Determination of the reference range for semi-quantified elasticity of healthy supraspinatus muscles using real-time tissue elastography and its clinical use in patients after rotator cuff repair.

BACKGROUND

The quantitative assessment of healthy supraspinatus muscle elasticity may provide clinically useful preliminary information after rotator cuff repairs. We aimed to determine the reference range for supraspinatus muscle semi-quantified elasticity and describe how it can be used clinically after rotator cuff repair.

METHODS

The elasticity of healthy bilateral supraspinatus muscles in 43 participants aged between 24 and 75 years (categorized into two subgroups: <50 and ≥ 50 years) was measured as a strain ratio at 0° and 60° of shoulder abduction using real-time tissue elastography. The reference and modified reference ranges calculated by excluding outliers for elasticity were determined using normal distribution methods for logarithmically transformed data. The modified reference range was applied to eight cases of rotator cuff repair.

FINDINGS: Strain ratios under and over 50 years of age were 1.63 vs. 2.21 at 0° of shoulder abduction (P = 0.028) and 0.92 vs. 1.29 at 60° of shoulder abduction (P = 0.002), respectively. Modified reference ranges for under and over 50 years of age were 0.72-4.17 and 0.98-4.50 at 0° of shoulder abduction and 0.38-1.95 and 0.56-2.76 at 60° of shoulder abduction, respectively. Among eight cases, two showed strain ratios above the reference range at 1 month postoperatively, and rehabilitation protocols were adjusted.

INTERPRETATION: A strain ratio above the reference range, especially above the upper limit at 0° of shoulder abduction, may indicate increased passive stiffness of the musculotendinous unit. Clinically, the reference range has the potential to be used as a baseline after rotator cuff repairs.