Surgeons continue to debate the optimal approach to reverse total shoulder arthroplasty (rTSA) implant selection and position: Should we maximize lateralization? Is a stemless implant viable? How critical is glenosphere position, or humeral version?
Here's a review of 13 recent articles exploring component geometry, implant design, biomechanics, and clinical outcomes in rTSA.
Readers will come to their own conclusions; mine are that it’s not the implant company that defines the outcome—rather it is the positioning of components to provide the best range of motion and optimal muscle tension.
Remember this book?
My takeaways
Don't overlateralize the humerus much beyond its preoperative position (don't worry too much about version). Short humeral stems may be associated with component malalignment. Tight fitting short stems may be associated with stress shielding. The value of stemless rTSA has yet to be demonstrated.
Place the glenosphere low on the prepared glenoid (don't worry too much about version except avoid excess ante version) and tilt it inferiorly (correcting the reverse shoulder angle) to reduce the risk of greater tuberosity collision with the acromion. Increasing the size of and lateralizing the glenosphere may increase impingement-free motion, while smaller, lateralized glenospheres may optimize deltoid and rotator cuff muscle-tendon lengths.
The lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) may not correlate with clinical outcome.
Here are the articles. I have colored the number before the clinical studies in green and the number before ex vivo models in red.
(1) Eccentricity and greater size of the glenosphere increase impingement-free range of motion in glenoid lateralized reverse shoulder arthroplasty: A computational study Increasing the impingement-free range of motion (ROM) can optimize the patient’s functional outcome and reduce the rate of scapular notching. This study used a virtual model of reverse shoulder arthroplasty with glenoid lateralization (L-RSA) to compare (1) the impingement-free range of movement (ROM) between 155◦ Grammont-style inlay stem and 135◦ flushlay stems (i.e. the polyethylene cup located “flush” with the plane of the humeral bone cut and 135◦ neck shaft angle (NSA)); 2) the effect of glenosphere size and type (centered vs eccentric) on impingement-free range of movement (ROM) using a 135◦ NSA flushlay stem. They analyzed 200 CT-scans of patients undergoing shoulder replacement for cuff tear arthropathy, virtually implanting different humeral components using the same glenoid implant.
When comparing inlay and flushlay designs, flushlay showed greater impingement-free ROM in all movements except for abduction.They found that increasing the glenosphere size resulted in an increase in impingement-free ROM. Improved impingement-free ROM was found when using eccentric glenoid components
(2) The authors of Humeral Component Version Has No Effect on Outcomes Following Reverse Total Shoulder Arthroplasty conducted a double-blinded, randomized controlled trial to examine the relationship of humeral component version (neutral or 30° of retroversion) to humeral rotation and two-year patient outcomes in reverse total shoulder arthroplasty (rTSA).
The 2 groups did not differ significantly in terms of improvement at 2 years in active shoulder abduction, forward elevation, internal rotation measured as the highest spinal level reached, internal rotation with the arm abducted 90°, external rotation, or muscle strength. The 2 groups did not differ significantly in terms of improvement in postoperative ASES, PROMIS-10 physical, or VAS pain scores at the time of final follow-up. Similar rates of scapular notching were observed between the two groups (21% of the patients in neutral version group and 15 % of the patients in the 30° retroversion group).
(3) The authors of Greater distance from the glenosphere center to the acromion reduces risk of acromial impingement in semi-inlay reverse shoulder arthroplasty assessed the relationship of differences in the distance between the glenosphere center and the greater tuberosity (DGT) and the distance between the glenosphere center and the acromion (DA) to the closest distance between the greater tuberosity and the acromion during active abduction in shoulders with reverse total shoulder arthroplasty. They used models created from computed tomography of the shoulders and fluoroscopic images to examine 3D kinematics of the implants. DA and DGT were measured from 3D surface models.
There were 7 shoulders with DA ≥ DGT, and 4 shoulders with DA < DGT. Although DA was significantly greater in shoulders with DA ≥ DGT than in those with DA < DGT there was no significant difference in DGT between the two groups.
When DA < DGT, contact between acromion and the greater tuberosity is predicted to occur when the arm is abducted. However, in this series there were no significant differences in maximum abduction between the two groups.
(4) Shoulder Geometry After Reverse Total Shoulder Arthroplasty with a Medialized Glenoid and a Lateralized Humerus Predicts Subacromial Notching and Acromial or Scapular Spine Fractures found that implanting components such that DA is greater than DGT in rTSA is associated with a lower incidence of subacromial notching and acromion or scapular spine fractures.
In a prior post, we noted that DGT (yellow) and DA (green) could be determined on plain films (Grashey view), avoiding the need for and cost of postoperative CT scans.
In a prior post, we noted that DGT (yellow) and DA (green) could be determined on plain films (Grashey view), avoiding the need for and cost of postoperative CT scans.
(5) While a number of papers have studied the theoretical effects of humeral lateralization and distalization, the most important thing (MIT) is exploring the effects of humeral position on the patient's clinical outcome. The authors of Lateralization and Distalization Shoulder Angles May Not Predict Clinical Outcomes in Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-Analysis performed a literature review to assess the evidence supporting the prognostic value of the lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) following reverse total shoulder arthroplasty (rTSA).
4 studies met inclusion criteria, representing a total of 974 shoulders with a minimum follow-up of 24 months with functional outcomes (American Shoulder and Elbow Surgeons score, Constant score) or range of motion (ROM) (active anterior elevation [AAE] and active external rotation).
The overall correlation coefficient for LSA and DSA with postoperative outcomes was only 0.023. Similarly, no significant correlations were found between LSA or DSA and AAE or active external rotation, with the random effects model showing an effect size of −0.097 for AAE and DSA and 0.056 for AAE and LSA.
A prior blog post provides further analysis of LSA and DSA, pointing out that it seems unusual to use angles in an attempt to reflect the linear dimensions of distalization and lateralization, especially when these linear dimensions can be measured directly and normalized to the known dimensions of the implant.
(6) The function of a rTSA depends in large part on getting the most out of the muscles remaining in the shoulder. Optimizing Muscle-Tendon Lengths in Reverse Total Shoulder Arthroplasty used a geometric model of the shoulder to systematically examine surgical placement and implant-design parameters to determine which RTSA configuration most closely reproduces native muscle-tendon lengths of the deltoid and rotator cuff.
The configuration that most closely restored anatomic muscle- tendon lengths in a small shoulder was a 30-mm glenosphere with a centered position, 5 mm of glenoid lateralization, 0 mm of humeral offset, and a 135° neck-shaft angle. For a medium shoulder, the corresponding parameters were 36 mm, centered, 5 mm, 0 mm, and 135°. For a large shoulder, the parameters were 30 mm, centered, 10 mm, 0 mm, and 135°. When only inferior glenoid component placement was considered, the configuration that most closely restored anatomic muscle-tendon lengths in a small shoulder was 36 mm, inferior, 5 mm, 0 mm, and 135°. For a medium shoulder, it was 30 mm, inferior, 10 mm, 0 mm, and 135°. For a large shoulder, it was 36 mm, inferior, 10 mm, 0 mm, and 135°.
A combination of a smaller, lateralized glenosphere, a humeral socket placed at the anatomic neck plane, and an anatomic 135° neck-shaft angle best restored native deltoid and rotator cuff muscle-tendon lengths in RTSA.
(7) Lack of internal rotation limits important functions after rTSA. Preoperative Planning and Inferior Glenosphere Overhang Increases the Odds of Achieving High Internal Rotation After Univers Reverse Total Shoulder Arthroplasty sought to compare patient characteristics, use of 3-dimensional computed tomography (3D CT)-based preoperative planning, and postoperative implant position between patients with high IR (T12 or better, n=98) or low IR (below the hip, n=50) two years after primary rTSA.
Decreased body mass index, high preoperative IR, and arthroplasty on the dominant arm correlated with an increased odds of high IR. Increased DSA and increased inferior glenoid overhang were associated with a greater chance of being in the high-IR group. However, the standard deviations were larger than the differences (effect sizes), indicating substantial overlap between the two groups:
High IR DSA 48.3±8.9 degrees, Inferior overhang 3.7±2.3 mm.
Low IR DSA 43.6±9.6 degrees, Inferior overhang 2.3±3.0 mm.
(8) While prosthetic design might correlate with outcomes of rTSA, ultimately the position of the component may be more important. Variability in Ultimate Humeral Height of an Inlay Humeral Stem Does Not Impact Outcomes Following Reverse Shoulder Arthroplasty. analyzed radiographic and clinical data from 194 reverse shoulder arthroplasties performed with a 135° humeral component. The distance from the anatomical neck of the humerus to the glenosphere was measured to categorize the implantation as inlay or onlay.
Postoperative humeral position was classified as a true inlay in 25.3% and some degree of onlay in 74.7%. At 2-year follow-up, most of the patient reported outcomes (ASES, Constant, SANE, VAS pain) were not significantly different for the two groups.
(9) The authors of Optimizing range of motion in reverse shoulder arthroplasty used planning software to model the rTSA glenosphere positioning to provide the best theoretical impingement-free ROM for a 3 mm symmetric 135° inclined polyethylene liner: 1) no correction of the RSA angle and no lateralization (C-L-); 2) correction of the RSA angle with medialization by inferior reaming (C+M+); 3) correction of the RSA angle without lateralization by superior compensation (C+L-); and 4) correction of the RSA angle and additional lateralization (C+L+).
The configuration with lateralization and correction of the RSA angle (C+L+) led to better ROM in flexion, extension, adduction, and external rotation. The configuration where correction of the inclination was done by medialization (C+M+) led to the worst ROM. They concluded that with a 135° inlay reversed humeral implant, correcting glenoid inclination (to a RSA angle of 0°) and lateralizing the glenoid component by using an angled bony or metallic augment of 8 to 10 mm provides optimal impingement-free ROM.
(10) Anatomic restoration of lateral humeral offset and humeral retroversion optimizes functional outcomes following reverse total shoulder arthroplasty point out that cadaveric and computer simulations suggest lateral humeral offset (LHO) and humeral retroversion (HR) are associated with strength and range of motion (ROM) after reverse total shoulder arthroplasty (rTSA), but in vivo data is lacking. This study aimed to evaluate the effects of implant parameters (i.e. LHO and HR) on strength and ROM in 30 rTSA patients at an average follow-up of 2.4 years. LHO was measured on two-dimensional axial CT images as the distance between the medial edge of the base of the coracoid process and the most lateral point of the humerus. Humeral retroversion was calculated using the humeral angle derived from subject-specific three-dimensional bone/implant models relative to the epicondylar axis
Higher post-op LHO values were predictive of greater postoperative strength across all movements. However, lateralization of the implant beyond pre-op values (i.e. post-op LHO > pre-op LHO) was associated with poorer strength performance across all ranges of motion and poorer IR ROM.
Patients with minimal deviations in HR (post-op HR within 10◦ of pre-op HR) and minimal deviations in LHO (post-op LHO ≤ pre-op LHO) displayed the greatest postoperative ER ROM.
The authors concluded that anatomic restoration of LHO combined with anatomic restoration of HR may be ideal for maximizing strength and ROM following rTSA.
Overlateralization beyond anatomic may have negative consequences.
(11) Baseplate version in reverse shoulder arthroplasty: does excessive retroversion or anteversion affect functional activities of daily living? While bone grafting and augmented components can help restore reverse shoulder arthroplasty (RSA) baseplate version close to neutral, the indication for version correction in RSA is unclear. The purpose of this study was to compare the clinical outcomes of RSA baseplates in high degrees of retroversion and anteversion to components in more neutral version.
Four groups were identified:
≥ 10 degrees (moderate to severe anteversion; n = 14),
4 studies met inclusion criteria, representing a total of 974 shoulders with a minimum follow-up of 24 months with functional outcomes (American Shoulder and Elbow Surgeons score, Constant score) or range of motion (ROM) (active anterior elevation [AAE] and active external rotation).
The overall correlation coefficient for LSA and DSA with postoperative outcomes was only 0.023. Similarly, no significant correlations were found between LSA or DSA and AAE or active external rotation, with the random effects model showing an effect size of −0.097 for AAE and DSA and 0.056 for AAE and LSA.
A prior blog post provides further analysis of LSA and DSA, pointing out that it seems unusual to use angles in an attempt to reflect the linear dimensions of distalization and lateralization, especially when these linear dimensions can be measured directly and normalized to the known dimensions of the implant.
(6) The function of a rTSA depends in large part on getting the most out of the muscles remaining in the shoulder. Optimizing Muscle-Tendon Lengths in Reverse Total Shoulder Arthroplasty used a geometric model of the shoulder to systematically examine surgical placement and implant-design parameters to determine which RTSA configuration most closely reproduces native muscle-tendon lengths of the deltoid and rotator cuff.
The configuration that most closely restored anatomic muscle- tendon lengths in a small shoulder was a 30-mm glenosphere with a centered position, 5 mm of glenoid lateralization, 0 mm of humeral offset, and a 135° neck-shaft angle. For a medium shoulder, the corresponding parameters were 36 mm, centered, 5 mm, 0 mm, and 135°. For a large shoulder, the parameters were 30 mm, centered, 10 mm, 0 mm, and 135°. When only inferior glenoid component placement was considered, the configuration that most closely restored anatomic muscle-tendon lengths in a small shoulder was 36 mm, inferior, 5 mm, 0 mm, and 135°. For a medium shoulder, it was 30 mm, inferior, 10 mm, 0 mm, and 135°. For a large shoulder, it was 36 mm, inferior, 10 mm, 0 mm, and 135°.
A combination of a smaller, lateralized glenosphere, a humeral socket placed at the anatomic neck plane, and an anatomic 135° neck-shaft angle best restored native deltoid and rotator cuff muscle-tendon lengths in RTSA.
(7) Lack of internal rotation limits important functions after rTSA. Preoperative Planning and Inferior Glenosphere Overhang Increases the Odds of Achieving High Internal Rotation After Univers Reverse Total Shoulder Arthroplasty sought to compare patient characteristics, use of 3-dimensional computed tomography (3D CT)-based preoperative planning, and postoperative implant position between patients with high IR (T12 or better, n=98) or low IR (below the hip, n=50) two years after primary rTSA.
Decreased body mass index, high preoperative IR, and arthroplasty on the dominant arm correlated with an increased odds of high IR. Increased DSA and increased inferior glenoid overhang were associated with a greater chance of being in the high-IR group. However, the standard deviations were larger than the differences (effect sizes), indicating substantial overlap between the two groups:
High IR DSA 48.3±8.9 degrees, Inferior overhang 3.7±2.3 mm.
Low IR DSA 43.6±9.6 degrees, Inferior overhang 2.3±3.0 mm.
(8) While prosthetic design might correlate with outcomes of rTSA, ultimately the position of the component may be more important. Variability in Ultimate Humeral Height of an Inlay Humeral Stem Does Not Impact Outcomes Following Reverse Shoulder Arthroplasty. analyzed radiographic and clinical data from 194 reverse shoulder arthroplasties performed with a 135° humeral component. The distance from the anatomical neck of the humerus to the glenosphere was measured to categorize the implantation as inlay or onlay.
Postoperative humeral position was classified as a true inlay in 25.3% and some degree of onlay in 74.7%. At 2-year follow-up, most of the patient reported outcomes (ASES, Constant, SANE, VAS pain) were not significantly different for the two groups.
(9) The authors of Optimizing range of motion in reverse shoulder arthroplasty used planning software to model the rTSA glenosphere positioning to provide the best theoretical impingement-free ROM for a 3 mm symmetric 135° inclined polyethylene liner: 1) no correction of the RSA angle and no lateralization (C-L-); 2) correction of the RSA angle with medialization by inferior reaming (C+M+); 3) correction of the RSA angle without lateralization by superior compensation (C+L-); and 4) correction of the RSA angle and additional lateralization (C+L+).
The configuration with lateralization and correction of the RSA angle (C+L+) led to better ROM in flexion, extension, adduction, and external rotation. The configuration where correction of the inclination was done by medialization (C+M+) led to the worst ROM. They concluded that with a 135° inlay reversed humeral implant, correcting glenoid inclination (to a RSA angle of 0°) and lateralizing the glenoid component by using an angled bony or metallic augment of 8 to 10 mm provides optimal impingement-free ROM.
(10) Anatomic restoration of lateral humeral offset and humeral retroversion optimizes functional outcomes following reverse total shoulder arthroplasty point out that cadaveric and computer simulations suggest lateral humeral offset (LHO) and humeral retroversion (HR) are associated with strength and range of motion (ROM) after reverse total shoulder arthroplasty (rTSA), but in vivo data is lacking. This study aimed to evaluate the effects of implant parameters (i.e. LHO and HR) on strength and ROM in 30 rTSA patients at an average follow-up of 2.4 years. LHO was measured on two-dimensional axial CT images as the distance between the medial edge of the base of the coracoid process and the most lateral point of the humerus. Humeral retroversion was calculated using the humeral angle derived from subject-specific three-dimensional bone/implant models relative to the epicondylar axis
Higher post-op LHO values were predictive of greater postoperative strength across all movements. However, lateralization of the implant beyond pre-op values (i.e. post-op LHO > pre-op LHO) was associated with poorer strength performance across all ranges of motion and poorer IR ROM.
Patients with minimal deviations in HR (post-op HR within 10◦ of pre-op HR) and minimal deviations in LHO (post-op LHO ≤ pre-op LHO) displayed the greatest postoperative ER ROM.
The authors concluded that anatomic restoration of LHO combined with anatomic restoration of HR may be ideal for maximizing strength and ROM following rTSA.
Overlateralization beyond anatomic may have negative consequences.
(11) Baseplate version in reverse shoulder arthroplasty: does excessive retroversion or anteversion affect functional activities of daily living? While bone grafting and augmented components can help restore reverse shoulder arthroplasty (RSA) baseplate version close to neutral, the indication for version correction in RSA is unclear. The purpose of this study was to compare the clinical outcomes of RSA baseplates in high degrees of retroversion and anteversion to components in more neutral version.
Four groups were identified:
≥ 10 degrees (moderate to severe anteversion; n = 14),
10 to -10 degrees (neutral; n = 69),
-10 to -20 (moderate retroversion; n = 25), and
≤ -20 degrees (severe retroversion; n = 7).
There were no differences in final Simple Shoulder Test (SST), final American Shoulder and Elbow Surgeons score (ASES) or change in SST from pre- to post-operative across the four version groups. There was no linear correlation between baseplate version and final SST. There were no statistically significant differences in difficulty performing tasks related to internal rotation, external rotation, and cross-body adduction among the four baseplate version groups; however, patients with moderate to severe anteversion had a greater frequency of difficulty putting on a coat (86%) compared to patients with neutral version (42%), moderate retroversion (45%) and severe retroversion (0%). There were no differences in rates of complications and revisions across the four groups.
This study did not find evidence that high values of baseplate retroversion or anteversion were associated with inferior patient reported outcomes or functional rotation after reverse total shoulder arthroplasty.
(12) Effects of Different Humeral Stem Length on Stem Alignment and Proximal Stress Shielding in Reverse Total Shoulder Arthroplasty This study aimed to investigate the effects of different humeral stem lengths on stem alignment and proximal stress shielding after rTSA in 320 patients who underwent primary rTSA with at least 2 years of follow-up. The participants were classified into 3 groups according to the humeral stem length of different prostheses types: group A (short stem, range: <80 mm, n = 88), group B (medium stem, range: 80-100 mm, n = 155), and group C (standard stem, range: ≥100 mm, n = 77). Filling ratios were assessed.
Humeral stem malalignment was significantly higher in group A (21.6%) than in groups B (11.6%) and C (9.1%).
However, stress shielding at the lateral metaphyses (36.4%) was more frequently observed in group C.
Longer stem, stem malalignment, and higher diaphyseal canal filling ratio were independent risk factors for stress shielding occurrence, with stem malalignment showing the highest odds ratio.
The authors concluded that although shorter stems could be beneficial for bone preservation, they could lead to stem malalignment, resulting in increased humeral stress shielding if the filling ratios were high.
(13) Stemless Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-analysis. Stemless humeral components in reverse total shoulder arthroplasty are only approved for clinical trials in the United States with an investigational device exception with limited data. A systematic review on stemless reverse total shoulder arthroplasty evaluated 10 studies that used either the Total Evolutive Shoulder System (TESS) or Verso implant. The mean follow-up period ranged from 6.4 to 101.6 months per study. There was an overall trend of improved clinical outcome scores, a 0.2% humeral component loosening rate, and an 11.2% complication rate.
There were no differences in final Simple Shoulder Test (SST), final American Shoulder and Elbow Surgeons score (ASES) or change in SST from pre- to post-operative across the four version groups. There was no linear correlation between baseplate version and final SST. There were no statistically significant differences in difficulty performing tasks related to internal rotation, external rotation, and cross-body adduction among the four baseplate version groups; however, patients with moderate to severe anteversion had a greater frequency of difficulty putting on a coat (86%) compared to patients with neutral version (42%), moderate retroversion (45%) and severe retroversion (0%). There were no differences in rates of complications and revisions across the four groups.
This study did not find evidence that high values of baseplate retroversion or anteversion were associated with inferior patient reported outcomes or functional rotation after reverse total shoulder arthroplasty.
(12) Effects of Different Humeral Stem Length on Stem Alignment and Proximal Stress Shielding in Reverse Total Shoulder Arthroplasty This study aimed to investigate the effects of different humeral stem lengths on stem alignment and proximal stress shielding after rTSA in 320 patients who underwent primary rTSA with at least 2 years of follow-up. The participants were classified into 3 groups according to the humeral stem length of different prostheses types: group A (short stem, range: <80 mm, n = 88), group B (medium stem, range: 80-100 mm, n = 155), and group C (standard stem, range: ≥100 mm, n = 77). Filling ratios were assessed.
Humeral stem malalignment was significantly higher in group A (21.6%) than in groups B (11.6%) and C (9.1%).
However, stress shielding at the lateral metaphyses (36.4%) was more frequently observed in group C.
Longer stem, stem malalignment, and higher diaphyseal canal filling ratio were independent risk factors for stress shielding occurrence, with stem malalignment showing the highest odds ratio.
The authors concluded that although shorter stems could be beneficial for bone preservation, they could lead to stem malalignment, resulting in increased humeral stress shielding if the filling ratios were high.
(13) Stemless Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-analysis. Stemless humeral components in reverse total shoulder arthroplasty are only approved for clinical trials in the United States with an investigational device exception with limited data. A systematic review on stemless reverse total shoulder arthroplasty evaluated 10 studies that used either the Total Evolutive Shoulder System (TESS) or Verso implant. The mean follow-up period ranged from 6.4 to 101.6 months per study. There was an overall trend of improved clinical outcome scores, a 0.2% humeral component loosening rate, and an 11.2% complication rate.
Geometry is important
Black-necked Stilt
Malheur
May 2025
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link)
Shoulder rehabilitation exercises (see this link).
Follow on twitter/X: https://x.com/RickMatsen
Follow on facebook: https://www.facebook.com/shoulder.arthritis
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/
Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link)
Shoulder rehabilitation exercises (see this link).
