Acromial Stress Fracture After a Reverse Shoulder Replacement: The New Pain on Top of the Shoulder

An acromial stress fracture is a crack in the bony roof of the shoulder blade (the acromion, or the spine of the scapula behind it) where the deltoid muscle attaches, and it is a complication largely specific to reverse shoulder replacement: a 2019 systematic review of 2,857 reverse replacements found it in about 4.0%, diagnosed on average 9.4 months after the operation.¹ It tends to arrive just as people think the hard part is over, which is part of what makes it so unsettling.

I had not heard of it until someone on this site’s roundtable described a new, pinpoint pain on top of a shoulder that had been doing well for months. The surgeon who reviews these pages had named it to me before my own reverse, in a list of things I mostly forgot. This is the plain account of what it is, why a reverse is prone to it, the signs, and what treatment and recovery actually look like, checked line by line by a consultant shoulder surgeon. The wider list of complications is in shoulder replacement risks and complications.

What the acromion is, and why a reverse loads it

The acromion is the flat bony shelf at the top of the shoulder, continuous with the spine of the scapula along the back of the shoulder blade, and much of the deltoid muscle hangs from it.² In a normal shoulder, the rotator cuff and deltoid share the work of lifting. After a reverse replacement, the deltoid does almost all of it.

That is the design working as intended. A reverse moves the centre of rotation and lengthens the deltoid so it can lift the arm without a functioning cuff, which is why it suits cuff tear arthropathy.³ The price is that the deltoid now pulls harder, on every lift, on the bone it is attached to. In some shoulders, particularly where the bone is thinner, that repeated load produces a stress fracture rather than one dramatic break. How the deltoid takes over is explained in reverse shoulder replacement.

How common it is, and when

In the 2019 systematic review of 15 studies, the overall incidence of acromial or scapular spine fracture after reverse replacement was 4.0%, with individual studies ranging from 1.0% to 15.8%; the average age at fracture was about 73, and women outnumbered men by roughly five to one.¹ The fractures split almost evenly between the acromion itself and the scapular spine.

Timing is the detail most people do not expect. The average time from operation to diagnosis was 9.4 months, but the range ran from 1 month to 94 months.¹ So while most appear in the first year, a new pain in this area is worth taking seriously at any stage. The review’s authors also thought the true incidence is likely higher than reported, because these fractures are easy to miss on plain X-rays. Reverse replacements also carry a higher overall complication rate than anatomic ones across long-term series, and this fracture is part of that difference.⁴

Who is more likely to get one

The factors linked to acromial fracture include osteoporosis, implant design, the surgical approach, the position and length of the screws in the socket component, and excessive tension in the deltoid.¹ Most of these are surgical or anatomical rather than anything a patient does.

Design made a measurable difference in the review: fractures were most common with implants that are medialised on both the socket and humeral sides (about 8.4%), and less common with designs that move the joint outward on the socket side (about 4.0%) or the humeral side (about 2.8%).¹ That is one reason implant choice is tailored rather than generic. Older age and thinner bone are part of why the fracture is seen more often in older women, the same group in whom reverse replacements are frequently done. If osteoporosis is known, it is worth raising before surgery; candidacy and bone health are covered in am I a candidate for shoulder replacement.

The signs to report

The typical story is new, localised pain on the top or back of the shoulder, tender over one spot, in someone whose recovery had been going well, often with a sudden loss of the ability to lift the arm or a lift that has become painful and weak.¹ It frequently happens without a fall, after an ordinary day, or after a modest strain such as lifting something heavier than usual.

What separates it from ordinary recovery is the pattern. Rehabilitation aches tend to be diffuse and improve week on week; this is a new pain in a particular place, and it gets in the way of lifting the arm the reverse had given back. Any new pain like that after a reverse replacement is worth a prompt call to the surgical team rather than waiting for the next scheduled review. The general rule from the recovery pages applies too: pain that climbs rather than eases, fever, or a red or weeping wound is a same-day call. The normal course of recovery is set out in the week by week recovery.

How it is diagnosed

The diagnosis is made by examination and imaging, but plain X-rays can miss these fractures at first, so a CT scan is often used when the story fits and the X-ray looks normal.¹ One study included in the review found that about a third of patients later diagnosed with a displaced fracture had initially unremarkable X-rays.

This is why reporting the pain early, and being specific about where it is, matters. Undisplaced fractures caught early can usually be treated conservatively, whereas a fracture that has moved by the time it is found is harder to manage and more likely to heal badly or not at all.¹ Describing the pain as “on top, here, since last Tuesday, and I can’t lift the arm like I could” gives the surgeon a lot more to work with than “the shoulder is sore.”

Treatment and what recovery looks like

Most acromial fractures are treated without surgery: in the 2019 review, about 88% were managed with a sling or abduction brace, usually for 6 to 8 weeks, and about 12% had surgery to fix the bone with plates or wires.¹ Fractures of the acromion itself were mostly managed conservatively; surgery was used more often for fractures of the scapular spine and for displaced fractures.

The honest part is the outcome. Only about half of the fractures in the review fully united (about 44% with conservative treatment and 88% with surgery, though the surgical group was small and different), and average function and lift at follow-up were lower than after an uncomplicated reverse, with forward lift around 100 degrees.¹ Pain scores, by contrast, were generally low by the end. Many people end up with a comfortable shoulder that lifts less well than they had hoped; some do very well; a few are left with a weak arm. The review’s own conclusion was that this complication is “neither uncommon nor negligible.”

Keeping it in proportion

An acromial stress fracture is a real and specific risk of reverse replacement, affecting roughly 1 in 25 shoulders in the pooled data, which also means that about 24 in 25 never have one.¹ It does not make a reverse the wrong operation for a shoulder whose rotator cuff has failed; it is part of the trade that comes with an operation that works without a cuff, alongside a higher dislocation and overall complication rate than an anatomic total.⁵

What a patient can usefully do is narrow. Ask your surgeon before the operation how often they see this complication and whether your bone density is a concern. Follow the early lifting limits your surgeon sets, which keep heavy loads off the shoulder while everything settles. And if, months later, a new pain appears on top of a shoulder that had been doing well, do not explain it away as a bad night. Report it, say exactly where it hurts, and let the surgeon decide whether it needs a scan. Whether your own shoulder has this problem is a judgement for someone who can examine it and see the images, not something a page can settle.