[Hemi-atlas: report of five cases].

C1 partial aplasia is a rare congenital deformity which can produce unacceptable progressive severe torticollis. Five such cases treated in two regional Pediatric Hospitals of Argentin are presented here. There were 4 girls and 1 boy, with a mean age of 6 years; four of them had formation defect of articular mass (Villa's Area 3) causing fixed torticollis in 3 who underwent surgery. In another case the defect consisted of a posterior hemi-arch (Area 2). Surgical procedures consisted on isolated posterior occipito-cervical arthrodesis in two cases, and associated with a posterior decompression by suboccipital craneotomy in the third, due to the presence of preoperative neurological deficit. Some internal fixation was achieved with sutures (non reabsorbibles in younger patient and wire suture in older ones). Average postoperative immobilisation with Halo-vest was 4.5 months, and it was followed with extended Philadelphia collar until complete consolidation. Non-operated patients responded to conservative therapy. Mean followup was 1 year 8 months. All patients presented correction of the deformity. The 3 surgically treated patients showed good arthrodesis and disappearance of preoperative delicit when present. In conclusion, the unilateral hipoplasias of C1 in children with unyielding deformity can be satisfactorily managed by means of CO-C2/C3 arthrodesis with or without decompression, always associated to external immobilization.