Due to the complex muscular layers in the posterior cervical region, there are various potential target for interfascial block (Table 1). Local anesthetics (LAs) injected into the interfascial plane diffuse along the fascial-covered areas toward regions of lower resistance [18], while avoiding the potential toxic effects of intramuscular administration. This allows for extensive and safe analgesia through a single injection. By understanding the muscular and fascial layers of the posterior neck and mastering the characteristics of fascial plane blocks in this region, anesthesiologists can better comprehend and utilize these techniques to enhance clinical practice.

Table 1 Common techniques for posterior cervical interfascial plane blockTrapezius Plane (TP) Block

Under ultrasound guidance, LAs are injected into the interfascial plane between the investing fascia and the prevertebral fascia, deep to the trapezius [29]. Cadaveric studies have demonstrated that the drug spreads between the trapezius and levator scapulae, rhomboid muscles. Within this interfascial plane, the drug infiltrates the dorsal rami that provide motor and sensory innervation to the trapezius. The LA blocks the muscular branches of the nerve and alleviates pain, thereby inducing muscle relaxation and facilitating early physical rehabilitation [29]. As the trapezius is one of the muscles most frequently affected by myofascial pain syndrome, TP block is currently primarily employed in managing this condition [30]. Domingo et al. [29] achieved rapid and significant analgesia by injecting 8–10 ml of 0.125% bupivacaine deep to the trapezius muscle at trigger points. More recently, Galvez et al. [31] further validated the efficacy of TP blocks. Arici et al. [32] recently reported that TP blocks effectively treat cervicogenic headache (CEH) by inactivating myofascial trigger points, demonstrating significant improvements in pain intensity, frequency, disability index, and analgesic consumption. Meanwhile, Kukanti et al.[33] reported that TP blocks can prolong postoperative analgesia following nerve transfer surgeries in the shoulder and neck region. As research progresses, additional clinical applications are expected to emerge, with promising potential for perioperative analgesia in posterior cervical surgeries.

LAs injection into the compartment superficial to the investing fascia above the trapezius muscle can also effectively block nerves traversing this layer, making it suitable for procedures such as excision of superficial occipital masses in the posterior cervical region. Under ultrasound guidance, Shao et al. [34] injected 0.3% ropivacaine superficially to the investing fascia at the deep margin of the cervico-occipital mass, effectively blocking the superficially coursing GON, TON, and lesser occipital nerve (LON) as they traveled toward the subcutaneous tissues. Subsequent subcutaneous injections were administered laterally and caudally to the mass, creating a “cup-shaped” blockade around the mass. This technique simultaneously blocked ascending cervical cutaneous branches and cross-intersecting small branches of the GON, TON, LON, and great auricular nerve. Satisfactory analgesia was achieved with a single injection. This approach establishes a novel superficial interfascial plane blockade strategy for clinical practice.

Greater and Third Occipital Nerve (GTO) Block

The atlanto-occipital (AO) joint, atlanto-axial (AA) joint, and C2–C3 zygapophyseal joints can all serve as generators in CEH. Consequently, GON and TON, which originate from the C2–C3 spinal segments, represent key targets for nerve blockade in managing this condition. However, isolated nerve blocks demonstrate limited clinical efficacy [12].

Kariya et al. [12] injected local anesthetic into the medial head of SCA at the C1 level, allowing LA to spread medially within the tendinous septum. Since both TON and GON course between the OCI and SCA before ultimately penetrating the medial head of SCA to ascend cephalad, this injection technique simultaneously envelops and blocks both nerves [35]. The fascia-like septum covers the OCI and GON creating a diffusion barrier. When LA is injected superficially to the OCI, this septum restricts diffusion of the solution, resulting in selective GON blockade without affecting TON. Consequently, intramuscular injection within the medial head of SCA remains the necessary approach [12]. However, this method inherently carries risks of myotoxicity, necessitating careful consideration of anesthetic type, concentration, and injection frequency [12]. Furthermore, larger-scale clinical studies are required to validate its efficacy.

Multifidus Cervicis Plane (MCP) Block

Under ultrasound guidance, the needle is advanced at the C5 level sequentially through the trapezius, splenius capitis, SCA, and SCE, ultimately depositing LA within the interfascial plane between the multifidus and SCE (Fig. 3). The extensive longitudinal span of the multifidus-SCE interfascial plane allows for wide spread of the injectate, blocking wide range of cervical dorsal ramus’ medial branches, achieving comprehensive cervico-occipital analgesia ranging from the C4 level superiorly to as far caudally as the T4 level [36]. Cadaveric studies [35] demonstrate that the tendinous septum of SCA is continuous with the dorsal fascia of SCE, forming a natural anatomical barrier between the C3 and C4 dorsal rami. This explains why the injectate in a MCP block does not spread cranially above the C4 level, and the injectate in a GTO block does not diffuse caudally to affect the C4 dorsal ramus.

Fig. 3

Transducer position and corresponding ultrasound image of MCP block. a Demonstration diagram of short-axis C5 level scan on a healthy individual. b Ultrasound image of MCP and ISP in short-axis scanning and the ideal needle trajectory (yellow dashed line for MCP, green dashed line for ISP), injecting local anesthetic into the interfascial plane between the MC and SCE. c Demonstration diagram of long-axis C5 level scan on a healthy individual. d Ultrasound image of the MCP and ISP in long-axis scanning. SP spinous process, MC multifidus cervicis, SCE semispinalis cervicis, SCA semispinalis capitis, SC splenius capitis; TZ, Trapezius

In 2017, Ohgoshi et al. [36] first reported the application of bilateral MCP block for postoperative analgesia following C3–C6 posterior cervical spine surgery, administering 20 ml of 0.375% ropivacaine per side. Subsequently, Mohamed et al. [37] demonstrated that MCP block provided superior clinical outcomes for cervicogenic headache management compared to GON blocks. Notably, the multifidus cervicis muscle resides within the deepest layer of the deep cervical musculature, making ultrasound visualization challenging in patients who are older or obese and potentially compromising needle placement accuracy. Most critically, an outside-to-inside needle approach carries significant risk of intrathecal injection, necessitating advanced operator expertise [36].

Inter-Semispinal Plane (ISP) Block

Initial studies by Ohgoshi et al. [13, 38] proposed the ISP block as a reliable alternative when ultrasound visualization for MCP block proves inadequate. The ISP block demonstrates comparable anesthetic coverage and duration of sensory loss to MCP block. The inter-semispinal plane serves as a pathway for dorsal rami of cervical nerve. Injection of LA between SCA and SCE at the C5 level effectively targets these posterior rami (Fig. 3b). However, due to the presence of septum within the semispinalis muscles, the cranial spread of ISP block is also limited to no higher than the C4 level. Tseng et al. [39] reported that neither ISP block nor MCP block interferes with neurophysiological monitoring, thus preserving the accuracy of intraoperative neural injury assessment. Ramachandran et al.'s prospective randomized controlled trial (RCT) [40] demonstrated that compared to general anesthesia alone, the ISP block group showed significantly improved postoperative analgesia and earlier mobilization following posterior cervical spine surgery, thereby exhibiting enhanced safety and efficacy profiles.

When compared to MCP blocks, the semispinalis muscle's relatively superficial location facilitates easier needle placement, while reducing the risk of intrathecal injection. Furthermore, the absence of major blood vessels in this plane minimizes the potential for arterial injury.

Erector Spinae Plane (ESP) Block

The ESP block was first reported in 2016 for managing chronic thoracic neuropathic pain [41]. By injecting LA deep to the erector spinae muscle, close to the transverse processes at various vertebral levels, LA spreads craniocaudally along the deep surface of the erector spinae muscle, covering multiple dermatomes to provide perioperative analgesia for thoracic, abdominal, and lumbar regions [14, 42]. For posterior cervical analgesia, ESP blocks are typically performed at T1–T3 levels, achieving dermatomal coverage from C3 cephalad to as far caudally as T4 [43, 44] (Fig. 4).

Fig. 4

Ultrasound image of ESP in long-axis scanning and the ideal needle trajectory (yellow dashed line), injecting local anesthetic deep to the ESM. The probe is placed along the long-axis over the tips of the T1–T3 transverse processes, with the needle sequentially passing through the TZ, RMM, and ESM to gently contact the transverse process. ESP erector spinae plane, TP transverse process, ESM erector spinae muscle, RMM rhomboid major, TZ trapezius

Local anesthetic deposited at the transverse process follows two primary diffusion pathways: (1) the injectate may traverse the costotransverse ligament to enter the paravertebral space, blocking dorsal and (or) ventral rami of spinal nerves—serving as an alternative to conventional paravertebral block; (2) the injectate can diffuse laterally to anesthetize the lateral cutaneous branches of intercostal nerves, producing hemithoracic sensory blockade [45]. The erector spinae plane provides the anatomical basis for cephalad spread of the injectate. As the longissimus capitis and cervicis muscles longitudinally span the cervical and upper thoracic vertebra, LA injected between the transverse process and erector spinae fascia diffuses cranially along the longissimus muscles, subsequently either penetrating into paravertebral space along its diffusion pathway, or directly blocking branches of cervical nerve dorsal rami coursing deep to the longissimus muscles.

To further elucidate the diffusion mechanisms of ESP block, Ohgoshi et al. [46] conducted cadaveric studies demonstrating that the SCA muscle and its fascia form an anatomical barrier. This structural boundary limits the injectate deeply penetrating into either ISP or MCP, thereby restricting coverage of branches of spinal nerve dorsal rami. However, Tsui et al. [47] proposed that the injectate may permeate through myofascial layers within the prevertebral fascia compartment. Their findings suggest that increasing anesthetic volume could potentially enhance this penetration.

Numerous clinical studies have confirmed the efficacy of upper thoracic ESP block in achieving multi-level dorsal rami blockade. In a RCT by Kanna et al. [48], bilateral ESP blocks performed at the T1 level to provide postoperative analgesia for posterior cervical spine surgery, injected 15 ml of 0.25% bupivacaine with 8 mg dexamethasone per side. Their outcomes demonstrated significantly superior pain control and recovery rate compared to conventional analgesia protocol. Tulgar et al. [49] performed bilateral ESP blocks at the T3 level, administering 10 ml of a LA-corticosteroid mixture per side, which provided sustained relief for chronic myofascial pain of lower cervical and scapular region. Notably, ESP blocks may also exert significant ventral rami blockade effects that warrant clinical consideration. Superior sulcus tumors can induce pain by invading adjacent structures including vertebral bodies, ribs, the brachial plexus, and sympathetic nerves. Kalagara et al. [50] successfully managed this pain using continuous ESP block at the T1 level in an affected patient. Given the potential anterior ramus blockade effect of ESP blocks, some researchers recommend avoiding bilateral ESP block for cervical spine procedures, or utilizing MCP and ISP blocks that specifically target dorsal rami, thereby minimizing the risk of nerve palsy [51].

Retrolaminar Cervical Block

The retrolaminar block serves as another viable alternative to paravertebral block [5]. Under ultrasound guidance, the needle is inserted 1–1.5 cm lateral to the spinous process until contacting the lamina, where local anesthetic is then injected. Cadaveric studies [45] demonstrate two diffusion pathways: (1) anterior spread into the paravertebral space and intervertebral foramen, achieving analgesia via dorsal ramus blockade; (2) vertical dispersion along the transversospinalis muscles posterior to the lamina.

Current research on retrolaminar cervical blocks remains limited, primarily focused on cervical radicular pain, the C6 level injections can reach cranial C2 and caudal T3 levels. This technique may potentially serve as a safer alternative to epidural steroid injections and decompressive surgery for radicular pain [5]. Compared to ESP block, the retrolaminar block reduces the risk of deep cervical artery injury, while maintaining effective craniocaudal and lateral diffusion, because of its medial injection site (closer to the spinous process). Furthermore, the lamina serves as a more distinct anatomical landmark for needle targeting, significantly reducing technical difficulty [52].

C0–C1 Joint Injection

AO joint injection serves as an etiological treatment for CEH. The AO joint is innervated by the ventral ramus of C1 and its sinuvertebral nerve branch. Analgesia is achieved through intra-articular injection of LAs or anti-inflammatory agents into the AO joint capsule [53]. With the patient in prone position and slight neck flexion, the needle is advanced under ultrasound guidance via a posterolateral approach to the AO joint capsule. The target is the superior aspect of the cup-shaped margin of the C1 superior articular process, with the needle trajectory maintained above the C0–C1 joint line to ensure avoidance of the vertebral artery [53].

Intra-articular injections exhibit limited drug diffusion, and current indications for AO joint injection are confined to the management of AO joint pain and CEH. Different studies employing intra-articular corticosteroid or lidocaine injections—though with differing follow-up periods—have consistently shown effectiveness pain relief in short-term [54, 55]. However, higher-quality evidence is required to further validate its efficacy and explore potential additional indications. Given the needle insertion site's location within the suboccipital triangle, meticulous technique is essential to avoid serious complications such as vertebral artery injury.

Serratus Posterior Superior Intercostal Plane (SPSIP) Block

In 2023, Tulgar et al. [15] first described the SPSIP block, performed in the interfascial plane between the SPSM and intercostal muscles along the medial scapular border at the T2–T3 intercostal space. The needle passes sequentially through the trapezius, rhomboid minor, and SPSM before reaching the rib or intercostal muscles (Fig. 5). Cadaveric studies [15] revealed injectate spread covering the rhomboid major, erector spinae, the deep fascia of SPSM, and intercostal nerves, the researchers hypothesized that the injectate diffused to the lateral cutaneous branches of intercostal nerves at C3–T7 levels, with potential additional spread along the erector spinae and rhomboid muscles to reach the dorsal rami of spinal nerves. In patients, SPSIP resulted in an almost complete sensory block in the back of the neck, shoulder, and hemithorax at C3–T7 dermatomes.

Fig. 5

Ultrasound image of SPSIP in long-axis scanning and the ideal needle trajectory (yellow dashed line), injecting local anesthetic into the interfascial plane between the SPSM and intercostal muscle. Probe placement at the medial border of the scapula in the 2nd–3rd intercostal space, with the needle sequentially traversing the TZ, RMM, and SPSM. SPSM serratus posterior superior muscle, RMM rhomboid major, TZ trapezius

To date, the SPSIP block has primarily been utilized for thoracic pain management and postoperative analgesia for video-assisted thoracoscopic surgery, breast surgery, clavicular surgery, and minimally invasive cardiac surgery [15, 56,57,58]. However, based on clinical observations, we suppose that the SPSIP block may contribute to posterior cervical sensory blockade. Tulgar et al. [15] demonstrated that the area of sensory blockade extends cranially to the posterior cervical region. The physiological continuity between thoracic dorsal fascia and posterior cervical fascia provides a potential diffusion pathway for the SPSIP block. Ciftci et al. [59] further identified that the SPSIP block exhibits brachial plexus blockade effects, confirming drug diffusion into the prevertebral fascia. This diffusion effect appears to be volume- and concentration-dependent, potentially enhanced with increased injectate volume or concentration.

This technique carries inherent risks. The spinal accessory nerve courses between the trapezius and rhomboid minor muscles, where iatrogenic injury during needle insertion may lead to trapezius dysfunction and winged scapula. Similarly, the dorsal scapular nerve and dorsal scapular artery traverse between the rhomboid minor and SPSM, with potential damage causing rhomboid muscle impairment [15].

C2 Dorsal Root Ganglion (DRG) Block

The C2 DRG innervates the AA joint and is also the origin of LON and GON, making it one of the common sources of cervicogenic headache [60]. Anatomically, the C2 DRG is not obstructed by vertebral structures, allowing relatively straightforward needle access. These characteristics establish it as an ideal target for interventional treatment of CEH.

The OCI serves as a critical anatomical landmark for C2 DRG block. The C2 DRG is located deep to the OCI, which spans the C1–C2 intervertebral space and the entire C2 lamina. Consequently, the space between the OCI fascia and C2 lamina forms a natural compartment housing the C2 DRG. To enhance precision and safety during the procedure, the needle is advanced beneath the OCI along the C2 lamina, with injection performed at the "entry point" of the OCI–C2 lamina interfascial space (Fig. 6). This technique allows the injectate to diffuse spontaneously to the C2 DRG, ensuring effective blockade while avoiding complications associated with excessive needle depth [61].

Fig. 6

Ultrasound image of C2 DRG and “three-in-one” block. a Ideal needle trajectory (yellow dashed line) for C2 DRG block. The local anesthetic is injected at the "entry point" of the OCI-C2 lamina interfascial space. b “Three-in-one” method. Combined blockade of TON and C3 deep medial branch in the same scanning plane (yellow arrows), with local anesthetic injection during needle withdrawal into the interfascial planes between the OCI and SC, the SCA and SC, the SCA and TZ, or the SC and TZ (red arrows). DRG dorsal root ganglion, OB occipital bone C1-C2 lateral AA joint, C1 the posterior arch of atlas, C2–C3 C2–3 facet joint, C3–C4 C3-4 facet joint, OCI obliquus capitis inferior, SCA semispinalis capitis, SC splenius capitis, TZ trapezius

The C2 DRG block demonstrates limited efficacy in both pain relief and duration of analgesia for CEH. Current evidence suggests that patients who respond to C2 DRG block may achieve more significant and sustained therapeutic effects through pulsed radiofrequency [62]. Ma et al. [61] reported a “three in one” approach to enhance the clinical efficacy of C2 DRG block. Following C2 DRG block under the same ultrasound plane, they performed concurrent TON and C3 medial branch blocks to comprehensively cover multiple pain generators including the AO joint, C2–C3, and C3–C4 facet joints. Subsequently, during needle withdrawal, they administered injections into the interfascial planes between the OCI and SCA, the SCA and trapezius, the SCA and splenius capitis, or the splenius capitis and trapezius. This multimodal approach aims to relieve occipital and upper cervical muscle tension, thereby reducing potential compression on the GON and TON.

The primary risk of C2 DRG block is spinal cord injury. It is recommended to employ a long-axis scanning approach with in-plane needle insertion. The transducer should be shifted mediolaterally until the anterior and posterior complexes just disappear while the lateral AA joint becomes visible. Strict control of needle advancement depth is mandatory to prevent medial penetration beyond the DRG [61]. For the "three in one" approach, larger-scale clinical trials are required to validate its efficacy.