Effect of Scapular Orientation on Shoulder Internal Impingement in a Cadaveric Model of the Cocking Phase of Throwing

Abstract

Increasing internal scapular rotation and decreasing upward scapular rotation significantly increase glenohumeral contact pressure and the area of impingement of the rotator cuff tendon between the greater tuberosity and glenoid during simulated throwing motion.

Humeral torsion and throwing proficiency in early human evolution

“…It appears, therefore, that in ball players with low humeral torsion there is a tendency for compensatory scapular repositioning that echoes the configuration I have suggested for the shoulder transitional phase in early H. erectus (Larson, 2007;Larson et al, 2007). For a pitcher, however, such changes can disrupt normal throwing mechanics and are associated with a variety of clinical problems (Kibler, 1998;Burkhart et al, 2003;Mihata et al, 2012). There are soft tissue factors that contribute to GIRD in addition to low humeral torsion, and as Polster et al (2013) conclude, the interplay between the various factors is complex.…”

Clinical implications of scapular dyskinesis in shoulder injury: the 2013 consensus statement from the ‘scapular summit’

“…Mechanical internal impingement risk as defined by GH contact pressure and impingement area has recently been demonstrated to be affected by scapular position in a cadaver model 42. In this model, a scapular position of less upward rotation and increased internal rotation (protraction), commonly seen in scapular dyskinesis, increased the area of contact of the humerus with the posterior superior glenoid and increased scapular internal rotation also increased the GH contact pressure.…”

“…It is increasingly apparent that two-dimensional or three-dimensional representations of minimal acromiohumeral distance are not fully characterising the complex relationships between shoulder kinematics and rotator cuff mechanical impingement risk,10 41 42 as these minimal distances are not consistent with rotator cuff tendon proximity to potential impinging structures. The acromiohumeral distances are typically minimised at 90° humerothoracic elevation, while the supraspinatus humeral insertion has cleared the undersurface of the anterolateral acromion earlier in the range of humerothoracic elevation 10 41.…”

“…The altered position and motion of internal rotation and anterior tilt is believed to change GH alignment, placing increased tensile strain on the anterior ligaments,22 increases ‘peel-back’ of the biceps/labral complex on the glenoid,65 potentially creates pathological internal impingement42 66 and weakens the rotator cuff cocontraction strength. These effects are magnified in the presence of GIRD, which creates increased protraction due to ‘windup’ of the tight posterior structures in follow through.…”

Scapulothoracic kinematics during scaption after one year of tennis practice in elite girl players

“…The extreme humeral external rotation associated to the arm elevation at the end of the cocking phase during tennis serve repeats the natural contact between the greater tuberosity and the posterosuperior part of the glenoid cavity (Mihata et al 2012). An improper positioning of the scapula onto the thorax may exacerbate the area and/or the pressure of this contact, and posterosuperior and superior impingement can occur (Mihata et al 2012). Studies focusing on scapular motion are recent, and few information are available on the alterations in scapulothoracic kinematics with tennis playing.…”