The importance of stabilisation in enabling bone fusion demonstrated by successful revision of failed occipitocervical fusion using patient-specific atlantoaxial joint spacers: a case report.

Background: The surgical management of occipitocervical junction (OCJ) pathologies is challenging due to the unique anatomy and biomechanics. Ehlers-Danlos syndrome (EDS) is a heterogeneous group of rare hereditary disorders of connective tissue (HDCTs) resulting from mutations in collagen genes. In OCJ pathologies related to EDS, occipitocervical fusion (OCF) is preferred when conservative treatment proves insufficient. The literature indicates that complications associated with OCF are more common in patients with EDS and other HDCTs. The management of failure in OCF surgery is particularly challenging. This case report provides an example of surgical management of failed OCF using patient-specific atlantoaxial joint spacers. Case Description: In this case report, we describe a male patient with EDS who underwent OCF and experienced complete reabsorption of the bone graft and nonunion. The condition was then successfully treated using custom-made, anatomically conforming 3D-printed titanium alloy (Ti-6Al-4V) facet joint devices. The clival-axial angle was increased from 127.5 degrees after the first operation to 152.4 degrees with the facet joint devices. At 8 months postoperatively, X-rays demonstrated no change in alignment. At the 15-month follow-up, the patient reported no symptoms except for morning muscle spasms. Conclusions: Although an extensive body of literature studies the effects of EDS on connective tissue and its clinical manifestations, studies investigating its impact on bone biology and bone fusion are limited. The C1-2 level is the most susceptible to nonunion and implant failure in OCF procedures. In the case we present, nonunion and implant failure occurred specifically at this level. One of the significant advancements in C1-2 fusion in recent years is the technique described by Goel in 2004, particularly for basilar invagination and atlantoaxial dislocation. This method involves C1-2 facet distraction using intraarticular spacers and bone grafts. In this case report, the 2004 technique developed by Goel was modified to use patient-specific 3D-printed titanium cages in the C1-2 joint space. The addition of patient-specific titanium cages aided physiological realignment, which may have led to greater stability than screw fixation alone and most importantly a solid fusion in an obviously difficult fusion environment.