# The elastic properties of the tendinous and capsular layers of the rotator cuff complex using fresh tissue—a biomechanical study

## TL;DR

This study measures the elasticity of rotator cuff tissues using fresh samples and digital image correlation, finding that tendinous layers are stiffer than capsular layers.

## Contribution

The novel use of digital image correlation on fresh tissue to compare elastic moduli of tendinous and capsular layers in the rotator cuff complex.

## Key findings

- Tendinous layers of the supraspinatus, infraspinatus, and subscapularis had higher elastic moduli than their capsular layers.
- Elastic moduli values for tendinous layers ranged from 59.6 MPa to 67.1 MPa, while capsular layers ranged from 29.0 MPa to 41.5 MPa.
- The study suggests that surgical repair should treat tendinous and capsular layers separately to prevent biomechanical imbalance.

## Abstract

Elastic modulus is an important biomechanical component that indicates stiffness or elasticity of biological material. Recently the use of digital image correlation (DIC) in elastic modulus studies on fresh tissue has shown great accuracy in estimating elastic properties; thus, the aim of this study was to investigate the elasticity of capsular and tendinous layers of the rotator cuff complex employing this method.

The supraspinatus, infraspinatus, and subscapularis from eight (n = 8) fresh/frozen tissue shoulders were reverse dissected from their origins. The muscles were separated from one another and dissected to produce 20 × 20 mm tendinous and capsular strips for each muscle. DIC was employed to measure the strain of the tendinous and capsular portions of each of the muscles during tensile testing, and tangent elastic modulus values were obtained.

The tendinous layers for supraspinatus, infraspinatus, and subscapularis yielded higher average tangent elastic moduli readings (62.1 MPa, 67.1 MPa, and 59.6 MPa, respectively) compared to their capsular counterparts (29.0 MPa, 32.5 MPa, and 41.5 MPa, respectively).

Different elastic moduli findings for the tendinous and capsular layers suggest these layers should be considered independently during surgical repair to avoid biomechanical imbalance which may result if these layers were to be repaired as one singular layer.