[Preoperative planning and computer assisted surgery in ankylosing spondylitis]

The following study describes a technique for preoperative planning and computer-assisted correction osteotomy in the treatment of ankylosing spondylitis. The effect on the overall sagittal profile is evaluated.

Kyphosis was corrected by a posterior closing wedge osteotomy. Angle and localisation of the wedge were exactly planned preoperatively and transferred to a navigation system. The osteotomy was then performed along the premarked lines with image-guided tools. Nine patients aged 40 to 61 years (average 46 years) were operated on. Follow-up time averaged 12 months (1 to 33 months).

The planned angle of the wedge osteotomy was an average of 30 degrees (range 24 degrees to 40 degrees ) preoperatively. Postoperatively, the angle averaged 30 degrees as well (range 22 degrees to 41 degrees ). The individual difference between real and planned angle was an average of 2.7 degrees (range 1 degrees to 6 degrees ). Sacral inclination was 23 degrees preoperatively (range-- 6 degrees to 40 degrees ) and was corrected to 40 degrees (range 27 degrees to 49 degrees ). Anterior displacement of the gravity line averaged 112 mm preoperatively (range 47 to 196 mm) and was corrected to 31 mm (range--7 to 135 mm) postoperatively and 38 mm (range-- 21 to 137 mm) at latest follow-up.

Precise preoperative planning and correction osteotomy exactly according to this planning allow for an excellent correction of the sagittal profile even in severe ankylosing spondylitis. Pelvic tilt and gravity line are normalised, the patient is able to adopt an ergonomic upright position. Navigation facilitates the intraoperative transfer of the preoperative planning.