Herein, we describe a series of cases involving an alternative analgesic technique, the parascapular sub-iliocostalis plane (PSIP) block for patients suffering from posterior rib fractures.

The PSIP block was previously described only as single case report1 being this report the first case series in posterior rib fracture patients. The PSIP block may be an alternative whenever contraindications for erector spinae plane (ESP) block or paravertebral block (PVB) are present, due to its less action in the anterior spinal nerves or to its less risk of inadvertent neuraxial involvement.1

To date there are no studies, neither cadaveric nor clinical, related to mechanism of action and local anesthetic (LA) spread of the PSIP block.

Details about the patients and about patients’ condition, comorbidities, analgesia approach, clinical scenario, progression of the case and outcome are described in Table 1.

The PSIP blocks were performed with the patient lateral decubitus under American Society of Anesthesiologists standard monitoring. A high-frequency linear ultrasound probe (Acuson 300; Siemens, Munich, Germany) was placed in a parasagittal plane orientation to 2cm from the medial scapular border at the level of the edge of the scapula spine under sterile conditions (between the fourth rib level and sixth rib level depending on the location of the posterior rib fractures) (Fig. 1). The trapezius, rhomboid major, iliocostal, and intercostal muscles were visualized from the superficial to deep muscular layers cranial to 5th rib; distal to 5th rib only trapezius and iliocostalis muscles are observed (Fig. 1). A sonovisible 100mm 18G needle (Contiplex S ultra; B. Braun, Melsungen, Germany) was inserted with a cranial to caudal orientation using an in-plane technique and advanced in the iliocostal-intercostal myofascial plane in the vicinity of the rib (Fig. 1). The needle location was confirmed with a 2mL saline solution, after which ropivacaine (Fresenius Kabi Pharma, Santiago de Besteiros, Portugal) was administered (Table 1). A catheter was then inserted 6cm beyond the needle tip and tunneled under the skin. No sensitive alterations were noted in all the patients.

Figure 1.

Description of the parascapular sub-iliocostalis plane block performed in patient 3.

With the patient in a lateral position, with both arms along the body, a high-frequency linear ultrasound probe was placed with a parasagittal orientation, immediately adjacent to the medial scapular border at the level of the edge of the sixth rib level. Identification of the lateral border of the iliocostalis muscle and performance of the parascapular sub-iliocostalis plane block. The tendinous insertion of the ILCM at the rib is in the superolateral direction (it should not be confounded with the insertion of the levatore costarum muscles whose insertion is in the inferior-lateral direction). The rhomboid major or minor muscle and the posterior superior serratus muscles are observed between the trapezius muscle and the iliocostalis muscles at upper levels. Abbreviation: LA, local anesthetic spreading.

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During this period, all the patients maintained intravenous conventional analgesia. The patient remained under continuous monitoring of the vital signs in an intermediated care unit.

The PVB and ESP block may promote a central sympathetic blockade that can be associated with significant hypotension and bradycardia, affect ventricular function, and decrease cardiac output, which can increase pulmonary edema and result in worsened dyspnea. Additionally, significant chest wall weakness can arise from these techniques, affecting thoracic expansion and, indirectly, venous return.1–5

These features may put patients at risk of aggravation of preexisting cardiovascular disease, such as in patient 1 case, or aggravate respiratory distress resulting from concomitant pulmonary contusion, post-traumatic atelectasis, undrained pneumothorax, diaphragmatic paralysis or rupture or when there is a preexisting lung disease, such as in the case of patients 1–4, due to the neuromuscular block that may arise from the ESP block or PVB (the thoracic expansion is less likely to be affected with the PSIP block mainly due to the reduced risk of bilateral block and to the limited action of the PISP block on the spinal nerves in opposition to the ESP block or PVB).1,10

The ESP block and the PVB may be hazardous whenever concomitant brain trauma is present, such as in the case of patient 1 and 3. The presence of sepsis or hemostasis alterations may turn out preferable the placement of a catheter away of the vicinity or the neuraxial region.10

Indeed, some studies failed to demonstrate that the ESP block spreads to the paravertebral space,6 whereas others concluded that, beyond the paravertebral compartment, epidural spread is the main component of its analgesic properties.4

It has been reported a circumferential epidural spread of LA after an ESP block, which can worsen cardiac condition in high-risk patients.2

Potentially, the PSIP block would provoke less epidural-like effects compared with the ESP block due to a lateral injection point, which lowers the risk of massive epidural/paravertebral spread or bilateral block.1,10 On the other hand, the epidural spread of LA epidurally or the inadvertent dural puncture or direct epidural injection may affect the intracranial pressure when an ESP or PVB are used.10

Rhomboid intercostal blocks have been successfully performed in patients with multiple lateral-posterior rib fractures and other causes of chest wall pain.7

However, in the study by Elsharkawy et al., the staining stopped at the lateral edge of the ESM (iliocostalis muscle) in one-third of the specimens, and in cadavers, no staining was observed to the erector spinae muscle (ESM).7

Therefore, this block may have limited action at the fracture sites medial to the lateral border of the iliocostalis muscle (ILCM), as this muscle may represent an obstacle for the LA present in the sub-rhomboid plane or lateral to the ILCM, preventing its spread to the fractured rib plane below the ESM.

The eventual criticism to this novel technique may be hypothetically related to its nomenclature, nevertheless an Expert Consensus in 2021 (ASRA-ESRA Delphi Consensus)8 stablished the retrolaminar (RL) block as an independent entity from the ESP block: in the RL block the injection is done between the laminae and the ESM, in the latter the injection is done between the transverse process and the ESM; on the other hand, in the PSIP block, the injection is done between the most lateral component of the ESM and the ribs, which lead to completely different properties in terms of dispersion pattern, mode of action, contraindications, benefits and complications comparing to the RL and ESP blocks. Of note, the PSIP block is the only block of this group that does not have any component of the vertebrae as a sono-anatomical reference, which makes it a complete novel technique, as the retrolaminar block is when compared to the ESP block.1,10

The PSIP block has also potential benefit for thoracic spine surgery or trauma, as it was shown in a recent report by Almeida et al.,9 due to its action in the posterior rami of the spinal nerves, with less direct action in the anterior spinal nerves, as such, when concomitant thoracic spinal fractures are present the PSIP block can be an interesting alternative to limit neuroaxial LA spread because meningeal membranes or dura-mater can be disrupted, which can be hazardous and complicate neurological check when the ESP or PVB are used.

In the PSIP block the catheter is placed underneath the ILCM, enhancing the craniocaudal LA spread across the longitudinal myofascial sub-ILCM plane and the deeper spread of LA through the disrupted tissue. The observed significant reduction of pain with motion may be related to the LA spread to deep intercostal layers in the fracture sites, direct infiltration of the fractured bone, and action in the proximal intercostal nerves.1

The additional spread along the deep intercostal layers is likely, but LA would not reach easily the paravertebral space. The PSIP block could also spread medially below the ESM to block mainly the posterior spinal nerves, contributing to vertebrae analgesia as it was described by Almeida et al. in a case of thoracic spine fixation surgery.9 It should be emphasized than if concomitant anterior-lateral fractures are present the PSIP block should not be a reliable alternative to the ESP block or the PVB. The clinical scenarios in which the PSIP block, despite lacking significant direct action in the ventral spinal rami, could be preferable to the ESP block or PVB for posterior rib fractures, are expressed in Table 2.

The PSIP block has now revealed its potential in the small series of cases, further large studies are necessary to confirm our results, but we are very convinced of its merits based on our experience.

None declared.

The authors declare that they have no conflicts of interest.