Purpose: Single-segment wedge osteotomy is classically proposed to correct for kyphosis subsequent to ankylosing spondylitits. We analysed the usefulness of this technique for other indications (revision procedures for flat back and deformed calluses of the lumbar spine) by studying the overall sagittal balance of the spine and tilt of the sacrum.

Material and methods: Between 1980 and 1999, we retained 68 patients with complet clinical and radiological data (37 patients with ankylosing spondylitis and 31 patients with “post-operative” flat back, including nine trauma cases and 22 degenerative spines). Opening osteotomy was performed in the first 19 patients and closure osteotomy in the next 49. The correction level was L2L3 in 26 patients and lower in 42. Digitalised lateral views of the entire spine were obtained at minimum follow-up of three years to measure:

- posterior displacement of T9 (between the vertical line and a line joining the geometric centre of T9 and the femoral heads (normal 11±5°),

Results and discussion: The overall angle of local correction was 44° and the correction of T9 displacement was 30.6°. For the low osteotomies, the local correction was 49° and the T9 displacement was +28° (−2° to +26°). Tilt of the sacrum varied from 4° to 7°. Tilt of the sacrum was influenced more and more for lower and lower osteotomies. T9 displacement stabilised between 12° and 26° (mean 19°) irrespective of the osteotomy level, although the angle of local correction was greater (up to 60°). This discordance was explained by adaptation of the pelvis. Seven patients developed secondary functional kyphosis (limited hip movement preventing the necessary adaptation to the overall correction of the sagittal balance).

Conclusion: Single-segment spinal osteotomy remains difficult but offers very important correction possibilities affecting the position of the trunk and adaptation of the pelvis. The level for the correction must be chosen with care because it conditions final adjustment and function consequences affecting the pelvis.