The effect of lateral malleolar malrotational deformity on ankle stability-a study of 3D CT reconstruction

Abstract

Objective To evaluate the ankle stability on lateral malleolar rotational models based on three-dimensonal CT reconstruction and volume rendering technique.Methods Eighteen cadaveric specimens were utilized in the study (male 11;female 7; 68.2 years in average) and were divided into 2 groups in which the first group only cut the anterior tibiofibular ligament and defined as intact deltoid ligament group.Another group additionally cut the deltoid ligament and defined as deltoid ligament injured group.Fibular transverse osteotomy was performed at 3 cm proximal to the ankle joint and lateral malleolar rotational malunion model of 5°,10°,15° and 30° were built in every specimen.CT scanning was performed for each model then and all CT data were imported into Mimics 10.01 software.The structures of distal syndesmosis,ankle mortise as well as talus in the mortise were outlined by automatic dense identifying and manually modified later.Three-Dimensional models of these structures and their volume were outputted in the software.The volume of ankle clear space was calculated as the difference value of ankle mortise and talus in the mortise.Ankle stability was reflected by comparison of these volumes to the normal condition.Results With the rising of malrotational degree,the volume of inferior syndesmosis and mortise were increased and the volume of talus in the mortise was reduced.In the deltoid ligament intact group,10° of malrotation would significantly enlarged the volume of distal syndesmosis and ankle clear space when compared to normal condition.However,in the deltoid ligament injured group,5° of rotational deformity would significantly enlarge the volume of ankle clear space and distal syndesmosis.Conclusion The condition of deltoid ligament has significant impact on ankle stability in cases of lateral malrotional deformity.Distal syndesmosis and ankle clear space were significantly enlarged at 10° malrotation deformity.However,additional deltoid ligament injury can significantly reduce ankle stability at just 5° of distal fibular rotational deformity. Key words: Ankle joint; Fractures bone; Ligament; Tomography, X-ray computed