Abstract
Background:
The balance between the subscapularis muscle and the infraspinatus/teres minor muscles, often referred to as the rotator cuff ‘force couple’, has been proposed to be critical component for glenohumeral stability. Function of these muscles can be estimated with the evaluation of muscle atrophy. In clinical practice, muscle cross-sectional area (CSA) rather than 3D muscle volume measurement have been used because it is less time consuming. Because combined anthropometric measures of length and width more accurately define the muscular volume it seems logical to study the transversal rotator cuff force couple in the transversal plane an not in the sagittal plane of the body because both parameters can be included. But is it not clear which transversal CSA has the best correlation with muscle volume
Purpose:
To determine the optimal transversal CSA that has the best correlation with muscle volume.
Material and Methods:
A total of 30 CT images containing the full scapula were used. Using Mimics® and 3-Matic® the correlation between CSA's and volume has been evaluated. Two methods have been evaluated. The first method was the CSA measured on transversal plane without 3D editing. The second method is a CSA measured on a new defined transversal plane using 3D reconstruction and reslice editing techniques.
Results
Both techniques showed a very high inter and intraobserver reliability (ICC for single measures in both techniques > 0.97, p < 0.001).
Correlation of the muscle volume/CSA of the subscapularis showed a high correlation in both the non-reconstructed (ρ = 0,699, p = 0,002) and reconstructed technique (ρ = 0,842, p < 0,001)
Correlation of the muscle volume/CSA of the infraspinatus/teres minor showed a moderate correlation in the non-reconstructed (ρ = 0,591, p = 0,013) and a high correlation in reconstructed technique (ρ = 0,779, p < 0,001)
There is a significant higher correlation with the volume with the reconstructed technique compared to the non-reconstructed technique (ρ = 0.638, p < 0.001 for the conventional transversal section versus ρ = 0.818, p < 0.001 for the resliced section)
Conclusion
Muscular volume of the rotator cuff force couple can be quantified using a non-reconstructed CSA, but is significant more accurately quantified by a 3D reconstructed technique. In the future, balance of the force couple in different shoulder pathologies can be quantified with this measurement technique.
