Abstract
Study DesignBasic Science. To investigate humeral head translations and glenohumeral ligament elongation with a dual fluoroscopic imaging system.BackgroundThe glenohumeral ligaments are partially responsible for restraining the humeral head during the extremes of shoulder motion. However, in-vivo glenohumeral ligaments elongation patterns have yet to be determined. Therefore, the objectives of this study were to 1) quantify the in-vivo humeral head translations and glenohumeral ligament elongations during functional shoulder positions, 2) compare the inferred glenohumeral ligament functions with previous literature and 3) create a baseline data of healthy adult shoulder glenohumeral ligament lengths as controls for future studies.MethodsFive healthy adult shoulders were studied with a validated dual fluoroscopic imaging system (DFIS) and MR imaging technique. Humeral head translations and the superior, middle and inferior glenohumeral ligaments (SGHL, MGHL, IGHL) elongations were determined.ResultsThe humeral head center on average translated in a range of 6.0mm in the anterior-posterior direction and 2.5mm in the superior-inferior direction. The MGHL showed greater elongation over a broader range of shoulder motion than the SGHL. The anterior-band (AB)-IGHL showed maximum elongation at 90° abduction with maximum external rotation. The posterior-band (PB)-IGHL showed maximum elongation at 90° abduction with maximum internal rotation.DiscussionThe results demonstrated that the humeral head translated statistically more in the anterior-posterior direction than the superior-inferior direction (p = 0.01), which supports the concept that glenohumeral kinematics are not ball-in-socket mechanics. The AB-IGHL elongation pattern makes it an important static structure to restrain anterior subluxation of the humeral head during the externally rotated cocking phase of throwing motion. These data suggest that in healthy adult shoulders the ligamentous structures of the glenohumeral joint are not fully elongated in many shoulder positions, but function as restraints at the extremes of glenohumeral motion. Clinically, these results may be helpful in restoring ligament anatomy during the treatment of anterior instability of the shoulder.
Highlights
The glenohumeral ligaments are partially responsible for restraining the humeral head during the extremes of shoulder motion
The results demonstrated that the humeral head translated statistically more in the anterior-posterior direction than the superior-inferior direction (p = 0.01), which supports the concept that glenohumeral kinematics are not ball-in-socket mechanics
There appeared to be a reciprocal function between the AB-IGHL and PB-IGHL during invivo shoulder motion, similar to the mechanism proposed by O’Brien et al and Warner et al in cadaveric studies [2,3]
Summary
The glenohumeral ligaments are partially responsible for restraining the humeral head during the extremes of shoulder motion. The shoulder (glenohumeral) joint has the widest range of motion of all major joints, due to its limited articular constraint and lax capsuloligamentous structures. The capsuloligamentous structures have defined thickenings called ligamentous bands [1,2,3] at. While these in-vitro investigations have provided data on the biomechanical response of the shoulder under externally applied loads, the in-vivo ligament kinematics under physiological loading conditions have remained unclear. The in-vivo glenohumeral ligamentous bands elongation patterns during functional shoulder motion have not been reported
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