What Is the Sulcus Sign for Shoulder Instability?

The sulcus sign is a hands-on clinical test in which an examiner pulls a patient’s relaxed arm straight downward while looking for a visible depression, or “sulcus,” that forms just beneath the bony tip of the shoulder. That dimple appears when the ball of the upper arm bone slides excessively downward inside the shoulder socket, and its size tells the clinician how much inferior laxity the joint has. The test is one of the cornerstones of evaluating shoulder instability, especially the multidirectional variety, yet its meaning depends heavily on context and technique.

How the Test Is Performed

The patient sits or stands with the arm hanging loosely at the side, muscles completely relaxed. The examiner grasps the elbow or distal forearm and applies a steady downward (inferior) traction force. While pulling, the examiner watches and feels the space between the top of the humeral head and the lateral edge of the acromion. If the humeral head drops away from the acromion, a visible groove or hollow appears in the skin over that gap. That groove is the sulcus sign.

Arm position matters. The standard version is done with the arm in a neutral rotation, hanging naturally. But the real diagnostic power comes from repeating the test with the arm rotated outward, because the behavior of the sulcus in external rotation reveals something different about which structures are compromised. We’ll get to that distinction shortly, because it changes the clinical decision-making significantly.

Grading the Sulcus Sign

Clinicians grade the sulcus sign based on how far the humeral head translates downward, measured by the width of the gap that opens up beneath the acromion:

Grade 1: Less than 1 centimeter of inferior translation. This is generally considered within the range of normal laxity for many people.
Grade 2: Between 1 and 2 centimeters. This suggests meaningful laxity and, in a symptomatic shoulder, is often clinically significant.
Grade 3: Greater than 2 centimeters. This indicates substantial inferior instability and is strongly associated with multidirectional instability.

In a study of athletes undergoing arthroscopic treatment for multidirectional instability, all patients had increased joint laxity on exam, and the majority had a grade 2 or greater sulcus test.¹ So while a grade 1 sulcus is common even in healthy shoulders, grade 2 and especially grade 3 tend to show up in patients who actually have instability problems.

The Anatomy Behind the Sulcus

The shoulder is the most mobile joint in the body, which comes at the cost of inherent instability. The socket (glenoid) is shallow, covering only about a third of the humeral head’s surface at any given position. What keeps the ball centered in the socket is a combination of active stabilizers like the rotator cuff muscles and passive stabilizers like the joint capsule and its thickened ligament bands.

When you pull the arm downward, you’re testing the passive restraints against inferior translation. The structures most responsible for resisting that downward pull depend on arm position. With the arm at the side in a neutral or internally rotated position, the negative pressure inside the sealed joint capsule is a major stabilizer. A cadaver study found that simply venting the capsule (breaking that seal) significantly increased how far the humeral head could slide up and down.² In other words, the vacuum effect inside the joint does a lot of the work when the arm is just hanging at your side.

When the arm is rotated outward, the coracohumeral ligament becomes the key restraint against inferior displacement.² Meanwhile, when the arm is raised away from the body, the inferior glenohumeral ligament complex takes over. That complex acts like a hammock slung beneath the humeral head, with its anterior and posterior bands tightening depending on whether the arm is rotated inward or outward.³ The inferior glenohumeral ligament is also an important passive stabilizer during external rotation specifically.⁴

These ligaments also have viscoelastic properties, meaning they stiffen when loaded quickly. Research on the inferior glenohumeral ligament showed that its superior band and anterior pouch stiffened under rapid loading, which may help restrain the humeral head from sudden abnormal displacement during explosive movements like throwing.⁵ This is one reason a shoulder can tolerate the forces of overhead sports under normal conditions but give way when these structures are compromised.

Why the External Rotation Modification Changes Everything

This is arguably the most clinically useful nuance of the sulcus sign, and it’s the part most often glossed over in casual descriptions. When you repeat the downward traction test with the patient’s arm externally rotated, the coracohumeral ligament and the tissue of the rotator interval (a gap between two rotator cuff tendons at the top-front of the shoulder) should tighten and resist the inferior pull. In a normal shoulder, the sulcus either disappears or shrinks when the arm is externally rotated.

If the sulcus persists in external rotation, it signals that the rotator interval structures are incompetent. This finding has specific surgical implications. A review of rotator interval closure techniques noted that a persistent sulcus in external rotation is considered one of the key indications for surgically tightening the rotator interval, along with significant inferior laxity in the setting of multidirectional instability.⁶ Without this modification, the standard sulcus sign tells you the shoulder is loose inferiorly but doesn’t pinpoint which structures are failing.

Laxity Is Not the Same as Instability

One of the biggest misconceptions about the sulcus sign is that a positive result automatically means something is wrong. It doesn’t. Many healthy, asymptomatic people have detectable inferior translation. A study of asymptomatic athletes found that about half of men had a grade 1 sulcus and roughly 46 percent had a grade 2 sulcus, while only about 3 percent reached grade 3. Women showed even more laxity: about 36 percent were grade 1, 54 percent grade 2, and 9 percent grade 3.⁷

So a grade 2 sulcus is present in nearly half of healthy athletes and most of them have no symptoms whatsoever. Laxity is a physical property of the joint: how much it moves. Instability is a clinical problem: the shoulder moves enough to cause pain, subluxation, or dislocation, and the person can’t function normally. You can be lax without being unstable. The sulcus sign becomes meaningful only when it’s interpreted alongside symptoms, the patient’s history of dislocations or subluxations, and other provocative tests like the apprehension and relocation maneuvers.

Reliability Between Examiners

Any physical exam test is only useful if different examiners can agree on what they’re finding. The sulcus sign has fair to good agreement between examiners, with a reliability coefficient of 0.60 in a study that specifically assessed interexaminer consistency for shoulder instability tests in symptomatic patients.⁸ That’s respectable but not outstanding. The same study found that careful attention to arm positioning and using apprehension as the positive criterion for provocative tests improved reliability across the board.

A 0.60 reliability score puts the sulcus sign in a middle range: better than many orthopedic physical exam findings, but not a test where two different clinicians will always assign the same grade. This is one reason the test is used as part of a broader exam rather than as a standalone diagnostic tool. A clinician who finds a grade 2 sulcus will also check for anterior and posterior translation with the load-and-shift test, look for apprehension with the arm in the throwing position, and consider imaging before making a diagnosis.

Generalized Laxity and the Sulcus Sign

You might expect that people who are “double-jointed” everywhere would automatically have a large sulcus sign. Generalized joint hypermobility is typically measured with the Beighton score, a quick screen that checks flexibility at the fingers, elbows, knees, spine, and thumbs. However, a study specifically examining whether the Beighton score correlated with shoulder-specific laxity measures found a poor correlation with the sulcus sign, with a correlation coefficient of just 0.29. No difference was found in the mean sulcus sign grade between groups with high and low Beighton scores.⁹

This is a genuinely surprising finding. It means that someone who scores high on generalized hypermobility won’t necessarily show more inferior shoulder laxity on exam. The shoulder has its own set of local stabilizers, and those structures can be tight even in a person whose elbows hyperextend and whose fingers bend backward easily. For clinicians, this means the Beighton score shouldn’t be used as a shortcut to predict what the sulcus sign will show. You have to test the shoulder itself.

Imaging to Quantify What the Hands Feel

The sulcus sign is inherently subjective: the examiner estimates translation by sight and feel. Imaging can add precision. A study comparing dynamic ultrasound and stress radiography for measuring inferior glenohumeral laxity in asymptomatic shoulders found that the average inferior translation was about 4.7 millimeters by stress X-ray and about 4.4 millimeters by ultrasound, with good agreement between the two methods.¹⁰ These numbers give some reference for what “normal” looks like on imaging. In practice, imaging for inferior laxity is used mainly in research or when clinical exam findings are equivocal. Most clinicians rely on the manual test for day-to-day assessment.

Rehabilitation for a Symptomatic Sulcus

When the sulcus sign is positive and the patient has symptoms of multidirectional instability, conservative treatment with structured rehabilitation is usually the first approach. The goal is to train the dynamic stabilizers, especially the rotator cuff and the muscles that control the shoulder blade, to compensate for the loose passive structures.

A rehabilitation study of patients with multidirectional instability found large improvements in all functional instability questionnaires, with the greatest effect seen on a shoulder-specific quality-of-life measure. Scapular upward rotation improved in the early ranges of arm elevation, and all strength measures improved substantially.¹¹ In other words, patients felt better, moved their shoulder blades more efficiently, and got stronger, even though the underlying capsular laxity presumably didn’t change.

Not all exercise programs are created equal, though. A randomized trial comparing two rehabilitation approaches found that a program specifically designed for multidirectional instability outperformed a more traditional strengthening protocol at both three and six months of follow-up.¹² The evidence base for exercise-based management is still growing, though. A systematic review cautioned that the overall quality of evidence for improvements in shoulder kinematics, clinical scores, and strength from exercise programs was very low by formal grading standards.¹³ The direction of the findings is encouraging, but the research is still catching up with clinical practice.

When Surgery Becomes the Discussion

For patients who have completed a thorough rehab program and still have disabling instability, surgical options exist. The classic procedure for multidirectional instability is the inferior capsular shift, in which the surgeon tightens the redundant, baggy capsule by shifting and overlapping the tissue to reduce the overall volume of the joint. This can be done open or arthroscopically.

Long-term results have been favorable. A study following 75 patients for a minimum of seven years after arthroscopic inferior capsular shift found that only three patients (about 4 percent) experienced a redislocation, and those were all after significant trauma. Shoulder scores for function and pain improved significantly across the board, and range of motion was largely preserved, with only a modest decrease in external rotation of about five degrees on average.¹⁴ A separate study of athletes who underwent open capsular shift for multidirectional instability found a failure rate of about 8 percent at a median follow-up of roughly four and a half years, with a high rate of return to demanding overhead sports.¹⁵

Rotator interval closure is sometimes added to these procedures, particularly when the sulcus sign persists in external rotation, signaling that the rotator interval tissue is contributing to the instability.⁶ The decision to close the rotator interval is not automatic; it depends on the specific pattern of laxity found on exam and during surgery. Over-tightening this area can restrict external rotation, which is a real concern for athletes who need full range of motion for throwing or swimming.

Gender Differences in Baseline Laxity

As the data on asymptomatic athletes showed, women tend to have more inferior translation than men. The proportion of women reaching grade 3 was roughly three times that of men (about 9 percent versus 3 percent), and women had a higher proportion of grade 2 findings as well.⁷ This has practical implications for interpreting the sulcus sign. A grade 2 sulcus in a female athlete may represent her normal baseline, whereas the same finding in a male patient is less common and warrants closer scrutiny.

This sex-based difference is thought to relate to hormonal influences on collagen and connective tissue properties, though the exact mechanisms are still debated. What it means at the clinic is that the examiner should always compare both shoulders and consider the patient’s sex, sport, and baseline flexibility when deciding whether a positive sulcus sign is clinically relevant or just a normal variant. A positive test in isolation, without pain or a history of instability episodes, is rarely enough to justify invasive treatment.

The Sulcus Sign in the Context of a Full Shoulder Exam

No single test tells the whole story of shoulder instability. The sulcus sign is specifically designed to detect inferior laxity, but most patients with instability problems have laxity in more than one direction. A clinician performing a complete instability workup will combine the sulcus sign with anterior and posterior load-and-shift testing, the apprehension test (arm in abduction and external rotation), the relocation test (posterior force on the humeral head during apprehension), and the release or surprise test (removing that posterior force suddenly). The reliability of these provocative tests improves when the examiner uses the patient’s sense of apprehension, rather than just pain, as the criterion for a positive finding.⁸

Taken together, these maneuvers map the shoulder’s stability in all directions. The sulcus sign’s unique contribution is identifying the inferior component, and its behavior in external rotation distinguishes rotator interval pathology from generalized capsular laxity. That distinction matters because it directly influences which surgical procedure, if any, is appropriate. A shoulder with isolated anterior instability after a traumatic dislocation is a fundamentally different problem from a shoulder that’s loose in every direction, and the treatment for each is different.