Acromioclavicular joint injuries are commonly known as shoulder separations. Injuries to the acromioclavicular joint usually are the result of downward force on the acromion. Acromioclavicular joint injuries are commonly called AC joint separation or AC joint dislocation.
The true incidence is much higher than reported because many patients with a low-grade injury don’t seek medical attention.
Acromioclavicular joint injuries occur most commonly in young adults who take part in sports but it is increasingly seen in children as well as sporting activities become popular in kids.
The acromioclavicular joint is part of the shoulder girdle and is the joint between the acromion process and lateral end of the clavicle.
This joint is enhanced by many ligaments and ligament injuries can lead to acromioclavicular joint injuries.
Anatomy of Acromioclavicular Joint
The acromioclavicular joint is a diarthrodial joint between the lateral end of the clavicle and the acromion process with a meniscus in the joint which could be complete or incomplete.
The normal width of the acromioclavicular joint is 1-3 mm. It reduces with age and reduces to < 0.5 mm or less in people older than 60 years due to a reduction in size of the disc.
The AC joint has a thin capsule stabilized by ligaments and by attachment of the fibers of the deltoid and trapezius muscles. The horizontal, anteroposterior stability is provided by the acromioclavicular ligaments.
Vertical stability is provided by Coracoclavicular ligaments (conoid and trapezoid) ligaments, positioned medial to acromioclavicular joint, which pass from the inferior surface of the clavicle to the base of the coracoid process of the scapula. The Coracoclavicular ligaments are the prime suspensory ligaments of the upper extremity.
The deltoid and trapezius muscles are especially important in providing dynamic stabilization when these ligamentous structures are damaged.
The coracoacromial ligament is between the coracoid process to the inferior surface of the acromial process in a nearly horizontal direction and could be harvested for reconstruction of the torn coracoclavicular ligament.
[Read detailed anatomy of shoulder joint]
Superior Shoulder Suspensory Complex
The superior shoulder suspensory complex is a bony and soft-tissue ring composed of the glenoid process, the coracoid process, the coracoclavicular ligament, the distal clavicle, the acromioclavicular joint, and the acromial process.
Type III, IV, V, and VI acromioclavicular injuries [see below for classification] are double disruptions of the Superior Shoulder Suspensory Complex characterized by disruptions of both the coracoclavicular and acromioclavicular ligaments.
Mechanism of Injury to Acromioclavicular Joint
The most common mechanism of injury is a fall directly onto the shoulder. A direct force applied to the superior aspect of the acromion, usually from a fall with the arm in an adducted position drives the acromion inferiorly. The acromioclavicular joint is stabilized by a combination of muscular and ligamentous forces. As the joint is transversely oriented downward forces may cause disruption of these stabilizing structures. The clavicle rests against the first rib, and the rib blocking further displacement of the clavicle. If the result is not a clavicle fracture, then acromioclavicular and coracoclavicular ligaments are ruptured.
Mostly these injuries occur in sports but are also common in motor vehicle accidents. This same mechanism of injury can result in sternoclavicular dislocations, fractures of the clavicle or acromion.
Acromioclavicular ligament and coracoclavicular ligament are the primary static stabilizers of the acromioclavicular joint. The anterior and posterior acromioclavicular ligaments are responsible for maintaining stability in the anteroposterior plane. The trapezoid and conoid ligaments are parts of coracoclavicular ligaments that restrain compression and superior-inferior translation, respectively. The deltoid and trapezius muscles provide dynamic stabilization.
Acromioclavicular joint injuries are seen especially in competitive athletes, such as rugby or hockey players, and occur most frequently in the second decade of life. Males are more commonly affected than females.
Less commonly, an indirect force may be transmitted up the arm as a result of a fall on an outstretched hand.
Classification of Acromioclavicular Injuries [Rockwood]
The degree of damage to the acromioclavicular ligaments and coracoclavicular ligament with resultant displacement of the clavicle relative to the acromion is the primary criterion for the classification of AC separations.
Type I
Neither acromioclavicular nor coracoclavicular ligaments are disrupted. The radiographs of the acromioclavicular joint are normal, except for mild soft tissue swelling, as compared with the uninjured shoulder. There is no widening, no separation, and no deformity.
The clavicle is not elevated with respect to the acromion
Structures involved
- Acromioclavicular ligament: mild sprain
- Coracoclavicular ligament: intact
- Joint capsule: intact
- Deltoid muscle: intact
- Trapezius muscle: intact
Type II
The acromioclavicular ligament is disrupted, and the coracoclavicular ligament is intact. The lateral end of the clavicle may be slightly elevated. The AC joint, when compared with the normal side, may appear to be widened. The widening probably is the result of a slight medial rotation of the scapula and slight posterior displacement of the clavicle by the pull of the trapezius muscle.
The coracoclavicular space of the injured shoulder is the same as that of the normal shoulder.
The clavicle is elevated but not above the superior border of the acromion
Structures involved
- Acromioclavicular ligament: ruptured
- CC ligament: sprain
- joint capsule: ruptured
- deltoid muscle: minimally detached
- trapezius muscle: minimally detached
Type III
Both ligaments are disrupted. The distal clavicle appears to be displaced superiorly as the scapula and shoulder complex droop inferomedialy. The deltoid and trapezius muscles are detached from the distal clavicle.
Clavicle elevated above the superior border of the acromion but coracoclavicular distance is less than twice normal (i.e. <25mm)
Structures involved
- Acromioclavicular ligament: ruptured
- coracoclavicular ligament: ruptured
- joint capsule: ruptured
- deltoid muscle: detached
- trapezius muscle: detached
Type IV
Ligaments are disrupted, and distal end of the clavicle is displaced posteriorly into or through trapezius muscle. The clavicle is posteriorly displaced into or through the trapezius muscle as the force applied to the acromion drives the scapula anteriorly and inferiorly.
This is a very rare injury.
Clavicle displaced posteriorly into trapezius.
Structures involved
- Acromioclavicular ligament: ruptured
- coracoclavicular ligament: ruptured
- Joint capsule: ruptured
- Deltoid muscle: detached
- Trapezius muscle: detached
Type V
Ligaments and muscle attachments are disrupted, and clavicle and acromion are widely separated. The distal clavicle has been stripped of all its soft tissue attachments (i.e., AC ligaments, coracoclavicular ligament, and the deltotrapezius muscle attachments) and lies subcutaneously near the base of the neck.CC
Clavicle is markedly elevated and coracoclavicular distance is more than double normal (i.e. >25 mm)
Structures involved
- Acromioclavicular ligament: ruptured
- coracoclavicular ligament: ruptured
- joint capsule: ruptured
- deltoid muscle: detached
- trapezius muscle: detached
Type VI
Ligaments are disrupted, and distal clavicle is dislocated inferior to coracoid process and posterior to biceps and coracobrachialis tendons.
Clavicle inferiorly displaced behind coracobrachialis and biceps tendons, which is rare
Structures involved
- Acromioclavicular ligament: ruptured
- coracoclavicular ligament: ruptured
- joint capsule: ruptured
- deltoid muscle: detached
- trapezius muscle: detached
Presentation
In the acute presentation, there is a history of fall on the apex of the shoulder or on an outstretched hand. The patient complains of pain over the superior part of the shoulder.
There would be shoulder swelling and generalized tenderness of the shoulder, especially over acromioclavicular joint. Bruises may be noted. Simultaneous examination of the contralateral shoulder may help.
A prominence of the distal clavicle may be noted.
In a delayed presentation, the patient may complain of pain with specific exercises/activities such as with the use of the bench press and dips.
Pain in the night especially when rolling onto the involved shoulder may lead to awakening, which puts pressure on the acromioclavicular joint. Rarely, the patient may report popping or catching in the region of the acromioclavicular joint.
In types I and II sprains, the deformity is usually minimal.
In type III injuries, the distal clavicle is abnormally prominent.
The patient has a limited range of motion and attempting the motion is painful.
Cross Body Abduction Test
This test assesses the stability of the affected shoulder. The patient elevates the arm on the affected side 90°, while the examiner grasps the elbow and adducts the involved arm across the body.
Although reproduction of pain with this maneuver may occur in patients with posterior capsule tightness or subacromial impingement, pain is suggestive of acromioclavicular joint pathology. The test should not be done in acute conditions
The shoulder should be examined in detail to rule out concomitant injuries.
A distal neurovascular examination must be carried out.
If there is a doubt, the findings may be clearer when the patient is asked to hold a 10- to 15-pound weight in the hand of the affected arm.
Differential Diagnoses
- Clavicle Fractures
- Rotator Cuff Injury
- Shoulder Dislocation
- Shoulder Impingement Syndrome
- Superior Labrum Lesions
Imaging
X-rays
Imaging helps to confirm the diagnosis and differentiate acromioclavicular injuries from other shoulder injuries, clavicle injuries or scapula injuries.
A minimum of two radiographic views (eg, anteroposterior, lateral, axillary views of the shoulder are done. Lateral views of the scapula are desirable.
A radiograph of the entire upper thorax showing bilateral acromioclavicular joint is useful to compare the vertical distance between the clavicle and the coracoid process on both sides.
Following features suggest acromioclavicular injury
- Soft tissue swelling/stranding
- maybe the only finding in grade I injuries
- Widening of the AC joint
- normal: 5-8 mm (narrower in the elderly)
- > 2 mm asymmetry than the contralateral side)
- Increased coracoclavicular distance
- normal: 10-13 mm
- > 5 mm asymmetry than the contralateral side
- Superior displacement of the distal clavicle [normally undersurface of the acromion is at level with the under the surface of the clavicle]
The severity of injury on radiographs is assessed as below:
- Type I: Normal
- Type II – Subluxation of acromioclavicular joint space < 1 cm, normal coracoclavicular space
- Type III – Subluxation of the acromioclavicular joint space > 1 cm, widening of the coracoclavicular space > 50%
- Types IV-VI: Findings in type III and associated displacement of the clavicle
With complete acromioclavicular/coracoclavicular ligament rupture, cross-body adduction films will show the scapula rotated anteromedially, and the acromion will migrate medially.
Stress views
These views are done if
- X-rays are normal but suspicion of injury is there
- For making the decision for surgery in a grade III injury
- In a follow-up to assess the stability of joint
Stress views are taken after attaching 5-7 kg weights to the wrist of the affected side, and an AP view can be taken. This stress tests the integrity of the coracoclavicular ligament.
If the joint is normal, then acromioclavicular alignment should stay normal and symmetric.
Magnetic Resonance Imaging
Magnetic resonance imaging is not generally required in the routine management of these injuries.
It is important in differentiating between type II and type III injuries, to check for a possible rotator cuff tear and very rarely to determine if the cartilaginous disk has been damaged.
Treatment of Acromioclavicular Injuries
Approach to Treatment
Depending on severity, acromioclavicular injuries can be treated conservatively or operatively.
As a general rule, type I and II are managed with conservative treatment and type IV, V, VI require surgery.
Treatment of type III injury is controversial and can be managed both surgically and conservatively.
The occupation of the patient affects the choice of treatment. Surgical treatment can be considered for persons who have a high level of activity of upper limbs such as soldiers, athletes or heavy laborers.
Open fractures, neurovascular injury, and those with compromised skin should be treated surgically.
Acromioclavicular injuries requiring open reduction and internal fixation should be repaired within 2 weeks of the time of injury.
Standard surgical treatment is a reconstruction of the torn coracoclavicular ligaments with either local tissue or an allograft.
For repair of type III-VI injuries open reduction and stabilization of the dislocation with repair of the usually torn deltotrapezial fascia and debridement of the acromioclavicular articulation has also been described.
Fixation is done with K-wires or screws
For patients where late arthritic changes have developed and conservative treatment has failed clavicle excision is considered.
The presence of infection is a contraindication to repair.
Type I
Type I injuries are intrinsically stable and are treated by sling application, activity modification, ice, and analgesic agents.
Patients get better in 1-2 weeks.
Patients who have pain beyond this period may require steroid injections. Patients who have prolonged pain may need excision of the distal clavicle.
Type II
The acromioclavicular ligament is completely torn. Treatment is similar to type I injuries followed by a rehabilitation.
Type II injuries take longer to improve than those with type I injuries.
Strap immobilization for 2-4 weeks and avoiding heavy activity for 6-12 weeks are appropriate.
Patients who have pain beyond this period may require steroid injections. Patients who have prolonged pain may need excision of the distal clavicle.
Type III
Type III acromioclavicular injuries have a complete rupture of both the coracoclavicular and acromioclavicular ligaments. Nonoperative management similar to that for a type II injury.
If the trial of conservative treatment fails, surgical treatment must be considered. Some authors advocate recommending surgical treatment in people with active occupations like baseball pitchers, manual laborers, and soldiers. Surgery in these people offers greater benefits.
Standard procedure for these patients is a reconstruction of the torn coracoclavicular ligaments with either local tissue or an allograft.
Type IV-VI Injuries
Surgical repair is the norm.
Open reduction and internal fixation is required along with repair of the deltopectoral fascia.
Patients undergoing reconstructive procedures remain in a sling for 2 weeks followed by the range of motion exercises. The patient’s affected arm remains in the sling between sessions. At 6 weeks, healing is sufficient to allow patients to discontinue protection and to encourage progressive functional use.
Physiotherapy continues until the patient’s range of motion and strength are maximized. Heavy physical use of the shoulder is prohibited for an additional 6 weeks. Patients undergoing a distal clavicle resection are simply protected in a sling for 2 weeks to allow soft-tissue healing to occur.
If a coracoclavicular screw or a trans-acromioclavicular joint pin is used for stabilization, the device is removed 6 weeks postoperatively.
Prognosis and Complications
Grade I and II injuries may cause persistent pain and late radiographic changes through more than half of the patients have good to excellent functions after 5 years. Some individuals may give up sports and decreased performance[ about 105 in grade I and 30% in grade II]
was up to 9% for grade I injury and up to 42% for grade II injury.
In others, acromioclavicular joint resection may be needed.
In severe injuries, the patients may develop impingement symptoms secondary to the drop down of the shoulder and the abnormal biomechanics. Patients might also report muscle-fatigue discomfort.
These may require a surgical reconstruction.
Other complications from acromioclavicular joint injuries may include the following:
- Cosmetic deformity
- Accelerated degeneration of the joint
- Decreased shoulder range of motion/upper extremity strength
- Distal clavicle osteolysis
Whiplash injury to the shoulder
These are patients with a history of shoulder trauma involving the shoulder wearing the seatbelt at the time of the accident. The injury occurs due to whiplash movement of the shoulder on clavicle which is restrained by a seatbelt.
Soft tissue injuries of the neck may be associated. The injuries to the shoulder may involve acromioclavicular joint injuries type 1 and 2.
Pediatric Acromioclavicular Joint Injuries
Acromioclavicular joint injuries in children are rare. The anatomy in children is different than adults. The immature clavicle is encased in a periosteal tube. The coracoclavicular ligament is within this tissue, whereas the acromioclavicular ligament is exterior to it.
Therefore, the acromioclavicular ligament is frequently injured but the coracoclavicular ligament is not.
The pediatric Rockwood classification of acromioclavicular injuries is as follows :
Type I
- Stable clavicle
- Radiographically normal joint
Type II
Partial tear of the periosteal tube
some mobility of the distal clavicle
disrupted acromioclavicular ligament
Types III-VI
- Larger tear through the periosteal tube
- Greater clavicle mobility and gross instability with clavicle positioning
- the coracoclavicular ligament remains attached to the clavicle periosteal tube
For type I-III injuries in pediatric patients, closed reduction can be effective, although surgical intervention for selected cases may be indicated to achieve better functional results. Other injuries require surgery.
References
- Shaffer BS. Painful conditions of the acromioclavicular joint. J Am Acad Orthop Surg. 1999 May-Jun. 7(3):176-88.
- Goss TP. Double disruptions of the superior shoulder suspensory complex. J Orthop Trauma. 1993. 7(2):99-106.
- Macdonald PB, Lapointe P. Acromioclavicular and sternoclavicular joint injuries. Orthop Clin North Am. 2008 Oct. 39(4):535-45, viii.
- Allman FL Jr. Fractures and ligamentous injuries of the clavicle and its articulation. J Bone Joint Surg Am. 1967 Jun. 49(4):774-84.
- Nemec U, Oberleitner G, Nemec SF, Gruber M, Weber M, Czerny C, et al. MRI versus radiography of acromioclavicular joint dislocation. AJR Am J Roentgenol. 2011 Oct. 197(4):968-73
- Press J, Zuckerman JD, Gallagher M, Cuomo F. Treatment of grade III acromioclavicular separations. Operative versus nonoperative management. Bull Hosp Jt Dis. 1997. 56(2):77-83.
- Rolf O, Hann von Weyhern A, Ewers A, Boehm TD, Gohlke F. Acromioclavicular dislocation Rockwood III-V: results of early versus delayed surgical treatment. Arch Orthop Trauma Surg. 2008 Oct. 128(10):1153-7.
- Phillips AM, Smart C, Groom AF. Acromioclavicular dislocation. Conservative or surgical therapy. Clin Orthop Relat Res. 1998 Aug. 10-7..
- Lizaur A, Sanz-Reig J, Gonzalez-Parreño S. Long-term results of the surgical treatment of type III acromioclavicular dislocations: an update of a previous report. J Bone Joint Surg Br. 2011 Aug. 93(8):1088-92.
Leave a Reply