Arthroscopic Suprascapular Nerve Release

Laurent Lafosse

Thibault Lafosse

INTRODUCTION

This chapter is about an arthroscopic surgical solution to a suprascapular nerve (SSN) entrapment at the coracoid notch (CN) of the scapula. Since the technique was described, many papers have been published about technique and indications,¹ but not so many about the tips and tricks, the difficulties, and the traps. I (LL) will relate my personal experience in this field, which started by open surgery when I was a young fellow back in the 1980s and discovered this pathology and will try to explain step by step how I discovered the arthroscopic technique, focusing on the practical landmarks and tricks that I discovered with experience.

Owing to the body’s anatomy, it is obvious to say that the open technique is very difficult to perform. I remember being a fellow assisting very advanced shoulder surgeons struggling to perform this very challenging procedure. That was the reason for developing an arthroscopic technique. For this pathology’s treatment, there is no doubt that arthroscopy is easier than open surgery. The term “arthroscopy” is not technically accurate, as we are not talking about a pathology inside the joint. The SSN remains outside the joint; therefore, the correct word should be “endoscopic” SSN release. That being said, arthroscopy remains the current, most commonly used term. Endoscopy is the beauty of shoulder arthroscopic evolution: moving to outside the borders of the joint and accessing areas that were not suspected initially.

Other than hand surgeons, who moved to shoulder surgery, most shoulder surgeons are not comfortable navigating around nerves. As dictated by shoulder anatomy, the plexus is very close to this joint and the treatment of many pathologies must deal with the nerves. A perfect knowledge of nerve anatomy is crucial in shoulder open surgery and even more for endoscopic treatment, as the nerves may be at risk for “outside the border” portals.

Endoscopy allows better visualization of the SSN area than open surgery for two major reasons:

FIGURE 10-1 A and B, The suprascapular nerve runs on the deep and narrow space between the clavicle, supraspinatus muscle, and supraspinatus fossae. A, Ant-post perspective. B, Postero-anterior perspective.

The anatomic location of the nerve at the CN is around 10 cm from the skin at the deepest part of the suprascapular fossae, on a triangular space limited by the clavicle anterosuperiorly, the supraspinatus (SSP) muscle superoposteriorly, and the scapula spine of the SSP fossae inferiorly (Figure 10-1A and B). The open access to this narrow area is terribly difficult. Conversely, the scope is long enough and can lead to the area through lateral or superior portals with no major difficulties, and the instrumentation for exposure, coagulation, shaving soft tissues, and nerve release can be introduced by a superior portal directly anterior to the SSP, posterior to the clavicle. Interestingly, this portal was originally described by a French rheumatologist for cortisone injection in the SSN area back in 1960s.
The endoscopic technique allows inflow of liquid and distension of the soft tissue by high pressure for easier exposure.

These two factors create the most important benefit for the patient because of the main usual advantages of mini-invasive surgery.

ANATOMY

Nerves and Vessels: Bony and Ligament Landmarks

SSN is a major motor branch nerve that innervates the SSP and infraspinatus (ISP). Some sensitive branches, difficult to visualize, are going to the skin around the SSP fossae. SSN is the first superior branch of the plexus,² coming at the superior side of C5 root and going directly to the CN, maintained superiorly in the fossae by the transverse ligament (TL)³ (Figure 10-2). The CN may present many types of three-dimensional (3D) shape variations,⁴ but one of the most frequent is the TL ossification, which creates a 360° bony notch⁵ (Figure 10-3). What is important to understand for arthroscopic surgery is the 3D SSN anatomy as it courses from C5 to the CN. The SSN goes in an oblique direction inferiorly and posteriorly to the CN and converges at this level with the suprascapular artery and the two small veins which come from the more anterior vascular structures, just superior to the TL. Frequently, a branch of the artery goes posteriorly to the TL and dives deeply anteriorly, deep to the TL and lateral to the SSN. This anatomic variation may explain a few SSN idiopathic syndromes and may create some confusion during the surgery as well as some artery going from front to back under the TL together with SSN⁶ (Figure 10-4).

FIGURE 10-2 The suprascapular nerve runs under the transverse ligament.

FIGURE 10-3 Bony notch on 3D CT.

FIGURE 10-4 Suprascapular nerve (SSN) at the coracoid notch.

A branch of the suprascapular artery goes back under the transverse ligament together with the SSN.

Once the nerve and vessels are posterior to the TL, it is tremendously important to notice that they continue posteriorly to the anteroinferior side of the SSP muscle (Figure 10-5) where the SSN for SSP ends directly by multiple small and very short branches into the muscle body (Figure 10-6) while its ISP branch circles superior to the bony floor of the scapula fossae to the spinoglenoid notch and follows the bone of the ISP fossae a few centimeters before giving the branches to the ISP muscle. This is very important for the visualization of the SSN and vessels. While performing the lateral arthroscopic visualization, the SSP muscle should always remain a landmark and is located on the posterior side of the scope path.

FIGURE 10-5 The suprascapular nerve gives two branches: one very short to the supraspinatus muscle and one much longer to the infraspinatus muscle running into the spinoglenoid notch.

FIGURE 10-6 The supraspinatus (SSP) suprascapular nerve branch goes toward the deepest part of the SSP muscle.

Ligaments and Subacromial Bursae

The important lateral landmark structures are the bony and ligamentous structures of the subacromial space.⁷ The coracoid bone is located at the superior portion of the glenoid, medial to its superior border. While moving more medially, still superior to the glenoid, the coracoclavicular (CC) ligaments are attaching the clavicle to the coracoid. The most anterior and lateral of these structures is the trapezoid ligament; the most posterior is the conoid ligament (Figure 10-7). The shape of the trapezoid ligament is approximately rectangular and twisted like a propeller. The conoid ligament appears as a triangle with its base superior on the clavicle and its tip at the level of the lateral side of the TL, which is a perfect landmark (Figure 10-8). Some distance may separate the conoid and trapezoid ligaments (Figure 10-9), which may allow the surgeon to mistakenly lead the scope much anteriorly, just at the posterior border of the trapezoid ligament and anterior to the conoid ligament. This error in scope placement may cause difficulty in identifying the TL. The key to avoiding this mistake is to remember that the SSP muscle should always be visualized in the scope image, so the scope path remains posterior to the CC ligaments.

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