Purpose: This study was conducted to evaluate Scottie dog sign in plain X-ray oblique image and the cleft distance in CT image of terminal stage of lumbar spondylolysis.
Methods: The subjects were 75 people with 150 lumbar spondylolysis who were diagnosed with bilateral terminal stage of lumbar spondylolysis at the first visit to our hospital from April 2014 to March 2022. The mean age was 15.0 years old, the male to female ratio was 53:22, 1 patient at the L3, 3 patients at the L4, and 71 patients at the L5. Patients with no bone marrow edema on MRI and interarticular bone defect on CT image at the first visit were diagnosed as terminal stage of lumbar spondylolysis. Based on plain X-ray oblique image taken at the first visit to our hospital, the patients were classified into group P, which was Scottie dog sign positive, and group N, which was Scottie dog sign negative. The cleft distance in the sagittal and horizontal sections of each CT image was measured, and the cleft distance in group P and group N were compared. A t-test was used as a statistical method, and the significance level was set at 0.05.
Results: Subjects were classified into 88 lumbar spondylolysis in group P and 62 lumbar spondylolysis in group N. The cleft distance in the sagittal slice of CT image was 3.05±1.99mm in group P and 1.95±2.38mm in group N, respectively(p＜0.01). The cleft distance in the horizontal slice of CT image was 2.64±1.70mm in group P and 1.92±2.38mm in group N, respectively(p＜0.01).
Discussion: In case of pseudarthrosis, bone marrow edema will not be detected and appear normal on MRI. If the cleft distance is small, Scottie dog sign looks negative even in terminal stage of lumbar spondylolysis. For this reason, lumbar spondylolysis may be missed even when X-ray and MRI, which are standard for diagnosing low back pain, are performed. On the other hand, regardless of the disease stage of lumbar spondylolysis, only 32% of cases of lumbar spondylolysis diagnosed by CT image can be diagnosed by X-ray oblique image; therefore, there are only a limited number of cases in which lumbar spondylolysis can be diagnosed using X-ray oblique image alone.
Conclusion： Some young patients have small cleft distances; therefore, we need to be aware that lumbar spondylolysis may be missed in young patients with low back pain.