Relationship between the Scottie Dog Sign and Cleft Distance in Lumbar Spondylolysis

Introduction: The Scottie dog sign on plain oblique radiography is an imaging evaluation indicator for detecting lumbar spondylolysis; however, if the cleft distance is small, the sensitivity of this method is low, making it difficult to detect the Scottie dog sign. Detailed studies on this aspect are scarce. Therefore, this study aimed to investigate the relationship between the Scottie dog sign and cleft distance in patients with terminal-stage bilateral lumbar spondylolysis. Methods: The retrospective, cross-sectional study included 75 patients with 150 clefts of lumbar spondylolysis, all of whom had terminal-stage bilateral lumbar spondylolysis at the time of their first visit to our hospital. Patients were classified into the Scottie dog sign-positive group (P) and negative group (N). The mean cleft distance between the two groups was compared by a t-test using the sagittal and axial planes of computed tomography (CT) images. Results: The mean cleft distance in groups P and N, respectively, was 3.05±2.00 mm and 1.96±2.38 mm in sagittal planes (p<0.01), and 2.64±1.70 mm and 1.92±1.93 mm in axial planes (p<0.01), with significant differences observed between groups. However, in some cases, the Scottie dog sign was negative even when the cleft distance was large, depending on the angle of the bone defect. Conclusions: We observed an association between the Scottie dog sign and cleft distance in patients with terminal-stage bilateral lumbar spondylolysis. The cleft distance in cases where the Scottie dog sign was positive was larger than that in cases where the Scottie dog sign was negative. These findings suggest that measuring the cleft distance using CT may help predict the visibility of the Scottie dog sign on plain radiography, thereby aiding in the diagnostic evaluation of lumbar spondylolysis.