Abstract
Shoulder function is important in patients who underwent reverse shoulder prosthesis surgery for cuff tear arthropathy in the postoperative period to implement their daily routines. Therefore, we aimed to predict the repairability of the subscapularis tendon in reverse shoulder arthroplasty by looking at the radiological findings. A total of 107 shoulders of 101 patients were examined retrospectively. Preoperative and postoperative shoulder AP radiographs of the patients were evaluated according to acromiohumeral distance, lateral humeral offset, acromiohumeral distance difference, lateral humeral offset difference, Hamada classification, and rotator cuff Goutallier staging. The subscapularis tendon could not be repaired in 31 (28.97%) of 107 shoulders and could not be repaired in 13 of 17 patients who used an onlay prosthesis. There was no significant correlation between preoperative Hamada staging, preoperative lateral humeral offset and lateral humeral offset difference, and subscapularis repair (p < 0.05). Preoperative and postoperative acromiohumeral distance cut-off values were found to be 0.59 and 3.22 cm, respectively. A statistically significant correlation was found in terms of preoperative acromiohumeral distance, postoperative acromiohumeral distance, acromiohumeral distance difference, Goutallier stage with the repair of subscapularis tendon. Fatty atrophy in rotator cuff muscles and distalization of the humerus can be considered as negative predictive values in terms of repairability of the subscapularis tendon.
Keywords: Acromiohumeral distance, lateral humeral offset, radiological findings, reverse shoulder prosthesis, shoulder, subscapularis repair
Introduction
Reverse shoulder arthroplasty (RSA) has become a mainstay in the treatment of rotator cuff arthropathy. Postoperative improvement in shoulder flexion and abduction is expected in RSA, however efforts must be made to have functional internal rotation because it is often constrained. 1 Internal rotation is necessary for washing the back in the bathroom, closing the bra for women, taking the wallet from the back pocket for men, and toilet hygiene. 2
It has been studied many times to date that factors related to surgery and the chosen implant can affect the functional outcome of RSA. Lateralization of the center of rotation (COR), inferior positioning of the baseplate, decreased glenosphere size, decreased humeral insert thickness, a neck shaft angle of < 155°, an intact subscapularis (SSC) and a humeral retroversion < 20 are positively associated with an internal rotation function. 3
Subscapularis repair after RSA remains a controversial topic in the literature. Werner et al. 4 argue that subscapularis repair will increase the anterior stability of the reverse shoulder prosthesis and contribute to functional internal rotation. It is not always possible to repair the subscapularis tendon in the same tension as the vectors of the muscles will alter depending on the size of the prosthesis chosen. However, a taut subscapularis repair may reduce the external rotation function of the antagonist teres minor. 5 Therefore, making the decision to repair the subscapularis tendon requires a great deal of experience and mastery. Friedman et al. 6 could not successfully repair the subscapularis tendon because the onlay prosthesis they used in their study distalized the humerus. In this study, prosthesis design obviates the question of subscapularis repair for the purposes of joint stability. The proposed mechanism is lateralization of the humeral component, which increases the stability of the deltoid and rotator cuff tension. 6 Our aim in this study is to explain the predictability of the subscapularis tendon repair by looking at preoperative and postoperative shoulder radiographic parameters regardless of the size of the prosthesis.
Material and methods
Patients who underwent RSA surgery for cuff tear arthropathy in our institution between 2015 and 2022 are included in the study. Patients with unrepairable rotator cuff tear and proximal humeral fractures who underwent reverse shoulder replacement surgery are excluded from the study. This study was evaluated and approved by the ethics committee of our institution.
In total, 107 shoulders of 101 patients were examined. Two different reverse shoulder prostheses were applied. Inlay reverse shoulder prosthesis is applied to 90 (84.11%) shoulders and onlay reverse shoulder prosthesis is applied to 17 (15.89%) shoulders of the patients. All patients had standard shoulder anteroposterior (AP) radiographs.
When evaluating patients radiographically in the study, an effort was made to see the standard shoulder AP view. AP images were obtained with the patient in a standing upright position, with the coronal plane of the body parallel to the tape and the arm in a neutral position. The standard AP view of the shoulder shows the glenohumeral joint in its natural anatomical position. In the AP view, there should be a superposition of the humeral head over the glenoid rim. It also images the entire clavicle, AC joint, scapula, upper ribs, SC joint, and proximal humerus. Additionally, the lateral border of the scapula and the medial cortex of the proximal humerus form a soft, smooth convex arch known as the arch of Moloney. All films that did not meet these criteria were removed by the observers. 7
Preoperative and postoperative AP shoulder radiographs of the patients are evaluated according to acromiohumeral distance (AHD), lateral humeral offset (LHO), AHD difference, LHO difference, Hamada classification, 8 and rotator cuff Goutallier staging. 9 Radiographic evaluation was performed by two independent viewers blinded to the outcomes. Preoperative and postoperative VAS (Visual Analogue Scale), Constant-Murley, and ASES (American Shoulder and Elbow Surgeons) scores of the patients were measured. At the same time, active abduction, flexion, external rotation, and internal rotation were evaluated. Internal rotation was measured by vertebral segments and was scored by the following discrete assignment: 0 degrees, 0; hip, 1; buttocks, 2; sacrum, 3; L4 to L5, 4; L1 to L3, 5; T8 to T12, 6; and T7 or higher, 7.
Radiological assessment
AHD was measured as the distance from the acromion undersurface to the greater tuberosity in centimeters (in line with the humeral shaft) (Figure 1). 10 LHO was measured as the distance from the glenoid to the greater tuberosity in centimeters (parallel to glenoid or baseplate) (Figure 2). 10 The medialization of the COR was measured as the distance from the base of the coracoid (center of the ellipse) to the COR of the humeral head (preoperatively) or the COR of the glenosphere (postoperatively) (Figure 3). 10 The difference between the preoperative and postoperative AHD, LHO, and COR values of the patients are calculated as the “difference.”
Figure 1.
Preoperative and postoperative acromiohumeral distance (AHD).
Figure 2.
Preoperative and postoperative lateral humeral offset (LHO).
Figure 3.
Preoperative and postoperative center of rotation (COR) measurement.
Statistical analysis
The sample size required for the study depends on the AHD in the repaired and unrepaired groups according to the difference. Accordingly, for the d = 0.8 effect size value, which shows a large effect, the sample was sampled with the t-test in independent groups at 80% power and 0.05 significance level. When the calculation is made, the sample size required for this study is 26 in each group and 52 in total. GPOWER 3.1 was used for the sample size. 11
For statistical analysis, the StataMP13 (StataCorp. Stata Software:Release 13) program was used. Shapiro–Wilk test was used for normality analysis. Numerical variables showing normal distribution were given as mean ± standard deviation values, and variables not showing normal distribution were presented as median (minimum–maximum) values. Categorical variables were expressed as numbers (n) and percentages (%). Chi-square and Fisher's exact tests were used for categorical variables. T-test for parametric data, Mann–Whitney U for non-parametric data in pairwise group comparisons. A value of p < 0.05 was accepted as statistically significant.
Results
Of the 101 patients, 22 (20.56%) are male and 79 (73.83%) are female, and the mean age of the patients is 74.21 ± 7.6. Ninety-two of 107 shoulders (85.98%) are the dominant side of the patient (Table 1).
Table 1.
The baseline characteristics of the patients in the study.
| RS (mean) | US (mean) | |
|---|---|---|
| Shoulders | 76 (71%) | 31 (29%) |
| Gender (male/female) | 16 (72.7%)/60 (70.6%) | 6 (27.3%)/25 (29.4%) |
| Age | 73.32 ± 7.36 | 76.38 ± 7.79 |
| Dominant side (right/left) | 68 (70.1%)/8 (80%) | 29 (29.9%)/2 (20%) |
| Operated side (right/left) | 58 (71.6%)/18 (69.2%) | 23 (28.4%)/8 (30.8%) |
RS: repaired subscapularis; US: unrepaired subscapularis; SD: standard deviation.
The decision to repair the subscapularis during surgery was made by the treating physician based on the quality of the existing tendon and whether the repair could be performed without excessive tension. In patients who underwent subscapularis repair, the SSC tendon was first removed with a peeling technique and repaired at the end of the surgery with the continued locking loop no: 2 FiberWire which was passed through the bone tunnels opened into the bicipital groove. Subscapularis tendon cannot be repaired in 31 (29%) of a total of 107 shoulders.
Subscapularis tendon could not be repaired in 13 of 17 patients (76.5%) in whom onlay prosthesis is used and repaired in four patients (23.5%) (Table 2). The repairability of the subscapularis in the onlay prosthesis was found to be significantly lower than the inlay prosthesis (p < 0.05).
Table 2.
Repairability of the subscapularis muscle according to the type of prosthesis used.
| Inlay/onlay | UR | RS | Total | p value |
|---|---|---|---|---|
| Inlay | 18 (20%) | 72 (80%) | 90 (100%) | |
| Onlay | 13 (76.5%) | 4 (23.5%) | 17 (100%) | |
| Total | 31 (29%) | 76 (71%) | 107 (100%) | |
| <0.001 |
RS: repaired subscapularis; US: unrepaired subscapularis.
No significant correlation was found between preoperative Hamada grade, preoperative and postoperative LHO, and LHO difference and subscapularis repair (Tables 3 and 4). A statistically significant correlation is found in terms of preoperative and postoperative AHD, AHD difference, AHD cut-off values, Goutallier staging of grade ≥ 2, and the repair of subscapularis tendon (p < 0.05) (Tables 3, 5 and 6). Liu method was used to determine the AHD cut-off values. The cut-off values of the preoperative and postoperative AHD are calculated as 0.59 and 3.22 cm, respectively. The AHD difference cut-off value was 2.12 cm.
Table 3.
Results of preop and postop X-ray measurements.
| RS | US | p value | |
|---|---|---|---|
| AHD (preop) | 1.17 ± 0.65 | 0.815 ± 0.73 | 0.014 |
| AHD (postop) | 3.37 ± 0.81 | 3.94 ± 0.78 | 0.001 |
| LHO (preop) | 4.5 (min: 3.66, max: 6.2) | 4.5 (min: 3.3, max: 6.2) | 0.716 |
| LHO (postop) | 4.7 (min: 4, max: 6.02) | 4.9 (min: 4.14, max: 6.04) | 0.069 |
| COR (preop) | 5.45 (min: 4.19, max: 7.3) | 5.6 (min: 4.3, max: 7.46) | 0.496 |
| COR (postop) | 3.18 ± 0.51 | 2.72 ± 0.67 | 0.001 |
| AHD difference | 1.55 (min: 0.12, max: 5.3) | 2.71 (min: 1.29, max: 4) | 0.006 |
| LHO difference | 0.25 ± 0.61 | 0.47 ± 0.68 | 0.272 |
| COR difference | 2.31 ± 0.74 | 2.77 ± 1.11 | 0.162 |
RS: repaired subscapularis; US: unrepaired subscapularis; SD: standard deviation; min: minimum; max: maximum; AHD: acromiohumeral distance; LHO: lateral humeral offset; COR: center of rotation.
Table 4.
Hamada classification of patients according to preop X-ray images.
| Hamada classification | US | RS | Total | p value |
|---|---|---|---|---|
| 3 | 0 (0%) | 4 (100%) | 4 (3.7%) | |
| 4A | 4 (25%) | 12 (75%) | 16 (15%) | |
| 4B | 18 (30.5%) | 41 (69.5%) | 59 (55.1%) | |
| 5 | 9 (32.1%) | 19 (67.9%) | 28 (26.2%) | |
| Total | 31 (29%) | 76 (71%) | 107 (100%) | |
| 0.631 |
RS: repaired subscapularis; US: unrepaired subscapularis.
Table 5.
Goutallier classification of patients according to preop MRI.
| Goutallier classification | US | RS | Total | p value |
|---|---|---|---|---|
| Grade 0 | 2 (16.7%) | 10 (83.3%) | 12 (11.2%) | |
| Grade 1 | 8 (15.7%) | 43 (84.3%) | 51 (47.7%) | |
| Grade 2 | 17 (47.2%) | 19 (52.8%) | 36 (33.6%) | |
| Grade 3 | 4 (50%) | 4 (50%) | 8 (7.5%) | |
| Total | 31 (31%) | 76 (76%) | 107 (100%) | |
| 0.002 |
MRI: magnetic resonance imaging; RS: repaired subscapularis; US: unrepaired subscapularis.
Table 6.
Goutallier classification of patients divided into two groups according to preop MRI.
| Goutallier classification | US | RS | p value |
|---|---|---|---|
| Group 1 | 10 (15.9%) | 53 (84.1%) | |
| Group 2 | 21 (47.7%) | 23 (52.3%) | |
| <0.001 |
MRI: magnetic resonance imaging; RS: repaired subscapularis; US: unrepaired subscapularis.
Group 1 contains Goutallier grades 0 and 1.
Group 2 contains Goutallier grades 2, 3, and 4.
In this study, VAS, ROM, and functional scores were examined in two different groups as inlay and onlay prosthesis. Preoperative to postoperative internal rotation difference was slightly better in the repaired inlay group, and this difference was significant in statistical analysis (p < 0.001). When the onlay group was examined, repairing the subscapularis did not affect any outcome or range of motion (Table 7).
Table 7.
Comparison of joint range of motion and functional scores of patients who used inlay and onlay prosthesis in patients with and without repaired subscapularis muscle.
| RS | US | p value | ||
|---|---|---|---|---|
| Inlay | VAS (preop) | 9 (min: 7, max: 10) | 9 (min: 8, max: 10) | 0.737 |
| VAS (postop) | 4 (min: 1, max: 6) | 4 (min: 1, max: 6) | 0.557 | |
| Constant-Murley (preop) | 29 (min: 10, max: 38) | 23 (min: 10, max: 38) | 0.606 | |
| Constant-Murley (postop) | 58 (min: 39, max: 69) | 53 (min: 39, max: 66) | 0.076 | |
| ASES (preop) | 25 (min: 3, max: 37) | 26.5 (min: 3, max: 37) | 0.899 | |
| ASES (postop) | 55 (min: 37, max: 67) | 49 (min: 37, max: 65) | 0.14 | |
| Flexion (postop) | 115.08 ± 17.7 | 110.27 ± 15.28 | 0.294 | |
| Abduction (preop) | 65 (min: 30, max: 105) | 80 (min: 45, max: 95) | 0.024 | |
| Abduction (postop) | 105 (min: 70, max: 140) | 120 (min: 100, max: 140) | 0.002 | |
| Internal rotation (preop) | 3 (min: 1, max: 7) | 3 (min: 1, max: 5) | 0.541 | |
| Internal rotation (postop) | 5 (min: 3, max: 7) | 4.5 (min: 3, max: 6) | 0.004 | |
| External rotation (preop) | 10 (min: 0, max: 50) | 20 (min: 10, max: 40) | <0.001 | |
| External rotation (postop) | 45 (min: 20, max: 65) | 50 (min: 20, max: 75) | 0.107 | |
| Abduction (difference) | 40 (min: 15, max: 90) | 50 (min: 5, max: 65) | 0.211 | |
| Internal rotation (difference) | 2 (min: 0, max: 5) | 1 (min: 0, max: 2) | <0.001 | |
| External rotation (difference) | 35 (min: −15, max: 55) | 27.5 (min: −10, max: 60) | 0.285 | |
| Flexion (difference) | 25.33 ± 25.19 | 25.72 ± 21.32 | 0.952 | |
| Onlay | VAS (preop) | 10 (min: 9, max: 10) | 9 (min: 8, max: 10) | 0.079 |
| VAS (postop) | 4 (min: 2, max: 5) | 4 (min: 2, max: 5) | 0.999 | |
| Constant-Murley (preop) | 22 (min: 10, max: 32) | 30 (min: 12, max: 38) | 0.245 | |
| Constant-Murley (postop) | 41 (min: 39, max: 49) | 62 (min: 42, max: 69) | 0.006 | |
| ASES (preop) | 8 (min: 3, max: 18) | 30 (min: 7, max: 37) | 0.003 | |
| ASES (postop) | 42 (min: 37, max: 53) | 58 (min: 42, max: 65) | 0.01 | |
| Flexion (postop) | 107.5 (min: 95, max: 115) | 120 (min: 95, max: 145) | 0.163 | |
| Abduction (preop) | 80 (min: 75, max: 90) | 75 (min: 40, max: 105) | 0.35 | |
| Abduction (postop) | 127.5 (min: 125, max: 135) | 120 (min: 80, max: 135) | 0.079 | |
| Internal rotation (preop) | 3.5 (min: 2, max: 6) | 3 (min: 1, max: 4) | 0.549 | |
| Internal rotation (postop) | 5.5 (min: 5, max: 7) | 5 (min: 3, max: 6) | 0.079 | |
| External rotation (preop) | 10 (min: 5, max: 15) | 20 (min: 5, max: 30) | 0.079 | |
| External rotation (postop) | 42.5 (min: 40, max: 50) | 50 (min: 35, max: 65) | 0.202 | |
| Abduction (difference) | 47.5 (min: 45, max: 50) | 45 (min: 20, max: 60) | 0.624 |
RS: repaired subscapularis; US: unrepaired subscapularis; min: minimum; max: maximum; VAS: Visual Analogue Scale; ASES: American Shoulder and Elbow Surgeons.
Discussion
There are some studies in the literature evaluating the radiological parameters and outcomes of reverse shoulder prostheses. In the study of Jeon and Rhee, 12 only postoperative LHO was found to be a significant risk factor for postoperative poorly active anterior elevation. Although postoperative LHO is necessary for functional internal rotation, it was not found to be an important radiographic parameter in terms of repairability of the subscapularis in our study. Engel et al. 13 evaluated patients with and without subscapularis repair in reverse shoulder prosthesis in terms of postoperative ultrasound imaging and functional scores. Subscapularis tendon repair in reverse shoulder prosthesis improves Constant score (CS) and internal rotation 12 months after surgery. It is known that subscapularis refixation can result in good functional internal rotation and a good shoulder score.13,14 In our study, we do not know whether the subscapularis tendon healed or not, since no imaging control was performed. It should be kept in mind that external rotation may be restricted with a taut subscapularis repair, as well. Internal rotation is good and external rotation is weak, which is not desirable for the patient.
Therefore, we started by investigating a radiographic value that could predict our desire to refix the subscapularis. This article is the first in the literature to evaluate the repairability of the subscapularis with radiological findings.
Ackland et al. 15 in a cadaver study showed that subscapularis is the strongest internal rotator of all shoulder muscles and internal rotation strength increased with arm abduction. RSA implantation converts the subscapularis to a functional adductor and internal rotator and potentially limits external rotation. The significance of the subscapularis in internal rotation should not be underestimated. Implant design can greatly influence the functional role of the subscapularis. If we evaluate the SSC according to the prosthesis design, the onlay type prosthesis, with a larger glenosphere and a higher head-neck shaft angle, the offset increases, and the tension of the SSC also increases, this leads to improved stability and internal rotation, but also potentially limits external rotation. 16
The onlay prosthesis design eliminates the problem of subscapularis repair for joint stability. The mechanism that increases stability here is the lateralization of the humeral component, which increases deltoid and rotator cuff tension. 17
In this study, we predicted the ability of tension-free repair of the subscapularis tendon by examining X-ray and magnetic resonance imaging (MRI) films regardless of the implant design.
Compared to the inlay, the onlay prosthesis makes subscapularis repair more difficult because of lateralization of the greater tuberosity. A biomechanical study with a lateralized prosthesis with SSC repair showed that an increased force of 262%–460% was required to maintain external rotation with the abduction of the arm. 18
These findings raise the concern that subscapularis repair in patients treated with a lateralized design may not only have a beneficial effect but may actually be harmful. Therefore, unlike the inlay prosthesis, the authors do not make a special effort for SSC refixation in the onlay prosthesis design. For these reasons, X-ray measurements can be ignored in onlay prosthesis design.
For onlay prosthesis rather than a forced repair good positioning of the implants and proper soft tissue tensioning may be of more importance. 14
Hasegawa et al. 19 published the results of a study in which they examined the underlying rotator cuff pathology with the Hamada grade. In Hamada 3, the rate of subscapularis tear concomitant with posterosuperior cuff tear increased. In Hamada 4 and 5, progression of fatty degeneration is detected in the subscapularis muscle. In our study, no significant relationship was found between Hamada grade and the subscapularis repair.
Monroe et al. 20 examined the relationship between subscapularis repair results and rotator cuff fatty infiltration. As a result, if the quality of the infraspinatus muscle is poor in patients who underwent arthroscopic subscapularis repair, the patient-reported outcomes are also poor. In our study, subscapularis cannot be repaired in patients with Goutallier stage ≥ 2 fatty degeneration. In fact, there is no need to force repair in Goutallier stage ≥ 2, as the repair will not work.
Today, it is known that lateralization improves active external rotation (AER) and distalization improves active arm elevation in RSA. 21 Less preoperative to postoperative distalization of the greater tuberosity is a risk factor for poor postoperative functional internal rotation after RSA. 1 We had difficulty in repairing the subscapularis as the distalization increased. Lateralization, which is the most important factor in RSA today, did not affect the repairability of the subscapularis tendon. Perhaps these two variables together compromise the tendon repair by altering the subscapularis vector. Any shoulder surgeon does not want to limit AER by performing a taut subscapularis repair.
Boileau et al. 22 found that 10 patients who underwent RSA using a 155° prosthesis with an intact subscapularis preoperatively had a positive belly press test at follow-up, indicating subscapularis insufficiency. These outcomes are because of poor healing of the subscapularis or displacement of the humerus inferiorly relative to the scapula, increasing the tension on the repaired subscapularis tendon. Therefore, it is useful to repair the subscapularis tendon, which has a healing potential.
Actually, the results vary depending on the prosthesis design between the repaired and unrepaired groups. While repairing SSC in an onlay prosthesis does not have a positive effect on the results, repairing SSC in an inlay prosthesis results in better functional internal rotation. Considering the patient's functionality in daily activities, repairing SSC increases patient satisfaction and results in slightly better functional scores. Friedman et al. 6 observed slight improvement in the SSC repair group, especially in internal rotation similar to this study. We also did not find any deterioration in abduction and external rotation in patients with SSC repair in this study.
Friedman et al. 6 demonstrated comparable stability in the repair and nonrepair groups. Unlike other studies, no instability was encountered as a result of unrepairing SSC in the inlay prosthesis. This situation can be explained by the fact that the stability weakened by unrepairing the SSC was replaced by meticulous implant sizing. In our study, work on instability was not possible since there was no dislocation in any of the cases during postoperative follow-ups. We believe that positioning of the prosthesis and soft tissue tensioning is more important than the integrity of the subscapularis in the development of undesirable instability.
In the onlay prosthesis group of 17 patients, the physician repaired the SSC in four patients. In this repaired group, functional scores were slightly worsened and the ROM was narrowed. Even this result may make a positive contribution to the literature in favor of unrepairing SSC in onlay prosthesis designs.
The retrospective nature of the study and the small number of samples can be counted as the limitations of this study. In our study, there is no “belly press” test, which is a physical examination finding, no ultrasound or MRI findings showing biological healing, or an EMG finding showing innervation of the SSC. The only valuable finding we have is the functional internal rotation, which increased statistically significantly in the inlay prosthesis design in the SSC repaired group. We did not investigate where and how the subscapularis tendon was repaired to bone or whether the repaired tendon was biologically healed.
Conclusion
There are many retrospective studies on the management of the SSC tendon in reverse shoulder prosthesis, but there is no study on radiology and repair.
Goutallier stage ≥ 2 fatty atrophy in the rotator cuff and distalization of the humerus can be considered as negative predictive radiological parameters in terms of subscapularis tendon repair. As a result, if a choice is made to repair the subscapularis for RSA, more lateralized but less distalized components will contribute to better functional internal rotation and anterior stability.
Acknowledgements
There is no acknowledgement.
Footnotes
Contributorship: Uğur Bezirgan: wrote the paper, collected, and interpretation the data. Yener Yogun: performed the analysis, collected, and interpretation the data. Orhun Eray Bozkurt: performed the analysis, collected the data, and wrote the paper. Ebru Dumlupinar: performed the analysis and statistics. Mehmet Armangil: performed the analysis, collected, and interpretation the data.
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Ethical approval: We obtained ethical approval from the review board of Ankara University Faculty of Medicine (No. 2022000558-1).
Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.
ORCID iD: Orhun Eray Bozkurt https://orcid.org/0000-0003-1164-3098
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