Yamamoto, Nobuyuki

Purpose To investigate the alteration of passive stiffness in the supraspinatus muscle after double‐row (DR) and knotless transosseous‐equivalent (KL‐TOE) repair techniques, using shear wave elastography (SWE) in cadavers with rotator cuff tears. We also aimed to compare altered muscular stiffness after these repairs to that obtained from shoulders with intact rotator cuff tendon. Methods Twelve fresh‐frozen cadaveric shoulders with rotator cuff tear (tear size: small [6], medium‐large [6]) were used. Passive stiffness of 4 anatomic regions in the supraspinatus muscle was measured based on an established SWE method. Each specimen underwent DR and KL‐TOE footprint repairs at 30° glenohumeral abduction. SWE values, obtained at 0°, 10°, 20°, 30°, 60°, and 90° abduction, were assessed in 3 different conditions: preoperative (torn) and postoperative conditions with the 2 techniques. The increased ratio of SWE values after repair was compared among the 4 regions to assess stiffness distribution. In addition, SWE values were obtained on 12 shoulders with intact rotator cuff tendons as control. Results In shoulders with medium‐large‐sized tears, supraspinatus muscles showed an increased passive stiffness after rotator cuff repairs, and this was significantly observed at adducted positions. KL‐TOE repair showed uniform stiffness changes among the 4 regions of the supraspinatus muscle (mean, 189% to 218% increase after repair), whereas DR repair caused a significantly heterogeneous stiffness distribution within the muscle (mean, 187% to 319% after repair, P = .002). Although a repair‐induced increase in muscle stiffness was observed also in small‐sized tears, there were no significant differences in repaired stiffness changes between DR and KL‐TOE (mean, 127% to 138% and 127% to 130% after repairs, respectively). Shoulders with intact rotator cuff tendon showed uniform SWE values among the 4 regions of the supraspinatus muscle (mean, 38.2 to 43.0 kPa). Conclusions Passive stiffness of the supraspinatus muscle increases after rotator cuff repairs for medium‐large‐sized tears. KL‐TOE technique for the medium‐large‐sized tear provided a more uniform stiffness distribution across the repaired supraspinatus muscles compared with the DR technique. Clinical Relevance Based on this insight, investigating rotator cuff muscle stiffness changes, further studies using SWE may determine the optimal repair technique for various sizes of rotator cuff tears.

Purpose The purpose of this in vitro biomechanical study was to assess the effects of the remplissage procedure for small‐ and large‐sized Hill‐Sachs lesions (HSLs) on shoulder range of motion (ROM) with a special interest in the apprehension position. Methods HSLs of 50% and 100% of the glenoid width were simulated in 7 cadaveric shoulders as small and large lesions, respectively, and the postoperative condition was reproduced by placing suture anchors on the articular surface and tying down the infraspinatus at the medial edge of the would‐be lesion site. ROMs were measured in abduction, internal rotation, and external rotation with the humerus in the adducted and abducted position. In addition, the ROM was measured in the anterior apprehension position, in which 2 torques of external rotation and extension were applied simultaneously, and external rotation and horizontal extension ROMs were measured with the humerus in different abduction angles (20°, 40°, and 60°). Results For standard ROMs, the procedure for the 50% HSL maintained complete ROMs, whereas the procedure for the 100% HSL significantly decreased external rotation ROM with the humerus in both the adducted and abducted positions, as well as abduction ROM. In the apprehension position, remplissage for the 50% HSL decreased extension ROM with the humerus abducted to 40° and 60°. Remplissage for the 100% HSL significantly decreased both external and extension ROMs regardless of the humeral abduction angle. Conclusions In the cadaveric model with an intact humeral head and the simulated postoperative condition, the remplissage procedure for a large HSL caused significant restrictions in ROM of abduction in the scapular plane and external rotation with the humerus in both adduction and abduction. It also caused significant restrictions in both external rotation and extension ROMs in the apprehension position. Clinical Relevance The indication for the remplissage procedure for the larger HSL should be considered carefully, especially for the competitive throwing athlete who needs exceptional external rotation ROM for optimal overhead throwing performance.

Background Tightness of the posteroinferior capsule is assumed to be the cause of internal rotation loss in baseball pitchers. Although the relationship between posterior capsule and subacromial impingement has been recognized, this relationship during the baseball-pitching motion is unclear. Hypothesis Contact pressure during baseball-pitching motion increases with posterior capsule tightness. Study Design Controlled laboratory study. Methods Eight fresh-frozen shoulders were used. The peak contact pressure and area on the coracoacromial arch were measured on a custom-designed shoulder experimental device capable of 6 degrees of freedom motion. Simultaneously, the sites of peak pressure on the coracoacromial arch and humerus were observed from various angles. The posteroinferior capsule tightness was simulated by plicating the capsule in the region from 6 to 8 o'clock. The static testing positions correlated to the early cocking, late cocking, acceleration, deceleration, and follow-through phases of the pitching motion. Results The peak contact pressure during the follow-through phase (0.63 ± 0.50 MPa) significantly increased with posteroinferior capsule tightness (1.00 ± 0.65 MPa) (P = .014). Additionally, the contact area on the coracoacromial ligament during the follow-through phase (0.98 ± 0.67 cm2) significantly increased with posteroinferior capsule tightness (1.47 ± 0.91 cm 2) (P < .001). The site of the peak contact pressure did not change between the 2 conditions. Conclusion Our findings demonstrate that posteroinferior capsule tightness leads to higher contact pressure under the subacromial arch and increased contact area, particularly on the coracoacromial ligament during the follow-through phase. Clinical Relevance This tightness may affect risk of injury of the rotator cuff and its surrounding tissues by increasing subacromial contact during pitching.

Background There have been few biomechanical studies to clarify which size of a glenoid defect is critical. However, those studies have assumed that the defect occurred anteroinferiorly. Recent studies have reported that the defect is located anteriorly rather than anteroinferiorly. Therefore, the effect of the anterior, not anteroinferior, glenoid defect on shoulder stability needs to be investigated. Hypothesis The anterior glenoid defect would have a similar effect on anterior shoulder stability as that of the anteroinferior glenoid defect. Study Design Controlled laboratory study. Methods Eight fresh-frozen cadaveric shoulders were used (mean age, 74 years). The specimen was attached to a shoulder-testing device with the arm in abduction and external rotation. An osseous defect was created stepwise with a 2-mm increment of the defect width. The stability ratio was used to evaluate joint stability. With a 50-N axial force, the translational force applied to the humeral head was measured by a force transducer. Results The stability ratio without a defect (32% ± 6%) significantly decreased after creating a 6-mm defect (17% ± 5%; P = .0001), which was equivalent to 20% of the glenoid length. Conclusion An osseous defect at 3 o'clock with a width that was equal to or greater than 20% of the glenoid length significantly decreased anterior stability. Clinical Relevance The results suggest that reconstruction of the glenoid concavity might be necessary in shoulders with an anterior glenoid defect of at least 20% of the glenoid length.