PRINCIPLES OF ARTHROSCOPIC SUBACROMIAL DECOMPRESSION & ARTHROSCOPIC ACROMIOCLAVICULAR JOINT RESECTION

Wesley M. Nottage, M.D.
The Sports Clinic
Orthopaedic Medical Associates, Inc.
Laguna Hills, California

INTRODUCTION:

Arthroscopic subacromial decompression has quickly replaced open traditional subacromial decompression techniques as the procedure of choice for refractory subacromial “impingement.” The evolution of the arthroscopic surgical techniques has occurred since its original description by Ellman in 1983-84 where orientation was facilitated by the placement of two percutaneous needles at the margin of the acromioclavicular ligament. Current arthroscopic subacromial decompression techniques expect good visualization and allow for reproducible results technically, when specific guidelines are followed.

Initial factors affecting the performance of the surgical procedure include those of SETUP access to the shoulder, FLOW DYNAMICS and the use of ELECTROCAUTERY.

SETUP of the shoulder should allow easy access to both the posterior and superior surface of the shoulder unimpeded by either the patient’s head or the anesthesiologist. Frequently, this will require positioning the anesthesiologist at the chest site of the patient if they are in the decubitus position. The arm position should be one of minimal abduction to avoid placing the greater tuberosity into the subacromial space. A minimal amount of “traction” will aid in extraction of the humeral head inferiorly away from the acromion and enlarge the work space in which to perform the procedure (approximately 7 pounds).

Portal placement is critical to allow proper access to the subacromial space. Utility posterior portal was chosen 1 finger breadth from the posterosuperior angle of the acromion and generally is utilized for both glenohumeral arthroscopy and subacromial arthroscopy.

The anterolateral working portal for the subacromial space is optimally made 2 finger breadths lateral to the anterolateral corner of the acromion and in line with the anterior edge of the acromion. This would allow easy access beneath the acromion and place one straight in line for resection of the anterior margin of the acromion as well as subacromial space work.

FLOW DYNAMICS requires an understanding that arthroscopic visualization is best when bleeding is minimized usually by keeping a resting pressure in the bursa at all times equal to or greater than that of the diastolic pressure. This would require proper assessment of the patient’s systolic blood pressure and, if possible, lowered to 90-100 mm of mercury coupled with adequate inflow volume and pressure either by gravity or a pump. A pump mechanism is certainly convenient and optional but will not necessarily solve the problem. The most common error in visualization is too rapid egress, specifically excessive suction or too many portals which allow fluid to escape from the subacromial space.

ELECTROCAUTERY is a helpful adjunct to performing arthroscopic surgical procedures. It not only allows a coagulation of bleeding vessels, it can be used to cut tissues such as the coracoacromial ligament but also allows for shrinkage of tissue by its heat effect. This is especially helpful in the anterolateral portal area to improve visualization when viewing from the lateral portal. Normally, coagulation only is utilized at a setting of approximately 30, and with use of the standard shielded electrode, no specific fluid or medium changes are required. It will operate easily in ionic medium such as saline or lactated Ringers.

ENTRY into the subacromial space should be preceded by both a thorough examination under anesthesia to document both range of motion and laxity of the shoulder and complete glenohumeral joint arthroscopy. A number of conditions easily mimic rotator cuff symptomatology and left ruled out prior to entering the subacromial space can lead to failure. Wrong diagnosis is not an infrequent cause of failure of subacromial decompression.

Entry into the bursal cavity is aided by remembering that the subacromial bursa is a “anterior” structure lying approximately one—half uncovered and one—half covered by the acromion. The center of the bursal cavity is at the anterolateral corner of the acromion and the posterior bursal curtain lies at the mid acromial line. It is critical to develop a technique which will allow easy immediate penetration into the bursa which appears like “a room with a view” rather than an obliterated cavity, since obtaining this view initially is critical to confirm the arthroscopic diagnosis of impingement.

The mechanics of impingement can be readily visualized arthroscopically but will be destroyed if initial debridement of the subacromial space is carried out with a shaving in it prior to entry into the bursal cavity. A clean entry into the bursal cavity can easily allow for confirmation of the diagnosis manifest by fraying and frank breakdown of both the coracoacromial ligament and the superior surface of the rotator cuff.

DEBRIDEMENT of the subacromial space is best accomplished by viewing posteriorly and debriding from the anterolateral portal using as large an instrument as possible, commonly a 5.5 mm tip device. Careful clearing of the undersurface of the entire acromion in the anterior one—third should be carried out including to the margins both anteriorly and laterally and to the level of the acromioclavicular joint.

THE CORACOACROMIAL LIGAMENT can be released in selected cases by the use of electrocautery to avoid causing bleeding in the immediately adjacent deltoid muscle which commonly occurs with the use of a shaving unit in this area. Its relief should clearly allow “end on” visualization of the ligament and usually will require freeing up of both its bursal attachments medially and laterally to allow it to drop away from the acromion. It is important to remember that release of the coracoacromial ligament should not be carried out routinely particularly in the view of a large irreparable rotator cuff defect. The coracoacromial arch provides secondary stability when the primary stabilization of the rotator cuff is ineffectual and its absence will allow subluxation of the humeral head forward on forward elevation of the shoulder.

ABRASION of the undersurface of the acromion is predictably performed by viewing laterally and abrading from the posterior surface. By using the posterior acromion as a “cutting block” as advocated by Sampson, abrasion creates a tapered effect from anterior to posterior and is carried out until flat using the posterior acromion as a guide. Abrasion is facilitated by periodic suction. It is imperative to make sure that the anterior acromion is resected and flush in line with the acromioclavicular joint and that the lateral margin of the acromion is well—seen so that any remaining lateral bony prominences will not be left behind. The prominence of the articular facet adjacent to the acromioclavicular joint and the acromion should also be trimmed with confirmation of the end point of flat enough deemed when the instrument from the posterior portal is laid across to the anterior surface and no gap exists beneath this instrument.

It is important not to cavitate the undersurface of the acromion by an aggressive localized acromioplasty which will weaken the acromion and make is prone to fracture. Placement of the posterior entry portal may affect the angle of the taper from this method of resection but will not lead to cavitation if done correctly.

ACROMIOCLAVICULAR JOINT RESECTION:

In selected cases, the acromioclavicular joint can be resected either in a transbursal (coupled with arthroscopic subacromial decompression) or purely intra—articular resection technique.

Transbursal resection is the most common method and represents an extension of the subacromial decompression technique. Once the arthroscopic decompression has been completed, the undersurface of the acromioclavicular joint must be cleared of soft tissues using both electrocautery and a shaving unit. Once the bone is exposed, the abrasion tip is introduced from posteriorly and while viewing laterally the undersurface of the clavicle is abraded until flat and coplanar with the acromion.

At this point, visualization from the lateral portal is carried out through the acromioclavicular joint and an anterosuperior acromioclavicular joint portal is created at the anterior margin of the acromioclavicular joint. At this level, the shaver tip is introduced and subsequently the abrasion tip to both debride and remove either the acromial facet (Nevaiser) or distal clavicle to create a 10—15 mm space between these bony structures. An attempt should be made to maintain integrity of the superior ligaments. Once completed, it is strongly advised that digital palpation with the little finger through the superior portal is carried out to confirm that no bone fragments have been left anteriorly or in the interval of resection. It is not uncommon for bone fragments to be left at the margins of this resection and this can be entirely avoided by careful palpation at completion of the procedure to identify and remove any bony fragments which might remain.

The most common reason for failure of subacromial decompression is either wrong diagnosis (bicipital disease, degenerative joint disease, instability, rotator cuff tear, suprascapular neuropathy, or frozen shoulder) or the failure to resect bone anterior with the acromion flush and in line with the anterior surface of the acromioclavicular joint. These errors can be minimized by proper attention to detail and diagnosis with documenting both range of motion, stability examination and glenohumeral joint arthroscopy prior to entering the bursal cavity, and careful attention to technique using the posterior cutting block to resect and visual anterior acromial margin clear of bone to the level of the acromioclavicular joint. It should be reinforced that this is not a “blind” or “partially blind” procedure but rather a clearly visualizable procedure with specific steps which, if carried out and seen clearly, will lead to reproducible surgical procedures which accurately resect the underside of the acromion and create a type I (flat) acromion in the postoperative status.