Influence of glenoid component design and humeral component retroversion on internal and external rotation in reverse shoulder arthroplasty: a cadaver study.

A common disadvantage of reverse shoulder arthroplasty is limitation of the range of arm rotation. Several changes to the prosthesis design and implantation technique have been suggested to improve rotation range of motion (ROM). Glenoid component design and degree of humeral component retroversion influence rotation ROM after reverse shoulder arthroplasty. The Aequalis Reversed™ shoulder prosthesis (Tornier Inc., Edina, MN, USA) was implanted into 40 cadaver shoulders. Eight glenoid component combinations were tested, five with the 36-mm sphere (centred seating, eccentric seating, inferior tilt, centred with a 5-mm thick lateralised spacer, and centred with a 7-mm thick lateralised spacer) and three with the 42-mm sphere (centred with no spacer or with a 7-mm or 10-mm spacer). Humeral component position was evaluated with 0°, 10°, 20°, 30°, and 40° of retroversion. External and internal rotation ROMs to posterior and anterior impingement on the scapular neck were measured with the arm in 20° of abduction. The large glenosphere (42 mm) was associated with significantly (P<0.05) greater rotation ROMs, particularly when combined with a lateralised spacer (46° internal and 66° external rotation). Rotation ROMs were smallest with the 36-mm sphere. Greater humeral component retroversion was associated with a decrease in internal rotation and a significant increase (P<0.05) in external rotation. The best balance between rotation ROMs was obtained with the native retroversion, which was estimated at 17.5° on average in this study. Our anatomic study in a large number of cadavers involved a detailed and reproducible experimental protocol. However, we did not evaluate the variability in scapular anatomy. Earlier studies of the influence of technical parameters did not take humeral component retroversion into account. In addition, no previous studies assessed rotation ROMs. Rotation ROM should be improved by the use of a large-diameter glenosphere with a spacer to lateralise the centre of rotation of the gleno-humeral joint, as well as by positioning the humeral component at the patient's native retroversion value.

Berhouet J ，Garaud P ，Favard L 《Orthopaedics & Traumatology-Surgery & Research》

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 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 ... -  《-》

Reverse total shoulder arthroplasty: a biomechanical evaluation of humeral and glenosphere hardware configuration.

Various reverse total shoulder arthroplasty (rTSA) implant options are available for the humeral and glenosphere components. This study used a cadaveric biomechanical shoulder simulator to evaluate how hardware configurations in 2 common rTSA systems affect (1) abduction/adduction range of motion (ROM), (2) rotational ROM, and (3) forces to elevate the arm. Seven pairs of shoulders were tested on a biomechanical shoulder simulator before and after rTSA implantation. The Aequalis Reverse Shoulder (Tornier, Edina, MN, USA) and the Reverse Shoulder Prosthesis (RSP; DJO Surgical, Austin, TX, USA) were implanted in opposing shoulders. Aequalis implant options included humeral polymer insert thickness and eccentricity and glenosphere tilt. RSP implant options included glenosphere diameter and lateralization, humeral shell offset, and polymer insert depth. Both the RSP and Aequalis shifted the center of rotation inferior and medially compared with native shoulders (P < .001). Increased Aequalis insert thickness reduced adduction (P < .003) and internal/external (P < .028) passive ROM. The 10° inferiorly tilted glenosphere increased deltoid abduction forces (P < .032). In the RSP, smaller glenosphere diameter (P < .012), a semiconstrained humeral insert (P < .023), and a neutral humeral shell offset (P < .002) all decreased adduction deficit, whereas lateral glenosphere offset increased passive abduction ROM (P < .028). Increased humeral shell offset decreased passive internal/external rotation ROM (P < .050). Hardware configurations in rTSA have different effects on passive ROM and deltoid forces required for abduction. Identifying these changes may guide surgical decision making during rTSA placement.

Tashjian RZ ，Burks RT ，Zhang Y ，Henninger HB ... -  《-》

The effect of articular malposition after total shoulder arthroplasty on glenohumeral translations, range of motion, and subacromial impingement.

Williams GR Jr ，Wong KL ，Pepe MD ，Tan V ，Silverberg D ，Ramsey ML ，Karduna A ，Iannotti JP ... -  《JOURNAL OF SHOULDER AND ELBOW SURGERY》