Through our primary outcome analysis, our study showed a higher proportion of fusion rate for LB (95.3%) compared to AIC (88.6%), ALG (87.8%) and ALP (85 .8%). This finding was not expected because LB has less trabecular bone, which would theoretically result in less bone marrow and less availability of pluripotent cells and growth factors.25. Additionally, LB’s limited harvestable volume reduces its surgical recommendations, and it is commonly applied to the cervical spine (implying a smaller area to cover and less body burden to bear compared to the lumbar spine).
Our sample consisted mainly of AIC patients (2529), followed by ALP (766), ALG (516) and LB (366) patients. This size discrepancy could explain the LB fusion effect among our pooled samples, which could exacerbate the LB effect. Additionally, most studies did not present baseline assessments of participants, and since the quality of fusion of distinct grafts may diverge depending on age, metabolic activity, or graft bed preparation.26.27, it is difficult to confirm the superiority of LB graft fusions over the other options studied. Similarly, most of the studies reviewed did not follow FDA guidelines for spinal fusion assessments.28increasing their evaluation bias.
Additionally, the literature has often identified conflicting opinions regarding the optimal association between surgical techniques and underlying patient predictors for spinal fusions and spinal grafts. Other meta-analyses, which have examined various graft materials or surgical approaches, have demonstrated higher fusion rates using rhBMP27,29,30 or when grafts are combined with the anterior lumbar interbody fusion technique31. Additionally, minimally invasive procedures did not demonstrate differences in fusion rate compared to open surgical techniques.32.
Given data inconsistencies in our main analysis, which precluded other associations (e.g., fusion rate × graft type × surgical technique), we performed a subgroup analysis of fusion rates with or without implants metallic. In this subgroup, LB had lower fusion rates when combined with metal implants, and this finding could be explained by the limitations of LB in graft volume availability.33 and/or a small sample of patients.
Rates of pseudoarthrosis and adverse events were studied as secondary outcomes. Our analysis of nonunion revealed that the data reported showed a higher proportional rate of nonunion in the lumbar spine (14.2%) than in the cervical spine (4.1%), consistent with previous analyses.6which is explained by the increased difficulty of stabilizing areas that support higher loads34.35. Additionally, our analysis of bone graft types revealed that LB had a higher combined proportional non-union rate (10.5%). However, some considerations are worth mentioning. Rates of non-union were not systematically assessed in the studies reviewed (AIC 17 out of 51 analyses; ALG 4 out of 9 analyses; ALP 6 out of 20 analyses; and LB 5 out of 10 analyses), which could have exacerbated the discrepancy between the number of patients and the effects analysed. Likewise, the authors’ descriptions of their results do not suggest that non-union can be assumed to result directly from the absence of fusion rate in fusion rate analyses. Moreover, the literature did not present a conclusive role governing the influence of bone grafts on rates of nonunion.6.
Higher rates of non-union have previously been associated with older age (due to delayed bridge maturation and increased bone resorption)36degenerative disease and build length6. Longer fusions can allow load distribution, minimizing excessive movement and helping to reduce non-union34.37. However, they can also increase load break points for each adjacent segment34, require more transplants and increase patient exposure to complications (due to major surgery). Nevertheless, our literature review examined a limited sample for this subgroup analysis, and it included many studies with moderate to high heterogeneity, reflecting the diversity of assessments of nonunion. For example, Choudhri et al.38 recommend CT imaging with axial and thin-section multiplanar reconstruction to assess spinal fusions. However, no radiographic reference standard is available to assess pseudarthrosis.38 compared to open surgical exploration. Therefore, as in the literature, our review did not find a conclusive role governing the influence of bone grafts on nonunion rates.6.
In addition, many available studies had significant methodological flaws regarding adverse events, limiting the analyses. AIC pain corresponded to a combined proportional rate of 23.4% and a significant proportion of donor site morbidity (23.2%), corroborating the disadvantages of transplantation mentioned previously and already described in the literature.11,12,13,14,15,16. Unsurprisingly, and as mentioned, foreign bodies can carry some inherent risks, which could explain the proportional rates of infection (10.2%) and transplant-related events (35.1%) higher than the ALP.
Our study encountered other limitations. Heterogeneity was found in different aspects of the populations of the studies reviewed. This heterogeneity stemmed from clinical diversity in the two treatment groups, supported by insufficient analyses, a small group of subjects, differences in baseline assessment and patient outcomes, and lack of systematic reporting (e.g., ., the use of tobacco or nonsteroidal anti-inflammatory drugs could have led to misinterpretation of fusion rates). Additionally, a standard data collection tool could improve data availability for fusion rate analysis and assessment of nonunion. Moreover, we did not include all available ALP grafts due to the large existing variability, which could weaken the proportional analysis. One example is platelet-rich plasma, which is increasingly recognized as an important supplement in the spine transplant market.39. Finally, an overall higher RoB – which could influence evaluations of the effects of interventions – indicated a lack of structured randomized trials. Additionally, successful treatments should be interpreted in light of decreased patient exposure to nosocomial events, acceptable survival rates, and function after treatment.
Comparing the contributions of more than three decades of medical evolution is a challenge, given technical improvements, instrumental variations and a greater range of equipment. Competition for better material outcomes will continue, along with the difficulty of medical updates and the discernment of industry interests. Structured clinical trials are strongly encouraged to promote the availability of optimal and cost-effective treatments for patients.
The results of our analysis demonstrate a substantial variety of spinal grafts and the need for more rigorous studies to better address and help surgeons choose the best graft options. Standardized methods for evaluating spinal fusion and non-union are encouraged.