Comparative analysis of stress-strain changes at the humeral head cartilage in different types of glenoidlabrum injuries
Background. The glenoid labrum injury is a fairly common problem in the shoulder. Localization in posterior glenoid labrum depending on the type of its damage significantly increases the load on the articular cartilage, which leads to the development and progression of degenerative changes of the humeral cartilage, aggravation of arthritis and posterior glenohumeral instability. Such situation focuses the surgeon on determining the surgical strategy aimed at unloading the affected area and eliminating biomechanical imbalance.The purpose was tostudy clinically significant damages of the glenoid labrum depending on its type at the basis of biomechanical analysis of stress-strain changes of the humeral head cartilage and grounding the treatment strategy. Materials and methods. Calculations of the stress-strain state of the humeral cartilage elements were carried out by the finite element method. Based on the computed tomography scans of the intact shoulder, the spatial geometry of the shoulder was reconstructed using the Mimics software package. SolidWorks simulated computer 3D models of the intact shoulder and joint with three types of glenoid labrum damages were created. The stress-strain state has been registered at the glenohumeral structures for different angles of humeral abduction and rotation (neutral, 0-20-40-60° abduction, 0-20-40° internal rotation and a combination of these movements). The criteria for assessing were contact stress by von Mises and maximum strain. Results. All types of the glenoid labrum damages at various upper extremity abduction and rotation positions lead to a significant increase in stress and strain at the contact zone. In the neutral position, type I of glenoid labrum damage causes an increase by 20 % in stress on the humeral head cartilage, type II - by 260 % and type III - by 50 % compared to the intact model. In the extremity abduction position to 60° and internal rotation to 40°, type I of glenoid labrum causes an increase in stress on the humeral head cartilage by 23 %, type II - by 43 % and type III - by 7 % compared with the intact model. The maximum values of stress-strain state in the elements of the glenohumeral joint (labrum, humeral head) are observed in the position of the upper extremity abduction to 60° and internal rotation to 40°, higher than in the neutral position. There is an extreme increase in the stress values at the glenoid labrum (30 times) and humeral head cartilage (2.7 times) in all upper extremity positions. The least increase in stress-strain state is observed in type III glenoid labrum damage. Conclusions. It was revealed that the greatest imbalance in the stabilizing structures of the glenohumeral joint arises when the glenoid labrum is detached and becomes critical when combined with a rupture, while the rupture itself does not lead to critical changes in stress and strain values on the structures of the glenohumeral joint. It is rational to fix exfoliated part of the labrum when that disorder is detected during arthroscopic intervention, this leads to balance of loading at the joint structures during the most typical movements. Such procedure allows avoiding the early development of arthritis and posterior instability of the joint.