[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 capsule [Joints and ligaments](https://durgical.com/en/anatomy/system/joints-and-ligaments/) · [Upper limb](https://durgical.com/en/anatomy/region/upper-limb/) # AC capsule The acromioclavicular capsule seals the joint between the collarbone and the tip of the shoulder blade; it tears in a shoulder separation. Official name: Acromioclavicular joint capsule [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=upper_limb&select=ac_capsule&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The capsule of the joint at the top of the shoulder. ## What it does Seals the AC joint; it is torn in a shoulder separation. ## Key points - Rockwood types of AC separation: I sprains the AC capsule and ligament, II tears them, III also tears the coracoclavicular (conoid and [trapezoid](https://durgical.com/en/anatomy/trapezoid/)) ligaments; IV–VI add displacement - The capsule and [AC ligament](https://durgical.com/en/anatomy/acromioclavicular-ligament/) (strongest above and behind) resist front-to-back movement of the clavicle; the coracoclavicular ligaments resist upward displacement - AC joint osteoarthritis is common with age; osteophytes on its underside can narrow the subacromial space ## Key facts **Attaches** Margins of the acromion and the lateral end of the clavicle **Function** Thin; reinforced above by the acromioclavicular ligament and the deltoid-trapezius fascia ## Relations **Above** Deltoid and [trapezius](https://durgical.com/en/anatomy/trapezius-muscle/) aponeuroses blend over it; the [skin](https://durgical.com/en/anatomy/skin/) is thin, so the [clavicle](https://durgical.com/en/anatomy/clavicle/) end is easy to feel **Below** [Subacromial bursa](https://durgical.com/en/anatomy/subacromial-subdeltoid-bursa/) and [supraspinatus tendon](https://durgical.com/en/anatomy/supraspinatus-tendon/) **Medial** [Conoid ligament](https://durgical.com/en/anatomy/conoid-ligament/) and [trapezoid ligament](https://durgical.com/en/anatomy/trapezoid-ligament/), a little medial, running from the clavicle's underside to the coracoid **Contents** [AC disc](https://durgical.com/en/anatomy/acromioclavicular-joint-disc/), often incomplete and wearing away with age ## How to find it The lateral end of the clavicle is followed outward until a small step or dip marks the joint, just medial to the edge of the acromion; bringing the arm across the [chest](https://durgical.com/en/anatomy/region/chest/) moves the joint under the finger. ## Examination - Cross-body adduction (scarf) test: pain over the joint when the arm is brought across the chest suggests AC joint disease - O'Brien active compression test: pain on top of the shoulder (rather than deep inside) points to the AC joint - Pain relief after local anaesthetic is placed in the joint supports it as the source ## On imaging The Zanca view (AP with the beam tilted about 10–15° upward) shows the joint clear of the scapular [spine](https://durgical.com/en/anatomy/region/spine/). Comparison with the other side and the coracoclavicular distance grade a separation; MRI shows capsular oedema and cysts. ## Clinical notes - Distal clavicle osteolysis in weightlifters: pain and bone resorption at the clavicle end - Distal clavicle excision for a painful arthritic joint keeps the superior and posterior capsule to avoid instability - Type III separations are often managed without surgery; types IV–VI are usually reduced and reconstructed ## Anatomical variants - A coracoclavicular joint or bony bar between the clavicle and the coracoid is an occasional finding (close to 1 in 10 in one large series) ## Development The clavicle ossifies mainly in membrane and the acromion from cartilage; tissue left between them may persist as an articular disc, which is often missing or only partial and wears down early in adult life. ## 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. ## What does the AC capsule with the acromioclavicular ligament resist, compared with the coracoclavicular ligaments? Front-to-back movement of the clavicle; the coracoclavicular ligaments resist upward displacement. ## What structures are torn in a Rockwood type III AC separation? The AC capsule and ligament plus the coracoclavicular (conoid and trapezoid) ligaments. ## Which test suggests AC joint disease? The cross-body adduction test: pain over the AC joint when the arm is brought across the chest. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/anatomy/acromioclavicular-joint-capsule/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** capsula articularis articulationis acromioclavicularis TA2 1536 **Official Spanish (DeCS)** Cápsula articular de la articulación acromioclavicular **English (TA2)** Acromioclavicular joint capsule ## Related - [AC ligament](https://durgical.com/en/anatomy/acromioclavicular-ligament/) - [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/); [8.5 Development of the Appendicular Skeleton](https://openstax.org/books/anatomy-and-physiology-2e/pages/8-5-development-of-the-appendicular-skeleton) (OpenStax (Rice University), 2022) · adapted, [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); Anatomy of the Human Body (20th ed.): Development of the Joints (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain; Anatomy of the Human Body (20th ed.): Acromioclavicular Articulation (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain. ## **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-joint-capsule/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/acromioclavicular-joint-capsule/