Ultrasound-Guided Modified Clavipectoral Fascial Plane Block With Superficial Cervical Plexus Block for Midshaft Clavicular Surgery: A Prospective Randomized Controlled Trial

Introduction

Clavicle fractures constitute 35% to 45% of adult shoulder girdle injuries; approximately 80% occur in the midshaft [1]. The complex and highly variable innervation of the clavicle [2] presents a challenge in selecting optimal regional anesthesia techniques [3,4]. Although interscalene brachial plexus block (ISBP) has historically been considered the standard approach for clavicular surgery [5], its associated incidence of hemidiaphragmatic paralysis ranges from 45% to 100% [6], posing substantial risks to patients with limited respiratory reserve (eg, those with obesity or chronic obstructive pulmonary disease) [7]. Clavipectoral fascial plane block (CPB) can avoid phrenic nerve injury [8], but its conventional 2-point injection pattern provides incomplete coverage of the posterior-inferior quadrant of the clavicle [9], leading to limited effectiveness in complex cases such as comminuted fractures. Recent research has demonstrated that adding an injection point medial to the subclavius muscle between the clavipectoral fascial layers, based on the CPB technique, enables uniform diffusion of local anesthetic to all 4 quadrants of the clavicle [10], providing an anatomical basis for modified CPB (mCPB). However, mCPB alone cannot block the supraclavicular nerves that innervate the skin incision; it requires combination with a cervical plexus block. Given the minimal impact of superficial cervical plexus block (SCPB) on phrenic nerve function [11], we hypothesized that a combined SCPB plus mCPB technique would provide comprehensive circumferential anesthesia of the clavicle while preserving respiratory and motor function. This randomized controlled trial compared the SCPB plus mCPB technique with the conventional SCPB plus ISBP approach; it evaluated anesthetic quality, postoperative analgesia, motor function preservation, and complication profiles in patients undergoing midshaft clavicular fracture surgery.

Material and Methods

STUDY DESIGN AND ETHICS:

This single-center, randomized controlled trial was conducted at Wuxi People’s Hospital. The research protocol was reviewed and approved by the Research Ethics Committee of Wuxi People’s Hospital on November 25, 2024 (approval number: KY24189). The trial was registered in the Chinese Clinical Trial Registry prior to patient enrollment (registration number: ChiCTR2500101968; registration date: May 6, 2025). Patients were enrolled between July 1, 2025, and October 1, 2025. Written informed consent was obtained from all participants before trial participation.

PATIENTS, RANDOMIZATION, AND BLINDING:

Patients scheduled for midshaft clavicular surgery under regional anesthesia were enrolled. Eligible participants were aged 18 to 65 years, classified as American Society of Anesthesiologists (ASA) physical status I or II, and included regardless of sex. Exclusion criteria included patient refusal; body mass index (BMI) at least 35 kg/m²; coagulopathy; known allergy to any study medication; infection at the puncture site; pre-existing neurological deficit in the operative limb; prior neck surgery; cervical irradiation; or chronic analgesic therapy.

This was an assessor-blinded, parallel-group randomized controlled trial. Randomization was performed by an independent statistician using SAS software (SAS Institute, Cary, NC, USA) to generate a block randomization sequence (block sizes of 4 and 6; allocation ratio 1: 1). Allocation concealment was ensured using sequentially numbered, opaque, sealed envelopes, which were maintained by an anesthesiologist not involved in patient recruitment or outcome assessment. After enrollment and informed consent had been obtained, envelopes were opened sequentially on the day of surgery to disclose group allocation to the anesthesiologist performing the block. The anesthesiologist administering the nerve block was not involved in randomization, patient recruitment, or outcome evaluation. Due to distinct ultrasonographic anatomical differences between the 2 block techniques, both the performing anesthesiologist and the participants could not be blinded. However, all postoperative follow-up and statistical analyses were conducted by independent personnel blinded to group allocation, ensuring assessor blinding. Participants in the control group received ultrasound-guided SCPB plus ISBP, whereas those in the experimental group received SCPB plus mCPB.

METHODOLOGY:

All patients followed standard preoperative fasting protocols. Upon arrival in the operating room, routine cardiac monitoring was initiated, and peripheral intravenous access was established. Five minutes before nerve block, all patients received a single intravenous bolus of sufentanil (0.1 μg/kg) and midazolam (0.03 mg/kg) for sedation. No other analgesics or sedatives were administered intraoperatively. Throughout the procedure, 100% oxygen was delivered at a rate of 2 L/min via nasal cannula.

In the control group, ultrasound-guided combined SCPB and ISBP were performed. Patients were positioned supine with the head rotated 45° to the contralateral side, and a 5- to 8-cm pillow was placed under the ipsilateral shoulder to optimize lateral neck exposure. Strict aseptic technique was utilized, including sterile skin preparation and ultrasound probe sheathing. A high-frequency linear transducer (6–13 MHz, X-Porte, FUJIFILM SonoSite Inc., USA) was placed transversely at the root of the operative-side neck. Depth was set to 3 to 4 cm; gain was set to 60 to 70 dB. The C7 transverse process was identified, and the probe was slid cephalad to locate the C4 transverse process. Slight lateral adjustment allowed visualization of the sternocleidomastoid muscle (Figure 1A). Using an in-plane technique, a 22-gauge, 80-mm short-beveled insulated needle (Stimuplex D, B. Braun, Melsungen, Germany) was advanced from lateral to medial at a 30° to 45° angle. Real-time sonoanatomic monitoring ensured needle tip placement superficial to the sternocleidomastoid muscle. After negative aspiration for blood, 5 mL of 0.375% ropivacaine were injected. With the probe maintained in the transverse orientation, it was moved caudally to the level of the cricoid cartilage (approximately C6) to visualize the interscalene groove between the anterior scalene muscle and middle scalene muscle. The brachial plexus roots appeared as a characteristic “beaded, hypoechoic” structure (Figure 1B). The probe was adjusted to achieve symmetrical visualization of the anterior scalene muscle and middle scalene muscle, with neural structures centered. Using an in-plane approach from lateral to medial, the needle trajectory avoided the external jugular vein. After negative aspiration had been confirmed, 28 mL of 0.375% ropivacaine were slowly injected circumferentially around the plexus. Throughout the procedure, the patient’s respiration, blood pressure, pulse, and other vital signs were closely monitored; airway patency was maintained at all times.

In the experimental group, ultrasound-guided combined SCPB and mCPB were performed. Preoperative anesthetic preparation and the ultrasound-guided SCPB technique were identical to methods used in the control group. After completion of SCPB, mCPB was performed under ultrasound guidance. The linear ultrasound probe was placed over the medial third of the clavicle, approximately 2 cm lateral to the sternoclavicular joint. The sonographic image clearly visualized the clavicle, subclavius muscle, and pectoralis major muscle. Using an in-plane technique, a 22-gauge, 80-mm short-beveled insulated needle (Stimuplex D, B. Braun, Melsungen, Germany) was inserted from caudal to cephalad at a 0° to 15° angle. Real-time sonographic monitoring of the needle tip trajectory ensured placement between the clavicular surface and the clavipectoral fascia. After negative aspiration for blood and air, 7 mL of 0.375% ropivacaine were injected. The needle was then withdrawn to the subcutaneous tissue and the insertion angle was adjusted to 30° to 45°; the needle was then readvanced under continuous sonographic visualization to position the tip between the deep surface of the subclavius muscle and the clavipectoral fascial layer. After negative aspiration had been reconfirmed, an additional 7-mL volume of 0.375% ropivacaine was administered. The probe was repositioned to the lateral third of the clavicle, approximately 3 cm medial to the acromioclavicular joint, and the identical 2-plane injection sequence was repeated. Figure 2 illustrates the sonoanatomic landmarks and in-plane needle trajectory. All blocks were performed by 2 attending anesthesiologists (Operators A and B), each with at least 5 years of experience in ultrasound-guided regional anesthesia, following a standardized training protocol. This protocol included completion of 20 supervised procedures per operator, a pre-study consensus meeting on sonographic landmarks and injection technique, and monthly intra-procedural peer review. Operator allocation was balanced using a randomized case order to minimize bias.

In the event of intraoperative nerve block failure, the protocol stipulated that general anesthesia would be administered. However, all randomized patients achieved successful blocks as defined below, and no post-randomization exclusions occurred. Successful block was defined as the patient reporting no sharp pain (Numerical Rating Scale [NRS] ≤3) upon pinprick testing of the surgical area (skin and subcutaneous tissue over the middle third of the clavicle) with a 23-gauge needle at 30 minutes after the final injection of local anesthetic. Postoperatively, intravenous flurbiprofen axetil (50 mg) was administered as rescue analgesia when the NRS score reached or exceeded 4. The dose could be repeated as needed, up to a maximum daily dose of 200 mg.

OUTCOMES:

The prespecified primary outcome was the NRS score at 12 hours postoperatively, as registered in ChiCTR2500101968. The NRS is an 11-point scale ranging from 0 to 10, designed for subjective pain assessment. A score of 0 corresponds to “no pain,” whereas 10 represents “the most severe pain one can conceive.” All NRS scores were assessed with the patient in a supine position after a 5-minute rest period; evaluation was avoided immediately after activity or coughing. Two researchers, who had undergone standardized training, assessed pain using a standardized script: “Please rate your current pain at rest on a scale of 0 to 10, where 0 represents no pain and 10 represents the worst pain you can imagine.” Patients were required to self-report pain intensity according to their personal perception.

The prespecified secondary outcomes, as detailed in the trial registration, included the following. (1) NRS scores at 4, 8, and 24 hours postoperatively, and the 24-hour postoperative frequency of rescue analgesic administration. (2) Effectiveness of the block: a nerve block was considered successful if no additional analgesic agents were required to enhance the block. Conversely, block failure was defined as the inability to achieve sufficient surgical anesthesia within 30 minutes after local anesthetic administration, requiring conversion to general anesthesia to complete the surgical procedure. (3) Motor block assessment of the upper extremity: baseline motor function was evaluated before nerve blockade; follow-up assessments were performed at 30 minutes and 4 hours post-procedure. Key nerve distributions tested included the ulnar (thumb/finger adduction), median (wrist flexion), radial (wrist extension), musculocutaneous (elbow flexion), and axillary (shoulder abduction) nerves. A 3-point scale was used to grade muscle strength: 0=normal, 1=paresis, and 2=paralysis [12], with a maximum possible motor block score of 10. (4) Incidence of hemidiaphragmatic paralysis: 30 minutes after block completion, diaphragmatic excursion was quantified using real-time M-mode ultrasonography with the patient seated upright. The distance of diaphragmatic movement between resting expiration and deep inspiration (sigh test) was recorded. Paralysis was defined as follows: no paralysis, less than 25% reduction in diaphragmatic excursion compared with baseline; partial paralysis, 25% to less than 75% reduction; and complete paralysis, at least 75% reduction. The overall incidence of hemidiaphragmatic paralysis represented the combined frequency of partial and complete paralysis cases [13].

Exploratory outcomes (not prespecified but collected for quality control and comprehensive technique evaluation) comprised the following. (1) Heart rate and mean arterial pressure measured at the following time points: baseline (T0, pre-block), 10 minutes after the block (T1), surgical opening (T2), and 30 minutes post-incision (T3). (2) Time required for the block procedure and its onset: procedure time was recorded in minutes from the moment the ultrasound probe contacted the skin until the block needle was removed. In contrast, onset time was defined as the interval (in minutes) from block needle withdrawal to the development of complete cold insensitivity over the target clavicular region. These process-related metrics were included to characterize the technical performance of the novel mCPB technique and ensure adequate patient safety monitoring.

SAMPLE SIZE CALCULATION AND STATISTICAL ANALYSIS:

Sample size calculation was based on preliminary trial results. PASS 11.0 software (NCSS, Kaysville, UT, USA) was used for sample size estimation; the NRS score at 12 hours postoperatively was considered the primary outcome measure. Although the NRS is an ordinal scale, it was treated as a continuous variable for the purposes of sample size estimation and primary analysis, consistent with common practice in analgesic clinical trials. The experimental group demonstrated a mean±standard deviation NRS score of 2.9±0.5; the control group demonstrated a mean±standard deviation NRS score of 3.4±0.7. Given a 2-sided α of 0.05 and power (1-β) of 0.80, a total sample size of 50 patients was required. Allowing for a 10% dropout rate, 56 patients were ultimately enrolled.

All statistical analyses were performed using SPSS version 23.0 (IBM, Armonk, NY, USA) and R version 4.3.0 (R Foundation for Statistical Computing, Vienna, Austria), following the intention-to-treat principle. The full analysis set comprised all 56 randomized patients. Because all randomized patients received the allocated intervention without post-randomization exclusions, loss to follow-up, or missing data, the full analysis set and per-protocol set were identical in composition.

Statistical methods were selected according to the scale, distribution, and longitudinal structure of each outcome. Continuous variables with approximately normal distributions were summarized as mean±standard deviation and compared using Student’s t-test; between-group mean differences and corresponding 95% confidence intervals (CIs) were reported. Non-normally distributed continuous or count variables were presented as median (interquartile range [IQR]) and compared using the Mann-Whitney U test; effect sizes were quantified using the Hodges-Lehmann estimator and corresponding 95% CI. Categorical variables were expressed as counts and percentages, with comparisons using the χ² test or Fisher’s exact test, as appropriate. Proportions with exact (Clopper-Pearson) 95% CIs and between-group risk differences with corresponding 95% CIs were reported.

Postoperative pain scores assessed via the NRS at multiple time points (4, 8, 12, and 24 hours) were analyzed as longitudinal continuous outcomes using a mixed-effects model for repeated measures (Table 1). The model included treatment group, time, and group-by-time interaction as fixed effects; patient-specific random intercepts were incorporated to adjust for within-participant correlations. Estimated marginal means and between-group mean differences with 95% CIs were obtained using the Kenward-Roger approximation for degrees of freedom. Although the NRS is an ordinal scale, it was treated as a continuous variable in the primary analysis, consistent with common practice in analgesic clinical trials involving multilevel ordered scales. Median (IQR) values are provided for descriptive purposes only. Multiplicity arising from repeated time-point comparisons in the longitudinal pain analysis was controlled via Bonferroni adjustment. Unless otherwise specified, all reported P values in Table 1 are Bonferroni-adjusted. Two-sided P values <0.05 were considered statistically significant.

Results

Twenty-eight participants were assigned to each group; no patient dropouts or loss to follow-up occurred throughout the study. Figure 3 shows the CONSORT flow diagram. Baseline demographic and clinical characteristics, including age, sex, BMI, ASA status, surgical side, and operative duration, were comparable between the 2 groups (P>0.05; Table 2).

Pain scores at rest were analyzed using a mixed-effects model for repeated measures based on estimated marginal means. A significant group × time interaction was observed (P<0.001). Compared with the control group, the experimental group demonstrated significantly lower NRS scores at 12 hours (estimated mean difference −1.29, 95% CI −1.70 to −0.87; adjusted P<0.001) and 24 hours (estimated mean difference −2.36, 95% CI −2.77 to −1.94; adjusted P<0.001). Median (IQR) NRS values at each time point are presented in Table 1 for descriptive purposes.

All patients successfully received nerve blocks, obviating the need for general anesthesia. The block success rate in both groups was 100% (Table 3). No block failures occurred; accordingly, no patients were excluded after randomization, fulfilling the intention-to-treat principle. As presented in Table 3, no differences were observed between the 2 groups in block performance time or onset time. During the first 24 hours after surgery, the frequency of rescue analgesic administration was significantly lower in the experimental group (median [IQR], 1 [1–2]) than in the control group (2 [1.5–3]; Hodges-Lehmann estimate, 0.6; 95% CI, 0.18–1.06; P=0.002). Hemidiaphragmatic paralysis occurred in 20 of 28 patients (71.4%; 95% CI, 53.2–85.3%) in the control group and 0 of 28 patients (0%; 95% CI, 0%–12.4%) in the experimental group (risk difference, −71.4%; 95% CI, −87.8% to −49.5%; P<0.001) (Table 3). The control group demonstrated significantly higher motor blockade scores at 30 minutes (median [IQR], 7 [6–8.5] vs 0 [0–0], P<0.001) and 4 hours after block completion (median [IQR], 8 [6–9] vs 0 [0–0], P<0.001). Incidences of Horner’s syndrome (10.7% vs 0%, P=0.075) and hoarseness (7.1% vs 0%, P=0.471) did not significantly differ between groups.

Mean arterial pressure and heart rate at different time points were compared between the 2 groups. Both mean arterial pressure and heart rate remained stable over time, without significant between-group differences (all P>0.05). Temporal trends are illustrated in Figure 4.

Discussion

Compared with other upper limb structures, the clavicle possesses particularly complex and variable innervation patterns that remain under active investigation. Thus, debate persists regarding the optimal regional anesthesia technique for postoperative clavicular surgery pain management. Although supraclavicular nerves (branches of the cervical plexus) clearly innervate the overlying skin, the sensory innervation of the clavicle itself remains controversial. Some studies have suggested that the clavicular periosteum is primarily innervated by supraclavicular nerves, whereas others have implied substantial contributions from brachial plexus branches, including the subclavian nerve, long thoracic nerve, and suprascapular nerve [14]. This anatomical variability complicates selection of an optimal regional anesthetic strategy and often requires combined nerve blocks to achieve complete surgical anesthesia.

In the present study population of patients with ASA I or II and BMI below 35 kg/m2, the combination of SCPB and mCPB was associated with effective surgical anesthesia for midshaft clavicular fractures. Both ISBP and cervical plexus block may cause phrenic nerve paralysis [15,16], which can adversely affect specific patient subgroups, including individuals with obesity or severe underlying pulmonary disease. To reduce the incidence of hemidiaphragmatic paralysis, anesthesiologists have explored various modified approaches, including the use of ultrasound-guided visualization techniques [17] and low-concentration, low-volume local anesthetic strategies [18,19]. Although ultrasound guidance has improved safety and patient satisfaction, the incidence of hemidiaphragmatic paralysis remains near 45% to 100%, highlighting the need for novel regional block techniques to prevent this outcome.

Since its introduction by Valdés-Vilches in 2017 [20], CPB has emerged as a promising alternative technique. Conventional clavicular periosteal block involves dual-point injection into periosteal-fascial spaces at the medial and lateral aspects of the clavicle [8]. However, Heredia-Carques et al [10] demonstrated that this approach inadequately infiltrates the posteroinferior quadrant and deep muscular layers; drug diffusion is primarily confined to the anterosuperior quadrant. This limitation may represent the anatomical basis for insufficient analgesia in complex cases, such as comminuted fractures. Building upon the dual-point injection method proposed by Xu et al [21], the mCPB technique incorporates supplementary injections into the interfascial plane between the subclavius muscle and clavicular periosteum, achieving comprehensive circumferential coverage of the clavicular fascial compartment. Given that the supraclavicular nerve (C3–C4) provides sensory innervation to the overlying skin [22], mCPB alone cannot provide adequate sensory blockade for the skin incision, and combined cervical plexus blockade becomes essential [23]. Previous studies have demonstrated that SCPB performed at the C4 to C5 level with ropivacaine leverages the barrier effect of the prevertebral fascia to effectively restrict local anesthetic spread; no patients have developed partial or complete hemidiaphragmatic paralysis [24–27]. Consequently, the present study implemented a combined SCPB plus mCPB strategy, where SCPB blocks the supraclavicular nerve using a low volume of 5 mL while substantially minimizing the risk of phrenic nerve infiltration.

Building on the work of Xu et al [21] and Zhuo et al [28], our findings suggest that an mCPB technique using low-concentration ropivacaine can provide effective anesthesia for midshaft clavicular fracture surgery in this specific patient population. Unlike conventional ISBP, patients in the mCPB group maintained complete upper limb motor function without evidence of motor block. This selective blockade reflects precise anatomical targeting: mCPB deposits local anesthetic within the clavipectoral fascial space and subclavius muscle sheath, potentially blocking terminal sensory branches of multiple nerves (eg, suprascapular, subclavian, lateral pectoral, and long thoracic nerves), while appearing to spare brachial plexus motor fibers [20]. This preservation of motor function could theoretically facilitate earlier postoperative mobilization of the affected upper limb; however, the present study was not designed to assess long-term functional outcomes or rehabilitation metrics.

Importantly, no patient in the mCPB group developed complications such as motor block, Horner’s syndrome, hoarseness, or hemidiaphragmatic paralysis – a safety advantage attributable to the natural barrier effect of the costocoracoid fascia, which limits local anesthetic spread to the brachial plexus. This finding is particularly relevant given that 7% to 24% of patients with midshaft clavicular fractures exhibit concomitant brachial plexus injury [29]; in such patients, ISBP may exacerbate nerve damage through a “double-crush” mechanism. Although hemidiaphragmatic paralysis can reduce vital capacity by approximately 30% [13], clinically significant respiratory symptoms are uncommon in healthy individuals, likely due to compensatory mechanisms such as accessory phrenic nerve function [30] or recruitment of accessory respiratory muscles. Consistent with this observation, although 71.4% of patients in the ISBP group displayed hemidiaphragmatic paralysis in the present study, none developed hypoxemia or respiratory distress. However, these findings cannot be extrapolated to patients with compromised respiratory reserve, who were explicitly excluded from this trial. The significantly lower NRS scores observed in the mCPB group at 12 and 24 hours postoperatively likely reflect the relatively avascular nature of the injection site, which may delay systemic absorption and prolong analgesic duration. Collectively, these preliminary findings suggest that mCPB plus SCPB represents a viable regional anesthesia strategy for clavicular surgery that integrates both safety and efficacy.

Several limitations merit consideration. First, the single-center design and limited sample size (n=56) may restrict external validity. Second, the study population was limited to patients with ASA I or II and BMI below 35 kg/m2, explicitly excluding individuals with obesity, severe cardiopulmonary disease, or other clinically significant comorbidities. Consequently, the results cannot be extrapolated to higher-risk populations. Although mCPB may theoretically mitigate respiratory risks in such cohorts (eg, ASA III, obesity, severe pulmonary disease), the absence of these patients in the present study warrants cautious interpretation of potential benefits. Third, the 24-hour follow-up period may have been insufficient to fully characterize the duration of analgesia, given that fascial plane blocks often exhibit delayed absorption kinetics. Fourth, although the assessor-blinded design was methodologically appropriate, the possibility of performance bias could not be entirely eliminated due to inherent differences between the block techniques. Finally, long-term functional outcomes, patient satisfaction, and cost-effectiveness were not evaluated, all of which are important considerations for clinical implementation. Future multicenter studies with larger sample sizes should include stratified validation in patients with obesity, ASA III populations, and individuals with chronic respiratory disease to systematically define safety margins and efficacy profiles. Extended follow-up periods (48 hours to 7 days) are needed to fully characterize long-term analgesic efficacy and its impacts on sleep quality and functional recovery.

Conclusions

In this single-center randomized controlled trial of low-risk patients (ASA I–II, BMI <35 kg/m2) undergoing midshaft clavicular surgery, combined mCPB and SCPB provided effective anesthesia with superior analgesia at 12 and 24 hours relative to ISBP plus SCPB, while completely avoiding hemidiaphragmatic paralysis. Although these findings suggest a viable alternative when preservation of respiratory function is prioritized, they do not support universal superiority or routine replacement of ISBP. Validation in larger multicenter trials – including higher-risk populations (ASA III, BMI ≥35 kg/m2, and patients with respiratory comorbidities) – is warranted before widespread clinical implementation.