Shoulder Replacement Dislocation: How Likely It Is, the Positions That Risk It, the Signs, and What Happens Next

Dislocation after a shoulder replacement is uncommon, but it is more common after a reverse replacement than an anatomic total: instability is reported in roughly 1 to 5% of reverse cases in modern series, against about 1% or less for anatomic ones, and most reverse dislocations happen in the first weeks to months while the soft tissues are healing.¹ It is the complication that shapes the early rules after a reverse, which is why surgeons ask you to keep the arm out of certain positions before the joint has settled.

Mine was a reverse, and dislocation was the word that followed me around the first six weeks. I had spent two years sleeping upright in an armchair before the operation, and the instinct to plant my right hand behind me and shove myself up out of that chair was exactly the movement I was told not to make. This is the plain account of what dislocation is, how likely it actually is for each operation, the positions that risk it, what it feels like, and what happens next, checked line by line by a consultant shoulder surgeon. The wider list of what can go wrong is in shoulder replacement risks and complications.

What dislocation of a shoulder replacement is

A dislocation is the artificial ball leaving the artificial socket, so the two components are no longer articulating, and the shoulder cannot work until they are put back.² The natural shoulder is the most mobile joint in the body and the least constrained, a large ball on a shallow socket held in place by the capsule, the labrum, and the muscles around it, above all the rotator cuff. A replacement inherits that arrangement, so stability depends on the soft tissues and on how the components have been sized and positioned, not on the parts locking together.

The word covers a spectrum. A full dislocation is the ball completely out and staying out. Subluxation is a partial slip where the ball rides to the edge of the socket and comes back, which people feel as a clunk or a momentary give. Instability is the surgeon’s term for a joint that does either repeatedly. All three are recognised complications of shoulder arthroplasty, and how they are handled depends on which operation you had and why the joint moved.³

Why a reverse dislocates more than a total

A reverse replacement dislocates more often than an anatomic one because it is designed to work without a rotator cuff, so the muscles that would normally hold the ball centred are absent or failed, and the joint relies on the deltoid, the capsule, and the geometry of the components instead.¹ Switching the ball and socket lets the deltoid lift the arm, which is the whole point of the operation, but it also removes the natural compression that a working cuff provides.

In an anatomic total replacement the cuff is intact, and the surgeon repairs the subscapularis tendon at the front of the shoulder after opening the joint through it. A total dislocates rarely, and when it does the usual cause is that front tendon failing to heal or tearing later, letting the ball slip forward. The design difference is why the figures differ: about 1% or less for an anatomic total, and roughly 1 to 5% for a reverse in modern series, with older designs and revision or fracture cases at the higher end.⁴ The full mechanics of the deltoid trade are in reverse shoulder replacement, and none of this makes a reverse the wrong operation for a shoulder whose cuff is gone; an anatomic total in that shoulder would fail early, which is exactly why the reverse exists.

The positions that risk a reverse dislocation

The dangerous combination after a reverse is the arm behind the line of the body, held in against the side, and turned inward, because that position levers the humeral cup off the ball on the socket side.¹ Surgeons describe it as extension, adduction, and internal rotation together. On its own, none of those is a problem; it is the three at once that matter.

Translated into a day at home, that is pushing yourself up out of a chair or bed with the operated hand behind you, reaching into a back trouser pocket, tucking a shirt in behind your back, doing up a bra or apron behind you, and lying on the operated side with the arm trapped underneath. The early sling, and the instructions about how to get in and out of bed and how to sleep, are largely about keeping the arm out of that position while you are not thinking about it.⁵ What the nights are like, and why the sling often stays on in bed, is in sleeping after shoulder replacement.

The armchair was my particular hazard. For two years the only way I could get any sleep had been upright in that chair, and the only way out of it was a shove with the right hand planted behind my hip. After the operation I had to relearn getting up using my left arm and my legs, and for the first few weeks I put a cushion on the right armrest so the hand physically could not go where habit sent it. It felt absurd. It was also the single most useful thing I did in the first month.

When the risk is highest and how it falls

The risk of a reverse dislocating is highest in the first weeks to three months after surgery and falls steeply afterwards, because the capsule and muscles around the new joint heal and the deltoid regains its strength and tone.⁴ Instability that appears within the first few months is generally treated as a problem of healing tissues or of component position; a dislocation years later more often follows a fall or a failure of a component.

This is why the rules are strict early and relax later. The arm rests in a sling for about 2 to 6 weeks, reverse replacements are often out of it sooner, and physiotherapy builds from passive and pendulum movements to active movement and then strengthening on the surgeon’s schedule.⁶ Once the shoulder has settled, most surgeons allow the ordinary reaching and turning of daily life again, and the lasting caution is the one that applies to every replaced shoulder: avoid sudden heavy lifting and impact, and do not load the joint like an undamaged one. The staged return of movement is set out in the week by week recovery.

Certain shoulders carry more risk than the averages suggest. A reverse done for a fracture, as a revision of an earlier replacement, or in a shoulder with previous surgery and scarred or thinned soft tissue is more likely to be unstable than a straightforward primary reverse for cuff tear arthropathy. A weak or damaged deltoid, poor bone on the socket side, and a very loose soft-tissue envelope also raise it. Surgeons adjust the size of the metal ball, the thickness of the plastic cup, and how far the joint is moved outward to compensate, which is one reason implant choice is tailored rather than generic.³

The signs of a dislocated shoulder replacement

A dislocation is usually obvious rather than subtle: a sudden clunk or give, new pain unlike the ordinary ache of recovery, an arm that will not lift or move as it did the day before, and a shoulder that feels or looks out of place.² Some people also describe a hollow or a bump where there was none, or an arm that seems to hang differently, and a reverse that has dislocated typically loses the overhead lift the operation had restored.

Subluxation is harder to read. A single clunk that comes and goes with no lasting change may be the components riding to the edge and settling, and it is worth reporting rather than ignoring, because repeated slips are how instability shows itself. The rule the sleeping and recovery articles both use applies here: pain that is climbing rather than easing, a sudden step backward in what the arm can do, or a joint that feels wrong is a same-day call to the surgical team, who can examine you and take an X-ray that shows immediately whether the components are where they should be.⁵ It is not a wait-and-see problem and not something a forum can assess.

What happens next: reduction, protection, and revision

A first dislocation is commonly reduced, meaning put back into place, under sedation or a short anaesthetic, and then protected in a sling for a period while the soft tissues settle; recurrent instability is one of the recognised reasons a replacement goes back to surgery.¹ Before deciding, the surgeon looks at why it dislocated: the position and size of the components, the state of the deltoid and any remaining cuff, whether there is an infection or a fracture around the implant, and whether the shoulder went out with a specific movement or with no obvious cause.

If the components are well placed and the cause was an early movement into the risky position, a closed reduction and a slower rehabilitation often settle it. If the joint keeps going, the surgical options in a reverse are to change the geometry: a larger ball on the socket side, a thicker or more constrained plastic cup, or lateralising the joint to tension the soft tissues. In an anatomic total that has become unstable because the subscapularis has failed, converting it to a reverse is the common route, since a reverse does not need that tendon. Any of these is a revision, a bigger operation than the first with a higher complication rate and a more variable result for movement; what that involves is in revision shoulder replacement. An infection, which affects roughly 1 in 100 primary replacements and sits somewhat higher after a reverse, can also present as a shoulder that has become loose or unstable, so it is checked for rather than assumed absent.⁶

Keeping the risk in proportion

Dislocation is a real and named risk, not a likely outcome: for the great majority of people it never happens, primary reverse replacements remain over 90% in place at 10 years, and the early rules exist so that the small window of highest risk passes without incident.⁴ Reverse replacements carry a higher overall complication rate than anatomic ones, dislocation among them, and that is the price of an operation that works without a functioning cuff rather than evidence that it is the lesser choice.

What I would tell someone about to have a reverse is that the position rules are boring, specific, and temporary, and that following them is the one part of the dislocation risk you actually control. Ask your surgeon which movements to avoid, for how long, and what their own instability figures are for cases like yours, because the ranges above are pooled from the literature and your shoulder is one shoulder. Ask, too, how they want you to get out of a chair and out of bed, and rehearse it before the day. Whether your joint is settled enough to relax those rules is a judgement for the surgeon and physiotherapist who can examine it, and not something to work out from a page.