Abstract: BACKGROUND: The morphological indexes of ankle point may change after ankle fracture, and there is a certain correlation between the coronal angle change of ankle point and the functional recovery of ankle joint. Most previous studies have studied the height recovery of ankle point after surgery, so the correlation between the fluctuation of coronal angle of ankle point and the functional recovery of ankle joint after ankle fracture has certain reference significance.
OBJECTIVE: To investigate the effect of coronal angle change of ankle point on joint function recovery after ankle fracture. 
METHODS: A total of 86 patients with ankle fracture who underwent surgical treatment were selected as the study objects, and were divided into excellent group (n=45) and poor group (n=41) according to the results of American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot-ankle score during the last follow-up, and the general data of the two groups were compared. The morphological indexes of ankle points on the affected side and healthy side were compared after surgery based on ankle acupoints and lateral X-rays of the ankle joint, including the width and depth of ankle points, coronal angle and sagittal angle, and the difference of ankle points between the affected side and healthy side, and further comparison and analysis were conducted in each group. A joint model was constructed and Cox regression analysis was used to evaluate the relationship between coronal angle fluctuation and joint function recovery. Least absolute shrinkage and selection operator regression method and multivariate Logistic regression were used to analyze the risk factors affecting the recovery of joint function. The patients were divided into 5-quartile array (Q1-Q5) according to the angle of coronal position at ankle point from low to high. The clinical data characteristics of the five groups were compared, and the correlation between the change of coronal position at ankle point and the risk of poor recovery of joint function was analyzed by multivariate Logistic regression. A restricted cubic spline Logistic regression model was established to analyze the dose-response relationship. The prediction model of regression equation y=1-1/(1+e-z) was established and verified. 

RESULTS AND CONCLUSION: (1) The width and depth of ankle point on the affected side, coronal angle and sagittal angle were significantly higher than those on the healthy side (all P < 0.05), and compared with the excellent group, the difference of ankle point width, depth difference, coronal angle difference and sagittal angle difference were greater in the poor group (P < 0.05). (2) The combined model showed that the risk of poor joint function was increased by 3% for every 1˚ increase in coronal angle, regardless of whether the angle was within the normal range. (3) Least absolute shrinkage and selection operator regression and multivariate Logistics regression analysis showed that after adjusting for potential confounding factors, it was found that age, lack of functional exercise in early stage, no calcaneal traction, failure to remove internal fixation, postoperative complications, and increased ankle coronal angle were independent risk factors for joint function recovery (P < 0.05). (4) The coronal angle within 3 months after surgery was independently correlated with the risk of poor joint function recovery (OR=1.57, 95%CI:1.38-1.76, P=0.002), and the trend test of the coronal angle from low to high quintile in each postoperative period had statistical significance (Ptrend < 0.001). (5) Restricted cubic spline model analysis showed that there was no nonlinear relationship between the coronal angle change of ankle point and the risk of poor joint function recovery in males or females. Through Bootstrap self-sampling, the prediction model has good differentiation and accuracy. (6) The reduction of coronal angle of ankle point after ankle fracture plays a significant role in promoting the recovery of joint function. Therefore, the detection of coronal angle of ankle point after ankle fracture is helpful to understand the recovery of joint function of patients.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: ankle fracture, ankle point, coronal angle, joint function, Logistic regression analysis