Correlation of OPLL with Spinal Instability

PURPOSE: To evaluate the relationship between spinal instability and ossification of the posteriorlongitudinal ligament(OPLL). MATERIALS AND METHODS: In 70 patients(M:F=45:25, mean age=53years) diagnosed as OPLLon the bosis of with surgical operation field findings and radiological evaluation[ plain film(n=70), CT(n=64),MRI(n=55) ], involved levels were the cervical spine(n=32), lumbar spine(n=23), and both the cervical and lumbarspine(n=15). Spinal instability was radiologically diagnosed as horizontal displacement of one vertebra by anotherof more than 3.5mm, or a difference in rotation from either adjacent vertebra by more than 11degree in lateralcervical spine and a difference of more than 1.5mm from the posterior body margins to the point of intersection oftwo lines drawn parallel to the opposing segmental endplate in extension lateral lumbar spine. We divided OPLLinto group I(continuous, segmental, mixed) and group II(retrodiscal), and compared spinal instability in these twogroups. RESULTS: In cervical OPLL, group I comprised 33 cases and group II 14. In group I, spinal instability wasnoted in 8/33 cases(24%)) or 10/123 segments(8.1%). Spinal instability in group II, on the other hand, was foundin 13/14 cases(93%) or 17/26 segments(65%). Ossification occurred at the retrodiscal level in 37 cases, byt incase was continuous. In group II, spinal instability was found in 25 of 37 cases(69%), oe in 29 of 55segments(53%). CONCLUSION: Compared to other types of OPLL, the frequency of retrodiscal OPLL in association withspinal instability was high. Spinal instability may thus be the most important cause of retrodiscal OPLL.

Sagittal MR Findings of L5 Spondylolysis: Changes of Spinal Canal

PURPOSE: To evaluate changes in the spinal canal in cases of L5 spondylolysis, as seen on sagittal MR images. MATERIALS AND METHODS: We retrospectively analysed the MR findings of 27 patients suffering from L5 spondylolysis without spondylolisthesis and compared them with 100 control subjects. Spondylolysis had been confirmed by conventional radiography. On midsagittal MR images, sagittal canal ratio (SCR) was defined as midsagittal canal diameter at L5 devided by that at L1. We analysed the frequency of posterior epidural fat deposition (posterior epidural fat between the posterior margin of the dural sac and the anterior cortical margin of the spinous process on the midsagittal line), and compared this with the frequency in 100 control subjects. RESULTS: Mean SCR value in 27 patients with L5 spondylolysis (1.22) was significantly greater than 100 control subjects (0.96, p<0.001). Mean SCR value in 17 patients with L5 spondylolysis and posterior epidural fat deposition (1.27) was significantly higher than in nine control subjects with posterior epidural fat deposition (0.97). Posterior epidural fat deposition was more frequently indentified in patients with L5 spondylolysis (63%) than in control subjects (9%). CONCLUSION: The possibility of L5 spondylolysis is suggested when on midsaggital MR imaging, the anteroposterior diameter of the L5 spinal canal is seen to be widened and posterior epidural fat deposition is noted.

CT Findings of Isthmic Spondylolisthesis and Degenerative Spondylolisthesis

PURPOSE: To evaluate the finding useful for differential diagnosis and associated abnormalities of isthmic spondylolisthesis and degenerative spondylolisthesis on CT. MATERIALS AND METHODS: We reviewed retrospectively the CT images of 164 patients who were diagnosed spondylolisthesis. One hundred twelve patients had isthmic spondylolisthesis and 52 patients had degenerative spondylolisthesis. RESULTS: Isthmic spondylolisthesis mostfrequently occurred at L5. The degree of anterior displacement was grade I and II. The defect had a horizontal plane, an irregular surface, a sclerotic margin, and protruding hypertrophic bony spur in the spinal canal. The most frequently associated structural abnormality was a herniated nucleus pulposus at the upper level of the defect. Degenerative spondylolisthesis most frequently occurred at L4-5 and were grade I. The degenerative facet joint had a vertical plane, a hypertrophic bony spur, and a vacuum facet phenomenon. We frequently detected apseudobulging disk. The most frequently associated structural abnormality was a herniated nucleus pulposus at the level of the displacement. CONCLUSION: In spondylolisthesis, the findings in CT were valuable for differential diagnosis of isthmic and degenerative types and the detection of associated symptomatic abnormalities.