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AC Joint Impingement

Causes, Symptoms, Treatment Options, and Other Resources

Shoulder pain can be disabling.  Simple chores like grabbing something from the overhead cabinet or putting on a sweater can be almost impossible at times.   A common cause of shoulder pain found on MRI or diagnosed by your doctor is AC Joint impingement. What is the AC joint?  And what does it mean for it to be “impinged”?  Let’s dig in.

What Is the AC Joint?

The acromioclavicular (AC) joint is where the shoulder bone called the acromion meets the collar bone (clavicle) and forms a joint.  It is the bony point on the top of the shoulder.  If you put your fingers on your collar bone and follow it back towards your shoulder you will feel a bony bump which is the AC joint. The AC joint provides important stability to the shoulder joint.

The space immediately underneath the AC joint is called the subacromial space and is depicted by the red area in the illustration below.  The subacromial space contains the rotator cuff tendons and bursae (1).

What Is AC Joint Impingement?

AC joint Impingement is a painful condition that occurs when the space beneath the acromion bone is narrowed.   This narrowing can result in irritation of the rotator cuff tendons and bursa.  A bursa is a fluid-filled sac that reduces the friction on tendons and muscles as they cross bony surfaces.  A tendon is thick collagen tissue that connects muscles to bones.  The rotator cuff tendons provide important support and enable movement in the shoulder.   If severe,  impingement can cause tears in the rotator cuff tendons.  Patients with AC joint impingement typically have pain with elevation of the arm and or while lying on the shoulder (2).

There are three grades of impingement (3).

Grade 1:  Inflammation of the bursa and tendons

Grade 2:  Progressive thickening and scarring of the bursae

Grade 3:  Rotator cuff tendon degeneration and tears

What Causes AC Joint Impingement

Three major structures in the shoulder can cause AC joint impingement (4).


Inflammation and or thickening of the bursae often time referred to as bursitis can cause impingement

Rotator Cuff Tendons

Inflammation, thickening or tears in the rotator cuff tendons can cause impingement.

AC Joint

Injury and strain of the AC joint can lead to instability which in turn can cause ligament thickening and AC joint arthritis.  Both of these cause impingement.

Symptoms of AC Joint Impingement

Symptoms usually develop gradually over weeks to months. The following are signs of shoulder impingement syndrome:

  • Pain when your arms are extended above your head.
  • Pain while lifting your arm, lowering your arm from a raised position, or when reaching.
  • Pain and soreness in the front of your shoulder.
  • A pain that starts in the front of your shoulder and travels to the side of your arm.
  • Being unable to sleep owing to pain or aching during the night is common..
  • It’s painful to reach behind your back.
  • Aching, tight muscles in the shoulders and arms.

Arm Pain at Night

Arm pain at night can be miserable.  The pain can interrupt your sleep and erode your quality of life. Irritability becomes increasingly more common.  What are the causes?  When should I worry about it?  What are the treatment options for arm pain at night? The neck is composed of 7 boney building blocks numbered 1- 7. Sandwiched between the bones is a disc that functions as an important shock absorber. The cervical discs are susceptible to injury due to trauma, degeneration, repetitive motion, and surgery. Common disc injuries include disc bulges, and herniations. The injured disc can compress or irritate one or more nerves resulting in arm pain at night. It can…

Read More About Arm Pain at Night

Left Shoulder Blade Pain

Learn to know the symptoms and causes of shoulder blade pain as well as the diagnostic tests to run for it and its treatment options. Shoulder blade pain can be a common, annoying, hard to diagnose problem. There are many different causes of shoulder blade pain and the exact cause of the shoulder blade pain will determine what type of treatments would be recommended.

Read More About Left Shoulder Blade Pain

Shoulder Joint Pain

Shoulder joint pain is the third most common reason that people see their primary care physician (1). It is commonly experienced by people who use their hands overhead a lot, particularly in occupations such as painting and construction. Individuals who train with repetitive overhead movements, such as tennis players, swimmers, and basketball players, are also prone to develop shoulder joint pain. The symptoms and progression of pain in the shoulder joint can vary from person to person, depending on what is causing it. We’ll discuss the causes of shoulder pain, how it is diagnosed, and how it is treated.

Read More About Shoulder Joint Pain

Shoulder Pain When Reaching Across Body

Shoulder pain can make simple chores almost impossible.  Have you ever reached for an object high on a shelf only to have pain that takes your breath away?  What causes shoulder pain when reaching across the body?  What is shoulder impingement?  What does shoulder impingement feel like?  Can a shoulder X-ray show shoulder impingement?  What are the treatment options for shoulder pain when reaching across the body? ulder impingement and rotator cuff injuries are among the most common causes of shoulder pain (1).  Both can cause shoulder pain when reaching across the body. Shoulder impingement is a painful condition in which the bursa and muscles of the shoulder are pinched or compressed. 

Read More About Shoulder Pain When Reaching Across Body

Shoulder Pain When Sleeping

There are several reasons why shoulder pain at night occurs or is aggravated; The common explanations include: Sleep typically involves a static position lasting hours at a time with little or no movement. Sleeping on your side places additional pressure on the tendons and bursa of the shoulder. Sleep can cause muscles and tendons to settle in a slightly different position resulting in additional pressure and reduced blood flow. Identifying the underlying problem is important!  This allows therapy to focus exclusively on the exact problem or problems.  When appropriate conservative care is always the first line of treatment.  Focus is typically on strengthening and improving range of motion. 

Read More About Shoulder Pain When Sleeping

Why Does My Shoulder Hurt When I Lift My Arm?

Shoulder pain can be very non-specific, meaning that multiple structures and issues can cause identical pain in the shoulder. Most shoulder examination maneuvers are very limited in their ability to assess exactly what the problem is.  With pain when lifting your shoulder, it is critical to take a detailed history, good examination, coupled with imaging to fully understand what is causing the shoulder pain.  Many conditions can present with these symptoms

Read More About Why Does My Shoulder Hurt When I Lift My Arm?

What Can Be Done for AC Joint Impingement?

Activity Modification

Overuse or repetitive motions can cause impingement and therefore rest is important.

Physical Therapy

Physical therapy programs focusing on improving range of motion, rotator cuff, and scapula strengthening have been associated with good outcomes (5).


Safe anti-inflammatory agents such as fish oil and curcumin are appropriate and can reduce swelling.  Nonsteroid anti-inflammatory agents such as Motrin and Advil have significant side effects which include acceleration of arthritis, GI bleeding and increased risk of a heart attack.

Steroid Injections

While often recommended as a treatment option to those who do not respond to physical therapy, steroids are toxic to orthopedic tissue and can lead to rotator cuff tendon shrinkage and reduced ability to heal (6).


Shoulder decompression surgery is a common surgery for AC joint impingement.  Also known as an Acromioplasty, it involves removing part of the bone and ligaments from the AC joint.  The rationale is that the AC joint and ligaments are pressing on and injuring the rotator cuff tendons.  A high-level study has demonstrated that shoulder surgery with the removal of a portion of the AC joint is no better than physical therapy (7).

To understand what an Acromioplasty is and why it can lead to shoulder instability click on the video below.

Nonsurgical Options

Bone marrow-concentration injections are effective in the treatment of shoulder and AC joint arthritis.  In 2015 we treated 102 patients with shoulder arthritis and or rotator cuff tears.  On average patients reported a 48.8% improvement after bone marrow concentrated injections (9).  Patients avoided the risks associated with surgery and extensive rehabilitation.  Bone marrow concentrate is rich in mesenchymal stem cells which can differentiate into cartilage, bone, and tendon as well as facilitate repair (10).

Prolotherapy Injections

It has been successful in the treatment of many disorders including neck, shoulder, knee, and ankle pain. Dr. Centeno recently published an article in The Journal of Prolotherapy in which he discusses the use of x-ray guidance with prolotherapy. This ensures that the injection is in the correct place to maximize clinical results. Dr. Centeno discusses the use of prolotherapy for the treatment of neck, knee, sacroiliac joint, ankle, ischial tuberosity, and shoulder pain. At the Centeno-Schultz Clinic x-ray guided prolotherapy is just one of the therapies utilized in the successful treatment of pain. Regenerative injection therapy (RIT) or prolotherapy…

Read More About Prolotherapy Injections

PRP Injections

PRP is short for platelet-rich plasma, and it is autologous blood with concentrations of platelets above baseline values. The potential benefit of platelet-rich plasma has received considerable interest due to the appeal of a simple, safe, and minimally invasive method of applying growth factors. PRP treatments are a form of regenerative medicine that utilizes the blood healing factors to help the body repair itself by means of injecting PRP into the damaged tissue. In regenerative orthopedics, it is typically used for the treatment of muscle strains, tears, ligament and tendon tears, minor arthritis, and joint instability. There have been more than 30 randomized controlled trials of PRP…

Read More About PRP Injections

In Conclusion

The AC joint is an important joint in the shoulder that provides support.  The AC joint is compromised of the acromion bone from the shoulder and the collar bone (clavicle).  Underneath the AC joint is the subacromial space that contains the rotator cuff tendons and bursa.  AC joint impingement occurs when there is the narrowing of the subacromial space and puts the rotator cuff and bursa at risk for injury.  Injury, instability, and arthritis of the AC joint can cause AC joint impingement.  Treatment options include activity modification, physical therapy, and medications.  Steroids are toxic and should be avoided.  Decompression surgery involves the removal of a portion of the acromion and ligaments which destabilizes the shoulder and puts additional stress on the rotator cuff tendons.  Surgery has been shown to be no more effective than PT.  Bone marrow concentration injections are an effective, non-surgical option in the treatment of AC joint impingement.

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Our Doctors Who Assist with AC Joint Impingement

Christopher J. Centeno, MD

Christopher J. Centeno, M.D. is an international expert and specialist in Interventional Orthopedics and the clinical use of bone marrow concentrate in orthopedics. He is board-certified in physical medicine and rehabilitation with a subspecialty of pain medicine through The American Board of Physical Medicine and Rehabilitation. Dr. Centeno is one of the few physicians in the world with extensive experience in the culture expansion of and clinical use of adult bone marrow concentrate to treat orthopedic injuries. His clinic incorporates a variety of revolutionary pain management techniques to bring its broad patient base relief and results. Dr. Centeno treats patients from all over the US who…

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John Schultz, MD

John R. Schultz M.D. is a national expert and specialist in Interventional Orthopedics and the clinical use of bone marrow concentrate for orthopedic injuries. He is board certified in Anesthesiology and Pain Medicine and underwent fellowship training in both. Dr. Schultz has extensive experience with same day as well as culture expanded bone marrow concentrate and sees patients at the CSC Broomfield, Colorado Clinic, as well the Regenexx Clinic in Grand Cayman. Dr. Schultz emphasis is on the evaluation and treatment of thoracic and cervical disc, facet, nerve, and ligament injuries including the non-surgical treatment of Craniocervical instability (CCI). Dr. Schultz trained at George Washington School of…

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John Pitts, M.D.

Dr. Pitts is originally from Chicago, IL but is a medical graduate of Vanderbilt School of Medicine in Nashville, TN. After Vanderbilt, he completed a residency in Physical Medicine and Rehabilitation (PM&R) at Emory University in Atlanta, GA. The focus of PM&R is the restoration of function and quality of life. In residency, he gained much experience in musculoskeletal medicine, rehabilitation, spine, and sports medicine along with some regenerative medicine. He also gained significant experience in fluoroscopically guided spinal procedures and peripheral injections. However, Dr. Pitts wanted to broaden his skills and treatment options beyond the current typical standards of care.

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Jason Markle, D.O.

Post-residency, Dr. Markle was selected to the Interventional Orthopedic Fellowship program at the Centeno-Schultz Clinic. During his fellowship, he gained significant experience in the new field of Interventional Orthopedics and regenerative medicine, honing his skills in advanced injection techniques into the spine and joints treating patients with autologous, bone marrow concentrate and platelet solutions. Dr. Markle then accepted a full-time attending physician position at the Centeno-Schultz Clinic, where he both treats patients and trains Interventional Orthopedics fellows. Dr. Markle is an active member of the Interventional Orthopedic Foundation and serves as a course instructor, where he trains physicians from around the world.

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Brandon T. Money, D.O., M.S.

Dr. Money is an Indiana native who now proudly calls Colorado home. He attended medical school at Kansas City University and then returned to Indiana to complete a Physical Medicine and Rehabilitation residency program at Indiana University, where he was trained on non-surgical methods to improve health and function as well as rehabilitative care following trauma, stroke, spinal cord injury, brain injury, etc. Dr. Money has been following the ideology behind Centeno-Schultz Clinic and Regenexx since he was in medical school, as he believed there had to be a better way to care for patients than the status quo. The human body has incredible healing capabilities…

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Other Resources for Shoulder Pain

  • Treatment For A Torn Rotator Cuff Without Surgery: Exploring Your Options

    Welcome to the Guide for Rotator Cuff Tear Relief Without Surgery. Rotator cuff injuries affect millions of people globally (1). The incidence vastly increases with age. Irrespective of the cause, there are many treatment options for rotator cuff injuries apart from surgery. If you want to avoid rotator cuff surgery, you’re in the right place!…

  • Rotater Cuff Tear Surgery

    Shoulder Pain Shoulder pain can come in many different forms and be caused by many different issues. Many structures exist in a small area making it more difficult to accurately diagnose what is causing pain without spending appropriate time to diagnose the issue. Common causes of shoulder pain include shoulder arthritis, acromioclavicular (AC) joint sprain…

  • Regenexx Rotator Cuff Tear Home Self-Exam

    Hi It’s Dr. Centeno, and this is my series “You’ve Got the Power”, which is all about what you can do at home to understand why various issues are going on. In this episode, we’re going to cover why your shoulder hurts and focus on your Rotator Cuff. So, if you’re stuck at home, what…

  • Vulcan Shoulder Support

    Specialized doctor discussed the use of Vulcan shoulder support and other therapies for shoulder injuries.

  • Sleep Apnea and Shoulder Arthroscopy Complications: Is There a Link?

    Many Americans suffer from sleep apnea (SA), so many (estimates range between 18 million and 25 million), in fact, it’s become quite an epidemic. Snoring is an indicator of sleep apnea, and while many who snore might not be too concerned about it, the truth is, there are many reasons to be concerned, and it’s…

  • Can a Stem Cell Injection Treat Severe Shoulder Arthritis?

    Our bodies shouldn’t be treated like machines in which if a part breaks down, like a shoulder or a knee, for example, we just replace it. Yet this is often the result in the traditional orthopedic-care model. With severe shoulder arthritis, and other musculoskeletal conditions, when conservative treatments are no longer effective and dangerous drugs,…

1. Ludewig PM, Braman JP. Shoulder impingement: biomechanical considerations in rehabilitation. Man Ther. 2011;16(1):33-9. doi: 10.1016/j.math.2010.08.004

2.Garving C, Jakob S, Bauer I, Nadjar R, Brunner UH. Impingement Syndrome of the Shoulder. Dtsch Arztebl Int. 2017;114(45):765-76. doi: 10.3238/arztebl.2017.0765.

3.Khan Y, Nagy MT, Malal J, Waseem M. The painful shoulder: shoulder impingement syndrome. Open Orthop J. 2013;7:347-51. doi: 10.2174/1874325001307010347

4. Escamilla RF, Hooks TR, Wilk KE. Optimal management of shoulder impingement syndrome. Open Access J Sports Med. 2014;5:13-24. doi: 10.2147/OAJSM.S36646.

5.Dickens VA, Williams JL, Bhamra MS. Role of physiotherapy in the treatment of subacromial impingement syndrome: a prospective study. Physiotherapy. 2005;91(3):159–164.

6.Kennedy JC, Willis RB. The effects of local steroid injections on tendons: a biomechanical and microscopic correlative study. Am J Sports Med. 1976;4(1):11-21.DOI: 10.1177/036354657600400103.

7. Kukkonen J, Joukainen A, Lehtinen J, et al. Treatment of non-traumatic rotator cuff tears: A randomised controlled trial with one-year clinical results. Bone Joint J. 2014;96-B(1):75-81.DOI: 10.1302/0301-620X.96B1.32168

8. Ketola S, et al. Long term acromioplasty results no better than structured exercise for anterolateral shoulder pain. Presented at: European Society of Sports Traumatology, Knee Surgery and Arthroscopy Congress; May 4-7, 2016; Barcelona.

9. Centeno CJ, Al-Sayegh H, Bashir J, Goodyear S, Freeman MD. A prospective multi-site registry study of a specific protocol of autologous bone marrow concentrate for the treatment of shoulder rotator cuff tears and osteoarthritis. J Pain Res. 2015;8:269-76. DOI: 10.2147/JPR.S80872.

10. Pittenger MF, Mackay AM, Beck SC, et al. Multilineage potential of adult human mesenchymal stem cells. Science. 1999;284(5411):143-7.DOI: 10.1126/science.284.5411.143.

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