Intraoperative and Postoperative Issues With Acromioplasty and Distal Clavicle Excision

Introduction

The complex osteology of the shoulder predisposes it to a variety of pathological states, several of which can be related to impingement of soft tissues between osseous surfaces. Additionally, repeated overhead weight-bearing activities can predispose the glenohumeral articulation and its surrounding joints to arthritic changes that can manifest clinically as pain and dysfunction. Subacromial impingement syndrome and acromioclavicular (AC) joint disease are widely recognized sources of shoulder pain and dysfunction, implicated in 48% and 4%, respectively, of shoulder pain complaints in general practice. Surgical recontouring of the anterolateral acromion and distal clavicle are commonly performed to address the aberrant contact between adjacent structures. One new and potentially modifiable biomechanical index of interest is the critical shoulder angle (CSA), which references the angle subtended by two lines: a line tangent to the glenoid fossa and a second line from the inferior glenoid to the lateral aspect of the acromion on a Grashey radiograph. Larger CSAs have been associated with a higher incidence of rotator cuff retear, and the effects of decreasing CSA through lateral edge resection of the acromion continue to be elucidated.

Anatomic Considerations

Understanding the intricate anatomy of the AC joint complex can help avoid intraoperative complications. The acromion is a continuation of the scapular spine projecting laterally and then anteriorly over the glenoid, creating the superior shoulder contour. The deltoid has seven muscular segments which attach around the scapular spine posteriorly, acromion laterally, and clavicle anteriorly. In a cadaveric and computer-modeled study, resection of 4 mm on the undersurface of the acromion detached an average of 41.3% (range: 38.7%–42.8%) of the deltoid direct fibers from various aspects of the acromion. Laterally, the deltoid originates in the anterior, middle, and posterior facets of the acromion, separated by three bony tubercles, whereas the trapezius originates on the medial acromion and posterior clavicle. ^, Both muscles insert and interdigitate with the superior capsule of the AC joint.

The AC joint is created by the convergence of the distal clavicle with the medial aspect of the acromion as it projects forward. The joint is diarthodial, with hyaline cartilage on the articular surfaces and an interposed meniscal homologue, both of which degenerate in the first few decades of life. ^, The joint has variable inclination, with average dimensions of 9 mm superior to inferior and 19 mm anterior to posterior. It is surrounded by a synovial membrane and capsule with pronounced ligamentous thickenings, rendering it an inherently stable joint. Biomechanical studies have shown that the posterosuperior capsular complex is crucial in preventing posterior translation and axial rotation of the clavicle. The superior AC capsular ligament attachments, as characterized by Renfree et al., terminate 5.5 mm ± 1.7 and 3.6 mm ± 0.78 from the articular surface of the distal clavicle in men and women, respectively.

The corococlavicular (CC) ligaments consist of the trapezoid laterally, which limits vertical translation of the clavicle, and the conoid medially, which prevents axial compression of the AC joint. ^, The relevant literature is replete with anatomic descriptions of these ligamentous structures. The conoid attaches on the undersurface of the posterior aspect of the most lateral curvature of the clavicle, with its lateral and medial borders an average of 2.6 cm and 4.7 cm, respectively, from the distal end of the clavicle. The trapezoid insertion extends anterolaterally on the undersurface of the clavicle starting just lateral to the conoid. The lateral and medial borders of the trapezoid are on average 1.0 cm and 2.6 cm, respectively, from the distal clavicle. A more reliable guide to CC ligament anatomy uses a ratio of distal clavicle to ligament center distance and total clavicular length (0.17 trapezoid, 0.24 conoid) ( Fig. 33.1 ).

Keys to Avoiding Complications

Obtaining and maintaining adequate visualization is a central tenet of arthroscopic surgery. Unsurprisingly, previous studies on distal clavicle excision (DCE) repeatedly cite poor visualization as a common cause of an inadequate resection. Blood in the surgical field is a common source of visual obstruction, and arthroscopic pumps capable of tightly controlling inflow pressure, epinephrine in arthroscopic fluid, and hypotensive anesthesia can all help dramatically improve hemostasis and visualization in the subacromial space.

Hypotensive anesthesia is generally better tolerated in the lateral decubitus position, especially in elderly patients with cardiac risk factors because there are reports of cerebrovascular events in the beach chair position because of permissive hypotension. ^, An appreciation for and application of Bernoulli’s principle as it relates to the cause (and effects) of turbulent flow can optimize visualization in the subacromial space. As Burkhart and associates have stressed, Bernoulli’s principle dictates that an increase in the velocity of fluid results in a decrease in pressure. A simple example of this is an airplane wing: as air travels over top of a curved wing, it must travel further in the same period of time as the air moving straight across the under surface. The corresponding higher velocity of air on the upper surface creates a decrease in pressure above the wing and thus a pressure gradient, allowing for lift. The same principle is true of arthroscopy when fluid leaks from portals. Fluid under high pressure in the shoulder ejects into the low-pressure operating room with high velocity because of Bernoulli’s principle. In its wake, a pressure gradient is created which pulls blood from surgically cut vessels. Making matters worse, the pressure gradient creates turbulent flow, which can further exacerbate poor subacromial visualization. A simple and highly effective solution to combat this problem is to plug leaking portals to minimize fluid extravasation, reducing the detrimental effects of pressure gradients and turbulent flow.

Although a 30-degree arthroscope is commonly used during the initial arthroscopic inspection and debridement of the subacromial space, a 70-degree arthroscope is an indispensable instrument and should be routinely used to visualize the distal clavicle throughout the procedure. Viewing from the lateral subacromial portal, a radiofrequency wand introduced through an anterior working portal that is made in line with the AC joint is used to skeletonize the distal clavicle from its posterior to anterior extent, removing all soft tissue that may obscure the surgeon’s view of the osseous structures to be resected. A spinal needle can be used to localize the AC joint ( Fig. 33.2 ) and ensure that resection begins at the appropriate position medial to lateral. If the AC joint is not clearly delineated, inadvertent resection of the medial aspect of the clavicle is possible. An arthroscopic burr of known width is introduced through the anterior working portal. A burr’s width of bone is resected from the anterior edge of the distal clavicle, thereby “setting the level” of resection in the medial to lateral direction ( Fig. 33.3 ). The 30-degree arthroscope is then exchanged for a 70-degree arthroscope, which allows for visualization of the superior aspect of the AC joint ( Fig. 33.4 ). The white fibers of the AC joint capsule should be identified and not violated during the resection. The resection proceeds posteriorly to the posterior aspect of the clavicle, whereupon the resection is then continued superiorly. Care should be taken to completely resect the posterior aspect of the clavicle because this is a frequent location for larger osteophytes. At no point is the resection continued medial to the level initially “set” at the beginning of the procedure. At the completion of the resection, careful inspection is performed to verify that the AC joint has been completely decompressed and that the superior AC joint capsule has not been violated ( Fig. 33.4 ). If DCE is to be performed in an open fashion, full-thickness flaps should be raised as the AC joint is approached, and the superior AC joint capsule should be preserved and closed in a layered fashion.

With respect to acromioplasty, presurgical identification of the acromial morphology, including slope and width, can prevent inappropriate resection. Intraoperatively, identification of the lateral edge of the acromion with both visualization and tactile sensation from instruments can ensure acromioplasty does not violate the deltoid insertion. ^, A radiofrequency wand is used to remove soft tissue from the inferior surface of the acromion, working posterior to anterior until the lateral and anterolateral acromion edges are visualized ( Fig. 33.5 ). Moving medially, the coracoacromial ligament insertion is palpated with an arthroscopic instrument. Care must be taken so as to not transect this structure. Typically, the subacromial spur is viewed as an inferior projection of the anterolateral acromial edge. Similar to the previously described technique for arthroscopic DCE, an arthroscopic burr of known dimension is introduced through the lateral working portal, and a burr’s-width step resection is performed starting laterally and moving medially until the inferior surface of the acromion has been evenly contoured medial to lateral and anterior to posterior ( Fig. 33.6 ).

A methodical approach to resection is very important to avoid either under- or overresection. For DCE, this entails using the width of the burr to establish an initial step cut and respecting that boundary posteriorly and superiorly, while using the burr on reverse to assist in accommodating an even and controlled resection. Similarly, for acromioplasty, care should be taken to avoid burr deviation laterally by maintaining tactile sensation, and when using the cutting block technique, vertical trajectory must be scrutinized via a lateral viewing portal to avoid overresection anteriorly.