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Ac Joint Arthritis

Ac Joint Arthritis is a common source of shoulder pain that is often neglected by clinicians and orthopedic surgeons. It is the most common disorder of the acromioclavicular joint.

Ac Joint Arthritis Causes

Acromioclavicular Joint Osteoarthritis may arise from a number of pathologic processes, including primary (degenerative), posttraumatic, inflammatory, and septic arthritis:

Post traumatic Osteoarthritis

Although many patients become asymptomatic with the passage of time, symptoms related to a previous AC joint injury may reappear in the form of post-traumatic osteoarthritis many years after the initial injury. It is presumed that nonoperative treatment of the initial injury (or non- treatment when patients do not seek medical attention) allows repetitive micromotion and elevated shear stresses to occur across articular surfaces during shoulder motion until joint destruction leads to the development of pain.

In addition, many patients with chronic AC joint dislocations display evidence of scapular dyskinesis which may increase the risk for other conditions such as rotator cuff impingement. Therefore, these patients should also undergo a complete evaluation of scapular motion throughout the course of their treatment, especially in those with chronic dislocations who complain non-AC joint-related shoulder pain.

progression of posttraumatic AC joint osteoarthritis
Illustration showing the progression of posttraumatic Ac Joint Arthritis. The initial articular cartilage injury creates a catabolic biochemical environment that is exacerbated by repetitive micromotion. Uneven articular surfaces create stress risers that are subjected to elevated shear stresses when motion occurs, thus accelerating cartilage degeneration. The joint may eventually become eburnated with characteristic radiographic findings of osteoarthritis such as a narrowed joint space, subchondral cysts, subchondral sclerosis, and osteophytosis.

Repetitive Microtrauma

Repetitive microtrauma is also an important cause of chronic AC joint Osteoarthritis and, similar to post-traumatic AC joint osteoarthritis, is mostly attributed to abnormally high stresses placed upon the distal clavicle which increases the rate of bone turnover in the area.

As a result of this remodeling process, joint surfaces become incongruent and the articular cartilage degenerates due to abnormally elevated contact stresses and shear forces. Distal clavicle osteolysis most commonly occurs in those who regularly perform bench press exercises, possibly as a result of repeated maximal contraction of the clavicular head of the pectoralis major muscle which may lead to the development of small stress fractures within the subchondral bone of the distal clavicle and subsequent bony remodeling.

Although this diagnosis is difficult to distinguish from posttraumatic AC joint osteoarthritis due to similar symptomatology, physical examination findings, and imaging findings, surgical resection of the AC joint is usually indicated for either case when nonoperative treatment fails to relieve the patient’s symptoms.

AC Joint Osteoarthritis
Ac Joint Arthrosis

Advancing Age

Acromioclavicular Joint Osteoarthritis Osteoarthritis can also develop as an atraumatic, age-related phenomenon that is most often associated with degeneration of the intra-articular disk which occurs with normal aging.

Several authors have suggested that the intra-articular disk is almost always nonfunctional beyond 40 years of age. Symptomatic disk degeneration is usually observed in patients over 50 years of age; however, the degenerative process may begin during adolescence and it is unknown when symptoms begin to occur, if they occur at all.

In fact, a study by Stein et al. found that up to 93 % of asymptomatic patients over 30 years of age had MRI evidence of AC joint osteoarthritis. Similar results were found by Needell et al. in which 75 % of asymptomatic volunteers had Ac Joint Arthritis as evidenced by MRI.

Ac Joint Arthrosis
Ac Joint Arthrosis on MRI

Inflammatory Arthropathies

Similar to other synovialized joints, the AC joint is also susceptible to inflammatory arthropathies such as rheumatoid arthritis and psoriatic arthritis along with crystal deposition diseases such as gout and pseudogout.

Patients with inflammatory arthropathies typically present with pain over the AC joint in the presence of warmth, redness, swelling, and fever. Infectious etiologies related to the AC joint, such as osteomyelitis and septic arthritis, can occur due to hematogenous spread or direct inoculation (such as during a joint injection) and may be related to immunocompromised. Infection should always be ruled out before any treatment interventions are undertaken.

See Also: Clavicle Anatomy

Synovial Cysts

Synovial cysts can occur near the AC joint and may be associated with various AC and glenohumeral joint arthritides along with massive rotator cuff tears. Although painless, these cysts can be alarming for some patients since the lesion may enlarge very rapidly.

According to Hiller et al., a type 1 cyst is isolated to the AC joint and probably involves overproduction of synovial fluid in response to degenerative changes. Type 2 cysts occur as a result of anterosuperior humeral head migration (as in some cases of massive rotator cuff tears) which produces damage to the posteroinferior aspect of the AC joint capsule and the anterosuperior glenohumeral joint capsule.

With concomitant synovial fluid overproduction by the glenohumeral joint as a result of cuff arthropathy, synovial fluid can then transfer between glenohumeral and AC joint compartments, thus potentially producing an AC joint synovial cyst.

Lesions should be illuminated to confirm its cystic appearance before aspiration since solid tumors in this area have been reported in the literature. These painless cysts may fluctuate in size over a period of time and, especially in cases of cuff arthropathy, cysts may reappear after aspiration since due to the existence of a persistent communication tract between the AC and glenohumeral joints.

Synovial cyst involving the AC joint
(A) Synovial cyst involving the AC joint. (B) Distal clavicle hypertrophy. These entities can be differentiated by palpation and illumination.
Acromioclavicular Joint Synovial Cysts
Acromioclavicular Joint Synovial Cysts

Physical Examination

In contrast to acute injuries, chronic pain related to the Acromioclavicular Joint Osteoarthritis can have numerous etiologies and determining the correct diagnosis can sometimes be difficult.

The spectrum of AC joint disease can produce symptoms that often overlap with other common shoulder conditions. While some patients may present with global, diffuse shoulder pain and dysfunction, others may only have mild point tenderness located precisely at the AC joint.

In addition, physical examination findings can also be confusing since many provocative testing maneuvers designed for other types of pathologies can induce AC joint pain. However, motion-dependent AC joint pain is mostly induced by scapular motion when the humerus is either extended or elevated above approximately 90°. Thus, patients who experience pain mostly during simultaneous scapular motion are more likely to have AC joint pathology than patients who experience pain throughout the entire range of motion. Possible exceptions include those with inflammatory or infectious conditions in which AC joint pain is not motion-dependent.

Perhaps one of the more important methods used in the physical diagnosis of AC joint arthritis is simple observation of the patient’s shoulders. Although there is a wide range of variation in AC joint anatomy, comparison of the overall contour of each AC joint can often provide a helpful hint.

Although not diagnostic, relative prominence of one AC joint relative the other may direct the clinicians towards a more thorough examination of the AC joint, especially if the prominence is located on the symptomatic side. As mentioned above, there are numerous potential causes of a prominent AC joint such as osteoarthritis, synovial cysts, tumors, chronic dislocations, and many others and therefore may necessitate full examination and diagnostic imaging.

Special Tests for AC Joint include:

  1. Cross-Body Adduction Test
  2. Distal Clavicle Manipulation
  3. Paxinos Test
Distal Clavicle Manipulation
Distal clavicle manipulation. The examiner places one hand over the lateral shoulder to stabilize the upper torso and uses the fingers and thumb of the other hand to grasp the mid-shaft of the clavicle. When instability is present, the distal clavicle can then be translated anteriorly, posteriorly, superiorly, and/or inferiorly.
Paxinos test
Paxinos test. The examiner places one hand over the patient’s shoulder with the thumb over the scapular spine and the fi ngers over the distal clavicle. The scapula and the clavicle are gently squeezed together, thus translating the clavicle posteriorly relative to the acromion

Deferential Diagnosis

Before making the physical diagnosis of a chronic AC joint arthritis, it is important to rule in or out other potentially coexistent conditions that may contribute to the patient’s pain and dysfunction:

  • Pain associated with rotator cuff disease is perhaps the most common contributor and may be perceived by the patient as involving the superior aspect of the shoulder. Impingement signs may also be positive since all of these tests involve overhead motion which requires motion to occur across the AC joint. While pain related to rotator cuff disease and the AC joint often occur simultaneously, it is important to determine which condition is the primary instigator since the treatment options for each can vary significantly.
  • SLAP tears are also commonly identified in patients with AC joint pain and may be related to a previous traumatic injury, such as an AC joint dislocation, for which the patient has developed symptomatic post-traumatic osteoarthritis. The quality and distribution of pain related to SLAP tears frequently overlaps that of AC joint pain which can therefore complicate the diagnosis.
  • Patients with cervical spine diseases, such as zygoapophyseal joint degeneration and/ or nerve root irritation, may also complain of superior shoulder pain, however, this type of pain is often dependent on the position of the neck and is usually localized to the superior border of the trapezius muscle. Spurling’s test, among other provocative cervical spine maneuvers, can be used to successfully differentiate between shoulder pain and neck pain.

Ac Joint Arthrosis Treatment

Initial nonoperative Treatment of Ac Joint Arthrosis is aimed at relieving pain and restoring function. Typical treatments include:

  1. Anti-inflammatory medications,
  2. physical therapy,
  3. Steroid AC Joint Injection.
See Also: AC Joint Injection

Patients who continue to exhibit symptoms after appropriate nonsurgical treatment may be candidates for operative resection of the distal clavicle through either open or arthroscopic techniques.

Acromioclavicular Joint


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