Acromioclavicular Osteoarthritis
Acromioclavicular Osteoarthritis: Introduction
Osteoarthritis of the acromioclavicular (AC) joint is a common condition that often causes pain in the anterior or superior part of the shoulder, particularly during overhead movements and activities that require the arm to move across the body. The condition is common in middle-aged adults and develops as a result of age-related degeneration of the fibrocartilaginous disc that acts as a cushion between the two bones of the joint.
Degeneration of this disc allows the acromion and clavicle to come into closer contact, creating friction that can lead to pain and inflammation. Pain is usually felt in the anterior or superior shoulder and is often aggravated by lifting the arm overhead or moving it across the body.
Diagnosis is based on a combination of the patient's medical history, clinical examination, imaging such as X-ray and MRI, and sometimes diagnostic local-anesthetic injections to identify the source of pain and confirm involvement of the joint[1]. This can help distinguish AC-joint pain from pain arising from other shoulder structures, such as the rotator cuff.
In many cases, patients are asymptomatic and the condition is discovered incidentally on shoulder X-ray or MRI, often during assessment of another complaint[2]. It is important to note that degenerative changes in the AC joint do not always produce obvious symptoms, and many people may have the condition without significant pain or functional impairment.
Clinically Relevant Anatomy
Acromioclavicular Joint (AC Joint)The acromioclavicular (AC) joint is a synovial joint with a limited range of motion and is the only articular connection between the axial skeleton and the scapula. It connects the distal end of the clavicle with the acromion. The clavicle has a convex surface that articulates with the slightly convex surface of the acromial facet.
The hyaline-cartilage-covered facets of the AC joint are separated by a fibrocartilaginous disc, which in some respects can be compared with the meniscus of the knee. This disc acts as a shock absorber and contributes to joint stability during shoulder movement. Over time, as part of the normal aging process, the fibrocartilaginous disc undergoes degenerative changes and may be almost completely degraded by early adulthood, leaving only fibrous remnants[3]. This degeneration can contribute to clinical symptoms including pain, reduced mobility and stiffness in the AC joint.
Epidemiology
Although AC-joint osteoarthritis is less common than osteoarthritis of joints such as the knee and hip, it remains a relatively common cause of shoulder pain, particularly in older populations. One study found radiographic degenerative changes in the AC joint in approximately 54–57% of older patients. This means that many people may have osteoarthritis in this joint without symptoms. Clinically relevant AC-joint osteoarthritis that causes pain and functional problems is less common than radiographic changes alone[3]. Estimates suggest that AC-joint osteoarthritis accounts for around 20% of shoulder-pain cases, with reported figures ranging from 12.7% to 24%. Symptoms typically begin during the fourth decade of life[4].
Etiology
AC-joint osteoarthritis can be divided into two main types according to the cause of its development.
Primary osteoarthritis: This type develops without a clear underlying cause. It results from long-term loading of the joint and is often seen in people who repeatedly perform upper-body lifting activities, such as heavy overhead lifting. Repeated loading can cause wear of the articular cartilage and progressive degenerative changes over time.
Secondary osteoarthritis: This form results from other underlying factors that impair joint health. It may develop after previous trauma or other diseases such as rheumatoid arthritis. A common cause of secondary AC-joint osteoarthritis is post-traumatic injury, as the AC joint is vulnerable to both direct trauma and repetitive loading. One study reported arthritic symptoms following acute AC-joint injury, including grade I and II sprains, with symptoms observed in 8% and 42% of patients respectively[5].
Diagnosis
Accurate diagnosis of AC-joint pathology is essential for selecting an appropriate treatment plan and avoiding persistent shoulder pain. Diagnosis of AC-joint osteoarthritis requires a thorough history, physical examination, radiographs and, when appropriate, a diagnostic local-anesthetic injection[6].
Diagnostic Imaging
X-ray and MRI provide detailed information about the AC joint and associated pathology. Both can demonstrate degenerative changes, while MRI is more sensitive to soft tissues and may provide additional information about involvement of surrounding structures. X-rays are used primarily to identify bony changes such as irregularity, osteophytes, fractures or narrowing of the joint space that may indicate osteoarthritis.
Ultrasound (US) is also useful in the diagnosis of AC-joint osteoarthritis. It can readily identify inflammatory and structural changes and is therefore commonly used. Ultrasound-guided injection has also become an important diagnostic and therapeutic technique, allowing accurate administration of medications such as local anesthetic to help confirm the diagnosis while providing pain relief[3].
Subjective Assessment
A thorough subjective assessment can identify relevant symptoms and historical factors that support an accurate diagnosis of AC-joint osteoarthritis. Important aspects of the history include:
History of trauma: Previous trauma directly affecting the AC joint, or a fall onto an outstretched arm, may indicate prior injury or contribute to the development of osteoarthritis in the region.
Occupational history: Occupations involving repeated overhead lifting or other strenuous activities that load the AC joint may contribute to the development of AC-joint osteoarthritis.
Sporting activities: Participation in sports that place additional stress on the AC joint, such as weightlifting or rugby, may increase the risk of injury and subsequent osteoarthritis[2].
Symptoms
Patients with AC-joint osteoarthritis often report characteristic symptoms including:
Night pain: Many patients report pain at night, particularly when sleeping on the affected shoulder. This may reflect irritation and degenerative change within the joint.
Popping, clicking or grinding: Patients may describe popping, clicking or grinding sensations in the shoulder during movement, which may indicate degenerative or mechanical changes in the AC joint[7].
Functional Limitations
Patients with AC-joint osteoarthritis commonly experience functional limitations, particularly during resistance exercise:
Difficulty with resistance training: Shoulder positions that place the AC joint under high load or in an extended position can aggravate symptoms, which is common among weightlifters. For this reason, AC-joint osteoarthritis is also known as "weightlifter's shoulder"[8].
Associated Injuries and Complications
AC-joint pathology may also be accompanied by supraspinatus tendon pathology. Osteophytes arising from an arthritic AC joint can contribute to subacromial impingement, potentially worsening shoulder pain and creating a cycle of further irritation and functional impairment[2].
Objective Assessment
Several objective tests can help identify AC-joint osteoarthritis and related pathology and contribute to a more precise diagnosis:
Cross-body adduction test: The test involves flexing the shoulder to 90° and then horizontally adducting the arm across the chest. Reproduction of localized pain over the joint suggests AC-joint involvement.
Restricted Movement: Patients with AC-joint osteoarthritis often retain a relatively full shoulder range of motion, except during specific movements such as cross-body motion, reaching behind the back or overhead movements. These movements typically reproduce pain localized to the AC joint[5].
Localized pain at the top of the shoulder: Pain is commonly localized to the superior shoulder and may be associated with increased tenderness on palpation of the AC joint. Swelling may also be present, particularly with distal clavicle osteolysis[8].
Clinical Pain-Provocation Tests: Pain may also be reproduced in the deltoid region by shoulder flexion to 90° followed by horizontal adduction, or during pressing movements such as the bench press[5]. These tests can indicate pain originating from the AC joint.
Point-tenderness testing and the Paxinos test: The most sensitive tests for AC-joint pain include direct tenderness over the AC joint and the Paxinos test[2]. These tests can help identify the precise location of pain and support confirmation that the AC joint is the pain source.
Resisted tests: The resisted AC-joint extension test may also help identify AC-joint pathology, particularly when pain or restriction is reproduced during testing.
Diagnostic Injection: Another method for confirming AC-joint involvement is injection of local anesthetic directly into the AC joint. Injection of 0.5–2 mL of 1% or 2% lidocaine, or 0.5 mL of 0.25% or 0.5% bupivacaine, should produce a significant reduction in symptoms when the AC joint is the pain source. Persistent pain after injection suggests that symptoms are more likely to arise from another shoulder pathology, such as rotator-cuff disease[5].
Differential Diagnoses
Several conditions may produce symptoms similar to AC-joint osteoarthritis, making differential diagnosis important for appropriate treatment. Common differential diagnoses include:
Calcific tendinopathy: This condition involves deposition of calcium salts within tendons, commonly the rotator cuff. Calcific deposits can cause pain and inflammation, particularly during movement. Symptoms may closely resemble AC-joint osteoarthritis, especially pain during overhead activity.
Glenohumeral osteoarthritis: This involves wear and degeneration of the glenohumeral joint, the main joint of the shoulder. It can also cause pain and reduced range of motion, but should be distinguished from AC-joint osteoarthritis because pain and stiffness are generally localized differently.
Adhesive capsulitis (frozen shoulder): This condition is characterized by shoulder pain and stiffness, particularly when attempting to move the arm away from or around the body. Although pain may be felt near the AC joint, adhesive capsulitis primarily causes global shoulder stiffness and marked restriction of movement.
Rotator-cuff impingement syndrome: Rotator-cuff tendons can become compressed and irritated against the acromion during shoulder movement, producing pain particularly with overhead activity. Although this can resemble AC-joint osteoarthritis, pain and functional restriction are often more pronounced through several directions of arm movement.
Treatment
Treatment of AC-joint pain depends largely on pain intensity and the degree of functional impairment. The goals are to reduce pain, improve function and limit further degeneration. Treatment options may include:
Conservative treatment: Physiotherapy can aim to strengthen the stabilizing muscles of the shoulder and improve mobility. Exercises to reduce stiffness and improve posture may also be helpful.
Pharmacological treatment: Nonsteroidal anti-inflammatory drugs (NSAIDs) may be used to reduce pain and inflammation. In selected cases, corticosteroids may be injected directly into the AC joint to reduce inflammation.
Surgical treatment: If conservative measures fail to provide adequate relief and pain persists or worsens, surgery may be considered. Procedures may include removal of osteophytes or partial resection of the distal clavicle to unload the AC joint. Surgery is generally considered a last resort.
Local-anesthetic and corticosteroid injections: Injections directly into the AC joint may reduce pain and inflammation and can provide meaningful relief in patients with persistent symptoms.
Ergonomic and lifestyle modifications: Avoiding activities that aggravate the condition, such as repeated overhead lifting, can be an important part of treatment. Patients may also benefit from education on ergonomics to reduce excessive loading of the AC joint.
The treatment plan should be individualized according to the patient's symptoms, activity level and response to initial treatment.
Conservative / Non-Surgical Treatment
Conservative management is usually the first-line approach for AC-joint osteoarthritis and combines several strategies to reduce pain, improve function and limit further joint irritation. Treatment varies with symptom severity, but commonly includes:
Local Corticosteroid Injections
Corticosteroid injections into the AC joint may reduce inflammation and provide substantial short-term pain relief. Commonly described options include injections of betamethasone sodium phosphate and acetate or methylprednisolone, with doses of 0.25–0.5 mL of each substance. Injections are typically limited in frequency. Excessive corticosteroid exposure may cause adverse effects such as subcutaneous fat atrophy and dermal thinning around the joint. Although corticosteroid injections may provide useful pain relief, evidence suggests they are not an effective long-term treatment. They may, however, be useful diagnostically when an injection produces significant relief of AC-joint pain.
Activity Modification
An important part of conservative management is modifying activities that place high loads on the AC joint and aggravate pain. This may include avoiding repetitive movements such as push-ups, dips, flyes and bench pressing. Repeated overhead loading, common in weightlifting and some sports, may also need to be reduced until symptoms improve and return to activity is appropriate. This can help limit further irritation and support long-term symptom control.
Physiotherapy and Pain Management
Physiotherapy plays an important role in conservative management of AC-joint osteoarthritis. Treatment aims to strengthen the muscles surrounding the shoulder, improve movement quality and reduce pain. Specific exercises may focus on shoulder stability and flexibility to reduce stress on the AC joint during activity.
Use of oral analgesic medications such as NSAIDs may also help reduce inflammation and pain, particularly during an acute symptomatic phase.
Long-Term Management
Conservative management can be effective for short-term symptom control, but more invasive treatment may be considered in patients with chronic or persistent pain despite comprehensive non-surgical care.
Physiotherapy Treatment of AC-Joint Osteoarthritis
Physiotherapy for AC-joint osteoarthritis should be individualized according to the severity of osteoarthritis, pain level and functional limitations. A comprehensive approach addressing pain, movement, strength and posture is important for achieving the best possible resu
lts.
Impairment-Based Treatment
Pain relief using electrotherapy and manual therapy
Manual therapy and electrotherapy such as TENS (transcutaneous electrical nerve stimulation) may be used to reduce pain and promote relaxation of the muscles around the AC joint. These treatments may provide temporary relief and help patients perform necessary exercises with less discomfort.
Maintaining active range of motion (ROM) and strengthening shoulder stabilizers
Maintaining active shoulder movement is important. Exercises may be used to improve flexibility and stability and to strengthen the muscles that support the scapula, which are essential for overall shoulder function.
Strengthening the rotator cuff
The rotator cuff plays an important role in shoulder stability and force transfer through the upper limb. Strengthening these muscles may reduce stress on the AC joint, which can decrease pain and improve function.
Postural correction
Another important component of treatment is improving posture, particularly by stretching the pectoral muscles and strengthening the scapular retractors. This can help reduce unnecessary stress on the AC joint.
Evidence for Treatment
A prospective cohort study by Harris et al. in 2012 investigated the effect of manual therapy on pain associated with non-acute AC-joint pain. The study reported statistically significant and clinically meaningful improvements in both functional and clinical outcome measures at 4 weeks and 6 months following a course of manual therapy.
Study protocol:
Patients attended 30-minute clinical treatment sessions twice weekly for 3 weeks.
The primary treatment techniques included passive accessory glides of the distal clavicle in different physiological positions selected to make treatment less painful.
At the 4-week follow-up, patients were given a home exercise program consisting of strengthening exercises and exercises to maintain range of motion.
Results:
The study found significant and clinically meaningful improvements in all outcome measures at 4 weeks and 6 months. These findings suggest that manual therapy may be useful for managing pain and improving function in patients with AC-joint osteoarthritis.
Conclusion
Physiotherapy can be effective for patients with AC-joint osteoarthritis, particularly when treatment is individualized. Manual therapy, activity modification, targeted strengthening and flexibility exercises, and postural improvement may all help reduce pain and improve shoulder function. Evidence supports manual therapy as a potentially effective method for improving both function and clinical outcomes in this population.
Surgical Treatment of AC-Joint Osteoarthritis
Surgical treatment is generally considered only after conservative treatment has failed and the patient continues to experience persistent symptoms affecting daily activities despite at least six months of intensive non-surgical management.
Distal Clavicle Excision (DCE)
Distal clavicle excision, also known as the Mumford procedure, is a surgical approach commonly used for persistent AC-joint pain. The procedure was first described as an open surgical technique in 1941 but is now commonly performed arthroscopically.
The aim of the procedure is to create a gap between the acromion and clavicle by resecting bone from the distal end of the clavicle without compromising joint stability.
Complications of Open Surgery
Although arthroscopic techniques have substantially reduced complication rates, complications after open surgery have been reported in 0% to 64% of cases. Potential complications include:
Infection
Heterotopic ossification (abnormal bone formation)
Joint instability
Suprascapular neuropathy (nerve injury)
Fracture of the distal clavicle
Anesthesia-related complications. Other complications may include weakness of the deltoid and trapezius muscles and instability of the clavicle.
Long-Term Effects and Caution
A study by Eskola et al. examined long-term outcomes after distal clavicle excision (DCE) for AC-joint pain. Nearly one third of patients had poor long-term outcomes, and the authors cautioned against DCE in patients with high functional demands on the shoulder, such as athletes or people who depend heavily on shoulder function for work. This highlights the importance of considering functional demands before selecting this treatment.
Future Directions
A scoping review published in 2017 highlighted a substantial lack of primary evidence regarding treatment options and pathways for AC-joint osteoarthritis. The review found no direct comparisons between arthroscopic surgery, open surgery, steroid injections and rehabilitation programs for AC-joint pain.
This makes it difficult to determine the precise source of shoulder pain and evaluate treatment effectiveness, because many patients with AC-joint pathology also have concurrent shoulder conditions such as rotator-cuff disease.
Comprehensive Treatment Approach
The review also emphasized the need for appropriate assessment and a comprehensive approach to shoulder-pain management. This may include lifestyle modification, education, medical treatment, physiotherapy and, when necessary, surgery followed by appropriate rehabilitation. Such a holistic approach helps ensure that treatment is individualized and effective.
Sources:
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Chaudhury S, Bavan L, Rupani N, Mouyis K, Kulkarni R, Rangan A, Rees J. Managing acromio-clavicular joint pain: a scoping review. Shoulder & Elbow. 2018 Jan;10(1):4-14.
Precerutti M, Formica M, Bonardi M, Peroni C, Calciati F. Acromioclavicular osteoarthritis and shoulder pain: a review of the role of ultrasonography. Journal of Ultrasound. 2020 Sep;23(3):317-25. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7441096/
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Buttaci CJ, Stitik TP, Yonclas PP, Foye PM. Osteoarthritis of the acromioclavicular joint: a review of anatomy, biomechanics, diagnosis, and treatment. American journal of physical medicine & rehabilitation. 2004 Oct 1;83(10):791-7.
Vaishya R, Damor V, Agarwal AK, Vijay V. Acromioclavicular arthritis: A review. Journal of arthroscopy and joint surgery. 2018 May 1;5(2):133-8.
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