ASKyphoplan Manual

The computational program ASKyphoplan [1] is based on the biomechanical and mathematical principles described by Van Royen et al. in 2000 [2]. In the present description of an ASKyphoplan run, we define the plumb line from the centre of the vertebral body of C7 and we plan the osteotomy at level L4. The normal sacral endplate angle (SEA) or sacral slope (SS) is defined at 40 degrees with the horizontal.  Obviously, all variables can be changed independently for each case.

Radiographic analysis
A standard full-length lateral radiograph of the whole spine with the patient standing in relaxed standing position is made. Preferably, the radiograph is acquired and saved in a picture archiving and communication system (PACS). However, the use of a digitized regular film is also possible. The centre of body C7, the posterior superior corner of the sacrum (PSCS), the sacral endplate (SEA) or sacral slope (SS), and the rotation point (RP) on the anterior cortex of L4 are marked on the radiograph. In addition, the 50 mm grid of the film or two randomly chosen points are measured using ‘measuring distance’ tool displayed on the digital system for calibration. Finally, the marked radiograph is saved in JPEG, Dicom or PNG format on a personal computer.

ASKyphoplan run
Open the file with the saved radiograph in ASKyphoplan and upload the digitalized radiograph including the marks. Five consecutive pages are followed: ‘Calibration’, ‘Draw’, ‘Set SEA’, ‘Calculate’, and ‘Report’.

  1. Calibrate: Mark the two measured reference points or the two marks on the grid of the film and define the distance in mm for calibration in the program.
  2. Draw: The preceding marked reference points on the radiograph serve as guidance for drawing the deformity planning.
    1. PSCS: The posterior superior corner of the sacrum (PSCS) is marked and a co-ordinate system appears.
    2. SEA: Than, the sacral endplate angle (SEA) from the posterior superior corner of the sacrum, parallel to the sacral endplate is drawn. The individual (compensated) SEA will appear in degrees.
    3. C7: The centre of body C7 is marked, and the plumb line from C7 appears. The sagittal vertical axis (SVA), defined as the horizontal distance between the posterior corner of the sacrum and the plumb line from C7, will be shown.
    4. RP: Finally, the aimed hinge or rotation point (RP) at the anterior cortex of L4 is marked.
  3. Set SEA: The normal SEA is assumed to make an angle of approximately 40 degrees with the horizontal [1,2,3]. By defining the SEA at 40 degrees, the radiograph will be projected onto the co-ordinate system with the SEA at 40 degrees. The pre-operative SVA without compensation appears in millimeters.
  4. Calculate: The relation between the correction angle, the level of osteotomy and the sagittal balance of the spine is calculated and visualized in the computer program. By planning the osteotomy at level L4 and aiming the post-operative SVA at 0 mm or 50 mm for example, the aimed correction angle at L4 and resulting correction of the view angle correction (CBVA) follows. By using the ‘visibility’ bar, the virtual post-operative radiograph can be visualized. The effect of changing the level of osteotomy on the SVA and CBVA correction or the effect of changing the correction angle on the SVA and CBVA can be visualized clearly by changing these variables in the program. 
  5. Report: The preoperative deformity planning, calculation and visualization of the osteotomy can be saved in PDF file and printed for documentation.

References:

  1. Van Royen BJ, Scheerder FJ, Jansen E, Smit TH. ASKyphoplan. A Program for deformity planning in Ankylosing spondylitis. Eur Spine J. 2007 Sep;16(9):1445-9.
  2. Van Royen BJ, De Gast A, Smit TH (2000) Deformity planning for sagittal plane corrective osteotomies of the spine in ankylosing spondylitis. Eur Spine J 9:492-498
  3.  Jackson RP, Peterson MD, McManus AC, Hales C (1998) Compensatory spinopelvic balance over the hip axis and better reliability in measuring lordosis to the pelvic radius on standing lateral radiographs of adult volunteers and patients. Spine 23:1750-1767