Components
Direction of stability
Acromioclavicular ligament
(Superior, inferior, anterior, and posterior components). Superior ligament is strongest, followed by posterior
Horizontal stability
Coracoclavicular ligaments
Trapezoid and conoid ligaments
Vertical stability
Trapezoid ligament inserts <2 cm from lateral end of clavicle
Horizontal and vertical stability
Conoid ligament inserts 3.2 cm from the lateral end of clavicle at the posterior border
Vertical stability
Others
Deltotrapezial fascia, capsule
Horizontal and vertical stability
Static stabilisers of the acromioclaviclar joint (courtesy of Lennard Funk, http://www.shoulderdoc.co.uk)
The CC ligament complex is made up of the conoid and trapezoid ligaments. These are extremely strong, with a tensile strength of over 800 N. The anatomical landmarks and isometric points of the CC ligaments on the undersurface of the clavicle have been well described [9–11]. The trapezoid is at a mean of 14.7 mm and the conoid is a mean of 32.1 mm from the distal end of the clavicle. The origin of the CC ligaments varies between genders while keeping the same ratio of the origin to clavicular length [11].
Biomechanical studies have demonstrated that the ACJ capsule and ligaments act as a primary constraint for posterior displacement and posterior axial rotation of the clavicle [4]. Additional studies have confirmed that the ACJ ligaments and capsule provide the majority of anterior-posterior (Horizontal) stability whereas the CC ligaments provide a large percentage of superior-inferior (vertical) stability [5]. The trapezoid ligament is the primary restraint to axial loading of the ACJ. The ACJ ligaments are responsible of 90% the resistance to posterior loading forces, but also provide some vertical and rotational stability. An injury to any one structure does not specifically predict the type or direction of instability. Injuries of the static restraints does not occur in isolation, so single directional instability is unlikely. This highlights the complex three dimensional stability and importance of anatomic reconstruction of both the ACJ and CC ligaments. Fukuda et al. [4] affirmed that “if maximum strength of healing after an injury to the AC joint is the goal, all ligaments should be allowed to participate in the healing process.”
The ACJ acts as a pivot between the clavicle and the scapula, which allows a complex motion pattern that is not fully understood. The clavicle rotates 40–50° posteriorly with shoulder elevation with 8° of rotation through AC joint. The remainder is from scapula rotation and sternoclavicular motion. There is 5–8° of rotation, in line with the scapula, observed in the ACJ with forward elevation and abduction to 180° [3, 12–14]. Therefore, disruption of the ACJ is recognized as a scapula disorder [15].
Codman described the motion of the ACJ nicely as: “I have come to the conclusion, that the acromioclavicular joint moves very little indeed, but this motion may occur in many different planes. Its surfaces slide a little, rotate a little, tip apart a little and act like hinges to some degree” [16]. He highlighted the importance of having an intact ACJ for scapula motion to be synchronously coupled with arm motion by the clavicle; the CC ligaments guide this coupled motion. Subsequently, the ACJ should not be fixed, either by fusion (screws, plates, pins) or by CC screws. If these implants are used, motion will be lost, limiting shoulder function, or the hardware may eventually fail because of the obligatory coupling of clavicle rotation with scapula motion and arm elevation. This correlates with Gumina et al. [15], who found that longstanding type III ACJ injuries led to scapula dyskinesis in 71% of patients. Fifty-eighty percent had SICK scapula syndrome (Scapula malposition, Inferior medial border prominence, Coracoid pain and malposition, and dyskinesis of scapula movement). The authors proposed that dyskinesis is due to loss of function of the ACJ which is no longer a stable fulcrum of the shoulder girdle.
8.3 Mechanism of Injury
Commonest mechanism of acromioclavicular joint dislocation, with a fall onto the point of the shoulder. The scapula is forced inferior and anterior, relatively displacing the clavicle postern-superiorly (courtesy of Lennard Funk, http://www.shoulderdoc.co.uk)
8.4 Classification of ACJ Injuries
In 1917, Cadenat [18] originally described the mechanisms of ACJ dislocation and the classical features of its presentation. He explained a sequential injury beginning with the AC ligaments disruption, progressing to the CC ligaments failure, and finally involving the deltoid and trapezial muscles and fascia. This formed the basis for future classifications.
Rockwood classification of acromioclavicular joint injuries
Rockwood classification of ACJ injuries into six grades | |
|---|---|
I | AC joint sprain |
II | Subluxated ACJ with intact CC ligaments |
III | Dislocated ACJ with disrupted CC ligaments |
IV | Superiorly and posteriorly dislocated ACJ |
V | Dislocated ACJ with 100–300% separation |
VI | ACJ dislocated and Inferiorly displaced under the coracoid |
Rockwood classification of acromioclavicular joint injuries (courtesy of Lennard Funk, http://www.shoulderdoc.co.uk)
Most physicians use radiographs to classify ACJ dislocations, but this has been proven to be an unreliable method for determining the pathological classification [21]. Visual assessment of radiographs is not reliable although bilateral panoramic digital comparative measurements are more accurate in determining the degree of vertical displacement [22]. Even with the addition of 3D CT scanning, the inter- and intra-observer reliability of the classification systems are poor [23]. The addition of MRI scans to the clinical and radiographic findings, may improve the accuracy [24].
In 2014 a consensus document was published by the ISAKOS Upper Limb Committee to diversify the Rockwood classification [25]. The group recognized the primary problem was a scapula disorder and focused on ACJ instability. They recognized that there was a lack of information to adequately identify the factors that made a patient more suitable for surgical intervention. Based on their combined experience and expertise, they subdivided the contentious Type III injuries into Type IIIA and Type IIIB, with IIIA being functional stabley and IIIB functional unstable, when reviewed 3–6 weeks post-injury. The ‘stability’ was based on a number of clinical factors, comprising: ongoing pain (usually on the anterior acromion, rotator cuff, and medial scapular area), weakness during rotator cuff testing, decreased flexion and abduction range of motion, and demonstrable scapular dyskinesis on observation. Special radiographic views (i.e. cross-body stress view) may provide some objective information.
8.5 Clinical Examination
Dropped right scapula and arm, with a complete acromioclavicular joint dislocation. Note that the clavicles remain in the same horizontal plane
Limited elevation of left shoulder due to scapula ‘locked’ under clavicle, thus limiting scapula and glenohumeral elevation
Other disruptions are less obvious and don’t fit the standard classifications (Grade II–II). They can clinically be diagnosed by asking the patient to adduct their arm across their chest. This manoeuvre accentuates the injury, displacing the clavicle superiorly and posteriorly. Standard radiographs may be normal, but the deformity can be demonstrated on adduction radiographs.
The lateral clavicle should also be assessed for both vertical and horizontal laxity and compared to the opposite (normal) side. This is done by direct manual palpation. Often excess laxity after injury is indicative of a significant Grade II injury and suggests instability without a true dislocation.
ACJ injury is identified by a triad of point tenderness, ACJ pain with cross-arm adduction, and pain relief by local injection of an anesthetic agent [17]. Walton et al. [26] described using the Paxinos test (thumb pressure at the posterior ACJ).
8.6 Radiographic Evaluation
Comparative Zanca views showing the subluxation of the left acromioclavicular joint
8.7 Treatment
Traditional teaching for ACJ injury treatment has been to surgically repair type IV and V dislocations acutely, whilst managing type I and II non-operatively. Type III has been contentious. However, as we have seen above, classifying the injuries can be difficult with poor agreement. Recent evidence supports initial primary nonoperative treatment of complete ACJ dislocations. A review of 1172 patients reported successful outcomes in 88% of patients treated non operatively [31]. There was no difference when compared with an equivalent group managed operatively.
The ISAKOS Upper Limb Committee consensus approach to type III injuries is to reassess clinically at 3–6 weeks post-injury, which is a sensible approach since many patients will have improved by that time. The decision for surgery in the ISAKOS consensus article is then based on ‘overriding of the distal clavicle’ on cross body adduction radiographs. Unfortunately, there is no good evidence for this and the group admit that studies will be needed to support this consensus approach.
We therefore do not use the grade of ACJ injury as the primary determinant for defining treating options, given the poor inter/intra-observer reliability of the injury grades and no good correlation with clinical symptoms [21]. M any patients do well without surgery [25]. Surgical reconstruction should be reserved for those patients with high functional demands, symptomatic locked, or unstable (shocked) scapula, and failure to improve in the first 3–6 weeks. The patient’s symptoms and early response to non-operative symptomatic management primarily defines the indication to offer surgery.
8.8 Treatment Protocol
Acute injury (<1 week):
Assess and diagnose.
Sling for comfort only, analgesia and rehabilitation with early active mobilization as comfortable
Surgery indicated if: Clearly in agony with clavicle button-holed through trapezius; Overhead athlete; Neurovascular injury; Open injury
3 week review:
Settling and improving—continue symptomatic management and gradually return to sports and manual activities. Arrange review at 3 months.
Not coping—offer early surgical reconstruction
3 month review:
Returned to sports and little symptoms—discharge
Not coping—offer surgical stabilization
8.9 Treatment
8.9.1 Nonoperative Treatment
Non-operative treatment of acute injuries includes simple analgesia, topical ice therapy and rest in a sling for comfort. The use of a supportive broad arm sling is preferable to a collar and cuff because it supports the elbow and supports the weight of the shoulder. It is recommended that the sling be discarded once the symptoms settle, usually within one week. Physiotherapy focuses on dynamic scapula stabilization and activity-specific rehabilitation. Contact sports and heavy lifting can be started as comfortable, usually about 6–12 weeks post-injury. Local discomfort may be felt with activity for up to 6 months. The literature reports that, at 1 year, there is a 17% chance of reduced bench press strength, although 80% of those patients do not find that a problem.
The results of non-operative treatment of grade III injuries has been variable in the literature. Tibone et al. found no significant difference in strength in patients with type III injuries, when treated nonoperatively versus operatively, at 2 years follow-up [32]. However, Schlegel demonstratedi a 20% chance of suboptimal outcome with nonoperative treatment [33]. Types I and II injuries also have a 25% chance of requiring surgery by 2 years post-operatively [34].
However, in athletes, Cox [35] showed that a large proportion of ACJ injuries remained symptomatic at 6 months post-injury (36% of Grade I, 48% of Grade II and 69% of Grade III injuries). Also, 30% of overhead athletes are unable to continue at the same level of sport, and 9% had to change sport. Patients performing strength training, in particular climbers, and had to reduce their activities [36]. In contact athletes, many are able to return to sport but struggle with many of the strength and overhead training exercises required to keep them at high level sport.
