Direction of non-recoverable strain in the glenohumeral capsule following multiple anterior dislocations: Implications for anatomic Bankart repair

The study aimed to analyze the direction of non-recoverable strain and determine the optimal direction for anatomic capsular plication within four sub-regions of the inferior glenohumeral capsule following multiple dislocations. Seven fresh-frozen cadaveric shoulders were dissected. A grid of strain markers was affixed to the inferior glenohumeral capsule. Each joint was mounted in a 6-degree-of-freedom robotic testing system and repeatedly dislocated in the anterior direction 10 times at 60 degrees of abduction and 60 degrees of external rotation of the glenohumeral joint. The 3D positions of the strain markers were compared before and after dislocations to define the non-recoverable strain. The strain map was divided into four sub-regions. The angles of deviation between each maximum principle strain vector and the anterior band of the inferior glenohumeral ligament (AB-IGHL) or posterior band of the IGHL (PB-IGHL) for the anterior and posterior regions of the capsule were determined. The mean direction of all strain vectors in each sub-region was categorized. The direction of the non-recoverable strain in the anterior-band and anterior-axillary-pouch sub-regions was categorized as parallel to the AB-IGHL, whereas the posterior-axillary-pouch and posterior-band sub-regions were mostly perpendicular to the PB-IGHL. Clinical Significance: Plication of the anteroinferior capsule parallel to the AB-IGHL may be preferred during arthroscopic Bankart repair to restore anatomy; posteroinferior capsular plication may also be necessary and best performed perpendicular to the PB-IGHL. The direction of the capsular injury remains the same irrespective of the number of dislocations. This study provides the scientific and quantitative rationale for an anatomic approach to capsular plication.