Orthopaedic Surgery - Acromioclavicular Joint Arthritis

Basics

Acromioclavicular joint arthritis is the most common disorder affecting the acromioclavicular joint (ACJ). Degenerative changes typically begin during the third or fourth decade of life and become increasingly common with advancing age.

Degeneration of the ACJ is more frequent than osteoarthritis of the glenohumeral joint. The ACJ is formed by the distal clavicle articulating with the acromion, and a small fibrocartilaginous disc is normally present between the opposing articular surfaces.

ACJ arthritis may occur as an isolated degenerative condition, as part of an inflammatory arthropathy, or together with other painful shoulder disorders. Frequently associated conditions include rotator cuff tears, biceps tendinopathy, and adhesive capsulitis.

The condition is particularly common in individuals who repeatedly load the shoulder overhead, including manual laborers, weight lifters, and overhead athletes.

General Prevention

Prevention is difficult because the exact cause of ACJ osteoarthritis is multifactorial and not completely understood.

Degeneration appears to result from a combination of genetic susceptibility and environmental exposure, particularly repetitive mechanical loading.

In patients with rheumatoid arthritis, early and effective control of systemic inflammatory disease can reduce the severity and progression of ACJ involvement.

Epidemiology

Manual laborers have an increased prevalence of ACJ arthritis. The likelihood of degeneration appears to rise with the number of years spent performing manual work.

There may also be a weak association with prolonged exposure to vibration during occupational activity.

The frequency of ACJ degeneration increases substantially with age.

Incidence

The true incidence of symptomatic ACJ arthritis is uncertain because radiographic degeneration is common even in individuals without shoulder pain.

Anatomical studies have demonstrated degenerative ACJ changes in approximately 11.6% of cadaveric specimens, with increasing prevalence in older individuals and no significant difference between males and females or between the right and left sides.

Ultrasound studies have shown evidence of ACJ osteoarthritis in approximately 65% of asymptomatic men between 40 and 79 years of age.

ACJ involvement is also common in inflammatory disease, with arthritis of the joint reported in approximately 59% of patients with rheumatoid arthritis.

Risk Factors

Important risk factors include advancing age, previous ACJ separation, prior distal clavicle fracture, manual labor, and participation in sports involving repetitive shoulder loading.

Patients with spinal cord injury have been reported to have a substantially increased risk of severe ACJ degeneration, possibly up to four times that of the general population.

Certain anatomical features may also predispose to ACJ pathology, including a type III acromion and a relatively narrow supraspinatus outlet.

Genetics

Osteoarthritis has a familial tendency, suggesting a genetic contribution to susceptibility.

However, the specific genes involved in the development of ACJ osteoarthritis remain poorly defined.

Genetic predisposition likely interacts with age, mechanical loading, occupational exposure, and previous injury.

Etiology

Primary osteoarthritis of the ACJ probably develops through an interaction between genetic susceptibility and cumulative mechanical stress.

Repetitive heavy lifting, weight training, and overhead sporting activities can accelerate articular cartilage degeneration.

In rheumatoid arthritis, synovial inflammation leads to pannus formation and release of destructive inflammatory mediators that progressively damage the articular cartilage and subchondral bone.

Osteonecrosis and Post-Traumatic Arthritis

Avascular necrosis of the distal clavicle may cause subchondral bone death, structural collapse, and secondary arthritis.

Post-traumatic arthritis may occur after a distal clavicle fracture. Irregular healing or joint incongruity can alter load distribution across the ACJ and lead to abnormal wear.

Similarly, previous acromioclavicular joint separation can damage cartilage and bone while also producing ligamentous laxity or soft-tissue contracture. These changes alter joint mechanics and may eventually result in degenerative arthritis.

Associated Conditions

ACJ arthritis frequently coexists with other abnormalities of the shoulder.

Associated conditions include distal clavicle osteolysis and ACJ cyst formation.

Rotator cuff tears have been reported in a high proportion of patients with symptomatic ACJ arthritis, while labral pathology and biceps tendon abnormalities may also occur.

Reported associations include approximately 81% with rotator cuff tears, 33% with labral tears, and 22% with biceps tendon abnormalities in selected patient populations.

Diagnosis

Signs and Symptoms

Pain may be sharply localized directly over the ACJ or may present less specifically as aching involving the superior shoulder or adjacent neck region.

Symptoms are commonly aggravated by overhead activity, reaching across the body, lifting, or weight-bearing through the upper extremity.

Patients may also experience nocturnal pain, particularly when lying on the affected shoulder.

Physical Examination

Patients frequently identify the ACJ itself as the precise source of pain.

Shoulder range of motion is usually preserved, with both active and passive motion remaining relatively intact unless another shoulder disorder is present.

Both shoulders should be inspected and compared for asymmetry, deformity, swelling, or prominence of the distal clavicle.

Palpation

The ACJ is typically tender to direct palpation in symptomatic patients.

However, firm pressure over the joint may also cause discomfort in asymptomatic individuals. Tenderness should therefore be compared with the opposite shoulder and correlated with the patient’s usual symptoms.

Localized pain that reproduces the patient’s typical complaint is more clinically meaningful than tenderness alone.

Cross-Body Adduction Test

The cross-body adduction test is commonly used to provoke pain from the ACJ.

The shoulder is flexed to approximately 90° and then brought horizontally across the chest into adduction.

Reproduction of focal pain directly over the ACJ is considered a positive finding and supports the diagnosis of ACJ pathology.

Active Compression Test

The active compression test may also help identify ACJ pathology.

The arm is forward flexed to approximately 90° and adducted slightly across the body, usually by about 10°.

Resistance is applied while the forearm is pronated, and the maneuver is then repeated with the forearm supinated.

Pain localized to the ACJ during resisted pronation that improves or disappears with resisted supination is considered a positive test.

Imaging

Plain Radiographs

Standard shoulder radiographs are usually sufficient for initial evaluation of the ACJ.

Typical degenerative findings include joint-space narrowing, marginal osteophytes, subchondral sclerosis, cyst formation, and irregularity of the distal clavicle or acromial surface.

However, radiographic findings must be interpreted together with the clinical examination because degenerative changes are common in asymptomatic individuals.

Zanca View

The Zanca view provides a particularly useful radiographic assessment of the ACJ.

This projection uses approximately 15° of cephalad angulation, allowing improved visualization of the joint space and distal clavicle compared with routine shoulder radiographs.

It can help demonstrate subtle joint-space narrowing, osteophytes, distal clavicular changes, and other ACJ abnormalities.

Limitations of Radiographs

Radiographic appearance does not always correlate with symptoms.

Some patients have substantial degenerative changes on imaging but remain completely asymptomatic.

Conversely, patients may have significant ACJ pain despite apparently normal or only mildly abnormal radiographs because cartilage wear may not always be visible on routine imaging.

Clinical correlation is therefore essential.

MRI

MRI is not routinely required when isolated ACJ arthritis is clinically obvious.

It becomes useful when the diagnosis is uncertain or when additional shoulder pathology is suspected.

In symptomatic ACJ arthrosis, MRI may demonstrate edema within the distal clavicle or adjacent acromion, which can support the diagnosis.

MRI is particularly helpful for identifying associated rotator cuff tears, labral pathology, biceps tendon disease, or other soft-tissue disorders.

Ultrasonography

Ultrasound may demonstrate osteophytes, narrowing of the ACJ, capsular abnormalities, and associated soft-tissue pathology.

It can also be used to guide needle placement for joint aspiration or corticosteroid injection, improving the accuracy of intra-articular procedures.

Pathological Findings

Histopathological examination is not routinely required for the diagnosis of ACJ arthritis.

Diagnosis is usually established clinically with the assistance of imaging and, when necessary, a diagnostic injection.

Differential Diagnosis

Important conditions that may mimic ACJ arthritis include ACJ infection, osteonecrosis of the distal clavicle, distal clavicle osteolysis, and ACJ cyst formation.

Crystal arthropathies such as gout or calcium pyrophosphate deposition disease should also be considered in appropriate patients.

Other shoulder disorders that can produce similar symptoms include superior labral anterior-posterior (SLAP) tears, rotator cuff tears or tendinitis, and biceps tendinopathy.

Treatment

General Measures

Initial management is usually nonoperative.

Treatment should focus on reducing painful mechanical loading while maintaining shoulder mobility and function.

A diagnostic injection of local anesthetic, such as lidocaine, into the ACJ may be useful when the source of pain is uncertain.

Significant temporary pain relief following injection supports the ACJ as the primary pain generator.

Activity Modification

Patients should reduce or temporarily avoid activities that reproduce pain.

Examples include heavy bench pressing, repetitive overhead lifting, cross-body loading, and sleeping directly on the affected shoulder.

Modification rather than complete cessation of activity is usually appropriate.

Ice and Heat

Ice may be helpful during painful inflammatory exacerbations, particularly after activity.

Heat can sometimes reduce stiffness and improve comfort before exercise or rehabilitation.

The choice depends largely on patient preference and symptom response.

Physical Therapy

Physical therapy has a less clearly established role in isolated ACJ arthritis than in many other shoulder disorders.

Because the degenerative process is localized to a small joint, therapy cannot reverse the underlying cartilage damage.

Nevertheless, selected patients may benefit from a short course of rehabilitation aimed at optimizing shoulder mechanics, maintaining motion, and strengthening the surrounding musculature.

Physical therapy may be particularly valuable when ACJ arthritis coexists with rotator cuff weakness, scapular dysfunction, or other shoulder abnormalities.

Medication

First-line pharmacological treatment commonly includes nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen.

These medications may reduce pain and improve tolerance of daily activities.

Medication should generally be combined with activity modification rather than used as the sole treatment.

Corticosteroid Injection

Injection of corticosteroid into the ACJ can provide both diagnostic and therapeutic benefit.

A local anesthetic is commonly combined with corticosteroid.

Pain relief may be temporary, but injections can reduce inflammation and improve shoulder function in appropriately selected patients.

Repeated injections should be used cautiously, particularly if only brief benefit is obtained.

Surgery

Surgical treatment is generally reserved for patients with persistent symptoms despite an adequate trial of nonoperative management.

The standard operative treatment is distal clavicle excision, also known as distal clavicle resection.

The procedure removes a small portion of the distal clavicle to eliminate painful bone-to-bone contact while preserving overall shoulder function.

Open Distal Clavicle Excision

Distal clavicle excision may be performed using an open surgical approach.

The distal portion of the clavicle is resected while attempting to preserve the stabilizing structures of the ACJ.

Careful repair of the deltotrapezial fascia is important because inadequate closure may contribute to weakness, deformity, or postoperative pain.

Arthroscopic Distal Clavicle Excision

Arthroscopic resection can achieve the same basic goal through a minimally invasive technique.

Potential advantages include smaller incisions, reduced soft-tissue disruption, and the ability to assess and treat associated intra-articular or subacromial shoulder pathology during the same procedure.

Appropriate resection is essential because insufficient bone removal may leave persistent contact and pain, whereas excessive resection can produce instability.

Follow-Up

Patients managed conservatively should be reviewed periodically, often at intervals of approximately 3–4 months, depending on symptom severity and treatment response.

At follow-up, pain, function, range of motion, activity tolerance, and associated shoulder pathology should be reassessed.

Patients whose symptoms remain localized and disabling despite conservative treatment may be considered for surgical management.

Postoperative Care

After distal clavicle excision, a sling is commonly provided for comfort during the early postoperative period.

Active shoulder range-of-motion exercises can generally begin as pain permits.

Rehabilitation is advanced progressively according to wound healing, pain, strength, and the presence of any additional procedures performed during surgery.

Prognosis

The prognosis is generally favorable.

Intra-articular ACJ injections can provide short-term pain relief and may improve shoulder range of motion, although the duration of benefit varies considerably among patients.

Both open and arthroscopic distal clavicle excision have been associated with good clinical outcomes when the diagnosis is accurate and an adequate but not excessive amount of bone is removed.

Factors Affecting Outcome

Surgical results may be less predictable in patients involved in workers’ compensation claims, ongoing litigation, or very heavy manual occupations.

Persistent symptoms may also occur when associated shoulder disorders are not recognized before surgery.

Rotator cuff, biceps, labral, and other shoulder abnormalities should therefore be evaluated and treated when clinically appropriate.

Complications

The most common postoperative problem is persistent pain.

One important cause is inadequate distal clavicle resection, leaving residual contact between the clavicle and acromion.

Excessive resection or overly aggressive disruption of the surrounding ligaments may instead produce ACJ instability.

Other Surgical Complications

Additional complications include infection, postoperative stiffness, fracture, complex regional pain syndrome, and heterotopic ossification.

Regrowth or reossification of the distal clavicle may occasionally recreate painful contact.

Following open surgery, inadequate repair of the deltoid or deltotrapezial fascia may cause deltoid dehiscence, weakness, and persistent discomfort.

Patient Monitoring

Patients undergoing nonoperative treatment should be reassessed regularly to determine whether symptoms are improving and whether additional investigations or interventions are needed.

After surgery, monitoring should include wound healing, pain, shoulder motion, strength, ACJ stability, and return to functional activity.

The sling is used primarily for comfort, and active range of motion can generally be advanced as pain allows.