Abstract
A total of 297 patients who classified as subscapularis (SC) tears through arthroscopic evaluation were retrospectively enrolled, and Fifty-seven patients with impingement syndrome were also enrolled as the control group for normal-population comparison. The coracohumeral distance (CHD) and humeral head anterior translation (HHAT) were measured on magnetic resonance imaging. Our study demonstrated that the anterior translation of the humeral head is related with a decrease in the coracohumeral distance in subscapularis tear. Although, correlation between radiologic parameters (coracohumeral distance and anterior translation of the humeral head) and severity of subscapularis tear was note detected.
Level of evidence
Level IV, retrospective study.
Keywords: Rotator cuff, Subscapularis, Coracohumeral distance
Abbreviations: SC, subscapularis; HHAT, by humeral head anterior translation; CHD, coracohumeral distance; MRI, magnetic resonance imaging
1. Introduction
Although the etiology of degenerative subscapularis (SC) tears is uncertain, intrinsic tendon degeneration is a mechanism of SC tear pathogenesis.1, 2, 3, 4, 5, 6 In 2003, Lo and Burkhart3 suggested that SC tears can result from tensile failure by the roller-wringer effect at the coracoid tip on the axial plane.3 Subcoracoid impingement is another pathogenesis of SC tear, and several studies have noted a relationship between SC tears and a decreased coracohumeral distance (CHD).1, 2, 3, 4, 5 In an effort to explain the etiology of subscapularis tears, research has investigated whether subcoracoid stenosis, a gap of less than 6 mm between the coracoids and the humeral head is associated with partial- or full-thickness tears of the SC tendon.7,8 However, subcoracoid stenosis is also related to rotator cuff insufficiency which can produce a humeral head anterior translation (HHAT), because the HHAT leads to a decrease in the CHD.9,10 Lafosse et al.11 defined the most severe SC tear as complete subscapularis tear with anterior subluxation of the humeral head.
However, it is unknown whether the stenotic subcoracoid space is an outcome of the SC tear or a cause of tear.3,4,12 Analyses of the relationship between an anterior translation of the humeral head and subcoracoid stenosis is limited. Thus, this study aimed to evaluate the relationship between SC tear, HHAT and CHD. We hypothesized that the severity of subscapularis tear would be associated with HHAT and CHD.
2. Methods
Following receipt of institutional review board exemption (DKUH 2020-02-011), a total of 297 patients aged over 40 years diagnosed with SC tears through an arthroscopic evaluation were retrospectively enrolled between 2016 and 2019. Fifty-seven patients with normal rotator cuff tendons and muscles on magnetic resonance imaging (MRI) were enrolled as the control group. Subjects who had a record of previous surgery on the affected shoulder, combined supraspinatus or infraspinatus tears >1 cm, osteoarthritis, tumors, severe deformity of the glenoid and humerus, and faulty radiologic images were excluded from this study (Fig. 1). Patient information including age, sex, height, dominant hand, body mass index, weight, level of work activity, and smoking history were obtained from the medical records.
Fig. 1.
Study flow diagram.
2.1. Radiologic measurement protocol
A standard MRI shoulder protocol was applied for each patient, includingT1-and T2-weighted fat-saturated images with the arm in a neutral position. MRI was performed at our institution's radiology department on a 3.0 T system (Ingenia 3.0 T; Philips, Houston, TX, USA) applied with the same protocol used for each patient. The MRI protocol included obtaining proton density- and T2-weighted oblique-coronal fat-saturated spin-echo images (3300/14–95 [repetition time, ms/echo time, ms]; section thickness, 3 mm; intersection gap, 0.8 mm; field of view, 16 cm), T1-weighted oblique-coronal fat-saturated spin-echo images (777/12 [repetition time, ms/echo time, ms]; section thickness, 3 mm; intersection gap, 0.6 mm; field of view, 16 cm), T1-weighted oblique-sagittal spin-echo images (600/12 [repetition time, ms/echo time, ms]; section thickness, 3 mm; intersection gap, 1.2 mm; field of view, 16 cm), and T1-weighted transverse spin-echo images (600/12 [repetition time, ms/echo time, ms]; section thickness, 3 mm; intersection gap, 0.9 mm; field of view, 16 cm).
The CHD was measured as described by Kim et al.6 on transverse sections of T2-weighted images to make use of their better definition of the cortical margins. One line was drawn tangential to the cortical margin of the humeral head and the second parallel to this and tangential to the cortical margin of the coracoid process. The distance between these two parallel lines was considered to be the CHD (Fig. 2A). HHAT was determined by measuring the shortest distance of the center of rotation of the humeral head, defined by the midpoint of the best-fit circle, to a line parallel to the tangential line to the cortical margin of the humeral head and across the midpoint of the glenoid line (Fig. 2B).
Fig. 2.
(A) Measurement of the coracohumeral distance. Two parallel lines are drawn as close as possible to each other; one is tangential to the cortical margin of the humeral head, and the other is tangential to the coracoid process. The distance between these two parallel lines is the coracohumeral distance. (B) Measurement of the humeral head anterior translation. It was determined by measuring the shortest distance of the center of rotation of the humeral head, defined by the midpoint of a best-fit circle, to a parallel line to the tangential line to the cortical margin of the humeral head and across the midpoint of the glenoid line.
All measurements were independently calculated by two orthopedic surgeons (M.G.K. and J.S.Y) at two different times 1 month apart. The observers were blinded to each other's measurements and group identities. The intra-observer and inter-observer reliability scores for CHD and HHAT measurements were in almost perfect agreement (Table 1). The mean value of duplicate measurements was used as the representative value.
Table 1.
Reliability of radiologic parameters.
| Radiologic parameters | ICC (JSY vs JSY) | ICC (MGK vs MGK) | ICC (JSY vs MGK) |
|---|---|---|---|
| Coranco-humeral distance | 0.91 | 0.89 | 0.86 |
| Humeral head anterior translation | 0.92 | 0.91 | 0.88 |
ICC, Intraclass correlation coefficient; JSY vs JSY and MGK vs MGK, intraobserver variation test; JSY vs MGK, interobserver variation test.
2.2. Arthroscopic evaluation and SC classification
SC tears were evaluated in accordance with the intraoperative SC findings using 30° and 70° arthroscopes from the posterior portal of the glenohumeral joint and subacromial space. Minimal fraying of the articular side of the SC was considered an intact SC, and SC tears were described as by Lafosse et al.11 The SC tears were classified by two shoulder surgeons (J.B.S. and J.S.Y.), and the arthroscopic findings were repeatedly interpreted by a consensus readout of another blinded observer (M.G.K.). The shoulder surgeons (J.B.S. and J.S.Y.) were considered the primary assessors, and the evaluation by another observer (M.G.K.) was used to assess the interobserver correlation. The interobserver correlations mostly had perfect agreement (J.B.S. vs. M.G.K., 0.84; J.S.Y. vs. M.G.K., 0.81).
2.3. Statistical methods
Intergroup differences in age, sex, dominant hand, height, body mass index, weight, CHD, and HHAT were examined using the independent t-test. Differences in sex, dominant arm, smoking, and level of work activity were compared using Pearson's chi-square test. The weighted kappa coefficient was used to evaluate the inter-observer and intra-observer reliability for the CHD and HHAT measurements. Reliability was classified in accordance with the kappa coefficients: “slight agreement,” 0.00–0.20; “fair agreement,” 0.21–0.40; “moderate agreement,” 0.41–0.60; “substantial agreement,” 0.61–0.80; and “almost perfect agreement,” 0.81–1.00. Within SC tears, differences in radiologic parameters according to the Lafosse criteria11  were examined with the Kruskal–Wallis test using the Mann–Whitney U test. Spearman's correlation coefficient was used to estimate the correlation between CHD and HHAT. All statistical analyses were performed using SPSS version 25.0 (SPSS Inc., Chicago, IL, USA). Statistical significance was set at p < 0.05.
3. Results
Of the 354 patients included in this study, 297 had SC tears (SC tear group), while the remaining 57 did not (control group). The basic demographic data showed no statistically significant differences among groups except in age and level of work activity (Table 2).
Table 2.
Demographic data.
| Subscapularis tear group (n = 297) | Control group (n = 57) | p- value | |
|---|---|---|---|
| Age (Mean ± SD) | 57.8 ± 8.4 | 51.3 ± 9.8 | <0.001 |
| Sex (Male/Female) | 200/97 | 41/16 | 0.173 |
| Dominant arm/Non-dominant arm | 166/131 | 31/26 | 0.132 |
| Weight (kg, Mean ± SD) | 66.7 ± 10.1 | 67.2 ± 12.4 | 0.380 |
| Height (cm, Mean ± SD) | 163.3 ± 8.9 | 166.2 ± 9.0 | 0.783 |
| Body mass index (Mean ± SD) | 24.8 ± 2.7 | 24.3 ± 3.5 | 0.589 |
| Level of work activity, high:medium or low | 177/120 | 11/46 | <0.001 |
| Smoking/Non-smoking | 88/209 | 19/38 | 0.841 |
The mean CHD was 8.10 ± 1.34 mm in the SC tear group and 9.91 ± 2.04 mm in the control group. The CHD of the SC tear group was significantly lower than that of the control group (Table 3; P < 0.001). The mean HHAT was 0.58 ± 1.43 mm in the SC tear group and 0.26 ± 1.39 mm in the control group. The HHAT of the SC tear group was significantly larger than that of the control group (Table 3; P = 0.036).
Table 3.
Comparison of radiologic parameters between two groups.
| Subscapularis tears group (n = 297) | Control group (n = 57) | p- value | |
|---|---|---|---|
| Coraco-humeral distance (mm) | 8.10 ± 1.34 | 9.91 ± 2.04 | <0.001 |
| Humeral head anterior translation (mm) | 0.58 ± 1.43 | 0.26 ± 1.39 | 0.036 |
None of the radiologic parameters showed statistically significant differences according to the Lafosse classification11 in the SC tear group (Table 4). However, CHD had statistically significant negative correlation with HHAT (correlation coefficient = −0.541, p = 0.016), while CHD (correlation coefficient = 0.132, p = 0.127) and HHAT (correlation coefficient = 0.174, p = 0.361) had no statistically significant correlation with Lafosse classification (Table 5).
Table 4.
Radiologic parameters according to the Lafosse classification.
| Type 1 (n = 136) | Type 2 (n = 93) | Type 3 (n = 37) | Type 4 (n = 31) | p- value | |
|---|---|---|---|---|---|
| Coraco-humeral distance (mm) | 7.68 ± 1.40 | 8.35 ± 2.05 | 9.13 ± 1.38 | 7.94 ± 2.39 | 0.382 |
| Humeral head anterior translation (mm) | 0.31 ± 1.53 | 0.39 ± 1.32 | 1.11 ± 1.07 | 0.74 ± 1.40 | 0.226 |
Table 5.
Correlation of Radiologic parameters and Lafosse classification.
| Correlation coefficient | p- value | |
|---|---|---|
| Coraco-humeral distance vs Humeral head anterior translation | −0.541 | 0.016 |
| Lafosse classification vs Coraco-humeral distance | 0.132 | 0.127 |
| Lafosse classification vs Humeral head anterior translation | 0.174 | 0.361 |
4. Discussion
This is the first study to show associations between SC tears, HHAT, and CHD. As we hypothesized, SC tears showed large HHAT and low CHD values than those of the control group; moreover, large HHAT values were associated with low CHD values. However contrary to our hypothesis, none of the radiologic parameters showed statistically significant differences according to the Lafosse classification in the SC tear group.
Although the pathogenesis of SC tear is uncertain, a variety of mechanisms are involved, including intrinsic tendon degeneration, enlargement of a supraspinatus tear through the rotator interval, and trauma.13 Lo and Burkhart3 suggested that subscapularis tears are attributed to tensile failure by a roller-wringer effect in a stenotic subcoracoid space. Several studies have also noted the relationship between SC tears and shortened CHD.1,3,14 Lo and Burkhart3 reported that the mean CHD in patients with SC tears was 5.0 ± 1.7 mm compared to 10.0 ± 1.3 mm in the control group. They defined subcoracoid stenosis as a coracohumeral interval of less than 6 mm.3 Friedman et al.15 also described a significant decrease in the normal space between the humeral head and the coracoid process in symptomatic patients compared to a healthy population with kinematic MRI and shoulders positioned in maximal internal rotation. They reported that the mean CHD in symptomatic patients was 5.5 mm, whereas the mean CHD in asymptomatic patients was 11 mm.15 However, not every SC tear yields a decreased CHD. Kim et al.6 also reported that the preoperative CHD was approximately 6.5 mm or greater. Lanz et al.2 reported that the preoperative CHD was approximately 10 mm in large subscapularis tendon tears (Lafosse type IV) and other rotator cuff tears. In the present study, we evaluated the relationship between SC tear and CHD. Contrary to our hypothesis, CHD did not show statistically significant differences with regard to the Lafosse classification, although the SC tear group showed lower CHD values than those of the control group. Therefore, we believe relation between SC tear and CHD is still unclear.
With this growing interest in subscapularis pathology, there has been an attempt to explain the etiology of the torn subscapularis. Nevertheless, it is unclear whether SC tears can occur secondary to acquired subcoracoid impingement as subacromial impingement causing SC tears.4,14 In several studies, subcoracoid stenosis has been suggested as a plausible cause for partial-to full-thickness tears of the subscapularis.3,15,16 Otherwise, subcoracoid stenosis also occurs due to HHAT according to the progression of SC tear.9,10 If a short CHD is causative, coracoplasty would be imperative to prevent the recurrent roller-wringer effect. However, no literature has demonstrated that coracoplasty improves the structural integrity of subscapularis after repair. If a short CHD is a result of HHAT due to the SC tear, coracoplasty cannot be expected to improve outcomes. However, controversy still exists as to whether concomitant coracoplasty with SC repair is necessary.6 Therefore, we analyzed the relationship between HHAT and CHD according to the severity of SC tear in this study and found that CHD had a statistically significant negative correlation with HHAT, while CHD and HHAT had no statistically significant correlation with Lafosse classification. These results suggest that a short CHD is a result of HHAT due to the SC tear rather than the SC tears that could occur secondary to acquired subcoracoid impingement.
Our study has several limitations. First, the control group did not include normal healthy patients with normal MRI findings, although they had shoulder pain. Undetected tears found on MRI can be a cause of selection bias. Second, patients in the control group were younger than those in the SC tear group. Age-matched comparisons are necessary to prove the difference in the connection of radiologic parameters between the control and SC tear groups because radiologic parameters may change with increasing age. Third, MRI was routinely performed in a neutral position despite the radiologic measurements being dependent on the scapular version, position, viewing perspective, and rotation of the upper arm. Despite the excellent inter-observer agreement, the errors in measurement could still exist. To reduce such errors, the measurements were independently performed the results shared between surgeons. Fourth, there is a lack of consensus on the definition of HHAT. It is unclear that it indicates whether normal anatomical variation between the glenoid center and humeral head center or the anterior translation after subscapularis tear. In addition, HHAT could be underestimated because MRI was routinely performed in the supine position. Fifth, the difference between the HHAT and CHD with or without rotator cuff tears was approximately 0.32–1.81 mm, whereas the SD was >1.34 mm. Therefore, these results should be carefully interpreted to determine the clinical application of HHAT and CHD values. Sixth, the lack of an association between CHD, HHAT, and Lafosse classification might have been a source of type 2 error due to the sample size. This should also be considered as a limitation even though a retrospective power analysis determined that a sample size of 16 patients was sufficient for detecting a meaningful 10% difference between the groups, with an α level of 0.05 and a β value of 0.80. Finally, this study did not investigate other morphologic parameters of the coracoid or lesser tuberosity, such as coracoid overlap, coracoglenoid angle, coracohumeral angle, lesser tuberosity height, and lesser tuberosity angle.17, 18, 19
5. Conclusion
This study demonstrated that HHAT is associated with a decrease in CHD in subscapularis tear. However, correlation between radiologic parameters (CHD and HHAT) and severity of the subscapularis tear was observed.
Ethics approval and consent to participate
This article does not contain any studies with human participants or animals performed by any of the authors. This study was reviewed and accepted by the Dankook University medical center Institutional Review Board (no. IRB 2020-02-011).
Consent for publication
All of authors agree to publication.
Availability of data and material
It is available when reviewers request.
Conflicts of interest
The authors declare that they have no conflict of interest.
Funding
There is no funding source.
Authors' contributions
J.B.S designed this study, J.S.Y. and M.G.K. took the radiologic measurements, S.H.Y. and M.G.K gathered the retrospective data.
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Data Availability Statement
It is available when reviewers request.