Surgical Techniques for the Shoulder and Elbow
Arthroscopic Subacromial Decompression
Posterior (Cutting Block) Approach

Indications

1. Primary extrinsic impingement syndrome with subacromial bursitis and/or cuff tendinosis with type II or III acromion.
    
2. Chronic secondary impingement with adaptive pathologic sub-acromial bony/soft tissue changes (e.g., anterior acromial traction spur or undersurface acromial fraying or bursal cuff degeneration).
    
3. Lack of response to diligent conservative treatment program including scapular and rotator cuff retraining, non-steroidal anti-inflammatory drugs, subacromial injection, and activity modification for 6 to 12 months.
    

Contraindications

1. Secondary impingement with underlying subluxation.
    
2. Internal posterior-superior impingement with/without superior labrum anterior and posterior (SLAP) lesion.
    
3. Anterior subcoracoid impingement.
    
4. Pseudo-impingement.
    

Mechanism of Injury

Elevation of arm abuts the greater tuberosity against the prominent anterior acromial hook or coracoacromial spur, resulting in inflammation and bursal side degeneration/tearing of the rotator cuff and/or biceps tendon.
 

Physical Examination

1. Pain with impingement maneuvers (Neer and Hawkins signs) relieved with subacromial injection of lidocaine.
    
2. Tenderness to palpation of anterior acromion and anterior and superior cuff when arm is extended.
    
3. Pain with resisted abduction and flexion (cuff tendinosis) and/or positive Speed's test (biceps tendinosis).
    

Diagnostic Tests

1. Standard shoulder radiographs including outlet, glenohumeral anteroposterior (AP), axillary, and acromioclavicular (AC) views to evaluate acromial morphology and AC disease.
    
2. Magnetic resonance imaging, arthrogram, or ultrasound may be utilized to further evaluate rotator cuff and biceps tendon.
    
3. Selective lidocaine injections into subacromial space versus AC joint versus bicipital groove to delineate pathology.
    

Special Considerations

Impingement symptoms in younger patients with benign bony morphology are likely secondary to underlying scapular or cuff/deltoid muscle imbalance or glenohumeral instability, and these problems should be addressed prior to consideration of arthroscopic subacromial decompression.  Success with arthroscopic subacromial decompression (ASAD) can only be expected with extrinsic primary impingement, or chronic secondary as noted above.
 

Preoperative Planning and Timing of Surgery

1. Outlet and axillary views are key to evaluating the acromion. AP of AC joint and axillary views are key for the AC joint.
    
2. Determine the shape (should be type II or III or you are likely performing an inappropriate procedure) and thickness of acromion on outlet view. Draw two lines: one on the undersurface of the acromion from the front tip to the back edge; a second line along the posterior one half of the undersurface of the acromion extending through the anterior acromion. The distance between these two lines approximates the amount of undersurface anterior bone that will be resected (Fig. 10-1A).

	Figure 10-1 A.   Radiographs allow determination of the shape and thickness of the acromion on the outlet view.

3. Visualize the AC joint and acromion on the axillary view to determine the amount of anterior acromial protuberance that extends anterior to the AC joint. This approximates the amount of bone that will be taken off anteriorly :is one resects the AC spur in addition to the undersurface bone (Fig. 10-1B).

	Figure 10-1 B.  The axillary view allows determination of the amount of a nterior acromial protuberance that will be removed. Co=coracoid, Cl=clavicle, Ac=acromion, H=humerus

4. It is important on the outlet view to evaluate the thickness and shape of the acromion because those that are very thin and curved will not be candidates for the "cutting block" technique as too much bone would be resected, risking acromial fracture or deltoid detachment. A limited resection of the anterior hook would he more appropriate in these cases (Fig. 10-2).

	Figure 10-2.  In cases with a very thin and curved acromion, a limited resection of the anterior hook is more appropriate.

Special Instruments

1. An arthroscopic eIectrocautery/ablation device is strongly recommended in the subacromial space to control hemorrhage, improve visualization, and aid in removal of soft tissue.
    
2. A high-torque bone-cutting burr greatly facilitates anterior acromial resection.
    
3. Anesthetic Options:
           General anesthesia.
           Scalene block.
    

Patient and Equipment Position

1. Lateral decubitus.
    
2. Anesthesia anterior to the abdomen for 180-degree surgical access to the superior shoulder with careful axillary and peroneal padding.
    
3. Arm abducted 30 degrees and flexed 10 to 15 degrees with 7 to 15 pounds of distraction, depending on the patient's body habitus.
    
4. Patient rolled back 25 degrees to get the plane of the glenoid parallel to the floor.
    
5. Beach chair position (alternative).
    

Surgical Approach

1.  After an exam under anesthesia and a thorough arthroscopic glenohumeral exam from both a standard posterior and high anterior approach, the scope is removed and redirected at a 15-degree caudad angle to the acromion. The scope is placed far enough anteriorly (under the anterior one half of the acromion) to enter the bursal chamber that is distended.
    
2. With scope and flow posterior and outflow through anterior cannula (placed through previous high anterior portal with Wissinger rod), a lateral working portal is established 3 to 4 cm from the lateral border of the acromion, slightly anterior to the midpoint of the acromion and directed slightly upward so the shaver/ablator does not impinge on the lateral cortex.
    
3. Define anterior one half of the bony acromion with shaver and cautery/ ablation from the lateral portal. Ablate or transect the coracoacromial ligament with the cautery unit or shaver and resect the anterior 3 to 4 mm of acromial bone from the anterolateral corner to the AC joint with burr. Also thin down the lateral border of the anterior one half of the acromion tapering posteriorly (Fig. 10-3). Eighteen-gauge needles at the anterolateral corner and AC joint aid in orientation.

4. Place scope in lateral portal to view arch of acromion and introduce burr through posterior portal directly on undersurface of posterior one half of the acromion. Using this as a "cutting block" the burr is advanced anteriorly with a sweeping motion medially to laterally (Figs. 10-4)

	Figure 10-4.  The burr is advanced anteriorly using the posterior half of the acromion as a "cutting block" to remove the bone with a sweeping motion medially to laterally.

5. The scope is then placed posteriorly to view the acromion and ensure it is flat in the medial-lateral plane (Fig. 10-6). One can also view a burr from an anterior AC portal, resecting the superior remaining clavicle while performing a Mumford.

6. The flow pressure is reduced and hemostasis obtained with the electrocautery unit.

Postoperative Care and Rehabilitation

1. A simple absorptive sterile dressing is applied to the skin with foam tape and ice is used intermittently for 36 hours. Immediate active and passive range of motion and daily activities are allowed as tolerated, with sling usually not utilized unless associated cuff repair performed.
    
2. Scapular stabilization and cuff exercises arc instituted at week 1.

Tips and Pearls

1. Take care to keep the burr tightly on the undersurface of the posterior one half of the acromion as one comes forward on the "cutting block." If portal is too low or soft tissue gets interposed posteriorly, the burr may falsely angle upward, resulting in excess anterior bone resection and risking subsequent acromial fracture or deltoid detachment (Fig. 10-7).

2. Resect 3 to 4 mm of anterior acromial bone from the anterolateral corner of the acromion to the AC joint and taper back along the lateral aminion from the lateral portal before placing the burr posteriorly to use the "cutting block." This clearly outlines the bony anatomy, improves visualization, and lessens the potential for inaccurate resection (Fig. 10-3).
    
3. If the AC joint is asymptomatic preoperatively and has no inferior osteophytes or degenerative changes on X-ray, an effort should be made not to violate the inferior capsule or joint as this may destabilize the joint and a percentage of these may become symptomatic postoperatively. If the AC joint is degenerative or has prominent inferior osteophytes, then beveling the inferior tip of the clavicle (co-planing) or arthroscopic distal clavicle resection (Mumford) is appropriate.

Suggested Readings

• Gartsman GM. Arthroscopic acromioplasty for lesions of the rotator cuff. J Bone Joint Surg Am 1990;72:169-180.
   
• Gerber C. Terrier F, Ganz R. The role of the coracoid process in the chronic impingement syndrome. J Bone Joint Surg Br 1985;B7:703-708,
   
• Jobe KW, Kvitne KS, Giangarra CE. Shoulder pain in the overhand or throwing athlete: the relationship of anterior instability and rotator cuff impingement. Orthrop Rev 1989;18:963-975.
   
• Neer CS. Anterior acromioplasty for the chronic impingement syndrome in the shoulder: a preliminary report. J Bone joint Surg Am 1972:54:41-54.
   
• Sampson TG, Nisbel JK, Glick JM. Precision acromioplasty in arthroscopic subacromial the decompression of the shoulder. Arthroscopy 1991;7;301-307.
   
• Walch G, Boilean P, Noel E, Donell ST. Impingement of the deep surface of the supraspinatus tendon on the posterior or superior glenoid rim: an arthroscopic study. J Shoulder Elbow Surg 1992;l:238-245.
   

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3/1/2006

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