AC joint arthritis is wear in the small joint on TOP of your shoulder, where the collarbone meets the tip of the shoulder blade. It causes pain you can point to with one finger, worse reaching across your body, lying on that side, and pressing weight such as a bench press or push-ups.
Most people can manage their shoulder AC joint pains and arthritis WITHOUT surgery.
Changing the movements that squeeze the joint, plus shoulder exercises, settles it for many. A steroid injection can confirm the diagnosis and ease pain, though the relief often doesn’t last.
If pain keeps coming back, a small operation removes a short piece from the end of the collarbone. Most people do well after it, especially when the AC joint is clearly the only problem.
What the AC joint is
- The AC joint (acromioclavicular joint) is the small bump you can feel on top of your shoulder, a few inches in from the edge
- It takes a lot of force whenever you push, press or reach across your body, because those movements squeeze the collarbone against the shoulder blade
- Wear here is very common with age. Around half of older adults show it on X-ray, and most of them have no pain. So “arthritis” on your report doesn’t prove this joint is the one hurting
Symptoms
- Pain on top of the shoulder, right over the joint, rather than down the outside of the arm
- Tender to press on the bump itself. It may look a little bigger than the other side
- Pain reaching across your body: washing the opposite armpit, doing up a seatbelt, or tucking in a shirt
- Pain in the gym: bench press, dips, push-ups and overhead pressing are common triggers
- Night pain lying on that side, because your body weight squeezes the joint
- A click or grind on top of the shoulder, sometimes painless
Who gets it
- People over about 40, as part of normal wear
- Weightlifters and manual workers, from years of heavy pressing and overhead work
- People who have had an AC joint separation, where the joint was sprained or torn in a fall. See AC joint separation
- Younger lifters can get a related problem where the end of the collarbone softens and wears away from repeated heavy pressing. It’s treated in much the same way
Not the same as impingement
- AC joint pain sits on top of the shoulder, and hurts most at the end of lifting and reaching across
- Rotator cuff pain usually sits on the outside of the upper arm, and hurts most in the middle of lifting the arm out to the side. See shoulder impingement
- The two often come together, which is why an injection into the AC joint alone can help sort out which one is the main problem
If you can point to it with one finger on top of the shoulder, think AC joint.
What helps
- Change the movements that squeeze the joint: less reaching across your body, less heavy pressing and overhead work for a few weeks
- Strengthen around it: exercises for the rotator cuff and shoulder blade muscles help the shoulder move well and take load off the joint
- Ice or heat: whichever eases it. Neither changes the joint, but both can take the edge off
- Anti-inflammatory tablets or gel for a flare, if they’re safe for you. Check with your pharmacist
- A steroid injection: placed into the joint, often with ultrasound guidance. If the pain goes, even for a few hours, the AC joint is the likely source. Relief can last weeks or months, but for most people it doesn’t last long term. See cortisone shot side effects
Changes in the gym
- Narrow your bench press grip: wide grips load the AC joint more. Keep your hands less than about one and a half times your shoulder width apart
- Stop short: end the lowering phase a couple of inches above your chest instead of touching it
- Swap the worst offenders: dips, deep push-ups and heavy straight-bar bench press. Incline or decline dumbbell pressing, narrow-grip bench and cable work are usually kinder
- Cut back on heavy, frequent pressing: very heavy bench pressing more than once a week, over years, is linked to this problem
In lifters with the related collarbone problem, more than 9 in 10 settle without surgery once they change how they train.
Surgery: removing the end of the collarbone
- What it is: the surgeon removes less than half an inch (about 0.5 to 1 cm) from the end of the collarbone. The gap fills with scar tissue, so the bones no longer grind. Doctors call it a distal clavicle excision
- Who it’s for: people with clear AC joint pain that keeps coming back after several months of the steps above, usually with good but short-lived relief from an injection
- How it’s done: usually through small keyhole cuts, sometimes as part of other shoulder surgery
- Recovery: a sling for comfort for a short time, then early movement. In one group of patients, people went back to sport after about 2 months and to work after about 3 on average, with a wide range either side
- Results: most people get much less pain, and in that same group nearly 8 in 10 said their shoulder felt completely normal. Results are less reliable when other shoulder problems are present, and a small number need a second operation
- Removing too much can make the collarbone unstable, which is why surgeons take only a small piece
The AAOS guide to shoulder arthritis explains how AC joint arthritis differs from arthritis in the main ball-and-socket joint. For that, see shoulder arthritis.
Go to the emergency department if
- Pain on top of the shoulder comes with chest pain, breathlessness, sweating or feeling sick. The heart can refer pain here
- The joint becomes hot, red and swollen and you feel feverish or unwell, especially after an injection
Get it checked if
- Pain hasn’t eased after 6 to 8 weeks of changing what you do
- The lump on top of the shoulder is growing
- You had a fall onto the shoulder and the bump is new
- The arm feels weak, not just painful, or you can’t lift it
- Night pain is stopping you sleeping, whichever side you lie on
Common on X-rays, easy to point to, and usually settled by changing how you push.