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Diagnostic Arthroscopy and Normal Anatomy
Only with an understanding of normal glenohumeral joint and subacromial space anatomy can the surgeon appreciate which structures are damaged.
Diagnostic Glenohumeral Arthroscopy
Portal placement is critical, so it is important to take sufficient time to mark the portal sites precisely. Draw the bone outlines of the acromion, the distal clavicle, and the coracoid with a surgical skin marker. Be careful not to draw the most superficial bone landmarks, but rather draw their inferior surfaces (which takes into account bone thickness), because portal entry points are referenced from these surfaces ( Figs. 3.1 and 3.2 ).
Although trocar entry into the glenohumeral joint is simple and almost intuitive for an expert, surgeons new to arthroscopy may find joint entrance difficult. The standard advice to “start in the soft spot and aim for the coracoid” is only slightly helpful. Actual joint entry requires precision, and even small deviations of 3 to 5 mm from the desired portal location make the operation more difficult. An additional complication is that portals vary from patient to patient because they are related to the patient's position on the operating table as well as his or her size, rotundity, and kyphosis. The ideal portal location changes throughout the operation as soft tissue swelling increases and alters the local anatomy. Portal placement is also affected by the underlying diagnosis. For instance, posterior portal placement for an acromioclavicular joint resection differs from that for a superior labrum anterior to posterior (SLAP) lesion repair. There are no absolute rules, but there are a number of guidelines that are helpful.
The most reliable landmarks are bone. Anteriorly, outline the coracoid process, the acromioclavicular joint, and the anterior acromion. Laterally, identify the lateral acromial border, and posteriorly, outline the posterior acromion. The most important landmark is the posterolateral corner of the acromion, which can be palpated even in large patients ( Fig. 3.3 ). Even with these initial landmarks outlined, be prepared to use them only as a guide.
Posterior Portals
Traditionally, surgeons describe the location of the posterior portal as being in the “soft spot” approximately 2 cm inferior and 2 cm medial to the posterolateral acromial edge. Although this location is adequate for glenohumeral joint arthroscopy, it is not optimal for subacromial space operations. If you make the incision in the traditional soft spot, you will enter the joint parallel to the glenohumeral joint line and slightly superior to the glenoid equator. This site allows you to enter and adequately visualize the glenohumeral joint, but you will be at a disadvantage if you try to use the same incision to enter the subacromial space. Once you insert the cannula into the subacromial space, the soft-spot portal directs the cannula superiorly and medially, and causes two problems. First, because the arthroscopic view is now directed medially, the lateral insertion of the rotator cuff is more difficult to visualize. Second, the superior angle of the arthroscope makes it difficult to “look down” on the rotator cuff tendons and appreciate the geometry of rotator cuff lesions. One solution to this problem is a second posterior portal; another solution is to alter the posterior portal's location ( Fig. 3.4 ).
As noted, the exact location of the posterior portal varies with the clinical diagnosis. For rotator cuff repairs and subacromial decompressions, we make the posterior incision for the portal in a more superior and lateral position, approximately 1 cm inferior and 1 cm medial to the posterolateral acromion, or virtually at the acromial corner. The more superior and lateral location minimizes the aforementioned difficulties. The superior entry allows the cannula to enter the subacromial space immediately beneath the acromion, parallel to its undersurface . This maximizes the distance between the arthroscope and the rotator cuff, allowing a better appreciation of rotator cuff lesions. The superior position (parallel to and immediately inferior to the acromion) also facilitates acromioplasty because the surgeon is afforded a better view of the acromial shape. The more lateral position (immediately medial to the lateral acromion) places the arthroscope in line with the rotator cuff tendon insertion. The glenohumeral joint can be easily viewed with this more lateral portal with simple medial translation of the arthroscope cannula after entry through the skin. For operations restricted to the glenohumeral joint, such as a Bankart or SLAP repair, the joint can be entered with the more traditional medially placed portal, but we still prefer the more lateral portal placement for nearly all of our procedures (see Fig. 3.4 ).
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