This cadaveric study measured how each rotator cuff muscle contributes to anterior glenohumeral stability. It compared the mid-range (neutral rotation) with the end-range apprehension position (90 degrees external rotation), where anterior instability occurs. The authors built a new metric, the dynamic stability index, combining each muscle's compressive and shear forces with the concavity-compression mechanism.
The old teaching was that static capsuloligamentous restraints handle end-range stability and muscles only matter in mid-range. This study shows the cuff provides real anterior stability in the vulnerable apprehension position too.
The mental model: in the cocked, externally rotated position, the subscapularis and posterior cuff (infraspinatus, teres minor) pull the head posteriorly and press it into the glenoid, protecting the anterior capsule. The supraspinatus does the opposite and pushes the head anteriorly.
This supports rehab that emphasizes the internal and external rotators in anterior instability, and it lines up with EMG data showing these muscles are underactive in unstable throwers. Remember it is cadaveric with simulated single-line muscle pulls and the capsule removed, so it isolates muscle action rather than reproducing in-vivo loading.
This cadaveric study measured how each rotator cuff muscle contributes to anterior glenohumeral stability. It compared the mid-range (neutral rotation) with the end-range apprehension position (90 degrees external rotation), where anterior instability occurs. The authors built a new metric, the dynamic stability index, combining each muscle's compressive and shear forces with the concavity-compression mechanism.
The old teaching was that static capsuloligamentous restraints handle end-range stability and muscles only matter in mid-range. This study shows the cuff provides real anterior stability in the vulnerable apprehension position too.
The mental model: in the cocked, externally rotated position, the subscapularis and posterior cuff (infraspinatus, teres minor) pull the head posteriorly and press it into the glenoid, protecting the anterior capsule. The supraspinatus does the opposite and pushes the head anteriorly.
This supports rehab that emphasizes the internal and external rotators in anterior instability, and it lines up with EMG data showing these muscles are underactive in unstable throwers. Remember it is cadaveric with simulated single-line muscle pulls and the capsule removed, so it isolates muscle action rather than reproducing in-vivo loading.