In-vivo glenohumeral translation and ligament elongation during abduction and abduction with internal and external rotation

Abstract

Study design: Basic Science. To investigate humeral head translations and glenohumeral ligament elongation with a dual fluoroscopic imaging system.

Background: The 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.

Methods: Five 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.

Results: The 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.

Discussion: 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. 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.

Figure 1

“Shoulder joint surface model” A typical shoulder joint model constructed from a patient specific MRI shown with the glenoid coordinate system definition used in this study.

Figure 2

“Glenohumeral ligaments on shoulder model” A typical shoulder joint with the superior, middle and anterior-band of the inferior glenohumeral ligament (SGHL, MGHL and AB-IGHL) insertion areas shown. The posterior-band of the inferior glenohumeral ligament (PB-IGHL) is not shown for clarity.

Figure 3

“Testing environment of DFIS” Dual fluoroscopic imaging system (DFIS) showed with (A) a subject in 90° abduction (B) a subject in 90° abduction with 90° external rotation.

Figure 4

“Shoulder angles in the coronal plane measured with a gonimeter” (A) 0° abduction neutral rotation (B) 45° abduction neutral rotation (C) 90° abduction neutral rotation (D) 90° abduction with 90° external rotation (E) 90° abduction with maximum active external rotation (F) 90° abduction with maximum active internal rotation.

Figure 5

“Computer environment of DFIS” A virtual computer generated dual fluoroscopic imaging system (DFIS) in Rhinoceros 3D modeling software with a shoulder joint model positioned to reproduce the kinematics on the fluoroscopic images.

Figure 6

“Humeral head translations” Translations of the humeral head center relative to the glenoid at the shoulder positions tested. The humeral head center location at 0° abduction was used as the reference position. The translations of the humeral head center along the anterior-posterior, superior-inferior, and medial-lateral directions are reported.

Figure 7

“Glenohumeral ligament measured lengths” The average measured lengths of the superior, middle, anterior-band and posterior-band of the inferior glenohumeral ligaments (SGHL, MGHL, AB-IGHL and PB-IGHL). Significant differences between ligaments length as a function of shoulder position have been denoted with a horizontal bracket.

Figure 8

“Glenohumeral ligament elongations” Ligament elongations of the SGHL, MGHL, AB-IGHL and PB-IGHL are reported for the shoulder positions tested. The ligament length at 0° abduction was used as a reference to calculate ligament elongation.