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Clavicle fractures account for 2 to 3% of all fractures and approximately 35% of shoulder girdle injuries. Nearly 80% of these occur at the midshaft of the clavicle, with about 20% at the distal third, and only 2 to 3% at the proximal third. 1 These fractures cause moderate to severe postoperative pain and given the brachial plexus’s proximity to the surgical field carry a perioperative nerve injury risk of 7 to 24%.2 In recent years, the incidence of surgical fixation for clavicle fractures has risen.1 At the same time, regional anesthesia has become more prominent because of its clear advantages over general anesthesia: superior analgesia, reduced postoperative opioid use, shorter hospital stays, and higher patient satisfaction.3 Traditionally, the interscalene brachial plexus block, alone or combined with a superficial cervical plexus block, has been considered the gold standard for clavicle anesthesia.4 However, unwanted side effects have been reported, such as ipsilateral diaphragmatic paralysis due to phrenic nerve block, dysphonia or hoarseness, and Horner’s syndrome.5 In 2019, Valdés-Vilches et al. described the clavipectoral fascia plane block (CPB), an innovative technique for anesthesia and analgesia midshaft clavicle fractures as an alternative to traditional brachial plexus approaches. It is simple to perform, uses clear superficial landmarks, and relies on the clavicle itself as a bony ‘stop’ for needle placement. By targeting the peripheral nerve branches that innervate the clavicular periosteum, it provides effective anesthesia and analgesia without causing diaphragmatic, motor, or sensory block of the ipsilateral upper extremity. The technique’s name reflects a modern understanding of the clavipectoral fascia (CPF), which is thought to facilitate circumferential diffusion of anesthetic around the clavicular periosteum. Anatomically, this is based on a proposed fascial continuity between the cervical and thoracic fasciae, forming a CPF that completely envelops the clavicle and allows homogeneous, circumferential spread of anesthetic.6 Classically, CPF is described as a broad sheet of connective tissue in the anterior thorax, running along the coronal plane between and enclosing the pectoralis minor and subclavius muscles, and laterally fusing with Gerdy’s axillary suspensory ligament to form the roof of the axillary fossa.7 In contrast, in contemporary descriptions of the CPF, at least two distinct layers are proposed, each enveloping different anatomical structures in the region. The first, larger retropectoral (or interpectoral) layer inserts on the anterior border of the clavicle, lies in intimate continuity with the pectoral fascia, surrounds the pectoralis major muscle, and merges superiorly with the investing layer of the deep cervical fascia around the sternocleidomastoid and trapezius muscles. The second, smaller retropectoral layer inserts on the posterior border of the clavicle and is associated with the prevertebral layer of the deep cervical fascia also known as the omohyoid fascia. This deeper layer encases the axillary artery, axillary vein, and brachial plexus, fully isolating them from the anterior compartment. Inferiorly, it also envelops the coracoclavicular Caldani ligament.8 This complex fascial architecture underscores a key distinction between the classical and contemporary views of the CPF’s pattern of insertion and periosteal coverage. The modern hypothesis posits a continuous fascial plane between the cervical and thoracic fasciae, allowing the CPF to circumferentially envelop the clavicular periosteum in its entirety.8 In contrast, traditional anatomical texts locate the CPF’s origin on the posteroinferior aspect of the clavicle, from which it descends to encase only the subclavius and pectoralis minor muscles.7 In 2023, Labandeyra et al. performed the first cadaveric study of the CPB on specimens with intact clavicles. They found that while superficial dissection revealed methylene blue in supraclavicular nerve branches and the superficial muscular plane, neither the deep muscular plane nor the CPF showed any staining. On the periosteum, dye was predominantly anterosuperior (53.5%), with minimal posteroinferior spread (4%).9 Additionally, in another anatomical study that evaluated the CPB technique in midshaft clavicle fractures, diffusion remained largely anterosuperior (57.3%) with just 6.5% posteroinferior and there was no staining at the fracture site or in deeper structures such as pectoralis minor, subclavius, or CPF. These findings suggest that although both CPF layers anchor to the clavicle’s inferior margin around subclavius, they do not connect with cervical or thoracic fasciae, challenging the notion of complete circumferential diffusion via the CPF.10 Also, in 2023, Heredia-Carqués et al. conducted a cadaveric study comparing the distribution patterns of CPB versus direct subclavius injection. The CPB stained mainly the anterosuperior periosteum, whereas subclavius injections consistently stained the posteroinferior region. From this, they hypothesized that combining both approaches might achieve full periosteal coverage.11 Building on that, in 2024 Labandeyra et al. introduced the Midclavicle Block (MCB): CPB plus an additional injection through the subclavius targeting the posteroinferior periosteum. In their cadaveric study, methylene blue stained 37 ± 16% of the anterosuperior periosteum and 23 ± 13% of the posteroinferior, both focused at the midshaft without full circumferential coverage. Anterosuperior staining was centered on the midshaft with minimal lateral or medial (sternoclavicular-joint) involvement, while posteroinferior staining was confined to the subclavius insertion at the mid-to-lateral third junction. Although the stained regions did not align directly opposite each other, both surfaces showed significant uptake, indicating relevant coverage.12 These anatomical findings demonstrated a consistent anterosuperior periosteal staining pattern after CPB, with limited posteroinferior spread, even in the presence of fracture lines, suggesting that the CPF does not fully envelop the clavicle. In contrast, a separate cadaveric study using the SM approach showed consistent posteroinferior periosteal staining.9–11 These complementary results supported the hypothesis that combining both approaches could improve coverage. This ultimately led to the development of the MCB, a dual approach technique designed to enhance periosteal diffusion at the clavicle midshaft, challenging the contemporary fascial model and offering a more targeted anatomical solution.12 The clavicle functions as a transitional structure between the thorax and upper limb and is covered by multiple muscular and ligamentous insertions that influence both mobility and the organization of surrounding fascial planes. On its superior surface, muscles such as the sternocleidomastoid, trapezius, deltoid, and pectoralis major insert, while on its inferior aspect, the costoclavicular and coracoclavicular ligaments (trapezoid and conoid) and the SM are attached.13 These structures act as physical barriers that limit anesthetic spread, favoring its concentration around the midshaft region. The SM, originating from the first rib and inserting on the undersurface of the clavicle, courses within the CPF. Its anatomical position facilitates diffusion toward the posteroinferior periosteum and, given its proximity to the neurovascular structures of the brachial plexus, plays a critical role in balancing efficacy and safety in regional anesthesia.14 In this context, the MCB represents an anatomically grounded technique that takes advantage of natural muscular and ligamentous barriers to achieve a localized anesthetic diffusion pattern at the midshaft. Future clinical validation will be essential to determine its real world effectiveness and define its role among regional anesthesia techniques for clavicle surgery.References Ropars M, Thomazeau H, Huten D. Clavicle fractures. Orthopaedics and Traumatology: Surgery and Research 2017;103(1):S53-S59. doi:10.1016/j.otsr.2016.11.007Clitherow HDS, Bain GI. Major neurovascular complications of clavicle fracture surgery. Shoulder Elbow 2015;7(1):3–12. doi:10.1177/1758573214546058Hutton M, Brull R, Macfarlane AJR. Regional anaesthesia and outcomes. 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