To investigate the characteristics, diagnostic criteria and treatment of ulnar carpal impingement syndrome without a clear history of trauma and with atypical radiographic presentation. Methods Patients with ulnar carpal impingement syndrome without a clear history of trauma and atypical radiographic presentation were diagnosed and treated. Based on the kostas diagnostic criteria, the positive rates of ulnar carpal stress test, dynamic ulnar orthogonal variation, MRI examination and wrist arthroscopy were observed, and the influence of the observed indexes on the diagnostic results and clinical significance were analyzed. The treatment was ulnar shortening surgery with horizontal osteotomy (Darrow method) and oblique osteotomy (Rayhack method) and internal fixation with compression plate screws. The Darrow criterion was used to evaluate the efficacy. The rate of positive ulnar carpal stress test was 84%, the rate of positive dynamic ulnar variation was 52%, the rate of signal alteration of the carpal bone was 82% on MRI, most commonly in the proximal ulnar part of the lunate bone and the lumbar part of the deltoid bone, and the rate of TFCC degeneration and cartilage degeneration of the ulnar and lunate bones on wrist arthroscopy was 100%, with a follow-up time of 4 to 48 months and a mean of 26 months. 25 cases healed. All fractures healed, and the mean healing time was 4.5 months for horizontal osteotomies and 2.5 months for oblique osteotomies, with significant differences (P<0.05). No serious postoperative complications occurred, and the treatment results were satisfactory. Conclusion Non-traumatic ulnar carpal impingement syndrome is difficult to differentiate from other causes of ulnar pain in the wrist joint due to the lack of a clear history of trauma, especially when the radiographic presentation is atypical, and the application of ulnar carpal stress test, dynamic ulnar orthotropic variation examination and early MRI examination can clarify the diagnosis early and improve the diagnosis rate effectively. Wrist arthroscopy can be used as a supplementary means for diagnostic difficulties and differential diagnosis. The application of ulnar shortening surgery can significantly improve the symptoms, and oblique osteotomy is the recommended osteotomy method.