Identifying Factors Predictive of Atlantoaxial Fusion Failure in Pediatric Patients

Lessons Learned From a Retrospective Pediatric Craniocervical Society Study

Douglas L. Brockmeyer, MD; Walavan Sivakumar, MD; Marcus D. Mazur, MD; Christina M. Sayama, MD; Hannah E. Goldstein, MD; Sean M. Lew, MD; Todd C. Hankinson, MD; Richard C.E. Anderson, MD; Andrew Jea, MD; Philipp R. Aldana, MD; Mark Proctor, MD; Daniel Hedequist, MD; Jay K. Riva-Cambrin, MD

Disclosures

Spine. 2018;43(11):754-760. 

In This Article

Discussion

This report demonstrates that Down syndrome was a significant risk factor predictive of surgical nonunion (odds ratio 14.6, 95% confidence interval [3.7–64.0]) in a multicenter cohort of 131 pediatric patients undergoing posterior atlantoaxial instrumentation and fusion. Interestingly, instrumentation type, bone graft type, biological adjunct use, and BMP use were not independent predictors of surgical failure.

Previous smaller single-center studies have shown that very high rates of success, from 87% to 100%, can be achieved in pediatric patients undergoing posterior atlantoaxial fusion.[1–9,11–21] In one combined adult and pediatric study of 52 patients pooled from multicenter data, Hood et al[21] showed that a fusion rate of 100% could be achieved in posterior instrumented atlantoaxial fusions using allograft and rhBMP; however, no patients with Down syndrome were included in the study. Gluf and Brockmeyer[4] included 11 patients with DS in their report of 67 pediatric patients who underwent C1–2 transarticular screw fixation for atlantoaxial instability; however, no fusion failures were reported in the DS group.

This study differs from previous work in that it includes data from seven pediatric spine centers in the United States and includes results from both neurosurgical and orthopedic practices. The length of time over which patients were included (1995–2014) ensures that the distribution and variety of case types are representative of a typical pediatric spine practice and not biased from a sample from a combined adult–pediatric cohort. The variety of surgical techniques and orthoses used gives further real-world generalizability to the findings.

Down Syndrome and Atlantoaxial Fusion

It is commonly known that Down syndrome is a risk factor for atlantoaxial instability;[23–28] however, over the years, quantifying that risk in terms of patient safety and need for surgical stabilization has been difficult.[23] In its seminal paper, the American Academy of Pediatrics reviewed the evidence surrounding Down syndrome and atlantoaxial instability and concluded that an atlantodental interval of 4.5 mm was sufficient to exclude a patient from participation in the Special Olympics.[29,30] In the intervening years, it is impossible to know how many Down syndrome patients have undergone atlantoaxial fusion as a result of those guidelines. Although a discussion of the indications for atlantoaxial fusion in patients with Down syndrome is beyond the scope of this article, it is important to point out that the surgical management of atlantoaxial or craniovertebral instability for Down syndrome patients is still evolving.[23,31–34] The previous reports are primarily concerned with the anatomical, pathophysiological, and surgical aspects of the disorder, with little comment on surgical success. In fact, until this report, no study has previously identified Down syndrome as a risk factor for surgical failure in either atlantoaxial or craniocervical fusion.

The fact that Down syndrome is a risk factor for surgical failure in atlantoaxial fusion makes intuitive sense. Patients with Down syndrome have been identified as having lower bone density as well as collagen abnormalities with soft tissue laxity, which may contribute to associated surgical complications and pseudoarthrosis.[35–37] Most patients with Down syndrome are known to have some degree of immunodeficiency.[38–41] Since bone healing relies on a complex cascade of immunological phenomena, our findings should come as no surprise. Clearly, further work needs to be done to understand the biological basis of this topic.

Lessons Learned

There are two main lessons from this study. First, it appears that the technical challenges associated with pediatric atlantoaxial fusion have mostly been overcome and that a variety of rigid instrumentation and bracing techniques can be used to provide a high degree of surgical success. Second, since 7 of the 11 surgical failures in this study occurred in children with Down syndrome, further work is clearly needed to understand the underlying biological factors responsible for fusion failure in that population.

Limitations

There are several limitations to this study. First, the noncontrolled, retrospective nature of the data introduces the usual inherent biases. Second, there was no standardized definition of fusion or instrumentation failure between each center. Similarly, although the length of follow-up was at least 2 years, it varied between centers and surgeons. At each site, the senior surgeon's clinical judgment was used to determine the outcome measures. The radiographic method (x-ray or CT) for recording fusion status was not recorded in each case; thus, we cannot confirm how many were assessed with CT (the criterion standard). Third, for those patients in whom BMP or biological adjunct was used, there was no standardized dose prescribed during surgery. In addition, although the inclusion of reoperations in this cohort was important to the generalizability of the study results and patients undergoing reoperations were included from all study centers, this may limit the interpretation of the results. Finally, the duration of external orthosis use varied widely between centers and could not be controlled for.

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