Precision Acromioplasty in Arthroscopic Subacromial Decompression

of the Shoulder

Thomas G. Sampson, M.D., Jon K. Nisbet, M.D.,

and James M. Glick, M.D.

Summary: Arthroscopic techniques for subacromial decompression have been criticized for lack of precision in resecting the anterior acromial undersurface and evaluating the amount of bone resected. The goal of subacromial decompression is production of a flat undersurface for the acromion and acromioclavicular joint, thus enlarging the supraspinatus outlet and deterring impingement. Achieving this goal using the arthroscope requires preoperative evaluation of the acromial morphology, planning of the dimensions of bony resection, a reproducible acromioplasty method with intraoperative evaluation of the adequacy of resection, and postoperative confirmation of the resulting acromial shape. A precise technique for arthroscopic acromioplasty has been developed in the course of performing over 200 shoulder arthroscopies. This method adheres to conventional open surgical goals for bony resection and allows for reliable intraoperative evaluation of the result. Using this technique, over 90% good and excellent results may be achieved in treatment of stage II subacromial impingement syndrome.

Key Words: Shoulder—Subacromial impingement syndrome—Subacromial decompression—Acromioplasty.

In 1972, Neer (1) described the anterior acromioplasty as a method of surgical treatment of advanced stages of the subacromial impingement syndrome. This technique entails anterior exposure of the subacromial space with limited deltoid detachment from the acromion, resection of the coracoacromial ligament and inflamed subacromial bursa, and removal of the anterior lip and undersurface of the anterior process of the acromion. The proper execution of this procedure requires removal of a wedge of bone that is 0.9 cm thick anteriorly and tapers posteriorly for a distance of 2.0 cm. Furthermore, the undersurface of the acromion is then inspected to ensure that the remaining bone is flat in contour without excrescences from either the newly-contoured acromion or the acromioclavicular joint. Several authors (1—5) have since published long-term series confirming the efficacy of this technique for the appropriate impingement stages.

Several authors have described techniques for arthroscopic subacromial decompression with the same anatomic goals (6-8) Andrew JR. (personal communication, 3/24/88). The early results of these methods have been promising, but several major criticisms remain. In particular. arthroscopic subacromial decompression has demonstrated a prolonged learning curve (7). and does flt)t readily allow intraoperative evaluation of the amount of bone removed. Because of the progressive whittling nature of the power burr. no single fragment of bone is removed for inspection or measurement. The inherent distortion of the arthroscopic lens also compromises the visual assessment of the final result.

More recently. Morrison and Bigliani have correlated acromial morphology with the incidence of partial and complete tear of the rotator cuff using both cadaveric dissections and clinical series. Their data imply that a flat acromial undersurface protects the rotator cuff in the impingement syndrome. Attention may be better directed to the final shape and contour of the remaining acromion than to the bone wedge removed.

To produce flat acromial undersurfaces from a variety of acromial shapes, the acromial morphology must be assessed preoperatively so that bony resection may be appropriately individualized. Intraoperatively, one must be able to perform a reproducible bony resection and then confirm the contour and dimension of the remaining acromial bone. Postoperative documentation should demonstrate the decompression of the coracoacromial arch and the appropriately flattened acromial shape.

During the past 10 years the senior authors (T.G.S., J.M.G.) have performed over 200 shoulder arthroscopies for treatment of subacromial impingement syndrome. While initially struggling with the learning curve, a precise method has evolved for arthroscopic acromioplasty. This technique allows preoperative planning, reproducible acromial resection with intraoperative verification, and postoperative evaluation and documentation.

PREOPERATIVE EVALUATION AND PLANNING

The impingement syndrome is diagnosed by clinical means and further elucidated by plain radiographs, arthrograms, ultrasound, and double-contrast computed tomography (and will likely be amendable to magnetic resonance imaging modalities). These studies add to preoperative planning if evidence of bony spurs or a complete rotator cuff tear is present.

Additional surgical planning information is available by use of the supraspinatus outlet view (9) of the acromion. Like the transcapular Y view of the shoulder trauma series (10), the x-ray beam is directed in the plane of the scapula, but then angled caudal by 5 to 10*. The resultant radiograph demonstrates the supraspinatus outlet and reveals the contour of the acromial undersurface.

Using this view, a line is drawn connecting the anterior- and posterior-inferior edges of the acromion and demonstrating a gap between the straight line and the undersurface midsection of the acromion. A second line is then constructed beginning again at the posterior-inferior acromial edge but now passing through the anterior-inferior acromion to produce a new flat acromial undersurface These two lines will be reconstructed and visualized during the arthroscopic procedure.

A final measurement is taken to determine the distance from the anterior acromial edge to the point at which the resection line intersects the undersurface of the acromion This measurement is corrected for magnification and will be used during the arthroscopic procedure to determine the appropriate starting point for the bony resection

SURGICAL TECHNIQUE

The patient is placed in the lateral decubitus position with Buck’s traction applied to the forearm and the shoulder in neutral flexion with 40 to 70* of abduction. Suspension generally requires 10 lb of traction, but varies with the size of the patient. The anesthesiologist is positioned at the patient’s abdomen and, after a standard surgical scrub, the shoulder is draped free so that unobstructed wide access is available to all sides of the acromion. We have had no experience using the beach chair position for this procedure.

Glenohumeral arthroscopy is performed in standard fashion to evaluate concurrent pathology and the undersurface of the rotator cuff. The posterior portal, however, must be positioned somewhat more inferior than usual to allow for proper burr placement later, during the acromioplasty. The portal must be inferior to the slope-line of the acromion on sagittal section (Fig. 9). A superior portal will lead to struggling with the soft tissue and will be further aggravated with swelling of the shoulder upon fluid extravasation. A variable pressure irrigation pump is helpful for hemostasis, but the surgeon must be vigilant to avoid excessive swelling.

After glenohumeral arthroscopy is complete, the instruments must be repositioned in the subacromial space. A lateral portal is created just anterior to the mid point of the acromion and some 3 to 4 cm lateral to the bony edge to allow passage of the arthroscope into the subacromial space parallel to the acromial undersurface. A switching stick is passed through the posterior portal, just beneath the acromial surface and out the anterior portal. cannula for outflow anteriorly and instruments posteriorly are thus delivered into the subacromial space. Through the posterior portal a large full radius resector is passed for bursal resection while the subacromial space is distended and visualized using the arthroscope in the lateral portal. Rapid bursal excision will prevent excessive fluid extravasation, but an arthroscopic electrocautery unit is helpful to lower pump pressures. Concept, Largo (FL U.S.A.) markets its electrocautery unit with a coated tip which works well with lactated Ringer’s irrigation solution. A simple orientation of the video image Triangulation within the subacromial space. At this point the surgeon is standing al the head of the table and views the shoulder in an upside-down position. Therefore, the monitor image should be sim . Acromion shapes with measurement of the distance ilarly anatomically upside-down In this manner, the instrument entering the shoulder from the surgeon’s right hand also enters the monitor screen from the right-hand side. Thus, instrument and monitor orientation resemble that used in standard knee arthroscopic procedures, and triangulation is familiar. In this inverted position, the floor of the viewing compartment is the undersurface of the acromion and the roof is the superior surface of the rotator cuff. Other visible landmarks are the coracoacromial ligament, the acromioclavicular joint, and the spine of the scapula. With the arthroscope in the lateral portal, the monitor shows the undersurface of the acromion in a supraspinatus outlet profile, just as in the preoperative radiographic view. Once the bursal tissue and periosteum of the acromion have been adequately resected to allow identification of the anatomic landmarks, the coracoacromial ligament is resected. During this procedure the acromial branch of the thoracoacromial artery is encountered, and bleeding will obscure visualization. Again, the electrocautery may be used to resect the ligament and obtain hemostasis. We have found that an end-cutting instrument (Turboaggressor, Dyonics. Andover, Massachusetts. U.S.A.) can be used to transect the ligament. If this is performed quickly, with removal of the contiguous deltoid fascial attachments as well, the ligament will retract toward the coracoid and bleeding will stop upon this retraction. Next, a nerve hook probe with measurement demarcations on its shank is inserted through the posterior portal and applied to the undersurface of the acromion with the hook over the anterior edge. The arthroscope confirms that the probe is contacting the posterior and anterior edges of the acromion and allows a gross estimate of the gap centrally between the straight probe and the undersurface of the acromion. This maneuver duplicates the preoperative planning step in Fig. 6. As in the planning exercise, the gap will be eliminated by removing enough of the anterior acromion to allow the probe to lay fiat on the resultant surface. The starting point for the bony resection is then identified by measuring (using the shank demarcations on the nerve hook) from the anterior acromion edge backward by the predetermined distance, I), from Fig. 8. Adjacent local landmarks are chosen to mark this point while the probe is exchanged for the burr. A sharp aggressive barrel-shaped burr (Acromionizer by Dyonics or Acufex Microsurgical, Norwood, Massachtisetts, U.S.A.) is used to create a recognizable starting spot. The manner of bony resection is akin to the cutting-block technique employed in many total knee instrumentation systems. In this case, the posterior aspect of the acromial undersurface will serve as a cutting block to guide the resection of the anterior acromion bone wedge. The burr sheath is firmly applied to the undersurface of the acromion so that medial—lateral sweeping of the burr tip creates a shallow groove just at the predetermined point. The burr is now slowly advanced anteriorly while maintaining the medial—lateral sweeping motion. The burr sheath is applied to the posterior acromion to maintain the appropriate plane of resection during the sweeping advance of the burr tip. The resection is completed when the burr no longer Inverted acromion with burr positioned to begin the cutting-block” technique of acromioplasty contacts bone during the sweeping advance of the burr sheath and the anterior edge of the acromion is removed. The resultant contour of the acromial undersurface may be evaluated by applying the probe again. looking for flat apposition and absence of a gap. Finally, the arthroscope may be switched to the posterior portal to better evaluate the most lateral edge of the acromion, as this edge is often too close to the arthroscope lens to allow safe burring when viewing from the lateral portal. Similar probe and burr technique may be used through the lateral portal if modification is necessary. The shoulder will often be quite remarkably swollen by the end of the procedure, due to fluid extravasation, but no neurovascular or wound complications have arisen as a result. The patient returns home on the day of surgery and is seen in the surgeon’s office within a week to begin an exercise program and early shoulder motion. At that time, a repeat supraspinatus outlet view is obtained to document the bony resection and compare with preoperative views

RESULTS

While the senior authors have performed over 200 shoulder arthroscopies, this technique has been applied only during the last 2 to 3 years. Recent review of 91 patients with at least I-year follow-up has shown good or excellent results (using the UCLA Shoulder Scale) in over 90% of stage II and III impingement (no rotator cuff tear). Results for acromioplasty and debridement of massive rotator cuff tears have also been quite favorable, with over 80% achieving significant pain relief (done for patients with limited functional goals). Results for acromioplasty and debridement of complete rotator cuff tears in otherwise high-functioning patients have been less successful, and we currently recommend open repair of any cuff tears with arthroscopic or open acromioplasty.

DISCUSSION

The indications for arthroscopic subacromial decompression are the same as those for open surgical procedures. In general, this means advanced stage LI and stage ILL impingement lesions as evaluated by history, clinical examination, arthrography, or ultrasonography. Despite advances in staging the lesion radiographically, the arthroscope still offers an unparalleled opportunity for evaluation of the rotator cuff, short of open surgery. If the patient fails adequate conservative treatment for a period of 6 to 12 months (including physical therapy for strengthening the rotator cuff muscles, NSAIDS, and several subacromial steroid injections), then the staging procedure of choice is the arthroscopic exam. At the time of diagnostic arthroscopy, subacromial decompression with adequate acromioplasty may be performed arthroscopically or by subsequent open technique. If a complete tear of the rotator cuff is discovered at arthroscopy, open repair or arthroscopic debridement may be entertained, depending on the clinical situation.

In deciding whether open or arthroscopic technique for acromioplasty should be employed, one must balance the time-proven effectiveness of the open procedure with the advantages of an arthroscopic acromioplasty. When done arthroscopically, acromioplasty may be accomplished in the outpatient setting, with less disruption to the deltoid insertion and thereby more rapid rehabilitation. The inherent complications of open procedures, including infection and cosmetic appearance of the scar, are also lessened. In medical-economic terms, savings may be appreciated from elimination of the I-or 2-day inpatient stay, from the less expensive outpatient surgical status, and from earlier return to employment from quicker full rehabilitation.

Criticisms of the arthroscopic method of subacromial decompression have revolved around the learning curve and the inability to accurately gauge the amount of bony resection intraoperatively or postoperatively. Both of these points can be addressed by application of the technique described herein.

First, triangulation is facilitated by inverting the monitor image so that hand position in front of the surgeon duplicates instrument position in the viewing field. Preoperative planning with the supraspinatus radiograph allows consistent determination of the point at which to start the resection. Use of the cutting-block resection technique enables controlled and consistent contouring of the undersurface of the acroinion. Use of a nerve hook probe in apposition to the acromial undersurface allows easy evaluation of the adequacy of the resection. Finally, this technique may be applied consistently to a variety of pathology with a standardized result and confidence as to the adequacy of the resection. There are some inherent difficulties to reorient hand-eye coordination using this approach. In most cases, after a few attempts, the surgeon should feel confident and comfortable with this approach.

SUMMARY

This arthroscopic technique enable results in subacromial decompression which are comparable to those attributed to open acromioplasty. Lt also retains all of the advantages of the outpatient setting with less extensive exposure and greater diagnostic power, while allowing confident bony resection as defined by preoperative planning and ready intraoperative evaluation of the resultant acromial contour. The practitioner will find that adherence to this method will standardize the resultant acromioplasty while leaving room to accommodate a spectrum of pathology We feel that this technique will shorten the learning curve associated with arthroscopic subacromial decompression.

Preoperative planning

1. Supraspinatus outlet view to grade acromial shape

2. Construct resection lines to create flat acromial undersurface

3. Measurement of distance from anterior acromiom edge for start of resection

Surgical technique

1. Posterior portal placement inferior to slope of acromion

2. Arthroscopic viewing through lateral portal

3. Inverted monitor image

4. Bursal resection and hemostasis

5. Coracoacromial ligament resection

6. Measure distance from anterior lip to establish starting point

7. Barrel-shaped burr in posterior portal

8. Cutting-block technique using posterior acromial undersurface

9. Apply nerve hook again to demonstrate flat contour of acromial undersurface and elimination of gap

Postoperative care

1. Early shoulder motion and exercises

2. Repeat supraspinatus outlet view to demonstrate bony resection

REFERENCES

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