There are many bone graft substitutes marketed as effective options without the morbidity and time costs associated with harvesting autologous bone. It’s important to evaluate such claims critically.
One of the main challenges in determining whether a graft material works is the difficulty in confirming if a solid fusion has truly occurred. Studies assessing the accuracy of thin-cut CT scans show a false negative rate of about 30%—meaning a scan may indicate fusion when a nonunion (pseudarthrosis) actually exists. High-resolution flexion–extension studies or surgical exploration can reveal these nonunions. Planar pseudarthroses are especially difficult to detect on CT and may only be visible when the construct is stressed mechanically. Therefore, studies reporting success rates based solely on CT findings should be interpreted cautiously.
Historically, some studies that included surgical exploration demonstrated the limitations of CT in accurately detecting nonunion. A recent example involving patients with persistent symptoms after cervical fusions found intraoperative evidence of nonunion in 81% of cases, while CT criteria identified nonunion in only 63% of cases. This reinforces that even in cervical procedures—where fusion is often considered easier to achieve than in the lumbar spine—many patients believed to be fused may still have symptomatic pseudarthroses.Some argue that the presence of pseudarthrosis may not matter if a patient’s symptoms improve significantly. While this may be true in the short term, longer follow-up tells a different story. One-year postoperative studies suggest nonunion is less likely to correlate with poor outcomes at that stage. However, studies at five or more years show significantly worse outcomes in non-fused patients compared to those with solid fusion. Short-term positive results can mask problems that become apparent later.
Some bone graft substitutes have gained regulatory approval based on studies comparing them to “local bone” autograft. In many cases, this local bone—such as cortical osteophytes removed during cervical decompressions—is far from optimal cancellous graft. It often contains mostly cortical bone or cartilage, with minimal living cellular content. When a substitute is compared against this suboptimal control, results may appear more favorable than if compared to the gold standard of fresh cancellous autograft from sites such as the iliac crest.
Other substitutes have been evaluated without any autograft control group, sometimes in small studies, and with fusion rates determined solely by CT criteria—criteria which may include classifications that allow probable or partial pseudarthroses to be counted as successful fusions. For example, some grading systems consider “probable pseudarthrosis” or “locked pseudarthrosis” as “fused,” which can inflate reported success rates.
While these alternatives to autologous cancellous bone may result in some fusions, their true effectiveness remains uncertain because of:
- Limitations in fusion assessment methods
- Lack of comparison to the gold standard autograft
- Small study sizes and selective reporting of outcomes
Similarly, earlier studies on certain bone morphogenetic proteins in spine fusion often downplayed complications while emphasizing positive results. Manufacturers sometimes
sponsor studies with ambiguous or overly generous definitions of success, and less skeptical surgeons may accept the conclusions at face value.
It’s important to scrutinize these studies closely, push back on questionable claims, and encourage critical evaluation of bone graft choices. Many patients with symptomatic nonunion are told they are fused and sent to pain management, when in reality they might benefit from revision surgery—and may have had a better initial outcome with true gold standard cancellous autograft.
