Although recent advances have been made in the treatment of acromioclavicular (AC) joint injuries, they are still challenging for shoulder surgeons. There is a consensus that type I and II injuries should be treated nonoperatively, whereas acute type IV, V, and VI injuries should be treated surgically. There is no algorithm for correctly diagnosing and treating type III injuries, but the current trend is toward nonoperative treatment except for those with persistent symptoms and functional limitations after a course of conservative management. If surgery is indicated, newer anatomic techniques of reconstructing the coracoclavicular (CC) and AC ligaments are recommended.
Key points
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Nonsurgical treatment is recommended for type I and II injuries.
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Surgical treatment is recommended for type IV, V, and VI injuries.
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Type III injuries are controversial.
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Current operative techniques are trending toward anatomic reconstruction of acromioclavicular and coracoclavicular ligaments.
Introduction
The AC joint serves as a primary link in the suspension of the upper extremity from the axial skeleton, and its injury represents 30% to 50% of athletic shoulder injuries. Despite the frequency of injury, the treatment of the AC joint remains subject to debate because there is a lack of consensus regarding optimal management. More than 60 different procedures have been described to treat these injuries, which indicates the difficulty and problems with their management. The uncertainty surrounding management of AC joint injuries centers on 2 debates: first, nonoperative versus operative treatment; and second, different operative techniques.
Introduction
The AC joint serves as a primary link in the suspension of the upper extremity from the axial skeleton, and its injury represents 30% to 50% of athletic shoulder injuries. Despite the frequency of injury, the treatment of the AC joint remains subject to debate because there is a lack of consensus regarding optimal management. More than 60 different procedures have been described to treat these injuries, which indicates the difficulty and problems with their management. The uncertainty surrounding management of AC joint injuries centers on 2 debates: first, nonoperative versus operative treatment; and second, different operative techniques.
Relevant anatomy and biomechanics
The AC joint is a diarthrodial joint formed by the distal end of the clavicle and the medial facet of the acromion with a variable inclination ranging from nearly vertical to more than 50° of obliquity, with the superior edge of the clavicle more lateral. Within this joint resides a fibrocartilaginous disk of variable size and thickness that degenerates over time and becomes nonfunctional in most individuals after 40 years of age.
During development, the AC joint first appears at 3 to 5 years of life. The clavicle first appears intrauterine at week 5. It has 2 epiphyses that contribute to its longitudinal growth: the medial epiphysis is responsible for most of this growth via enchondral activity. The medial epiphysis appears at age 18 years and fuses between 22 and 25 years. The lateral epiphysis is less consistent. The acromion has between 2 and 5 ossification centers appearing at puberty, and fusing by age 25 years.
The AC joint has both static and dynamic stabilizers. Static stabilizers include the AC joint capsule and 4 AC ligaments (superior, inferior, anterior, and posterior). These AC ligaments are the principal restraints to anteroposterior translation between the clavicle and acromion. The posterior and superior AC ligaments contribute most to the horizontal stability of this joint. Recent studies showed that a distal 1-cm clavicle resection results in a 32% increase in posterior translation compared with the intact state. No consensus exists regarding the amount of increased horizontal instability that may be clinically significant, but even a small resection of as little as 2.6 mm could completely release the clavicular insertion of the AC ligaments in some patients.
Vertical stability of the AC joint is provided by the CC ligaments, which include the conoid ligament medially and the trapezoid ligament laterally. A cadaveric study has shown that the distance from the lateral edge of the clavicle to the medial edge of the conoid averages 47 mm and, to the center of the trapezoid, is 25 mm in male patients. Mazzocca and colleagues further showed that, with superior load, the conoid ligament always failed before the trapezoid. The ligamentous attachments on the coracoid process are less well studied, but cadaveric studies have shown the trapezoid to have a broad attachment to the lateral upper side and the conoid to have a smaller attachment on the medial posterior margin, suggesting independent function of the ligaments.
The AC joint is not a rigid structure, because it has micromotion in all planes. If not for this natural motion, then arthrodesis of the joint would be a viable option after injury. Inman and colleagues and Graichen and colleagues reported an in vivo motion of the AC joint of approximately 20°. With shoulder elevation and abduction, the clavicle has been shown to rotate more than 40°, but relative to the acromion it only rotates 5° to 8° because of concomitant sternoclavicular motion. After injury to the AC joint, the degree of clavicular displacement depends primarily on the extent of the injury to the AC and CC ligaments.
Causes
Injuries to the AC joint can be the result of direct or indirect forces. The most common cause is fall onto the anterior, superior edge of the acromion with the arm in the adducted position. This force drives the acromion downward and medially. The downward displacement of the distal clavicle is first resisted by the sternoclavicular ligaments, and, if no fracture of the clavicle occurs, the force first sprains then ruptures the AC ligaments and capsule, followed by the CC ligaments and deltotrapezial fascia. At this point, the upper extremity has lost its suspensory support from the clavicle. Although conventional thought is that this results in superior displacement of the clavicle, the major deformity is the inferior displacement of the shoulder.
Classification
AC joint injuries are best classified according to the extent of damage, thus they are graded according to the amount of injury to the AC and CC ligaments. In the past, these injuries have all been referred to as AC joint injuries, although these injuries include a spectrum of disruption between all the joints of the scapula and the clavicle. Rockwood’s group developed the most widely accepted classification system, based on the original work of Tossy and colleagues in 1963. This modified classification is described later and is summarized in Table 1 .
| Type | AC Joint | AC Ligament | CC Ligament | Deltoid and Trapezius Muscles |
|---|---|---|---|---|
| I | Intact | Sprain | Intact | Intact |
| II | Displaced | Torn | Sprain/Intact | Intact |
| III | Disrupted | Torn | Torn | Usually intact |
| IV | Disrupted | Torn | Torn | Detached |
| V | Disrupted | Torn | Torn | Detached |
| VI | Inferior displacement of clavicle | — | — | — |
Type I
There is no visible deformity. The patient may have tenderness over the AC joint, but none over the CC ligament region. There is mild strain to the fibers of the AC ligaments because they remain intact, and the AC joint remains stable. Radiographs appear normal.
Type II
A moderate force is strong enough to rupture the ligaments of the AC joint. The distal end of the clavicle is unstable in the anteroposterior plane, but superoinferior stability is preserved because the CC ligament is intact. There may be a slight upward displacement of the distal end of the clavicle caused by stretching of the CC ligaments, and widening of the AC joint may be present ( Fig. 1 ). There may be tenderness overlying the CC ligaments.
Type III
A severe force tears the AC and CC ligaments, resulting in complete AC dislocation. The distal clavicle appears to be displaced superiorly, although the AC joint is reducible by an upward force placed on the elbow. Radiographic findings include a 25% to 100% increase in the CC space compared with the contralateral shoulder.
Type IV
Posterior dislocation of the distal end of the clavicle is rare. With an anterior and inferior force to the acromion, the clavicle is displaced posteriorly into or through the trapezius muscle. Tenting may be seen on the posterior aspect of the shoulder. Crucial for this diagnosis is the axillary view radiograph showing the posterior displacement of the clavicle in relation to the acromion.
Type V
This dislocation is a more severe type III in which the distal clavicle has been stripped of all of its soft tissue attachments, including the deltotrapezial fascia. The clavicle lies subcutaneously. Compared with type III dislocations, the AC joint is not reducible. On radiographs, the CC space is increased greater than 100% compared with the contralateral shoulder. There is marked disfiguration of the shoulder with droop of the extremity.
Type VI
Inferior dislocation of the distal end of the clavicle is rare, resulting from hyperabduction and external rotation. This injury is often the result of severe trauma and is frequently combined with multiple injuries. The distal clavicle occupies either a subacromial or subcoracoid location. Gerber and Rockwood’s series of 3 patients is the largest reported in the literature.
Imaging
Routine imaging for AC joint evaluation includes routine anteroposterior (AP) and axillary views. The AP view identifies the amount of vertical migration of the clavicle, whereas the axillary view evaluates anteroposterior displacement. The Zanca view (an AP with a 10°–15° cephalic tilt) provides improved visualization of the AC joint because it removes the scapula from the field. AP and Zanca views should ideally be taken with a wide plate to show bilateral AC joints on the same film so that the 2 AC joints can be directly compared. Stress views of the AC joint, taken while the patient is holding weights in each arm, have fallen out of favor because they are uncomfortable for the patient and do not provide additional information.
Management
Type I Injury
There is no role for operative management in the acute setting. Nonsurgical treatment consists of a sling for 7 to 10 days, ice, and nonsteroidal medications. The sling is used for comfort, with gradual return to unrestricted daily activities usually within 2 weeks.
Type II Injury
Nonsurgical treatment is generally recommended for all type II injuries. Most investigators suggest a period of immobilization in a sling to remove the stress from the injured AC and CC ligaments, generally for up to 2 weeks. Once the pain has subsided, an early and gradual rehabilitation program is initiated with a focus on passive-assisted and active-assisted range of motion. The patient is not allowed to do any heavy lifting, pushing, pulling, or contact sports for at least 3 to 6 weeks to allow the ligaments to heal. Earlier return to athletics can be facilitated through use of protective padding over the superior aspect of the joint. Continued, unrelieved pain can be treated with a corticosteroid or an anesthetic injection into the AC joint. There is a general consensus for nonoperative treatment of type I and type II injuries.
Type III Injury
In contrast with type I and type II injuries, there is general uncertainty regarding treatment of type III injuries, but initial nonoperative treatment is favored in most cases. When managing these injuries, patient characteristics should be taken into account, including type of sport, level of play, timing relative to the season, and throwing demands of the sport. There have been many reports of nonoperative and operative management, with various techniques of surgical treatment. Current literature suggests that the decision for treatment should be made on a case-by-case basis with an emphasis on initial nonoperative management.
No prospective, randomized controlled trial (level 1) has been published to compare nonoperative and operative treatment of these injuries, and thus only retrospective case series are available. A recent meta-analysis by Smith and colleagues concluded that operative management resulted in a better cosmetic outcome but greater duration of sick leave. They found no difference in strength, pain, throwing ability, and incidence of AC joint osteoarthritis compared with nonoperative management. Only 1 study has shown a higher Constant score for operative management compared with nonoperative management. A prior meta-analysis by Philips and colleagues advised against surgical treatment of these injuries. Thus the operative versus nonoperative debate has remained in effect, and so too has the debate surrounding surgical technique, because many options have been described. Even the diagnosis of a type III injury has come into question, because much of the uncertainty when managing type III injuries is in differentiating them from type V injuries. In summary, the debate remains, but it has been proposed that surgical indications for type III separations are patients with persistent symptoms and functional limitations after a course of nonoperative management (minimum of 6–12 weeks) focused on attaining full range of motion and scapula stabilization.
Type IV
There is consensus in the literature that the treatment of type IV injuries should be surgical. The CC ligaments are usually, but not always, torn, in addition to the AC ligaments. Thus, surgical treatment focuses on AC joint reduction, AC ligament fixation, and reconstruction of the deltotrapezial fascia, with CC reconstruction if necessary.
Type V
Surgical treatment is generally recommended for these types of injuries.
Type VI
All type VI injuries in the literature have been treated with surgery. Two subtypes must be distinguished: a subacromial type with the CC ligaments intact and a subcoracoid type with completely torn CC ligaments. The treatment is always operative with reduction of the distal clavicle and AC joint stabilization.
Surgical techniques
The orthopedic literature is replete with an abundance of case series and comparative studies on surgical techniques for AC joint reconstruction. This large body of work is evidence that no single, conclusively effective surgical technique exists. However, they all share a common goal: to stabilize the distal clavicle. Surgical techniques can be grouped into 3 basic categories: (1) AC joint fixation, (2) CC fixation, and (3) ligament reconstruction.
Acromioclavicular Joint Fixation
Many methods of intra-articular AC joint fixation are described in the literature; however, clinicians should be cautious when using these techniques, because the placement of hardware across the AC joint can be problematic. Eskola and colleagues compared 3 different methods, including transfixion with 2 smooth Kirschner wires, 2 threaded Kirschner wires, and 1 cortical screw. In a 4-year follow-up on 70 of the 100 cases, the results were graded as good in 67 of 70 patients. The investigators preferred the use of the threaded Kirschner wires. This method has been abandoned because of potentially catastrophic occurrence of pin migration. Another technique of primary AC joint fixation is the hook plate. In 1976, Balser first introduced this plate, which is fixed by screws on the superior surface of the distal clavicle end and ensures AC joint reduction by a transarticular hook engaging at the undersurface of the acromion. This technique is still popular in Europe, although it requires a second surgery for implant removal at 3 months. One recent study of 225 patients with hook plate fixation showed 89% excellent results at a mean of 36 months, but with an overall complication rate of 10.6%. The potential complications with this technique are acromion osteolysis or fractures caused by the subacromial hook. Another report of 16 patients reported 8 complications, including 1 bent plate, 1 plate dislocation, and 6 infections.
Coracoclavicular Fixation
The technique of placing a screw between the clavicle and the coracoid was described by Bosworth in 1941. This surgery consists of an open reduction of the AC joint dislocation with the insertion of a screw from the distal clavicle to the coracoid process. Because of the high rate of hardware migration and screw breakage over time, a second surgery is usually recommended between 8 and 12 weeks postoperatively. This screw may be placed percutaneously, although Tsou reported a 32% technical failure rate in 53 patients with this technique. Placement of synthetic loops between the coracoid process and clavicle have been described by several investigators. Stam and Dawson and Goldberg and colleagues described the use of cerclage Dacron ligaments looped between the clavicle and coracoid. Morrison and Lemos reported 12 of 14 good and excellent results when using a synthetic loop placed through drill holes in the base of the coracoid and anterior third of the clavicle.
Anatomic reconstruction techniques have recently been adopted in an effort to provide physiologic conditions that restore strength and stiffness of the normal AC joint. Some of these use autograft or allograft soft tissue, whereas others use synthetics. A prosthetic device, such as the TightRope device (Arthrex, Naples, FL) can be placed as a synthetic CC ligament reconstruction. Titanium buttons are placed on top of the clavicle and under the coracoid and connected with a continuous loop of no. 5 FiberWire suture (Arthrex, Naples, FL) ( Figs. 2 and 3 ). To ensure local CC ligament healing, it is recommended that this technique only be performed within the first 3 weeks after trauma. Other modifications have been described. The first generation consisted of a single construct, and now second-generation techniques use 2 TightRope systems. Midterm results were recently published, with a mean Constant score of 91.5 and Taft score of 10.5 points at 24-month follow-up. Jensen and colleagues followed 26 patients for 17 months and found a Constant score of 92.4 and Taft score of 10, with no removal of hardware necessary. Beris and colleagues studied 12 patients at 18-month follow-up treated with this technique and found a mean Constant score of 94.8 with no significant distance in CC distances compared with the contralateral shoulder. No. 5 FiberWire fails biomechanically at 485N, whereas the native CC ligament complex fails at 589N, so the tensile strength of 2 strands of FiberWire is greater than that of the native ligament. Other biomechanical studies have confirmed the strength of the fixation. The usage of TightRope systems is promising, and these procedures are able to be performed arthroscopically or open with good preliminary results; however, radiographic anteroposterior instability has been observed in up to 43% of patients. Venjakob and colleagues presented the longest term follow-up of 23 patients using fixation with 2 suture-button devices and, at 58 months postoperatively, 96% remained very satisfied or satisfied with the procedure outcome with an average Constant score of 91.5, despite 8 radiographic failures.
