Shoulder:Disorders of the Acromioclavicular Joint

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Bullet Points:

  • Osteology: The acromioclavicular joint is a diarthrodial joint fibrocartilaginous. The intraarticular disc is located between the osseous segments.
  • Stability: The acromioclavicular ligament (superior, inferior, anterior, and posterior components) provides horizontal stability. The superior ligament is the strongest, followed by posterior. The coracoclavicular ligaments (trapezoid and conoid) provide vertical stability. The trapezoid inserts 2.5 cm from end of clavicle. It is a stabilizer against horizontal and vertical loads. The conoid inserts 4.6 cm from end of clavicle in the posterior border more important ligament vertical stabilizer of acromioclavicular joint. The normal coracoclavicular distance (superior coracoid to inferior clavicle) is 11-13 mm. The deltotrapezial fascia, capsule, deltoid and trapezius act as additional stabilizers
  • Arthritis: The rate of asymptomatic acromioclavicular joint arthritis is high (65%) found the age of 40.
  • Distal clavicular osteolysis: this condition is classically seen in body builders.
  • Acromioclavicular joint dislocation: Surgery might be considered only in high grade (4-5).

Key words

Acromioclavicular joint; Anatomy; Biomechanics; Arthritis; Distal clavicular osteolysis; Instability; Dislocation; Separation; Imaging; SAPHO syndrome; Distal clavicular osteolysis; Gorham-Stout disease; Conservative; Nonoperative Treatment; Stabilization; Reconstruction: Coracoclavicular cerclage; Mazzocca; Acute; Chronic; Complication.

Anatomical Considerations

  1. REDIRECT [[1]]

The acromioclavicular joint that anchors the clavicle to the scapula. It is a diarthrodial joint that primarily rotates as well as translates in the anterior-posterior and the superior-inferior planes. The joint is surrounded by a capsule with synovium and an articular surface that is made up of hyaline cartilage containing an intra-articular meniscus-type structure. The mean width of the articular surface is 24.3+/-3 mm (range, 17-30 mm) for the acromial side and 24.6+/-3 mm (range, 17-30 mm) for the clavicular side.[1] The mean anterior overhang of the acromion (anterior acromion-anterior joint distance) is 2.6+/-2.6 mm (range, 0-10 mm), whereas the mean anterior oversize of the clavicle (anterior clavicle-anterior joint distance) is 2.2+/-1.9 mm (range, 0-5 mm) (Figure). Only 60% of the acromioclavicular joints are aligned anteriorly, 3% have minor overhang of the acromion, 3% have minor overhang of the clavicle, 24% have major overhang of the acromion, and 10% have major overhang of the clavicle (Figure). Therefore, major misalignment anteriorly is found in 34% of the cases. The only reliable landmarks are the articular facets of both the acromion and the clavicle.[1] The center of the conoid ligament inserts under the posterior part of the clavicle 46 mm medially to the acromioclavicular joint. The center of the trapezoid ligament has an anterior insertion under the clavicle, 25 mm medially to the acromioclavicular joint.[2][3][4][5] The normal coracoclavicular distance (superior coracoid to inferior clavicle) is 11-13 mm. The acromioclavicular joint has dual innervation from both the suprascapular nerve and the lateral pectoral nerve.

Photograph (a) and drawing (b) showing measurement methods. The anterior (A) and posterior (P) borders of the capsule are marked and connected with a straight line (AP line). Two parallel lines perpendicular to the AP line are created that passed through points A and P. Two anterior parallel lines perpendicular to the AP line are drawn: one passing at the most anterior edge of the acromion (acromion anteriorly [ACA]) and the other passing at the most anterior edge of the clavicle (clavicle anteriorly [CLA]). The same procedure is followed for the posterior part of the joint, and the lines passing from the acromion posteriorly (ACP) and clavicle posteriorly (CLP) were drawn. Reproduced with permission from Barth et al.[1]

Biomechanics of the Acromioclavicular Joint

  1. REDIRECT [[2]]

The acromioclavicular joint is stabilized both by static and dynamic stabilizers. The static stabilizers include 1) the four acromioclavicular ligaments (superior, inferior, anterior, and posterior), 2) the lateral coracoclavicular ligaments (conoid and trapezoid), 3) the medial coracoclavicular ligaments (Figure and Video) and 4) the coracoacromial ligament.[6][7] The latter, when transferred during standard Weaver-Dunn repair is only 1/4 as strong as the intact coracoclavicular ligaments; such technique of stabilization does not provide sufficient strength and is considered by many as obsolete.[8][9][10]

Medial coracoclavicular ligament (asterisk) in a right shoulder region. View from in front. C clavicle, CP coracoid process (horizontal portion), DM deltoid muscle (resected), PM pectoralis minor, SM subclavius muscle. Reprinted from Stimec et al.,[6] with permission.


The capsular ligaments acted as a primary restraint to posterior displacement of the clavicle (Video).[11]

The superior ligament is the strongest, followed by posterior. Both ligaments provide the most restraint to posterior translation of the acromioclavicular joint and must be preserved during a Mumford procedure. The coracoclavicular ligaments (trapezoid and conoid) provides vertical stability. The dynamic stabilizers include the deltoid and trapezius muscles.[12]

The coracoclavicular ligaments’ main contribution is to vertical stability. However, its double bundle configuration contributes also partially to horizontal stability due to their relative orientation.[13][14]

After lesion of the acromioclavicular ligaments, the conoid ligament acts as the primary restraint against anterior and superior loading, while the trapezoid functioned as the primary restraint against posterior loading.[15] When a load is applied in a superior direction, the conoid ligament fails first in its midsubstance region.[16] [17]

During elevation of the arm, the clavicle with respect to the thorax generally undergoes elevation (11 to 15 degrees), retraction (15 to 29 degrees), and posterior long-axis rotation (15 to 31 degrees). Motion of the scapula (protraction-retraction) plays a major role in the motion at the acromioclavicular joint.[18]

Radiological or Radiographic Evaluation of the Acromioclavicular Joint


Proper radiographic evaluation of the acromioclavicular joint requires multiple views. Zanca view is performed by tilting the x-ray beam 10 to 15 degrees toward the cephalic direction. This view allows to analyze the acromioclavicular joint as well as the coracoclavicular interspace.[19] The average distance between the clavicle and coracoid process is usually between 1.1 to 1.3 cm.[20] An increase in the coracoclavicular distance of 25% to 50% over the normal side indicated complete coracoclavicular ligament disruption.[21] The axial view of the shoulder was thought to be important in differentiating a type III from a type IV acromioclavicular joint injury. However, physiological misalignment between the anterior or posterior borders of the acromion and the clavicle exits.[22] This finding explains probably why the axial view is not reliable and should not isolated be taken into account when planning a surgery.[23][24] Alexander view demonstrate acromioclavicular instability (Figures). Recent data has shown that the CC distance systematically underestimated the degree of AC joint displacement when compared with the new published acromial center line to dorsal clavicle (=AC-DC) measurement as the severity of injury increased, particularly in the presence of posterior horizontal displacement such as that seen in Rockwood IV injuries. From this point of view, a classic Zanca view may may therefore mask an underlying element of posterior horizontal displacement, which is always the first displacement direction in a rupture of the four acromioclavicular ligaments.[25]

Right normal Alexander views
Left pathologic Alexander views


Acromioclavicular joint pathology is relatively easy to analyze using ultrasound imaging. Pathological signs can be detected (osteophytes, erosions, effusion and geyser phenomenon, being a large synovial cyst extending into the supraclavicular fossa) (Figure) and joint tenderness evaluated by applying pressure on the probe whilst above the joint line. Dynamic analysis (the patient’s arm being brought from neutral position to a “cross arm” position) can reveal joint subluxation. This tool is also useful to guide intra-articular cortisone injection.[26]

Acromioclavicular joint and visualization of “bulging” of the acromioclavicular ligament signifying presence of an effusion. Ultrasound image (a) with superimposed anatomy (b) and patient/probe position (c). Reproduce from Plomb-Holmes et al.,[26] with permission.

Magnetic Resonance Imaging

Magnetic resonance imaging allows excellent anatomical display of acromioclavicular joint structures and can give clinically relevant information on the type and extension of acromioclavicular joint trauma and associated pathologies, which may influence treatment.[27] However, it is not feasible to use on a routine basis because of its costs and limited local availability. Magnetic resonance imaging is not helpful in making the diagnosis of symptomatic acromioclavicular joint arthritis. A focused history and clinical examination remain the mainstay for surgical decision making.[28]



The hyaline articular cartilage becomes fibrocartilage on the acromial side of the joint by the age of 17 and on the clavicular side by the age of 24. The meniscus undergoes afterwards rapid degeneration and is no longer functional beyond the 4th decade.[29] This could explain the high rate of asymptomatic acromioclavicular joint arthritis (65%) found after the age of 40 (Figure). Consequently, acromioclavicular joint width varies between 1 and 3 mm in the young adult and 0.5 mm in 60-year-old patients.[30] The condition can be associated to an arthrosynovial cyst (Figures, Video).

Clinical aspect of an exuberant left acromioclavicular arthritis.
Massive arthrosynovial cyst in a 53 years old patient with acromioclavicular arthritis.
T2 fat saturation coronal plane magnetic resonance imaging of a 81 years old woman. Observe the massive subcutaneous arthrosynovial cyst.

SAPHO syndrome

Synovitis-acne-pustulosis-hyperostosis-osteitis (SAPHO) is an acronym for various osteoarticular and dermatological manifestations that can appear in the same patient. It is a rare autoimmune disease of unknown cause, which due to its clinical presentation and symptoms is often misdiagnosed and unrecognized.[31] It is estimated that about 50-70% of patients who might have SAPHO, also suffer from shoulder girdle pain including acromioclavicular joint. These characteristics are related to an underlying chronic inflammatory sterile osteitis resulting in swelling, tenderness and pain of bone structures and adjacent tissues.[32] Therapy is empirical and aimed at easing pain and modifying the inflammatory process. It includes nonsteroidal anti-inflammatory drugs as the first-line agents. Antibiotics, corticosteroids, disease-modifying anti-rheumatic drugs, biologicals targeting tumor necrosis factor alpha or interleukin-1, and bisphosphonates have all been used with variable success. Surgery is reserved to treat complications.[33]

Distal Clavicular Osteolysis

Dupas et al. first describe in 1936 osteolysis in the distal clavicle as a result of trauma. Even if a trauma is not necessary, this condition is mainly found in weight trainers,[34] judo player, handball player (Figure).[35][36]

Acromioclavicular joint injection. The needle is inserted at the mid-line of the lateral edge and parallel to the probe, allowing it to be visualized entering the acromioclavicular joint. US image (a) with superimposed anatomy (b). From Plomb-Holmes et al.,[26] with permission.

Operative Treatment of Arthritis, SAPHO and Distal Clavicle Osteolysis

A patient whose condition does not respond to conservative management or who is unwilling to alter his or her exercise training and performance regimen requires surgery.


Open distal clavicle resection was reported separately in 1941 by Mumford[41] and Gurd.[42]

Arthroscopic Distal Clavicle Excision


This procedure is only indicated if there is acromioclavicular pain (most of acromioclavicular arthritis are not painful). Joint instability is a contraindication.

Operative technique

Perform a subacromial bursectomy along with excision of the medial fibrofatty tissue around the distal clavicle and the scapular spine. The acromioclavicular joint is then exposed using instrumentation through an anterior working portal. First remove using a power burr through an anterior portal 2-3 mm of the acromion (bipolar disease necessitate bipolar resection).[43]

This will improve visualization of the distal clavicle, and then resect 7 mm of the clavicle. It is important to preserve at least one of the acromioclavicular ligaments, if possible the superior that contributes for 56% (versus 25% for the posterior) of the resistance to posterior displacement of the clavicle. The end-point is to create a 1 cm space. The use of a 70 degrees scope through the posterior or the anterolateral portal allows a better view of the superior part of the joint.

Coplaning of Distal Clavicle


Coplaning of distal clavicle is indication when the acromioclavicular joint is not painful but associated to a prominent inferior osteophyte that make an impression on the musculotendinous junction of the supraspinatus. The latter osteophyte might be responsible for musculotendinous junction lesion.[44] It is important to limit the removal of inferior clavicle osteophytes, to avoid partial resection of the distal clavicle that could destabilize the joint and generate more pain.[45]

Operative Technique

If an acromioplasty is indicated, begin by acromioplasty first. All soft tissue from the undersurface of the distal clavicle must be cleaned while viewing through a posterior or a lateral portal. Coplaning of the distal clavicle is achieved by alternately viewing through a posterior portal while using a burr through a lateral portal, then viewing through a lateral portal while using a burr through an anterolateral or an anterior portal.

Postoperative Care

Isolated distal clavicle excision or coplaning do not require any type of postoperative immobilization. Range of motion is regained actively the day after the surgery. Day life activities then begin according to the pain. Light sports such as brake stroke is authorized after two to four weeks. Strengthening is not recommended.

Acromioclavicular Joint Dislocation


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Two common mechanisms account for acromioclavicular joint injury. Direct injuries occur during falls or blow onto acromioclavicular joint with the arm in the adducted position. Indirect injury occurs as the result of a fall on an outstretched hand driving the humeral head into the acromion.

Physical Examination

Swelling, deformity and tenderness locally at the acromioclavicular joint are observed.

Figure. 10 Acromioclavicular dislocation
Left acromioclavicular joint dislocation
Superior view
Figure. 10 Acromioclavicular dislocation
Posterior view

Instability should be tested dynamically and in all planes (Video 4).

Video 4.

Reducibility of the dislocation should be tested if not too painful. These are the most reliable symptoms/signs. The cross body adduction stress is performed with the arm elevated to 90 degrees and then adducted across the chest. This produce pain specifically at the acromioclavicular joint due to compression across the joint and may reveal posterior intricateness of the clavicle in the trapezius (Video).



The radiographic classification of acromioclavicular joint injuries described by Rockwood includes six types:

Injuries the acromioclavicular ligaments are sprained, but the joint is intact.
Injuries, the acromioclavicular ligaments are torn, but the CC ligaments are intact.
Injuries both the acromioclavicular and the coracoclavicular ligaments are torn.
Injuries are characterized by complete dislocation with posterior displacement of the distal clavicle into or through the fascia of the trapezius.
Injuries are characterized by a greater degree of soft tissue damage.

Type VI

Injuries are inferior acromioclavicular joint dislocations into a

subacromial or subcoracoid position.

The Rockwood classification based on the severity of the radiological displacement on both planes (vertical and horizontal planes) is widely accepted by the shoulder trauma surgeon community for the decision making, despite the low reliability.[46][47] Cho et al. demonstrated an overall lack of reliability of the Rockwood classification of acromioclavicular joint dislocations and of decisions regarding their treatment. There is especially poor agreement between experienced shoulder surgeons. The addition of tridimensional computed tomography did not improve reliability of classification and treatment of acromioclavicular joint dislocations.[48]

The ISAKOS consensus group has recently further expanded this classification by suggesting the addition of subgroups of the type III lesions. The IIIA (stable) and IIIB (unstable) in an effort to provide effective guidance in the management of this group of injuries. The subclassification criteria are rather clinical with the unstable type IIIB lesions presenting with continuous pain, rotator cuff weakness, diminished abduction range of motion, and scapular dyskinesis. Differentiation between IIIA and IIIB on a radiographic basis is important as it may guide the doctor towards a treatment strategy. The acromial center line to dorsal clavicle (AC-DC) measurement and use of the Alexander view provides the clinician with a more realistic appreciation of true acromioclavicular joint displacement, especially in defining watershed cases (ie, IIIA/IIB/IV) and may better inform the decision-making process regarding management options and recommendations.


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Treatment option

Clinical Practice Guideline

The goal of this section is to provide clinicians with recommendations based on the best available evidence; to inform clinicians of when there is no evidence; and finally, to help clinicians deliver the best health care possible. The main goals of treatment, whether surgical or non-surgical, are to achieve a pain-free shoulder with full range of motion, normal strength, and no limitations in activities. The demands on the shoulder will differ from patient to patient, and these demands should be considered during the initial evaluation.

Conservative Treatment (Nonoperative Treatment)

All types of acromioclavicular joint dislocation can be treated non-surgically, at least at the beginning. The actual surgical recommendations are mainly based on small retrospective series or obsolete techniques. There is nowadays no formal indication for acute reconstructions. The rare exceptions are open acromioclavicular dislocation, or dislocation associated to Ideberg III to V glenoid fractures, floating shoulders,…

In case of treatment failure of neglected acromioclavicular dislocation, secondary reconstructions are still possible and give actually results as good as primary treatment. Consequently, evaluation must be done on a case-by-case basis, taking into account hand dominance, occupation, labor, sport, and the risk for reinjury (rugby, american football).

The rehabilitation program of acute acromioclavicular dislocation treated conservatively evolve by four different phase:[49][50]

  1. First, short immobilization to decrease pain and inflammation is recommended. Patients should be encouraged to cease sling use as soon as their symptoms allow. Immediate glenohumeral mobility exercises such as internal/external rotation elbow at the side and flexion/extension of the elbow are recommended to avoid potential secondary frozen shoulder. After two weeks, progressive forward elevation is encouraged. According to patient’s own pain thresholds, closed-chain exercises with the hand fixed to a wall, table, or floor starts to improve scapular control.
  2. Then, strengthening exercises using isotonic contractions are prescribed.
  3. Open-chain exercises with the goal of increasing strength, power, endurance, and neuromuscular control are progressively added. Reinforcement with diagonals exercises in which persistent deficit are observed are recommended.
  4. Finally, return to activity with sport-specific functional drills is allowed.

Surgical Treatment

A basic principle in the treatment of acute acromioclavicular joint dislocations is to restore joint congruity and mechanical stability as accurately as possible, in order to provide physiologic conditions for the development of rigid scar tissue healing. Acute acromioclavicular joint dislocation requires stabilization in both planes, i.e., at the coracoclavicular junction and at the acromioclavicular joint.[50][51][52][53] The weight of the upper limb should be taken into account, with six weeks of immobilization to unload the construct in patients who have high (> 25 kg/m2) body mass index values.[51] Different types of acromioclavicular reconstructions are possible and it is unclear if there is individual differences between the constructs (Figure).[54]

Different constructs can be created such as a horizontal cerclage (A), a superior figure of eight (B), a combination of horizontal cerclage and figure of eight (C), or a vertical cerclage (D). The constructions including a figure of 8 seems to be the more stable (unpublished data).

Open and arthroscopic AC joint reconstruction techniques have no differences in loss of reduction, the complication rate, and the revision rate based on the available literature.[55]

Open Reduction for Acute Dislocation
Acromioclavicular and coracoclavicular cerclage reconstruction for acute acromioclavicular joint dislocations

Surgery is performed in the beach-chair position under general anesthesia, and an interscalene regional block is often added. A saber cut incision is made from the posterior acromial angle to the coracoid process along Langer’s lines. After subcutaneous dissection, traumatic detachment of the deltoid and trapezius permits visualization of the clavicle, base of the coracoid process, acromioclavicular joint, and acromion. The base of the coracoid process is then exposed by blunt dissection, and subcoracoid transfer of 4 non-resorbable No. 6 sutures is then performed using a long clamp with a 90 degree angulation.

These sutures are then inserted in the clavicle through two 3.2 mm drill holes made to approximate the normal insertion points of the coracoclavicular ligaments (25 mm and 46 mm from lateral end of the clavicle). The sutures are passed through the bone with a shuttle relay technique and a long Mayo needle. Two knots are placed under the clavicle to avoid skin irritation.

Two AP 2.5 mm drill holes are made 5 mm from the lateral end of the clavicle and 5 mm from the medial end of the acromion. Two No. 6 sutures are passed around the acromioclavicular joint with an untwist Mayo needle and tied tightly to reduce anteroposterior translation. The cerclage is realized in a figure of 8 configuration that is the more stable construct. As described by Barth et al., the acromion and clavicle are not perfectly aligned with acromioclavicular joint. Consequently, the articular facets that are the most reliable landmark are reduced under direct visualization. The reduction and the acromioclavicular and coracoclavicular cerclages are tied tightly. The deltotrapezial interval is carefully repaired and the wound that measure usually 6 cm is closed in routine fashion.[56]

Arthroscopic Reduction for Acute Dislocation

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Open Reduction for Chronic Dislocation: Mazzocca Technique and its Variants

Proper indications are irreducible dislocations or dislocations with severe displacement for patients who complain of persistent pain, muscle fatigue, popping, loss of strength, or scapular dyskinesis after a reasonable period of appropriate physiotherapy, in a supple shoulder. The use of a free tendon graft placed in an anatomic position reproduce the conoid and trapezoid ligaments and perform as the intact coracoclavicular ligament complex.[10][57]

Postoperative Rehabilitation

Immobilization is recommended during six weeks, the time needed for the reconstruction to develop biologic stability. Immediate glenohumeral mobility exercises such as internal/external rotation elbow at the side and flexion/extension of the elbow with the arm supported or in the supine position are recommended to avoid potential secondary frozen shoulder. After six weeks, progressive forward elevation is allowed and exercises against resistance are added. Emphasis should be placed on strengthening the scapular stabilizers. Consequently, sports such as brace stroke, nordic walking, elliptic machine and rowing are permitted at six weeks. Overhead sports and heavy labor are not allowed before three to four months postoperative.


Hardware migration is not anymore a complication as most surgeons abandon their use. Loss of reduction of the acromioclavicular joint is found in around 30% of the cases. The cause depends of the type of repair. The weight of the arm and scapula places tremendous static forces on the coracoclavicular reconstruction. The quality of the AC reduction comparing a reduced, subluxated (<50%) or dislocated (>50%) joint affected the clinical outcome scores (Constant, DASH) in a statistically significant manner (P < .005), with improved results with a better reduction. Persistent instability explains most of the chronic pain found after reconstruction.[50][51][58] Migration of the fixation device or erosion through the clavicle or the coracoid process from non absorbable materials used to augment the repair not uncommonly (Figures).


Osteolysis of the distal clavicle can be observed particularly when the graft or the non absorbable materials goes around the clavicle, creating a complete discontinuity between the medial and lateral clavicle (Figure 14).

Complication of primary and revision coracoclavicular reconstructions in the same patient. A) Left Acromioclavicular Joint Dislocation. B) Postoperative coracoclavicular and acromioclavicular joint reconstruction demonstrating an anatomic reduction. C) 6 months follow-up showing a loss of reduction. Observe the enlargement of bony tunnels in clavicle. D) Postoperative left X-ray after revision surgery by a modified Mazzocca technique with coracoclavicular cerclage passing under the coracoid process and through the clavicular holes and gracilis allograft passing under the coracoid and above the clavicle. E) Fatigue clavicular fracture medial to initial reconstructions.

Coracoclavicular calcification is frequent but should not be considered as a complication as they do not influence clinical results. In fact, the calcification maintained reduction and the stability of the reconstruction seems to be enhanced. Similarly, acromioclavicular arthritis is frequently found on both operated and nonoperated sides and do not compromise clinical outcome.[50][59]


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