Multiquadrant digital analysis of shoulder capsular thickness

Purpose: Nonablative thermal capsular shrinkage has been developed in an at tempt to address the plastic capsule deformation thought to cause increased rates of recurrent instability following arthroscopic stabilization proced ures. Although the temperature required to optimize collagen shrinkage is k nown, a safe depth of thermal penetration, in various locations about the s houlder capsule, has not been defined. The purpose of this study was to mea sure shoulder capsule thickness by quadrant and circumferentially from the glenoid to the humerus so that thermal energy in shoulder procedures can be more precisely applied to limit possible injury to pericapsular structures . Type of Study: This is an anatomic study using a cadaveric shoulder speci mens. Materials and Methods: Soft tissue was dissected from 8 fresh cadaver ic shoulders to isolate intact glenohumeral joint capsules. The humeral ins ertion was released and the capsule was cut into 6 longitudinal quadrants a round the glenoid. The capsule specimens were then flash frozen and stored at -80 degrees C. Quadrant tissue was cut into longitudinal sections 14 to 16 mu m wide and stained with hematoxylin and eosin. The specimens were the n digitized under a dissecting microscope and measured using computer imagi ng software at approximately 4-mm intervals. Two-way analysis of variance ( ANOVA) was performed on the measurements of the intact capsule specimens 2. 5 cm off the glenoid. Humeral insertion data were recorded separately. Resu lts: A total of 248 separate measurements were made throughout the capsule in 8 specimens, Capsular thickness increased from an average of 2.42 mm ant eriorly to 2.80 mm in the inferior capsular pouch and again thinned to 2.22 mm posteriorly. Global shoulder capsule thickness ranged from 1.32 to 4.47 mm. When analyzed by position, from glenoid to humerus, a general thinning was noted with a mean thickness of 3.03 mm at the glenoid to 2.17 mm at th e humeral insertion. Two-way ANOVA showed a significant thickness variation along the specimen (P < .05), a nearly significant thickness variation wit h regard to quadrant (P < .03), and no significant interaction (P > .07) wh en applied to specimen measurements approximately 2.5 cm off the glenoid. C onclusions: The thickness of the shoulder capsule ranges from 1.32 to 4.47 mm, with a significant thinning laterally from the glenoid to the humerus. Further, capsule thickness ranges from 2.76 to 3.18 mm in the regions in cl osest proximity to the axillary nerve. These data may help determine the pr oper amount of thermal penetration necessary when performing shrinkage proc edures and provide safety guidelines to limit the depth of thermal penetrat ion to avoid possible injury to pericapsular structures.