Abstract
Background
It remains unclear whether the deep layer of the rotator cuff is an articular layer of the supraspinatus (SS) or infraspinatus (IS), rotator cable, or superior capsule. Therefore, this study aimed to analyse the relationship between occupation ratios and delamination patterns of rotator cuff tears (RCTs). We hypothesised that the deep layers are related to the occupation ratios of the deep SS and IS sections.
Materials and Methods
A total of 265 patients with RCTs were retrospectively enrolled between 2013 and 2017 and divided into four groups: A, non-delaminated tear; B, delaminated tear with the deep layer equally retracted to the superficial layer; C, delaminated tear with the deep layer more retracted; D, delaminated tear with the superficial layer more retracted. Muscle volume was evaluated by measurement of each occupation ratio of the SS and IS, and the IS muscle was additionally divided into two areas, deep and superficial.
Results
The SS occupation ratio was significantly lower in group C than in the other groups (p = 0.009). Conversely, comparison of the IS occupation ratios revealed no significant intergroup differences. The occupation ratio of the superficial IS was significantly lower in group D than in the other groups (p = 0.003). In group C, the occupation ratios of the deep IS section were significantly decreased according to RCT size (p = 0.034).
Conclusion
Our findings demonstrate that the superficial layers are related to the IS superficial section and the deep layers to the SS and IS deep sections.
Level of Study
IV.
Keywords: Magnetic resonance imaging, Rotator cuff, Delaminated, Delamination, Occupation ratio
Introduction
Delamination is a horizontal and partial thickness split of the tendon between the layers of a ruptured rotator cuff [1, 2]. A widely ranging incidence of 38–92% has been reported; however, the precise cause of delamination remains unknown [1–3]. Sonnabend et al. [4] demonstrated in a histological study that laminated tears of the rotator cuff generally occur between two layers of different collagen fibre orientations. Nimura et al. [5] suggested that a large portion of the deep layer observed in delaminated rotator cuff tears (RCTs) could include an articular capsule. However, using magnetic resonance imaging (MRI) scans in patients with delaminated RCTs, Cha et al. [6] demonstrated that the deep layer reaches the musculotendinous junction and serves as a tendon.
In 2008, Mochizuki et al. [7] anatomically demonstrated overlap of the distal supraspinatus (SS) tendon with the anterior section of the infraspinatus (IS); the insertion area of the IS is positioned more anteriorly than is currently believed [7]. As a result, the anterior section of the IS tendon overlapped with the SS tendon to achieve an insertion that is more anterior to the greater tuberosity of the humerus [8]. In 2019, Yoo et al. [9] described that articular-sided partial-thickness RCTs are related to the SS occupation ratios.
Tanaka et al. [10] reported the prevalence of delaminated RCTs by size (small, 20.5%; medium, 53.3%; large, 67.6%; massive, 60.0%). In 2008, Mochizuki et al. [7] reported that the mean anteroposterior width of the SS footprint was only 12.6 ± 2.0 mm. In 2013, Han et al. [11] and Tanaka et al. [10] described that the larger the RCT, the more frequent the appearance of the torn site delamination in the posterior versus the anterior section. In 2016, Cha et al. [6] demonstrated that 98.1% of the delaminated deep layer progressed in the posteromedial direction, leading to the assumption that the deep layer is most likely associated with the IS and serves as a tendon.
In 2012, Kato et al. [5] revealed that the IS consisted of oblique and transverse sections in accordance with the muscle fibre direction. They described that both sections had partially independent morphologies and that the insertion point of the transverse section was a thin tendinous membrane in the main tendinous portion of the oblique section [5]. In 2017, Bacle et al. [12] revealed that IS muscles consisted of three groups of fibres (cranial, central, and caudal) and were organised into two planes. They reported that the directions and distributions of the three groups of fibres are different (cranial and caudal portions of the superficial plane versus the central portion of the deep plane) [12]. MRI is a valuable tool for the diagnosis and preoperative assessment of rotator cuff diseases [13]. Rotator cuff muscle atrophy is typically assessed using the occupation ratio on oblique-sagittal MRI images [14]. Several studies have reported that the occupation ratio is associated with medial retraction of the rotator cuff [15–17].
This study aimed to evaluate the relationship between RCT occupation ratios and delamination patterns. The authors hypothesised that the deep layers are related to the occupation ratios of the SS and the deep IS.
Materials and Methods
Once the study received institutional review board exempt approval (DKUH 2018-10-019), a total of 265 patients with RCTs were retrospectively enrolled between 2013 and 2017. All patients were diagnosed with RCTs using the same type of MRI to enable their evaluation under the same conditions. In the present study, the subjects were divided into four groups as a modification of Choo et al.’s method [18]: group A, non-delaminated tear; group B, delaminated tear with the deep layer equally retracted to the superficial layer; group C, delaminated tear with the deep layer more medially retracted than the superficial layer; group D, delaminated tear with the superficial layer more medially retracted than the deep layer (Fig. 1).
Fig. 1.
a Group A, non-delaminated tear; b Group B, delaminated tear with the deep layer equally retracted to the superficial layer; c Group C, delaminated tear with the deep layer more medially retracted than the superficial layer; d Group D, delaminated tear with the superficial layer more medially retracted than the deep layer. D deep layer, S superficial layer
The exclusion criteria were partial-thickness RCT, concealed interstitial delamination, neuromuscular disease, shoulder instability, and previous surgery on the affected shoulder.
The delaminated RCTs were classified by two orthopaedic shoulder surgeons (J.S.Y. and K.H.). In cases in which the two orthopaedic surgeons did not agree on the classification, the participant was excluded despite the interobserver correlation showing almost perfect agreement (k = 0.82) (Table 1).
Table 1.
Reliability of grouping and occupation ratio measurements
| Measurement position | ICC (JSY vs JSY) | ICC (KH vs KH) | ICC (JSY vs KH) |
|---|---|---|---|
| Grouping | – | – | 0.82 |
| Occupation ratio of supraspinatus | 0.95 | 0.90 | 0.89 |
| Occupation ratio of infraspinatus | 0.92 | 0.89 | 0.86 |
| Occupation ratio of infraspinatus (deep section) | 0.90 | 0.86 | 0.81 |
| Occupation ratio of infraspinatus (superficial section) | 0.90 | 0.86 | 0.81 |
ICC intraclass correlation coefficient, JSY:JSY and KH:KH intraobserver variation test, JSY:KH interobserver variation test
MRI Evaluation
Magnetic resonance imaging was performed using a 3.0 T system (Ingenia 3.0 T; Philips, Houston, TX, USA) following the same protocol for each patient. The MRI protocol included obtaining proton density-weighted 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].
RCT size was measured using the maximum tear diameter in the oblique-sagittal T2-weighted images (Fig. 2a) [19]. The patients were divided into four groups by diameter: group A (< 1 cm), group B (≥ 1 cm, < 2 cm), group C (≥ 2 cm, < 3 cm), and group D (> 3 cm). RCT retraction was measured using the maximum tear diameter on the oblique-coronal T2-weighted images (Fig. 2b) [19].
Fig. 2.
a The maximum anteroposterior tear diameter was measured on a series of consecutive oblique-sagittal T2-weighted images. When a tear width was too large to measure with a single straight line over the convex humeral head, more than one straight line was drawn. b The maximum medial-to-lateral diameter of retraction was measured on a series of consecutive coronal T2-weighted images. When the retraction width was too large to measure with a single straight line over the convex humeral head, more than one straight line was drawn
Muscle volume was evaluated using the measurement of each occupation ratio of the SS and IS on the most lateral view of the T1-weighted oblique-sagittal images in which the scapular spine remained in contact with the scapular body [20]. The occupation ratios of the SS to the fossa were measured using Thomazeau et al.’s method [20]. The number of pixels in the segmented area of the muscle belly was automatically measured using the INFINITT PACS software (INFINITT, Seoul, Republic of Korea), after which the cross-sectional area of the muscle was measured. In the same manner, the cross-sectional area of the SS fossa was also measured. The occupation ratio of the SS was calculated using the SS area divided by the SS fossa area. The occupation ratios of the IS were measured according to Kikukawa et al.’s method [21]. The anatomic external rotation (aER) muscle was defined as the area surrounded by the posterior surface of the scapula, inferior margin of the teres minor (TM) muscle, and anterior surface of the posterior deltoid, including the areas of the IS and TM muscles [21]. The occupation ratios of the IS were calculated as IS area divided by aER muscle area. Additionally, the IS was divided into two compartments (deep and superficial) with modifications to the concept of Bacle et al. [12] and the method of Seo et al. [19] (Fig. 3).
Fig. 3.
T1-weighted oblique-sagittal image. The white line surrounds the supraspinatus fossa and the aER muscle, while the white dotted line surrounds the SS and IS muscles. The central group is classified as the deep section, while the cranial and caudal sections are classified as the superficial section. SS supraspinatus, aER anatomic external rotator, IS infraspinatus
All MRI scans were assessed based on consensus readout of two blinded observers (J.S.Y. and K.H.). Measurements were performed independently, and the results were not disclosed to the other surgeon. The mean value of the duplicate scores was used as the representative value. Intra- and interobserver correlations had almost perfect agreements (Table 1).
Statistical Analysis
Differences in age, size, and occupation ratios among the four groups were examined using one-way analysis of variance and post hoc analysis with Tukey’s test. Differences in sex and right arm involvement were compared using the Pearson Chi-square test. Spearman’s correlation coefficient was used to estimate the correlation of IS occupation ratio to RCT size. Subgroup evaluation of the IS occupation ratios according to delamination pattern and RCT size was performed using the Kruskal–Wallis test, while the post hoc test was performed using the Mann–Whitney test. The weighted kappa coefficient was used to estimate the interobserver reliability of the group division. Interobserver reliability was classified according to 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. All statistical analyses were performed using SPSS version 21.0 (SPSS Inc., Chicago, IL, USA); values of p < 0.05 were considered significant. A retrospective power analysis determined that 16 patients were needed in each group to obtain a 10% difference in occupation ratio between the groups with an α level of 0.05 and a β value of 0.80. In the comparative analysis, the sample sizes of the non-delaminated and delaminated RCTs groups were sufficient; however, when subgroups were formed according to the RCT size, the sample size was insufficient for an α level of 0.05 and a β value of 0.80.
Results
Demographic Data
A total of 265 patients with RCTs were divided and classified into the following groups: group A, 69; group B, 54; group C, 126; group D, 16. There were no significant differences in demographic data, including age, sex, or ratio of right arm involvement (Table 2).
Table 2.
Demographic data
| Group A (n = 69) | Group B (n = 54) | Group C (n = 126) | Group D (n = 16) | p value | |
|---|---|---|---|---|---|
| Age (mean ± SD) | 57.4 ± 7.0 | 58.3 ± 7.6 | 58.4 ± 6.7 | 59.0 ± 9.1 | N.S. |
| Sex (male/female) | 43/26 | 27/27 | 71/55 | 7/9 | N.S. |
| Right/left | 52/17 | 36/18 | 96/30 | 13/3 | N.S. |
N.S. non-significant
MRI Findings
The length of the RCTs were 17.8 mm in group A, 18.5 mm in group B, 17.6 mm in group C, and 19.6 mm in group D, showing no significant intergroup differences. The mean amount of retraction was 19.6 mm in group A, 22.1 mm in group B, 18.5 mm in group C, and 29.5 mm in group D. The retraction in group D was significantly greater than that in the other groups (p < 0.001) (Table 3).
Table 3.
MRI findings by delamination pattern
| Group A (n = 69) | Group B (n = 54) | Group C (n = 126) | Group D (n = 16) | p value | |
|---|---|---|---|---|---|
| Size, mm | 17.8 ± 7.2 | 18.5 ± 6.8 | 17.6 ± 5.6 | 19.6 ± 8.9 | N.S. |
| Retraction, mm | 19.6 ± 9.9 | 22.1 ± 11.2 | 18.5 ± 8.5 | *29.5 ± 9.1 | < 0.001 |
| Occupation ratio, %, mean ± SD | |||||
| Supraspinatus | 56.9 ± 10.6 | 55.2 ± 10.4 | *51.8 ± 11.2 | 57.2 ± 15.1 | 0.009 |
| Infraspinatus | |||||
| Total | 59.2 ± 11.1 | 58.7 ± 9.8 | 61.4 ± 8.3 | 56.9 ± 11.7 | N.S. |
| Deep | 31.2 ± 6.7 | 30.5 ± 5.9 | 30.2 ± 6.9 | 31.0 ± 9.2 | N.S. |
| Superficial | 28.0 ± 8.1 | 28.2 ± 7.6 | 31.1 ± 7.2 | *25.9 ± 8.5 | 0.003 |
N.S. non-significant
*Statistically significant
The mean SS occupation ratios were 56.9 in group A, 55.2 in group B, 51.8 in group C, and 57.2 in group D (Table 3). The SS occupation ratio in group C was significantly lower than that in the other groups (p = 0.009) (Fig. 4a).
Fig. 4.
a Comparison of the SS occupation ratios. b Comparison of the total IS occupation ratios. c Comparison of the occupation ratios of the deep IS. d Comparison of the occupation ratios of the IS superficial section. Significant differences are indicated by asterisks. SS supraspinatus, IS infraspinatus
The mean IS occupation ratios were 59.2 in group A, 58.7 in group B, 61.4 in group C, and 56.9 in group D, no significant intergroup difference (Fig. 4b). The mean occupation ratios of the deep IS were 31.2 in group A, 30.5 in group B, 30.2 in group C, and 31.0 in group D. There was no significant difference between the groups (Fig. 4c). The mean occupation ratios of the superficial IS section were 28.0 in group A, 28.2 in group B, 31.1 in group C, and 25.9 in group D. The occupation ratio of the superficial IS section in group D was significantly lower than that of other groups (p = 0.003) (Table 3; Fig. 4d).
IS Occupation Ratio by Delamination Pattern and RCT Size
The occupation ratios of the total (p = 0.004, correlation coefficient = − 0.179), deep (p = 0.001, correlation coefficient = − 0.201), and superficial (p = 0.019, correlation coefficient = − 0.144) IS were negatively associated with RCT size. The occupation ratio of the deep IS in group C was significantly decreased in contrast to that in the other groups (p = 0.034). Moreover, the occupation ratios of the deep IS of RCTs was smaller than that of the superficial IS in group C by more than 2 cm; however, the occupation ratios of the deep IS were higher than those of the superficial IS section in the other groups (Table 4).
Table 4.
Occupation ratio of infraspinatus division by delamination pattern and rotator cuff tear size
| Groups A and B (n = 123) Non-delamination and equally retraction |
p value | ||||
|---|---|---|---|---|---|
| Rotator cuff tear size | Group A (n = 9) < 1 cm |
Group B (n = 76) ≥ 1 cm, < 2 cm |
Group C (n = 29) ≥ 2 cm, < 3 cm |
Group D (n = 9) > 3 cm |
|
| Occupation ratio, infraspinatus, %, mean ± SD | 65.0 ± 7.2 | 59.8 ± 8.7 | 57.6 ± 10.4 | 50.5 ± 20.1 | N.S. |
| Deep | 34.6 ± 8.4 | 30.8 ± 5.1 | 31.1 ± 5.5 | 27.0 ± 12.8 | N.S. |
| Superficial | 30.4 ± 6.6 | 28.9 ± 6.7 | 26.5 ± 9.4 | 23.5 ± 1.6 | N.S. |
| Group C (n = 126) Deep layer dominant retraction |
p value | ||||
|---|---|---|---|---|---|
| Rotator cuff tear size | Group A (n = 9) < 1 cm |
Group B (n = 77) ≥ 1 cm, < 2 cm |
Group C (n = 36) ≥ 2 cm, < 3 cm |
Group D (n = 4) > 3 cm |
|
| Occupation ratio, infraspinatus, %, mean ± SD | 61.3 ± 9.0 | 62.0 ± 7.8 | 60.6 ± 8.9 | 54.5 ± 11.3 | N.S. |
| Deep | 31.8 ± 6.0 | 31.3 ± 6.7 | *29.3 ± 7.1 | 26.8 ± 4.6 | 0.034 |
| Superficial | 29.5 ± 6.8 | 30.7 ± 6.6 | 31.3 ± 8.3 | 27.7 ± 10.1 | N.S. |
| Group D (n = 16) Superficial payer dominant retraction |
p value | ||||
|---|---|---|---|---|---|
| Rotator cuff tear size | Group A (n = 0) < 1 cm |
Group B (n = 11) ≥ 1 cm, < 2 cm |
Group C (n = 3) ≥ 2 cm, < 3 cm |
Group D (n = 2) > 3 cm |
|
| Occupation ratio infraspinatus, %, mean ± SD | – | 60.1 ± 9.1 | 54.5 ± 16.6 | 42.6 ± 11.2 | N.S. |
| Deep | – | 33.7 ± 7.2 | 27.8 ± 14.7 | 21.5 ± 12.5 | N.S. |
| Superficial | – | 26.4 ± 9.3 | 26.8 ± 2.7 | 21.1 ± 1.3 | N.S. |
N.S. non-significant
*Statistically significant
Discussion
The major finding of the present study was that the occupation ratio of the superficial IS was decreased in the superficial layer of more retracted delaminated tears. Moreover, the SS occupation ratio was decreased in the deep layer of the more retracted delaminated tears. In the deep layer of the more retracted delaminated tears, occupation ratios of the deep IS were significantly decreased according to RCT size.
Muscle atrophy of the SS was previously assessed using the occupation ratio along the oblique-sagittal plane on MRI [20]. When this method is used, the cutting plane is defined by osseous landmarks such as the scapular spine and fixed in any series of examinations [16, 17]. The cutting plane of the muscle belly, where the cross-sectional area is measured, changes due to the tendons, which are repaired by lateral traction toward the facet of the greater tuberosity. Increases in the occupation ratio may simply indicate a change in the cutting plane of the muscle belly owing to structural changes caused by the operation rather than the recovery of the muscle volume [16, 17]. Furthermore, Lhee et al. [17] reported that the increase in occupation ratio observed soon after surgery depended on the degree of the preoperative SS tendon medial retraction. Chung et al. [22] also described that SS cross-sectional area and volume increased immediately postoperatively evaluated through a combination of two-dimensional (2D) and three-dimensional (3D) images. Although the occupation ratio does not reflect the muscle volume of the rotator cuff, it is related to the retraction of the torn tendon. Therefore, in the present study, the occupation ratio is used to evaluate medial retraction according to the delamination pattern of the RCTs.
Nimura et al. [5] removed the rotator cuff to study the attachment of the articular capsule on the greater tuberosity. The width of the articular capsule was 3.5–9.1 mm, with a thicker footprint than previously believed [5]. Their study suggests that a large portion of the deep layer observed in delaminated RCTs is composed of an articular capsule [5]. However, Cha et al. [6] revealed that the deep layer reached the musculotendinous junction on MRI scans of patients with delaminated RCTs and that the deep layer serves as a tendon connected to the IS and SS rather than acting a static structure consisting of only a capsule. They demonstrated that the retraction pattern of the delaminated deep layer may be affected by the IS and SS [6]. Michelin et al. [8] reported that the overlapping of the posterior SS section and the IS tendons was distinguishable on MRI. They also revealed that a linear area of increased signals was observed between the SS posterior section and the IS tendons and demonstrated that the anterior section of the IS tendon overlapped with the SS tendon to reach an insertion point that is anterior to the greater tuberosity of the humerus [8]. Rahu et al. [23] demonstrated that the SS tendon consists of superficial and deep sections. Moreover, the superficial portion extends directly to the humerus, while the deep layer is tightly connected to the rotator cable and crescent areas [23]. Therefore, we hypothesised that the deep layer of delaminated RCTs is related to the posterior (deep) section of SS tendons, although the division of the SS muscle on T1-weighted oblique-sagittal images was not performed, as this was not the objective of the study. As a result, this study shows that SS occupation ratios were significantly decreased in the group with delaminated tear with the deep layer more medially retracted than the superficial layer versus that of the group with non-delaminated tear.
However, Cha et al. [6] revealed that 98.1% of the delaminated deep layer progressed in the posteromedial direction, leading to the assumption that the deep layer is most likely associated with the IS and works as a tendon. Mochizuki et al. [7] reported that the mean anteroposterior width of the SS footprint was 12.6 ± 2.0 mm. Rahu et al. [23] revealed that the SS tendon’s insertion point is more posterior and the IS tendon’s insertion point is more anterior than previously reported. In 2012, Kato et al. [5] reported that the IS consisted of two groups (oblique and transverse) according to muscle fibre direction. Their histological study demonstrated that almost all of the tendinous portions of the IS are derived from the inferior section and that the tendinous portion of the superior section consists of thin membrane-like tissues that attach to the tendinous portion of the oblique section [5]. In 2017, Bacle et al. [12] demonstrated that IS muscles consisted of three groups of fibres (cranial, central, and caudal) organised into two planes. In this study, the central group of fibres was classified as the deep section and the cranial and caudal sections as the superficial section. As a result, this study revealed that the occupation ratio of the superficial IS section of group D was significantly lower than that of the other groups and that the occupation ratios of the deep IS of group C were significantly decreased according to RCT size.
Boileau et al. [1] and Flurin et al. [2] reported that delamination is a negative prognostic factor of the anatomical results of RCT repair. Moreover, Park et al. [24] reported that the RCT repair failure rate was also significantly higher in patients with a tear > 2 cm (34.2%) in size than in patients with a tear ≤ 2 cm (10.6%) in size. Zilber et al. [25] reported that eight (28%) of 29 patients showed grade II fatty infiltration of the IS muscles despite the lack of a tear. In addition, external rotation weakness was found in half of their patients [25]. They also reported that nine SS tendons (31%) were continuous but thin [25]. These findings imply that their treatment method for IS delamination may have been inadequate and that re-tearing of the deep layer may have caused fatty infiltration, IS weakness, and thinning of the repaired SS tendon [25]. In this study, the occupation ratios of the deep IS with RCTs > 2 cm in size were lower than those of the superficial IS section in group C; however, the occupation ratios of the deep IS were higher than those of the superficial IS section in the other groups.
There were several limitations to the present study. First, despite the excellent interobserver agreement, measurement errors such as that in terms of the grouping according to IS delamination and division were still possible. To reduce such errors, cases in which the orthopaedic shoulder surgeons did not agree were excluded; moreover, the measurements were performed independently and the results were not discussed between surgeons. The mean value of the duplicate scores was used as the representative value. Second, the occupation ratio evaluation using 2D MRI scans was performed without a 3D evaluation. Vidt et al. [26] revealed no significant associations between single-image assessments and 3D measurements of fatty infiltration of the SS and IS. However, muscle evaluation based on oblique-sagittal MRI films is still widely performed for simplicity and relevance with respect to various factors [27, 28]. Third, although muscle atrophy is affected by medial retraction of the cuff tendon as well as age, sex, activity level, general condition, symptom duration, and trauma history, this study only evaluated the relationship between RCT pattern and occupation ratios due to medial retraction of the tendon using MRI scans without considering the symptoms, duration, and arthroscopic findings. Finally, the lack of an association between delamination patterns and RCT size might have been a source of type 2 error due to the sample size; this should also be considered a limitation despite a retrospective power analysis determining 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.
In conclusion, our findings demonstrated that the SS occupation ratio was lower in the superficial and deep layers in cases of more retracted delaminated tears. In the deep layer of more retracted delaminated tears, IS occupation ratios were significantly decreased in relation to RCT size. According to these findings, we conclude that the superficial layers are related to the superficial IS section, while the deep layers are related to the deep SS and IS sections.
Compliance with Ethical Standards
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical standard statement
The study was approved by the local ethics committee and has therefore been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.
Informed consent
For this type of study informed consent is not required.
Footnotes
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Change history
6/12/2020
The original version of
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