Anterior and posterior shoulder instability. A cadaver study.

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Anatomy

Background:

• The glenohumeral joint relies on a complex interplay of rotator cuff muscles and capsular ligaments for stability.
• Understanding the specific contributions of these structures to anterior and posterior displacement is vital for treating shoulder instability.

Purpose of the Study:

• To investigate the biomechanical role of the rotator cuff and capsular structures in glenohumeral joint stability.
• To quantify the contribution of anterior and posterior structures to anterior and posterior humeral head displacement.

Main Methods:

• Cadaveric study involving 10 glenohumeral joint specimens.
• Application of constant force to the humerus to measure anterior and posterior displacement.
• Sequential cutting of rotator cuff and capsular structures to assess stability changes.

Main Results:

• Posterior structures significantly influence anterior stability within the initial 40 degrees of abduction.
• Anterior subluxation to luxation occurred after anterior rotator cuff and capsule lesions.
• Posterior rotator cuff and capsule were critical for posterior displacement between 40-90 degrees of abduction.

Conclusions:

• Major anterior displacement requires significant posterior structure lesions.
• Posterior displacement leading to subluxation is associated with major anterior injuries.
• Both rotator cuff and capsular integrity are essential for maintaining glenohumeral joint stability across various abduction angles.