Abstract
Background
Anatomic total shoulder arthroplasty (aTSA) is a viable option for select patients with favorable long-term outcomes. However, instability with static decentering and eccentric wear remains a concern. An important factor contributing to the stability of aTSA is the liner-generated stability ratio, constituted by jump-height and radius of curvature. This study aimed to measure jump height and radius of curvature as well as to assess the liner stability ratio (LSR) of various aTSA glenoid components, enabling comparisons of the degree of constraint between implant systems.
Methods
Using manufacturer-independent planning software, glenoid component height, jump height, and radius of curvature in the longitudinal and transverse axes were measured across 28 aTSA systems from 14 companies by two independent raters, with transverse measurements taken at the broadest diameter (t1) and at the corresponding midpoint level of the longitudinal axis (t2); data were validated by comparison with manufacturer-provided specifications. LSR were calculated using a previously validated mathematical formula. The inter-rater reliability was determined using the intraclass correlation coefficient. Visual diagrams illustrated the relationship between glenoid component height, jump height, and LSR across glenoid components of various aTSA designs.
Results
The mean glenoid component height was 32.8 ± 4.9 mm (range, 22.3-43.8 mm), while the mean jump height and radius of curvature were 5.1 ± 1.5 mm (range, 2.4-9.9 mm) and 29.7 ± 3.6 mm (range, 21.7-38.1 mm) in the longitudinal axis, 2.7 ± 0.7 mm (range, 1.5-5.1 mm) and 29.5 ± 3.9 mm (range, 19.9-38.5 mm) in the transversal axis (t1), and 2.6 ± 0.7 mm (range, 1.3-4.7 mm) and 29.7 ± 3.9 mm (range, 20.1-39.7 mm) for t2, respectively. Calculated LSR ranged from 39% to 115% (68% ± 15%) for the longitudinal axis, 31% to 71% (47% ± 8%) for t1, and from 28% to 65% (45% ± 8%) for t2, across available aTSA systems. Manufacturer-provided specifications from two companies showed high concordance with the obtained measurements. Regarding LSR consistency, only 2 systems were consistent (≤5% variation) in both axes. Slight inconsistencies (>5-10%) appeared in 3 systems longitudinally and 5 transversely, while most showed >10% variation across sizes. Inter-rater reliability demonstrated near-perfect agreement between testers.
Conclusion
This study highlights significant variability in the LSR across different glenoid components of aTSA systems, with inconsistencies often even observed within the same system. While the direct clinical impact remains uncertain, the LSR of the glenoid component in aTSA may have an effect on aTSA stability, component wear and loosening attributed to the rocking horse phenomenon. Further research is needed to clarify the biomechanical consequences of LSR variations on aTSA.
Keywords: Liner stability ratio, Anatomic shoulder arthroplasty, Glenoid components, Jump height, Radius of curvature, Degree of constraint
The original anatomic shoulder prosthesis first developed by Neer22 in 1974 was proposed to restore joint function and kinematics and has been shown to be a reliable procedure for patients with primary glenohumeral arthritis.3,7,27 Nevertheless, a recent systematic review by Al-Asadi et al2 revealed a diverse range of complications, ultimately prompting revision of anatomic total shoulder arthroplasty (aTSA) to reverse total shoulder arthroplasty (rTSA). Accurate restoration of the humeral center of rotation through appropriate humeral component positioning was proven to be critical to the success of aTSA,33 as improper positioning of components may disrupt joint mechanics, increasing the risk of complications such as polyethylene wear, which may, in turn, precipitate failure mechanisms including rotator cuff dysfunction, static subluxation, and glenoid loosening.31,35 Particularly, preserved integrity of the rotator cuff is crucial for aTSA stability as it serves as a dynamic stabilizer that helps maintain the humeral head's central position throughout the midrange of motion.26
Glenoid loosening, responsible for up to 63% of revision cases in aTSA, is thought to be a consequence of altered geometric interaction between the prosthetic joint surfaces during motion.5,9,29 First described by Franklin et al8 in 1988 as the ‘rocking horse’ phenomenon, repetitive eccentric loading of the humeral head on the glenoid rim generates increased moment arms and tensile stresses at the bone-cement-implant interface, progressively compromising fixation and leading to implant failure.28 Although eccentric loading may occur in multiple planes, superior-inferior forces are particularly prominent due to humeral head migration in the setting of rotator cuff dysfunction.8
Besides the previously mentioned factors, conformity of the glenohumeral articulation (defined as the difference in the radii of curvature between the humeral head and glenoid components surfaces) is thought to be related to stability in aTSA, with existing evidence suggesting that an optimal radial mismatch between 4.5 and 10 mm may balance joint stability, reduce glenoid component radiolucency, and improve implant longevity.10,32
Fundamentally, aTSA is intended to replicate the biomechanics of the native shoulder joint, where the concavity-compression mechanism plays a central role in maintaining stability,18 as the depth of the glenoid concavity correlates with the stability ratio, which measures the maximum translational force resisted by a given compression force.19 A reduction in this concavity has been linked to atraumatic posterior or multidirectional shoulder instability.13,21,37 In a recent study, Moroder et al20 employed a previously developed19 and biomechanically validated6 formula to quantitatively assess the liner stability ratio (LSR) across multiple rTSA systems, revealing substantial variability both between different implant designs and occasionally even among components within the same system.
Even though aTSA is often referred to as an “unconstrained’’ prosthesis, variations in the degree of constraint (concavity depth) across different glenoid component designs directly impacts the stability ratio, potentially affecting biomechanical performance and joint stability (Fig. 1). To our knowledge, a direct comparison of the LSR among glenoid components of various aTSA systems has not been previously reported in the literature. The aim of this study was to measure the jump height, radius of curvature, and subsequently determine the LSR of different aTSA glenoid components, allowing comparisons of the degree of constraint among commercially available implant systems.
Figure 1.
Example of a polyethylene glenoid component designed for anatomic total shoulder arthroplasty (Univers VaultLock Glenoid System; Arthrex, Naples, FL, USA).
Methods
An implant-provider independent three-dimensional (3D) planning software mediCAD 3D Shoulder (v.7.0), module (v.2.1.84.173.43; mediCAD; Hectec, GmbH, Altdorf/Landshut, Germany) was used to perform the measurements. This software enabled analysis across 28 aTSA systems of 14 companies, all of which were available as predefined templates within the program (Table I). Measurements included all available sizes for each glenoid component.
Table I.
Total shoulder arthroplasty glenoid systems available in mediCAD 3D Shoulder software.
| Nr. | Manufacturer | aTSA system |
|---|---|---|
| 1 | 3S Ortho | ARAMIS |
| 2 | Arthrex | Univers VaultLock Glenoid System |
| 3 | Depuy Synthes | Global |
| 4 | Enovis | AltiVate Anatomic |
| Turon Shoulder System | ||
| 5 | Evolutis | UNIC |
| 6 | Exactech | Equinoxe Anatomic Posterior Augmented Glenoid 8° |
| Equinoxe Anatomic Posterior Augmented Glenoid 16° | ||
| Equinoxe Keeled Glenoid | ||
| Equinoxe Pegged Glenoid | ||
| 7 | FH Ortho | Arrow Prime |
| 8 | Implantcast | Agilon |
| 9 | Lima | SMR cemented |
| SMR cemented with 3 pegs | ||
| SMR glenoid insert with metal back | ||
| SMR TT Hybrid Glenoid | ||
| 10 | Link | LINK Embrace |
| 11 | Mathys | Affinis Glenoid PE cemented |
| Affinis vitamys cemented | ||
| Affinis vitamys cementless | ||
| 12 | Medacta | PE Glenoid Medacta Shoulder System |
| 13 | Stryker | ReUnion TSA |
| Tornier Aequalis Perform | ||
| 14 | Zimmer Biomet | Anatomic Shoulder System |
| Bigliani/Flatow Shoulder System | ||
| Comprehensive Total Shoulder System | ||
| T.E.S.S Shoulder System | ||
| Zimmer Trabecular Metal Shoulder System |
3D, three-dimensional; aTSA, anatomic total shoulder arthroplasty; TSA, total shoulder arthroplasty; SMR, Systema Multiplana Randelli; PE, polyethylene; T.E.S.S, Total Evolutive Shoulder System.
Within the planning environment of the mediCAD 3D Shoulder software, the glenoid component templates were carefully positioned and aligned for measurement. Initially, the maximum superoinferior diameter of all glenoid components was measured. Next, in the sagittal plane view, the longitudinal axis was defined by aligning it along the maximum superoinferior diameter of the glenoid component. This alignment automatically generated the corresponding coronal (frontal) plane view (which by default is orthogonal to the sagittal plane, with the longitudinal axis defining the intersection of the sagittal and coronal planes), which was used for subsequent measurements along the longitudinal axis (Fig. 2). Measurements along the transverse axis were conducted at two standardized planes: the first (t1) was obtained by aligning the component's maximal anteroposterior diameter with the software's transverse axis (Fig. 3) and the second (t2) by setting the software's transverse axis to pass through the midpoint level of the longitudinal axis (Fig. 4). These orientation adjustments enabled the software to reconstruct the corresponding axial planes. Based on these standardized views, both the jump height (d) and the radius of curvature (r) were measured in each axis (Figs. 3 and 4).
Figure 2.
Measurement workflow using the mediCAD 3D Shoulder software. In the sagittal plane view (Left), the longitudinal axis was aligned along the maximal superoinferior diameter of the glenoid component, generating the corresponding coronal plane view for measurements along the longitudinal axis (Right). The corresponding jump height (d) and radius of curvature (r) measurements are displayed in the Right Panel. 3D, three-dimensional.
Figure 3.
Measurement workflow using the mediCAD 3D Shoulder software. In the sagittal plane view (Left), the transversal axis was aligned along the maximal anteroposterior diameter of the glenoid component, generating the corresponding axial plane view for measurements along the transversal axis (Right). The associated jump height (d) and radius of curvature (r) measurements to are shown in the Right Panel. 3D, three-dimensional.
Figure 4.
Measurement workflow using the mediCAD 3D Shoulder software. In the sagittal plane view (Left), the transversal axis was aligned along the midpoint level of the longitudinal axis of the glenoid component, generating the corresponding axial plane view for measurements along the transversal axis (Right). The associated jump height (d) and radius of curvature (r) measurements to are shown in the Right Panel. 3D, three-dimensional.
To determine the jump height, a tangential line was drawn along the upper edge of the glenoid component's concavity. The midpoint of the tangential line was identified, and an orthogonal line was drawn from this point to the base of the concavity. The length of this orthogonal line represented the jump height (Figure 2, Figure 3, Figure 4, right panel). The radius of the glenoid component was calculated by fitting a best-fit circle congruent with the articular surface, with the software providing the radius measurement (Figure 2, Figure 3, Figure 4, right panel).
All measurements were independently performed by two orthopedic surgeons (A.S. and M.M.). Inter-rater reliability was assessed using the intraclass correlation coefficient (two-way random-effects model, consistency type), with corresponding 95% confidence intervals. Analysis was performed in Python (v3.10.12) using the Pingouin package (v0.5.3; Raphael Vallat, Berkley, CA, USA). The obtained data were then validated by comparison with manufacturer-provided specifications from two different companies.
Calculation of anatomic total shoulder arthroplasty liner stability ratio
The LSR was calculated using a validated mathematical formula6 that has previously been employed for LSR calculations in rTSA.20 In the present study, the same principles were applied to aTSA glenoid components to define the LSR of glenoid components of different aTSA systems.
The LSR quantifies the maximum translational force that can be resisted by the aTSA system, under a specific compressive load, before dislocation occurs. The final formula used for the aTSA LSR calculation stability was:
Consistency of anatomic total shoulder arthroplasty liner stability ratio among different sizes within the same system
The consistency of LSR across different implant sizes within each aTSA system was assessed based on measurements obtained in both longitudinal and transverse axes. For each system, LSR values were calculated for all available sizes, and the percentage deviation as well as the trend across various sizes was determined. Systems were categorized as consistent (≤5% deviation), slightly inconsistent (>5% to ≤10%), or largely inconsistent (>10%), reflecting the degree of LSR variation attributable to implant size within the same design.
Results
The mean glenoid component height measured 32.8 ± 4.9 mm (range, 22.2-43.8 mm). Along the longitudinal axis, the mean jump height was 5.0 ± 1.5 mm (2.4-9.9 mm), and the mean radius of curvature was 29.7 ± 3.6 mm (21.7-38.1 mm). Corresponding values for the transverse axis were 2.7 ± 0.7 mm (range, 1.5-5.1 mm) and 29.5 ± 3.9 mm (range, 19.9-38.5 mm) for t1, and 2.6 ± 0.7 mm (range, 1.3-4.7 mm) and 29.7 ± 3.9 mm (range, 20.1-39.7 mm) for t2, respectively. The LSR in the longitudinal axis across all evaluated aTSA systems ranged from 39% to 115%, with a mean of 68% ± 15%. In the transverse axis, LSR values ranged from 31% to 71%, with a mean of 47% ± 8% for t1, and from 28% to 65%, with a mean of 45% ± 8% for t2.
The inter-rater reliability was excellent, with excellent agreement between two testers (intraclass correlation coefficient = 0.999 for jump height and 0.998 for radius of curvature). Furthermore, manufacturer-provided specifications from two companies showed high concordance with the independently obtained measurements (Table II). All measurements obtained along the longitudinal and transverse axes (t1 and t2) and calculated LSR values are presented in Table III, Table IV, Table V, respectively.
Table II.
Comparison of measured jump height and radii of curvature with corresponding manufacturer-provided values.
| aTSA system | Size | RoC (company) | RoC (measured) | Longitudinal jump height (company) | Longitudinal jump height (measured) | Transversal jump height (company) | Transversal (t1) jump height (measured) |
|---|---|---|---|---|---|---|---|
| PE Glenoid Medacta Shoulder System (Medacta) | 40 | 23.0 | 23.0 | 2.8 | 2.7 | 1.6 | 1.6 |
| 42 | 24.0 | 23.9 | 2.9 | 2.9 | 1.7 | 1.7 | |
| 44 | 25.0 | 25.4 | 3.1 | 3.1 | 1.8 | 1.8 | |
| 46 | 26.0 | 26.5 | 3.3 | 3.2 | 1.9 | 1.9 | |
| 48 | 27.0 | 27.0 | 3.5 | 3.4 | 2.0 | 2.0 | |
| 50 | 28.0 | 28.2 | 3.6 | 3.6 | 2.1 | 2.1 | |
| 52 | 29.0 | 28.9 | 3.8 | 3.8 | 2.2 | 2.2 | |
| 54 | 30.0 | 30.0 | 4.0 | 4.0 | 2.3 | 2.3 | |
| 56 | 31.0 | 31.1 | 4.2 | 4.2 | 2.4 | 2.4 | |
| 58 | 32.0 | 31.9 | 4.4 | 4.4 | 2.5 | 2.5 | |
| Univers VaultLock (Arthrex) | Small | 29.0 | 28.9 | 5.2 | 5.1 | 2.4 | 2.4 |
| Medium | 30.5 | 30.6 | 5.9 | 5.8 | 3.0 | 2.9 | |
| Large | 32.0 | 31.9 | 6.6 | 6.6 | 3.5 | 3.5 | |
| X-large | 33.5 | 33.6 | 7.4 | 7.4 | 4.1 | 4.1 |
RoC, radius of curvature; PE, polyethylene.
Table III.
Glneoid component height, jump height, radius of curvature, and calculated liner stability ratios in the longitudinal axis across different glenoid component sizes of various anatomical total shoulder arthroplasty systems.
| Anatomic total shoulder arthroplasty system | Glenoid component size | Glenoid component height (mm) | Jump height (mm) | Radius of curvature (mm) | Liner stability ratio (%) |
|---|---|---|---|---|---|
| Univers VaultLock (Athrex) | Small | 32.8 | 5.1 | 28.9 | 69% |
| Medium | 35.6 | 5.8 | 30.5 | 72% | |
| Large | 38.7 | 6.6 | 31.9 | 76% | |
| Extra large | 41.9 | 7.3 | 33.6 | 80% | |
| ARAMIS (3S ORTHO) | 30 | 29.5 | 3.8 | 29.9 | 56% |
| 33 | 32.4 | 4.7 | 29.9 | 63% | |
| 36 | 35.2 | 5.6 | 30.0 | 72% | |
| Global (Depuy Synthes) | 40 | 29.5 | 5.3 | 22.7 | 84% |
| 44 | 32.3 | 5.9 | 25.1 | 84% | |
| 48 | 35.1 | 6.4 | 26.8 | 86% | |
| 52 | 37.8 | 7.1 | 29.1 | 86% | |
| 56 | 40.8 | 7.6 | 31.1 | 87% | |
| 56XL | 43.8 | 9.1 | 31.1 | 99% | |
| Altivate Anatomic (Enovis) | 38 | 29.4 | 4.9 | 24.7 | 74% |
| 42 | 30.1 | 5.2 | 26.9 | 73% | |
| 46 | 34.6 | 5.7 | 28.7 | 74% | |
| 50 | 37.0 | 6.1 | 31.2 | 74% | |
| 54 | 39.5 | 6.6 | 33.1 | 75% | |
| Turon Shoulder System (Enovis) | 38 | 29.5 | 4.4 | 26.6 | 66% |
| 42 | 31.9 | 4.8 | 28.8 | 67% | |
| 46 | 34.5 | 5.3 | 30.8 | 67% | |
| 50 | 37.4 | 5.7 | 33.0 | 68% | |
| 54 | 39.8 | 6.1 | 34.7 | 69% | |
| UNIC (Evolutis) | 30 | 29.5 | 4.1 | 28.3 | 61% |
| 33 | 32.5 | 5.0 | 28.1 | 70% | |
| 36 | 35.4 | 6.2 | 28.2 | 80% | |
| Equinoxe Anatomic Posterior Augmented Glenoid 8° (Exactech) | Small | 28.3 | 3.8 | 27.6 | 59% |
| Medium | 32.8 | 4.8 | 29.7 | 65% | |
| Large | 37.0 | 5.9 | 31.7 | 71% | |
| Extra large | 41.6 | 7.7 | 31.8 | 86% | |
| Equinoxe Anatomic Posterior Augmented Glenoid 16° (Exactech) | Small | 28.3 | 3.8 | 27.5 | 59% |
| Medium | 32.8 | 4.8 | 29.3 | 66% | |
| Large | 37.2 | 5.9 | 32.0 | 71% | |
| Extra large | 41.5 | 7.6 | 31.8 | 85% | |
| Equinoxe Keeled Glenoid (Exactech) | Beta small | 28.7 | 4.0 | 27.2 | 61% |
| Beta medium | 33.2 | 5.6 | 26.9 | 77% | |
| Beta large | 37.1 | 7.4 | 27.1 | 94% | |
| Equinoxe Pegged Glenoid (Exactech) | Beta small | 28.6 | 4.0 | 27.2 | 61% |
| Beta medium | 32.5 | 5.6 | 26.9 | 77% | |
| Beta large | 37.1 | 7.4 | 27.1 | 94% | |
| Beta extra large | 41.8 | 8.1 | 31.0 | 91% | |
| Arrow Prime (FH Ortho) | 50 | 43.7 | 9.9 | 29.0 | 115% |
| Agilon (Implantcast) | Size 2 | 28.8 | 3.4 | 32.0 | 50% |
| Size 3 | 31.9 | 4.1 | 31.9 | 57% | |
| Size 4 | 34.6 | 5.0 | 31.7 | 64% | |
| SMR Cemented (Lima) | Small-R | 25.4 | 2.3 | 34.7 | 39% |
| Small | 25.9 | 2.3 | 35.2 | 39% | |
| Standard | 29.9 | 3.0 | 37.7 | 43% | |
| SMR Cemented with 3 Pegs (Lima) | Extra-small | 24.7 | 2.4 | 32.6 | 41% |
| Small | 26.6 | 2.6 | 34.8 | 41% | |
| Standard | 30.5 | 3.2 | 37.1 | 45% | |
| Large | 34.9 | 4.1 | 37.1 | 52% | |
| SMR glenoid insert with metal back (Lima) | Small-R | 25.3 | 2.6 | 31.9 | 43% |
| Small | 28.4 | 2.9 | 35.2 | 44% | |
| Standard | 25.8 | 2.6 | 32.0 | 43% | |
| Large | 33.4 | 3.8 | 37.2 | 49% | |
| SMR TT Hybrid Glenoid (Lima) | Small | 26.4 | 2.8 | 31.9 | 45% |
| Standard | 30.7 | 3.5 | 35.5 | 48% | |
| Large | 34.6 | 4.2 | 36.9 | 52% | |
| LINK Embrace (Link) | Small | 24.6 | 3.1 | 25.9 | 55% |
| Medium | 29.3 | 3.9 | 29.4 | 57% | |
| Large | 33.5 | 4.7 | 32.0 | 61% | |
| X-large | 37.5 | 6.0 | 31.8 | 73% | |
| Affinis Glenoid PE cemented (Mathys) | 1 | 27.3 | 4.0 | 24.9 | 65% |
| 2 | 31.6 | 4.9 | 26.9 | 70% | |
| 3 | 35.5 | 5.8 | 29.0 | 75% | |
| 4 | 39.6 | 6.9 | 31.1 | 81% | |
| Affinis vitamys cemented (Mathys) | 1 | 25.1 | 3.1 | 26.0 | 54% |
| 2 | 29.5 | 4.0 | 27.9 | 60% | |
| 3 | 33.6 | 4.8 | 29.9 | 65% | |
| 4 | 37.5 | 5.8 | 32.0 | 70% | |
| Affinis vitamys cementless (Mathys) | 1 | 25.1 | 3.1 | 25.8 | 55% |
| 2 | 29.4 | 3.9 | 28.1 | 60% | |
| 3 | 33.6 | 4.9 | 29.6 | 66% | |
| 4 | 36.9 | 5.8 | 32.2 | 70% | |
| Medacta Shoulder System PE Glenoid (Medacta) | 40 | 22.2 | 2.7 | 23.0 | 54% |
| 42 | 23.3 | 2.9 | 23.9 | 55% | |
| 44 | 24.8 | 3.1 | 25.4 | 55% | |
| 46 | 25.7 | 3.2 | 26.5 | 55% | |
| 48 | 27.0 | 3.4 | 27.0 | 56% | |
| 50 | 28.0 | 3.6 | 28.2 | 57% | |
| 52 | 29.1 | 3.8 | 28.9 | 58% | |
| 54 | 30.5 | 4.0 | 30.0 | 58% | |
| 56 | 31.7 | 4.2 | 31.1 | 58% | |
| 58 | 32.8 | 4.4 | 31.9 | 59% | |
| ReUnion TSA (Stryker) | 40 | 31.8 | 6.4 | 22.9 | 96% |
| 44 | 34.1 | 6.7 | 24.8 | 94% | |
| 48 | 36.5 | 7.0 | 26.9 | 91% | |
| 52 | 38.9 | 7.6 | 28.6 | 93% | |
| 56 | 41.9 | 8.3 | 30.9 | 93% | |
| Tornier Aequalis Perform (Stryker) | S30 | 30.2 | 4.5 | 27.3 | 66% |
| S35 | 30.2 | 4.5 | 27.8 | 65% | |
| S40 | 30.2 | 4.5 | 27.7 | 65% | |
| M30 | 33.7 | 5.1 | 29.9 | 68% | |
| M35 | 33.7 | 5.2 | 29.7 | 69% | |
| M40 | 33.7 | 5.2 | 29.6 | 69% | |
| L40 | 37.4 | 5.9 | 31.6 | 72% | |
| L50 | 37.4 | 5.9 | 31.5 | 72% | |
| L60 | 37.4 | 5.9 | 31.6 | 72% | |
| XL 40 | 40.7 | 6.7 | 33.8 | 75% | |
| XL 50 | 40.7 | 6.6 | 33.5 | 75% | |
| XL 60 | 40.7 | 6.8 | 33.7 | 75% | |
| Anatomic Shoulder System (Zimmer Biomet) | Small | 33.7 | 5.1 | 29.3 | 69% |
| Medium | 36.6 | 5.9 | 30.7 | 73% | |
| Large | 39.8 | 6.4 | 32.7 | 74% | |
| Bigliani/Flatow Shoulder System (Zimmer Biomet) | 40 | 27.5 | 4.9 | 21.9 | 81% |
| 46 | 32.0 | 5.9 | 24.7 | 85% | |
| 52 | 33.6 | 5.6 | 27.7 | 76% | |
| Comprehensive Total Shoulder System (Zimmer Biomet) | Small | 28.0 | 2.7 | 38.1 | 40% |
| Medium | 31.7 | 3.4 | 37.6 | 46% | |
| Large | 34.1 | 4.0 | 37.3 | 51% | |
| T.E.S.S Shoulder System (Zimmer Biomet) | S0 | 27.9 | 4.4 | 24.1 | 71% |
| S1 | 28.0 | 4.5 | 23.9 | 72% | |
| S2 | 29.6 | 4.5 | 26.3 | 67% | |
| S3 | 30.7 | 4.5 | 28.4 | 64% | |
| Zimmer Trabecular Metal Shoulder System (Zimmer Biomet) | 40 | 27.8 | 4.9 | 21.7 | 82% |
| 46 | 32.3 | 5.8 | 24.8 | 85% | |
| 52 | 34.0 | 5.6 | 27.8 | 76% |
TSA, total shoulder arthroplasty; SMR, Systema Multiplana Randelli; PE, polyethylene; T.E.S.S, Total Evolutive Shoulder System.
Table IV.
Jump height, radius of curvature, and calculated liner stability ratios in the transversal axis (t1) across different glenoid component sizes of various anatomical total shoulder arthroplasty systems.
| Anatomic total shoulder arthroplasty system | Glenoid component size | Jump height (mm) | Radius of curvature (mm) | Liner stability ratio (%) |
|---|---|---|---|---|
| Univers VaultLock (Athrex) | Small | 2.3 | 28.0 | 44% |
| Medium | 2.9 | 29.9 | 48% | |
| Large | 3.4 | 31.1 | 52% | |
| Extra large | 4.1 | 33.4 | 54% | |
| ARAMIS (3S ORTHO) | 30 | 1.9 | 29.7 | 38% |
| 33 | 2.3 | 29.7 | 42% | |
| 36 | 2.7 | 29.5 | 47% | |
| Global (Depuy Synthes) | 40 | 2.7 | 22.6 | 55% |
| 44 | 3.1 | 25.1 | 55% | |
| 48 | 3.4 | 26.5 | 56% | |
| 52 | 3.7 | 28.9 | 56% | |
| 56 | 4.1 | 31.1 | 57% | |
| 56XL | 4.6 | 31.1 | 62% | |
| Altivate Anatomic (Enovis) | 38 | 3.0 | 24.8 | 54% |
| 42 | 3.1 | 26.7 | 53% | |
| 46 | 3.3 | 28.7 | 53% | |
| 50 | 3.4 | 30.8 | 52% | |
| 54 | 3.5 | 32.8 | 51% | |
| Turon Shoulder System (Enovis) | 38 | 2.4 | 30.2 | 42% |
| 42 | 2.4 | 32.4 | 42% | |
| 46 | 2.7 | 34.3 | 42% | |
| 50 | 2.8 | 36.1 | 42% | |
| 54 | 3.0 | 38.5 | 42% | |
| UNIC (Evolutis) | 30 | 2.2 | 28.3 | 42% |
| 33 | 2.5 | 28.2 | 46% | |
| 36 | 3.1 | 27.4 | 52% | |
| Equinoxe Anatomic Posterior Augmented Glenoid 8° (Exactech) | Small | 2.0 | 27.5 | 41% |
| Medium | 2.5 | 29.1 | 45% | |
| Large | 3.1 | 31.3 | 48% | |
| Extra large | 3.9 | 31.3 | 56% | |
| Equinoxe Anatomic Posterior Augmented Glenoid 16° (Exactech) | Small | 1.9 | 27.1 | 40% |
| Medium | 2.5 | 29.4 | 44% | |
| Large | 3.1 | 31.3 | 48% | |
| Extra large | 3.9 | 31.3 | 55% | |
| Equinoxe Keeled Glenoid (Exactech) | Beta small | 2.1 | 26.1 | 42% |
| Beta medium | 2.8 | 26.3 | 50% | |
| Beta large | 3.7 | 25.9 | 61% | |
| Equinoxe Pegged Glenoid (Exactech) | Beta small | 2.1 | 26.7 | 42% |
| Beta medium | 2.8 | 27.1 | 50% | |
| Beta large | 3.7 | 26.2 | 60% | |
| Beta extra large | 4.1 | 30.4 | 58% | |
| Arrow Prime (FH Ortho) | 50 | 5.1 | 27.9 | 71% |
| Agilon (Implantcast) | Size 2 | 1.5 | 31.8 | 33% |
| Size 3 | 1.8 | 31.2 | 36% | |
| Size 4 | 2.6 | 31.9 | 43% | |
| SMR Cemented (Lima) | Small-R | 1.8 | 34.4 | 34% |
| Small | 1.8 | 34.2 | 34% | |
| Standard | 2.1 | 37.3 | 35% | |
| SMR Cemented with 3 Pegs (Lima) | Extra-small | 1.6 | 33.6 | 33% |
| Small | 1.7 | 34.9 | 33% | |
| Standard | 2.1 | 37.8 | 35% | |
| Large | 2.7 | 37.7 | 40% | |
| SMR glenoid insert with metal back (Lima) | Small-R | 1.8 | 32.5 | 36% |
| Small | 2.3 | 35.4 | 38% | |
| Standard | 1.8 | 32.0 | 36% | |
| Large | 2.7 | 37.3 | 40% | |
| SMR TT Hybrid Glenoid (Lima) | Small | 1.9 | 32.2 | 36% |
| Standard | 2.3 | 34.4 | 39% | |
| Large | 2.7 | 37.0 | 40% | |
| LINK Embrace (Link) | Small | 2.4 | 25.4 | 47% |
| Medium | 2.8 | 28.7 | 48% | |
| Large | 3.2 | 31.7 | 49% | |
| X-large | 4.0 | 31.6 | 56% | |
| Affinis Glenoid PE cemented (Mathys) | 1 | 2.2 | 25.4 | 45% |
| 2 | 2.7 | 27.3 | 48% | |
| 3 | 3.1 | 29.1 | 51% | |
| 4 | 3.7 | 31.1 | 54% | |
| Affinis vitamys cemented (Mathys) | 1 | 1.6 | 26.3 | 37% |
| 2 | 2.1 | 28.2 | 41% | |
| 3 | 2.5 | 29.9 | 44% | |
| 4 | 3.1 | 32.2 | 47% | |
| Affinis vitamys cementless (Mathys) | 1 | 1.7 | 25.1 | 39% |
| 2 | 2.1 | 27.7 | 42% | |
| 3 | 2.6 | 29.6 | 45% | |
| 4 | 3.1 | 31.4 | 48% | |
| Medacta Shoulder System PE Glenoid (Medacta) | 40 | 1.6 | 23.3 | 40% |
| 42 | 1.7 | 24.1 | 40% | |
| 44 | 1.8 | 24.9 | 41% | |
| 46 | 1.9 | 26.0 | 41% | |
| 48 | 2.0 | 27.3 | 41% | |
| 50 | 2.1 | 28.0 | 41% | |
| 52 | 2.2 | 28.8 | 42% | |
| 54 | 2.3 | 30.5 | 41% | |
| 56 | 2.4 | 31.2 | 42% | |
| 58 | 2.5 | 31.8 | 42% | |
| ReUnion TSA (Stryker) | 40 | 2.3 | 23.2 | 49% |
| 44 | 2.5 | 25.4 | 49% | |
| 48 | 2.9 | 26.2 | 52% | |
| 52 | 3.0 | 28.8 | 50% | |
| 56 | 3.4 | 29.8 | 53% | |
| Tornier Aequalis Perform (Stryker) | S30 | 2.3 | 26.4 | 46% |
| S35 | 2.4 | 26.4 | 46% | |
| S40 | 2.4 | 27.0 | 45% | |
| M30 | 2.9 | 29.0 | 48% | |
| M35 | 2.9 | 29.4 | 48% | |
| M40 | 2.9 | 28.9 | 48% | |
| L40 | 3.3 | 30.9 | 51% | |
| L50 | 3.2 | 30.3 | 50% | |
| L60 | 3.0 | 29.9 | 48% | |
| XL 40 | 3.6 | 32.5 | 52% | |
| XL 50 | 3.6 | 32.6 | 51% | |
| XL 60 | 3.8 | 33.1 | 53% | |
| Anatomic Shoulder System (Zimmer Biomet) | Small | 3.1 | 28.7 | 50% |
| Medium | 2.7 | 30.0 | 46% | |
| Large | 3.3 | 32.1 | 49% | |
| Bigliani/Flatow Shoulder System (Zimmer Biomet) | 40 | 2.5 | 20.2 | 55% |
| 46 | 3.3 | 22.8 | 62% | |
| 52 | 3.2 | 25.9 | 56% | |
| Comprehensive Total Shoulder System (Zimmer Biomet) | Small | 1.6 | 37.1 | 31% |
| Medium | 2.3 | 38.1 | 37% | |
| Large | 3.0 | 37.4 | 43% | |
| T.E.S.S Shoulder System (Zimmer Biomet) | S0 | 3.5 | 23.4 | 62% |
| S1 | 3.4 | 22.8 | 62% | |
| S2 | 3.5 | 25.6 | 59% | |
| S3 | 3.4 | 26.3 | 57% | |
| Zimmer Trabecular Metal Shoulder System (Zimmer Biomet) | 40 | 2.8 | 19.9 | 60% |
| 46 | 3.3 | 22.9 | 61% | |
| 52 | 3.2 | 26.1 | 55% |
TSA, total shoulder arthroplasty; SMR, Systema Multiplana Randelli; PE, polyethylene; T.E.S.S, Total Evolutive Shoulder System.
Table V.
Jump height, radius of curvature, and calculated liner stability ratios in the transversal axis (t2) across different glenoid component sizes of various anatomical total shoulder arthroplasty systems.
| Anatomic total shoulder arthroplasty system | Glenoid component size | Jump height (mm) | Radius of curvature (mm) | Liner stability ratio (%) |
|---|---|---|---|---|
| Univers VaultLock (Athrex) | Small | 1.9 | 27.6 | 39% |
| Medium | 2.5 | 29.3 | 44% | |
| Large | 3.0 | 32.0 | 46% | |
| Extra large | 3.6 | 33.3 | 51% | |
| ARAMIS (3S ORTHO) | 30 | 1.8 | 30.0 | 36% |
| 33 | 2.0 | 30.3 | 39% | |
| 36 | 2.4 | 29.8 | 43% | |
| Global (Depuy Synthes) | 40 | 2.8 | 22.7 | 55% |
| 44 | 3.1 | 25.1 | 55% | |
| 48 | 3.4 | 26.9 | 56% | |
| 52 | 3.7 | 29.0 | 56% | |
| 56 | 4.0 | 30.9 | 56% | |
| 56XL | 4.7 | 30.9 | 62% | |
| Altivate Anatomic (Enovis) | 38 | 2.8 | 24.8 | 52% |
| 42 | 2.9 | 27.0 | 50% | |
| 46 | 2.9 | 28.7 | 49% | |
| 50 | 3.0 | 31.1 | 48% | |
| 54 | 3.2 | 32.8 | 47% | |
| Turon Shoulder System (Enovis) | 38 | 2.2 | 30.7 | 40% |
| 42 | 2.3 | 32.8 | 40% | |
| 46 | 2.4 | 34.8 | 39% | |
| 50 | 2.5 | 36.8 | 39% | |
| 54 | 2.6 | 39.7 | 38% | |
| UNIC (Evolutis) | 30 | 2.0 | 28.3 | 40% |
| 33 | 2.4 | 28.5 | 44% | |
| 36 | 2.9 | 28.3 | 49% | |
| Equinoxe Anatomic Posterior Augmented Glenoid 8° (Exactech) | Small | 1.7 | 27.7 | 37% |
| Medium | 2.1 | 29.6 | 40% | |
| Large | 2.7 | 32.0 | 43% | |
| Extra large | 3.4 | 31.7 | 50% | |
| Equinoxe Anatomic Posterior Augmented Glenoid 16° (Exactech) | Small | 1.7 | 27.7 | 37% |
| Medium | 2.2 | 30.4 | 40% | |
| Large | 2.6 | 32.3 | 43% | |
| Extra large | 3.4 | 32.0 | 50% | |
| Equinoxe Keeled Glenoid (Exactech) | Beta small | 1.9 | 27.1 | 39% |
| Beta medium | 2.5 | 27.1 | 46% | |
| Beta large | 3.3 | 27.1 | 55% | |
| Equinoxe Pegged Glenoid (Exactech) | Beta small | 1.9 | 27.6 | 39% |
| Beta medium | 2.5 | 27.4 | 46% | |
| Beta large | 3.3 | 26.7 | 55% | |
| Beta extra large | 3.5 | 30.7 | 53% | |
| Arrow Prime (FH Ortho) | 50 | 4.6 | 28.7 | 65% |
| Agilon (Implantcast) | Size 2 | 1.3 | 32.7 | 28% |
| Size 3 | 1.6 | 33.2 | 32% | |
| Size 4 | 2.4 | 31.5 | 41% | |
| SMR Cemented (Lima) | Small-R | 1.9 | 34.3 | 34% |
| Small | 1.9 | 33.7 | 35% | |
| Standard | 2.1 | 36.7 | 35% | |
| SMR Cemented with 3 Pegs (Lima) | Extra-small | 1.8 | 32.1 | 35% |
| Small | 1.8 | 33.9 | 34% | |
| Standard | 2.1 | 36.5 | 36% | |
| Large | 2.7 | 37.0 | 40% | |
| SMR glenoid insert with metal back (Lima) | Small-R | 1.9 | 32.5 | 36% |
| Small | 2.3 | 34.5 | 38% | |
| Standard | 1.9 | 32.0 | 36% | |
| Large | 2.7 | 36.9 | 40% | |
| SMR TT Hybrid Glenoid (Lima) | Small | 1.9 | 32.0 | 36% |
| Standard | 2.3 | 34.4 | 38% | |
| Large | 2.4 | 34.2 | 39% | |
| LINK Embrace (Link) | Small | 2.5 | 26.1 | 47% |
| Medium | 2.7 | 27.9 | 48% | |
| Large | 3.3 | 30.9 | 50% | |
| X-large | 3.9 | 31.9 | 55% | |
| Affinis Glenoid PE cemented (Mathys) | 1 | 2.0 | 25.1 | 42% |
| 2 | 2.2 | 27.3 | 43% | |
| 3 | 2.8 | 29.4 | 47% | |
| 4 | 3.4 | 31.8 | 50% | |
| Affinis vitamys cemented (Mathys) | 1 | 1.5 | 25.0 | 37% |
| 2 | 1.9 | 28.6 | 39% | |
| 3 | 2.4 | 30.0 | 43% | |
| 4 | 2.8 | 32.2 | 44% | |
| Affinis vitamys cementless (Mathys) | 1 | 1.6 | 25.3 | 37% |
| 2 | 2.0 | 27.4 | 41% | |
| 3 | 2.3 | 29.3 | 42% | |
| 4 | 2.9 | 32.1 | 45% | |
| Medacta Shoulder System PE Glenoid (Medacta) | 40 | 1.6 | 22.8 | 39% |
| 42 | 1.7 | 24.5 | 40% | |
| 44 | 1.8 | 25.5 | 40% | |
| 46 | 2.0 | 26.4 | 41% | |
| 48 | 2.0 | 26.6 | 41% | |
| 50 | 2.2 | 28.7 | 41% | |
| 52 | 2.3 | 29.6 | 41% | |
| 54 | 2.4 | 29.8 | 42% | |
| 56 | 2.4 | 31.7 | 42% | |
| 58 | 2.6 | 32.0 | 43% | |
| ReUnion TSA (Stryker) | 40 | 2.4 | 22.3 | 51% |
| 44 | 2.5 | 24.8 | 49% | |
| 48 | 2.7 | 26.8 | 48% | |
| 52 | 2.8 | 28.1 | 49% | |
| 56 | 3.1 | 30.8 | 48% | |
| Tornier Aequalis Perform (Stryker) | S30 | 2.3 | 27.2 | 44% |
| S35 | 2.3 | 27.3 | 44% | |
| S40 | 2.3 | 27.6 | 44% | |
| M30 | 2.8 | 29.3 | 47% | |
| M35 | 2.8 | 29.6 | 47% | |
| M40 | 2.6 | 29.6 | 45% | |
| L40 | 3.2 | 31.4 | 49% | |
| L50 | 3.1 | 30.8 | 49% | |
| L60 | 3.1 | 31.0 | 49% | |
| XL 40 | 3.7 | 32.9 | 52% | |
| XL 50 | 3.7 | 33.4 | 51% | |
| XL 60 | 3.6 | 33.3 | 51% | |
| Anatomic Shoulder System (Zimmer Biomet) | Small | 2.1 | 29.5 | 40% |
| Medium | 2.6 | 30.1 | 44% | |
| Large | 3.0 | 32.3 | 46% | |
| Bigliani/Flatow Shoulder System (Zimmer Biomet) | 40 | 2.8 | 20.2 | 59% |
| 46 | 3.4 | 23.0 | 61% | |
| 52 | 3.3 | 25.9 | 56% | |
| Comprehensive Total Shoulder System (Zimmer Biomet) | Small | 1.6 | 36.7 | 30% |
| Medium | 2.2 | 37.8 | 36% | |
| Large | 2.9 | 37.7 | 42% | |
| T.E.S.S Shoulder System (Zimmer Biomet) | S0 | 3.4 | 23.4 | 61% |
| S1 | 3.7 | 23.5 | 64% | |
| S2 | 3.5 | 26.4 | 58% | |
| S3 | 3.5 | 28.0 | 55% | |
| Zimmer Trabecular Metal Shoulder System (Zimmer Biomet) | 40 | 2.8 | 20.1 | 60% |
| 46 | 3.5 | 23.4 | 61% | |
| 52 | 3.4 | 22.8 | 61% |
TSA, total shoulder arthroplasty; SMR, Systema Multiplana Randelli; PE, polyethylene; T.E.S.S, Total Evolutive Shoulder System.
LSR demonstrated marked variability across different aTSA systems and glenoid component sizes. When plotted against jump height, system-specific LSR distributions became evident, with some systems exhibiting more consistent LSR patterns across sizes, while others displayed substantial intrasystem dispersion (Fig. 5). Importantly, there was no uniform relationship between LSR and component size (represented by glenoid component height); in some cases, smaller components were associated with higher LSR (Fig. 6). Between systems, implants with similar size exhibited markedly different LSR values (Fig. 6). Within systems, some implants showed more consistent LSR values across sizes. However, others exhibited either increasing or decreasing LSR with larger size (Fig. 6).
Figure 5.
Graphs illustrating calculated liner stability ratios (LSRs; y-axis), derived from manually measured jump heights and radii of curvature of various anatomic total shoulder arthroplasty systems, plotted against jump height measurements. (A) Jump height plotted against LSR calculated along the longitudinal axis. (B) Jump height plotted against LSR calculated along the transverse axis (t1). (C) Jump height plotted against LSR calculated along the transverse axis (t2). Symbols of the same color represent LSR values from the same aTSA system but with different radii of curvature. Jump height values are not strictly proportional to glenoid component size. aTSA, anatomic total shoulder arthroplasty.
Figure 6.
Graph illustrating the relationship between glenoid component height and LSR across aTSA systems. Considerable variability in LSR is observed both between and within systems, without a consistent linear correlation to glenoid component height. aTSA, anatomic total shoulder arthroplasty; LSR, liner stability ratio.
Regarding LSR consistency across various sizes within each aTSA system, in the longitudinal axis (Table VI), 2 systems demonstrated consistency (≤5% variation across sizes), 3 systems showed slight inconsistency (>5% to ≤10%), and 22 systems showed large inconsistency (>10%). In the transverse axes (Table VII), 2 systems demonstrated consistency, 5 systems showed slight inconsistency, and 20 systems showed large inconsistency. One system (Arrow Prime, FH Ortho, Mulhouse, France) was available in a single size, precluding assessment of LSR variability across implant sizes.
Table VI.
Summary of liner stability ratio consistency and trends in the longitudinal axis across implant sizes within each anatomic total shoulder arthroplasty system.
| System | LSR % variation across sizes | Consistency assessment | LSR trend |
|---|---|---|---|
| Univers VaultLock (Arthrex) | 15.28 | Large inconsistency (>10%) | ↑ |
| ARAMIS (3S Ortho) | 25.25 | Large inconsistency (>10%) | ↑ |
| Global (Depuy Synthes) | 17.78 | Large inconsistency (>10%) | ↑ |
| AltiVate Anatomic (Enovis) | 01.89 | Consistent (≤5%) | ↔ |
| Turon Shoulder System (Enovis) | 04.08 | Consistent (≤5%) | ↑ |
| UNIC (Evolutis) | 27.58 | Large inconsistency (>10%) | ↑ |
| Equinoxe 8° augmented (Exactech) | 38.13 | Large inconsistency (>10%) | ↑ |
| Equinoxe 16° augmented (Exactech) | 37.10 | Large inconsistency (>10%) | ↑ |
| Equinoxe Keeled Glenoid (Exactech) | 42.55 | Large inconsistency (>10%) | ↑ |
| Equinoxe Pegged Glenoid (Exactech) | 40.62 | Large inconsistency (>10%) | ↔ |
| Agilon (Implantcast) | 23.77 | Large inconsistency (>10%) | ↑ |
| SMR cemented (Lima) | 10.14 | Large inconsistency (>10%) | ↔ |
| SMR cemented 3 pegs (Lima) | 25.32 | Large inconsistency (>10%) | ↑ |
| SMR metal back (Lima) | 13.94 | Large inconsistency (>10%) | ↑ |
| SMR TT hybrid (Lima) | 14.90 | Large inconsistency (>10%) | ↑ |
| LINK Embrace (Link) | 29.30 | Large inconsistency (>10%) | ↑ |
| Affinis PE cemented (Mathys) | 21.94 | Large inconsistency (>10%) | ↑ |
| Affinis vitamys cemented (Mathys) | 26.23 | Large inconsistency (>10%) | ↑ |
| Affinis vitamys cementless (Mathys) | 25.08 | Large inconsistency (>10%) | ↑ |
| Medacta PE Glenoid (Medacta) | 08.52 | Slight inconsistency (>5-10%) | ↔ |
| ReUnion TSA (Stryker) | 05.37 | Slight inconsistency (>5-10%) | ↔ |
| Tornier Aequalis Perform (Stryker) | 14.71 | Large inconsistency (>10%) | ↔ |
| Anatomic Shoulder System (Zimmer Biomet) | 08.15 | Slight inconsistency (>5-10%) | ↑ |
| Bigliani/Flatow Shoulder System (Zimmer Biomet) | 10.85 | Large inconsistency (>10%) | ↔ |
| Comprehensive Total Shoulder System (Zimmer Biomet) | 22.95 | Large inconsistency (>10%) | ↑ |
| T.E.S.S Shoulder System (Zimmer Biomet) | 10.69 | Large inconsistency (>10%) | ↔ |
| Zimmer Trabecular Metal Shoulder System (Zimmer Biomet) | 10.47 | Large inconsistency (>10%) | ↔ |
TSA, total shoulder arthroplasty; LSA, liner stability ratio; SMR, Systema Multiplana Randelli; PE, polyethylene; T.E.S.S, Total Evolutive Shoulder System.
Table VII.
Summary of liner stability ratio consistency and trends in the transverse axis (t1) across implant sizes within each anatomic total shoulder arthroplasty system.
| System | LSR % variation across sizes | Consistency assessment | LSR trend |
|---|---|---|---|
| Univers VaultLock (Arthrex) | 20.81 | Large inconsistency (>10%) | ↑ |
| ARAMIS (3S Ortho) | 19.86 | Large inconsistency (>10%) | ↑ |
| Global (Depuy Synthes) | 12.51 | Large inconsistency (>10%) | ↔ |
| AltiVate Anatomic (Enovis) | 6.7 | Slight inconsistency (>5-10%) | ↑ |
| Turon Shoulder System (Enovis) | 1.83 | Consistent (≤5%) | ↔ |
| UNIC (Evolutis) | 21.02 | Large inconsistency (>10%) | ↑ |
| Equinoxe 8° augmented (Exactech) | 31.89 | Large inconsistency (>10%) | ↑ |
| Equinoxe 16° augmented (Exactech) | 32.46 | Large inconsistency (>10%) | ↑ |
| Equinoxe Keeled Glenoid (Exactech) | 36.66 | Large inconsistency (>10%) | ↑ |
| Equinoxe Pegged Glenoid (Exactech) | 34.67 | Large inconsistency (>10%) | ↔ |
| Agilon (Implantcast) | 28.0 | Large inconsistency (>10%) | ↑ |
| SMR cemented (Lima) | 4.24 | Consistent (≤5%) | ↑ |
| SMR cemented 3 pegs (Lima) | 21.15 | Large inconsistency (>10%) | ↑ |
| SMR metal back (Lima) | 12.38 | Large inconsistency (>10%) | ↔ |
| SMR TT hybrid (Lima) | 10.53 | Large inconsistency (>10%) | ↑ |
| LINK Embrace (Link) | 18.33 | Large inconsistency (>10%) | ↑ |
| Affinis PE cemented (Mathys) | 17.26 | Large inconsistency (>10%) | ↑ |
| Affinis vitamys cemented (Mathys) | 23.07 | Large inconsistency (>10%) | ↑ |
| Affinis vitamys cementless (Mathys) | 20.47 | Large inconsistency (>10%) | ↑ |
| Medacta PE Glenoid (Medacta) | 6.18 | Slight inconsistency (>5-10%) | ↔ |
| ReUnion TSA (Stryker) | 7.23 | Slight inconsistency (>5-10%) | ↔ |
| Tornier Aequalis Perform (Stryker) | 15.61 | Large inconsistency (>10%) | ↔ |
| Anatomic Shoulder System (Zimmer Biomet) | 8.53 | Slight inconsistency (>5-10%) | ↔ |
| Bigliani/Flatow Shoulder System (Zimmer Biomet) | 11.09 | Large inconsistency (>10%) | ↔ |
| Comprehensive Total Shoulder System (Zimmer Biomet) | 33.41 | Large inconsistency (>10%) | ↑ |
| T.E.S.S Shoulder System (Zimmer Biomet) | 7.9 | Slight inconsistency (>5-10%) | ↔ |
| Zimmer Trabecular Metal Shoulder System (Zimmer Biomet) | 10.32 | Large inconsistency (>10%) | ↔ |
TSA, total shoulder arthroplasty; LSA, liner stability ratio; SMR, Systema Multiplana Randelli; PE, polyethylene; T.E.S.S, Total Evolutive Shoulder System.
Discussion
This study demonstrates considerable variability in jump height, radius of curvature, and the resulting LSR on both longitudinal and transversal axes across a range of commercially available aTSA systems. These variations reflect the underlying design differences between aTSA glenoid components and highlight the need for further investigation into their biomechanical implications.
Recently, Moroder et al20 applied a validated mathematical formula to calculate the LSR for all commercially available rTSA systems, given the reported high rate of postoperative instability17 and identified considerable variation in jump height and the corresponding degree of constraint both between different implant systems and within individual systems depending on liner design. Although the biomechanical principles of aTSA differ from those of rTSA, these findings prompted the authors to analyze the LSR of glenoid components designed for aTSA and interpret the results within the context of existing evidence in terms of implant performance and biomechanical behavior. While aTSA is typically classified as an ‘unconstrained’ prosthetic design, our findings—similar to those reported by Moroder et al20 in rTSA—demonstrate considerable variability in both jump height (concavity depth) and the resulting degree of constraint (quantified by LSR) across different implant systems as well as among configurations within the same system.
Even though the direct clinical implications remain to be established, variability in LSR may theoretically influence joint stability, distribution of forces across the glenoid component, and might facilitate progressive loosening driven by repetitive eccentric loading consistent with the rocking horse phenomenon. As identified in a recent systematic review,2 glenoid loosening constitutes the predominant indication for revision from aTSA to rTSA, and the influence of implant design on this failure mechanism remains an active area of research.
Given the manufacturer-specific variability in anatomical glenoid component design/shape, we standardized measurements at two defined planes along the transverse axis (Figs. 3 and 4): the level of maximal anteroposterior diameter (t1) and the midpoint level of the longitudinal axis (t2). Across most systems, slightly higher jump height and corresponding LSR values were observed at t1 compared to t2. However, in some components, the diameter at t1 was identical to that at t2, reflecting design uniformity along the transverse profile and resulting in comparable LSR values at both levels.
Instability (defined as static severe subluxation or dislocation as demonstrated by physical and radiographic examination)1 remains a prevalent and challenging complication in association with aTSA. Reported rates of instability vary across studies, with Wirth and Rockwood36 documenting horizontal instability in 5.2% of 1,496 total shoulder cases, while Kany et al14 observed an incidence of 3.57% in a cohort of 532 patients at three years postoperatively. Interestingly, the frequent association of superior instability with rotator cuff tears in aTSA,4,14 despite the relatively high LSR values observed in the longitudinal axis, may be explained by the fact that liner-generated stability may not fully compensate for the loss of rotator cuff function. Conversely, the relatively lower LSR values identified in the transverse axis may contribute to anterior-posterior instability, which has been reported at a prevalence of 1.9% in the meta-analysis by Bohsali et al4 These considerations remain theoretical and cannot be definitively validated within the scope of this study. Other recognized contributors to anterior-posterior instability following aTSA include subscapularis and rotator interval insufficiency in cases of anterior instability, and excessive glenoid retroversion, posterior capsular laxity, and humeral component malposition in cases of posterior instability.1 Furthermore, glenoid component inclination has a measurable impact on aTSA biomechanics. Knighton et al16 demonstrated that a 10° inferior tilt promotes joint distraction due to gravitational forces, in contrast to the compressive effect observed with superior inclination. However, superior inclination has also been associated with full-thickness rotator cuff tears and subsequent superior humeral head subluxation.24
In the present study, LSR values showed—as expected based on the underlying equation—a positive correlation with jump height in both the longitudinal and transverse axes (Fig. 5); however, jump height did not consistently scale with glenoid component size, as smaller components occasionally exhibited greater LSR values (Fig. 6).
Remarkably, the majority of implant systems demonstrated substantial size-dependent variability in LSR (Tables VI and VII). Only two systems exhibited consistent LSR values (≤5% variation) across sizes in both axes. Slight inconsistencies (>5% to ≤10%) were observed in three systems in the longitudinal axis and five systems in the transverse axis, while large inconsistencies (>10%) were observed in most remaining systems. These results suggest that dimensional scaling of glenoid components within some implant systems do not maintain proportional relationships between radius of curvature and jump height, ultimately affecting stability characteristics across sizes (Fig. 6). Ideally, the LSR should remain consistent across all component sizes within a given system; however, this was not observed. Based on these findings, it is advisable that surgeons are well-acquainted with the design-specific characteristics of their preferred aTSA system, including the associated LSR values. Implant size, defined by the glenoid component height and determined during preoperative planning, remains under the surgeon's discretion, whereas the jump height is predetermined by the manufacturer's design specifications and does not necessarily correlate with glenoid component size. This discrepancy makes the selection of the optimal implant configuration challenging.
In this context, it is important to note that only commercially available glenoid components were evaluated in this study, while the radius of curvature of the humeral counterparts was not considered. However, Ernstbrunner et al6 have recommended incorporating the ‘socket’ radius of curvature into the stability ratio calculation in cases of incongruent articulating surfaces, a situation that applies to most contemporary available implant designs. This recommendation is supported by their findings, demonstrating that using the glenoid concavity radius resulted in a mean relative difference of only 10% between calculated and experimentally measured stability ratios, whereas referencing the humeral head radius led to a substantially larger mean relative difference exceeding 40%.
Originally, Neer's prosthesis featured identical radii of curvature for both, the glenoid and humeral components22; however, this congruent design evolved in favor of increased mismatch to enhance range of motion. While increased radial mismatch permits greater humeral head translation across a relatively small articular surface, this biomechanical advantage is offset by potential drawbacks; enhanced translational freedom can exacerbate edge loading, accelerate polyethylene wear, increase the risk of glenoid component loosening, and contribute to joint instability.12,25,28,30,34 Biomechanical analyses have demonstrated that a radial mismatch between the humeral head and the glenoid of 4 mm in aTSA most accurately replicates native shoulder kinematics during simulated active elevation,15 whereas excessive mismatch beyond 10 mm results in significantly increased micromotion, with structural failure reported at 14 mm.25 Still, optimal mismatch parameters remain undefined, with conflicting evidence reported in the literature; Nho et al23 showed higher rates of component loosening with more conforming glenoid components. Furthermore, a computational modeling study by Hopkins et al11 demonstrated that increasing the contact surface in aTSA through reduced radial mismatch (ie, a more conforming design) resulted in decreased linear but increased volumetric polyethylene wear. These findings might suggest that also the degree of glenoid component constraint, reflected by LSR, may influence the wear pattern.
To our knowledge, this is the first study to systematically compare the LSR of glenoid components across a broad spectrum of commercially available aTSA systems. A key strength of this study lies in its comprehensive, system-wide comparison of glenoid components' stability ratio. By directly measuring both jump height and radius of curvature, and applying a standardized LSR calculation across all designs, we provide objective, quantifiable insight into the stability-related characteristics of these implants. Nevertheless, certain limitations should be acknowledged. First, not all glenoid components of aTSA systems were available in the planning software. Second, the reported LSR values are based on theoretical geometric calculations and do not incorporate physiological factors such as joint surface friction or the direction and magnitude of muscular and capsular force vectors. Further investigation is required to clarify the biomechanical significance and clinical relevance of LSR variability in aTSA.
Conclusion
This study demonstrates considerable variability in LSRs across different aTSA systems and glenoid component sizes. Although higher jump heights generally correlated with increased LSR, this relationship was inconsistent across implant sizes. While the direct clinical implications remain to be fully established, variations in LSR may influence joint stability, glenoid component wear, and the risk of loosening secondary to the rocking horse phenomenon. Further studies are needed to clarify the biomechanical and clinical consequences of LSR variations in aTSA.
Disclaimers:
Funding: No funding was disclosed by the authors.
Conflicts of interest: Philipp Moroder serves as a consultant, receives royalties and fellowship support from Arthrex, is a shareholder and receives royalties from Alyve Medical, is a shareholder of Kairos Medical and Zurimed, is a patent coapplicant with Johnson & Johnson, and receives royalties from Medacta and Medi. Patric Raiss, MD serves as a consultant and receives royalties from Arthrex. The other authors, their immediate family, and any research foundation with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.
Footnotes
Institutional review board approval was not required for this study as it did not involve human participants, identifiable personal data, or animal subjects.
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