Location and magnitude of capsular injuries varies following multiple anterior dislocations of the shoulder: Implications for surgical repair

Abstract

Capsular injuries can occur during multiple shoulder dislocations. The purpose of this study is to evaluate the location and magnitude of glenohumeral capsular injury following multiple dislocations. We hypothesized that the magnitude of capsular injury would increase and the location of peak injury would vary depending on the number of dislocations. Seven fresh‐frozen cadaveric shoulders were used. A 7 × 11 grid of strain markers was affixed to the anteroinferior capsule. Each joint was then mounted to a six degree‐freedom robotic testing system. Marker tracking was performed following 1, 2, 3, 4, 5, and 10 dislocations to determine the nonrecoverable strain as capsular injury. Following each dislocation, the magnitude of the maximum principal strain representing the nonrecoverable strain in the inferior glenohumeral capsule was quantified by comparing the strain marker positions following each dislocation. The peak value of nonrecoverable strain statistically increased with the number of dislocations in five of seven specimens (p = .0007). The capsular location that had the peak value of nonrecoverable strain varied according to the number of dislocations, and from specimen to specimen. The nonrecoverable strain was identified in the posterior capsule and anterior axillary pouch, which increased with the number of dislocations compared to the other regions of the capsule (p = .001–.012) by up to 16%. Clinical significance: While plication of the anterior axillary pouch is important following multiple dislocations, a more extensive anterior capsular shift may be necessary with an increased number of dislocations in addition to a posterior capsular shift when appropriate.

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

“…As the force required for dislocation decreases, 28 the humeral head goes further over the rim of the glenoid or the capsule could be experiencing micro‐tears. The previous study demonstrated location and magnitude of non‐recoverable strain varied following multiple dislocations 17 . On the other hand, the mean direction of the non‐recoverable remained consistent through multiple dislocations in this study.…”

“…Thus, no capsular injuries were observed in these regions. Magnitude and location of non‐recoverable strain were analyzed in a similar manner as previously described 17 . Finally, the categorization of the mean direction of non‐recoverable strain is binary, parallel, or perpendicular.…”

“…The robotic testing system utilizes coordinate systems to define motion of the humerus with respect to the scapula. Definition of the origin of the robotic system and the three axes ( x , y , and z ) of the scapular coordinate system were described in detail in our previous studies 17,28 …”

“…The process for determining the reference strain configuration was originally described by Malicky et al 6,8 and modified for our use 17,29,30 . Each joint was positioned in a reference strain position using the testing system.…”

“…The direction of non‐recoverable strain in the anteroinferior capsule was not aligned with the anterior band of the inferior glenohumeral ligament (AB‐IGHL). However, non‐recoverable strain has also been found in the posteroinferior capsule 7,17 …”