Article Text

Download PDFPDF

Evaluation of suprascapular nerve radiofrequency ablation protocols: 3D cadaveric needle placement study
  1. John Tran1,
  2. Philip Peng2 and
  3. Anne Agur1
  1. 1 Surgery (Division of Anatomy), University of Toronto, Toronto, Ontario, Canada
  2. 2 Anesthesia, University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to John Tran, Surgery (Division of Anatomy), University of Toronto, Toronto, ON M5S, Canada; johnjt.tran{at}mail.utoronto.ca

Abstract

Background and objectives Image-guided intervention of the suprascapular nerve is a reported treatment to manage chronic shoulder joint pain. The suprascapular nerve is conventionally targeted at the suprascapular notch; however, targeting of its branches, the medial and lateral trunks, which are given off just posterior to the notch has not been considered. Since the lateral trunk supplies the posterior supraspinatus and articular branches to the glenohumeral joint capsule, while the medial trunk provides motor innervation to the anterior region, it may be possible to preserve some supraspinatus activation if the medial trunk is spared. The main objective was to investigate whether midpoint between suprascapular and spinoglenoid notches is the optimal target to capture articular branches of lateral trunk while sparing medial trunk.

Methods In 10 specimens, using ultrasound guidance, one 17 G needle was placed at the suprascapular notch and a second at midpoint between suprascapular and spinoglenoid notches. The trunks and needles were exposed in the supraspinous fossa, digitized and modeled in 3D. Lesion volumes were added to the models to asses medial and lateral trunk capture rates. Mean distance of needle tips to origin of medial trunk was compared.

Results Conventional notch technique captured both lateral and medial trunks, whereas a midpoint technique captured only lateral trunk. Mean distance of needles from the origin of medial trunk was 5.10±1.41 mm (notch technique) and 14.99±5.53 mm (midpoint technique).

Conclusions The findings suggest that the midpoint technique could spare medial trunk of suprascapular nerve, while capturing lateral trunk and articular branches. Further clinical investigation is required.

  • anatomy
  • joint innervation
  • shoulder joint
  • radiofrequency ablation
  • suprascapular nerve

Statistics from Altmetric.com

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

Introduction

The shoulder is the second most common source of chronic joint pain, with a prevalence of 8.4 per 100 persons over the age of 18,1 often resulting in decreased quality of life and disability.2 Image-guided interventions of the suprascapular nerve (SSN), including pulsed radiofrequency (PRF) and radiofrequency ablation (RFA), provide alternative treatment methods to manage shoulder joint pain.3–18 Of the 16 studies that were found, 13 used PRF (8 fluoroscopy (FL)3–10/4 ultrasound (US)11–14/1 blinded15), and 3 used RFA (2 FL16 17/1 US18). The more common use of PRF has been attributed to the concern of lesioning the motor branches to the supraspinatus and infraspinatus, while RFA procedures have been reserved for patients with minimal to no baseline motor function of the shoulder.16–18 To landmark the SSN, 14 studies used the suprascapular (SS) notch3–13 15–17 whereas 1 study used the omohyoid/first rib18 and the remaining study used the floor of the supraspinous fossa.14

To further develop SSN radiofrequency (RF) protocols, a detailed understanding of the course of the SSN branches and their relationship to bony and soft-tissue landmarks is paramount. In a recent cadaveric study, the course and origin of the SSN branches were related to bony and soft-tissue landmarks.19 The SSN was found to bifurcate into medial (MT) and lateral (LT) trunks at the SS notch, coursing along the floor of the supraspinous fossa to supply sensory innervation to the glenohumeral joint (GHJ) and motor innervation to the supraspinatus and infraspinatus. More specifically, the MT has been found to primarily provide motor innervation to the anterior region of supraspinatus, whereas the LT provided articular branches to the GHJ and motor innervation to the posterior region of supraspinatus, as well as superior, middle, and inferior regions of the infraspinatus.19 20 In addition, branches to the acromioclavicular joint (ACJ) were found to originate from the SSN.19 Articular branches of the SSN, supplying the posterior GHJ, have been reported to consistently originate from the LT close to the midpoint of a line connecting the SS and spinoglenoid (SG) notches.19 This midpoint was proposed as an alternative landmark to selectively target the LT and articular branches, while sparing the MT. The selective targeting of the LT could potentially capture articular branches supplying the posterior GHJ while preserving activation of the supraspinatus which is innervated by the MT. However, the feasibility of this approach has not been investigated. Therefore, the objectives of this study were to: (1) perform US-guided RF needle placements using the SS notch and the midpoint between SS/SG notches as landmarks; (2) dissect, digitize, and model in 3D the course and origin of the SSN branches and needles; and (3) compare the MT and LT capture rates and quantify the distance between the MT and RF needles using the two techniques.

Methods

Ten lightly embalmed cadaveric specimens were used in this study. Sample size calculation was not possible due to the absence of previous data for quantitative analysis. Specimens with visible evidence of pathology, previous surgery, or trauma were excluded.

US scanning and needle placement protocol

US scanning was performed with a linear (6–15 Hz) probe (Edge I, Fujifilm Sonsite, Bothell, Washington, USA). The probe was orientated towards the supraspinous fossa, in the anteromedial direction, so that the probe was in the short axis plane of the SSN which courses between the SS and SG notches (figure 1A,B). The target for the needle was the floor of the supraspinous fossa at the midpoint between the SS and SG notches. The floor of the supraspinous fossa was evident as indicated by the smooth bright hyperechoic shadow (figure 1D). By aligning or moving the probe in the anteromedial direction, along the course of the nerve, the echogenicity of the floor diminishes at the SS notch (figure 1C). From the SS notch, translation of the probe in the posterolateral direction would reveal the hyperechoic floor of the supraspinous fossa at the midpoint. Continued translation of the probe posterolaterally would reveal a deepening of the smooth hyperechoic shadow of the SG notch (figure 1E). The location was confirmed by translating the probe further posterolaterally and the hyperechoic bony shadow disappeared. Using this scanning technique, the SS notch and the midpoint between the SS and SG notches were visualized in each specimen and a 17 G 100 mm needle was placed at each site using an out-of-plane approach. To prevent dislodgement, during dissection, the needles were driven into the scapula with a small mallet.

Figure 1

Methodology for landmarking radiofrequency needle placement. (A) Localization of needle placement at suprascapular notch (red curve), spinoglenoid notch (turquoise curve), and midpoint between the notches (green curve). Superior view of scapula. (B) Probe position at suprascapular notch (red box), spinoglenoid notch (turquoise box), and midpoint between the notches (green box). (C) Sonogram of suprascapular notch. Note the bony contour of the notch (dotted line) is not as hyperechoic as the adjacent scapular bone, which cast an anechoic shadow (*). The suprascapular ligament is hyperechoic as outlined by white arrows. (D) Sonogram of floor of the scapular fossa midpoint between the notches. (E) Sonogram of spinoglenoid notch. Note the contour of the bony floor is steeper than that of the floor of scapular fossa midpoint between the notches. AC, acromion; CP, coracoid process; G, glenoid fossa; SSF, supraspinous fossa; X, radiofrequency needle placement targets. Reprinted with permission from Philip Peng educational series.

Dissection, digitization, and 3D modeling

Following placement of RF needles, the skin, subcutaneous tissue, trapezius, and deep fascia were removed to expose the supraspinatus, infraspinatus, spine of scapula and acromion. Next, the main trunk of SSN was identified just anterior to the SS notch and followed deep to the SS ligament. The fiber bundles of the supraspinatus were carefully excised or reflected to expose the RF needles, MT and LT as well as their branches. All branches were followed to their termination in the muscle belly or the GHJ capsule. The needle tips, MT, LT, and branches of MT/LT as well as surface outline of the scapula were then digitized using a MicroScribe G2X Digitizer (Immersion Corporation, San Jose, California) along with custom software developed by our laboratory. Following the completion of digitization, the specimens were skeletonized and scanned using a Faro Laser ScanArm (FARO Technologies, Lake Mary, Florida) to create a high-resolution surface scan of the scapula, proximal humerus, and GHJ. Since both the Microscribe digitizer and Laser ScanArm collect cartesian coordinate data, in x, y, and z planes, the digitized nerves, needles, and outline of the scapula were registered with the scanned scapular surface data using Autodesk Maya (Autodesk, San Rafael, California). The completed 3D models included the RF needles, MT, LT, and branches of MT/LT in relation to the scapula and GHJ. Following reconstruction of the 3D volumetric models, an oval lesion with radius of 5 mm was generated and placed with the needle tip at its center (Diros Technologies, Markham, Ontario). A lesion with 5 mm radius was used as it represented a large size lesion created with conventional thermal RF using an out-of-plane technique.

Data analysis

The articular and motor branches of the MT and LT were identified in the dissected specimens and 3D models. This map, of the articular and motor branches, was used to define the location of RF needle relative to MT/LT and their branches: (1) spatially (medial, lateral, posterior, and anterior); and (2) relative to the SS and SG notches. Next, the map was used to document the location of lesion volumes with respect to the MT/LT, and their branches, that were captured by each technique (SS notch and SS/SG notches). The nerve capture rates were compared.

Next, using Autodesk Maya measurement tool, the distance between the needle, placed using (1) the SS notch technique and (2) the midpoint between the SS/SG notches technique, was quantified relative to the lateral border of the MT at its origin from the SSN (figure 2). The distance of the needle to the closest point of the margin of the LT was also documented for the needle placed using the midpoint between SS/SG notches technique. The mean (±SD) was computed and compared for the distance measurements described above. To determine if the mean distance from the lateral border of MT to needles placed with the two techniques was significantly different, an independent sample t test (p≤0.05) was used (Graphpad Software, San Diego, California).

Figure 2

Distance measurements from needle tips (1 and 2). (A) Measurement from lateral border of medial trunk at its origin to tip of needle 1. (B) Measurement from lateral border of medial trunk at its origin to tip of needle 2. Suprascapular (SS) notch technique; midpoint between SS/spinoglenoid notches technique (midpoint); white arrowhead (lateral border of medial trunk at its origin). Reprinted with permission from Philip Peng educational series.

Results

The position of needles varied between the two techniques, SS notch and midpoint between SS/SG notches. The needle placement using the SS notch technique, in all specimens, was found posterior to the SS ligament and in close proximity to the SS notch (figures 3 and 4). The needle was positioned medial to the LT in six specimens (figure 4A,B) and lateral in four specimens (figure 3A,B) In contrast, needle placement, using the midpoint between SS/SG notches technique, was found more posteriorly within the supraspinous fossa, in close proximity to the midpoint between SS and SG notches (figure 3A). In half the specimens (n=5), the needle was placed medial to the LT (figures 3 and 4C) and in the remaining specimens lateral to it (figure 4A,B).

Figure 3

Needle targets and lesion volumes registered on dissected specimen and 3D model, superior views. (A) Dissection of medial trunk (MT), lateral trunk (LT) and articular branches of suprascapular nerve (SSN) with radiofrequency (RF) needles. (B) Color- coded SSN branches with RF needles. (C) Color-coded SSN branches with RF needles and lesion volumes. (D) Reconstructed 3D model of scapula, SSN branches, and RF needles. (E) Reconstructed 3D model of scapula, SSN branches and RF needles with lesion volumes. ABR, articular branches of SSN; AC, acromion; ACBr, acromial branch; CL, clavicle; S, supraspinatus; SSF, supraspinous fossa; SSL, suprascapular ligament; X, location of needle tip placed using midpoint technique; 1 and 2, RF needles. Reprinted with permission from Philip Peng educational series.

Figure 4

Needle positions relative to SSN branches. (A)–(C) Three different patterns. ABR, articular branches of SSN; ACBr, acromial branch; CL, clavicle; LT, lateral trunk; MT, medial trunk; S, supraspinatus; SSL, suprascapular ligament; 1 and 2, radiofrequency needles. Reprinted with permission from Philip Peng educational series.

The nerve capture rates of the MT, LT and their branches differed between the two techniques. When using the SS notch technique, the lesion encompassed the MT in all 10 specimens and the LT in 9 (figure 4A,B). In the specimen where the LT was spared, the needle was placed medial to the SS notch rather than at its midpoint (figure 4C). In 4 of 10 specimens, the acromial branch of the SSN was also captured (figure 3D–F). In contrast, the midpoint between SS/SG notches technique captured only the LT and its articular branches that supplied the GHJ capsule in all specimens (figures 3 and 4). This technique did not capture the MT nor the acromial branch of the SSN.

The needle, placed using the SS notch technique, was significantly closer (p=0.000017) to the MT than the midpoint between SS/SG notches technique. The mean distance of the RF needles from the MT, when using the SS notch technique, was 5.10±1.41 mm and 14.99±5.53 mm when using the midpoint between SS/SG notches technique, on average about a 10 mm difference. The mean needle distance to the closest point on the margin of the LT using the SS/SG notches technique was 3.02±1.56 mm.

Discussion

This is a novel 3D cadaveric study comparing two US-guided needle placement techniques for SSN denervation. Moreover, this is the first study to use 3D modeling technology to visualize relationships and potential nerve targets captured.

The results of this study suggest that the midpoint between SS/SG notches technique could preserve partial supraspinatus function in comparison to the commonly used SS notch technique, where supraspinatus and infraspinatus are both compromised. Using the SS notch as a landmark, both the LT and MT of the SSN were captured. The LT supply sensory afferents to the GHJ capsule whereas the MT primarily provides motor innervation to the anterior region of supraspinatus.19–21 Therefore, conventional SSN denervation captures sensory afferents supplying the GHJ capsule, originating from the LT, and motor efferents to the supraspinatus and infraspinatus. In contrast, the midpoint between SS/SG notches technique was consistently found to only capture the LT and articular branches to the GHJ capsule, while sparing the MT. This finding suggests selective denervation of the LT while sparing that the MT is possible, thus partially preserving supraspinatus activation for the initiation of abduction. Our study also observed that the acromial branch of the SSN, originating prior to the bifurcation of the SSN into LT and MT, may be captured using a modified SS notch technique, with more lateral placement of the needle (ie, posterior margin of coracoid process). However, this lateral placement technique, for the potential ACJ RF lesioning, was not the objective of this study. Previous literature has also reported innervation of ACJ by the acromial branch of the SSN.19 21–25

Development of function-preserving US-guided protocols requires detailed understanding of the relationship of the SSN branches to bony and soft-tissue landmarks. Eckmann et al (2017) in a cadaveric study of the sensory innervation of the shoulder joint identified a ‘safe zone’, to localize the articular branches of the SSN, bounded by the glenoid fossa, acromion, and head/neck of the humerus.26 In a more recent cadaveric study, a single landmark, the midpoint of a line joining the center of the SS/SG notches, was proposed to capture the articular branches of the SSN.19 In this subsequent needling study, the midpoint between the SS/SG notches landmark was shown to be visible using US guidance. Needle placement using this technique was found in close proximity to the intended landmark and resulted in the capture of the LT and its articular branches, while sparing the MT. Sparing of the MT will result in the preservation of the function of the anterior region of the supraspinatus.20 21 Although the infraspinatus will be denervated, using either SS notch or midpoint between SS/SG notches techniques, compensatory movements can be provided by the teres minor and the posterior deltoid, which receive motor innervation from axillary nerve.27

There are a few limitations in this study. First, the sample size is small. Second, the lesion volumes are based on available data from the literature; however, these volumes have been determined using animal tissue,28 29 and therefore may not exactly replicate lesion volumes in vivo. Third, since this is an anatomical study, a clinical study is required to confirm this concept. During RF ablation procedures, motor testing is usually performed in the clinical setting. An optimal placement based on our finding can be confirmed by eliciting the contraction of the infraspinatus with minimal to no contraction of the supraspinatus. This is evident when the stimulation results in external rotation or muscle contraction in the infraspinous fossa only. Lastly, we did not examine the vascular supply in relation to needle positions in the SS fossa as our primary objective was to determine and compare the MT and LT capture rates. As in any procedure, involving needle puncture, vascular injury/hematoma is an inherent risk. The arterial supply to the supraspinatus is primarily provided by the SS, dorsal scapular and circumflex scapular arteries30; however, the risk of the vascular puncture resulting in muscle ischemia is unknown.

In conclusion, this cadaveric study suggests that the midpoint of a line joining the center of the SS/SG notches could spare the MT of the SSN while denervating the posterior GHJ capsule, by capturing the LT. The midpoint between the SS/SG notches techniques may represent an alternative US-guided SSN denervation protocol that may preserve some supraspinatus function. Further clinical investigation is required to assess functional and pain relief outcomes.

Acknowledgments

The authors wish to thank FARO Technologies for their generous technological support. They also wish to thank the individuals who donate their bodies and tissue for the advancement of education and research.

References

Footnotes

  • Presented at Interim data from this work were presented at the 2019 American Association of Anatomists Annual Meeting at Experimental Biology in Orlando, 6–10 April 2019 and 2019 International Symposium of Ultrasound in Regional Anesthesia and Pain Medicine in Porto, 9–11 May 2019.

  • Contributors All authors contributed to the experimental design, data acquisition, analysis of data, drafting and revising the manuscript critically for important intellectual content.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests AA is an Anatomy Faculty with Allergan Academy of Excellence. PP received equipment support from Sonosite Fujifilm Canada.

  • Patient consent for publication Not required.

  • Ethics approval Approval was received from the University of Toronto Health Sciences Research Ethics Board (#27210).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.