Study questions definition of critical-sized bone defect

BALTIMORE — Investigators here presented data culled from the more than 1,200 patient SPRINT trial that shows 47% of patients with a critical-sized defect went on to union, causing investigators to question the definition of those defects.

David W. Sanders, MD, started his presentation at the 2010 Annual Meeting of the Orthopaedic Trauma Association (OTA) with a question: “So what is a critical-sized defect?”

He explained, as one of the investigators in the multi-million dollar, multicenter Study to Prospectively evaluate Reamed Intramedullary Nails in Tibial fractures (SPRINT) trial, they had a hard time defining what a critical defect was. “Because there really isn’t much in the literature on it,” he said. Eventually they based their definition on what they found in the literature — one that involves more than 50% of the cortical diameter of the tibia and were greater than 1 cm in length.

A rare occurrence

David W. Sanders

The purpose of this study was to ascertain the clinical and functional factors of the critical-sized defect, in terms of the rate of secondary surgery and factors associated with nonunion.

“Of the more than 1,200 patients in the SPRINT trial group, only 37 had critical defect that fit the definition,” Sanders said. “I think that demonstrates the rarity of the large bone defect.”

The group of 37 was further subdivided into seven patients who had a planed reoperation, 14 who did not require any reoperation and 16 who had unplanned reoperations.

Sanders noted that the 14 patients who healed without requiring a secondary operation, represented a 47% union rate for patients with a critical-sized defect.

“In comparing patients who had the defect to those without the defect, there are some obvious characteristics in terms of their fractures and nature of the injury separating the two,” he said. “Patients with a large defect were more likely to have a high energy injury, an open fracture, and an AO/OTA type 42C fracture, and were more likely to have polytrauma as well.”

Reoperation factors

In terms of functional outcome the SF-36 physical component score was lower in patients with a defect compared to those with no defect.

The investigators also found factors associated with reoperation within the group that had a bone defect to be: men and patients whose initial treatment was with an unreamed nail.

“Bone defects are clinically important, the rate of union in these cases was lower than the overall report and the outcomes were worse,” Sanders said. “However, the natural history suggests that 47% had a primary union rate. Overall, the size of the defects varied and many were much larger than the 50% 1 cm-rule.”

He said, although they didn’t have enough statistical power to prove it, it seemed as though the patients with a partially intact posterior or lateral cortex may be more likely to heal.

“So, what is a critical sized defect? It is still one that is unlikely to heal in the absence of secondary intervention and this study defines that a 1 cm or greater defect with more than 50% of the cortical diameter of the tibia, however with our union rate of 47% I have to say that this sized critical defect is not really critical,” Sanders said.

Reference:
Sanders DW, et al. The critical-sized defect in the tibia: Is it critical? Results from the SPRINT trial. Paper #56. Presented at the 2010 Annual Meeting of the Orthopaedic Trauma Association. Oct. 13-16, 2010. Baltimore.

In reading the original paper I was thinking about the gaps that didn’t heal and wondered was it the size of the defect? There seemed to be such a wide range of defects … and on the other side there were the ones who healed who had these very large defects ... this could be a practice-changing finding.

— Pierre Guy, MD
Orthopaedic Trauma Association moderator

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