Stress-strain state of the suprahumeral-clavicular joint with damage to the ligaments of the clavicular-acromial joint and various methods of fixation

Background. There are two main methods of fixing the acromial end of the clavicle with the help of metal structures: hook plate, and Weber’s technique (tension band wiring). The disadvantages of modern fixing structures negatively affect treatment outcomes, which requires the development of advanced methods to stabilize the acromial end of the clavicle. Purpose: to conduct a comparative analysis on the fixation of the acromial end of the clavicle according to Weber, using hook plate and the proposed construction by studying the stress-strain state of the suprahumeral-clavicular joint with a combined injury of the lig.acromioclaviculare inferior and lig.acromioclaviculare superior and various methods of fixation. Materials and methods. In this study, we modeled a combined injury of the ligaments of the suprahumeral-clavicular joint, namely lig.acromioclaviculare inferior and lig.acromioclaviculare superior, with fixation of the acromial end of the clavicle in three ways: according to Weber, with hook plate and the proposed construction. We used loads that act on the suprahumeral-clavicular joint when the upper extremity is abducted to an angle of 90°. Results. It was found that all types of fixators in case of damage to the lig.acromioclaviculare inferior and lig.acromioclaviculare superior allow to obtain approximately the same level of stress in the bone elements of the model. An exception is Weber’s fixation, in which the stress on the acromial end of the clavicle and on the acromion process increases several times, which can be the cause for the destruction of bone tissue in the area of contact with metal elements. The stresses in the wire itself can even exceed the strength limit of surgical steel and, as a result, cause it to break. The hinge-type fixator provides the best stress distribution, both in the bone elements of the model, and a fairly low level of stress in the intact ligaments. Hook plate, from the point of view of stress values in the elements of the model, has good indicators for isolated ligament injuries and occupies an intermediate position according to all the studied indicators. In term of the criterion of minimizing relative deformations in the ligaments of the clavicular-scapular joint in case of damage to the lig.acromioclaviculare inferior and lig.acromioclaviculare superior, the Weber fixation method showed the best outcomes. But the results of the study on stress distribution in this model negate the advantages of minimizing the deformations of the intact ligaments. Conclusions. Fixation of the acromial end of the clavicle according to Weber provides good results in terms of reducing the level of stresses and relative deformations in the intact ligaments, but leads to a severalfold increase in the level of stresses on the acromial end of the clavicle and the acromion process. The level of stresses in the wire during abduction of the limb in case of damage to the ligaments of the clavicular-acromial joint may exceed the strength limit, which may be the cause of wire breaking and, as a result, loss of stability of the suprahumeral-clavicular joint. The hook plate occupies an intermediate position in terms of stress distribution in the model, but according to the index of relative deformations in the intact ligaments, it showed the worst result. Fixator of the proposed design provides the best balance, both according to the criterion of stress distribution in the model elements and the magnitude of relative deformations in the intact ligaments.