Allograft bone not reliable for atlantoaxial fusion, even with use of modern constructs

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The use of allograft is not reliable for posterior atlantoaxial fusion in an onlaid fashion, even with the rigid internal fixation of modern constructs, according to research from Honghui Hospital, Xi’an Jiaotong University Health Science Center, Xi’an, China. The study confirmed autograft as the gold standard for atlantoaxial fusion, in spite of its higher rate of donor-site morbidity. Secondarily, the research supports the claim that confirmation of fusion should be based on the presence of bridging bone on CT imaging.

The study was presented at the 30th Annual Meeting of the North American Spine Society (NASS; 14-17 October, Chicago, USA) by Dageng Huang, Xi’an, China. The research team wanted to investigate the option of using allograft rather than autograft bone in atlantoaxial fusion as a protective measure against the donor-site morbidity associated with autograft bone use. Concerned by the unreliability of defining fusion as the absence of movement on dynamic radiographs, they decided to evaluate the effectiveness of autograft and allograft using computed tomography (CT) imaging. “Because screw-rod systems offer firm fixation, there is no movement on dynamic radiographs unless there is hardware failure,” Huang told Spinal News International. “The absence of movement on dynamic radiographs can demonstrate stability, but it cannot demonstrate fusion.”

Forty-one consecutive patients participated in the prospective comparative study, and were given the option of choosing either autograft or allograft for their atlantoaxial fusion surgeries. The allograft group, whose members received the mixed material of morcellised allograft and local autograft for fusion, had 24 members. The autograft group, who received morcellised iliac crest autograft for fusion, was comprised of 17 members. The procedures were performed between December and January 2012 using a screw-rod fixation system. The patients were evaluated for fusion by CT imaging and for stability by dynamic radiographs. These images were taken six months after the procedure, and again every six months thereafter until the end of the study or until fusion could be confirmed by the presence of bridging bone on the CT image.

The median age of the groups were similar (allograft: 43.6±12 years, autograft: 41.1±14.1 years), as was the sex distribution (allograft: 58.3% male, autograft: 58.8% male). At the final follow-up, the rates of fusion in each group were markedly different. The autograft procedures reported a more than ten times greater rate of fusion than allograft (allograft: 8.3%, autograft: 88.2%). All procedures were 100% stable.

The expected higher rate of donor-site morbidity in autograft procedures was confirmed, with an 11.8% perioperative complication rate in this group, as opposed to a 4.2% rate in the allograft group. The estimated blood loss and operating times were both somewhat higher in the autograft group (235.8ml±46ml vs. 170.8ml±60.6ml, and 142.4±23.6 mins vs. 123.3±18.3 mins).

The research team concluded that allograft was not a reliable option for posterior atlantoaxial fusion, even with the use of modern fixation constructs. Successful fusion requires three key factors: osteogenic cells, osteoinductive factors, and an osteoconductive matrix,” said Huang. “Firm fixation is also needed as slight movement in the fusion region can lead to repeated breakage of the new callous, in formation. Autograft bone contains all three factors, while the screw-rod system can offer satisfactorily firm fixation.”

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