Analysis of changes of stress-strain state in scapula labrum in different types of its damage

I.A. Lazarev, S.S. Strafun, V.M. Lomko, M.V. Skiban

Abstract


Background. Damage to the glenoid labrum is a fairly common problem in the humeral cartilage. The presence of this pathology in posterior glenoid labrum and the type of its damage significantly increases the stress indices on the articular cartilage, which leads to the development and progression of degenerative changes of the humeral cartilage, acceleration of arthrosis and the realization of posterior humerus instability. This situation focuses the surgeon on determining the surgery strategy, aimed at unloading the damaged area and eliminating biomechanical imbalance. The purpose was to study the clinically significant damage of the scapula labrum, depending on the type of its damage, based on the biomechanical analysis of the change in the stress-strain state of the contact surfaces of the humeral cartilage and the rationale for the tactics of treating these injuries. Materials and methods. Calculations of the stress-strain state of the humeral cartilage elements by the finite element method were carried out on the basis of SCT scans of the intact humeral cartilage using the Mimics software package in automatic and semi-automatic modes, spatial geometry of the humeral cartilage. Imitative computer 3D-models of intact humeral cartilage and three types of scapula labrum damage were created using SolidWorks tools. We studied the stress-strain state of the structures of the humeral cartilage for different values of the angle with humerus abduction and rotation (neutral, abduction of the upper limb 0°–20°–40°–60°, internal rotation 0°–20°–40° and a combination of these movements). Criteria for assessing the stress-strain state were the stress by Mimics, contact stresses and maximum deformations. Results. All types of damage of labrum at various positions of the limb in the humeral cartilage lead to a significant increase in stress and strain in the contact zone. In the limb neutral position labrum damage causes an 8-fold increase in stress of the labrum, 30-fold in type II damage, 3-fold in type III, in comparison with the intact model. In the position of the limb retraction to 60° and an internal rotation of 40°, type I damage of the labrum causes an 5-fold increase in stress of labrum, 18-fold increase in type II damage, and 14 % in type III, as compared with the intact model. The maximum values of stress-strain state on the elements of the humeral cartilage (labrum, humerus head) are observed in the position of the limb retraction to 60° and internal rotation of 40°, higher than in the neutral position of the limb. In the conditions of type II damage of the labrum, extreme growth of stress indices is observed in all positions in the humeral cartilage, both on the joint itself (30-fold) and on the head of the humerus (2.7-fold). With the increase in the angle of retraction and internal rotation of the joint, the value of stress-strain state on the joint itself increases significantly (18-fold), reaching values of stresses of 101.68 MPa and deformations of 60.77 mm in the limb retraction position to 60° and internal rotation of 40°. The stress-strain state indices also increase on the humerus head (1.4-fold). Conclusions. It was revealed that the greatest imba­lance of the stabilizing structures of the humeral cartilage arises when the joint is detached and becomes critical when combined with a rupture, while the rupture itself does not lead to critical changes in stress and deformation on the structures of the humeral cartilage. It is rational to fix the labrum exfoliated part when this pathology is detected during arthroscopic intervention, this will allow balancing tension and strain of the humeral structures during the most typical movements. This procedure will avoid the early development of arthrosis and posterior instability of the humeral cartilage.

Keywords


humeral cartilage; glenoid labrum; posterior instability; finite element modeling; stresses and strain

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DOI: https://doi.org/10.22141/1608-1706.3.18.2017.105357

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