Analysis of the epidemiological characteristics of posterior malleolus fracture in adults
Authors: Li Yongqi , Luo Rui , Li Bing , Xia Jiang , Zhou Haichao , Huang Hui , Yang Yunfeng 
Published: July 2023

Abstract
Background
This study explores the latest epidemiological characteristics of posterior malleolus fracture and compares the epidemiological differences of posterior malleolus fracture in different periods, regions, and adult age groups.

Methods
Clinical information of inpatients with posterior malleolus fracture in Shanghai Tongji Hospital and Karamay Central Hospital from January 2014 to February 2022 was reviewed and collected. The imaging data of patients were acquired using the Picture Archiving and Communication Systems. A statistical analysis was performed as to gender, current age, year of admission, injury mechanism, fracture type, and posterior malleolus fracture classification. Moreover, a comparative analysis was conducted on the injury mechanisms and morphological differences of posterior malleolus fracture at different periods, regions, and age groups.

Results
A total of 472 patients (210 patients from Shanghai Tongji Hospital and 262 patients from Karamay Central Hospital) with posterior malleolus fracture and an average age of 48.7 ± 15.6 were included in this study. The peak of posterior malleolus fracture occurs in the age group of 50–59. The injury mechanisms mainly involve low-energy fall and sprain (411 cases, 87.1%), followed by traffic accidents (52 cases, 11.0%), and fall injury from height (9 cases, 1.9%). With aging, the number of fall and sprain cases increases and reaches the peak at the age of 50–59, followed by progressive decline. Traffic accidents presents a relatively flat small peak in the age group of 40–59. The number of cases according to different fracture types shows the following ascending order: trimalleolar fracture-supination external rotation (335 cases, 71.0%) > bimalleolar fracture (60 cases, 12.7%) > trimalleolar fracture-pronation extorsion (43 cases, 9.1%) > posterior malleolus + tibial shaft fracture (19 cases, 4.0%) > simple posterior malleolus fracture (15 cases, 3.2%). The numbers of cases corresponding to the Haraguchi I Type, II Type, and III Type of posterior malleolus fractures were 369 (78.2%), 49 (10.4%), and 54 (11.4%), respectively. The Tongji IIA Type represented the highest number of cases (249 cases, 52.8%), followed by the IIB Type (120 cases, 25.4%), I Type (54 cases, 11.4%), IIIB Type (36 cases, 7.6%), and IIIA type (13 cases, 2.8%). The trimalleolar fracture-supination external rotation, Haraguchi I Type and Tongji IIA Type of posterior malleolus fractures all presented an obvious peak of incidence in the age group of 50–59. However, no obvious statistical difference was observed in the injury mechanism, Haraguchi classification, and Tongji classification of posterior malleolus fractures among different years and regions in recent years (P > 0.05).

Conclusions
The injury mechanism of posterior malleolus fracture mainly involves low-energy fall and sprain cases. The trimalleolar fracture-supination external rotation, Haraguchi I type and Tongji IIA type of posterior malleolus fracture are predilection fracture types, and all present an obvious incidence peak in the age group of 50–59. Elderly patients have high risks of falling and their bones are more fragile, conditions which are potential risk factors of posterior malleolus fracture. Early positive control has important significance. This study provides references for relevant basic and clinical studies of posterior malleolus fracture.