIBG [4, 12–16]. In contrast, ALB has worse results for multi-level fusions compared with AIBG [16]. This reflects the shortages of ALB, including its relatively limited quantity for multi-level fusions, and urges us to determine whether the DBM and synthetic osteoconductive material could be used as a bone expander in conjunction with ALB especially for multi-level posterolateral fusions.
DBM is a form of allograft created from cadaveric bone without the mineral content and the risk of disease transmission. The remaining type I collagen and non-collagenous proteins can serve as an osteoconductive scaffold [3]. It also has been demonstrated to be osteoinductive, or capable of inducing bone formation in heterotopic sites [17]. Compared to recombinant growth factors, it is relatively less expensive and unlimited in quantity. DBM has some shortcomings, including its highly variable osteoinductive properties and possible nephrotoxicity in animal studies [3]. The products of different manufacturing companies, even of the same manufacturer, may contain variability of growth factors for osteoinductive properties. Bae et al. found significant lot-to-lot variability in bone morphogenetic protein concentrations, which resulted in variable rates of fusion in vivo [18]. In the current study, the authors did not use DBM alone for posterolateral fusion. All lots of commercially available DBM putty are tested for inductivity prior to release by manufacturing company. The testing methods have been correlated with new bone formation in athymic rat models, which is widely considered the gold standard for assessing the osteoiductivity of a material [19].
In addition, the hydroxyapatite-β-tricalcium phosphate granules used in the current study also provided the property of the osteoconductive scaffold that facilitated the fusion mass formation. In our previous study and as other literatures showed, the calcium sulfate or hydroxyapatite-β-tricalcium phosphate granules combined with ALB provided equivalent bone formation and fusion success to AIBG for one- or two-level short instrumented posterolateral fusion [4, 20]. These osteoconductive materials resorb completely as newly formed bone remodels and allow blood vessels and osteogenic cells in-growth [21]. ALB is an autogenous bone graft harvested from the posterior elements in the spine structure including lamina, facet joint and spinal processes. Theoretically, it may provide osteogenic cells and osteoinductive and osteoconductive functions although the ALB bone chips are mainly cortical in nature. The DBM provides osteoinductive and osteoconductive functions. The hydroxyapatite-β-tricalcium phosphate granules provide osteoconductive function. In combination with ALB, DBM and synthetic osteoconductive materials, these composites may provide an adequate amount of bone graft with all three components of bone formation for long multi-level posterolateral spine fusion.
This study had some limitations. First, using plain radiographs alone to determine the status of posterolateral spine fusion is still questionable. The use of CT scans with sagittal, coronal and 3-dimensional reconstruction is suggested to improve the accuracy of fusion evaluation. However, using CT scans increases the amounts of radiation to which the patient is subjected and not every patient would consent to CT scans examination. Second, the current study is retrospective and not randomized. The sample size is relatively small and not large enough to detect the difference. However, the present study has the advantage of consistency between the two groups. The included patients were in a consecutive series before and after the availability of DBM in our hospital. The two groups examined here appear comparable in terms of the fusion success since the demographic data between groups were similar. All the operative procedures and follow-ups were performed at a single institution and by the same surgeon, this study eliminated possible differences in surgical technique and had excellent compliance with follow-up. Since all the patients had been followed up on for at least 18 months, we could use the 12-month plain radiographs for fusion status evaluation and comparison.