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. 2023 Mar 29;243(3):467–474. doi: 10.1111/joa.13868

Anatomical analysis of the motor endplate zones of the suprascapular nerve to the infraspinatus muscle and its clinical significance in managing pain disorder

Hyung‐Jin Lee 1, Ji‐Hyun Lee 2, Kyu‐Ho Yi 3,4, Hee‐Jin Kim 4,✉
PMCID: PMC10439366  PMID: 36988105

Abstract

Myofascial pain syndrome caused by myofascial trigger points is a musculoskeletal disorder commonly encountered in clinical practice. The infraspinatus muscle is the region most frequently involved in the myofascial pain syndrome in the scapular region. The characteristics of the myofascial trigger points are that they can be found constantly in the motor endplate zone. However, localizing myofascial trigger points within the motor endplate zone and establishing an accurate injection site of the infraspinatus muscle has been challenging because the anatomical position of the motor endplate zone of the infraspinatus muscle is yet to be described. Therefore, this cadaveric study aimed to scrutinize the motor endplate zone of the infraspinatus muscle, propose potential myofascial trigger points within the muscle, and recommend therapeutic injection sites. Twenty specimens of the infraspinatus muscle for nerve staining and 10 fresh frozen cadavers for evaluation of the injection were used in this study. The number of nerve branches penetrating the infraspinatus muscle and their entry locations were analyzed and photographed. Modified Sihler's staining was performed to examine the motor endplate regions of the infraspinatus muscle. The nerve entry points were mostly observed in the center of the muscle belly. The motor endplate was distributed equally throughout the infraspinatus muscle, but the motor endplate zone was primarily identified in the B area, which is approximately 20–40% proximal to the infraspinatus muscle. The second‐most common occurrence of the motor endplate zone was observed in the center of the muscle. These detailed anatomical data would be very helpful in predicting potential pain sites and establishing safe and effective injection treatment using botulinum neurotoxin, steroids, or lidocaine to alleviate the pain disorder of the infraspinatus muscle.

Keywords: botulinum neurotoxin, infraspinatus muscle, motor endplate zone, myofascial pain syndrome, suprascapular nerve

Motor endplates of the suprascapular nerve were mainly observed in section B, which are the medial 2/5 of the ISM, and C3, which is the center of the ISM.

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1. INTRODUCTION

Myofascial pain syndrome (MFPS) caused by myofascial trigger points (MTrPs) is a representative musculoskeletal disorder commonly encountered in clinical practice. The MTrPs are hyperirritable spots within a taut band of the skeletal muscle (Simons et al., 2002). The most noticeable symptoms of the MFPS include local twist responses, regional muscle pains, and a limited range of motion (Touma et al., 2022). The infraspinatus muscle (ISM) is the region most frequently involved by MFPS near the scapular region (Bron et al., 2011; Sola & Kuitert, 1955; Villafane et al., 2019), and this muscle often contains multiple MTrPs (Kwon et al., 2017). One of the characteristics of the MTrPs that has been accepted so far is that it can be found in a taut band and constantly in the motor endplate zone (MEZ) (Simons et al., 2002). Additionally, MTrPs show spontaneous electrical activity, which is evaluated by electromyography, and this reaction tends to be more significant in the MEZ within the MTrPs (Kimura, 2013). Within the MEZ, the motor endplates are concentrated in the center of the MEZ and respond more significantly to electrical stimuli (Simons et al., 2002).

Thereby, MFPS has been generally managed by local anesthetics, such as botulinum neurotoxin (BoNT) (Kumar, 2018). The BoNT injection has been considered one of the most effective treatments for managing patients with MFPS (Kumar, 2018). Since BoNT hampers the leakage of acetylcholine at the neuromuscular junction and MTrPs are associated with MEZ (Margalef et al., 2019), injecting BoNT close to the intramuscular nerve ending adjacent to the motor endplate would result in better pain relief (Parratte et al., 2002). Reportedly, endplate‐targeted injections (e.g., targeting the nerve ending area), where most neuromuscular junctions are observed, are more effective than injections targeting the non‐endplate area (Gracies et al., 2009; Van Campenhout et al., 2013). However, the location of the motor endplates or MTrPs of the ISM in the previous studies has been determined by palpation and electromyography of the muscle, not based on anatomical consideration (Ge et al., 2008; Kwon et al., 2017; Simons et al., 2002). Furthermore, localization of MTrPs within the MEZ and establishing an accurate injection site or MFPS in the ISM has been challenging because the anatomical position of the MEZ of the ISM has yet to be previously described. Therefore, to overcome this limitation, we applied Sihler's whole mount nerve staining. Sihler's staining can be one of the effective methods with the advantage of revealing the location of the motor nerve endings (considered a location of the motor endplates) within the muscle (Kimura, 2013; Simons et al., 2002). This cadaveric study aimed to scrutinize the MEZ of the ISM, propose potential MTrPs within the ISM, and recommend therapeutic BoNT injection sites.

2. METHODS

This study included 20 specimens of the IS (12 men and 8 women) from 15 formalin‐embalmed cadavers for Sihler's staining and 10 fresh frozen cadavers for evaluation of the injection with a mean age of 82.7 years (range, 67–89 years). This study was performed in accordance with the principles outlined in the Declaration of Helsinki. All cadavers were legally donated to the Surgical Anatomy Education Centre of Yonsei University College of Medicine (approval number: YSAEC 21–005). All cadavers had intact shoulders with no medical history of trauma in the scapular region.

The skin in the scapular region was removed from the midline to the acromion of the scapula. After removal of the skin, subcutaneous tissue, and trapezius muscle from the scapular region, the dissection was carefully performed to expose the suprascapular nerve, artery, and vein distributed to the ISM. In addition, the three parts of the ISM, including superior, middle, and inferior parts, were revealed (Kato et al., 2012). The ISM was detached from the medial border of the scapula between the base of the spine and the inferior angle of the scapula to the humeral insertion (Al‐Redouan & Kachlik, 2022). After laterally detaching the ISM, the suprascapular nerve to the ISM was meticulously dissected to reveal the nerve entry point. The number of nerve branches penetrating the muscle and their entry locations were analyzed and photographed.

2.1. Modified Sihler's staining

Modified Sihler's staining was performed to examine the neural‐arborized regions of the ISM. The preparation and improved Sihler staining protocol were as follows:

2.2. Staining solutions

Fixation solution: 10% neutralized formalin.

– Maceration solution: 3% aqueous potassium hydroxide (KOH), obtained by adding 1 mL of 3% hydrogen peroxide to 1 L of 3% KOH solution for depigmentation.

Sihler I solution consists of one volume of glycerin, one volume of glacial acetic acid, and six volumes of distilled water.

Sihler II solution consists of one volume of Ehrlich's hematoxylin, one volume of glycerin, and six volumes distilled water.

Neutralization solution: 0.05% lithium carbonate.

– Dehydration solution: 70%–90% aqueous ethanol and pure ethanol.

– Clearing solution: formamide.

Sihler's staining includes seven steps as follows:

Fixation phase: The ISM was fixed for a week in 10% un‐neutralized formalin.

Maceration phase: The fixed specimens were washed overnight with running water. The ISM specimens were then macerated and depigmented for 2 weeks in a maceration solution.

Decalcification phase: The macerated ISM specimens were placed in Sihler I solution for 72 h for decalcification.

Staining phase: Once the ISM specimens were decalcified, they were stained with Sihler II solution for 3 days. This phase stained all tissues, including the nerve and muscle fibers.

Destaining phase: The stained ISM specimens were again placed in Sihler I solution for approximately 1–3 h. This phase destained the muscle fibers, excluding the stained nerves.

Neutralization phase: The destained ISM specimens were neutralized in running tap water for 30 min. They were then placed in 0.05% lithium carbonate for 30 min to obtain blue color.

Dehydration phase: As a preparation step for clearing, the ISM specimens were dehydrated with increasing concentrations (70%–100%) of ethyl alcohol for 1 day.

Clearing phase: The dehydrated ISM specimens were cleaned with absolute formamide for 3 day.

2.3. Analysis of the nerve entry points and MEZ

The stained samples were examined on a medical film viewer that offered adequate light to reveal the intramuscular course of nerve branches. The nerve entry points and intramuscular innervation of the ISM were investigated using photographs, sketches, and notes. Nerve entry points and MEZ were comprehensively scrutinized. The ISM was transversely divided into five equal sections, each indicating a division of 20% of the total length, and these sections were designated A, B, C, D, and E. The ISM was divided vertically into three equal sections, that is, 1, 2, and 3 (Figure 1). The nerve entry points and locations where the motor endplates were observed were identified in each section (A1, A2, A3, B1, and B2, etc.). When the total number of samples was 20, the nerve distribution was considered to be 50% when it was distributed in the B1 section in 10 samples. Therefore, in each section, we analyzed and quantified the number of innervated samples. Based on these detailed analytical methods, the most frequently observed nerve entry and the densest MEZ of the ISM were determined.

FIGURE 1.

FIGURE 1

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Reference lines and probability of a suprascapular nerve entry point for each section. The infraspinatus muscle (ISM) was divided into five equal sections (A to E) between the medial border of the scapula and the acromion (AC). The nerve entry points were present in multiple sections of the IS and were mostly observed in areas C1 and C2. IA: inferior angle of the scapula.

2.4. Validation of the injection site of the ISM on the fresh cadaver

Following the nerve staining, the blind injection based on the MEZ and surface landmarks was performed and verified by dissecting the cadaver. The medial border, inferior angle, deltoid tubercle, and acromion of the scapula were used as a surface landmarks. The green‐colored dye was used to confirm the accuracy of the injection site within the cluster area of the nerve endings of the ISM.

3. RESULTS

3.1. Location of the suprascapular nerve entry points of the ISM

The suprascapular nerve, which was stained violet, was distributed to the ISM. The main suprascapular nerve destined for the ISM is divided into two to three branches. They had multiple entry points, which were mostly observed in the C area that was located approximately at the center of the muscle belly (Figure 1). The branches of the suprascapular nerves within the muscle proceeded towards the origin of the ISM and extended from the superior area to the inferomedial area. In particular, we did not observe any visible twigs near the insertion area, which contained a tendinous portion. The location of the nerve entry points was observed at the C1 and C2 areas in all cases and at the C3 area in 30% of the cases.

3.2. Distribution and cluster area of motor endplates in the ISM

In all 20 specimens, we observed that the ISM was composed of the superior, middle, and inferior bellies located within the infraspinous fossa, with no variations in morphology (100% of cases) and the suprascapular nerve was distributed equally throughout the ISM. The suprascapular nerve is divided into two branches in 70% of cases (14 of 20) and three branches in 30% of cases (6 of 20), as shown in Figure 2. We summarized the overall suprascapular nerve distribution area in Table 1. When the suprascapular nerve was divided into two branches (70%, 14 of 20), we found that the first branch was distributed to the superior and middle parts of the ISM in all cases (100%, 14/14), while the second branch was distributed to the middle and inferior parts of the ISM in all cases (100%, 14/14).

FIGURE 2.

FIGURE 2

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The branching pattern of the suprascapular nerve to the ISM. The suprascapular nerve was divided into two or three branches to distribute throughout the entire ISM. When the suprascapular nerve was distributed into two branches (left), the first branch distributes to both the superior and middle parts of the ISM, and the second branch to both the middle and inferior parts of the ISM. When the suprascapular nerve divides into three branches, the first, second, and third branches were predominantly distributed to the superior, middle, and inferior parts of the ISM, respectively. Additionally, some branches were observed to distribute to the surrounding parts of the ISM.

TABLE 1.

The distribution area of the suprascapular nerve to the three parts of the infraspinatus muscle.

Number of branches Superior Middle Inferior

Two branches

(70%, 14/20)

 First br. 14/14(100%) 14/14(100%) ‐
Second br. ‐ 14/14(100%) 14/14(100%)

Three branches

(30%, 6/20)

 First br. 6/6(100%) 1/6(16.7%) ‐
Second br. 4/6(66.7%) 6/6(100%) 6/6(50%)
Third br. ‐ 5/6(83.3%) 6/6(100%)
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When the suprascapular nerve was divided into three branches (30%, 6 of 20), in five of six cases, the first branch was distributed to the superior part of the ISM, while in only one of six cases, it was distributed to both the superior and middle parts of the ISM. Among the second branch, it was distributed to both the superior and middle parts of the ISM in two of six cases, only to the middle part of the ISM in one of six cases, to the middle and inferior parts of the ISM in only one of six cases, and to the superior, middle, and inferior parts of the ISM in two of six cases. The third branch was distributed to the middle and inferior parts of the ISM in five of six cases and only to the inferior part of the ISM in one of six cases.

Greater arborization was observed toward the medial portion than that in the central portion of the middle part of the ISM. For the branch that supplied to the inferior part of the ISM, greater motor endplate was observed in the central and medial portions than that in the most medial portion, which is adjacent to the medial border of the scapula.

The suprascapular nerve motor endplate was distributed throughout the ISM, but it was primarily identified in the B area, which is approximately a medial 20%–40% portion of the ISM (Figure 3). The MEZ was observed in the B1, B2, and B3 areas in 100% (20/20) of the cases (Figure 4). The second‐most MEZ was observed in area C, which was approximately the center of the muscle. Among the three C areas, the C3 area showed the greatest motor endplate (19/20, 95% of the cases), followed by the C1 (14/20, 70% of the cases) and C2 areas (9/20, 45% of the cases). The A1 and A2 areas, which are adjacent to the medial border of the scapula, showed motor endplate in 60% of the cases (12/20). No motor endplate was observed in the D2 and E1‐3 areas, which are adjacent to the insertion of the ISM.

FIGURE 3.

FIGURE 3

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The intramuscular innervation provided by the suprascapular nerves to the ISM in a specimen stained using modified Sihler's staining method. Photograph of a stained specimen depicting the entire suprascapular nerve distribution within the ISM (left) and the corresponding illustration presenting motor endplate proportion of the suprascapular nerve into the ISM based on surface anatomical landmarks (right). Motor endplates were mainly observed in sections B1, B2, and B3, which are the medial 2/5 of the ISM, and C3, which is the center of the ISM.

FIGURE 4.

FIGURE 4

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Overall distribution pattern of the motor endplates within the IS. B1, B2, B3, and C3 (yellow color) showing the greatest motor endplate zone (MEZ). A1, A2, and C1 showed the second‐most common occurrence of the MEZ. The yellow‐shaded sections could be the ideal injection points of BoNT in the IS.

3.3. Blind injection to the ISM based on the motor endplate distribution and surface landmarks

The two injection sites (e.g., superior and inferior point) were determined based on the intramuscular distribution of the ISM and surface landmarks (Figure 5). Of the two injection points, the superior injection point was targeted for the middle part of the ISM and the inferior injection point was targeted for both the middle and inferior parts of the ISM. The dye that was injected into the superior injection point was found to be within the middle part of the ISM. The dye that was injected into the inferior injection point was found to be within both the middle and inferior parts of the ISM. Each injected dye was observed to spread horizontally with an average of 9.61 ± 4.29 mm (ranging from 3.11 to 20.51 mm) and vertically with an average of 3.82 ± 1.24 mm (ranging from 1.79 to 6.61 mm). As the dye injected into the muscle moves along the muscle fibers, it was found to be distributed longitudinally along the muscle and shorter in the opposite direction of the fibers. Therefore, the proposed injection sites can be regarded as accurate locations to reach the cluster area of the motor endplate and each compartment of the ISM.

FIGURE 5.

FIGURE 5

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Recommended injection point and technique based on the MEZ of the IS. The left and right photographs are volunteer and cadaveric views showing the surface landmark and projection for the recommended injection point. Deltoid tubercle (DT), inferior angle (IA), and acromion (AC) are key anatomical landmarks. The medial border of the scapula was divided into three equal parts (thirds); therefore, four points were established along the medial border of the scapula. A perpendicular line parallel to the medial border of the scapula and passing via the deltoid tubercle was established. The second and third points along the medial border of the scapula were connected to the acromion of the scapula. Subsequently, the meeting points (blue circles) between the line joining through the second and third points, and the line passing the DT, were designated as effective injection sites to target MEZ within the IS. DT, deltoid tubercle; IA, inferior angle of the scapula; ISMs, the superior part of the ISM; ISMm, the middle part of the ISM; ISMi, the inferior part of the ISM; Rh, rhomboid major muscle; BS, the base of spine of scapula; TM, teres major muscle; Tm, teres minor muscle; LD, latissimus dorsi muscle; S, superior; I, inferior; M, medial; L, lateral.

4. DISCUSSION

BoNT injection is a promising treatment method for patients suffering from MFPS. Consequently, numerous clinical trials have been conducted to check their effectiveness (Cheshire et al., 1994; Gobel et al., 2006; Hsu et al., 2020; Kim & Kim, 2018; Kumar, 2018). Gobel et al. conducted randomized, double‐blind, placebo‐controlled clinical trials in 145 patients with neck and shoulder MFPS to observe the effectiveness of BoNT injections. The authors found that patients who received BoNT injections showed significant pain relief in comparison with placebo groups over a follow‐up period of up to 12 weeks (Gobel et al., 2006). Harden et al. performed a similar study involving 23 patients with MTrPs. In their random‐sampling study, BoNT was found to be an effective treatment method (Harden et al., 2009). Many researchers have reported that BoNT injections could effectively reduce pain in patients with MFPS (Chang et al., 2020; Cheshire et al., 1994; De Andrés et al., 2003; Hsu et al., 2020).

The ISM is a muscle used as a BoNT injection site when treating patients with MFPS, and the effect of using this muscle as an injection site has been extensively studied. Numerous clinical trials have confirmed the effectiveness of injecting BoNT into the shoulder girdle muscles, including the ISM (Chang et al., 2020; Cheshire et al., 1994; Lim et al., 2008); however, the results of studies examining the pain‐relieving effects of BoNT injections have not always been positive (Ho & Tan, 2007; Qerama et al., 2006). The results obtained from randomized sampling studies varied among studies, most likely due to differences in BoNT doses, a lack of consistency in injection sites, or because the studies were sponsored by companies, resulting in an industrial‐related conflict of interest (Ahmed et al., 2019; Sung et al., 2013). These discrepancies have highlighted the need to establish the potential injection site based on topographical anatomical information when administering BoNT to effectively treat MFPS with ISM.

Until now, no anatomical research delineates MEZ of the suprascapular nerve to the ISM, and no attempts have been made to suggest potential MTrPs as well as the potential injection site for the ISM. Manual palpation and ultrasonography were the typical methods to identify the taut band or MTrPs (Do et al., 2018; Ge et al., 2008), in addition to the electromyographic technique of exploring the motor endplates (Gracies et al., 2009). However, these techniques are time‐consuming; further, contact of the needle with MEZs is painful (Gracies et al., 2009). Several clinical studies have verified that motor endplate‐targeted BoNT injections of the biceps brachii muscle, based on the anatomical landmarks showed superior efficacy compared to endplate non‐targeted injections, which results in greater reduction of elbow flexor spasticity and improvement in the active range of elbow extension (Gracies et al., 2009). Likewise, a longitudinal follow‐up study of motor endplate‐targeted BoNT injection in the psoas major muscle showed a larger volume reduction in the psoas major muscle (Van Campenhout et al., 2013). Despite these previous studies, no relevant anatomical study of the ISM has been conducted yet.

The results of the present study show that the nerve entry points were mostly observed in the center of the ISM. Furthermore, most of the motor endplates was observed in the medial 2/5 and 3/5 areas of the ISM. This result is consistent with the findings of a previous study showing that the medial 2/4 and 3/4 portions of the ISM were the most frequently involved areas by pain when the ISM was divided into four equal portions (Kwon et al., 2017). Moreover, this is also consistent with studies by Travell et al. and Ge et al., which found the MTrPs to be approximately at the muscle's center (Donnelly, 2019; Ge et al., 2008). Most of the MEZ in the ISM were concentrated in the B1, B2, and B3 sections (Figure 4). Using the deltoid tubercle of the scapula, the B1, B2, and B3 sections can be estimated on the skin surface, which is the vertical portion along the deltoid tubercle and can be found at the medial portion of the scapula as a rough prominence. It is easily palpable at the posterior aspect of the scapula from the skin surface. Based on the results of the present study, we established recommended injection points, injected color dye into the suggested points, and verified their locations within the ISM by dissecting the fresh‐frozen cadaver (Figure 5). The color dye was located within the ISM, especially along the deltoid tubercle, which is correspond to section B and close to most of the MEZ within the ISM. Therefore, the established injection points would be helpful to target the MEZ of the ISM based on the surface landmarks. Since IS occupies most of the area in the infraspinous fossa, and palpation of the entire muscle during physical examination can be time‐consuming (Kwon et al., 2017), the MEZ and surface anatomical landmarks (e.g., deltoid tubercle) described in the current study can provide practical guidance for locating MTrPs and designing the safest and most efficient injection treatment plan for the IS.

Knowledge about the location of common MTrPs within the ISM is essential to guide clinical identification of MTrPs in this muscle. Despite several clinical studies examining the common MTrPs (Travell, 1999; Ge et al., 2008; Kwon et al., 2017), no consensus has been reached yet. Most of the previous clinical studies use careful palpation and typically identify multiple MTrPs in the mid‐muscle belly region of the ISM (Ge et al., 2008) (Donnelly, 2019). Travel and Simons reported that the most common MTrPs were caudal to the junction of the most medial and adjacent quarter of the length of the spine of the scapula (upper medial lesion) (Kwon et al., 2017). The next most common was caudal to the midpoint of the spine of the scapula ((the lateral upper lesion) (Kwon et al., 2017). Kwon et al. found similar results compared to previous studies (Travell, 1999; Ge et al., 2008); additionally, they found another trigger point near the inferior angle of the scapula (Kwon et al., 2017). Considering that MTrPs are closely related to the location of motor endplates, knowledge of MEZ can potentially be used to predict the location of MTrPs. In the present study, the densest MEZ was observed in sections B and C, which were the medial 2/5 and 3/5 areas (25% and 50% when the distance between the muscle's origin and insertion was divided into 100, respectively) of the muscle, and these locations may be anatomically potential MTrPs of the ISM. However, clinical information regarding the relationship between the MEZ and MTrPs of the ISM is currently lacking. Thus, the significance of our results should be evaluated by clinical comparisons, especially in patients suffering from MFPS of the ISM.

Herein, intramuscular nerve distribution of the ISM was revealed through a reliable whole mount nerve staining method. However, the current study had a few limitations. First, Sihler staining provides less detailed information about the motor endplate's exact location than a microscopic evaluation. However, this is a trustworthy staining method, as the myelin sheath's terminal portion is close (a few μm) to the neuromuscular junction (Junqueira, 2010). The Sihler's staining method stains the end portion of the myelinated nerve fiber close to the motor endplates. Given that the BoNT diffuses a few centimeters from the injection site, the terminal myelinated portion, considered to be the MEZ in the present study, can be considered as an indicator of the neuromuscular junction. Second, the sample size assessed in this study was small, and all the specimens used were those of South Koreans. Hence, a larger sample evaluation, which may be generalizable among various populations, is needed; moreover, further studies addressing these shortcomings may provide a better understanding of the MEZ of the ISM. Third, the present study used cadavers, which were of elderly individuals. Since it is impossible to determine active trigger points from the cadavers, further study focusing on the correlation between the location of the active trigger point of the patient and the potential anatomical trigger point would provide further insight into pain management. Also, since the innervation can change with pathology (e.g., apoptosis or nerve ingrowth, which occurs with degenerative disc disease), the results may not represent the general population.

In conclusion, using whole mount nerve staining, it was found that the medial 2/5 area (e.g., section B) could be a potential anatomical trigger point in the ISM. The deltoid tubercle of the scapula may be considered a surface anatomical landmark to locate potential pain sites. The two potential injection sites may be at the center of the superior and middle part of the ISM directly inferior to the deltoid tubercle along the path of the perpendicular line. Anatomical knowledge of the location of the potential MTrPs and the MEZ of the ISM can be used to define BoNT injection sites to potentially treat MFPS in ISM.

AUTHOR CONTRIBUTIONS

HJ‐L and JH‐L (these authors contribute equally to this work) were involved in conceptualization, dissection, experiment, validation, and writing and editing of the original manuscript. KH‐Y was involved in experiment, validation, and visualization. HJ‐K was involved in project administration, conceptualization, supervision, and critical revision of the manuscript for intellectual content. Hee‐Jin Kim is responsible for the overall content as guarantor. All authors have read and agreed to the publication of this manuscript. Institutional Review Board Statement: This study was performed in accordance with the principles outlined in the Declaration of Helsinki. All cadavers were legally donated to the Surgical Anatomy Education Centre of Yonsei University College of Medicine (approval number: YSAEC 21–005).

FUNDING INFORMATION

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2022R1I1A1A01069499). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NRF NRF‐2019R1C1C1010776).

CONFLICT OF INTEREST STATEMENT

The authors declare no competing interests.

ACKNOWLEDGMENTS

The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase mankind's overall knowledge that can then improve patient care. Therefore, these donors and their families deserve our highest gratitude. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2022R1I1A1A01069499). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NRF NRF‐2019R1C1C1010776). The authors thank Soowan Kim from Johns Hopkins University and Shihyun Kim from Boston University for their revision of the English translation of this manuscript.

Lee, H.‐J. , Lee, J.‐H. , Yi, K.‐H. & Kim, H.‐J. (2023) Anatomical analysis of the motor endplate zones of the suprascapular nerve to the infraspinatus muscle and its clinical significance in managing pain disorder. Journal of Anatomy, 243, 467–474. Available from: 10.1111/joa.13868

Hyung‐Jin Lee and Ji‐Hyun Lee is contributed equally to this work.

DATA AVAILABILITY STATEMENT

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

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