Ultrasound-Guided Selective Cervical C3 and C4 Nerve Root Block: A Novel Anesthetic Approach to Perioperative Analgesia for Clavicular Fractures
The clavicle serves as a bony connection between the arm and trunk, connecting distally with the acromion and proximally with the sternum. Clavicular fractures make up approximately 2.6% of all fractures, occur more frequently in men, and involve the shoulder girdle in 44% of cases., They have been classified into three groups based on the Allman classification. Group I fractures occur in the middle third of the clavicle, group II the distal third, and group III the proximal third. Previous research has demonstrated that 69% of clavicular fractures are group I, 28% group II, and 2.8% group III.
Often, clavicular fractures are treated conservatively with oral analgesics (ie, acetaminophen, nonsteroidal anti-inflammatory drugs, and opioids). Use of a sling to provide limb immobilization may also improve pain control. However, complications may still arise, including nonunion, malunion, post-traumatic arthritis, refracture, or chronic pain syndrome. Unstable clavicular fractures may result in brachial plexus injuries, ulnar neuropathy, or inadequate shoulder stabilization and therefore may mandate surgical intervention and repair. Indications for primary open fixation include fracture comminution and tenting of the skin, significant clavicular displacement, or fractures that fail to respond to closed reduction or conservative management.
“Regional anesthesia techniques that target the C3 and C4 nerve roots can potentially maximize analgesia while minimizing upper-extremity motor blockade and may be preferable in patients undergoing clavicular surgery.”
Secondary to surgical manipulation and skin incision, clavicular surgeries may result in significant postoperative discomfort. Inadequate pain control in the recovery unit can delay discharge and increase hospital costs. In addition to efforts to maximize multimodal analgesics, regional anesthesia techniques, including low-volume interscalene and superficial or deep cervical plexus blocks, have been used to alleviate postoperative clavicle pain.,
Regional anesthesia techniques that target the C3 and C4 nerve roots can potentially maximize analgesia while minimizing upper-extremity motor blockade and may be preferable in patients undergoing clavicular surgery. The approach may also minimize motor blockade and improve a patient’s ability to participate in physical therapy.
Selective C3 and C4 Nerve Root Blockade
Figure 1: Ultrasound image of C4 transverse process showing double hump of the anterior and posterior tubercles and corresponding nerve root superficial to it.
AP, anterior tubercle of C4; PT, posterior tubercle of C4; TP, transverse process of C4
Anatomy. The third to the eighth cervical nerve roots exit the corresponding spinal foramen anterior to the transverse process between the anterior and posterior tubercle. In contrast to the other cervical transverse processes, C7 has a rudimentary or near-absent anterior tubercle with a prominent posterior tubercle.
Sonoanatomy. In a transverse axial view of the cervical transverse process, the spinal nerve root appears as a hypoechoic discoid shape between the anterior and posterior tubercles of the transverse process and has a “bull horn” or “double humped camel” appearance (Figures 1 and 2). However, at C7, the transverse process may be described as a “thumb sign” (Figure 3) because of the absent anterior tubercle and prominent posterior tubercle. The unique appearance of the transverse processes at these levels aids in the identification of nerve roots in the cervical region.
Figure 2: Ultrasound image of C5 transverse process showing double hump of the anterior and posterior tubercles and corresponding nerve root superficial to it.
AP, anterior tubercle of C5; NR, C5 nerve root; PT, posterior tubercle of C5; TP, transverse process of C5
Scanning technique. Position the patient supine with their head slightly elevated and turned to the contralateral side. A high-frequency linear transducer generally facilitates visualization of superficial structures. Using aseptic technique, place the transducer transversely to the lateral aspect of the neck and cephalad to the clavicle to obtain a transverse axial view. Move the transducer cephalad until the spinal nerve root and its corresponding transverse process comes into view. Count the level of the nerve roots using the landmarks described previously, and identify the vertebral artery with or without the aid of color doppler to prevent the risk of puncture. Once the C4 nerve root is identified on ultrasound, insert a 20-gauge short-beveled needle in-plane in a posterior to anterior direction. Inject 1 mL of 0.5% bupivacaine very slowly and observe cephalad spread of the local anesthetic (Figure 4). Move the probe more cephalad to identify the C3 transverse process and its corresponding nerve root, and inject another 1 mL of 0.5% bupivacaine into the area. Prior to local anesthetic injection, carefully aspirate or use dextrose 5% or normal saline to confirm the correct needle tip position and prevent any accidental intravascular injection because of the radicular arteries’ and epiradicular veins’ proximity to the target injection site.
Figure 3: Ultrasound image of C7 transverse process showing its rudimentary anterior tubercle and prominent posterior tubercle (thumb sign), C7 nerve root, the hypoechoic circular structure superficial to it, and the vertebral artery lateral to it.
C7, C7 nerve root; PT, posterior tubercle of C7; TP, transverse process of C7; VA, vertebral artery
Surgical repair of clavicular fractures may be associated with significant perioperative discomfort. Anatomically, injections of local anesthetic at the C3 and C4 nerve root levels with upward spread to levels C2 and C3 are effective in providing analgesia for the skin overlying the clavicle., Providing local anesthetic and sensory blockade to the supraclavicular nerve, one of the four branches from the superficial cervical plexus, offers significant cutaneous analgesia superficial to the clavicle.
Myotomes are the pattern of innervation of skeletal muscles by motor axons. Understanding the sensory innervation of myotomes may explain an additional component of the pain patients feel following clavicular fracture repair. The clavicle serves as an insertion point for many important muscles, including the sternocleidomastoid, pectoralis major, subclavius, deltoid, and trapezius. Effective regional treatment of pain resulting from muscular manipulation during clavicular fracture repair requires sensory blockade of muscles interconnecting at the clavicle. The myotome nerve supply of those insertion muscles varies from C2–C6. Targeting the cervical nerve roots at C3 and C4 with cephalad spread of local anesthetic can effectively treat clavicular pain from muscle manipulation.
Figure 4: Ultrasound image of C4 transverse process and corresponding nerve root showing needle tip and local anesthetic injection at C4 nerve root.
AP, anterior tubercle of C4; C4, C4 nerve root; PT, posterior tubercle of C4
Sclerotome refers to a single spinal segmental innervation of bone and periosteum. Currently published sclerotome maps are based on a small number of studies and therefore only demonstrate areas of vague referred pain not specific to any skeletal territories supplied by single spinal nerves. The clavicle’s sclerotomes have not been reliably identified in the literature; however, our experience with selective C3 and C4 nerve root blockade suggests that those levels are likely involved in clavicular innervation.
Finally, the technique requires only 2 mL of local anesthetic, certainly less than that for standard interscalene or superficial cervical plexus nerve blocks. By minimizing local anesthetic administration, significant motor and sensory blockade can be avoided. Nevertheless, the phrenic nerve, derived from C3–C5, can be blocked by the scant volume of local anesthetic and may illicit respiratory compromise in selected patients. Physicians should also take care to avoid intravascular injections because of the significant localized vascularity and observe for the development of epidural anesthesia because of the proximity of the injection point to the nerve roots.
In conclusion, the selective injection of minimal volumes of local anesthetic adjacent to the C3 and C4 nerve roots should be considered for the provision of perioperative analgesia in the setting of clavicular fracture repair. However, care should be taken to minimize potential risks (eg, vascular puncture, intravascular injection, epidural spread, phrenic nerve blockade). Further studies are required to evaluate the C3 and C4 nerve root block’s analgesic impact and risk profile when used for clavicular fractures.
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