MRI Measurement Of Lumbar Nucleus Pulposus Volume To Investigate The Influence Of Unilateral Pedicle Screw Fixation With A Single Cage On Adjacent Segment Degeneration

Objective : MRI measurement of lumbar nucleus pulposus volume to investigate the influence of unilateral pedicle screw fixation with a single cage on adjacent segment degeneration in treating lumbar degenerative disease.Methods : From October 2011 to October 2012, 34 patients with one level lumbar degenerative disease were treated by posterior lumbar interbody fusion（PLIF） with unilateral pedicle screw（UPS） fixation with a single cage insertion.34 patients(L_4⁵:9 males and 7 females; range,30⁵0 years, average age 46years; L_5^S1:10 males and 8 females; range,35⁵2 years, average age 47 years). The mean follow up period was 30 months（range, 24³6 months）,and 18 months postoperation take out the fixation. X-ray and magnetic resonance imaging（MRI）examinations were performed at 6, 12, 18, 30 months after treatment. The transverse diameter,sagittal diameter of the nucleus pulposus（NP） were measured by using the intervertebral axial images,while the NP height was measured by middle sagittal intervertebral upper T2-weighted images. The NP cross-section is sub-elliptical,using ellipsoidal volume formula to calculate the volume of NP. Based on X-ray films, height of intervertebral space was measured using angle bisectrix method. According to the postoperative change of nucleus pulposus volume and intervertebral disc height,can reveal the degeneration of adjacent intervertebral disc nucleus pulposus.Results :PLIF with UPS fixation at the L_4⁵ level:of male cases, the volume of NP at cranial adjacent L（3⁴） segment decreased at postoperative 30 months（4.542±1.1cm³,P=0.139）,while the female cases increased（3.775±0.71cm³,P=0.143）.But there were all no significant differences in terms of demographic data. Fixation at the L_5^S1 level: of male cases the volume of NP at cranial adjacent L_4⁵ segment has no significant decreased at postoperative 30 months（4.74±1.19cm3,P=0.096）,while the female cases increased at 6, 12, 18 and 30 months after infusion（3.851±1.22cm³, P =0.977;3.851±1.22cm3,P=0.983;3.852±1.22cm³,P=0.969;3.853±1.21cm3,P=0.965）. For the change of disc space height（DSH） at L_3⁴ level,all patients has no significant decrease at postoperative 30 months（males, 7.257±0.17 cm,P=0.195;females:6.95±0.03 cm,P=0.905）;for at L_4⁵ level,all patients has no significant decrease at postoperative 30 months（males:7.925±0.01 cm, P =0.653;females:7.791±0.01 cm,P=0.66）.Conclusion :Unilateral pedicle screw with a single cage could effectively prevent adjacent segment degeneration in treating partial lumbar intervertebral degenerative disease.