Introduction

Shoulder pain is a common and potentially debilitating musculoskeletal condition that reportedly up to 30 percent of the general population may experience. ^, It is consistently reported as one of the top three most common musculoskeletal conditions, along with back and neck pain.

The etiology of shoulder pain varies and includes pathology originating from the neck, glenohumeral joint, acromioclavicular joint, rotator cuff, and other soft tissues around the shoulder girdle. In more than two-thirds of cases the rotator cuff is the culprit. Management of shoulder pain consists of a multidisciplinary approach including physical therapy, pharmacotherapy, and invasive procedures (surgery, intraarticular steroid injections, regional anesthesia techniques, and neurolysis). Radiofrequency ablation (RFA) is a promising treatment that has been proven to help patients with chronic shoulder pain.

An important determinate of successful results from RFA is patient selection. RFA is indicated in patients who have clinical evidence of symptomatic osteoarthritis. Additionally, the ideal patients may have chronic shoulder pain of suspected peripheral origin that has not responded well to multimodal therapy, especially if they are not good surgical candidates. Certain studies have shown that ablation may have a role in treating primary rotator cuff injuries and chronic pain after total shoulder arthroplasty as well.

There are relatively few contraindications for radiofrequency ablation. Absolute contraindications include patient refusal and local infection. Relative contraindications include bacteremia and aberrant congenital or surgical anatomy. It is essential to weigh risks and benefits and document patient agreement and understanding due to the elective nature of this procedure.

Anatomy

Of the major joints, the shoulder has the most complex range of motion. The shoulder girdle, which connects the upper extremity to the thorax, includes four joints or articulations: (1) the glenohumeral joint, (2) the acromioclavicular joint, (3) the sternoclavicular joint, and (4) the scapulothoracic articulation. The bones that comprise these structures include the humerus, scapula, and clavicle, and the joint also relies on dynamic stabilization from the muscles of the rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis). Shoulder girdle muscles and their innervations are summarized in Table 12.1 .

The suprascapular nerve is typically the target of blockade for treatment of shoulder pain as it innervates up to 70% of the shoulder. RFA of the axillary nerve, nerve to subscapularis, and lateral pectoral nerve may also be performed depending on the location of pain. Both thermal and pulsed RFA of the suprascapular nerve have been described to treat chronic shoulder pain. However, these procedures do theoretically carry the risk of postablation weakness and the supraspinatus and infraspinatus muscles. RFA of sensory-only articular branches to the shoulder complex can disrupt nociceptive pathways while sparing motor function.

Sensory-only articular branches are best targeted in ablation safe zones, which have been defined by anatomic studies. ^, These are the area lateral to the spinoglenoid notch posteriorly (suprascapular branches), at the inferior-posterior portion of the greater tubercle (axillary branches), and over the coracoid process (lateral pectoral branches). ^, These safe zones are depicted in Fig. 12.1 .

Safe ablation zones (sensory-only articular branches) depicted by brackets both anteriorly and posteriorly.

The lateral trunk of the suprascapular nerve also could be ablated (which may spare supraspinatus function but compromise infraspinatus function) midway between the suprascapular notch and spinoglenoid notch in the supraspinous fossa. The nerve to subscapularis should be accessible over the anterior superior neck of the glenoid ; however, due to the proximity of this nerve to the brachial plexus and axillary artery, preclinical and clinical work on determining ideal ablation trajectory is ongoing.

Diagnosis

It is standard to perform diagnostic blocks to identify patients who should proceed to have RFA. This holds true for ablation techniques used for the spine and other major joints. Generally, a patient with greater than 50% pain relief is considered to have a positive diagnostic block. Some studies deem candidates appropriate for RFA after reporting greater than 50% pain relief from two independent sets of diagnostic blocks. There are no guidelines for the ideal number of blocks, block relief threshold, and volume of injectate for the diagnostic block; therefore further studies are necessary.

Nerve selection should follow zones of pain perception. Deep posterolateral pain would suggest that the suprascapular and axillary nerve should be targeted. Anterior pain may suggest that the lateral pectoral nerve and nerve to subscapularis should be targeted.

Diagnostic blocks

Diagnostic block technique: Prone approach

The posterior ablation zones are illustrated in Fig. 12.2 . The two sites labeled “1” are for targeting the suprascapular nerve, and the two sites labeled “2” are for targeting the axillary nerve. Prone positioning provides access to the posterior shoulder joint for denervation of suprascapular and axillary articular branches. Sedation is not usually needed for diagnostic blocks as it can confound analgesic interpretation of the procedure.

Posterior ablation zones. Two sites depicted by “1” target the suprascapular nerve. Two sites depicted by “2” target the axillary nerve.

Steps for targeting suprascapular articular branches ( Fig. 12.3 ) are:

• 1.
  

  Position the patient with the operative arm at the side to provide optimal visualization of the humerus.

  
  
• 2.
  

  Capture an image with ipsilateral obliquity to obtain the Grashey or true anterior-posterior view of the glenohumeral joint.

  
  
  
  
  • a.
    

    Additional modification of this view by declining the angle caudad provides better visualization of the glenoid neck and head of the humerus along with reducing image artifacts created by the spine of the scapula.

  
  
  
  
• 3.
  

  Identify the spinoglenoid notch (i.e., great scapular notch) by identifying the lateral border of the scapular spine to its attachment with the neck of the scapula. Marked by “*” in Fig. 12.3 .

  
  
• 4.
  

  The needle is advanced until it contacts the periosteum.

  
  
  
  
  • a.
    

    The needle depth in adults can exceed 3 inches.

  
  
  
  
• 5.
  

  Inject contrast as confirmation to exclude intravascular or intraarticular uptake (this is optional, but generally recommended).

  
  
• 6.
  

  Inject 0.5 ml of local anesthetic.

X-ray of posterior targets. Axillary articular branches (blue), suprascapular articular branches (red). Spinoglenoid notch marked by “*.”

For targeting axillary articular branches ( Fig. 12.3 ):

• 
  

  Repeat steps 1 and 2, then

  
  
• 3.
  

  Identify the greater tubercle; it appears as a step-off on the lateral head of the humerus with a tapering at its inferior margin.

  
  
  
  
  • a.
    

    If the head of the humerus appears rounded, this might indicate that the tubercle is anteriorly positioned, and further oblique rotation of the image is required.

    
    
  • b.
    

    An ideal view of the glenoid neck and the greater tubercle can be achieved in the same orientation, requiring no further adjustment between the two targets.

  
  
  
  
• 4.
  

  Once optimal view is obtained, repeat steps 4 to 6.