Introduction
Acromioclavicular (AC) joint and associated coracoclavicular (CC) ligament injuries frequently occur in active individuals when they fall directly onto their shoulder in an adducted position. The Rockwood classification is the most commonly used system for categorizing AC injuries, and helps to determine appropriate treatment. Nonoperative management of grade I and II injuries with a brief period of immobilization followed by a progressive return to activities is often successful, whereas grade IV, V ( Fig. 35.1 ), and VI ( Fig. 35.2 ) injuries are most effectively managed with surgical treatment. The initial treatment of grade III ( Fig. 35.3 ) injuries is more controversial, with some patients being able to return to their normal activities without surgery, whereas surgical reconstruction may provide more favorable outcomes for those wishing to return to occupations or sports with frequent overhead arm position or other high functional demands of the shoulder. However, surgical reconstruction has not consistently improved anatomical reduction, and a recent review of the literature reported a 11% reoperation rate within the first 6 months. Therefore, in contemplating surgical reconstruction, the surgeon and patient should discuss these factors and feel equipped to encounter an imperfect result.
Complications in the reconstruction of the AC joint are as diverse as the array of surgical techniques described to address AC joint instability. Because of the subcutaneous location of the distal clavicle and AC joint, surgery in this area is especially prone to complications such as skin healing issues, hardware prominence, and infection. Loss of reduction and/or continued instability, iatrogenic fracture, implant loosening, graft failure, erosion of suture or bone, osteolysis around implanted hardware, and stiffness are common enough complications that surgeons should be well aware of these issues and pursue strategies to avoid these pitfalls. The risk of iatrogenic injury to nearby neurovascular structures and the lung and complications related to autograft harvest at sites remote to the AC joint should also be in the forefront of the surgeon’s mind. This goal of this chapter is to elucidate what is known about these complications, offer tips on how to avoid them, and provide guidance on managing them when they do occur.
Anatomy
The clavicle is relatively flat in the coronal plate but S-shaped in the body’s axial plane, with the conoid tubercle prominent on the posterior aspect of the clavicle near its lateral end. The clavicle functions as both a strut from the axial skeleton to the scapula and a site for muscular attachment to control the shoulder.
The AC joint is a diarthrodial joint, incompletely divided by a disk with central perforations, that is the only articulation between the clavicle and scapula. The AC joint’s anteroposterior (AP) stability is primarily provided by the AC joint capsular ligaments that are thicker on the superior, anterior, and posterior surfaces, whereas the CC ligaments are the primary stabilizers in the vertical plane. The thickest and most consistent portion of the AC capsular ligament runs obliquely from the anterior acromion over the superior joint surface to the posterior distal clavicle at a 30-degree angle. The native anatomy allows approximately 8 mm of anterior translation, 9 mm of posterior translation, and 20 degrees of rotation through the AC joint. In about 40% of intact AC joints, the anterior and posterior borders of the distal clavicle and articulating acromion do not line up, with overhang possible on either side.
The CC ligaments, consisting of the more anterolateral trapezoid ligament and more posteromedial conoid ligament, both originate near the base of the coracoid, 28 mm and 22 mm posteriorly to its tip in males and females, respectively. They insert on the inferior surface of the distal clavicle, with the centers of the trapezoid and conoid ligament approximately 25 mm and 40 mm medial to the lateral edge of the clavicle and AC joint, respectively. ,
Ligament Injury
Recent cadaveric studies have reported that with the CC ligaments intact, complete resection of the AC joint capsule increases anterior translation by 4 to 6 mm and posterior translation by 3 to 4 mm, but only increases superior translation by 1 to 2 mm. , In another way of looking at this, the resistance to translation and rotation of the AC joint are reduced to less than 25% and 10% of the native state. AC dislocations of Rockwood grade III and above have complete disruption of the CC ligaments, allowing more vertical translation of the distal clavicle. In patients with Rockwood IV and V AC joint dislocations, the majority (71%) of AC ligament complex tears are on the clavicular side, but can also occur in an oblique pattern, in the midportion, or on the acromial side, whereas there is consistently an insertional avulsion of the deltotrapezial fascia. The manner in which CC ligaments fail is not well characterized, but may be immaterial because many current surgical techniques focus on replacing rather than repairing them when complete disruption has occurred.
Preoperative Complications
Avoiding complications at the preoperative stage can be achieved by performing a thorough history and physical. As already mentioned, the most common mechanisms of injury resulting in an AC joint separation are a direct blow to the affected AC joint or a fall onto the ipsilateral elbow forcing the humeral head into the AC joint. Physical examination findings that correlate with an AC joint injury include point tenderness at the AC joint and pain at the AC joint with cross-arm adduction. The cross-arm adduction test is performed with the arm elevated to 90 degrees and then adducted across the chest with the elbow bent at approximately 90 degrees. This maneuver should reproduce pain at the AC joint because of compression across the AC joint; if the patient experiences pain at the posterior or lateral aspect of the shoulder, he or she is more likely to have posterior capsular tightness or a rotator cuff injury. The sensitivity of the cross-arm adduction test has been reported to be 77%.
The O’Brien active compression test may also be helpful in differentiating AC joint pathology from intraarticular pathology of the superior labrum or biceps anchor. The O’Brien active compression test is performed with the shoulder in 90 degrees of forward elevation and 10 to 15 degrees of adduction, the elbow in extension, and the forearm in pronation with the thumb pointing toward the ground. The patient resists a downward force on the arm applied by the examiner. Pain at the superior shoulder at the AC joint indicates AC joint pathology, whereas symptoms felt deeper at the anterior glenohumeral joint reflect labral or biceps pathology. The O’Brien active compression test has been reported to have a 41% sensitivity and 95% specificity for AC joint pathology.
Initial evaluation of patients with AC joint pathology should include standard shoulder radiographs (AP, lateral scapular-Y, and axillary views) and additional films to specifically evaluate the AC joint. A Zanca view, performed with 10 to 15 degrees of cephalic tilt and 50% of the penetration strength for a shoulder AP radiograph, is the most accurate view to evaluate the AC joint. A bilateral Zanca view ( Figs. 35.1, 35.2, 35.3 ) that includes both AC joints in the same film allows for comparison with the contralateral uninjured side. The axillary view of the shoulder is useful in identifying a type IV AC joint injury with the clavicle displaced posterior to the acromion ( Fig. 35.4 ). If the CC distance appears normal in the setting of a complete AC joint dislocation, a Stryker notch view can help identify a coracoid fracture. Radiographs should also be evaluated for AC joint arthritis or osteolysis. A previous distal clavicle excision or Mumford procedure can impact AC joint stability, even in the setting of intact CC ligaments and AC capsule ( Fig. 35.5 ). Advanced imaging of patients with AC joint dislocations and CC ligament injuries is typically not required, although magnetic resonance imaging may show acute disruption of the CC ligaments. A stress examination under anesthesia with fluoroscopy can help elucidate whether there is an element of AP instability or posterior rotation that is not readily evident on standard radiographs.
Intraoperative Complications
There are numerous surgical techniques described in the literature to treat high-grade AC dislocations, including primary AC and CC ligament repair and fixation, reconstruction of the CC ligaments and/or AC capsule with autograft or allograft, augmentation with suture material or artificial ligaments, and arthroscopic fixation or reconstruction techniques. Combination techniques have also been described. The various intraoperative complications and potential complications specifically associated with surgical technique (including those that may occur postoperatively) are discussed in this section, with a brief overview of techniques. General postoperative complications are discussed in a subsequent section of this chapter.
Early fixation and repair constructs include cerclage wires around the clavicle and coracoid, lag screws from the clavicle to the coracoid (also known as the Bosworth screw), and screws or pins across the AC joint from the acromial side ( Fig. 35.6 ). Although good outcomes of these procedures were initially reported, they are generally biomechanically inferior to the native anatomy and can be associated with numerous hardware-related complications including fracture, hardware breakage, loss of reduction, or hardware migration. In particular, migration of wires into the neck or chest is a potentially catastrophic complication that can occur even years after fixation. Furthermore, the rigid construct created by these procedures blocks the normal coupling of clavicle rotation with scapular motion and arm elevation, which is likely to lead to either hardware failure or loss of shoulder motion. These procedures have largely fallen out of favor owing to their potential complications and advancements in other surgical techniques. If these techniques are chosen, the surgeon should obtain frequent radiographs postoperatively to monitor for hardware breakage or migration and plan for elective hardware removal to avoid late complications.
The Weaver–Dunn procedure was first described in 1972 as a treatment option for acute and chronic grade III AC joint injuries, although Neviaser described transfer of the coracoacromial ligament to treat AC dislocations several years earlier and Cadenat performed a transfer of the coracoacromial ligament in 1917. As described by Weaver and Dunn, the procedure included resection arthroplasty of the AC joint with fixation of the clavicle in an anatomic position by suturing the acromial end of the coracoacromial ligament into the medullary canal of the clavicle. Early reports of the Weaver–Dunn procedure and modifications were favorable, , , but patients with residual subluxation or dislocation had inferior results. , The coracoacromial ligament transferred to the clavicle has only 20% of the strength of the native CC complex, , thus it is not surprising that loss of reduction is a frequent complication. Clinical and biomechanical studies have demonstrated inferiority of the Weaver–Dunn procedure compared with anatomic CC reconstruction. If there is a symptomatic loss of reduction after a Weaver–Dunn procedure, we recommend revision surgery with an anatomic reconstruction.
Acute treatment of high-grade AC joint injuries with hook plate fixation has been widely used, particularly outside of the United States. The plate acts as an internal splint while the native tissues heal and is then typically removed at a planned second surgery. Good outcomes have been reported with hook plate fixation, particularly if performed in the acute setting. Reported complications associated with hook plate fixation include loss of reduction, loss of hardware fixation, acromial erosion, subacromial impingement, rotator cuff tear, clavicle fracture, shoulder stiffness, heterotopic ossification, periincisional numbness, and infection. , , Although hardware removal is frequently performed 6 months after surgery, patients who experience acromial erosion, subacromial impingement, or rotator cuff tear may require earlier hardware removal. Similar to other techniques employing hardware fixation, frequent postoperative radiographs should be obtained to monitor for hardware-related complications, and patients counseled that they should expect to undergo hardware removal to avoid late complications. Loss of reduction after hardware removal is still possible and can be as high as 12%. Given the high incidence of hardware-associated complications, routine second procedure to remove hardware, and significant loss of reduction after hardware removal, we do not advocate for the acute treatment of AC joint injuries with hook plate fixation. This viewpoint is further supported by a recent multicenter randomized trial by the Canadian Orthopedic Trauma Society comparing operative treatment with hook plate fixation versus nonoperative treatment for high-grade AC joint dislocations (grades III, IV, and V); the authors reported no difference in Disabilities of the Arm, Shoulder, and Hand (DASH) or Constant scores at 2 years between groups, and patients actually had improved outcome scores before 6 months with nonoperative treatment.
In an effort to avoid some of the hardware-associated complications seen with hook plate fixation, suture button device techniques have also been developed to treat acute high-grade AC joint injuries ( Fig. 35.7 ). Again, the goal of these procedures is to anatomically reduce the joint to allow healing of the native ligaments, and is best performed in the acute setting. Single- and double-button techniques have been described and often employ arthroscopic assistance. Biomechanical studies have shown that double-suture button techniques are able to withstand as much or more force than the native ligaments. , Complication rates after suture button fixation range from 20% to 44%. , , Reported complications include clavicle fracture, coracoid fracture, loss of reduction, loss of fixation, hardware migration ( Fig. 35.8 ), clavicular erosion, AC joint arthrosis, stiffness, hardware irritation, CC calcification, and infection. , , Although the rate of hardware irritation may be as high as 35%, most authors do not report routinely performing hardware removal (unlike hook plate fixation). The acute treatment of AC joint dislocations with suture button constructs has a relatively low rate of loss of reduction, with authors reporting pooled results of only 8% loss of reduction, whereas individual series of acute injuries and similar arthroscopic techniques for chronic injuries have higher failure rates. , These constructs may not adequately address horizontal instability owing to vertical placement of the suture device, , thus the indications for suture button fixation may be fairly limited. It is our opinion that the surgeon should be selective in indicating patients for acute treatment suture button fixation given the high success rates of nonoperative treatment for acute injuries and the potential complications.
