ObjectiveTo discuss the imaging manifestations of ulnar impaction syndrome, and to evaluate the diagnostic value of MR imaging. MethodsThe clinical data of 18 patients with clinical standard-proved ulnar impaction syndrome between January 2010 and June 2013 were retrospectively reviewed. ResultsSeventeen cases were diagnosed as ulna positive variation (94.6%), and the range of ulnar variance was 1.5 to 3.8 mm and the average ulnar variance was 2.6 mm. Neutral variance was found in one case. Fourteen cases had avascular necrosis or bone sclerosis of semilunar bone, and avascular necrosis or bone sclerosis of the triquetrum and ulnar was presented in 12 cases and 3 cases respectively on X-ray detection. CT scan showed that 16 cases of semilunar bone abnormalities (6 with ischemic necrosis), triquetrum osteonecrosis in 4 cases, and both necrosis of semilunar bone and triquetrum in 3 cases. On MRI, all cases had different degrees of damage, degeneration of semilunar bone, triquetrum, ulnar and triangular fibocartilage complex (ulnar side of the proximal end of the lunate in 18, radial side of the triquetrum in 17, distal joint surface of ulnar in 12, and triangular fibocartilage complex in 15). In the early stage, lesions were presented as edema of bone marrow and followed as different sizes of cystic change. Articular surface was collapsed later. ConclusionUlnar positive variance has important reference value in the diagnosis of ulnar impaction syndrome. MRI can show the early change of ulnar impaction syndrome, and provide reliable decision basis for clinical diagnosis and treatment.