[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) › AC ligament [Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # AC ligament The acromioclavicular ligament holds the outer end of the collarbone to the tip of the shoulder blade; it stops front-to-back sliding. Official name: Acromioclavicular ligament [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=ac_lig&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The band over the top of the joint between the collarbone and the acromion. ## What it does Stops the collarbone sliding forward and back on the acromion. ## Key points - The AC ligaments give front-back (horizontal) stability and the CC ligaments give vertical stability: a clavicle that only shifts front-back means an AC injury; one that rides up means the CC ligaments are torn too - Rockwood grades: I AC sprain; II AC torn; III AC and CC torn; IV clavicle pushed back into [trapezius](https://durgical.com/en/anatomy/trapezius-muscle/); V clavicle far up, fascia stripped; VI clavicle under the acromion or coracoid - Its upper and back part is the strongest and blends with the deltotrapezial fascia; it is preserved or repaired in a distal clavicle excision - Usual mechanism: a fall on the point of the shoulder with the arm at the side, driving the acromion down under the clavicle ## Key facts **Attaches** Acromion to the acromial end of the clavicle (superior, inferior) **Function** Horizontal (front-back) AC stability; first to tear in a separation **Tight in** Anterior-posterior translation of the clavicle ## Relations **Above** Deltotrapezial fascia and [skin](https://durgical.com/en/anatomy/skin/); the joint lies just under the skin **Below** [AC disc](https://durgical.com/en/anatomy/acromioclavicular-joint-disc/) and joint, then the [subacromial bursa](https://durgical.com/en/anatomy/subacromial-subdeltoid-bursa/) and the [supraspinatus tendon](https://durgical.com/en/anatomy/supraspinatus-tendon/) **Medial** Acromial end of the [clavicle](https://durgical.com/en/anatomy/clavicle/) **Lateral** Acromion **In front** Origin of the [front deltoid](https://durgical.com/en/anatomy/deltoid-anterior-part/) **Behind** Insertion of the [upper trapezius](https://durgical.com/en/anatomy/descending-part-of-trapezius-muscle/) ## How to find it The joint is felt as a small step at the outer end of the clavicle, a little medial to the lateral edge of the acromion; it moves under the finger when the arm is raised or the shoulder is shrugged. ## Examination - Cross-body adduction (scarf) test: pain on top of the shoulder as the arm is brought across the [chest](https://durgical.com/en/anatomy/region/chest/) points to the AC joint - Paxinos test: the thumb pushes the back of the acromion up while the index finger pushes the clavicle down; pain at the joint suggests AC pathology - O'Brien active compression test: pain felt on top of the shoulder (not deep inside) with the thumb down suggests the AC joint - Horizontal instability: holding the acromion and moving the end of the clavicle front to back shows abnormal translation when the AC ligaments are torn ## On imaging Zanca view (AP aimed at the AC joint with 10–15° of cephalic tilt and a softer exposure); bilateral views compare the coracoclavicular distance; an axillary view or a cross-body adduction (Basamania) view shows backward displacement and horizontal instability. ## Common problems - Shoulder separation: a fall on the point of the shoulder sprains or tears the AC ligament, then the coracoclavicular ligaments. - In severe cases the collarbone end sticks up as a visible bump. - Later wear and arthritis of the AC joint. ## How it is diagnosed Tenderness and a step at the top of the shoulder. X-rays (sometimes comparing both sides) grade the separation. ## Treatment - Sling, ice and early motion for mild and moderate separations. - Surgery to reconstruct the coracoclavicular ligaments for severe separations or ongoing pain. ## Clinical notes - Grades I–II are usually treated without surgery and IV–VI with surgery; the management of grade III is debated and depends on the person's demands and symptoms - Type IV is easily missed on a single AP view because the clavicle is pushed backward into or through the trapezius; an axillary view shows it - Persistent pain or instability after a grade I–II injury may lead to a distal clavicle excision; combined AC and CC reconstruction restores stability in both planes ## Related conditions - [Acromioclavicular joint separation](https://durgical.com/en/conditions/acromioclavicular-joint-separation/) ## Test yourself Think of the answer, then tap the question to see it. ## Which ligaments give horizontal and which give vertical stability at the acromioclavicular joint? The AC ligaments give front-back (horizontal) stability; the coracoclavicular ligaments give vertical stability. ## What is the usual mechanism of AC ligament injury? A fall on the point of the shoulder with the arm at the side, driving the acromion down under the clavicle. ## In Rockwood grade III, which ligaments are torn? Both the AC ligament and the coracoclavicular ligaments. ## Why is a Rockwood type IV AC injury easily missed? The clavicle is pushed backward into the trapezius, which a single AP view does not show; an axillary view does. ## Which test brings the arm across the chest to provoke AC joint pain? The cross-body adduction (scarf) test: pain on top of the shoulder points to the AC joint. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/acromioclavicular-ligament/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** ligamentum acromioclaviculare TA2 1745 **Official Spanish (DeCS)** Ligamento acromioclavicular **English (TA2)** Acromioclavicular ligament ## Related - [AC capsule](https://durgical.com/en/anatomy/acromioclavicular-joint-capsule/) - [AC disc](https://durgical.com/en/anatomy/acromioclavicular-joint-disc/) - [Clavicle](https://durgical.com/en/anatomy/clavicle/) - [Scapula](https://durgical.com/en/anatomy/scapula/) Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Acromioclavicular Joint](https://www.ncbi.nlm.nih.gov/books/NBK499858/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/acromioclavicular-ligament/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/acromioclavicular-ligament/