Acromioclavicular Articulation: Difference between revisions

Latest revision as of 11:25, 30 March 2025

Anatomy > Gray's Anatomy of the Human Body > III. Syndesmology > 6b. Acromioclavicular Articulation

The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula (Gray's Anatomy, 1918).

Acromioclavicular Articulation[edit]

The acromioclavicular joint (AC joint) or articulatio acromioclavicularis is a type of synovial joint located between the acromial end of the clavicle and the medial margin of the acromion of the scapula. It is classified as an arthrodial joint (plane-type synovial joint) and plays a critical role in the movement and stability of the shoulder girdle.

Ligaments of the Acromioclavicular Joint[edit]

The stability of the AC joint is maintained by several ligaments:

Articular capsule
Articular disk
Superior acromioclavicular ligament
Inferior acromioclavicular ligament
Coracoclavicular ligament (including the trapezoid ligament and conoid ligament)

Articular Capsule[edit]

The articular capsule (capsula articularis) surrounds the joint and is reinforced superiorly and inferiorly by the respective acromioclavicular ligaments.

Superior Acromioclavicular Ligament[edit]

This quadrilateral band strengthens the upper part of the joint. It connects the top of the lateral end of the clavicle to the upper surface of the acromion. The ligament fibers interlace with the aponeuroses of the trapezius and deltoid muscles.

Inferior Acromioclavicular Ligament[edit]

Thinner than the superior ligament, this band reinforces the lower portion of the capsule. It lies above the supraspinatus tendon and may occasionally be associated with the articular disk.

Articular Disk[edit]

The presence of an articular disk (discus articularis) in the AC joint is variable. When present, it partially or fully separates the articular cavity and contributes to joint stability.

Synovial Membrane[edit]

Typically, there is one synovial membrane, but when a complete disk divides the joint, two cavities are formed, each with its own membrane.

Coracoclavicular Ligament[edit]

Although not part of the AC joint proper, the coracoclavicular ligament (ligamentum coracoclaviculare) is critical for stabilizing the clavicle and suspending the shoulder girdle.

It consists of two parts:

Trapezoid Ligament[edit]

The trapezoid ligament (ligamentum trapezoideum) is flat and quadrilateral, running from the coracoid process to the trapezoid line of the clavicle.

Conoid Ligament[edit]

The conoid ligament (ligamentum conoideum) is cone-shaped, with its apex attached to the coracoid process and its base affixed to the conoid tubercle of the clavicle.

These ligaments function together to prevent excessive movement between the scapula and clavicle, particularly during upward displacement.

Movements of the Acromioclavicular Joint[edit]

Movements at the AC joint are mainly:

Gliding motion between the acromion and clavicle
Rotation of the scapula around a vertical axis drawn through the clavicle

The range of movement is limited by the coracoclavicular ligament:

The trapezoid ligament restricts forward rotation.
The conoid ligament restricts backward rotation.

These movements contribute to the elevation, depression, protraction, and retraction of the scapula and allow for greater range in shoulder movement, especially during activities like reaching overhead or throwing.

Functional Importance[edit]

The AC joint serves as a pivot allowing the scapula to rotate and adjust its position relative to the thoracic cage, enabling a wide range of shoulder movements. It ensures the scapula maintains proper contact with the ribcage during elevation or depression of the shoulder and permits smooth transmission of forces from the upper limb to the axial skeleton.

Ligaments of the Scapula[edit]

In addition to those directly associated with the AC joint, the following scapular ligaments contribute to shoulder joint stability:

Coracoacromial Ligament[edit]

This strong triangular ligament spans from the coracoid process to the acromion, forming a protective arch over the head of the humerus with these two bony projections. It is in close relation to the supraspinatus tendon and overlain by the deltoid.

Superior Transverse Scapular Ligament[edit]

Also called the suprascapular ligament, it bridges the scapular notch, converting it into a foramen for the suprascapular nerve. The corresponding artery and vein typically pass over this ligament.

Inferior Transverse Scapular Ligament[edit]

Also called the spinoglenoid ligament, it stretches across the spinoglenoid notch and transmits the suprascapular nerve and vessels to the infraspinous fossa.

Clinical Relevance[edit]

Injuries to the AC joint, including acromioclavicular joint dislocation or shoulder separation, are common in contact sports. Degenerative changes may lead to acromioclavicular joint osteoarthritis, especially in older individuals or those with a history of joint trauma.

External Links[edit]

Gray's Anatomy[edit]

Anatomy atlases (external)[edit]

[1] - Anatomy Atlases

Adapted from the Classic Grays Anatomy of the Human Body 1918 edition (public domain)

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+[[Anatomy]] > [[Gray's Anatomy|Gray's Anatomy of the Human Body]] > III. [[Syndesmology]] > 6b. Acromioclavicular Articulation
-[[Anatomy]] > [[Gray's Anatomy| Gray's Anatomy of the Human Body]] > III. Syndesmology > 6b. Acromioclavicular Articulation
+[[File:Gray362.png|thumb|300px|The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula (Gray's Anatomy, 1918).]]
+== '''Acromioclavicular Articulation''' ==
+The '''acromioclavicular joint''' ('''AC joint''') or '''articulatio acromioclavicularis''' is a type of [[synovial joint]] located between the [[acromial end of the clavicle]] and the medial margin of the [[acromion]] of the [[scapula]]. It is classified as an [[arthrodial joint]] (plane-type synovial joint) and plays a critical role in the movement and stability of the [[shoulder girdle]].
-[[Henry Gray]] (1821–1865).  Anatomy of the Human Body.  1918.
+== '''Ligaments of the Acromioclavicular Joint''' ==
+The stability of the AC joint is maintained by several ligaments:
-=='''Acromioclavicular Articulation'''==
-'''(Articulatio Acromioclavicularis; Scapuloclavicular Articulation)'''
+* [[Articular capsule]]
+* [[Articular disk]]
+* [[Superior acromioclavicular ligament]]
+* [[Inferior acromioclavicular ligament]]
+* [[Coracoclavicular ligament]] (including the [[trapezoid ligament]] and [[conoid ligament]])
-The acromioclavicular articulation is an arthrodial joint between the acromial end of the clavicle and the medial margin of the acromion of the scapula. Its ligaments are:
+=== Articular Capsule ===
+The articular capsule (''capsula articularis'') surrounds the joint and is reinforced superiorly and inferiorly by the respective acromioclavicular ligaments.
-The Articular Capsule.
+=== Superior Acromioclavicular Ligament ===
+This quadrilateral band strengthens the upper part of the joint. It connects the top of the lateral end of the [[clavicle]] to the upper surface of the [[acromion]]. The ligament fibers interlace with the [[aponeuroses]] of the [[trapezius]] and [[deltoid]] muscles.
-The Articular Disk.
+=== Inferior Acromioclavicular Ligament ===
+Thinner than the superior ligament, this band reinforces the lower portion of the capsule. It lies above the [[supraspinatus]] tendon and may occasionally be associated with the articular disk.
-The Superior Acromioclavicular.
+=== Articular Disk ===
+The presence of an articular disk (''discus articularis'') in the AC joint is variable. When present, it partially or fully separates the articular cavity and contributes to joint stability.
-The Coracoclavicular {Trapezoid and Conoid.
+=== Synovial Membrane ===
+Typically, there is one synovial membrane, but when a complete disk divides the joint, two cavities are formed, each with its own membrane.
-The Inferior Acromioclavicular.
+== '''Coracoclavicular Ligament''' ==
+[[File:Shoulder joint.svg|thumb|Diagram of the human shoulder joint, front view]]
+[[File:Shoulder joint back-en.svg|thumb|Diagram of the human shoulder joint, back view]]
-=== '''The Articular Capsule (''capsula articularis; capsular ligament'') ''' ===
+Although not part of the AC joint proper, the [[coracoclavicular ligament]] (''ligamentum coracoclaviculare'') is critical for stabilizing the clavicle and suspending the shoulder girdle.
-The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments.
-=== '''The Superior Acromioclavicular Ligament (''ligamentum acromioclaviculare'')''' ===
+It consists of two parts:
-This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the [[acromion]]. It is composed of parallel fibers, which interlace with the [[aponeuroses]] of the [[Trapezius]] and [[Deltoideus]]; ''below'' it is in contact with the articular disk when this is present.
-=== '''The Inferior Acromioclavicular Ligament''' ===
+=== Trapezoid Ligament ===
-This ligament is somewhat thinner than the preceding; it covers the under part of the articulation, and is attached to the adjoining surfaces of the two bones.
+The trapezoid ligament (''ligamentum trapezoideum'') is flat and quadrilateral, running from the [[coracoid process]] to the [[trapezoid line]] of the clavicle.
-It is in relation, ''[[above]]'' in rare cases with the articular disk; ''[[below]]'' with the tendon of the Supraspinatus.
-=== '''The Articular Disk (''discus articularis'')''' ===
+=== Conoid Ligament ===
-The articular disk is frequently absent in this [[articulation]]. When present, it generally only partially separates the articular surfaces, and occupies the upper part of the articulation. More rarely, it completely divides the joint into two cavities.
+The conoid ligament (''ligamentum conoideum'') is cone-shaped, with its apex attached to the [[coracoid process]] and its base affixed to the [[conoid tubercle]] of the clavicle.
-==== '''The Synovial Membrane''' ====
+These ligaments function together to prevent excessive movement between the scapula and clavicle, particularly during upward displacement.
-There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two.
-=== '''The Coracoclavicular Ligament (''ligamentum coracoclaviculare'') (Fig. 326)''' ===
+== '''Movements of the Acromioclavicular Joint''' ==
-This ligament serves to connect the clavicle with the coracoid process of the scapula. It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, called the '''[[trapezoid]]''' and '''[[conoid ligaments]]'''
+Movements at the AC joint are mainly:
-'''The Trapezoid Ligament''' (''ligamentum trapezoideum''), the anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the [[clavicle]]. It is attached, ''below'' to the upper surface of the [[coracoid]] process; ''above'' to the oblique ridge on the under surface of the clavicle. Its [[anterior]] border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward.
+* Gliding motion between the acromion and clavicle
+* Rotation of the scapula around a vertical axis drawn through the clavicle
-'''The Conoid Ligament''' (''ligamentum conoideum''), the posterior and medial fasciculus, is a dense band of fibers, conical in form, with its base directed upward. It is attached by its apex to a rough impression at the base of the coracoid process, medial to the trapezoid ligament; above, by its expanded base, to the coracoid tuberosity on the under surface of the clavicle, and to a line proceeding medialward from it for 1.25 cm. These ligaments are in relation, in ''front'' with the Subclavius and Deltoideus; ''behind'' with the Trapezius.
+The range of movement is limited by the coracoclavicular ligament:
+* The [[trapezoid ligament]] restricts forward rotation.
+* The [[conoid ligament]] restricts backward rotation.
-[[File:Gray362.png|thumb|FIG. 326– The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. (''Picture From the Classic Gray's Anatomy'')]]
+These movements contribute to the elevation, depression, protraction, and retraction of the [[scapula]] and allow for greater range in shoulder movement, especially during activities like reaching overhead or throwing.
-'''Movements'''
-The movements of this articulation are of two kinds: (1) a gliding motion of the articular end of the clavicle on the acromion; (2) rotation of the scapula forward and backward upon the clavicle. The extent of this rotation is limited by the two portions of the coracoclavicular ligament, the trapezoid limiting rotation forward, and the [[conoid]] backward.
-The acromioclavicular joint has important functions in the movements of the upper extremity. It has been well pointed out by Humphry, that if there had been no joint between the clavicle and [[scapula]], the circular movement of the scapula on the ribs (as in throwing the shoulders backward or forward) would have been attended with a greater alteration in the direction of the shoulder than is consistent with the free use of the arm in such positions, and it would have been impossible to give a blow straight forward with the full force of the arm; that is to say, with the combined force of the scapula, arm, and forearm.
-“This joint,” as he happily says, “is so adjusted as to enable either bone to turn in a hinge-like manner upon a vertical axis drawn through the other, and it permits the surfaces of the scapula, like the baskets in a roundabout swing, to look the same way in every position, or nearly so.” Again, when the whole arch formed by the clavicle and scapula rises and falls (in elevation or depression of the shoulder), the joint between these two bones enables the scapula still to maintain its lower part in contact with the ribs.
-=== '''The Ligaments of the Scapula''' ===
+== '''Functional Importance''' ==
-The ligaments of the scapula (Fig. 326) are  Coracoacromial, Superior and Inferior Transverse.
+The AC joint serves as a pivot allowing the [[scapula]] to rotate and adjust its position relative to the [[thoracic cage]], enabling a wide range of shoulder movements. It ensures the scapula maintains proper contact with the ribcage during elevation or depression of the shoulder and permits smooth transmission of forces from the upper limb to the axial skeleton.
-==== '''The Coracoacromial Ligament (''ligamentum coracoaromiale'')''' ====
+== '''Ligaments of the Scapula''' ==
-This ligament is a strong triangular band, extending between the [[coracoid process]] and the [[acromion]]. It is attached, by its [[apex]], to the summit of the acromion just in front of the articular surface for the [[Clavicle|clavicl]]<nowiki/>e; and by its broad base to the whole length of the [[lateral]] border of the coracoid process.
+In addition to those directly associated with the AC joint, the following scapular ligaments contribute to shoulder joint stability:
-This ligament, together with the coracoid process and the acromion, forms a vault for the protection of the head of the [[humerus]]. It is in relation, ''above'' with the clavicle and under surface of the Deltoideus; ''below'' with the tendon of the [[Supraspinatus]], a bursa being interposed. Its lateral border is continuous with a dense lamina that passes beneath the Deltoideus upon the tendons of the Supraspinatus and Infraspinatus.
+=== Coracoacromial Ligament ===
+This strong triangular ligament spans from the [[coracoid process]] to the [[acromion]], forming a protective arch over the head of the [[humerus]] with these two bony projections. It is in close relation to the [[supraspinatus]] tendon and overlain by the [[deltoid]].
-The ligament is sometimes described as consisting of two marginal bands and a thinner intervening portion, the two bands being attached respectively to the apex and the base of the coracoid process, and joining together at the acromion. When the Pectoralis minor is inserted, as occasionally is the case, into the capsule of the shoulder-joint instead of into the coracoid process, it passes between these two bands, and the intervening portion of the ligament is then deficient.
+=== Superior Transverse Scapular Ligament ===
+Also called the suprascapular ligament, it bridges the [[scapular notch]], converting it into a foramen for the [[suprascapular nerve]]. The corresponding artery and vein typically pass over this ligament.
-==== '''The Superior Transverse Ligament (''ligamentum transversum scapulæ superius; transverse'' or ''suprascapular ligament'')''' ====
+=== Inferior Transverse Scapular Ligament ===
-This ligament converts the scapular notch into a foramen. It is a thin and flat [[fasciculus]], narrower at the middle than at the [[extremities]], attached by one end to the base of the coracoid process, and by the other to the medial end of the scapular [[notch]]. The suprascapular nerve runs through the foramen; the transverse scapular vessels cross over the ligament. The ligament is sometimes [[ossified]].
+Also called the spinoglenoid ligament, it stretches across the [[spinoglenoid notch]] and transmits the [[suprascapular nerve]] and vessels to the [[infraspinous fossa]].
-==== '''The Inferior Transverse Ligament (''ligamentum transversum scapulæ inferius; spinoglenoid ligament'')''' ====
+== '''Clinical Relevance''' ==
-This ligament is a weak membranous band, situated behind the neck of the [[scapula]] and stretching from the [[lateral]] border of the spine to the margin of the glenoid cavity. It forms an arch under which the transverse scapular vessels and suprascapular nerve enter the infraspinatous fossa.
+Injuries to the AC joint, including [[acromioclavicular joint dislocation]] or [[shoulder separation]], are common in contact sports. Degenerative changes may lead to [[acromioclavicular joint osteoarthritis]], especially in older individuals or those with a history of joint trauma.
-==Function==
-The acromioclavicular joint provides the ability to raise the arm above the head. This joint functions as a pivot point (although technically it is a gliding synovial joint), acting like a strut to help with movement of the scapula resulting in a greater degree of arm rotation.
+== '''See Also''' ==
-==Additional images==
+* [[Clavicle]]
-<gallery>
+* [[Scapula]]
-File:Shoulder joint.svg|Diagram of the human shoulder joint, front view
+* [[Shoulder joint]]
-File:Shoulder joint back-en.svg|Diagram of the human shoulder joint, back view
+* [[Trapezoid ligament]]
-</gallery>
+* [[Conoid ligament]]
-==External links==
+* [[Coracoacromial ligament]]
-{{Commons category|Acromioclavicular joints}}
+* [[Synovial joint]]
-*[https://web.archive.org/web/20190301032440/http://www.melbourneradiology.com.au/mri-gallery/mri-shoulder.html Images from an MRI scan demonstrating AC Joint Injury - Grade II sprain]
+* [[Sternoclavicular joint]]
-*[https://web.archive.org/web/20110506005510/http://simonmoyes.co.uk/2011/02/18/what-is-acromioclavicular-joint-osteoarthritis/ What is Acromioclavicular Joint Osteoarthritis? - www.SimonMoyes.co.uk]
-*[http://www.shoulderus.com/ultrasound-of-the-shoulder/acromioclavicular-joint Acromioclavicular joint disease]
+== '''External Links''' ==
+* [https://web.archive.org/web/20190301032440/http://www.melbourneradiology.com.au/mri-gallery/mri-shoulder.html MRI images of AC joint injury]
+* [https://web.archive.org/web/20110506005510/http://simonmoyes.co.uk/2011/02/18/what-is-acromioclavicular-joint-osteoarthritis/ AC Joint Osteoarthritis article]
+* [http://www.shoulderus.com/ultrasound-of-the-shoulder/acromioclavicular-joint Diagnostic ultrasound of AC joint]
 {{Joints of upper limbs}}
-{{Authority control}}
 {{DEFAULTSORT:Acromioclavicular Joint}}
 [[Category:Joints]]
 [[Category:Upper limb anatomy]]
+[[Category:Synovial joints]]
+[[Category:Shoulder]]
-{{grays}}
+{{grays adapted}}