INTRODUCTION: Among adolescent patients with low back pain, there are some patients who feel backache on trunk extension and rotation, which is characteristic to spondylolysis, but don’t have spondylolysis. They sometimes have high signal intensity in interspinous ligament on MRI STIR images. We reported on this disease at the 2021 ISSLS meeting and have now expanded the number of cases and reviewed them in order to gain new findings.
SUBJECTS and METHODS: We included 352 adolescent patients with low back pain (Apr.2017-Aug.2023; men 267 case, women 85case; mean age 15.1y) in this study. MRI was performed on all the patients, and CT scans if necessary. We recorded the pain during trunk flexion, extension, rotation and side-bending. We also recorded tenderness on spinous process and straight leg raising test (SLRT). In this study, we defined that interspinous ligament lesion was positive “ISL (+)” when there was high intensity on STIR images with low intensity on T1-weighted images without other findings such as spondylolysis. These clinical findings, age and gender were compared between ISL (+) group and the other diagnoses groups.
RESULTS: There were 77 patients with spinous process signal change on MRI, and of these, ISL (+) only was 39. In the other 23 patients 18 had spondylolysis and 4 had LDH. There were 268 spondylolysis patients, 19 lumbar disc herniation (LDH), 12 endplate lesions (EL), 7 facet joint fluid (FF), and without abnormal images (NP) were 7. In each diagnosis group, the number of women was 28 ISL (+) only, 39 spondylolysis, 5 LDH, 3 EL, 3FF, 4 NP, respectively. ISL (+) had higher rates of women than spondylolysis significantly. The average age was 14.5, 15.3, 15.9, 14.2 ,14.7, 13.9-year-old respectively, and there was no significant difference between ISL (+) and the other groups. About examination findings, pain on trunk flexion was more seen significantly in ISL (+) than spondylolysis (34/39: 38/268). On the other hand, pain on side-bending and rotation were more seen in spondylolysis than ISL (+) significantly (247/268:17/39 and 259/268:19/39). Almost all ISL (+) patients and spondylolysis patients felt pain during trunk extension. Also, almost all spinous process tenderness was seen in both group without significant difference. SLRT of ISL (+) was significantly lower than LDH group.
DISCUSSION: Interspinous ligament connects adjacent spinous processes. It consists of three parts, and it is arranged so that the spinous processes are not separated and limits the flexion of facet joints. Iinterspinous ligament lesion is famous as Baastrup disease, which means bursitis of ligament and relates “kissing spine”. Fujiwara revealed that interspinous ligament lesion of low intensity on T1 and high intensity on T2-weighted images, which was same as ISL (+), was proliferation of cells and vascular invasion by histologic examination. We think ISL (+) is like sprain. Therefore, pain on forward bending is stretching stress and pain on backward bending is induced by compression between spinous processes. When seeing adolescent patient with low backpain, we should keep this lesion in our mind.