ObjectiveIn our retrospective study, we aimed to investigate the differences between the adductor ratio (AR) in knees with and without osteoarthritis, and its validity in determining the articular level.MethodsData from 80 knees of 80 patients were retrospectively evaluated. Anteroposterior weight-bearing knee radiographs of the patients with and without osteoarthritis (40 knees in each group) were obtained. The adductor ratio was determined using the following formula: ATJL/FW (adductor tubercle-joint line distance/femoral width). All radiographs were evaluated at the baseline and at one-month intervals afterwards. Intraobserver reliability of the two measurements was assessed using interclass correlations (ICC). Pearson's correlation test was used to evaluate the correlation between the ATJL and the FW. The differences between the adductor ratios of the two groups were evaluated by the independent samples two-tailed t-test.ResultsMost of the ICC values were well above 0.95, indicating a very high intraobserver reliability. The adductor ratio was significantly greater in Group 2 in comparison to Group 1 (Mean AR in Group 2: 0.522 ± 0.031 and Mean AR in Group 1: 0.502 ± 0.032; p = 0.005). There was a significant correlation between the ATJL and FW in the groups when assessed both separately and combined.ConclusionIn conclusion, we can assert that if the AR is used to determine the articular level in revision arthroplasty cases, it may be sensible to measure the FW intraoperatively rather than measuring it on primary or contralateral radiographs of arthritic patients.Level of evidenceLevel III, Diagnostic study.