Arthroscopic Subacromial Decompression

Dayne T. Mickelson

Dean C. Taylor

Background and Preoperative Planning

• Acromion anatomy (Fig. 11-1)

Figure 11-1 | Acromion Morphology (A) classified as type I (flat), type II (curved), or type III (hooked). Os acromiale types (B) preacromion (PA), mesoacromion (MSA), and meta-acromion (MTA).

• Acromion morphology¹

• Os acromiale

▪ Acromioplasty as a treatment for os acromiale should be used with caution because it may destabilize the acromion.

▪ Excision of a symptomatic unstable os acromiale is effective and safe if the deltotrapezial fascia is not disrupted.

• The subacromial bursa vascular supply encountered during bursectomy²:

▪ Anterior bursa: Superficial to the coracoacromial (CA) ligament is the acromial branch of the thoracoacromial artery (Fig. 11-2).

Figure 11-2 | Shoulder and subacromial bursa location as viewed from superolateral. The veil is posteriormost aspect of the bursa. Coracoacromial ligament with acromial branch of the thoracoacromial artery superficial to it.

▪ Posterior bursa: posteromedial acromial branch of the suprascapular artery.

▪ Medial bursa: Fat in this area is vascularized from the anterior and posterior arteries of the acromioclavicular joint.

• Pathology

• Neer initially described acromioplasty and extrinsic impingement of the rotator cuff from the CA ligament and anterior inferior edge of the acromion.³

• When the arm is elevated, the subacromial bursa helps decrease contact between the CA arch and the rotator cuff. However the bursa can become irritated and inflamed (Fig. 11-2).

▪ Pathologic changes to the rotator cuff are thought to arise from both intrinsic and extrinsic processes.

• Tears caused by intrinsic degenerative changes of the cuff

• Tears caused by extrinsic impingement from a hooked acromion or anteroinferior undersurface CA enthesophyte

• Indications—Failure of satisfactory nonoperative management (3-6 months) trial

• Consistent physical examination findings

▪ Neer impingement sign and Hawkins test are sensitive but not specific.⁴

• Physical therapy with emphasis on scapular stabilization and periscapular strengthening

• Response to diagnostic/therapeutic subacromial steroid and anesthetic injection.

• Continued significant pain affecting quality of life

• Anesthesia—regional block with monitored anesthesia care sedation

Sterile Instruments/Equipment

• Thirty-degree arthroscope, light source, and pump

• Fluid with epinephrine 1:1000 in each 3 L bag of lactated Ringer solution

• 10 cc 1% lidocaine with epinephrine (1:100 000)

• Instruments

• Spinal needle

• Probe

• Arthroscopic ablation wand

• Shaver 5.5 mm (4.0-mm shaver if small shoulder) or optional burr

• Two 5.5 mm × 70 mm cannulas without fenestrations

• Possible instruments for rotator cuff repair (Tip—see Table 11-1)

Table 11-1 | Subacromial decompression tips and tricks

Timing of Operation	Tip or Trick
Preoperatively	Always be prepared to do a rotator cuff repair. Have the necessary instruments available.
Before Prepping and Draping	Remember to complete a full shoulder examination under anesthesia once the patient is relaxed.
Prepping and Draping	A pneumatic limb positioner helps provide inferior traction on the humeral head during subacromial decompression to enlarge the space.
Diagnostic Arthroscopy	Verify you are in the glenohumeral joint by sweeping the trocar inferior and superior to feel the camera slide between the humeral head and glenoid.
Subacromial Bursoscopy	Avoid sweeping medial and lateral in the subacromial space, which can create unnecessary bleeding.
Subacromial Decompression	When entering the subacromial bursa, aim for the bursal space located under the anterolateral portion of the acromion (Fig. 11-5A)
Subacromial Decompression	Visualization may be difficult during initial bursectomy. Run shaver facing up (away from rotator cuff) and toward the camera to clear space for viewing.
Subacromial Decompression	Avoid the fat in the posteromedial aspect of the subacromial space—this area will bleed significantly.
Subacromial Decompression	Be prepared for bleeding from the acromial branch of the thoracoacromial artery when dissecting around the CA ligament.
Acromioplasty	If the anterior overhang is too large (and shaver/burr cannot advanced in an anterior direction), then move inferior to bone overhang and resect it from directly underneath.
Acromioplasty	Before closing, return the camera to the posterior portal and verify resection. Best view is a horizon tangential view: 30-degree scope rotated to view toward 6 o’clock while dropping hand to keep the tip of the scope on the undersurface of the acromion.

Positioning and Operative Preparation

• Sitting (beach chair) position (Fig. 11-3)

• Legs flexed at hips and knees.

• Head in neutral position in both coronal and sagittal plane.

• All bony prominences padded, including nonoperative arm on arm holder.

• Operative arm positioning device can be used (optional).

Figure 11-3 | Beach chair position and draping. Operative arm in pneumatic limb positioner. Extremity drape and additional sheets placed over bar located across anesthesia IV poles. Sterile Mayo table will be brought in over legs for instrument management.

• Preoperative physical examination (Tip—see Table 11-1)

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