Original articles
Structural and mechanical properties of the glenohumeral joint posterior capsule

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The purpose of this study was to quantify regional variations in material properties of the glenohumeral joint posterior capsule and to compare these data with the anterior band of the inferior glenohumeral ligament (AB-IGHL). Mechanical properties were determined for individual bands of the AB-IGHL, superior posterior capsule (SUP-PC), middle posterior capsule (MID-PC), and inferior posterior capsule (INF-PC). Significant differences in tissue thickness were found among the 3 posterior capsular regions and the AB-IGHL. The AB-IGHL was thicker than the MID-PC (P = .03) and INF-PC (P = .01), and the SUP-PC was thicker than the INF-PC (P = .02). Except for significant differences in failure strains, material properties were not significantly different among the 4 tissue regions. There were no significant differences between tissue bands in modulus (P = .2), maximum stress (P = .46), or strain energy density (P = .62). Specimens failed primarily near the glenoid insertion (75%), with 4 specimens failing at the humeral insertion and 2 others failing in the tissue’s mid substance.

Section snippets

Specimen preparation

In this study 7 healthy, fresh-frozen human cadaveric shoulders (3 left and 4 right) from 7 persons were used. To determine the appropriate sample size, we conducted a statistical power analysis after testing the first 3 specimens. The analysis indicated that a sample size of 7 was necessary to achieve a power of 80% at a significance level of P < .05 (β = .2, α = .05). Specimens with severe glenohumeral joint arthritis or visible rotator cuff pathology (ie, degeneration or fraying) were

Geometry

Significant differences in tissue thickness were found among the 3 regions of the posterior capsule and the AB-IGHL (Figure 2). Specifically, the AB-IGHL was thicker than the INF-PC (P = .01) and MID-PC (P = .03), whereas the SUP-PC was thicker than the INF-PC (P = .02). Somewhat surprisingly, there was no statistically significant difference in thickness between the AB-IGHL and the SUP-PC (P = .53).

Material properties

There were relatively few differences in the material properties between the 3 regions of the

Discussion

The purpose of this study was to quantify regional variations in the material properties of the glenohumeral joint’s posterior capsule. Although we originally hypothesized that the material properties of the posterior capsule would be significantly inferior to those of the AB-IGHL, we found relatively few differences between the posterior capsule and the AB-IGHL.

Contrary to our expectations, the only differences that were detected between the 4 tissue bands were in failure strain and thickness.

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