INTRODUCTION
The shoulder blade, or scapula, is a triangular flat bone of the shoulder girdle. Scapular surgeries are infrequently performed in routine clinical practice and may include surgeries for scapular fractures, tumors, or deformities that require correction. General anesthesia has been a common choice whenever such surgery is posted, which is mostly attributed to the complex anatomy of the surrounding structures that come in the surgical pathway and secondly to the position of the patient during surgery, which may make intubation challenging should the need arise. Regional anesthesia (RA) for scapular surgeries has not been attempted because of the paucity of cases, as most trauma cases are managed conservatively. However, even for a limited number of cases that require surgical correction, analgesic options are limited to drugs or local infiltrations, leaving patients in agony. Ultrasonography has revolutionized the field of RA by adding newer types of nerve or fascial plane blocks annually. However, the application of ultrasound-guided (USG) RA for scapular surgeries requires thorough knowledge of the functional and applied anatomy of the structures involved. As this is a literature review, we wanted the readers not only to know the names of the various blocks but also to understand how each of them can be performed. It is difficult to find all the aforementioned blocks in one article. Our study aimed to provide optimum insights into all these blocks in a concise manner. This article discusses the various possible ways in which nerve blocks can be combined, targeting specific scapular surgeries.
APPLIED ANATOMY OF SCAPULA
The embryological development of the scapula is complex and is believed to be closely related to upper limb development. However, most inferences are derived from embryonic development in lower animals. Detailed knowledge of the innervation of the surgical area, including the dermatomes, myotomes, and osteotomes, is of paramount importance for planning the RA technique that is most suitable for surgery (Figs. 1-3). The scapular innervation includes the following:
Dermatomes
Upper back skin overlying the scapula are supplied by (Fig. 1)
1. Superior cervical plexus
- Supraclavicular nerve (C3, C4) supplying skin over the spine of the scapula
2. Brachial plexus
- Suprascapular nerve (C5, C6)
- Superior lateral cutaneous nerve (a branch of the axillary nerve), which supplies the skin over the lateral scapular area overlying the deltoid muscle (C5, C6)
3. Medial branches of the dorsal rami of cervical nerves C4-C8 and thoracic nerves T1-T6: supply the skin of the scapular region [1].
Myotomes
Muscles of the scapular region are supplied by (Fig. 2)
1. Brachial plexus
- Dorsal scapular nerve (C5): levator scapulae, rhomboid major and minor
- Suprascapular nerve (C5, C6): supraspinatus, infraspinatus
- Upper and lower subscapular (C5, C6): subscapularis, teres major (lower subscapular)
- Thoracodorsal nerve: latissimus dorsi (C6-C8)
- Axillary nerve (C5, C6): teres minor, deltoid
2. Spinal accessary nerve (XI cranial nerve): Trapezius
Osteotomes
All are branches of the brachial plexus (Fig. 3)
- Suprascapular nerve (SSN) (C5, C6): posterior scapula, acromioclavicular joint, posterosuperior glenohumeral joint
- Subscapular nerve (C5, C6): anterior scapula, anterosuperior glenohumeral joint
- Lateral pectoral nerve (LPN) (C5-C7): acromioclavicular joint.
- Axillary nerve (C5, C6): anteroinferior glenohumeral joint, posteroinferior glenohumeral joint
SCAPULAR PATHOLOGIES
Scapular fracture
There has been a change in the epidemiology of scapular fracture, with a rising trend from a previously reported incidence of approximately 1% to 2.2% [1]. This increase can be attributed to the increasing use of computed tomography to diagnose this infrequent injury [2]. The distribution is:
• Body: 45%
• Glenoid Process: 35%
• Acromion: 8%
• Coracoid: 7%
Several classifications have been described, of which the Orthopedic Trauma Association classification is provided below (Fig. 4).
MECHANISM OF INJURY
The scapula is stabilized in its position by humerus muscles and ligaments; therefore, a very high-energy blunt or penetrating trauma is required to cause scapular fracture. Motor vehicle accidents account for over 70% of accidents and are often associated with other life-threatening injuries. Seizures and electric shocks were the other identified causes. Direct force can fracture any part of the scapula, whereas falling with humeral head impaction can result in glenoid and scapular neck fractures due to indirect force [3].
ASSOCIATED INJURIES
Kozanlı and Güler [4] studied the injuries associated with scapular fracture caused by blunt thoracic trauma. Intrathoracic injuries include rib fractures (91.9%), lung contusions (80.2%), pneumothorax (41.9%), hemothorax (37.2%), sternum fractures (15.1%), and clavicle fractures (10.5%). Extrathoracic injuries include vertebral fractures, intracranial injuries, extremity fractures, and intra-abdominal injuries (18.6%, 16.3%, 12.8%, and 5.8%, respectively), with intracranial hemorrhage being the most common cause of mortality [4]. Brachial plexus injury occurs in 5-13% of cases and has prognostic value in recovery parameters [3].
MANAGEMENT
Most scapular fractures (approximately 90%) are managed conservatively as they are non-displaced or minimally displaced [5]. Surgical corrections were as follows:
• Articular displacement or gap > 4 mm
• Articular involvement > 20-25%
• Medialization of the scapula > 20 mm (reduced to 10 mm for double disruptions and 15 mm when combined with 30° angulation)
• Glenopolar angle ≤ 22°
• Angulation ≥ 45°
Scapular tumors
In a large case series of 566 patients with bone tumors, scapular tumors accounted for only 1.6% of cases [6]. One retrospective study evaluated 193 patients with scapular tumors [7], in which osteochondroma was the most common (23.3%), followed by chondrosarcoma (17.6%), bone metastasis (16.6%), Ewing sarcoma (8.8%), and osteosarcoma (7.8%). They also found that increasing age was associated with an increased incidence of malignant tumors of the scapula, with an incidence as high as 91% after the age of 50 years [7].
Currently, the Malawer classification system and Musculoskeletal Tumor Society Classification of Skeletal Resections (Fig. 5) are the most utilized classification systems [8]. Surgical management may include curettage and partial or total scapulectomy, with or without reconstruction. Brachial plexus involvement in these tumors can be suspected due to intractable pain and motor deficits and is a contraindication for resection if the latter is likely to result in nonfunctional limbs where nerve or muscle grafting is not possible [9].
PROPOSED RA OPTIONS FOR SCAPULAR SURGERIES
Interscalene block (ISB) plus thoracic paravertebral block (TPVB)
In a case report, Vadhanan and Bokka combined ISB and T7-T8 TPVB with a catheter in situ to achieve surgical anesthesia in a patient with a comminuted and displaced scapular body fracture and multiple rib fractures [10]. They injected a mixture of 6 ml 2% lignocaine with adrenaline, 8 ml 0.5% bupivacaine, and 6 ml normal saline at the T7-T8 TPVB in the sitting position, followed by the insertion of a catheter. They administered 15 ml of 0.25% bupivacaine for ISB. They observed adequate anesthesia supplemented with dexmedetomidine infusion and good postoperative analgesia for 48 h, achieved with boluses administered via a TPV catheter.
Superior trunk block (STB) plus TPVB
In correspondence with the above-mentioned case report, Ravi et al. [11] suggested that using STB instead of ISB should be considered, as the former is associated with a much lower incidence of hemi-diaphragmatic palsy than ISB, which is especially desirable in patients with scapular injury as they often have combined thoracic injuries. Selective supraclavicular block (SCB) was added to the above combination by Yamak Altinpulluk et al. [12] in an older woman with multiple comorbidities who used 0.5% ropivacaine, 17 ml for STB, 3 ml for SCB, and 20 ml for TPVB. The patient underwent awake scapular fracture surgery with minimum sedation and was discharged the following day with a numeric rating score (NRS) of 1-2.
1. Continuous TPVB has also been described as a part of multimodal analgesia in patients with scapular body fractures. However, the authors inserted a catheter at the T2-T3 level so as to block a portion of the brachial plexus [13].
2. A superficial serratus plane catheter block providing sufficient pain relief was described in an older woman with dementia and coagulopathy following an inferior scapular fracture that was conservatively managed. Deeper blocks, such as TPV or thoracic epidural blocks, are contraindicated because of coagulopathy [14].
3. Elsharkawy et al. [15] reviewed the combination of ISB with rhomboid intercostal block using catheter techniques for both blocks, in two patients undergoing scapular surgery for postoperative analgesia. Both patients demonstrated adequate dermatomal coverage, with a mean NRS score of 3 on postoperative day 4.
4. Scapular block by Sonawane et al. [16] combined three injections covering all dermatomes, myotomes, and osteotomes required for scapular surgery. They prepared a local anesthetic (LA) mixture containing 20 ml each of 0.5% bupivacaine and 2% lignocaine with 8 mg of dexamethasone.
• 1st injection (10 ml): selective upper trunk (C5 and C6) and supraclavicular nerve block. They injected 2.5 ml of the LA mixture above and below C5 and 5 ml between the sternocleidomastoid and middle scalene muscles to block the supraclavicular nerves.
• 2nd injection (15 ml): subclavian perivascular block (13 ml) and sub-omohyoid suprascapular (SOS) nerve block (2 ml).
• 3rd injection (15 ml): erector spinae plane block (ESPB) at T2 to block the dorsal rami of C6-T5.
5. ESPB combined with ISB: Kilicaslan et al. [17] used 15 ml of LA at the T2 and T3 levels each for ESPB, along with 15 ml LA for ISB supplemented with moderate sedation in a patient with a glenoid fracture.
6. ISB with superficial cervical plexus block (CPB) with continuous ESPB at the T3 level was administered for intra- and postoperative analgesia in a patient undergoing partial scapulectomy with wide local excision of soft tissue sarcoma arising from the left latissimus dorsi. They used a 20-ml mixture of 0.5% ropivacaine and 8 mg dexamethasone for ISB and CPB. They performed a low ISB by placing the probe in the interscalene groove at the C7 vertebral level and depositing 10 ml of the drug. CPB was performed by directing the needle tip into the plane between the lateral border of the sternocleidomastoid and the prevertebral fascia, and 10 ml of the drug was administered. They injected 30 ml of 0.375% ropivacaine for ESPB at the T3 level in a slow bolus followed by 0.2% ropivacaine infusion at 5 ml/h. The authors reported remarkable pain relief with an NRS < 3 and comfortable breathing with a continuous ESPB in the postoperative period [18].
7. An isolated continuous dorsal scapular nerve block via a catheter was provided by Auyong and Cabbabe for postoperative pain relief in a patient with snapping scapula syndrome [19]. Targeting a single nerve provides sufficient pain relief in their report.
REGIONAL BLOCKS FOR GLENOID FRACTURES
Shoulder block
This technique was first described by Price and included a combination of the USG posterior approach of the SSN and axillary nerve blocks [20]. It is used as an alternative to ISB, which remains the gold-standard anesthetic technique for shoulder surgery. However, ISB invariably causes a phrenic nerve block; therefore, it is not preferred in patients with limited respiratory reserve. In contrast, shoulder block is associated with sparing the articular branches of both nerves, thus requiring a mild-to-moderate degree of sedation if used as an anesthetic technique.
Shoulder anterior capsular block
Galluccio et al. [21] described this block as an effective anesthetic technique for shoulder intervention in combination with the SSN block. Here, two injections are given: first at the inter-fascial plane between the deltoid and subscapularis muscle and second at the pericapsular space after crossing the subscapularis muscle before the hyaline cartilage of the shoulder joint. The authors demonstrated blocking of the articular branches of not only the axillary nerve but also the LPN and musculocutaneous nerve, irrespective of their origins with 10-15 ml of 0.2% ropivacaine with 8 mg dexamethasone.
Infraspinatus-teres minor (ITM) inter-fascial block
Another novel approach for combined block of SSN and axillary nerve is described in a cadaveric study and demonstrated over few patients [22]. Here, the authors first kept the linear probe sagitally over the back of the humerus, then moved it caudally and medially to find the ITM inter-fascial plane. They found that the catheter could be left in situ in this plane for continuous and effective analgesia after shoulder surgery.
Combination of peripheral nerve blocks
While shoulder blocks have become a popular modality for postoperative analgesia in shoulder surgery, individual nerves supplying various regions of the glenohumeral joint can also be targeted for optimum pain relief, prevention of chronic shoulder pain, or management of chronic shoulder joint pain conditions.
1. SSN block
1) Posterior approach: This was first described by Harmon and Hearty [23], where the patient is in the sitting or lateral position with the operator standing behind him. A linear probe is placed above the spine of the scapula (easily palpable) and moved from medial to lateral to identify the suprascapular notch (sudden dip in bony continuity). Suprascapular arterial pulsation may be observed close to the notch; otherwise, color Doppler can be used to identify suprascapular vessels. A 5-10 cm long echogenic needle is inserted from the medial to the lateral direction to touch the floor just medial to the notch, and 5-7 ml of the LA of choice is injected in the plane lifting the supraspinatus muscle above the bony surface. There are limitations to this approach: a) the articular branches of the SSN are already given off before entering the suprascapular notch in 50% of cases; thus, sparing is common; b) the suprascapular notch is absent in 15% of patients; c) the superior transverse scapular ligament covering the suprascapular notch is sometimes ossified, compromising image quality; and d) injury to the suprascapular vessels is common in this approach.
2) Anterior approach/SOS approach: This approach was described by Siegenthaler and was performed in the same position as that for the supraclavicular brachial plexus block [24]. After obtaining the supraclavicular brachial plexus view on the first rib, the neck was scanned up and down to observe the formation of the superior trunk (ST) from the C5 and C6 ventral rami and then scanned down and laterally to identify the origin of the SSN from the ST, which lies just below the omohyoid muscle. One can appreciate the “SPA” arrangement of SSN (S) and the posterior (P) and anterior (A) division of ST from lateral to medial direction. The LA is deposited just lateral to the SSN and below the inferior belly of the omohyoid muscle. A limitation of the anterior approach is hemi-diaphragmatic paresis because of the close proximity of the phrenic nerve, even with 10 ml of LA. In a cadaveric study, the minimum effective volume required to block the SSN in 90% of individuals, sparing the phrenic nerve was found to be 4.2 ml [25].
2. Axillary nerve
1) Posterior approach: Rothe et al. [26] described this approach. The patient’s ergonomics are the same as those described for the posterior SSN block approach. The linear probe is placed parasagittally over the back of the humerus and scanned from top to bottom to identify the head and shaft of the humerus. The neurovascular bundle (NVB) contains the posterior circumflex humeral artery and axillary nerve, which can be identified just inferior to the teres minor attachment in the facial plane. The 5-10 cm echogenic needle is inserted cephalocaudally to prevent direct injury to the NVB, and 5-7 ml of LA is deposited. The limitation of this approach is the sparing of articular branches, which are provided before entering the quadrangular space.
2) Anterior approach: This is also known as the Fazardo’s approach [27]; it is described to block even the articular branches in the inter-fascial plane between deltoid and subscapularis muscle, before entering the quadrangular space. In addition, it is the preferred approach for chronic shoulder pain management.
3) Inferior approach (Chang’s approach) [28]: With the patient in the supine position and the arm abducted, a linear probe is placed over the posterior axillary fold to visualize the latissimus dorsi and teres major muscles. Then the probe is moved towards the apex of the axilla, where the inter-fascial hyper-echoic plane containing NVB is identified and LA is deposited.
3. LPN block
1) Interpectoral plane or pectoral (PEC)-I block [29]: The inter-fascial plane between pectoralis muscles is identified. The pectoral branch of thoraco-acromial (TA) artery is a useful landmark in this plane. The LPN is believed to lie close to this artery and the drug deposited here is likely to block the LPN.
2) Blocking the acromial branch of the LPN [30]: This novel technique is mainly used in chronic shoulder pain conditions in combination with the other peripheral nerve blocks described above. The acromial branch of the TA artery and LPN lies in the space between the clavicle and coracoid process, superiorly covered by the anterior deltoid muscle and inferiorly covered by the coracoclavicular ligament. A small volume of LA is sufficient to block the nerve at this site. Neuromodulation and radiofrequency ablation of the LPN is also done in this space.
4. Subscapularis plane block
it is the same plane where axillary nerve is blocked via the anterior approach between the deltoid and subscapularis muscles. A 15-ml LA in this plane is sufficient to block both the axillary and subscapular nerves via dispersion of the drug along the ventral surface of the subscapularis muscle. The combination of the sub-omohyoid SSN and PEC-1 blocks with the subscapularis plane block has been described as a phrenic-sparing regional block for shoulder surgery [31].
CONCLUSION
The scapula has a very complex innervation with a major supply from the SSN, axillary nerve, subscapular nerve, LPN, musculocutaneous nerve, supraclavicular nerve, and dorsal rami of C5-T6. The identification and mapping of dermatomes, myotomes, and osteotomes are important for planning regional blocks for a particular procedure or surgery over the scapula or glenoid region. Although various combinations of these blocks have been described by some authors owing to the paucity of appropriately planned randomized controlled trials, none of them can be considered better in isolation. Nevertheless, there is still much scope for combining newer and upcoming ultrasound-guided nerve blocks to achieve the desired level of anesthesia and/or analgesia for scapular surgery or chronic scapular pain. Appropriate counseling, proper written informed consent, and adequate sedation for patient cooperation are of paramount importance in planning regional blocks for the scapula.
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