Biomechanical assessment of Type II superior labral anterior-posterior (SLAP) lesions associated with anterior shoulder capsular laxity as seen in throwers: a cadaveric study.
BACKGROUND
Type II superior labral anterior-posterior lesions in throwers are often associated with anterior shoulder capsular laxity.


OBJECTIVE
Shoulder instability in patients with type II superior labral anterior-posterior lesions may result from the associated shoulder capsular laxity rather than the superior labral anterior-posterior lesion alone.


METHODS
Controlled laboratory study.


METHODS
Six cadaveric shoulders were externally rotated to 20% beyond the maximum humeral external rotation at 60 degrees of glenohumeral abduction, which simulated 90 degrees of shoulder abduction, to detach the superior labrum and elongate the anterior shoulder capsular ligaments. The detached labrum was then repaired to isolate the effect of the detached superior labrum and that of the capsular laxity. Rotational range of motion was measured at 60 degrees of glenohumeral abduction. Anterior-posterior glenohumeral translation was measured at 30 degrees and 60 degrees of glenohumeral abduction. Superior-inferior glenohumeral translation was measured at 0 degrees and 60 degrees of glenohumeral abduction.


RESULTS
The experimentally created type II superior labral anterior-posterior lesion and capsular laxity significantly increased anterior translation at 30 degrees (mean difference, 1.0 +/- 0.8 mm; P < .05) and 60 degrees (mean difference, 2.2 +/- 2.0 mm; P < .05) of glenohumeral abduction. Subsequent superior labral anterior-posterior repair restored the anterior translation but only at 30 degrees of glenohumeral abduction (mean difference, 0.9 +/- 0.6 mm; P < .05).


CONCLUSIONS
Because of the anterior capsular laxity associated with type II superior labral anterior-posterior lesions, superior labral anterior-posterior repair of the peeled-back superior labrum may not restore anterior glenohumeral translation at 90 degrees of shoulder abduction.


CONCLUSIONS
Anterior shoulder capsular laxity associated with type II superior labral anterior-posterior lesions may cause anterior shoulder instability at 90 degrees of shoulder abduction in throwers even after superior labral anterior-posterior lesion repair.
Mihata
Teruhisa
T
Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, 5901 East 7th Street, Long Beach, CA 90822, USA.
McGarry
Michelle H
MH
Tibone
James E
JE
Fitzpatrick
Michael J
MJ
Kinoshita
Mitsuo
M
Lee
Thay Q
TQ
D001265:Athletic Injuries / Q000503:physiopathology; D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000502:physiology; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000503:physiopathology*; D013708:Tendon Injuries / Q000503:physiopathology*