Preoperative Planning and the Use of Free Available Software for Sagittal Plane Corrective Osteotomies of the Lumbar Spine in Ankylosing Spondylitis.

Preoperative planning of the lumbar osteotomy in AS involves assessment of the combined effect of location of the osteotomy, amount of bone resection, SVA, CBVA, and pelvic parameters. Two free available computer programs, ASKyphoplan and Surgimap, are easy to use in clinical practice to predict postoperative sagittal balance of lumbar osteotomies in patients with severe TLKD due to AS.