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.
Distal Clavicle Excision
DCE can be an effective treatment option for AC joint pathology that is refractory to conservative management. DCE was originally described through an open procedure, but proponents of minimally invasive surgery have adapted direct (superior) and indirect (bursal) arthroscopic techniques to access the joint. Higher-level studies comparing open with arthroscopic DCE are lacking, but one systematic review of 17 studies (two level II, one level III, and 14 level IV studies) by Pensak et al. reported good to excellent outcomes in 79% of open DCE (289 shoulders) and 91% of arthroscopic (142 shoulders, direct and indirect) DCE procedures. These numbers should be interpreted cautiously as few studies looking at open DCE used functional outcome measures, and approximately one-third of the patients, from three studies, were summarized to have good to excellent outcomes based on satisfaction or relief of pain symptoms without quantifying the degree of improvement. A more recent comparative analysis by Robertson et al. of open versus arthroscopic (indirect) DCE noted decreased VAS pain scores at final follow-up, favoring arthroscopic surgery, with no difference in American Shoulder and Elbow Surgeons scores, return to normal shoulder function, mean radiographic resection distance, or average operative time. One randomized control trial by Charron et al. comparing direct and indirect arthroscopic DCE in young athletes showed improved postoperative functional results at 6 weeks and faster return to sport for the direct approach (21 days vs. 42 days). However, indirect arthroscopy may be advantageous, particularly in an older population, as it facilitates detection of other intraarticular shoulder pathology because the glenohumeral joint is assessed before entry into the subacromial space.
Open and arthroscopic DCE have somewhat predictable complication profiles. The obvious benefit of arthroscopy is its minimally invasive nature which may decrease wound complications while avoiding disruption of the superior capsule; however, concern exists that limited visualization can lead to uneven or inappropriate resection. , , At present, the infrequency of complications for arthroscopic DCE has likely precluded an investigation of their incidence in the literature. One study by Berg et al. reported a 3.2% incidence of heterotopic ossification in arthroscopic (310 shoulders) and open (187 shoulders) DCE and/or acromioplasty, but did not provide an analysis of open versus arthroscopic or DCE versus acromioplasty. A systematic review of 14 papers with a total of 360 open DCEs revealed one infection, 10 patients with pain or weakness, and 16 patients with shoulder stiffness. Four of those studies, accounting for 75 procedures, commented on 11 skin-related issues including three painful scars, three nonpainful indurated scars, two hypertrophic scars, one keloid and two cases of skin numbness. The authors reviewed their institutional results from 42 patients who underwent isolated open DCE alongside the literature. They reported four infections (9.5%), three (7.1%) of which were deep and one (2.4%) superficial); 12 (29%) “stiff shoulders” including one patient with heterotopic ossification; 23 (55%) patients with AC joint region tenderness; 23 (55%) patients with scar hypersensitivity; and six (14%) with hypertrophic scar. The mean follow-up time was 16 months, but the minimum follow-up of 1 month limits the applicability of this portion of the study given that shoulder stiffness, sensitivity, and numbness may diminish with time. However, one of the reviewed papers in the study previously reported stiffness in 22% of patients at an average 9 years of follow-up, elevating the level of concern for this complication in an open approach. ,
It is the authors’ recommendation to perform an indirect arthroscopic DCE to avoid wound complications, stiffness, and iatrogenic instability caused by violation of the AC joint superior capsule that occurs with an open approach. Moreover, an indirect arthroscopic approach is preferable as it affords the surgeon the ability to assess for both glenohumeral and subacromial pathology that would otherwise not readily be assessed with an isolated open method.
Overresection and Management
The optimal amount of DCE remains somewhat a point of contention. , , When DCE was originally described, a minimum resection of 15 mm was standard. However, resection to this extent has largely been abandoned because of concerns about CC ligament violation, which can lead to superior-inferior clavicular instability. , , , A level IV study by Eskola et al. showed improved long-term outcomes for patients receiving resections less than 10 mm. These findings were supported by anatomic studies showing that resection of 1 cm detaches 8% of the trapezoid, whereas resection of 2 cm and 2.5 cm detaches 60% and 90%, respectively.
Disruption of the intrinsic stabilizers of the AC joint may also lead to shoulder dysfunction because worse pain scores have been associated with iatrogenic AC joint instability. , Anatomical studies have detailed the capsular insertions, showing that a resection of 1 cm would significantly, if not entirely, detach the capsule. , Moreover, a biomechanical study by Corteen et al. showed resection of 1 cm with capsular violation increased posterior translation of the clavicle by 32% which interestingly could not be reversed with capsular repair. Further clinical study is needed to evaluate the significance of these findings to reach definitive conclusions about ideal resection length. Based upon these data, we believe that no more than 1 cm of the distal clavicle should be excised.
Management of iatrogenic AC instability begins with a detailed patient evaluation. Instability of the AC joint commonly presents as pain with overhead activities, with some patients complaining of a painful click with forward elevation of greater than 90 degrees. Shoulder radiographs including Zanca, axillary, and stress views of the AC joint can delineate the extent of instability. Initially, patients are managed conservatively with rest, physical therapy, and activity modification, but persistent symptoms, especially with interference in daily function, necessitate surgical evaluation. Multiple surgical techniques have been described to increase AC joint stability. Corteen et al. proposed augmenting the capsular repair in an open procedure with a transclavicular suture through the coracoacromial ligament, showing it was able to significantly decrease posterior clavicular translation. However, for gross instability related to incompetent CC ligaments, ligament transfer, screw and suture fixation, and various graft reconstructions have all been developed. Early techniques, such as the Weaver–Dunn procedure and screw fixation, have led to less than desirable clinical outcomes with high rates of loss of reduction. More recently, anatomic reconstructions have seen a growth in popularity because of their preferred biomechanical profile. One study by Tauber et al. comparing 24 patients undergoing the modified Weaver–Dunn procedure or an anatomic reconstruction using free tendon graft (FTG) showed that both radiographic outcomes and clinical outcomes were superior in the anatomic reconstruction cohort. However, a recent systematic review by Moatshe et al. demonstrated comparable patient-reported outcomes among FTGs, suspensory devices (SDs) and synthetic ligament devices (SLDs) with similar rates of unplanned reoperations (FTG: 2% (2/165), SD: 2.7% (12/435), SLD: 0.9% (1/114)) and complications (FTG: 10.3% (17/165), SD: 6.2% (27/435), SLG: 4.4% (5/114)).
Underresection and Management
Incomplete DCE is frequently a cause of clinical failure following this procedure, but clinicians must first rule out missed concomitant shoulder pathology. , , Patients who remain symptomatic following an incomplete DCE may continue to complain of tenderness about the AC joint and/or pain with crossbody abduction. Provocative maneuvers include weighted overhead activities, movements behind the back, and adduction, including the cross-arm adduction test. Plain radiographs can demonstrate inadequate resection as seen in Fig. 33.7 , although a computer tomography scan more clearly characterizes the joint surface ( Fig. 33.7 ). Diagnostic AC joint injection can confirm the diagnosis and differentiate between AC joint pain, rotator cuff pathology, and subacromial impingement; however, injections are notoriously inaccurate, up to 61% of the time, when imaging adjuncts such a fluoroscopy or ultrasound are not used. Once persistent symptoms are confirmed to be secondary to incomplete resection, a reresection should be considered. Use of an open or arthroscopic approach is appropriate, with individualized considerations made for each patient. As more studies attempt to delineate parameters for an ideal resection, proponents of limited DCE have shown resection of 5 mm can eliminate bone-to-bone contact without compromising outcomes. , , Should a revision surgical procedure be undertaken to deal with symptoms attributable to underresection of the distal clavicle, the goal of the surgical procedure should be to plane the clavicular surface by removing any cortical remnants and resecting any residual posteroinferior spurs rather than performing an excessive medialization of the residual distal clavicle.
