PURPOSE OF THE STUDY The study analyses a cohort of patients with surgically treated ankle fractures who developed complete distal tibiofibular synostoses. It focuses on their occurrence and association with the extent of tibiotalar dislocation of the ankle joint on the trauma X-ray and its relation to the choice of surgery. MATERIAL AND METHODS The cohort of a total of 824 patients with type B and C fractures according to Weber classification was followed up for 9 years. The cohort consisted of 403 (48.9%) men and 421 (51.1%) women. The exclusion criteria included associated talus fractures, calcaneus fractures and fractures of the other bones of the foot. The studied data were obtained retrospectively from medical documentation and by evaluation of trauma X-rays and X-rays obtained during the postoperative checks. The ankle fractures were classified based on the Weber classification and the basic epidemiologic data (age and gender), type of fracture and extent of tibiotalar dislocation of ankle fractures on the trauma X-ray were evaluated. Posttraumatic ankle dislocation was divided into tibiotalar dislocation > 10 mm, tibiotalar dislocation < 10 mm and the group with regular ankle joint. When evaluating the treatment method, the cohort was divided into three groups: Group 1 with one-stage osteosynthesis, Group 2 with temporary K-wire transfixation or external fixation and subsequent secondary conversion to internal osteosynthesis, and Group 3 with definitive transfixation or external fixation of the ankle. The results were statistically evaluated using the Pearson s chi-square test, or the Fisher s exact test for low frequencies. A multivariant logistic regression model was created to identify statistically significant factors contributing to the development of synostosis. The results with the p-value < 0.05 were considered statistically significant. RESULTS In the whole cohort, the synostosis of distal tibiofibular joint was observed in a total of 131 (15.9%) patients. In men it was in 85 (21.1%) cases and in women in 46 (10.9%) cases, which was statistically significant (p < 0.0001). There was a statistically significant difference (p = 0.0020) between the mean age in the group of patients with synostosis (54.4 years) and the mean age in the group of patients without synostosis (49.1 years). Complete distal tibiofibular synostoses were found in 78 (12.7%) fractures classified as type B according to the Weber classification and in 53 (25.5%) type C fractures. When taking into account the gender, synostoses occurred more frequently in men in both types of fractures classified based on the Weber classification, only in type C fractures no statistical significance was established (p = 0.3026). Various size of posttraumatic tibiotalar dislocation was present in both types of fractures. The group with less severe type B ankle fractures showed a statistically significant dominance of synostosis development in cases with large tibiotalar dislocation of more than 10 mm (p<0.0001). In the group with type C fractures different results were obtained. The highest frequency of cases with synostosis was reported in the group with dislocation smaller than 10 mm (p = 0.0698). In the entire cohort, 615 (74.6%) one-stage osteosyntheses were performed and synostoses developed in 77 (12.5%) cases. In 165 (20.0%) patients, transfixation with K-wires or external fixation with subsequent conversion to secondary osteosynthesis were used and synostoses were identified in 50 (30.3%) cases (p < 0.0001). The open fractures showed an insignificantly smaller number of synostoses than the closed fractures (p = 0.5902). DISCUSSION Posttraumatic distal tibiofibular synostoses have varied morphology. A number of studies confirmed that they do not affect much the functional status of the ankle, even despite their extensive finding in the area of syndesmosis is evident on the Xray. Etiologically, a certain role in their development is reported to be played by posttraumatic hematoma in case of damage to deep soft and bony structures of the ankle. CONCLUSIONS A higher occurrence of synostoses was observed in male population, older age patients and also in type C fractures according to the Weber classification. Larger tibiotalar dislocation showed statistical significance in the development of synostoses in type B fractures according to the Weber classification, whereas in type C fractures it was not the main factor contributing to the development of synostosis. In cases where one-staged osteosynthesis was performed, the occurrence of synostoses was statistically significantly lower than in secondary osteosynthesis after temporary stabilisation. Key words: ankle fracture, distal tibiofibular synostosis, ankle joint dislocation, Weber classification, acute surgery, delayed surgery.