Lee SK, et al. - Since ulnar neuropathy is a common reason for referral to hand surgeons, and 10 to 30% of cubital tunnel syndrome (CuTS) is idiopathic. Researchers assumed that the cause of idiopathic CuTS is in the bony structure. In this study, 79 elbows (39 idiopathic CuTS and 40 without CuTS symptom) were examined using CT and Materialize Mimics software to match the differences between the two groups. They introduced a new bony cubital tunnel with a new boundary that could execute a role in ulnar nerve compression symptoms. The shape of the bony cubital tunnel is a major cause of CuTS, and the normal variation of the volume and cross-sectional area of the cubital tunnel and cubital tunnel angle could affect the appearance of idiopathic CuTS.