Characterizing Material Properties of Rotator Cuff Tendons Relevant in Reverse Total Shoulder Arthroplasty Using Video-Based Strain Measures.

Background: The material behavior of rotator cuff tendons that remain intact in patients indicated for reverse total shoulder arthroplasty influences the compressive stability of the reconstructed joint. However, the literature provides insufficient information about those material property definitions to accurately incorporate cuff tendons in computational stress (finite element) analysis of reverse total shoulder arthroplasty. Therefore, the goal of this study was to characterize the material properties of rotator cuff tendons relevant in reverse total shoulder arthroplasty.

Methods: Tensile testing was performed on the subscapularis (superior; inferior), infraspinatus (superior; inferior), and teres minor tendons in whole bone-tendon constructs acquired from two cadaveric shoulder specimens. Force and displacement outputs measured from the materials testing system and from two tissue-specific video-based strain measurement methods were used to derive stress-strain curves and associated elastic modulus values. Tendon elastic modulus values were statistically compared between analysis methods.

Results: Average elastic modulus values measured from the materials testing system (49 ± 8 MPa) were significantly lower than those measured using either video-based method (method 1: 217 ± 135 MPa and method 2: 186 ± 84 MPa; p<0.001 for both). Except for one teres minor specimen, no differences in individual tendon elastic modulus values were found between the video-based measurement methods.

Concluion: The data demonstrate that rotator cuff tendon elastic modulus values are underestimated by studies that only use materials testing system-based measurement, and any video-based measurement yields more relevant data.

Clinical relevance: Elastic modulus values determined in this study can be used to assign cuff tendon material behavior in finite element analysis of reverse total shoulder arthroplasty.