Deformity Planning for Thoracolumbar Kyphosis in Ankylosing Spondylitis
|Keywords||ankylosing spondylitis sagittal imbalance pelvic parameters heathrelated quality of life hilus pulmonis center of gravity|
Background The sagittal vertical axis (SVA) is a meaningful measurement and widely used for evaluating sagittal balance, and is considered a design standard for surgery, including most AS kyphotic deformity planning. However, recent research indicates that PT is a better parameter than SVA for evaluating global sagittal balance and the C7plumb line is actually not the center of gravity line. Therefore, what is the key radiographic parameters correlate to quality of life with sagittal imbalance in AS and whether there is a better radiological marker as the center of gravity of the trunk for AS thoracolumbar kyphosis remains unknown.Objective To investigate key radiographic parameters that we should be pay attention to and determine a radiological marker for the center of gravity of the trunk in lateral radiographs for adequate and convenient deformity planning for ankylosing spondylitis (AS) thoracolumbar kyphosis.Methods1.38patients were included in the research. Pre and postoperative radiological parameters, including CobbTl-S1, pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS) and sagittal vertical axis (SVA) were measured. Corresponding ODI, SRS-22were collected as well by questionnaire. Statistical correlation analysis was pursued to determine correlation (Partial Correlation) between radiographic parameters and overall or domain specific scores of Health Related Quality of Life (HRQOL) instruments.2. Pre-and post-operative radiological parameters were measured, including SVA, horizontal distance between hip axis and C7(HDHC), horizontal distance between hip axis and T5(HDHT5), horizontal distance between hip axis and T9(HDHT9), and horizontal distance between hip axis and hilus pulmonis (HDHH). Pre-and post-operative radiological parameter changes were compared by paired samples t-tests.3.20patients with ankylosing spondylitis underwent spinal osteotomy for correcting kyphotic deformity were studied. We calculated the ideal postoperative PT according to PI, and chose the plumbline of hilus pulmonis rather than C7as gravity line of upper trunk. Then the necessary angular correction at the level of osteotomy was calculated. Pre or postoperative radiological parameters, including CobbTl-S1, PI, PT, SS, SVA were measured, and corresponding ODI and SRS-22were collected as well by questionnaire filled before operation and at6months follow up.Results1. Though CobbTl-S1and SVA had partial correlation coefficients with ODI walking (r=0.86,0.53) and ODI standing (r=0.63,0.63) preoperatively, no statistical significance were found postoperatively. On the other side, PT and SS not only had partial correlation coefficients with ODI preoperatively (ODI walking r=0.72,0.72; ODI standing r=0.57,0.56), but also did postoperatively (ODI total scores r=0.52,0.53; ODI walking r=0.54,0.56; ODI standing r=0.77,0.77).2. Pre-operative SVA, HDHC, HDHT5, HDHT9, and HDHH values were, respectively,21.2cm,12.9cm,3.6cm,-3.7cm, and2.7cm, and their post-operative values were, respectively,9.1cm,4.2cm,-2.1cm,-5.6cm, and0.9cm. Changes in SVA, HDHC, HDHT5, and HDHT9were significant, while the change in HDHH was not.3. The preoperative and postoperative CobbTl-S1were52°and3°, respectively. All patients demonstrated changes in preoperative to postoperative radiographic parameters including decreased PT (from30°to11°) and increased SS (from16°to35°).Conclusion1.Backward pelvic rotation causes erect disability, PT and SS are the key radiographic parameters correlate to quality of life.2. The hilus pulmonis fell approximately on the hip axis both pre-and post-operatively. It was a better marker as the center of gravity of the trunk for AS thoracolumbar kyphosis.3. The deformity planning which uses PI to calculate PT and makes hilus pulmonis is individual and successful.