Although various techniques for arthroscopic rotator cuff repair have been introduced, optimal technique is still controversial. Biomechanical studies have been performed to assess tendon-bone interface properties. However, few studies have focused on the effect of the rotator cuff muscle after repair. To determine a technique with improved cuff function, in addition to repair strength, other factors such as stiffness changes in the rotator cuff muscle should also be analyzed. The purpose of this study was to investigate passive stiffness in the supraspinatus (SSP) muscle using shear wave elastography (SWE) after double-row (DR) and knotless transosseous equivalent (KL-TOE) techniques.

Twelve fresh-frozen cadaveric shoulders with rotator cuff tear (tear size; small [6], medium-large [6]) were used. Passive stiffness of 4 anatomical regions in the SSP muscle was measured based on an established SWE method. Each specimen underwent 2 types of footprint repair (DR and KL-TOE, in a random order) with the arm at 30° abduction. SWE values, obtained with the arm at 0°, 30°, and 90° abduction, were compared in 3 different conditions: preoperative (torn) and postoperative conditions with the 2 techniques.

In shoulders with medium-large size tears, SSP muscles showed increased stiffness values after rotator cuff repair with both techniques, and this was significantly observed at 0° abduction. In addition, stiffness of the SSP muscle was uniform among 4 regions after KL-TOE repair, whereas, DR repair caused significantly heterogeneous stiffness distribution within the muscle (P>0.01). SSP muscles with small size tear did not show any significant differences in stiffness values between regions and repair technique.

KL-TOE technique for the medium-large size tear provided a more uniform stiffness distribution in repaired SSP muscles compared to the DR technique. Imbalanced muscular stiffness might cause limited functional recovery after the cuff repair. In addition to established evidences of biomechanical properties, the alteration of cuff muscle stiffness should be evaluated to determine the optimal technique.