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.


OBJECTIVE
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.


METHODS
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.


CONCLUSIONS
Repetitive excessive humeral external rotation observed in throwers may be one of the biomechanical causes for increased shoulder laxity and increased humeral external rotation.
Mihata
Teruhisa
T
Orthopaedic Biomechanics Laboratory, VA Healthcare System, Long Beach, CA 90822, USA. tqlee@med.va.gov, tqlee@uci.edu
Lee
YeonSoo
Y
McGarry
Michelle H
MH
Abe
Muneaki
M
Lee
Thay Q
TQ
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D006811:Humerus / Q000502:physiology*; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology*; D008023:Ligaments, Articular / Q000033:anatomy & histology* / Q000502:physiology; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology*; D013177:Sports / Q000502:physiology*