Acromioclavicular Joint Injury
Injury to the acromioclavicular (AC) joint is a common injury among athletes and young individuals. Acromioclavicular joint injuries account for more than forty percent of all shoulder injuries. Mild injuries are not associated with any significant morbidity, but severe injuries can lead to significant loss of strength and function of the shoulder. Acromioclavicular injuries may be associated with a fractured clavicle, impingement syndromes, and more rarely neurovascular insults.
Earn CME credit as you help guide your clinical decisions.
The AC joint is a diarthrodial joint defined by the lateral process of the clavicle articulating with the acromion process as it projects anteriorly off the scapula. The joint is primarily stabilized by the acromioclavicular ligament, which is composed of an anterior, posterior, inferior, and superior component. Of note, the superior portion of the AC ligament is the most important component for the stability of the AC joint. Supporting structures include two coracoclavicular ligaments (trapezoid and conoid ligaments), which provide vertical stability, as well as the coracoacromial ligament. Mild injuries are not associated with any significant morbidity, but severe injuries can lead to considerable loss of strength and function of the shoulder. Acromioclavicular injuries may be associated with a fractured clavicle, impingement syndromes, and more rarely neurovascular insults.
AC injuries are frequently seen after sporting events, car accidents, falls from a bicycle, and other sports-related activities (e.g. skiing). AC joint injuries may account for as much as 40% of all shoulder injuries and nearly 10% of all injuries in collision sports such as football, lacrosse, and ice hockey.
The most common mechanism of injury is direct trauma to the lateral aspect of the shoulder or acromion process with the arm in adduction. Falling on an outstretched hand or elbow may also lead to AC joint separation.
History and Physical
Patients with an AC joint injury typically present with anterosuperior shoulder pain and will describe a mechanism of injury of blunt trauma to the abducted shoulder or landing on an outstretched arm, suggestive of this type of injury. They may describe pain radiating to the neck or shoulder, which is often worse with movement or when they try to sleep on the affected shoulder. On examination, the clinician may observe swelling, bruising, or a deformity of the AC joint, depending on the degree of injury. The patient will be tender at that location. They may have a restriction in the active and passive range of motion secondary to pain. "Piano key sign" may be seen, with an elevation of the clavicle that rebounds after inferior compression. Finally, It is essential to evaluate the entire clavicle for possible fracture or sternoclavicular injury as well as perform a full neurovascular exam on the affected extremity.
Standard X-rays are adequate to make a diagnosis of acromioclavicular joint injury and should be used to evaluate for other causes of traumatic shoulder pain. AC joint injuries may not always be evident on regular radiographic views (anteroposterior [AP], lateral). Additional views include the Zanca view; an AP view performed by tilting the beam 10 to 15 degrees cranial, as well as bilateral AP views to compare displacement to the contralateral shoulder. Weighted stress views may be useful to evaluate the displacement of the joint when the diagnosis is uncertain on standard AP views. If there is continued uncertainty in diagnosis, the provider may also consider ultrasound or MRI for further diagnostic evaluation.
Consider the Rockwood Staging System outlined below on the evaluation of radiographs, especially when compared to the contralateral shoulder, which will be important for guiding treatment. Identification of the coracoclavicular interspace distance compared to the contralateral view will help to guide treatment options in the majority of cases. An example of the appropriate method for measuring coracoclavicular interspace distance appears below.
Treatment / Management
Acromioclavicular joint injuries follow the Rockwood classification system of type I to type VI. Type I is referred to as a sprain of the acromioclavicular ligaments only and demonstrates no radiographic displacement. Type II involves tearing of the acromioclavicular ligament and sprain of the coracoclavicular ligament with less than 25% increase in the coracoclavicular interspace or with the clavicle elevated but not superior to the border of the acromion. Type I and II sprains are managed non-operatively with a sling, analgesia, ice, and physical therapy. Type III AC joint separation involves tearing of both the acromioclavicular ligament and coracoclavicular ligaments resulting in clavicle elevation above the border of the acromion with a 25 to 100% increased coracoclavicular distance on x-ray compared to the contralateral side. Type III injuries are frequently managed non-operatively similar to type I and II; however, if the displacement is greater than 75%; the patient is a laborer, elite athlete, or concerned about cosmesis; or is not improving with conservative management, then surgical intervention may be considered. Posterior displacement of the distal clavicle into the trapezius defines type IV injuries. Superior displacement of the distal clavicle by more than 100% compared to contralateral defines type V injuries. Type VI is rare and is defined as an inferolateral displacement in a subacromial or subcoracoid displacement behind the coracobrachialis or biceps tendon. Type IV through VI injuries are typically managed surgically, and warrants referral to an orthopedic surgeon.
Management of Acute Acromioclavicular Joint Disruption
If the AC joint injury presents within six weeks, it is considered acute. The main goal of treatment is acromioclavicular joint stabilization. Following techniques are used for stabilization and reduction of AC joint.
In the setting of Rockwood type Types III and V injuries, a distal clavicle hook plate may be employed to restore the alignment of the acromioclavicular joint. The "hook" portion of the hook plate is placed inferior to the acromion, with superior plating on the clavicle. While this does provide excellent reduction of the joint, the plate must be removed in a subsequent surgery to prevent subacromial irritation, subacromial impingement, acromion osteolysis, and iatrogenic damage to the rotator cuff. Kienast et al. reported 84 % good and excellent results (Taft score) in type III–V AC disruption with a hook plate. A superior approach is used for plate fixation. The hook is placed posteriorly under the acromion and screws are placed after the reduction of the AC joint.
All types of AC joint injuries can be treated with the Bosworth screw (CC screw fixation), which has outstanding results and is very cost-effective. Bosworth screw along with acromioclavicular (AC) and coracoclavicular (CC) ligament reconstruction provide excellent long-term outcomes. A 6.5mm screw is placed from the clavicle to the coracoid through a mini-open incision or percutaneously. Early screw removal (usually 8 weeks) is necessary to prevent fatigue failure and crew breakage.
Tension Band Wiring
Tucek et al. compared tension band wiring versus hook plate in 80 patients with type 5 AC joint disruption. Tension band wiring(TBW) provides comparable clinico-radiological results however hook plate allows an earlier range of motion and has a reduced rate of complications. TBW should be removed after 8 weeks to prevent wire malposition, migration, and breakage.
A suitable treatment option for acromioclavicular dislocation is coracoclavicular ligament reconstruction utilizing an endobutton, which has the benefits of solid fixation and an early functional range of motion.  Double or triple Ethibond no.5 loops are used with titanium endobuttons from clavicle to coracoid. Continuous and double loops minimize the risk of loop-knot slippage as compared to a single suspension system.
Management of Chronic Acromioclavicular Joint Disruption
There are three main goals of treatment
- AC joint debridement
- Ligament reconstruction ( acromioclavicular/ coracoclavicular)
- Stable fixation
Following procedures are used for chronic AC joint disruptions.
Modified Weaver-Dunn procedure
An incision is made from the acromioclavicular joint the tip of the coracoid. After raising skin flaps, the acromioclavicular joint is debrided and a distal 1cm of the clavicle is excised. The coracoacromial ligament is transferred to the distal end of the clavicle along with a small piece of the acromion. The modification in the original procedure is done in the form of added fixation with a screw or plate. 
The incision extends from the tip of the coracoid to 2 cm posterior to the AC joint. The distal 1 cm of the clavicle is excised after AC joint debridement. A semitendinosus autograft is prepared and looped around the coracoid. The anatomical reconstruction is done by making bony tunnels in the shaft of the clavicle at foot print of the conoid and trapezoid ligament.
The coracoacromial ligament is mobilized from the coracoid along with a small bony piece from its attachment site. K-wires are used to anchor the ligament to the distal end of the clavicle.
The original procedure includes the transfer of coracoacromial ligament from the acromion to the distal end of the clavicle. The bony tunnels are made through the lateral end of the clavicle to anchor this CA ligament. Stable reduction is provided by a Bosworth screw to secure this ligament reconstruction.
The coracoacromial ligament is transferred from the acromion into the distal end of the clavicle. The docking procedure involves tensioning the CA ligament into the distal clavicle's medullary canal by using 2 nonabsorbable sutures.
This procedure is required for chronic type 1 & 2 AC joint disruptions in which ligaments are intact. The distal 2.5 cm of the clavicle is excised to reduce joint pain. The soft tissue and periosteum are pilcated over the lateral end of the clavicle.
- Acromioclavicular distal clavicle osteolysis
- Acromioclavicular joint arthritis
- Acromion fracture
- Adhesive capsulitis
- Anterior humerus subluxation
- Complex pain syndrome
- Erb-Duchenne injury
- Glenoid labrum tear
- Os acromiale
- Rotator-cuff injury
- Superior labral tear
- Septic arthritis
- Shoulder dislocation
Rockwood Classification of AC Joint Injuries (acromioclavicular [AC], coracoclavicular [CC]).
- I: AC ligament sprain; CC ligament intact; no radiographic abnormalities
- II: AC ligament is torn; CC ligament sprain; the clavicle has elevated but is not superior to the border of the acromion, or exhibits a less than 25% increase in the CC interspace compared to the contralateral
- III: AC and CC ligaments are torn; clavicle has elevated above the border of the acromion, or there is an increase of 25% to 100% in the CC interspace compared to the contralateral
- IV: AC and CC ligaments are torn; posterior displacement of the distal clavicle into the trapezius
- V: AC and CC ligaments are torn; superior displacement of the distal clavicle by more than 100% in the CC interspace compared to the contralateral
- VI: AC and CC ligaments are torn; inferolateral displacement in a subacromial or subcoracoid displacement behind the coracobrachialis or biceps tendon
The Rockwood classification remains the gold standard for driving treatment decisions and is an excellent tool in the management of acromioclavicular joint injuries.
The prognosis for AC joint injuries is generally favorable. Most injuries receive non-operative management, and individuals typically regain functional motion by six weeks and return to normal activity by 12 weeks. Surgically managed injuries have a more extended recovery timeframe, including immobilization for six weeks and a gradual return to full activity around six months.
The most frequently encountered complication of AC joint separation is residual joint pain affecting anywhere from 30% to 50% of individuals. AC joint arthritis is also a known complication and is more common with surgical management. Hardware irritation, infection, adhesive capsulitis, coracoid, and clavicular fractures are common complications following fixation. Hook plate leads to acromion irritation, subacromial impingement, and osteolysis. 
Postoperative and Rehabilitation Care
- An arm sling is applied
- Ice packs are applied to shoulder
- Elbow and wrist mobilization is started
- Auxiliary hygiene is maintained
- Adequate analgesia is provided
- Limit abduction above 90 degrees
- Wean off polysling and start pendulum exercises
- Passive and then active range of motion exercises are started
- Start isometric and then strengthening exercises of rotator cuff
- Elbow and wrist mobilization is continued
- Start full range of motion of the shoulder above 90 degrees
- Proprioceptive and strengthening exercises are allowed
The patient is allowed to return to sports after 6 months.
Type I and II AC joint separations do not necessarily require an evaluation by a specialist; however, type III through VI should have an evaluation by an orthopedic surgeon or sports medicine physician.
Deterrence and Patient Education
Injuries of the acromioclavicular joint are common causes of shoulder pain and frequently occur in athletes and the setting of traumatic injury. Patients should seek an evaluation from a trained orthopedic or sports management physician. Early management with sling immobilization, ice, rest, and anti-inflammatory medications is generally an appropriate treatment for these injuries. Patients can generally return to normal activities after they have been evaluated and cleared by their treating physician.
Pearls and Other Issues
- The position of the AC joint makes it vulnerable to direct trauma to the superior or lateral aspect of the shoulder.
- In an isolated injury, patients typically have pain and swelling over the joint with or without a deformity depending on the degree of injury.
- All patients should receive a radiographic evaluation of the affected shoulder, and if the diagnosis is in question, obtain radiographs of the contralateral AC joint as well.
- Type I and II injuries occur twice as frequently as type III to VI injuries.
- Most injuries can have management non-operatively. If uncertainty exists or it is a Rockwell grade III or greater, an orthopedic physician should be urgently consulted.
- Non-operative management includes rest, protection with a sling, ice, NSAIDs, and physical therapy.
Enhancing Healthcare Team Outcomes
AC joint injuries commonly present to the emergency department. The mild injuries are usually managed conservatively, but the severe injuries may require surgery; hence it is crucial to consult an orthopedic surgeon when arriving at the diagnosis, to grade the injury. For mild injuries, the nurse practitioner, emergency department physician, and primary caregiver should recommend physical therapy, once the acute pain has resolved. Pharmacists and nurses should work with the team to educate the patient and family and assist in pain control. Those wishing to return to sports should first consult with the orthopedic surgeon.
(Click Image to Enlarge)
Gowd AK,Liu JN,Cabarcas BC,Cvetanovich GL,Garcia GH,Manderle BJ,Verma NN, Current Concepts in the Operative Management of Acromioclavicular Dislocations: A Systematic Review and Meta-analysis of Operative Techniques. The American journal of sports medicine. 2018 Oct 1 [PubMed PMID: 30272997]Level 1 (high-level) evidence
Hyland S,Varacallo M, Anatomy, Shoulder and Upper Limb, Clavicle null. 2018 Jan [PubMed PMID: 30252246]
Sirin E,Aydin N,Mert Topkar O, Acromioclavicular joint injuries: diagnosis, classification and ligamentoplasty procedures. EFORT open reviews. 2018 Jul [PubMed PMID: 30233818]
Ruiz Ibán MA,Sarasquete J,Gil de Rozas M,Costa P,Tovío JD,Carpinteiro E,Hachem AI,Perez España M,Asenjo Gismero C,Diaz Heredia J,García Navlet M, Low prevalence of relevant associated articular lesions in patients with acute III-VI acromioclavicular joint injuries. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2018 Aug 10 [PubMed PMID: 30097689]
Ernberg LA,Potter HG, Radiographic evaluation of the acromioclavicular and sternoclavicular joints. Clinics in sports medicine. 2003 Apr [PubMed PMID: 12825529]
Hashiguchi H,Iwashita S,Abe K,Sonoki K,Yoneda M,Takai S, Arthroscopic Coracoclavicular Ligament Reconstruction for Acromioclavicular Joint Dislocation. Journal of Nippon Medical School = Nippon Ika Daigaku zasshi. 2018 [PubMed PMID: 30135343]
Martetschläger F,Kraus N,Scheibel M,Streich J,Venjakob A,Maier D, The Diagnosis and Treatment of Acute Dislocation of the Acromioclavicular Joint. Deutsches Arzteblatt international. 2019 Feb 8; [PubMed PMID: 30892184]
Hung LK,Su KC,Lu WH,Lee CH, Biomechanical analysis of clavicle hook plate implantation with different hook angles in the acromioclavicular joint. International orthopaedics. 2017 Aug [PubMed PMID: 28097386]
Kienast B,Thietje R,Queitsch C,Gille J,Schulz AP,Meiners J, Mid-term results after operative treatment of rockwood grade III-V acromioclavicular joint dislocations with an AC-hook-plate. European journal of medical research. 2011 Feb 24; [PubMed PMID: 21463981]
Lowe GP,Fogarty MJ, Acute acromioclavicular joint dislocation: results of operative treatment with the Bosworth screw. The Australian and New Zealand journal of surgery. 1977 Oct; [PubMed PMID: 273410]
Jeong JY,Chun YM, Treatment of acute high-grade acromioclavicular joint dislocation. Clinics in shoulder and elbow. 2020 Sep; [PubMed PMID: 33330252]
Tuček M,Chochola A,Vaněček V,Bušková K, [Surgical treatment of acromioclavicular dislocation: Tension band wiring versus hook plate]. Rozhledy v chirurgii : mesicnik Ceskoslovenske chirurgicke spolecnosti. 2015 Oct; [PubMed PMID: 26556021]
Chen MM,Ye XY,Ni YP,Mou ZF,Huang LP, [Application of endobutton in the treatment of acute acromioclavicular joint dislocation]. Zhongguo gu shang = China journal of orthopaedics and traumatology. 2011 Mar; [PubMed PMID: 21485561]
Lim YW, Triple endobutton technique in acromioclavicular joint reduction and reconstruction. Annals of the Academy of Medicine, Singapore. 2008 Apr; [PubMed PMID: 18461213]
Galasso O,Tarducci L,De Benedetto M,Orlando N,Mercurio M,Gasparini G,Castricini R, Modified Weaver-Dunn Procedure for Type 3 Acromioclavicular Joint Dislocation: Functional and Radiological Outcomes. Orthopaedic journal of sports medicine. 2020 Mar [PubMed PMID: 32215276]
Pavlik A,Csépai D,Hidas P, Surgical treatment of chronic acromioclavicular joint dislocation by modified Weaver-Dunn procedure. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2001 Sep [PubMed PMID: 11685364]
Mazzocca AD, Arciero RA, Bicos J. Evaluation and treatment of acromioclavicular joint injuries. The American journal of sports medicine. 2007 Feb:35(2):316-29 [PubMed PMID: 17251175]
Sood A,Wallwork N,Bain GI, Clinical results of coracoacromial ligament transfer in acromioclavicular dislocations: A review of published literature. International journal of shoulder surgery. 2008 Jan [PubMed PMID: 21264150]
Millett PJ,Braun S,Gobezie R,Pacheco IH, Acromioclavicular joint reconstruction with coracoacromial ligament transfer using the docking technique. BMC musculoskeletal disorders. 2009 Jan 14 [PubMed PMID: 19144190]
Snyder SJ,Banas MP,Karzel RP, The arthroscopic Mumford procedure: an analysis of results. Arthroscopy : the journal of arthroscopic [PubMed PMID: 7794427]
Granville-Chapman J,Torrance E,Rashid A,Funk L, The Rockwood classification in acute acromioclavicular joint injury does not correlate with symptoms. Journal of orthopaedic surgery (Hong Kong). 2018 May-Aug [PubMed PMID: 29792117]
Stein T,Müller D,Blank M,Reinig Y,Saier T,Hoffmann R,Welsch F,Schweigkofler U, Stabilization of Acute High-Grade Acromioclavicular Joint Separation: A Prospective Assessment of the Clavicular Hook Plate Versus the Double Double-Button Suture Procedure. The American journal of sports medicine. 2018 Sep [PubMed PMID: 30106600]
Byrne PA,Hopper GP,Wilson WT,Mackay GM, Acromioclavicular Joint Stabilisation Using the Internal Brace Principle. Surgical technology international. 2018 Nov 11 [PubMed PMID: 30029288]
López-Alameda S,Fernández-Santás T,García-Villanueva A,Varillas-Delgado D,Garcia de Lucas F, Results of surgical treatment of acromioclavicular dislocations type III using modified Weaver Dunn technique. Revista espanola de cirugia ortopedica y traumatologia. 2018 Mar - Apr [PubMed PMID: 29428418]
Ma R,Smith PA,Smith MJ,Sherman SL,Flood D,Li X, Managing and recognizing complications after treatment of acromioclavicular joint repair or reconstruction. Current reviews in musculoskeletal medicine. 2015 Mar [PubMed PMID: 25663435]
LeVasseur MR,Mancini MR,Berthold DP,Cusano A,McCann GP,Cote MP,Gomlinski G,Mazzocca AD, Acromioclavicular Joint Injuries: Effective Rehabilitation. Open access journal of sports medicine. 2021; [PubMed PMID: 34093044]
Cheema SG,Hermanns C,Coda RG,Tarakemeh A,Mullen SM,Schroeppel JP,Vopat BG,Mulcahey MK, Publicly Accessible Rehabilitation Protocols for Acromioclavicular Joint Reconstruction Are Widely Variable. Arthroscopy, sports medicine, and rehabilitation. 2021 Apr [PubMed PMID: 34027451]
Müller D,Reinig Y,Hoffmann R,Blank M,Welsch F,Schweigkofler U,Stein T, Return to sport after acute acromioclavicular stabilization: a randomized control of double-suture-button system versus clavicular hook plate compared to uninjured shoulder sport athletes. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA. 2018 Dec [PubMed PMID: 29980805]Level 1 (high-level) evidence