Introduction: The etiology of subchondral cyst formation is not well known; however, there are several articles which address that it can be occurred by recurrent minor trauma which results in cartilage injury and consequently makes joint fluid to enter the bone marrow spaces of the subchondral bone to form a cyst. The purpose of this study was to find out the relationship between lunate cyst with ulnocarpal impaction which could give repeated mechanical stress to lunate. Methods: From March 2012 to January 2014, total of 387 patients’ 3D upper extremity computed tomography (CT) images at Chung-Ang University Hospital that includes wrist images were reviewed. Among these patients, 10 patients had been diagnosed of ulnocarpal impaction syndrome (group 1). Nine patients had been treated with ulnar shortening and 1 patient had injection to ulnar fovea. In the rest of 377 patients, none of the patients had specific ulnar side pain of their wrist (group 2). Among these images, 35 patients (9.26%) had lunate cysts positioned near distal ulna which can be suggested as ulnolunate impaction. They were assessed for difference, correlation, and logistic regression to evaluate if there is true relationship between lunate cyst and the degree of ulnar positive variance or age. Results: In total, 241 patients had ulnar positive variance on their wrist and 41 patients (17%) had lunate cyst. The prevalence of lunate cyst was significantly higher in group 1 (6 patients [60%] vs. 35 patients [9.26%], P < .001, respectively). However, there was no difference of the size of lunate cyst in groups 1 and 2 (P = .242). The size of lunate cyst had no correlation to ulnar positive variance or patient’s age as well (P = .857, P = .349, respectively). Logistic regression analysis demonstrated that the presence of lunate cyst was associated with the patient’s age (odds ratio = 1.045, P < .001) and also the association between the presence of lunate cyst and the degree of ulnar positive variance was found (odds ratio = 1.186, P = .022). Patients with lunate cyst had more positive ulnar variance (P = .020). However, only 15% of patients with lunate cyst had symptomatic ulnocarpal impaction syndrome. In addition, in the patients with lunate cyst, there was no difference of cyst size whether the patients had the symptomatic ulnocarpal impaction syndrome or not (P = .262). Conclusion: In our study, the lunate cyst was associated with patient’s age and ulnar positive variance. However, we could not find significant effect of symptomatic ulnocarpal impaction on the formation of subchondral cyst in lunate.
