Combined effect of change in humeral neck-shaft angle and retroversion on shoulder range of motion in reverse total shoulder arthroplasty - A simulation study.

We studied combined effect of change in humeral neck shaft angle and retroversion on shoulder ROM in reverse total shoulder arthroplasty using 3-dimensional simulations. Using a 3D model construct based on the CT scans of 3 males and a 3-dimensional analysis program, a humeral component of reverse total shoulder arthroplasty was implanted in 0°, 10°, 20°, 30°,40° retroversion and 135°, 145°, and 155° neck shaft angle. Total horizontal range of motion (sum of horizontal adduction and abduction) at 30° and 60° scaption, adduction in the scapular plane and IR behind the back were measured for various combinations of neck shaft angle and retroversion. Change in retroversion didn't show any effect on total horizontal range of motion. Total horizontal range of motion at both 30° and 60° scaption, showed maximum values at 135° neck shaft angle and minimum values at 155° neck shaft angle. With any combination of retroversion angles, adduction deficit was maximum at 155° neck shaft angle and no adduction deficit at 135° neck shaft angle. Every 10° decrease in neck shaft angle resulted in an average 10.4° increase in adduction. For every 10° increase in retroversion, there was loss of internal rotation behind the back up to at least one vertebral level. 135° neck shaft angle resulted in maximum total horizontal range of motion both at 30° and 60° scaption regardless of retroversion angles. 135° neck shaft angle also reduced the chances of scapular impingement. Decrease in retroversion angle resulted in more amount of internal rotation behind the back.

Jeon BK ，Panchal KA ，Ji JH ，Xin YZ ，Park SR ，Kim JH ，Yang SJ ... -  《-》

Biomechanical effects of humeral neck-shaft angle and subscapularis integrity in reverse total shoulder arthroplasty.

The variability in functional outcomes and the occurrence of scapular notching and instability after reverse total shoulder arthroplasty remain problems. The objectives of this study were to measure the effect of reverse humeral component neck-shaft angle on impingement-free range of motion, abduction moment, and anterior dislocation force and to evaluate the effect of subscapularis loading on dislocation force. Six cadaveric shoulders were tested with 155°, 145°, and 135° reverse shoulder humeral neck-shaft angles. The adduction angle at which bone contact occurred and the internal and external rotational impingement-free range of motion angles were measured. Glenohumeral abduction moment was measured at 0° and 30° of abduction, and anterior dislocation forces were measured at 30° of internal rotation, 0°, and 30° of external rotation with and without subscapularis loading. Adduction deficit angles for 155°, 145°, and 135° neck-shaft angle were 2° ± 5° of abduction, 7° ± 4° of adduction, and 12° ± 2° of adduction (P < .05). Impingement-free angles of humeral rotation and abduction moments were not statistically different between the neck-shaft angles. The anterior dislocation force was significantly higher for the 135° neck-shaft angle at 30° of external rotation and significantly higher for the 155° neck-shaft angle at 30° of internal rotation (P < .01). The anterior dislocation forces were significantly higher when the subscapularis was loaded (P < .01). The 155° neck-shaft angle was more prone to scapular bone contact during adduction but was more stable at the internally rotated position, which was the least stable humeral rotation position. Subscapularis loading gave further anterior stability with all neck-shaft angles at all positions.

Oh JH ，Shin SJ ，McGarry MH ，Scott JH ，Heckmann N ，Lee TQ ... -  《-》

Effect of humeral component version on impingement in reverse total shoulder arthroplasty.

Reverse shoulder arthroplasty is growing in popularity for patients with deficient rotator cuffs; however, the phenomenon of scapular notching continues to be a concern. This study examined the effects of humeral component version in the Aequalis Reversed Shoulder Prosthesis (Tornier, Edina, MN) on impingement of the humeral prosthesis against the scapula to test the hypothesis that the mechanical contact of the humeral component with the scapular neck is influenced by the version of the humeral component. Seven shoulders from deceased donors were tested after the Aequalis Reversed Shoulder was implanted. The deltoid, pectoralis major, and latissimus dorsi were loaded based on physiologic cross-sectional area. The degree of internal and external rotation when impingement, subluxation, or dislocation occurred was measured at 0°, 30°, and 60° glenohumeral abduction in the scapular plane. Testing was performed with the humeral component placed in 20° of anteversion, neutral version, 20° of retroversion, and 40° of retroversion. Maximum external rotation at 0° abduction was -1° ± 4° at 20° anteversion, 15° ± 3° at neutral, 28° ± 4° at 20° retroversion, and 44° ± 5° at 40° retroversion (P < .05). Maximum internal rotation at 0° abduction was 128° ± 9° at 20° anteversion, 112° ± 9° at neutral, 99° ± 8° at 20° retroversion, and 83° ± 8° at 40° retroversion (P < .05). Maximum external rotation at 30° abduction was 70° ± 6° at 20° anteversion, 84° ± 7° at neutral, 97° ± 6° at 20° retroversion, and 110° ± 5° at 40° retroversion (P < .05). There was no limitation to internal rotation at 30° abduction. No impingement occurred at 60° abduction. Version of the humeral component plays a role in range of motion and impingement in reverse total shoulder arthroplasty. Anteversion can significantly decrease the amount of external rotation achievable after reverse total shoulder surgery. Placing the Aequalis Reversed Shoulder humeral component at between 20° and 40° of retroversion more closely restores a functional arc of motion without impingement.

Stephenson DR ，Oh JH ，McGarry MH ，Rick Hatch GF 3rd ，Lee TQ ... -  《-》

Evaluation of the role of glenosphere design and humeral component retroversion in avoiding scapular notching during reverse shoulder arthroplasty.

Scapular notching is a common observation during radiological follow-up of reverse shoulder arthroplasty. The purpose of this study was to evaluate the effect of glenosphere design and humeral component retroversion on movement amplitude in the scapular plane and inferior scapular impingement. The Aequalis Reversed Shoulder Prosthesis (Tornier) was implanted into 40 cadaver shoulders. On the glenoid side, 8 different combinations were tested: 36-mm glenosphere: centered (standard), eccentric, with an inferior tilt, or with the center of rotation (COR) lateralized by 5 or 7 mm; and 42-mm centered glenosphere: used alone or with the COR lateralized by 7 or 10 mm. The humeral component was positioned in 0°, 10°, 20°, 30°, and 40° of retroversion. Maximum adduction and abduction were measured when inferior impingement and superior impingement, respectively, were detected. The average increase in abduction amplitude was 10° and inferior impingement occurred 18° later with a 42-mm glenosphere, especially when it was lateralized by 10 mm, relative to a 36-mm centered glenosphere (P < .05). These 2 combinations provided a 28° increase in the movement amplitude in the scapular plane. Positioning of the humeral component in 10° or 20° of retroversion or in anatomical retroversion was most effective at avoiding inferior impingement but had less effect on abduction range of motion (except with the 42-mm glenosphere). Our study confirmed published results with various glenosphere designs but was unique in describing the effect of humeral retroversion on scapular impingement. Inferior scapular notching can be most effectively prevented by using large-diameter glenospheres with lateralized COR and by making sure to replicate the patient's native humeral retroversion.

Berhouet J ，Garaud P ，Favard L 《-》

Effect of implant geometry on range of motion in reverse shoulder arthroplasty assessed using glenohumeral separation distance.

Whereas reverse shoulder arthroplasty has been successful in treating patients with cuff tear arthropathy, implant impingement after the procedure often causes complications, including reduced range of motion, bone loss, and instability. Attempts to simulate this problem in vitro typically rely on subjective visual methods to detect impingement. The purpose of this study was to determine the effect of humeral neck-shaft angle, implant diameter, humeral cup depth, and glenoid component eccentricity on minimum abduction angle and range of motion using an implant-tracking method for impingement detection. Tests were performed in a kinematic shoulder simulator with actuated cables representing the deltoid. The humerus was manually adducted and abducted past the point of impingement in either direction. Centers of the implant components were tracked with optical motion capture and processed with a thresholding algorithm to determine the minimum abduction angle where impingement occurred. Humeral cup depth had the largest effect on minimum abduction angle and range of motion, with a retentive cup reducing range of motion by 26°. A decreased neck-shaft angle reduced minimum abduction angle by 10° but had little effect on overall range of motion. Diameter and eccentricity had little effect. A reduced neck-shaft angle reduces minimum abduction angle but does not improve overall range of motion. A more retentive humeral cup increases minimum abduction angle significantly. Although retentive cups are intended to improve joint stability, the reduced range of motion that they impart to the joint may partly counteract the benefits of increased constraint.

North LR ，Hetzler MA ，Pickell M ，Bryant JT ，Deluzio KJ ，Bicknell RT ... -  《-》