Stress-strain state of the acromioclavicular joint in case of damage to the acromioclavicular ligaments and hook plate fixation (clinical and experimental study)

Background. The specific proportion of dislocations of the acromial end of the clavicle is up to 26 % of traumatic dislocations of the locomotor system and up to 10 % of traumatic lesions in the shoulder girdle. In world practice, the need to fix the acromial end of the clavicle is realized by using hook plates in 47 % of cases. However, this design, along with its advantages, has significant disadvantages, the most significant of them are shoulder pain, bone destruction, especially in the area of the acromion, and subacromial conflict. Objective: to establish the relationship between the negative consequences and the design features of the hook plate by investigating the stress-strain state of the acromioclavicular joint in case of damage to the acromioclavicular static ligament complex. Materials and methods. The experimental part is based on the study of finite element models of the supraclavicular joint in normal conditions, with damage to the acromioclavicular stabilizers, and with fixation of the acromial end of the clavicle with a hook plate. The clinical material is based on the analysis of the treatment outcomes in 36 patients who were diagnosed with combined damage to the lig. acromioclavicularе inferior and lig. acromioclaviculare superior and hook plate fixation. Results. When both ligaments of the complex are damaged, the hook plate allows you to reduce the stress level in the clavicle almost to the normal level, but the stress on the coracoid process remains at a fairly high level of 90.0 MPa. Also, significant stresses occur on the acromion — 55.3 MPa and on the edge of the scapular notch — 54.2 MPa. At the same time, the stresses in the plate itself increase to 433.3 MPa, which is quite close to the strength limit of the material from which it is made. Conclusions. When both ligaments of the acromioclavicular complex are damaged, the hook plate allows you to reduce the level of stress in the clavicle almost to the normal level, but the stress on the coracoid process remains at a fairly high level. Also, significant stresses occur at the acromial process and along the edge of the scapular notch, which explains the development of erosions and, accordingly, subacromial conflict, which negatively affects treatment outcomes.