Effects of repetitive subfailure strains on the mechanical behavior of the inferior glenohumeral ligament

Excessive humeral external rotation results in increased shoulder laxity

BACKGROUND

The quantitative relationship between increased anterior shoulder laxity and increased humeral external rotation observed in throwers remains unclear.

HYPOTHESIS

An elongated anterior capsule, especially the anterior band of the inferior glenohumeral ligament, produced by excessive humeral external rotation will result in increased anterior shoulder laxity and increased humeral external rotation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven cadaveric shoulders were tested to measure the humeral rotational range of motion, glenohumeral translations, and length of the anterior band of the inferior glenohumeral ligament. Data were collected for the intact shoulders and after nondestructive stretching of 10%, 20%, and 30% beyond maximum humeral external rotation.

RESULTS

Nondestructive excessive external rotational stretching resulted in a significant increase in superior (30%, 3.3 mm) and inferior (30%, 2.3 mm) length of the anterior band of the inferior glenohumeral ligament, external rotation (30%, 35 degrees), and anterior (30%, 2.4 mm), inferior (30%, 2.2 mm), and anterior-posterior (30%, 5.1 mm) translations. There were significant positive linear correlations between the length of the anterior band of the inferior glenohumeral ligament, external rotation, and anterior translation.

CONCLUSIONS

Excessive humeral external rotation results in an elongation of the anterior band of the inferior glenohumeral ligament and an increase in anterior and inferior glenohumeral translations and humeral external rotation.

CLINICAL RELEVANCE

Repetitive excessive humeral external rotation observed in throwers may be one of the biomechanical causes for increased shoulder laxity and increased humeral external rotation.

Neer Award 2001: nonrecoverable strain fields of the anteroinferior glenohumeral capsule under subluxation

Although tears of the glenohumeral capsule have been observed in anteroinferior instability, prefailure, nonrecoverable deformation is suspected but has not been shown to exist after shoulder subluxation. The inferior glenohumeral ligament in the anteroinferior capsule (AIC) is a primary stabilizer in anteroinferior instability. The aim of this study was to examine the nonrecoverable strain field of the AIC due to shoulder subluxation. Nonrecoverable strains were calculated between a nominal strain state and a postsubluxed state. AIC marker coordinates were reconstructed from stereoradiographs, and strains were calculated from these coordinates. Nonrecoverable strain was shown to develop, varying from 3% to 7% through a range of joint subluxation. High strain tended to occur on the glenoid side of the AIC. Interestingly, strains were generally not oriented along major ligamentous bands. This is the first study to quantify planar nonrecoverable strain fields in the glenohumeral joint capsule.

Interplay of the static and dynamic restraints in glenohumeral instability

Anterior glenohumeral instability is a common, yet complicated orthopaedic disorder. During the past few years, basic science research has improved the understanding of the glenohumeral joint stabilizing systems. The current authors review new contributions specifically detailing study of the interplay between the static and dynamic restraints. Simulation of the shoulder muscles in a recent study also has manifested the powerful contribution of the joint reaction force to concavity-compression. Continued advances, such as these, will improve the understanding, and allow better outcome, in treatment of glenohumeral instability.