A double-jointed shoulder doesn’t always look dramatically different at rest, but during movement it becomes obvious. The hallmark is an unusually large range of motion: the arm can rotate, extend, or reach behind the back far beyond what most people can achieve. In some cases, you can actually see the ball of the upper arm bone shift partially out of its shallow socket, creating a visible bump or gap at the front or top of the shoulder.
What You Can See During Movement
The most striking visual sign is extreme flexibility. Someone with a hypermobile shoulder can often reach their arm behind their head and down their back much farther than normal, or rotate the arm outward to an angle that looks uncomfortable but isn’t painful for them. When the arm is raised overhead or pulled across the body, the shoulder joint may visibly shift in ways that wouldn’t happen in a typical joint. You might notice the top of the shoulder dropping lower than expected, or the skin around the joint stretching and dimpling as the ball of the humerus (the upper arm bone) moves toward the edge of the socket.
Audible popping, clicking, or clunking sounds often accompany these movements. The joint may look like it briefly “catches” or “gives way” mid-motion. In more pronounced cases, the ball of the shoulder can slide partially out of the socket, a phenomenon called subluxation. When this happens, you can sometimes see the round head of the humerus bulging under the skin at the front or bottom of the shoulder before it slides back into place. This is different from a full dislocation, where the bone comes completely out and the shoulder looks visibly deformed, with a hollow or flattened area where the rounded contour should be.
The Sulcus Sign and Resting Posture
One of the most recognizable visual markers of a hypermobile shoulder is something called the sulcus sign. When the arm hangs relaxed at the side and gentle downward traction is applied (or sometimes just from the weight of the arm itself), a visible indentation or groove appears just below the bony point at the top of the shoulder. This gap reflects excessive looseness in the joint capsule, the fibrous tissue that normally holds the ball snugly in the socket. In people with tight, typical capsules, this groove doesn’t appear.
At rest, a double-jointed shoulder may also sit slightly lower than a normal shoulder. The shoulders can appear asymmetrical if only one side is hypermobile, with the affected side hanging a bit further from the ear. Some people have a naturally “sloped” look to both shoulders because the loose capsule allows the arm to drop lower in the socket.
Scapular Winging
People with hypermobile shoulders sometimes develop a related visual sign: a winged scapula. This is when the shoulder blade noticeably sticks out from the back instead of lying flat against the ribcage. It gets its name from the way the protruding bone resembles a small wing. One shoulder blade may look obviously out of place compared to the other, and the difference becomes more dramatic during movement.
A simple way to spot this is the wall pushup test. Stand facing a wall, press your palms flat against it, and push off like a standing pushup. If your shoulder blade tips upward and away from your back during the push, that’s winging. It happens because the muscles surrounding a hypermobile shoulder are often working overtime to compensate for the loose joint, and some of them fatigue or weaken over time, losing their ability to hold the shoulder blade in place.
Why Some Shoulders Are Hypermobile
The shoulder is already the most mobile joint in the body. The socket (called the glenoid) is shallow and flat, more like a golf tee than a deep cup. A ring of cartilage called the labrum deepens the socket slightly, and a network of ligaments and a fibrous capsule wrap around the joint to hold it together. In a double-jointed shoulder, one or more of these structures is looser than normal.
For many people, this looseness is simply genetic. Their connective tissue, particularly the collagen that makes up ligaments and the joint capsule, is stretchier than average. This is especially common in connective tissue conditions like Ehlers-Danlos syndrome and Marfan syndrome, where shoulder instability can be severe and lifelong. Overhead athletes like swimmers, baseball pitchers, and gymnasts can also develop hypermobile shoulders over time as repetitive motion gradually stretches out the capsule.
How Doctors Assess It
The standard screening tool for joint hypermobility is the Beighton score, a 9-point scale that checks flexibility in the little fingers, thumbs, elbows, knees, and spine. Notably, it doesn’t directly test the shoulder. Because of this limitation, clinicians increasingly use additional assessments that specifically measure shoulder range of motion to catch hypermobility that the Beighton score misses. These tests involve measuring how far the shoulder can rotate in each direction and comparing it to established norms.
During a physical exam, a doctor will also check for the sulcus sign described above, test whether they can shift the ball of the humerus forward and backward in the socket, and look for signs of instability like apprehension (a reflexive tensing when the shoulder is moved toward a position where it feels like it might slip out).
Stabilizing a Hypermobile Shoulder
You can’t tighten loose ligaments through exercise, but you can build a muscular “brace” around the joint. Strengthening the muscles that surround and support the shoulder is the primary approach for managing hypermobility and reducing the risk of subluxation. The key muscle groups include the rotator cuff (four small muscles that hold the ball in the socket), the deltoids that cap the shoulder, the trapezius and rhomboids in the upper back that control the shoulder blade, and the biceps and triceps that assist with arm stability.
Physical therapy programs for hypermobile shoulders focus on controlled, low-resistance strengthening rather than stretching. The goal is to train these muscles to activate reflexively during movement, compensating for the loose passive structures. For people with connective tissue disorders, this process takes longer and requires more careful progression because the underlying tissue abnormality means the joint will always have more play than normal. In severe cases where subluxations are frequent and painful, surgical tightening of the capsule is an option, though outcomes are less predictable in people with systemic connective tissue conditions.