INTRODUCTION: Among adolescent patients with low back pain, there are some patients who feel backache on trunk extension, which is characteristic to spondylolysis, but don’t have spondylolysis. They sometimes have high signal intensity in interspinous ligament on MRI STIR images. There have been few reports on this condition in adolescent patients, therefore we investigated this condition.
SUBJECTS and METHODS: We included 377 adolescent patients with low back pain who were performed MRI (Apr.2017-Oct.2024; men 288 case, women 89case; mean age 15.1y). We defined that interspinous ligament lesion was positive “ISL (+)”, when there was high intensity on STIR images with low intensity on T1-weighted images. As clinical findings, we recorded the pain during trunk flexion, extension, rotation, side-bending, and tenderness on spinous process. Because ISL(+) was often seen at the same time as other findings such as spondylolysis, we compared these clinical findings between ISL (+) alone (ISLA) group and spondylolysis without ISL (+) (spondylolysis WO) group.
RESULTS: There were 66 patients with ISL (+). Of these, ISL (+) alone (ISLA) was 34 cases. Of the other ISL (+) 32 patients, 28 had spondylolysis and 4 had disc degeneration. The imaging findings for the 377 patients was as follows.; 34 ISL (+) alone (ISLA), 249 spondylolysis without ISL (+) (spondylolysis WO), 32 spondylolysis with ISL (+), 19 lumbar disc herniation, 12 endplate lesion, 7 facet joint fluid, 4 disc degeneration, and without abnormal images in lumbar spine 10. The number of women was 24 ISLA, 39 spondylolysis WO. ISLA group had higher rates of women than spondylolysis WO group significantly (24/34: 39/249, p<0.001). The average age of ISLA was 14.3 and spondylolysis WO was 14.7. There was no significant difference between two groups. About examination findings, pain on trunk flexion was more seen significantly in ISLA than spondylolysis WO (30/34: 38/249, p<0.001). On the other hand, pain on side-bending and rotation were more seen in spondylolysis than ISLA significantly (10/34: 201/249, p<0.001 and 9/34: 222/249, p<0.001). Almost all ISLA patients and spondylolysis WO patients felt pain during trunk extension (30/34: 239/249, p=0.125). Also, almost all spinous process tenderness was seen in both group without significant difference (32/34: 239/249, p=0.957).
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. Interspinous 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 (+) of this study, was proliferation of cells and vascular invasion by histologic examination. We think high intensity in interspinous ligament on MRI means sprain. When we injected local anesthetic into interspinous ligaments for 11 patients of ISLA, pain disappeared at all of them temporally. We should keep this lesion in our mind when seeing adolescent patient with low back pain,