A partially dislocated shoulder, called a subluxation, often looks subtly deformed compared to a full dislocation. The ball of the upper arm bone shifts partially out of its socket but doesn’t pop out completely, so the visual changes can be mild enough to miss at first glance. Instead of the dramatic displacement you’d see with a full dislocation, you’re looking for an uneven shoulder contour, a visible dip or groove near the top of the shoulder, and swelling around the joint.
How It Looks Compared to a Normal Shoulder
The shoulder joint normally sits in a smooth, rounded contour. The ball at the top of your upper arm bone (the humerus) fits concentrically against the shallow socket of your shoulder blade. When subluxation happens, the ball shifts partially out of that centered position, and the joint space widens on one side while narrowing on the other. On X-ray, this creates a characteristic V-shaped gap between the bones, with the point of the V indicating which direction the bone has shifted.
What you’ll see on the surface depends on the direction and degree of the shift. The most common signs include:
- A visible groove or dip below the bony point of the shoulder. This is sometimes called a sulcus, and it appears because the upper arm bone has dropped or shifted downward, leaving a hollow where the joint normally fills out the skin.
- Asymmetry between your two shoulders. The affected side may look flatter, lower, or slightly squared off compared to the uninjured shoulder’s rounded shape.
- Swelling or puffiness around the joint. This develops as the soft tissues around the shoulder become irritated or inflamed from the bone shifting out of position.
- A slight bulge where the bone has shifted. If the humerus moves forward (the most common direction), you might notice a subtle bump at the front of the shoulder.
These changes are often less obvious than what you’d see with a full dislocation, where the shoulder looks clearly “wrong” with a large, visible gap or a lump where the bone has completely escaped the socket. With a subluxation, the bone is still partially in contact with the socket, so the deformity can be subtle, especially in someone with more muscle mass around the joint.
What It Feels Like
Because the visual signs can be hard to spot, what you feel is often the more reliable indicator. People with a shoulder subluxation typically describe stiffness, mild to moderate pain, and a sense of instability in the shoulder. Many people report a feeling that the bone is “sliding” or shifting within the joint, or a sensation that the shoulder could pop out entirely with certain movements. Some experience what’s often called “dead arm” syndrome, a brief episode of numbness, tingling, or weakness shooting down the arm when the bone shifts.
The pain tends to be less severe than a full dislocation. You can usually still move the arm, though certain positions feel unstable or provoke a sharp catch of pain. Reaching overhead, rotating your arm outward, or throwing motions are common triggers. The shoulder may feel like it “gives way” during these activities, then settles back into a more normal position on its own.
How Doctors Confirm a Subluxation
Because the visual signs of a partial dislocation are subtle, doctors use specific hands-on tests to evaluate the joint. These tests deliberately shift the upper arm bone in different directions to measure how much it moves and whether the movement reproduces your symptoms.
One of the most telling is the sulcus sign test. A doctor pulls your elbow gently downward while your arm hangs at your side. If a visible groove or dip appears just below the bony point of the shoulder, it confirms that the humeral head is translating too far in the downward direction. The apprehension test is another key exam: with your arm out to the side at 90 degrees and your elbow bent, the doctor rotates your arm outward. A positive result isn’t necessarily pain. It’s the instinctive feeling that your shoulder is about to pop out, causing you to tense up or pull away. A follow-up called the relocation test applies gentle backward pressure on the front of the shoulder during the same position. If that pressure relieves the apprehension, it strongly points to instability.
Imaging usually follows. Standard X-rays can reveal the V-shaped widening of the joint space, and an MRI can show whether the soft tissue structures, particularly the ring of cartilage (labrum) that deepens the socket, have been torn or detached.
Common Causes
Shoulder subluxations generally fall into two categories. Traumatic subluxations happen from a specific injury: a hard fall on an outstretched hand, a collision in contact sports, or a sudden forceful pull on the arm. The impact drives the humeral head partially out of the socket and stretches or tears the ligaments and labrum that normally hold it in place.
Atraumatic subluxations happen without a clear injury. Some people have naturally looser ligaments throughout their body, a trait sometimes associated with connective tissue conditions like Ehlers-Danlos syndrome. Others develop looseness in the shoulder capsule from repetitive overhead motions, common in swimmers, volleyball players, and baseball pitchers. In these cases, the shoulder gradually becomes unstable over time rather than shifting from a single event.
Why Repeated Subluxations Get Worse
One of the most important things to understand about a partial dislocation is that each episode can make the next one more likely. When the humeral head shifts out of position, it often damages the structures that are supposed to prevent exactly that kind of movement.
The most common injury is a Bankart lesion, a tear where the labrum detaches from the front-bottom edge of the socket. Studies have found this type of tear in 87% to 100% of first-time anterior dislocations, and subluxations can cause the same damage on a smaller scale. On the other side of the equation, the humeral head itself can develop a dent called a Hill-Sachs lesion, a compression fracture on the back of the ball created when it impacts the rim of the socket during displacement. This defect has been found in up to 90% to 100% of patients with recurrent shoulder instability.
The problem compounds over time. Each episode can make existing bone defects and labral tears larger, which leads to even less structural support and more frequent episodes. Without treatment, this cycle of chronic instability generally leads to degenerative arthritis in the shoulder joint. Young age, participation in contact sports, and naturally loose ligaments are all risk factors for falling into this pattern of recurrence.
Recovery and Treatment
The good news is that a single subluxation episode, especially a first-time event, often responds well to conservative treatment. The initial focus is on reducing pain and swelling with rest, ice, and a sling to immobilize the shoulder for a short period. Physical therapy is the cornerstone of recovery, focusing on strengthening the rotator cuff muscles and the muscles around the shoulder blade that help stabilize the joint dynamically.
Athletes with a first-time subluxation can sometimes return to activity within two to three weeks, though this comes with a higher risk of recurrence compared to taking a longer, more cautious rehabilitation approach. For people with recurrent subluxations or significant structural damage like large Bankart or Hill-Sachs lesions, surgical stabilization is often recommended. Arthroscopic repair typically requires about six months before a full return to demanding physical activity.
The timeline for non-athletes or people with desk jobs is generally shorter for returning to daily activities, but the underlying rehabilitation work is similar. Building the strength and coordination of the muscles that surround the shoulder is what ultimately prevents the joint from slipping again, regardless of whether surgery is involved.