Prediction of lateral malleolus malreduction by tibiotalar displacement in ankle fracture: a radiological study

Objective To explore the feasibility of predicting lateral malleolus malreduction by radiological parameters of tibiotalar displacement in ankle fracture with or without sectioned deltoid ligament.Methods Ten fresh cadaveric specimens of lower extremity below the knee were used to create shortening malreduction of 1 mm,2 mm and 3 mm and rotational malreduction of the lateral malleolus of 10°,20° and 30°.Medial clear space (MCS),superior clear space (SCS) and talar tilt angle (TT) were measured on the anteroposterior X-ray films of the ankle.The 3 parameters were evaluated for their diagnostic sensitivity to lateral malleolus malreduction,setting MCS≥4 mm,MCS≥SCS and TT≥5° as diagnostic criteria.Results In the group of sectioned deltoid ligament,the 3 radiological parameters of tibiotalar displacement were more sensitive than in the other group.The sensitivity of MCS ≥4 mm was superior in the specimens with lateral malleolus shortening more than 2 mm and sectioned deltoid ligament (sensitivity ≥ 0.8) but inferior in other kinds of lateral malleolus malreduction.MCS ≥ SCS could discover a subtle lateral malleolus malreduction,with a superior sensitivity compared with the other 2 parameters.Its sensitivity to sectioned deltoid ligament combined with lateral malleolus shortening of 1 mm,lateral malleolus shortening of 2 mm,lateral malleolus rotation of 10° and lateral malleolus rotation of 20° was respectively 0.6,1.0,0.4 and 0.8.The sensitivity of T≥5° was inferior to that of the other 2 parameters.It was 0.4 and 0.8 respectively for sectioned deltoid ligament combined with lateral malleolus shortening of 2 mm and 3 mm,and less than 0.2 for other conditions.Conclusions In the condition of sectioned deltoid ligament,radiological parameters of tibiotalar displacement can be used to predict lateral malleolus malreduction sensitively.The MCS ≥ SCS value may be more sensitive than MCS ≥4 mm and TT≥ 5° as threshold values for diagnosis in discovering tibiotalar displacement.In the condition of intact deltoid ligament,radiological parameters of tibiotalar displacement are not sensitive enough for prediction of lateral malleolus malreduction. Key words: Ankle fractures;  Fractures, bone;  Biomechanics;  Radiological study