Davidson, J Shoulder Elbow Surg 1995 - Rotator Cuff and Posterior-Superior Glenoid Labrum Injury Associated with Increased Glenohumeral Motion: A New Site of Impingement - Article Summary

Rotator Cuff and Posterior-Superior Glenoid Labrum Injury Associated with Increased Glenohumeral Motion: A New Site of Impingement

Davidson, Jobe, et al.·J Shoulder Elbow Surg·1995·231 citations·Case series

This case report describes two professional baseball pitchers with posterior-superior shoulder pain in the cocking phase of throwing. It introduces "internal impingement" as a new site of rotator cuff injury distinct from classic subacromial impingement. The authors frame this pathology within Jobe's instability continuum for the overhead athlete.

Key Findings

Internal impingement is contact of the articular-side posterior supraspinatus and anterior infraspinatus against the posterior-superior glenoid rim in the cocked position (90° abduction, maximum external rotation). This is fundamentally different from Neer's external impingement, which compresses the bursal side against the coracoacromial arch.
The two pitchers represent opposite ends of the instability spectrum. Case 1 had increased external rotation (120° vs 90°) without significantly increased anterior translation. Case 2 had markedly increased anterior translation plus generalized ligamentous laxity, and needed surgical stabilization.
Case 2 showed a cluster of intra-articular lesions on arthroscopy: partial-thickness articular-side cuff tear, anterior labral flap tear, a type II SLAP lesion, frayed posterior-superior labrum, and an indistinct IGHL. This constellation is the classic picture of the unstable throwing shoulder.
The shoulder relocation test is proposed as the clinical marker: anterior force in abduction and maximal external rotation produces posterior-superior pain, relieved by posterior pressure. Eliciting the sign often requires external rotation beyond 90°, potentially up to 140°.
Cadaveric work confirmed the greater tuberosity forces the cuff and labrum against the glenoid rim in maximum abduction and external rotation. Walch independently reported 17 arthroscopic cases of deep supraspinatus impaction on the posterior-superior glenoid.
The normal humeral head translates about 4 mm posteriorly in the cocked position. Anterior instability abolishes this protective motion and produces anterior translation, which intensifies the impingement.
Most throwers are managed without surgery using rotator cuff and periscapular strengthening plus mechanics correction, while carefully avoiding any stretching of the anterior-inferior capsule.

Board PearlInternal impingement pinches the articular-side posterior cuff against the posterior-superior glenoid in abduction and maximum external rotation — the throwing athlete's cuff injury.

Supplemental

Rotator Cuff and Posterior-Superior Glenoid Labrum Injury Associated with Increased Glenohumeral Motion: A New Site of Impingement

Davidson, Jobe, et al.J Shoulder Elbow Surg1995231 citationsCase series