OBJECTIVETo measure the correlative parameters of vertebral pedicles from L₁ to S₁ by CT scan in the patients with thoracolumbar kyphosis secondary to ankylosing spondylitis(AS) and disc degenerative disease(DDD), and analyze their anatomical difference in order to provide the selection and placement of pedicle screw during operation.

METHODSThe clinical data of 30 male AS patients (AS group) with the mean age of(35.7±9.5) years (ranged, 23 to 51) and 30 male DDD patients (DDD group) with the mean age of(52.4±8.9) years(ranged, 39 to 64) underwent surgery in our institution from March 2012 to November 2014 were analyzed. The CT scans of lumbar and sacrum were performed before surgery. The parameters of vertebral pedicle from L₁ to S₁ were measured and compared, including pedicle width (PW), pedicle screw path length (PL), pedicle height (PH), pedicle transverse angle (EA), and pedicle inclined angle (FA). Paired sample t-test was used to detect the divergence in the above-mentioned data between left and right sides. In addition, results between two groups were compared using independent sample t-test.

RESULTSThe study showed that a gradual increase in the average pedicle width both AS group and DDD group from L₁ to S₁. The average PW of AS group was bigger than DDD group in L₅ and S₁(<0.05), it was(16.47±2.66) mm and (21.76±2.97)mm vs. (14.51±2.11)mm and (18.87±2.14) mm respectively;the average PL of DDD group was smaller than AS group from L₁ to S₁(<0.05); the both maximum of PL were in L₃ segment; the average EA of AS group was smaller than DDD group from L₁ to S₁; the average FA of AS group was significantly smaller than DDD group from L₃ to S₁, (<0.05), was(-2.88±10.24)°, (-7.88±10.22)°, (-7.70±10.40)°, (-5.15±10.25)° vs. (4.05±2.21)°, (7.79±4.38)°, (7.07±3.21)°, (12.62±3.21)°, respectively.

CONCLUSIONSIncreasing the strength of internal fixation is feasible to insert the larger and bigger pedicle screws in low lumbar and S₁ among AS patients, while the EA should be decreased properly and the direction on the sagittal plane should be adjusted.