[Postoperative distal tibiofibular synostosis: radiographic characteristics and the influence on ankle mobility]

Objective: To investigate the clinical and imaging characteristics of distal tibiofibular synostosis in postoperative ankle fractures and its effects on the ankle mobility. Methods: The clinical and imaging data of 47 patients with distal tibiofibular synostosis treated surgically from October 1991 to June 2013 were analyzed retrospectively. There were 30 males and 17 females, aged from 15 to 68 years with a mean age of (39±13) years. The original fracture types, internal fixation profiles, imaging features of distal tibiofibular synostosis were recorded. Ankle range of motion (ROM) and complications at the last follow-up were also evaluated.The ROMs of healthy and fractured sides were compared with paired sample rank test. Results: The patients were followed up for 3 to 204 months (mean 25.4 months). Of the patients, 34(72.4%) were ankle fractures, 7(14.9%) were distal tibiofibular fractures, 1(2.1%) was tibiofibular shaft fracture, 2(4.3%) were tibial shaft fractures associated with lateral malleolus fracture and the resting 3(6.4%) were Pilon fractures. In patients with ankle fractures, 76.5%(26/34) of the synostosis occurred at the distal tibiofibular syndesmosis, while 23.5%(8/34) at the proximal of the tibiofibular sydesmosis; in patients with distal tibiofibular fracture, 85.7%(6/7) of the tibiofibular synostoses occurred at the fracture sites. The synostosis occurred at the level of syndesmotic screws in 8 patients (88.9%, 8/9) fixed with distal tibiofibular syndesmotic screws. And synostosis occurred at the sites of the distal locking screws in all (3/3) of the patients fixed with intramedullary nails. At the last follow-up, the active plantarflexion, active dorsiflexion and passive dorsiflexion in the affected side was 0°(0°, 5°), 2°(0°, 5°), 5°(0°, 10°) less than those in the healthy side, respectively (Z=-3.493, -4.491, -5.130, all P<0.05).During the follow-up, 4 patients complained of lateral ankle discomfort with no impact on daily life. Conclusions: Post-operative distal tibiofibular synostosis mainly occurs at the sites of fractures, distal tibiofibular syndesmotic screw sites and the sites of the distal locking screws of tibial intramedullary nails. ROM of the injured ankle decreases in comparison with that at the contralateral side, although no obvious symptoms are observed and no intervention needed.