PATHOLOGY OF THE ACROMIOCLAVICULAR JOINT (AC)
1. ANATOMY OF ARTICULATION AC:
The AC joint is the joint that joins the distal end of the clavicle with the acromion. It is an articulation that is involved in the movements of the shoulder and that can be affected of 2 pathologies fundamentally: degeneration or AC arthropathy (acromioclavicular arthrosis) and instability, which is generally post-traumatic.
Normal AC joint. Arthrosis AC. Luxation AC.
2. ARTHROPATHY OR ACROMYCLAVICULAR ARTHROSIS:
It consists of the degeneration of the joint. This causes pain on palpation, pain when lying on that side, difficulty and pain with certain movements such as fastening the bra, and sometimes, the palpation of a larger bulge in the joint compared to the healthy side.
The diagnosis is established after a detailed clinical history along with simple x-rays of the shoulder. Sometimes it is necessary to complete the study with an MRI to assess other structures and other factors of the shoulder.
The treatment of this pathology is performed by arthroscopy, where, under direct visualization, an acromioclavicular resection is carried out, that is to say a filing of the bone peaks that rub together, leaving a free space of 8 mm in width to remove the pain.
3. LUXATION OR ACROMIOCLAVICULAR INSTABILITY:
It is usually caused by trauma to the lateral aspect of the shoulder. There are several degrees, depending on the condition of the ligaments and the direction of the clavicle.
Generally the diagnosis is established by simple radiology in these cases.
In grades higher than grade 3, surgical treatment is recommended. In grade 3 (see photo below), you can opt for a conservative or surgical treatment based on the personal assessment of each patient and their needs, such as the type of work or sport.
If AC grade 3 dislocation is acute, and surgical treatment is chosen, the arm may be as- sessed and the acromioclavicular joint is reduced, stabilizing it with an osteosynthesis system with sutures specially designed for it, and allowing the healing of the coracoclavicular ligaments by reducing dislocation of the clavicle, as can be seen in the following figure. In contact sports such as rugby the patient may require a capsular reinforcement of the dorsal acromioclavicular ligaments.
If, on the other hand, the problem is chronic and causes impotence and pain, one of the options is to perform the technique of Weaver-Dunn by arthroscopic route, where an acromioclavicular resection and posterior transfer of the coracoacromial ligament will be performed as you can see in the following image, generally associating a reinforcement with some extra fixation system, like the one shown in the previous figure. In other cases, a technique can be performed using ligamentous plasties that mimic the anatomy and return stability to the acromioclavicular joint in the anteroposterior as well as the superior plane.
Clinical case of an AC Class III dislocation with consolidated clavicular external third fracture, solved by Weaver-Dunn arthroscopic technique and coracoclavicular containment system: