𝗧𝗵𝗲 𝗛𝗶𝗱𝗱𝗲𝗻 𝗩𝗮𝗿𝗶𝗮𝗯𝗹𝗲 𝗶𝗻 𝗙𝘂𝘀𝗶𝗼𝗻 𝗢𝘂𝘁𝗰𝗼𝗺𝗲𝘀: 𝗪𝗵𝘆 𝗕𝗶𝗼𝗹𝗼𝗴𝗶𝗰𝘀 𝗣𝗹𝗮𝗻𝗻𝗶𝗻𝗴 𝗗𝗲𝘀𝗲𝗿𝘃𝗲𝘀 𝘁𝗵𝗲 𝗦𝗮𝗺𝗲 𝗣𝗿𝗲𝗰𝗶𝘀𝗶𝗼𝗻 𝗮𝘀 𝗛𝗮𝗿𝗱𝘄𝗮𝗿𝗲

Preoperative spine planning is now exacting:

Pelvic incidence is measured to a degree.

Instrumentation is templated to the millimeter.

Yet one variable that directly impacts fusion success is still often left to intraoperative judgment:

𝗕𝗼𝗻𝗲 𝗴𝗿𝗮𝗳𝘁 𝘃𝗼𝗹𝘂𝗺𝗲.

A recent study in the European Spine Journal makes a compelling case that deserves more attention.

𝗗𝗲𝗳𝗼𝗿𝗺𝗶𝘁𝘆 𝗦𝘂𝗿𝗴𝗲𝗿𝘆 𝗮𝘀 𝗮 “𝗦𝘁𝗿𝗲𝘀𝘀 𝗧𝗲𝘀𝘁” 𝗳𝗼𝗿 𝗙𝘂𝘀𝗶𝗼𝗻 𝗕𝗶𝗼𝗹𝗼𝗴𝘆

Kazarian et al. reviewed 𝟯𝟭𝟬 𝗮𝗱𝘂𝗹𝘁 𝘀𝗽𝗶𝗻𝗮𝗹 𝗱𝗲𝗳𝗼𝗿𝗺𝗶𝘁𝘆 (𝗔𝗦𝗗) cases to identify drivers of mechanical failure (pseudarthrosis, screw loosening, rod breakage).

Their finding was strikingly quantitative:

𝗖𝗼𝗺𝗽𝗹𝗶𝗰𝗮𝘁𝗶𝗼𝗻 𝗿𝗮𝘁𝗲𝘀 𝗿𝗼𝘀𝗲 𝘀𝗵𝗮𝗿𝗽𝗹𝘆 𝘄𝗵𝗲𝗻 𝗺𝗶𝗻𝗲𝗿𝗮𝗹𝗶𝘇𝗲𝗱 𝗮𝗹𝗹𝗼𝗴𝗿𝗮𝗳𝘁 𝘃𝗼𝗹𝘂𝗺𝗲 𝗳𝗲𝗹𝗹 𝗯𝗲𝗹𝗼𝘄 ~𝟭𝟬.𝟯 𝗰𝗰 𝗽𝗲𝗿 𝗹𝗲𝘃𝗲𝗹

In other words, there appears to be a biological “volume floor” below which the fusion construct becomes vulnerable.

ASD may represent an extreme use case—but that is precisely why the signal is so clear.

𝗪𝗵𝘆 𝗧𝗵𝗶𝘀 𝗠𝗮𝘁𝘁𝗲𝗿𝘀 𝗕𝗲𝘆𝗼𝗻𝗱 𝗗𝗲𝗳𝗼𝗿𝗺𝗶𝘁𝘆

If complex deformity constructs fail biologically below ~10 cc/level, what does that imply for routine degenerative fusions?

The broader literature points in the same direction:

𝗩𝗼𝗹𝘂𝗺𝗲 𝗺𝗮𝘁𝘁𝗲𝗿𝘀: Yoo et al. showed significantly lower fusion rates in MIS-TLIF when total graft volume dropped below ~𝟭𝟮 𝗰𝗰

𝗦𝘂𝗽𝗽𝗹𝘆 𝗶𝘀 𝗼𝘃𝗲𝗿𝗲𝘀𝘁𝗶𝗺𝗮𝘁𝗲𝗱: Classic work by Carragee et al. suggests a standard laminectomy yields limited local bone.

𝗥𝗲𝘀𝗼𝗿𝗽𝘁𝗶𝗼𝗻 𝗶𝘀 𝗿𝗲𝗮𝗹: Kim et al. demonstrated that grafts may lose ~𝟱𝟬–𝟱𝟱% 𝗼𝗳 𝘃𝗼𝗹𝘂𝗺𝗲 during remodeling

Together, these data suggest many cases may unknowingly drift into a biologic risk zone.

𝗧𝗵𝗲 “𝗥𝗮𝘁𝗶𝗼 𝗧𝗿𝗮𝗽”

The Kazarian study also reinforced an important compositional insight:

A high DBM-to-bone ratio was associated with failure

The authors recommend a ratio favoring 𝗺𝗶𝗻𝗲𝗿𝗮𝗹𝗶𝘇𝗲𝗱 𝗮𝗹𝗹𝗼𝗴𝗿𝗮𝗳𝘁 (>𝟭.𝟱:𝟭)

At least for ADS's, DBM enhances biology—but does not replace the need for a durable scaffold capable of surviving resorption and consolidation.

𝗪𝗵𝗮𝘁 𝘁𝗵𝗲 𝗗𝗮𝘁𝗮 𝗜𝘀 𝗥𝗲𝗮𝗹𝗹𝘆 𝗦𝗮𝘆𝗶𝗻𝗴

Successful fusion is not just about having graft—it’s about 𝗲𝗻𝗴𝗶𝗻𝗲𝗲𝗿𝗶𝗻𝗴 the 𝘀𝗰𝗮𝗳𝗳𝗼𝗹𝗱:

𝗤𝘂𝗮𝗻𝘁𝗶𝗳𝗶𝗮𝗯𝗹𝗲 𝘁𝗮𝗿𝗴𝗲𝘁𝘀: >10 cc of graft volume per level appears to matter

𝗖𝗼𝗺𝗽𝗼𝘀𝗶𝘁𝗶𝗼𝗻 𝗱𝗶𝘀𝗰𝗶𝗽𝗹𝗶𝗻𝗲: DBM may be an adjunct, not a substitute

𝗣𝗹𝗮𝗻𝗻𝗶𝗻𝗴 𝗳𝗼𝗿 𝗹𝗼𝘀𝘀: If ~50% resorption is expected, biologics planning must account for it

As hardware and navigation continue to evolve, the evidence suggests that bone graft engineering deserves the same presurgical rigor.