Chronic shoulder pain is one of the most frequent reasons for consultation, corresponding to the third most common musculoskeletal complaint with a prevalence of up to 55% in the general population [1]. On a socioeconomic level, it represents 4.5 million visits to the doctor with an estimated cost of three billion dollars each year in the United States alone, representing an enormous economic burden and a diagnostic challenge for shoulder surgeons [2, 3].

There are multiple etiologies that produce chronic shoulder pain, and despite the existence of specific tests in the physical examination, diagnostic aids such as ultrasound and MRI, it is difficult to achieve an accurate approach to achieve an unequivocal diagnosis of the cause of pain or motor disability, resulting in persistence of symptoms even after surgical management, which is associated with a substantial decrease in the functional capacity of the glenohumeral joint [4].

In view of this situation, different approaches to pain management based on both pharmacological and non-pharmacological methods have emerged. Within this broad spectrum are included physical rehabilitation, opioid analgesics, non-opioid analgesics, and finally more invasive procedures such as analgesic interventionism, which is useful as a diagnostic procedure or as a differential diagnosis, based on the anatomical accuracy described in the latest available studies [3].

In different cadaveric and ultrasound interventional studies, it has been proposed to divide the innervation of the glenohumeral joint into four quadrants, establishing the suprascapular nerve (SSN) in the posterior portion and the axillary (AN) and lateral pectoral nerves for the anterior portion as the main ones involved [3, 5]. The SSN is the main source of innervation of the shoulder joint; therefore, it is one of the targets of analgesic interventionism [6]. Over time, the approach technique has been modified, with the intention of generating more selective joint sensory interventions. The current approach in medical practice indicates an approach to the nerve through the transverse ligament of the scapular [7], however, there are anatomical studies that suggest a distribution of the articular branch of the SSN above this transverse ligament [8]. Likewise, having an important representation of the articular capsule, the axillary nerve approach is a common practice, having as the therapeutic direction the interfacial infiltration between the deltoid and subscapularis muscles where the articular branches of the nerve run [3, 9].

Considering the current technical description and these two procedures that have proven to be effective in improving pain, an approach that combines the interfacial intervention for the axillary nerve and modifies the usual technique to approach the articular sensory branch of the SSN has become popular in our service. A retrospective study of patients operated between 2019 and 2021 was performed to determine the effectiveness of these interventions.

Methodology

The present study with a historical cohort design was conducted between 2019 and 2021 in two high complexity health institutions in Bogota, Colombia. Data collection was performed from the pain medicine service to those patients who had attended the consultation for chronic shoulder pain and had required for their treatment the SSN and AN block. The ENA (analogue numerical pain scale) was evaluated prior to the procedure (time 0), after the procedure was completed (time 1) and in the outpatient control in the days following the intervention (time 2). In this way, the medical records of the patients who were followed up from time zero to time two were reviewed, with documented ENA measurements.

Fifty patients, adults over 18 years of age, brought to the SSN and AN block with chronic shoulder pain of joint, muscle or ligament origin were included (the etiologies of chronic shoulder pain are the involvement of the rotator cuff muscles without total rupture, glenohumeral changes such as arthrosis, tendinitis and tendinosis). Patients were excluded from the analysis if they had peripheral nerve damage in the operated extremity, chronic regional pain syndrome, were postoperative for shoulder surgery and/or were receiving another type of interventional analgesic therapy.

The patients had undergone an unique time intervention based on the protocol established in the institutions, which included two approaches: the first one under ultrasound guidance via posterior approach in medial to lateral direction, the suprascapular notch is identified, the needle is advanced up to the portion superior to the transverse ligament of the scapula (modification to the classic technique), performing infiltration of 4 ml with 0.2% bupivacaine and corticosteroid, on the articular branches of the suprascapular nerve after identification of vascular structures, having the floor of the scapula as a safety repair to avoid accidental pleural puncture (fig. 1). Secondly, an anterior approach is performed in supine decubitus with the arm in 90 degrees abduction and external rotation, locating the fascia between the deltoid and subscapularis muscles where it was infiltrated with 6 ml of 0.2% bupivacaine and corticosteroid (fig. 2).

Fig. 1.

a — suprascapular block: * — classical intervention; + — proposal of new intervention. Transversus scapula ligament: arrow. Articular branches in yellow; b — procedure: Intervention above the transverse ligament, Needle: Arrows.

Fig. 2. Axillary block: Interfacial deltoid-subscapularis, Needle: arrows.

Clinical information was obtained from the patients, organizing them according to their sociodemographic characteristics and the outcome of the intervention. Pain control was established as the primary outcome based on its intensity in ENA and using means with confidence intervals to evaluate its statistical significance. Absolute pain control or a score of 0 was taken as a complete improvement. A reduction of pain intensity greater than 50% was taken as successful analgesic treatment, a reduction between 30% and 50% of the pain was described as moderate pain improvement and any reduction less than 30% was taken as no improvement. These values were considered from the numerical results assessed with the numerical analog pain scale (ENA) and taken from the clinical history recorded in the outpatient pain clinic and calculated on the day the block was performed. In addition, variables such as the amount and type of steroid used, and the modification in the requirements of non-opioid and opioid analgesic drugs after the intervention calculated in daily oral morphine equivalent dose (DEMOD) were analyzed. For the above, a p<0.05 was considered significant.

Results

Fifty patients between 18 and 90 years of age were included, with a median age of 54 years, 82% of whom were female. Of all the patients registered, 58% reported previous consumption of opioids, the most frequent being codeine, in combination with acetaminophen in 26%, followed by hydrocodone in 22% and finally tapentadol and Tramadol in 2% and 4% respectively. Regarding non-opioid analgesics, all patients consumed at least one: 90% were under management with acetaminophen, mainly associated with Neuromodulator in 60% and/or non-steroidal anti-inflammatory drugs 8% (table 1).

Table 1. Sociodemographic and clinical characteristics

Regarding other pathologies recorded, 34% of the patients did not report any in addition to the intrinsic pathology of the shoulder, 12% had a diagnosis of osteoarthritis, and 16% had fibromyalgia in association with other pathologies (graph 1). In 76% of the procedures, equal doses of corticosteroids were used (methylprednisolone 40 mg and betamethasone 6 mg) while in the rest higher doses of corticosteroids were used (betamethasone 9 mg). No adverse events were reported in the reviewed patient records.

Graph 1. Other pathologies.

For the primary outcome, a mean pre-intervention ENA score of 8/10, immediate post-procedure of 2/10, and ambulatory control of 4/10 were obtained, representing a significant improvement in pain (greater than 50% according to the initial ANS) for more than three weeks in 60% of the patients, an improvement for two weeks in 22%, for 1 week in 10%. However, 8% of patients never achieved a decrease in pain intensity (graph 2).

Graph 2. Total accumulated ANE in the pre-procedure, immediate procedure, and post-procedure.

When exploring the paired variables, a statistically significant difference was observed when comparing the ENA prior to the procedure with the ENA immediately after (p<0.001) as well as when compared with the ambulatory control (p<0.001). When assessing the behavior of the daily oral morphine equivalent dose, an average of 16 was observed before the procedure and 15 at the time of outpatient control. When analyzing the variables referring to the DEMOD, there was no statistically significant difference (p=0.117) (table 2).

Table 2. Daily oral morphine equivalent dose and Numerical Analog Scale post intervention changes

Discussion

Chronic shoulder pain is a painful syndrome of high prevalence that impacts the quality of life and constitutes an important socioeconomic burden for the health system; therefore, its timely diagnosis and management is of vital importance. Despite the difficult etiologic approach and the clinical challenge, it entails due to the poor clinical-imaging correlation, multiple therapeutic approaches have been addressed, among which interventional management is a relevant option in a population that is not a candidate for surgical management or even as a step prior to such procedure, with the aim of delaying and/or avoiding it as a symptomatic management strategy [2].

Although the suprascapular nerve provides about 70—80% of the innervation of the shoulder, there are other nerve structures that may be the cause of the patient’s pain. An example is the subacromial-subdeltoid bursa which plays an important role in chronic shoulder pain and can be clinically confused with tendon or muscle involvement, this structure receives its innervation from C5 and C6 from the SSE and AN, which may explain the clinical improvement in different chronic shoulder pain etiologies with interventions of these peripheral nerves [3, 10].

The approach for the infiltration of the AN was performed through the posterior approach considering the arterial circumflex branches as the main ultrasound repair, which presented variable effectiveness and was accompanied by low reproducibility [11]. The interfascial approach via the anterior approach made it possible to cover a greater number of structures by means of a less complex technique, which is why it was proposed as an analgesic tool, even though to date there are no studies describing transient motor block as an adverse effect associated with the volumes used [3, 12]. In our study, we sought to avoid the risk by using the combination of SSN block with a modification in a superior lateral approach to the transverse ligament and AN block at the interfacial level by decreasing the volumes, seeking an effective analgesic distribution over the possible nociceptor structures causing chronic shoulder pain and decreasing the possibility of the transient motor block following the procedure [13].

In 2021 a systematic review was performed analyzing which interventional methods and which analgesic mixtures were the most used for the management of chronic shoulder pain in patients who were not candidates for surgical intervention. The most relevant findings establish that the most commonly used mixture involved the joint use of bupivacaine with methylprednisolone, which is comparable to the present study; however, although the main therapeutic objective was SSN, wide heterogeneity was found in the techniques used, which did not allow us to draw a conclusion in this regard, and the alternative proposed in our research is an alternative to be considered in future interventions [10].

In Latin America there is little evidence about the interventional management of chronic shoulder pain, however, there is a retrospective observational study where they determined the effectiveness of the suprascapular nerve block achieving improvement of the symptomatology in a 6-month follow-up, where 43.7% of patients showed no pain, however, there is no clarity of the specific approach used and if this crossed the transverse ligament of the scapula for the infiltration of the analgesic mixture, or if only infiltration was performed on the articular branches [14].

The results of our study reflect a statistically significant difference in the decrease of pain intensity when compared to that assessed prior to the procedure by means of ENA, achieving, in addition, an effective analgesic result that is prolonged beyond three weeks in 60% of the patients. There is a paucity of studies comparing the combination of these blocks with other interventions, only one study was conducted in 2021 where an anterior approach was performed in the direction of the AN; however, they made a substantial modification by depositing the analgesic mixture in the peri-capsular space with favorable short-term results in single intervention or in conjunction with a classic SSN approach, but with the need to perform a second intervention to maintain the results for more than a week, which would limit the long-term benefits [9].

Finally, we consider that the modification of the SSN block provides safety to the intervention since it moves away from the motor branches and intervenes specifically in the articular branch [15], which added to the interfacial intervention is an interesting technique for future studies, being an observational study, its limitations in the follow-up of patients and generalization of results to clinical practice are recognized. Nevertheless, this is the first study that modifies the classic SSN intervention and adds the interfacial blockade of AN as a therapeutic intervention in the chronic shoulder pain.

Conclusion

Chronic shoulder pain is a highly prevalent condition. Analgesic interventionism is a strategy that, in many settings, has demonstrated a significant decrease in pain intensity and opioid requirements. In the present study, it was evidenced that after the combined approach both posterior (suprascapular with modification to articular branches) and anterior (axillary in subdeltoid fascia) pain intensity decreased significantly, and this analgesic effect was maintained for more than three weeks, which shows that this medication in the perineural approach of the shoulder as an interesting option for the treatment of chronic shoulder pain.

The authors did not receive funding to carry out this study.

We declare no conflict of interest.

All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

Informed consent has been obtained from all individuals included in this study.

Research involving human subjects complied with all relevant national regulations, institutional policies and is in accordance with the tenets of the Helsinki Declaration (as amended in 2013), and has been approved by the authors’ Institutional Review Board: Comite de Etica Hospital de San Jose, Bogota. 2022.