MRI Analysis for Clarification of Mechanism of Ankle Osteoarthritis: Prediction of Talar Lateral Process Impingement from X-Ray Findings

CATEGORY: Ankle Arthritis INTRODUCTION/PURPOSE: We have previously elucidated the pathological condition of osteoarthritis (ankle OA) by MRI by examining the relationship between X-ray findings and bone marrow edema (BME) and found a relationship between talar lateral process impingement (TLPI) in the subtalar joint and the incidence of BME in the talocrural joint as well as found an association of these MRI findings with clinical symptoms. In the present study, we focus on the three talar movements inversion, dorsiflexion, and forward displacement to report on our survey of X-ray findings involved in occurrence of TLPI. METHODS: We examined MRI imaging for 70 feet of 68 cases, which has diagnosed ankle OA in our hospital. X-ray measurements of the movement of the talus regarding the TMM, TBM, TTA, LTMT, and LTC angles as well as the T-T ratio(refer to the figure) were obtained. The incidence of BME on MRI was calculated after dividing the talus, the subtalar joint, and Chopart’s joint into 22 regions; cases where BME was observed in the talar lateral process were defined as TLPI (+). For statistical analysis, the study sample was divided into two groups depending on the presence/absence of TLPI, which their respective incidences of BME and values of X-ray measurement were compared using a t-test. Furthermore, for values in which significant differences were observed, cut-off values were obtained from the ROC curve, and the factors that were most independently involved in the incidence of TLPI were identified using multivariate analysis. RESULTS: On comparing the groups with the presence or absence of TLPI, the incidence of BME occurring at a region other than the lateral process was significantly higher in the TLPI (+) group, and significant differences were found for all values of X-ray measurement except for T-T Ratio. The multivariate logistic regression analysis with cut-off values at TMM = 46° or more, TBM = 77° or less, TTA = 4° or more, LTMT = 8° or more, and LTC = 35° or less demonstrated that LTC (odds ratio: 4.22, 95% CI: 1.28–14.0, p = 0.02) and TMM (odds ratio: 3.44, 95% CI: 1.12–10.6, p = 0.03) were significantly involved in the incidence of TLPI. CONCLUSION: Results of this study have led to the speculation that the incidence of TLPI is closely related to the positional relationship of the peripheral opening of the medial malleolus and the talocalcaneal bone as well as to the varus and dorsiflexion of the ankle joint. These new findings could be used as a new index to predict the incidence of TLPI.