The Overlooked Tennis Shoulder Problem: Posterior Shoulder Instability

If your shoulder aches at the back after you play, clicks or seems to slide through the follow-through, feels blocked reaching across your body, or has simply lost power you cannot explain, there is a problem worth knowing about — and it is one that regularly gets missed.

Most people associate an unstable shoulder with a dramatic dislocation. Posterior shoulder instability is not that. In tennis players it usually builds gradually, and pain is the presenting complaint rather than any sense of the joint coming out. A significant number of players with it have a completely normal MRI.

The good news? When it is recognized, it responds well to the right rehabilitation — in one study of overhead athletes, 22 of 24 returned to full activity. The catch is that the wrong treatment, including a stretch you may already have been given, can make it worse.

At Rooted Motion Physical Therapy, we believe a problem this easy to miss deserves to be explained properly. Here is what it is and how it is treated.

What Does It Mean When the Shoulder Slides Backward?

Your shoulder is a ball sitting against a shallow socket, held there by two systems: fixed structures — the rim of cartilage around the socket and the sleeve of tissue enclosing the joint — and the muscles that steer the ball and keep it centered as you move.

Posterior instability means the ball slides too far toward the back of the socket and starts causing symptoms. Specialists sort it into three groups. One follows a clear injury. One arrives with no obvious cause, in people whose shoulders are loose in several directions to begin with. The third — the one that matters in tennis — builds gradually from repeated load, such as months of steady play with a heavier than usual racquet.

Why Does Tennis Load the Back of the Shoulder?

Several tennis movements bring the arm forward, across the body and rotated inward. In those positions the tissue at the back of the joint is pulled tight, and repeated stress can stretch it, letting the ball travel further back than it should.

The positions that do it are specific: the serve follow-through, the forehand follow-through, backhand preparation, backhand volleys and kick serves. Your dominant arm is braking hard in all of them.

Imagine a Door Off Its Latch

A door with a working latch swings and stops where it should. Loosen the latch and the door still opens fine — it just travels a little too far each time, and the frame starts taking the impact.

The key idea: nothing about your shoulder is broken or falling apart. The stop is soft, so the joint drifts a little further than it should on every follow-through. Rehabilitation is about restoring the stop, and the muscles do most of that work.

How Much Force Are We Talking About?

More than you would guess. This problem was first described in baseball batters, where the shoulder rotates at around 937 degrees per second and the tissues at the back of the joint absorb the swing. In tennis, particularly on the serve, that figure may reach roughly 3,000 degrees per second — which is why the risk here may be greater than in the sport that named it.

Is Being Loose-Jointed the Same Thing?

No, and the difference matters. Around 13 percent of sportsmen and up to 42 percent of sportswomen have naturally loose shoulders, and on its own that is not a problem. A loose shoulder moves more because the tissue holding it is more elastic, and it does not hurt.

Instability is when that extra movement is no longer controlled and has started to cause symptoms. Looser tissue may send less information back to the nervous system about where the joint actually is, weakening the muscular control that keeps the ball centered. Add repeated stress, and a shoulder that was merely loose can become one that hurts.

Are Some Shoulders Simply Built for This?

Partly, yes. A socket facing further backward than usual, one that did not fully develop along its lower back rim, or one worn down by wear are all associated with this problem. Most authors treat a backward tilt of 10 degrees or more as excessive.

The angle appears to be mostly inherited, though heavy overhead use of the arm before roughly age 12, while the bone is still forming, may influence how the socket develops. None of this changes the first-line plan. It helps explain why two players with similar histories can have very different shoulders.

Why Is This Missed So Often?

Because it rarely looks like instability. Pain at the back of the shoulder, clicking, a sense of sliding, reduced power, a blocked feeling, or discomfort as the arm crosses the body all overlap with rotator cuff and pinching-type problems.

The standard tests do not always settle it either. Several were validated in patients with obvious, frank instability rather than the subtle version seen in overhead athletes. The gradual-onset form tends to show up as slight backward movement and pain rather than a shoulder visibly slipping out, which makes watching how you actually move far more informative than a checklist of tests.

The Trap: Treating It Like a Tight Shoulder

This is the most consequential error in the field, and it is worth understanding even as a patient. Losing inward rotation in the dominant shoulder is common in overhead athletes, and it is often treated with stretches designed to loosen the back of the shoulder.

But in some cases of posterior instability, that movement only looks restricted because you are guarding — the shoulder is quietly refusing a position it finds unsafe. Stretching into it can then make things worse. Those are the exact positions that provoke the symptoms, and repeated stretching may further loosen tissue that is already failing to hold the joint in place.

If a cross-body or sleeper stretch consistently makes your shoulder feel worse rather than better, that is worth mentioning rather than pushing through.

What Should an Examination Involve?

A therapist watches how you actually move: lifting the arm forward and out to the side, bringing it across the body, rotating it inward, and how the shoulder blade travels while you do it.

The most useful part is often a corrective test. The clinician gently stops the ball of the shoulder from sliding backward, then asks you to repeat the movement. If the range improves or the pain eases, that points toward a control problem you can retrain — and it signals early whether rehabilitation is likely to work.

Do You Need a Scan?

MRI is the best test for the soft tissue around the joint, and it is warranted after a significant injury, with repeated dislocations, or when symptoms persist despite proper rehabilitation.

But know what a scan often shows here. A significant proportion of tennis players with the gradual-onset form have nothing structurally wrong on MRI at all. That is not a normal result to be waved away — it points toward lost control or over-stretched tissue as the driver, which is a rehabilitation problem rather than a surgical one.

How Is It Treated?

The aim is to restore how the shoulder blade moves, stop the ball sliding backward, and address weak links elsewhere. When the shoulder blade moves well, it keeps the socket where the ball needs it and lets the surrounding muscles work at their best angle.

The sequence is deliberate: control first, then endurance, then strength, then sport-specific speed and power. The muscles at the back of the shoulder get particular attention, because they resist the backward slide directly. Only later are exercises pushed into the positions that used to hurt — and that step is the point, not an optional extra.

Getting more from your legs and trunk reduces the force the shoulder has to produce for the same shot. For a player with instability that does not replace shoulder rehabilitation. It makes it more likely to hold.

Does It Actually Work?

The most relevant study followed 24 overhead athletes, four of them tennis players, through a structured program of up to 18 sessions across 24 weeks. Scores improved significantly, and 22 of the 24 — about 92 percent — returned to full activity. The two who did not went on to surgery, and neither had a structural lesion. That is a single-group study rather than a guarantee, but the direction is encouraging.

Where surgery is needed, outcomes are generally good, with return-to-sport rates reported between 55 and 90 percent, though not all athletes reach their previous level. The only study in tennis players specifically followed 13 with tears of the cartilage rim: of the nine with return-to-sport data, 89 percent got back on court and 56 percent to their previous level.

One number worth having before you go back: patients who pass an objective strength test first may cut their risk of recurrence by nearly five times compared with those cleared without one.

The Rooted Motion Difference

Care is one-on-one, in your own home, and built around the strokes that actually provoke your symptoms. Here is what you can expect:

• An examination that watches how you move rather than relying on one test.

• A clear answer on whether your shoulder is stiff or loose, because the plans differ.

• Control work before strength work, in the order the evidence supports.

• Progression back into the positions that used to hurt.

• Objective testing before you return to unrestricted play.

• Convenient concierge mobile physical therapy delivered where you are.

Because recovery is not just about settling the pain — it is about trusting the shoulder through a follow-through again.

Ready to Find Out What Is Actually Going On?

If your shoulder hurts at the back, feels like it slides, or has lost power that rest has not restored, a normal scan does not mean nothing is wrong. It may mean the problem is one that rehabilitation is well placed to fix.

Ready to move better and live rooted? Contact Rooted Motion Physical Therapy to schedule a one-on-one evaluation and begin a personalized shoulder stability plan.

Research Used for This Article

1. Watson L, Hoy G, Wood T, et al. Posterior Shoulder Instability in Tennis Players: Aetiology, Classification, Assessment and Management. International Journal of Sports Physical Therapy. 2023;18(3):769-788. DOI

2. Kekelekis A, Nikolaidis PT, Moore IS, Rosemann T, Knechtle B. Risk Factors for Upper Limb Injury in Tennis Players: A Systematic Review. International Journal of Environmental Research and Public Health. 2020;17(8):2744. DOI

Educational disclaimer: This article is for general education and is not a substitute for an individualized evaluation. Seek prompt medical care after a traumatic injury or dislocation, for a sudden major loss of strength, or for new numbness, tingling or weakness in the arm.