Acromioclavicular joint instability and osteoarthritis

Ross A. Hauser, MD, Danielle R. Steilen-Matias, MMS, PA-C

Acromioclavicular joint osteoarthritis is a degenerative disease where the articular cartilage lining of the Acromioclavicular joint bones wears out over time.  In this condition, there is shoulder instability causing grinding and pain.

The shoulder joint is a juncture of three bones, the scapula (shoulder blade), the humerus (upper arm bone), and the clavicle (collarbone). The scapula and the clavicle meet to form the top or roof of the shoulder and is called the acromion. The joint where the acromion and the clavicle join is the Acromioclavicular joint or AC joint. Acromioclavicular (AC) joint osteoarthritis can develop as a result of chronic shoulder dislocation or normal wear and tear in the aging patient with heavy shoulder rotational loads in sports or work.

This combination of shoulder structures and the stress put on them will often manifest a patient diagnosed with acromioclavicular joint osteoarthritis as having many other challenges such as subacromial bursitis, rotator cuff tendinopathy, PASTA (partial articular supraspinatus tendon avulsion) rotator cuff lesion, SLAP tear, the aforementioned “old” acromioclavicular joint separations (some with surgical correction history) with some bone spurs.

Dynamic Digital Radiography

Watching a moving x-ray reveals the movement of the entire shoulder including the acromioclavicular joint, the sternoclavicular joint, and the scapula. This technology allows our clinicians to see the internal movements of a patient’s shoulder, especially those causing pain.

Article outline:

Part 1: Acromioclavicular joint instability

  • Doctors need to pay attention to the shoulder ligaments as a source of acromioclavicular joint instability.

Part 1: Acromioclavicular joint instability

The acromioclavicular joint contribution to your shoulder’s range of motion is to get your arm above your head. It also distributes the weight of the arm to the rest of the body. It is therefore not surprising that weight lifters and wrestlers who frequently lift large amounts of weights have significant incidences of AC joint sprains.

Tremendous weight or forces not only injure the AC joint but are transmitted down the clavicle to the sternoclavicular (SC) joint, which can also be sprained or dislocated. There is a direct correlation between the amount of weight lifted and the weight that is transmitted throughout the AC and SC joints. The greater the weight lifted, the greater the impact throughout the AC joint and, ultimately, the SC joint.

  • The sternoclavicular joint is a very difficult joint to dislocate, however, it can play a role in chronic shoulder dislocations.
  • One of the unrecognized problems of shoulder dislocation is that its causes can be widespread. A weakened sternoclavicular joint can create instability problems that extended throughout the chest and into the shoulder.

The pain gets worse when the arm is extended across the chest as this motion compresses the joint, or when lifting.

During the early stages, AC joint arthrosis (bone spur-fusion) usually manifests itself with tenderness and pain in the front of the shoulder around the joint. The pain gets worse when the arm is extended across the chest as this motion compresses the joint, or when lifting. A vague pain may be felt in the shoulder, the neck, and the front of the chest. The affected joint may also be disproportionate to the uninjured joint and may snap or click when used.

The acromioclavicular (AC) joint is one of the unsung heroes of the body. It is formed by the distal clavicle and medial facet of the acromion. (The end of the collar bone and that portion of the shoulder blade that meets to form the point of the shoulder). Interposed in the joint is a fibrocartilaginous disc, and the joint is covered by a capsule.

The acromioclavicular joint becomes injured or dislocated when a large force is applied to the acromion when the arm is in an adducted position, for example, during a wrestling takedown or a tackle in football.

The acromioclavicular joint is stabilized by three ligaments:

  • Acromioclavicular ligament,
  • Inferior Acromioclavicular Ligament
  • Superior Acromioclavicular Ligament.
  • A fourth ligament – the Coracoacromial Ligament is a strong triangular band that serves to prevent the upward dislocation of the shoulder (glenohumeral) joint.

A January 2023 paper led by Dr. Ausberto Velasquez Garcia of the Mayo Clinic and the Department of Orthopedic Surgery, Clinic University of the Andes in Chile, (10) assessed the stress and strain pattern in the ligaments of the acromioclavicular joint using a quasi-static model (or robotic device). The findings were: The coracoclavicular ligament complex (the ligaments that hold the scapula and clavicle together and prevent separation during complex shoulder movements) demonstrated a high stress-strain concentration during simulated passive shoulder abduction (lifting the arm upwards from an outstretched side position). Additionally, it was shown that the acromioclavicular ligament plays an important role in joint restraint during passive horizontal adduction (arm at shoulder length and moving from left to right and right to left) . . .”

In brief, moving the outstretched arm relies on specific ligaments to hold it in place.

Doctors need to pay attention to the shoulder ligaments as a source of acromioclavicular joint instability

Doctors at the Autonomous University of Barcelona writing in the Journal of Orthopaedics and Traumatology examined the use of surgery for acromioclavicular joint instability. What they found was a very strong need to pay attention to the shoulder ligaments.

“Several surgical strategies for the management of patients with chronic and symptomatic acromioclavicular joint instability have been described. The range of possibilities includes anatomical and non-anatomical techniques, open and arthroscopy-assisted procedures, and biological and synthetic grafts, (for ligament reconstruction).

Surgical management of chronic acromioclavicular joint instability should involve the reconstruction of the torn ligaments because it is accepted that from three weeks after the injury, these structures may lack healing potential.”(10)

In March 2020, (11) research lead by the Steadman Philippon Research Institute and published in the journal Orthopedic research and reviews also suggested that the shoulder ligaments play an important role in future dislocations

“Whereas the majority of acromioclavicular joint dislocations can be treated nonoperatively with a trial of immobilization, pain medication, cryotherapy, and physiotherapy, there are patients that do not respond well to conservative management and may require surgical treatment. Identifying and treating these patients according to the type and chronicity of AC joint dislocation is paramount. To date, a myriad of surgical techniques have been proposed to address unstable AC joint dislocations and are indicative of the uncertainty that exists in optimal management of these injuries. Historically research has focused on the restoration of the coracoclavicular ligament complex. However, recently the importance of the acromioclavicular capsule and ligaments has been emphasized.

This paper concentrated on ligament reconstruction as a vital part of shoulder surgery: In this regard, the researchers noted: “Treating acute and chronic acromioclavicular joint injuries is still a challenging task for orthopedic surgeons. Considering these injuries mostly affect younger patients, long-term consequences involving cosmesis and shoulder dysfunction are not yet well understood, and therefore must be anticipated. The myriad of existing (surgical) techniques is indicative of the uncertainty regarding this topic and a gold standard has not yet been determined. However, when diagnosed correctly and treated accordingly, the results are overall satisfactory.”

Conservative management and surgery for acromioclavicular joint osteoarthritis

Over 160 different surgical techniques described in the literature for acromioclavicular joint injury. Do any of them work? Ask the surgeons.

In the May 2019 edition of the medical journal Arthroscopy (13) researchers from the University Hospital Regensburg and Technical University of Munich in Germany made these observations regarding the confusion that surgery brings to acute acromioclavicular joint injury and the importance of treating and repairing ligaments.

“Over the past decade, the interest in acromioclavicular (AC) joint research has experienced a revolutionary increase. Biomechanical and anatomic studies have been carried out to investigate and obtain a better understanding of the function of this joint. The reason for this huge investigational effort is the fact that we do not have any gold standard for the treatment, diagnosis, or follow-up of patients with acute or chronic AC joint injuries.

This is reflected by the huge number of over 160 different surgical techniques described in the literature. . . Because of this wide variety, it is hard and nearly impossible to compare clinical data.

Within the past 5 years, we have focused not only on the vertical instability but also, more and more, on the horizontal instability and tried to understand the rotational component of this joint with the importance of scapulothoracic motion (very simply the ability to raise your shoulders as in shrugging your shoulders or the ability to reach out with your arm and pull something back or away from you).”

The researchers of this editorial concluded that: “We have changed our practice in the past few years in line with the newly derived data, by addressing the coracoclavicular ligaments as well as the AC capsule to restore horizontal and vertical stability but also allow for physiological rotation and movement.”

Simply, whatever repair you decide on, it is best to try to achieve nature’s original design. Something that many surgeries cannot do.

Danielle R. Steilen-Matias, MMS, PA-C discusses AC Joint injury.

Video summary points:

  • The usual treatment for this injury is a figure-eight splint to keep the joint immobile while the healing process occurs. While the initial immobilization may relieve pain, the weakening of the ligaments will occur if the immobilization continues indefinitely.
  • Physical therapy and an exercise program may restore strength and function to the shoulder, but the injured ligaments may continue to grind, pop, click, and cause pain, especially with overhead activities and when reaching across the chest.

Because these activities put a strain on the ligaments, the surrounding muscles may go into spasm and become chronically painful, inhibiting the ability of the patient, often an athlete, from using the shoulder normally.

Another standard practice is to inject steroids into the shoulder or to prescribe anti-inflammatory medications. However, in the long run, these treatments do more damage than good. Cortisone shots and anti-inflammatory drugs have been shown to produce short-term pain benefits, but both result in long-term loss of function and even more chronic pain by actually inhibiting the healing process of soft tissues and accelerating cartilage degeneration.

This is often the case in patients who have had numerous cortisone shots and are eventually recommended shoulder replacement surgery. However, in our experience, this type of surgery is avoidable. For patients who have already been through any type of shoulder surgery and still have pain or instability symptoms, a consultation outside of a surgeon’s office needs to be considered, particularly with a Prolotherapy specialist to determine instability from ligament failure or laxity.

Conservative care vs Surgery for acromioclavicular joint osteoarthritis management: Current treatment guidelines for acromioclavicular joint injury do not support patient treatment desires: “specific activities” that cause pain are not discussed or assessed in many cases.

A December 2019 paper in the journal Shoulder and Elbow (9) demonstrated the difficulty in prescribing treatments for acromioclavicular joint osteoarthritis short of surgery. The authors wrote: “The most commonly used nonpharmacological interventions in clinical practice for persistent acromioclavicular joint osteoarthritis include activity modification, physiotherapy, exercise therapy,  and ice therapy. However, evidence to support using these interventions is still unknown so clinicians have to be mindful of such limited evidence. It seems that current practice is to trial (try) both nonpharmacological and pharmacological interventions for at least 4–6 months before conservative management is deemed to have failed and surgical intervention is indicated. The most common conservative interventions (studied in the medical literature) include activity modification, oral NSAIDs, intra-articular steroid injections, and physiotherapy.

A May 2022 study in the journal Disability and rehabilitation (3) from the University of Ottawa and The Ottawa Hospital Research Institute asked shoulder pain patients to describe what they hoped they would achieve by way of positive outcomes following acromioclavicular joint surgery. What the study revealed is that there is a gap between what patients consider a successful treatment outcome and what the medical guidelines are for a successful acromioclavicular joint surgery. The researchers wrote: “Although many factors affecting the acromioclavicular joint were common to instability and osteoarthritis pathology, several factors appear to be unique to each and do not appear in existing acromioclavicular joint metrics.” What is being suggested is that patients with acromioclavicular joint instability have many common problems with acromioclavicular joint osteoarthritis patients but they are not the same and thus should not be treated as one problem. The researchers continued: “Patients in this study identified several themes relevant to assessment and rehabilitation program development including pain location, type of pain (eg. burning pain), and specific activities that induced pain that does not exist in current existing tools.” In other words, “specific activities” that cause pain are not discussed or assessed in many cases.

This study built on similar earlier studies that found a “knowledge gap.” A 2021 study published in the journal Knee surgery, sports traumatology, arthroscopy (4) sought to clarify the guidelines for managing acromioclavicular joint osteoarthritis, as well as to identify and understand any existing gaps in the current knowledge of treatment. What they found was “Conservative and surgical treatments are both effective in acromioclavicular joint osteoarthritis management. However, available data did not allow to establish the superiority of one technique over another.”

Typically, surgery is not required in acromioclavicular joint dislocation, however, there is a debate as to the best method of treatment.

Doctors at the University of Michigan describe the problem in their review published in Current reviews in musculoskeletal medicine:

“In high-grade injuries, acromioclavicular joint reconstruction procedures may be indicated for functional improvement. There is currently no gold standard for the surgical management of these injuries.

Multiple reconstructive options exist, including coracoclavicular screws, hook plates, EndoButton coracoclavicular fixation, and anatomic ligament reconstruction with tendon grafts”(1)

“You may get surgery for something that is not the problem”

Doctors in the Netherlands teamed up with researchers from The University of Texas at Austin and the Paul L. Foster School of Medicine, Texas Tech University Health Science Center to publish their May 2022 study findings in the Journal of orthopedics (2) questioning the current guidelines in treating patients suffering from shoulder pain where acromioclavicular joint osteoarthritis was not the primary concern.  The study writes: “Radiographic osteoarthritis of the acromioclavicular joint is a common incidental finding (not what the doctors were looking for) and an uncommon reason for people to seek care for shoulder symptoms (many patients are asymptomatic)” In other words, the patient has shoulder pain that has a suspected cause that is not the acromioclavicular joint.” The researchers go on to suggest that radiographic osteoarthritis of the acromioclavicular joint may not correspond with symptoms. Further, “diagnosis of symptomatic acromioclavicular joint osteoarthritis is subject to substantial inaccuracy and should be made sparingly, mindful of the potential harms of a diagnosis that can lead to ablative surgery. “You may get surgery for something that is not the problem.”

A December 2023 study in the Journal of orthopaedic science (11) investigated the incidence and clinical characteristics of bone marrow edema (fluid buildup in the acromioclavicular joint) after arthroscopic rotator cuff repair and resulting persistent postoperative acromioclavicular joint pain.

A total of 231 shoulders, post-arthroscopic rotator cuff repair were assessed. Here are the discussion points:

“Arthroscopic rotator cuff repair has been reported to yield good clinical outcomes; however, re-tear rates of 11–94 % have also been reported. While patients with re-tear demonstrate poor clinical outcomes, there are cases in which pain may persist despite the absence of postoperative (rotator cuff) re-tear.

The rate of occurrence of bone marrow edema in the acromioclavicular joint pain after arthroscopic rotator cuff repair was 9.96 %.

The rate of occurrence of bone marrow edema in the acromioclavicular joint pain after arthroscopic rotator cuff repair was 9.96 %. Patients with bone marrow edema were significantly more likely to have acromioclavicular joint tenderness and positive cross-body adduction test. Bone marrow edema in the acromioclavicular joint often occurs within 6 months to 1 year after arthroscopic rotator cuff repair of small-to-medium rotator cuff tears, suggesting a relationship with postoperative functional improvement of the shoulder joint. The acromioclavicular joint should be considered as a potential site of persistent pain after arthroscopic rotator cuff repair for small-to-medium rotator cuff tears.”


Chronic shoulder instability caused by Acromioclavicular joint dislocation treatments

Treating the patient with chronic shoulder dislocation with the “gold” standard of treatments, physical therapy, activity modification, anti-inflammatory medications, or cortisone shots has not shown success. Furthermore, the surgery following the failed conservative treatment fairs no better. This is pointed out by Finnish researchers in the journal Springerplus.

  • “Conservative treatment of acromioclavicular joint dislocation is not always successful. A consequence of persistent acromioclavicular joint dislocation may be chronic pain and discomfort in the shoulder region as well a sensation of constant acromioclavicular joint instability and impaired shoulder function.”(5)
  • In this cited research from doctors at the University of Rome examined 39 patients who underwent coracoclavicular (CC) ligament reconstruction. After surgery, almost half of the AC joints failed to stabilize. In chronic and acute cases of shoulder dislocation management remains controversial, and the debate about whether patients should be conservatively or surgically treated continues. (6)
  • In a seeming contradiction, a study from the University of Missouri says the majority of acromioclavicular surgeries utilizing modern techniques and instrumentation result in successful outcomes. However, clinical failures do occur with frequency. (7)

Lastly, the more surgery – the more bone loss

  • The more shoulder dislocations you have, the more bone breakdown and the more difficult the surgery, because now bone repair is involved. (8)

The acromioclavicular joint has a disk.

The acromioclavicular joint has a disk. The disk provides cushioning similar to that of a knee meniscus. As like the meniscus, the AC disk eventually starts to flatten out as we age. Like the knee the shoulder has its ligaments that provides stability, when there is instability, degenerative wear and tear can wear out the AC disk.

A March 2022 study in The American journal of sports medicine (12) examined how degenerative wear to the AC disk may cause the disk to be a potential source of pain in AC joint injuries. The researchers observed: “Injuries of the acromioclavicular joint are common shoulder injuries that often lead to pain and dysfunction of the affected shoulder. Regardless of operative or nonoperative treatment, a relatively large number of patients remain symptomatic and experience pain. However, the specific source of persistent pain in the ACJ remains ambiguous.” In cadaver studies, the researchers where able to determine that nerve fibers within the intra-articular disk of the acromioclavicular joint, recorded pain from the disk and the disk itself could be an independent source of pain after injury and thus a possible explanation for recalcitrant pain after treatment.

Caring Medical Research

Ross Hauser, MD discusses the Prolotherapy treatment outcomes published a few years back as part of our article series on the use of Hackett-Hemwall dextrose Prolotherapy, as well as shows a treatment demonstration from a Prolotherapy symposium he taught in 2021

Questions about our treatments?

If you have questions about Subacromial shoulder pain and how we may be able to help you, please contact us and get help and information from our Caring Medical staff.

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1 Lee S, Bedi A. Shoulder acromioclavicular joint reconstruction options and outcomes. Curr Rev Musculoskelet Med. 2016 Dec;9(4):368-377. [Google Scholar]
2 Rossano A, Manohar N, Veenendaal WJ, van den Bekerom MP, Ring D, Fatehi A. Prevalence of acromioclavicular joint osteoarthritis in people not seeking care: A systematic review. Journal of Orthopaedics. 2022 May 20. [Google Scholar]
3 Aldhuhoori S, Almasri M, Nicholls SG, Pollock JW, Rollins M, Howard L, Lapner P. What outcomes are important in the recovery from acromio-clavicular (AC) joint pathology? A focus group study with patients and surgeons. Disability and Rehabilitation. 2020 Aug 14:1-9. [Google Scholar]
4 Soler F, Mocini F, Djemeto DT, Cattaneo S, Saccomanno MF, Milano G. No differences between conservative and surgical management of acromioclavicular joint osteoarthritis: a scoping review. Knee Surgery, Sports Traumatology, Arthroscopy. 2021 Jul;29(7):2194-201. [Google Scholar]
5 Virtanen KJ, Savolainen V, Tulikoura I, et al. Surgical treatment of chronic acromioclavicular joint dislocation with autogenous tendon grafts. Springerplus. 2014 Aug 10;3:420.  [Google Scholar]
6 De Carli A, Lanzetti R, Ciompi A, Lupariello D, Rota P, Ferretti A. Acromioclavicular third degree dislocation: surgical treatment in acute cases.  J Orthop Surg Res. 2015 Jan 28;10(1):13. [Google Scholar]
7 Ma R, Smith PA, Smith MJ, Sherman SL, Flood D, Li X. Managing and recognizing complications after treatment of acromioclavicular joint repair or reconstruction. Curr Rev Musculoskelet Med. 2015 Feb 8. [Google Scholar]
8 Denard PJ, Dai X, Burkhart SS. Increasing preoperative dislocations and total time of dislocation affect surgical management of anterior shoulder instability.   Int J Shoulder Surg. 2015 Jan-Mar;9(1):1-5.  [Google Scholar]
9 Farrell G, Watson L, Devan H. Current evidence for nonpharmacological interventions and criteria for surgical management of persistent acromioclavicular joint osteoarthritis: A systematic review. Shoulder & Elbow. 2019 Dec;11(6):395-410.  [Google Scholar]
10 Garcia AV, Salamé F, Mura J. The stress and strain pattern in the ligaments of the acromioclavicular joint using a quasi-static model. Clinical Biomechanics. 2023 Jan 1;101:105859. [Google Scholar]
11 Kajita Y, Takahashi R, Sagami R, Harada Y, Iwahori Y. Bone marrow edema in the acromioclavicular joint after arthroscopic rotator cuff repair. Journal of Orthopaedic Science. 2023 Dec 22. [Google Scholar]

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