Single-stage anterior release and posterior instrumented fusion for irreducible atlantoaxial dislocation with basilar invagination

Abstract

Background ContextThe options available for treatment of irreducible atlantoaxial dislocation (IAAD) with basilar invagination are odontoidectomy, posterior decompression, and posterior atlantoaxial joint distraction. In 2006, Wang et al. described that most IAAD can be reduced following anterior release of contracted soft tissues. Anterior release may be done by transoral (TO) or retropharyngeal (RP) approach. Posterior instrumented fusion provides stability and helps in achieving further reduction. PurposeThis study aimed to study the neurologic and radiological outcome following treatment of basilar invagination associated with IAAD by anterior release and posterior instrumented fusion. Study DesignA retrospective case series was carried out. Patient SampleThe patient sample comprised 19 patients with IAAD. Outcome MeasurePatients were assessed for neurologic recovery by Benzel modified Japanese Orthopaedic Association (mJOA) score and radiologically by assessing reduction on lateral radiographs and comparing clivus-canal angle (CCA) on preoperative and postoperative computed tomography scan. MethodsNineteen consecutive patients with IAAD were surgically treated. Anterior release was done via TO approach in 12 patients and RP approach in 7. Following anterior release, all patients underwent posterior instrumented fusion. ResultsThis study included 15 men and 4 women with mean follow-up of 18 months. Pathology included occipitalization of atlas in 16 patients, os odontoideum in 2, and missing posterior elements of axis in 1. All patients had cervical myelopathy. Occipitocervical fixation was done in 18 patients and C1–C2 transarticular screw fixation in 1. Fifteen patients had anatomical reduction whereas four had partial reduction. The CCA improved from a mean preoperative angle of 111.47° to mean postoperative angle of 142.84°. The mJOA improved from preoperative mean mJOA of 12.89 to a postoperative mean mJOA of 16.84. Fusion was achieved in all patients. Maceration of posterior wound which healed by daily cleaning and dressing was noted in three patients. Implant breakage on one side was noted in 1 patient at 3 months post operation; however, the patient remained asymptomatic. ConclusionThis series reinforces the safety and efficacy of both TO and RP anterior release for reduction of IAAD. Posterior fixation helps in achieving further reduction and provides stability. Anterior release followed by instrumented posterior fusion is a safe and effective modality of treatment for IAAD associated with basilar invagination.