Influence of different plantar flexion angle on X-ray diagnosis of deltoid ligament injury

Abstract

Objective To improve the accuracy of X-ray diagnosis of the deltoid ligament injury by evaluating the influence of plantar flexion on the diagnosis.Methods Twenty-four patients with ankle supination-extemal rotation fracture which was distal fibula fracture but no medial malleolus fracture were treated from February 2010 to December 2010.All the patients were taken Mortise radiograph with the ankle in four positions of plantar flexion(0°,15°,30° and 45°)applied with rotational stress and the deltoid ligament injury was identified with MRI.The medical clear space(MCS)and the superior clear space(SCS)on each radiograph were measured.The results were tested by a one-way analysis of variance model(ANOVA),based on the following criteria:(1)the MCS≥ 4 mm and MCS ＞ SCS,or when MCS≥5 mm and MCS ＞SCS.The MRI examination was taken as the gold standard to compare the influence of X-ray diagnosis of the deltoid ligament injury with different plantar flexions and different standards.Results The average MCS in four positions of plantar flexion(0°,15°,30°,and 45 °)with rotational stress were(4.10 ±0.79)mm,(4.55 ±0.72)mm,(4.99 ±0.56)mm and(5.71 ±0.86)ram,with statistical difference(P ＜0.05).The average SCS in four positions of plantar flexion(0°,15°,30°,and 45°)were(3.56 ±0.41)mm,(3.50 ±0.43)mm,(3.71 +0.44)mm and(3.93 ±0.51)mm,with no statistical difference in the four groups(P ＞0.05).With the MSC≥4 mm and MSC ＞ SCS as the diagnostic criteria,the prevalence of false-positive findings of deltoid injury based on the ratio with the four positions of plantar flexion(0°,15°,30° and 45°)were 50.0％,66.7％,88.9％ and 94.4％ respectively.With the MSC≥5 mm and MSC ＞SCS as the diagnostic criteria,the prevalence of false-positive findings of deltoid injury based on the ratio with the four positions of plantar flexion(0°,15°,30° and 45°)were 5.6％,11.1％,38.9％ and 77.8％ respectively.Condusions Different plantar flexion angle is an important factor for X-ray diagnosis of deltoid ligament injury of the ankle joint.The prevalence of false-positive findings of deltoid injury increases with the increase of plantar flexion. Key words: Ankle joint; Ankle injuries; Ligaments; Diagnosis