| Isolated medial ankle sprains are relatively uncommon, with most deltoid injuries occurring in combination with medial malleolus fractures or syndesmosis injuries. In Brostrom"s series of281acute ankle sprains, medial side ankle sprains constituted only3%. Nearly all of the medial-side injuries were partial ligament tears. In Harper's review of42patients with complete deltoid ligament ruptures, all had other injuries. However, isolated injury to the deltoid ligament can occur during an eversion injury and several other conditions. The3most characteristic mechanisms of injury are pronation-abduction, pronation-external rotation, and supination-external rotation of the foot. In patients who have posterior tibial tendon disorder, trauma-and sports-related deltoid disruptions, and valgus talar tilting after triple arthrodesis or total ankle arthroplasty, the isolated injury of deltoid ligament can also be seen.Deltoid ligament injuries can be a significant source of pain and disability. According to Clanton, patients experience medial ankle discomfort and have slight valgus and abduction of the ankle with ambulation.Patients requiring a reconstructive operation typically exhibit rotatory instability as well as enhanced talar translation or valgus angulation in the coronal plane. Several approaches to deltoid reconstruction have been reported.Wiltberger and Mallory described a technique of reconstructing the deltoid by dividing the posterior tibial tendon longitudinally. The dorsal half of the tendon was left attached distally at the navicular, but transected proximally. A vertical drill hole was made in the medial malleolus through which the proximal end of the tendon was passed from plantar to dorsal and then sutured to itself.Deland et al described a technique for reconstruction in the setting of Stage IV posterior tibial tendon insufficiency. Their technique involves passing a peroneus longus tendon graft through a bone tunnel in the talus from lateral to medial and then through a second tunnel from the tip of the medial malleolus to the lateral tibia.Kitaoka et al described a deltoid ligament reconstruction technique in the setting of flatfoot deformity. The extensor hallucis longus tendon was harvested and passed through drill holes in the medial malleolus and medial cuneiform. It was then sutured back upon itself at both sites.Hintermann et al described a procedure for reconstruction of the deltoid ligament. Bone tunnels were created in the medial malleolus and navicular tuberosity. A free plantaris tendon autograft was harvested, placed through the bone tunnels, and sutured back on to itself.Though several techniques can be used for surgical reconstruction of the deltoid ligament, the ideal method is not known. The purpose of this study was to evaluate the biomechanical results of those deltoid ligament reconstructions using finite element analysis.In addition, the knowledge of stress inside the ligaments and reconstructed grafts which could help to better understand the biomechanical behavior of the reconstructed joint is extremely difficult in the experimental measurement. Therefore, in this paper the finite element analysis helps to assess this biomechanical parameter.Based on this, the study was divided into the following steps:Chapter One Development and validation of a three-dimensional finite element ankle model of humanObjective:To develop a three-dimentional finite element model of the intact human ankle and take the verification analysis in the kinematics of the model.Methods:An healthy ankle of a male (age25, height170cm and weight65kg) was scanned in neutral position using Computer Tomography(CT) and magnetic resonance image (MRI). The geometry of the skeletons of the ankle were rebuilt from the CT images and the articular cartilage from MRI images with Mimics10.01software. According to Mimics software, Magics9.9software which implemented in Mimics and Ansys software, a three-dimentional finite element ankle model was developed on the basis of CT and MRI images. The model consisted of the distal of the tibia and the fibula, the whole talus, the calcaneus bone, the navicular bone, the medial cuneiform bone, the articular cartilage, and the ligaments surrounding the ankle joint including the lateral ligaments and medial deltoid ligament complex. Bone structures were meshed with rigid surface elements due to their small strain compared to soft structures. Articular cartilage was meshed with3D tetrahedral deformable elements. Link elements that have only tension function capability were used to simulate ligaments and grafts bearing the tension load. The anterior drawer test of the talus was simulated in Ansys software to validate the model.Results:An effective and high simulative three-dimensional finite element model of the ankle including six bony structures, cartilage and nine principal ligaments surround the ankle joint complex was developed. The anterior drawer test of the talus in Ansys software validated the model compare to literatures.Conclusion:The three-dimensional finite element model of the ankle was effective so that it can be used to simulate the real ankle for the future study such as the kinematics and biomechanics of the ankle in the deficiency or reconstruction of the medial deltoid ligaments complex. Chapter two The finite element analysis of the intact and deficiency medial deltoid ligment in ankle model of humanObjective:To evaluate the kinematics and biomechanics of the ankles of which the medial deltoid ligament complex is nomal, the superficial deltoid and the whole deltoid is deficient respectively with finite element analysis.Methods:In addition to the intact ankle model, superficial deltoid-deficient, the whole deltoid-deficient models were simulated based on the intact finite elements ankle model. The forces in the ligaments and the kinematics of talus were predicted for an eversional or external torque through the range of ankle flexion in Ansys software.Results:When the superficial structure of the deltoid ligament complex is deficient, the talar tilt increased slightly under an eversional torque, however, the external rotational displacement of the talus increased drastically under an external torque(P<0.05). And, the difference of the external rotational displacement between the superficial deltoid-deficient and deltoid-deficient ankle was very small. However, the difference of the valgus angulation of the talus between them was tremendous relatively(P<0.05).Conclusion:This study showed that the superficial structure of deltoid ligament complex resist external rotation of the talus relative to the tibia mostly and the deep structure resists eversion of the one relatively. Chapter three The finite element analysis of the tenodesis reconstruction in ankle with medial deltoid ligment deficiency in ankle model of humanObjective:To evaluate the kinematics and biomechanics of the tenodesis reconstruction in ankle with deltoid ligament deficiency using finite element analysis.Methods:In addition to the intact ankle model, Wiltberger reconstruction, Deland reconstruction, Kitaoka reconstruction and Hintermann reconstruction models were simulated. The forces in the ligaments and grafts and the kinematics of talus were predicted for an eversional or external torque through the range of ankle flexion in Ansys software.Results:No reconstructions could completely restore the values for ankle stability and the stresses of the lateral ligaments to normality. But compatively, The Kitaoka procedure was most effective in limiting the external rotation(P<0.05), in addition to the Deland procedure, was in limiting the eversion(P<0.05). Conclusion:This study showed that Kitaoka has advantage with regard to rotational stabilities as well as ligaments stress in comparison with other methods. And the Deland procedure is good at the evertional stabilities in comparison with others. |
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