Age related biomechanical properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex

Abstract

Objective. To quantify the biomechanical properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex for the two age groups.

Design. In vitro human cadaver study evaluating the biomechanical properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex for a younger group (n=5, mean age 38.5, SD 0.5 years) and an older group (n=7, mean age 74.8, SD 5.3 years).

Background. Glenohumeral instability is more of a problem in younger than in older individuals, primarily because recurrence is much more common at a young age.

Methods. Tensile testing was performed on the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex in the shoulder apprehension position using a custom jig, Instron machine and a video digitizing system.

Results. In the younger individuals disruption of the complex most often occurred at the glenoid–labrum region of the glenoid insertion site. In the older individual, disruption most often occurred at the midsubstance region. The load and the stress at failure of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex showed that the older group was only 61% and 46% of the younger group, respectively.

Conclusions. The structural properties of the glenoid–anterior band of the inferior glenohumeral ligament–humerus complex and the material characteristics of the anterior band of the inferior glenohumeral ligament for the younger group were significantly superior than the older group.

Relevance

A stronger and more extensive repair, such as the traditional open technique, may be necessary for younger individuals with glenohumeral instability whereas in older individuals, a different repair technique, such as an arthroscopic technique, may be sufficient.

Introduction

Anterior dislocation of the shoulder has been considered primarily to be an injury of youth while its occurrence in the older age group is often minimized [1]. But, traumatic shoulder instability occurs in both younger and older individuals. One of the reasons for the seemingly decreased frequency in older patients is that recurrent instability correlates with the age of the individual [2]. After acute anterior instability in a younger individual (under 25 years of age) recurrence rates range as high as 60–94% [2], [3], [4], [5], [6], [7]. After a similar instability episode in the older population, recurrence is much less common. McLaughlin and Cavallaro [8] and Rowe [2] reported recurrence rates of 10% and 14% in those older than 40 years, respectively. However, initial shoulder dislocation after the age of 45 has been reported to be similar in frequency to that before the age of 45 [9], [10]. Since recurrence is less common in older individuals the entity of anterior instability may seem less common than in the young, but it remains meaningful.

The inferior glenohumeral ligament (IGHL) is one of the main components of the capsuloligamentous mechanism that works in concert with dynamic muscle stabilizers to provide stability for the glenohumeral joint [11], [12]. It is also the primary static stabilizer resisting anterior glenohumeral joint instability in 90° of shoulder abduction and at the extreme of external rotation [13]. The goal in treatment of anterior glenohumeral joint instability is the return of stability, range of motion and strength. Regardless of the age of the individual, when operative treatment is required the surgical technique is based on restoration of normal joint anatomy. Success of surgical repair depends on accurate identification of the stabilizing structures and correction of existing pathoanatomy. However, the pathoanatomy is often different in younger and older individuals. Matsen and coworkers reported that in their extensive experience, 97% of patients with traumatic, unidirectional anterior glenohumeral joint instability have a rupture of the glenoid attachment of the middle and/or inferior glenohumeral ligaments [14]. This describes the Bankart lesion, a tear of the IGHL origin and the anterior–inferior labrum from the glenoid bone [15], [16]. In older individuals a more common sequelae of acute anterior glenohumeral joint dislocation is a tear of the rotator cuff [6], [17], [18]. Because the rotator cuff is confluent with the lateral joint capsule, this results in lateral capsular avulsion.

Previous biomechanical investigations provided insight that age plays a role in surgical repair of the glenohumeral joint after an episode of instability. Reeves in 1968 tested the anterior capsule of glenohumeral joints in uniaxial tension and reported that the initial structure to fail in older joints was the anterioinferior capsule (62%) while younger joints failed at higher loads and more often (78%) at the glenoid insertion site [18]. Kaltsas also performed mechanical stress testing on the glenohumeral joint capsule and reported that the strength of the joint capsule bears an inverse relationship to age of the specimen, becoming weaker with advancing age [19]. Investigations of other functional ligamentous complexes in the body have also found decreased biomechanical properties with increased age [20], [21], [22]. To our knowledge, despite the position of apprehension being associated most often with anterior glenohumeral band of the IGHL in this position [23], [24].

The structural integrity and biomechanical properties of the anterior band of the IGHL complex are an important part of the pathology and treatment of recurrent glenohumeral joint instability. The purpose of this study was to compare the biomechanical properties of the “glenoid–anterior band of the IGHL–humerus” (G–ST–H) complex in the position of apprehension for both the older and younger age groups.