1 Introduction

Rotator cuff tears RCTs, often associated with shoulder pain and dysfunction, have a multifactorial etiology including age, smoking, high plasma cholesterol levels, handedness, and a history of trauma.¹ Evidence suggests that peripheral microcirculation plays an important role in tissue degeneration and tear, and any changes in the same can be evaluated by measuring blood flow velocity using ultrasound imaging.² A previous study reported increased blood flow velocity in the anterior humeral circumflex artery(AHCA) of patients with symptomatic RCTs, and this increase was seen to be associated with higher concentrations of inflammatory cytokines and nocturnal pain.^3,4 Therefore, changes in the microcirculation of patients with RCTs can potentially serve as a new method of evaluating the injury and determining treatment efficacy.

In addition, RCTs are often associated with changes in the position and kinematics of the scapula, with the dependence on scapular movement being directly proportional to the size of the tear.⁵ Patients with symptomatic RCTs may exhibit decreased posterior tilting of the scapula, increased internal rotation, increased elevation of the clavicle and scapula, and increased upward rotation during arm flexion when compared to healthy individuals.^6,7 Furthermore, the external rotation of the scapula may increase with that of the glenohumeral joint, while scapular upward rotation and posterior tilting can increase with scapular plane abduction.⁸ These changes often lead to abnormalities in scapular movements, functioning as a compensatory mechanism to minimize pain in patients with RCTs. Previous studies have shown that approximately 65.7 % of patients with symptomatic RCTs exhibit scapular dyskinesis (SD), and 52.1 % of patients with pre-operative SD exhibit improvement in the outcome and healing of the rotator cuff following arthroscopic rotator cuff repair (ARCR).⁹ This suggests that scapular movement plays a crucial compensatory role in patients with lost rotator cuff function as a consequence of a tear injury. Although much of the evidence focuses on dynamic scapular movements during upper limb activities, a relationship between these movements and static scapular position has also been shown to exist, with abnormalities in the scapular position being an independent predictor of RCTs.¹⁰ Additionally, muscle activity around the scapula at rest and during mechanical tasks has also been shown to be significantly associated with scapular position, while changes in the latter can also affect the former.¹¹ Furthermore, consequent changes in the subacromial space, increased impingement of the rotator cuff, and apoptosis within the tendon cells can increase the risk of RCTs.¹² All of these factors combined suggest that RCTs may be associated with changes in dynamic scapular movements as well as scapular position.

A potential relationship between blood flow and scapular positioning has also been suggested. The studies reporting a greater decrease in blood flow in the AHCA during internal rotation compared to external rotation of the scapula.¹³ A previous study reported a significant correlation between trapezius muscle stiffness and the peak systolic velocity (PSV) in the transverse cervical artery, which supplies the trapezius muscle, in patients with neck and upper-back stiffness.¹⁴ These findings suggest that abnormalities in scapular positioning and parascapular muscle tension, potentially leading to changes in the blood flow. In addition, the patients with symptomatic RCTs have also been shown to exhibit a significant increase in the PSV in the dorsal scapular artery (DSA), which branches from the subclavian or transverse cervical arteries and supplies blood to periscapular tissues such as the levator scapulae and rhomboid muscles, on the affected (i.e., with tear) side compared to the unaffected (i.e., without tear) side.^15,16

Based on these evidence, we hypothesized that there would be a relationship between the PSV in the DSA, which supplies the periscapular muscles, and scapular positioning in patients with symptomatic RCTs. Therefore, the aim of the current study was to test this hypothesis by comparing changes in blood flow velocity in the DSA by scapular position on the affected and unaffected sides in patients with symptomatic RCTs. We hypothesize that PSV in the DSA and scapular positioning are altered on the affected side and that these alterations are interrelated.

2 Materials and methods

2.3

2.3 Assessment of blood flow

The blood flow velocity was measured using the pulsed Doppler method, as per Kawabuchi et al., and the PSV of the DSA was recorded.¹⁵ An ultrasound imaging device (LOGIQ e, GE Health Care Japan, Tokyo, Japan) with a 7–12 MHz linear probe was used for this purpose. The patients were asked to sit in a relaxed position on a table with their hip and knee joints flexed at 90°, their head facing forwards, and their upper limbs hanging naturally by their sides, and the Doppler gain was then manually adjusted until the color box was uniformly filled with the initial color and a minimal amount of the next signal had begun to appear. The ultrasound linear probe was used to capture an image of the DSA on the first or second rib at the medial angle of the scapula along the short axis. Next, the probe was rotated to allow visualization of the vessel along the long axis and the Doppler signal was used to confirm pulsation. The insonation angle was set to 60°. Upon obtaining a stable blood flow waveform, the PSV was measured three times using the manual trace function of the device and the mean value was calculated (Fig. 1). All PSV measurements were carried out by a physiotherapist with 14 years of experience overall and six years of experience using ultrasound. To confirm reproducibility, the PSV in the DSA was measured twice at an interval of three days in 12 patients unrelated to this study, and calculation of the intraclass correlation coefficient (ICC [1,2]) showed a value of 0.95 (95 % confidence interval [CI]: 0.84–0.99) indicating high consistency between the measurements.¹⁵

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Fig. 1 Measurement of the peak systolic velocity of the dorsal scapular artery using an ultrasound imaging device. DSA, dorsal scapular artery; PSV, peak systolic velocity.

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2.4

2.4 Assessment of scapular position

The scapular position was assessed using X-ray images taken with the patients standing in a comfortable natural position. During imaging, a grid was placed (by an X-ray technician) against the patient's chest and they were asked to relax the shoulder girdle muscles and hold their breath. Image analysis was performed using Synapse Scope (Fujifilm Medical, Tokyo, Japan) to measure distances and angles, and the scapular and clavicular alignments were calculated from the X-ray images as per previous studies.¹⁸ The vertical distances between the centerline of the spine and the medial border of the scapula (i.e., DSS: distance between the superior border and the corresponding spine; DMS: distance between the medial border and the corresponding spine; DIS: distance between the inferior border and the corresponding spine) were also measured.¹⁸ The X-ray images were inverted to black and white to allow clear observation of the medial border of the scapula. The clavicular tilt angle (CTA) between the vertical line of the spine and the centerline of the clavicle was also measured (Fig. 2). The DSS, DMS, DIS, and CTA were measured thrice consecutively on two separate occasions at least seven days apart in ten patients unrelated to this study, The ICC (1,2) values for the two measurements were 0.86 (95 % CI: 0.65–0.94), 0.94 (95 % CI: 0.85–0.97), 0.93 (95 % CI: 0.82–0.97), and 0.76 (95 % CI: 0.41–0.90) for DSS, DMS, DIS, and CTA, respectively.

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Fig. 2 Measurement of scapular and clavicular alignment using X-rays.X-ray images were used to measure the vertical distances between the centerline of the spine and the medial border of the scapula (i.e., DSS: distance between the superior border and the corresponding spine; DMS: distance between the medial border and the corresponding spine; DIS: distance between the inferior border and the corresponding spine). Additionally, the clavicular tilt angle (CTA) between the vertical line of the spine and the centerline of the clavicle was also measured.

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The scapular anterior tilt angle was measured using a compact digital inclinometer (DI100M, Akatsuki, Kyoto, Japan) placed along the line connecting the scapular spine and the inferior angle, and the mean value of three measurements was calculated (Fig. 3).¹⁹ The reproducibility of the anterior tilt angle was assessed by taking three times measurements on two separate occasions in ten patients (ICC [1,2] value: 0.74; 95 % CI: 0.74 to 0.89).

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Fig. 3 Measurement of scapular anterior tilt angle. A digital inclinometer was placed along the line connecting the scapular spine and the inferior angle. D, digital inclinometer; S, scapular spine; I, inferior angle.

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3 Results

The demographic characteristics of the study sample have been shown in Table 1. Comparison of the affected and unaffected sides in patients with symptomatic RCTs showed that the ROM (i.e., AE, AB, ER), PSV in the DSA were significantly higher in the former (AE: p-value <0.01, 95 % CI: −64.3 to −32.7; AB: p-value <0.01, 95 % CI: −82.7 to −46.4; ER: p-value <0.01, 95 % CI: −30.9 to −12.9; PSV in the DSA: p-value = 0.04, 95 % CI: 0.6 to 7.4) compared to the latter (Table 2).

A significant negative correlation was observed between DMS and PSV in the DSA (r = −0.41, p = 0.02, Table 3).

4 Discussion

The current study examined the association between the PSV in the DSA and scapular positioning by comparing the affected and unaffected sides in patients with symptomatic RCTs. The findings indicated that the PSV in the DSA was significantly higher on the affected side. However, no significant differences were observed in any of the scapular position parameters. On the other hand, a significant negative correlation was observed between PSV in the DSA and the distance between the DMS of scapular position. Our findings clarify the relationship between periscapular blood flow responses and scapular positioning, providing new insights necessary for future interventions.

The PSV in the DSA was significantly higher on the affected side compared to the unaffected side. Previous studies have demonstrated an increase in the PSV of the AHCA, which directly supplies the rotator cuff, on the affected side and this is often accompanied by synovitis and an increased concentration of inflammatory cytokines.^3,4 Furthermore, the PSV of the DSA has also been shown to be significantly higher on the affected side compared to the unaffected side and this finding was in agreement with that of the previous study.¹⁵ Both the AHCA and the DSA originate from either the subclavian or transverse cervical arteries.¹⁶ These findings suggest that the observed increase in PSV may reflect inflammatory changes within tissues due to the tear, potentially resulting in increased blood flow not only in the AHCA but also in periscapular vascular structures. On the one hand, no significant differences were found in any of the scapular position parameters between the affected and unaffected sides. Ishikawa et al.²⁰ investigated the upward rotation of the scapula during arm elevation on both the affected and unaffected sides using an inclinometer. Their findings demonstrated that significant upward rotation was observed on the affected side at arm elevation angles above 60°, while no significant differences were observed at rest position. Therefore, since this study evaluated scapular position at rest, it is possible that differences between the affected and unaffected sides were harder to detect.

An investigation into the relationship between the PSV in DSA and scapular positioning revealed a significant negative correlation between the PSV in the DSA and DMS of scapular position. This finding suggests that cases with scapular retraction may exhibit an increase in the DSA in the PSV. Previous studies have reported that scapular retraction reduces tension in the suprascapular nerve, substantially lowering the pressure pain threshold in the infraspinatus muscle.²¹ Consequently, in cases of symptomatic rotator cuff tears, retraction of the scapula in a resting posture might alleviate neural tension on the nerves innervating the rotator cuff, potentially reducing mechanical stress on the associated muscle groups. Furthermore, given the established association between muscle stiffness and the PSV in the arteries supplying the muscle,¹⁴ it is plausible that increased stiffness in the rhomboid muscles, which contribute to scapular retraction to avoid pain, leads to an increase in both rhomboid muscle stiffness and the PSV of the DSA that nourishes them. However, as this study did not investigate muscle stiffness, further research is necessary to verify this association.

This study had several limitations. As this study compared the affected and unaffected sides, the influence of comorbidities could not be completely excluded. Therefore, future studies should include comparisons with healthy participants, matched for background, to further control for these factors. Although this study only examined static scapular position, future research should investigate changes in muscle stiffness of the periscapular muscles related to static scapular position, as well as its association with dynamic scapular position. Furthermore, changes before and after physical therapy were also not examined and future studies should address this to ascertain the relationship between the symptoms, PSV in the DSA, and scapular position.

5 Conclusion

This study examined the association between PSV in the DSA and scapular position by comparing the affected and unaffected sides of patients with symptomatic RCTs. The results showed that the PSV in the DSA were significantly higher on the affected compared to the unaffected side. Furthermore, a significant negative correlation was observed between PSV in the DSA and the DMS of scapular position. Therefore, the increase the PSV in the DSA on the affected side of patients with symptomatic RCTs can potentially be attributed to the condition of scapular position.

CRediT authorship contribution statement

KK contributed to study design and data collection, and drafted the manuscript, and made critical revision to the manuscript. MN contributed to check of study design and data and made critical revisions to the manuscript. All authors approved the final version of the manuscript and agreed to be accountable for all aspects of the work.

Ethical statement

This research has been approved by the authors’ affiliated institutions. (Approval No. 2024–13).

Funding statement

This study was not supported

Guardian/Patient’s consent

No applicable.