This article describes the structure of the acromioclavicular joint.
There are many bones in the upper shoulder girdle. All of them are interconnected by connecting nodes that perform complex functions.
- One of these joints is the acromioclavicular joint (ACJ) . This knot, consisting of complex elements, ensures the movement of the arms.
- The acromion is connected to the end of the scapula by muscles and ligaments.
- Their functions may be limited if there is an injury or risk of some disease.
- Read on to learn more about the structure and diseases of this part of the body.
Acromioclavicular joint: shape, structure, anatomy
Acromioclavicular node
The acromion is the coracoid process in the area of the scapula. This bony part, together with the humeral clavicular end, creates one simple, flat, but mobile unit. The hyaline circle divides this joint into 2 chambers.
The base of the joint, consisting of dense bone, is immobilized, since its functional feature is to ensure highly stable and controlled movement of the arm.
- The unique structure of the node helps that the clavicle bone acts as an excellent stabilizer of arm movement.
- It controls the movement of the arms, which allows a person to exercise without causing additional and unwanted stress on the joint.
- This rigidity of the unit allows for precise and active manual movements.
Due to the fact that our limbs are mobile and constantly moving, this helps to ensure 80% of the health of their anterior supporting apparatus along with the articular surface. The rest depends on the genetic predisposition to diseases of the cartilaginous nodes and excessive loads on the joint itself.
Causes and mechanism of damage to the acromioclavicular joint
The main causes of damage to the acromioclavicular joint:
- injuries from falling on an outstretched arm;
- injuries during sports competitions;
- injuries in contact sports;
- injuries in people leading an active lifestyle.
The classification of injuries to the acromioclavicular joint depends on the amount of damage received.
There are two types of damage to the acromioclavicular joint:
- partial rupture of the acromioclavicular joint, when only the acromioclavicular ligaments are damaged;
- complete rupture - damage to the coracoclavicular ligaments and acromioclavicular joint.
Acromioclavicular joint: classification, characteristics
According to the classification in medicine, this joint is simple, complex, flat, combined and multiaxial. The characteristics of the AK unit according to the plan will look like this:
Characteristics of the acromioclavicular node
Doctors use this characteristic when describing a joint in medical language. In ordinary words, on the one hand it is a simple joint, but at the same time it plays an important role in the functionality of the upper limbs and serves as a real shock absorber during their movement.
Diagnosis of acromioclavicular joint rupture
Damage to the acromioclavicular joint is diagnosed by an orthopedic traumatologist during a clinical examination. Final diagnosis of this damage using instrumental diagnostic methods. The most commonly used is radiography of the damaged segment.
Taking into account the anatomical features of the acromioclavicular joint and possible combined damage to neighboring structures, the use of computed tomography and magnetic resonance imaging devices located in our center allows us to more accurately diagnose injuries to the shoulder joint area.
Acromioclavicular joint: muscles, ligaments
AC joint ligaments
Muscles and ligaments provide additional strength to the joint. Thanks to them, the knot is fixed in the correct position and in this case there is a small likelihood of complex injuries.
Ligaments
The capsule of the AK knot, consisting of fibers, is attached to the edges of the knot and reinforced with two connecting fabric strips:
- Acromioclavicular - performs the function of connecting the acromion and the clavicular end of the entire joint.
- The coracoclavicular ligament is two connecting bundles, which in turn are connected by the trapezoid and conical ligaments.
But these internal assembly stabilizers are not the only ones in this department. In the area of the AK node there are fibers that form a belt with the connection of the shoulder line, woven into the capsule of the node. These fibers include the coracoacromial ligament, as well as elements of the scapula.
All the voids between the coarse fibers of the shock absorbers are filled with fatty tissue. This is an excellent medium for damping all kinds of vibrations, and it also protects the solid elements of the AK unit from various types of damage.
Muscles
The functions of muscle tissue in this area are complex and diverse. The following muscles are located near the AC node:
- Deltoid
- Supraspinatus
- Infraspinatus
- Teres minor and major muscles
- Subscapular.
The deltoid muscle is located above the shoulder. It helps to bend and straighten your arms. If the back and front parts of the muscle work alternately, the arm bends. If the entire tissue of the deltoid muscle is tense, then thanks to this the person can move the shoulder back.
The supraspinatus and infraspinatus muscles help flex and extend the shoulder without allowing the joint capsule to become pinched. These muscles, simultaneously with the movement of the shoulder, pull back and protect from injury not only the capsule of the joint, but also other elements of the joint.
The major and minor muscles allow pronation and supination of the shoulder girdle. The multipennate subscapularis muscle has excellent lifting force. All these and other muscles located near the AC node also serve as supinators and flexors of the forearm and other parts of the body of the shoulder girdle.
About the acromioclavicular joint
The loose upper belt of a person is connected to the body using the collarbone and muscles.
In turn, the clavicle has two articular ends. The sternoclavicular (proximal) and acromioclavicular (distal) joints. The collarbone is attached to the scapula in two places:
- to the acromion, creating the acromioclavicular joint;
- to the coracoid process of the scapula by a powerful ligament.
The acromioclavicular joint (articulatio acromioclavicularis) is a flat joint, inside of which there is meniscoid tissue that absorbs the load transmitted from the upper limb.
Acromioclavicular joint: movements, functional features
Functional features of the AC node
The collarbone connects to the sternum - firmly and motionlessly. Thanks to this structure, the long bone serves as a support for the hands, which helps to easily perform the following movements:
- Raise your limbs up.
- Perform different movements with your arms above your head.
- Apply the clutch to the upper lock.
- Place your hands behind your back, fastening them together.
At the back, at the level of the waist of the upper limbs, there is a scapula. It consists of a flat, large bone that stabilizes the two largest joints - the shoulder and AC joints. These nodes, together with ligaments and muscles, allow the hands to perform the following complex directed movements:
AK node movements
- Straight arm rotation.
- Retracting straight arms back.
- Raising the upper limbs above the head.
- Performing pronation and supination of the shoulder.
- Bringing the limbs straight in front of the body.
A special disk that divides the AK unit into two parts increases the capabilities and allows the hands to move in three planes. The complex structure is made in such a way that the bones of the node do not fit tightly to each other. This allows the shoulder girdle to perform movements with good amplitude, sufficient for the normal functioning of the arms in the required directions.
Acromioclavicular joint: blood supply
Blood supply to the AC
node The blood supply to the AC node is provided by the subclavian vein. It passes through two points of the joint: from below - at a distance of 3 cm inward from the coracoid process, from above - 3 cm down from the edge of the clavicle on the side of the chest. In infants, this vein runs through the middle of the collarbone, and only by the age of 5 will it change location and be located at two points, as in adults.
The subclavian vein is located obliquely relative to the center of the body. During movement, the topography of this vein will not change, since its walls are connected to the ribs and clavicle bone, as well as to the muscles in this area. The outflow of venous blood is carried out through the vascular network, which is located in this area.
Acromioclavicular joint (art. acromioclavicularis)
Classification. The shape of the joint is flat, multi-axial.
Structure. The joint is formed by the articular surfaces of the acromial end of the clavicle and the acromial process of the scapula. In 1/3 of cases, an articular disc is located between them. The capsule is attached along the edge of the articular surfaces. The joint is strengthened by the acromioclavicular and coracoclavicular
(ligg. acromioclaviculare et coracoclaviculare) ligaments.
Functions
.
In the acromioclavicular joint, movements around three axes are possible (see sternoclavicular joint), but their volume is insignificant, because
The ligaments that strengthen the joint limit these movements. Shoulder joint (art. humeri) – fig. 5.
Rice. 5. Shoulder joint, right (the joint is opened by a frontal incision): 1 – head of the humerus, 2 – articular capsule, 3 – acromion, 4 – articular labrum, 5 – articular cavity, 6 – tendon of the long head of the biceps brachii muscle.
Classification.
Simple,
typical ball and socket joint, multi-axial.
Structure. The joint is formed by the head of the humerus and the glenoid cavity of the scapula. The surface of the head of the humerus is 3 times larger than the surface of the glenoid cavity of the scapula. The depression is somewhat deepened by the articular cartilaginous lip. The joint capsule is thin and free, which allows the articular surfaces to move away from each other up to 3 cm during movement. The capsule is attached along the neck of the scapula and on the humerus along its anatomical neck. The joint is strengthened by the weak coracobrachialis
(lig. coracohumerale) ligament and surrounding muscles.
The role of the arch (roof) for the shoulder joint is performed by one of the scapula’s own ligaments - the coracoacromial (lig coracoacromiale), which prevents upward dislocation of the humerus.
Functions
.
Movements in the joint are carried out around the axes: sagittal - abduction (to the horizontal level) and adduction;
around the frontal axis - flexion (raising the arm forward) to a horizontal level and extension (bending backward); around the vertical axis - rotation of the shoulder together with the forearm outward and inward. Circular movements are possible in the shoulder joint. Elbow joint (art. cubiti) – fig. 6.
Rice. 6. Elbow joint (opened) and joints of the bones of the forearm, front view: 1 – head of the radius, 2 – head of the humerus, 3 – humerus, 4 – trochlea of the humerus, 5 – articular capsule, 6 – articular cavity, 7 – proximal radioulnar joint, 8 – ulna, 9 – distal radioulnar joint, 10 – radial bone, 11 – interosseous membrane, 12 – annular ligament of the radial bone.
The elbow joint is a complex joint because it is formed by the articulation of three bones: the humerus, the ulna and the radius. Between them, three joints are formed, enclosed in one articular capsule: humeroulnar, brachioradial and radioulnar (proximal). The articular capsule of the elbow joint is strengthened by three ligaments: annular, radial and ulnar collateral.
(ligg. anulare, collaterale radiale et ulnare).
Functions
.
Movements around the frontal and vertical axes are possible in the elbow joint.
The frontal axis coincides with the axis of the trochlea of the humerus; flexion and extension of the forearm are carried out around it. When bending the elbow joint, a slight movement of the forearm occurs inward (medially) - the hand rests not on the shoulder joint, but on the chest. Rotation occurs around a vertical axis. Shoulder-elbow joint (art. humeroulnaris).
Classification. Block-shaped (helical) joint, uniaxial.
Structure. The joint is formed by the articulation of the trochlea of the humerus and the trochlear notch of the ulna.
Functions
.
The existing recess on the block allows for a screw motion in the joint with a slight deviation from the midline of the block - flexion and extension around the frontal axis.
Diseases of the acromial joint and their treatment: dislocation, arthrosis, deforming osteoarthritis, rupture
Arthrosis of the AC
joint The anatomy of the AC node is aimed at performing the main function of this part of our body - the supporting one. Under the influence of external negative factors, this functional feature may be impaired. Because of this, the following joint pathologies appear:
Dislocations:
- Occur under the influence of external factors: impacts, injuries, and so on.
Ligament ruptures:
- The appearance of pathology is facilitated by injuries, falls, and sports activities.
- Dislocations of the joint and ruptures of the ligaments usually occur side by side, since displacement of the joint is impossible without violating the integrity of the ligaments.
- Accordingly, if a ligament is broken, then a dislocation follows, and if a dislocation occurs, then there will certainly be a rupture of the ligaments.
Arthrosis, osteoarthrosis:
- Develops from improper treatment of sprains, dislocations and other injuries.
- The cartilage peels off from the bone, spinous bones grow, which entails pain in the joint and the appearance of a local inflammatory process.
In case of dislocations and ruptures of ligaments , complete rest for the joint is recommended, no stress for a month or even more, depending on the severity of the disease. The doctor may also prescribe pain medications, fixative bandages, immobilization with an orthosis, and other conservative treatment.
AC joint arthrosis with cartilage destruction
Important: In rare cases, surgery may be necessary.
Sprains and torn ligaments must be treated immediately. If such pathologies develop into arthrosis , and then, if arthrosis starts, the degree of degeneration will constantly increase, and the pain will only intensify. As a result, joint mobility is limited to the point of contracture. Therefore, it will be difficult for the patient to even move a limb or simply cross his arms. Treatment in this case is only surgical.
Important to know: Inflammation in the form of arthritis is rare, since this node is surrounded by soft tissue and it is almost impossible for infections to penetrate inside the capsule.
On the one hand, the AC node is a simple joint, flat bone and small cartilage. On the other hand, it is a complex structure that plays a huge functional role in our body. Like all other joints, the AC joint should be protected from dislocations, sprains and the development of other diseases, so that there are no health problems in the future.
Arthrosis of the AC joint
Conservative treatment is usually effective for the initial manifestations of AC joint arthrosis. Such treatment consists of resting the shoulder joint, intra-articular injections of various local anesthetics and steroids into the joint cavity, as well as taking NSAIDs orally.
If, during treatment, the pain and swelling syndrome does not stop, there is significant degenerative degeneration of the acromioclavicular joint (articulation) with numerous bone growths (osteophytes) in its area, the issue of surgical treatment is considered.
Various surgical methods have been proposed for the treatment of AC joint pathology. At the present stage of development of medicine, closed, minimally invasive methods using arthroscopy are mainly used.
Faster recovery from the surgical field, low level of infectious complications, excellent cosmetic results - this is not a complete list of the advantages of the arthroscopic minimally invasive method of treating AC joint pathology over previously used open interventions.
It has been proven that arthroscopic treatment of AC joint diseases gives good results.
During surgery, a miniature video camera is inserted into the space under the acromion. The doctor can use the monitor to examine the acromioclavicular joint (articulation) in detail from the inside.
In the area of the AC joint, several small punctures of the skin are additionally formed to introduce mini-instruments into the joint area, with the help of which excess bone growths (osteophytes) can be removed in the right place. Pathologically altered tissues under the acromion, which cause pain when pinched, are also removed.
It is important that during arthroscopic surgery the ligaments stabilizing the clavicle are not damaged.
As noted earlier, surgery to remove altered tissues of the AC joint can be performed either openly or using arthroscopy. Today, all over the world, orthopedic surgeons prefer to perform such operations minimally invasively, using arthroscopy. Only an arthroscope allows the surgeon to work into the joint through very small incisions. Reducing damage to the normal healthy soft tissue surrounding the joint leads to faster healing and recovery after surgery.
Rehabilitation after surgery is usually aimed at reducing pain and swelling in the surgical area. Both painkillers and anti-inflammatory drugs, as well as the use of physical therapy and ice locally, help with this.
After arthroscopic intervention, rehabilitation proceeds faster, the patient gradually begins to work on increasing the range of motion in the shoulder joint, and subsequently on strengthening the muscles surrounding the joint.
Sutures after surgery are usually removed on days 10-12; for several weeks after surgery, a removable orthotic bandage like a scarf may be required.