Glenoid Track concepet: a finite elements evaluation

Abstract

Due to its anatomic configuration, which allows a wide and important range of motion, the glenohumeral joint has a high rate of dislocation, which may correspond up to half the cases of dislocations in some populations. . It was estimated the annual incidence of 69,486 cases of shoulder dislocation in the period of 2002-2006, in the United States, corresponding to an incidence of 23.9 cases per 100,000 people / year. Most of these dislocations become recurrent, leading to significant limitation of the patient to perform job- and sports activities. . There are many predictors of recurrence, especially among them the age of the first episode, the degree of activity and the presence of bone lesions.The main structural injury resulting from previous shoulder dislocation is the former capsuloligamentous labral avulsion called "Bankart lesion." The anterior labrum is critical in shoulder stability and its injury can lead to recurrent dislocation, requiring their reintegration into the glenoid in order to re-establishe the shoulder stability. The capsuloligamentous labral repair is called the "Bankart surgery." Other anatomical injuries that can occur are fractures of the glenoid rim (Bony Bankart) and impaction fracture of the humeral head (Hill-Sachs lesion). Treatment of the patient presenting these bone lesions is more complex and not well established.Young individuals, competitive level sport activity in young males, misdiagnosis of excessive capsular laxity and presence of a large glenohumeral bone defects increase the risk of Bankart repair failure. Recent studies show the importance of glenoid bone lesions (bony Bankart) and humerus lesions (Hill-Sachs lesion) in arthroscopic surgical failures. About 70% of patients with postoperative recurrence had some significant bone injury. The absence of reliable preoperative parameters to evaluate these bone defects generates difficulty in indicating the surgical technique to treat glenohumeral instability.Failure of capsuloligamentous labral repair (Bankart surgery) is more related when, sometime in the shoulder range of motion, the Hill-Sachs lesion comes into contact with the anterior edge of the glenoid (with or without injury ). To understand the limits outlined by the edge of the glenoid, a new research line introduced the concept of "glenoid track". This is a trail defined by the contact provided by the glenoid articular surface in the humeral head during range of motion. Since the Hill-Sachs lesion exceeds this track, a fulcrum mechanism occurs, generating new dislocations and repair failure.As an initial means of research we propose a finite elements evaluation. The use of finite element technology allows representation of the biomechanical characteristics of the various structures that compose the shoulder. The careful construction of a biomechanical model allows us to make comparisons about what occurs in vivo. Studies on cadavers and through imaging have limitations and, so far, no finite element research was used to characterize the glenoid track.Our proposal is to characterize the concept of glenoid track in a biomechanical finite element model. After carefully developing the model, we expect to see the characteristics of bone contact during range of motion, identifying vulnerable areas for the occurrence of an engaging Hill-Sachs lesion, and thus indicating surgery that can prevent the failure of Bankart surgery. (AU)