The labrum is an extension of the glenoid articular cartilage that helps retain the humeral head in the glenoid fossa. The superior portion is a thick soft tissue with a triangular cross sectional area, comparable to knee meniscus, w hile the inferior portion is a thin and flatter cartilaginous tissue comparable to articular cartilage.

The objective of this research was to compare the compressive load versus displacement responses of the glenoid labrum using rapid indentation and obtain the stiffness and modulus of the tissue. The compressive testing procedure w as a novel method of testing soft tissue in situ. Stiffness findings validated the testing procedure by showing repeatability and appropriate similarity.

Six embalmed and nearly intact labra were tested in six morphologically different sections delimited by other researchers as being susceptible to different injuries. Each section was indented at three sites. Site results were averaged and compared between labra. Similar sections were averaged among the different labra.

Testing assumed an elastic model and examined the linear regions of the load versus displacement curves for the labral and cartilaginous tissues. Results of the indentation testing demonstrated large differences in the stiffness and modulus between the superior and inferior sections of the glenoid labrum.

The stiffness results show ed some similarities within sections and confirmed the variability between various portions of the tissue.

The modulus was defined as the stress applied to the tissue by the indentor divided by the ratio of displacement and the tissue thickness (i.e.:​ Stress/[displacement/thickness]). The labral modulus ranged from 0.11 ± 0 .1 6 to 0.41 ± 0.32 MPa. As for the cartilage, the modulus ranged from 1.65 ± 0.78 to 4.82 ± 2.93 MPa. The modulus results for the labrum agreed with findings of Joshi (1995) for the stiffness of human meniscus (0.205 MPa). The inferior section, w hich C ooper (1992) believed to be structurally stiffer, was actually the least stiff as a material. AJthough to gross observations this section appeared to be the stiffest, the mechanical properties showed otherwise. This lead to believe that the inferior portion only seemed stiffer because it was a thinner tissue. This could imply that the lower section is less important for load bearing.

Results from the second linear portion of the data were in the range of the findings by Xiaowei (1995) (2 MPa) and Mow (1980) (2MPa) and Rasanen's (1996) (2.49-0.71 MPa) for articular cartilage. Using actual cartilage thickness values found by previous studies, the calculated cartilage moduli ranged from 1.29 to 2.00 MPa. These results are comparable to the previous studies.

Specimen morphology findings agreed with most of the results from previous studies. It was confirmed that the labrum added 5mm to the anterior posterior depth of the glenoid fossa as per Howell and Galinat (1988). However, it did not agree with their finding stating that the superior inferior depth was increased by 9mm. Gross observation of the specimens confirm ed the larger occurrence of tissue damage in the superior portion of the labrum. Large differences were found betw een the dominant and non-dominant arm of each cadaver. However, these differences were less than those found between cadavers.