Shoulder Instability

Shoulder instability is not one diagnosis

Shoulder instability exists on a spectrum.

At one end is the young athlete who experiences a first traumatic anterior dislocation with a structural capsulolabral lesion. At the other is the patient with constitutional laxity, multidirectional symptoms or altered muscle recruitment without a major structural lesion.

These patients may all describe their shoulder as “unstable,” but they should not automatically receive the same treatment.

The central clinical question is therefore not simply “Is the shoulder unstable?”

It is:

What type of instability is present, what structures are involved, and how much of the problem is structural versus functional?

Laxity and instability are different

A shoulder can demonstrate substantial translation without being pathological.

Laxity describes physiological joint translation without symptoms. It is common in populations such as swimmers, gymnasts and martial artists.

Instability requires symptoms: apprehension, pain, subluxation or dislocation associated with abnormal translation.

A positive laxity test therefore does not automatically identify a problem requiring treatment.

The result only becomes clinically meaningful when it matches the patient's history and symptoms.

Stability depends on both passive and active systems

The glenohumeral joint sacrifices bony stability for mobility. The humeral head sits on a relatively shallow glenoid, meaning stability relies heavily on surrounding structures.

Static stabilisers include the:

• glenoid labrum

• joint capsule

• glenohumeral ligaments

• negative intra-articular pressure

The inferior glenohumeral ligament complex is particularly important during abduction and external rotation, the position associated with many traumatic anterior dislocations.

Dynamic stability comes largely from the:

• rotator cuff

• deltoid

• long head of the biceps

• scapular stabilisers

The rotator cuff compresses and centres the humeral head within the glenoid, while scapular control determines how effectively the glenoid is positioned relative to the forces acting on the arm.

This explains why rehabilitation still matters when a clear structural lesion exists.

Two people can have similar bone or labral damage but very different functional stability depending on rotator cuff strength, scapular control and neuromuscular coordination.

Classification helps determine treatment

The traditional TUBS/AMBRI model provides a useful starting point.

TUBS describes the more typical traumatic presentation:

Traumatic → Unilateral → Bankart lesion → Surgery often considered

AMBRI describes the opposite end of the spectrum:

Atraumatic → Multidirectional → Bilateral → Rehabilitation first

However, many patients do not fit perfectly into either category.

The Stanmore classification therefore views instability as a triangle between:

Type I: traumatic structural instability
Type II: atraumatic structural instability
Type III: non-structural muscle-patterning instability

Type III is especially important for physiotherapy.

Here, instability may arise primarily from abnormal recruitment patterns rather than a structural defect. These patients generally need neuromuscular retraining rather than surgical stabilisation.

A motor-control component can also coexist with structural pathology, meaning neuromuscular rehabilitation remains important even after surgery.

The history may tell you more than the MRI

A structured history is one of the most valuable parts of assessment.

Important questions include:

• Was the first event traumatic or atraumatic?

• Which direction did the shoulder move?

• Was it a full dislocation or a subluxation?

• How many episodes have occurred?

• How old was the patient at the first episode?

• Is the patient involved in contact, collision or overhead sport?

• Is there bilateral or generalised joint laxity?

• Is there apprehension or avoidance of certain positions?

• Does the shoulder become unstable during specific movements or even low-load daily tasks?

Young age is particularly important.

After a first traumatic anterior dislocation, recurrence risk is considerably higher in younger individuals, particularly those under 20, and increases further in competitive contact or overhead athletes.

This is why a first dislocation in a teenage collision-sport athlete should not be approached in exactly the same way as a first episode in a recreational athlete in their thirties.

Bankart, Hill-Sachs and bone loss change the picture

A Bankart lesion involves detachment of the antero-inferior labrum and inferior glenohumeral ligament complex from the glenoid.

Repeated instability can progressively alter this tissue, making recurrent episodes clinically important rather than harmless repetitions of the original event.

A Hill-Sachs lesion is an impaction defect of the humeral head created during anterior dislocation.

Its presence alone does not necessarily determine instability. What matters is whether the humeral defect interacts mechanically with the glenoid during movement.

The modern glenoid track concept describes lesions as on-track or off-track.

An on-track lesion remains within the functional glenoid contact zone and carries a lower mechanical engagement risk.

An off-track lesion can move outside that contact area during abduction and external rotation, increasing the risk of recurrent instability.

Glenoid bone loss must also be quantified rather than simply described as present or absent.

Once meaningful bone loss is combined with a humeral defect, isolated soft-tissue repair may no longer provide sufficient stability.

Surgery is based on risk, not simply on whether a dislocation occurred

Not every first-time dislocation requires surgery.

After reduction, short-term immobilisation is generally followed by progressive mobilisation. Prolonged immobilisation has not demonstrated a clear recurrence advantage and can contribute to stiffness and strength loss.

The more important decision is identifying the patient's future recurrence risk.

The Instability Severity Index Score considers factors including:

• age under 20

• competitive sport

• contact or overhead sport

• shoulder hyperlaxity

• Hill-Sachs lesion

• loss of glenoid contour

The score can support decision-making but should not be treated as an automatic surgical algorithm.

The patient's anatomy, sport, age, bone loss, functional demands and preferences all remain relevant.

Different structural problems require different procedures

For appropriate lower-risk structural presentations, an arthroscopic Bankart repair may restore the capsulolabral restraint.

When a Hill-Sachs lesion contributes significantly to instability, a remplissage may be added to address the humeral defect.

With substantial glenoid bone loss or a higher-risk bipolar lesion, a Latarjet or other bony reconstruction may be required.

The physiotherapist does not choose the operation, but understanding what was performed matters because different procedures create different rehabilitation considerations, particularly regarding range of motion, external rotation and the progression of high-risk positions.

In-season return involves accepting risk

Managing an athlete during a competitive season requires shared decision-making.

A low-risk athlete with a first episode and limited structural damage may sometimes complete the season with intensive rehabilitation, neuromuscular training and a criteria-based return to play.

However, delaying stabilisation in a high-risk athlete is not a neutral decision.

Each recurrent episode can potentially increase glenoid bone loss, enlarge the Hill-Sachs lesion and further compromise capsulolabral tissue.

The athlete should therefore understand that continuing the season may change not only the recurrence risk but also the type of surgery eventually required.

Rehabilitation must rebuild dynamic stability

Regardless of whether treatment is conservative or surgical, rehabilitation should restore the active system responsible for keeping the humeral head centred.

This includes:

rotator cuff strength and co-contraction

scapular control

neuromuscular coordination

strength and endurance through progressively demanding ranges

control in the positions where instability originally occurred

For functional instability, rehabilitation may also involve retraining abnormal muscle recruitment patterns until control progresses from deliberate conscious correction toward automatic stability.

This is particularly important in overhead athletes, where the shoulder eventually needs to tolerate high velocity in end-range abduction and external rotation.

Return to sport is more than strength and range of motion

A fixed postoperative timeline alone is not enough to determine readiness.

Return-to-sport assessment should combine three areas.

First, the athlete needs functional physical capacity:

• full or near-full sport-specific range

• adequate rotator cuff strength

• adequate scapular strength and endurance

• acceptable symmetry with the opposite shoulder

• dynamic control in high-risk positions

• sport-specific power and plyometric capacity where relevant

Second, sport-specific movement should be pain-free at progressively increasing intensity.

Third, the athlete should no longer demonstrate significant apprehension or fear of reinjury.

Psychological readiness matters because an athlete can demonstrate excellent strength yet still avoid the very position required for their sport.

Shoulder-specific tools such as the SIRSI or SIRSI-5 can help identify whether confidence, fear of reinjury or emotional factors remain barriers to return.

Treat the instability pattern, not just the damaged structure

Shoulder instability cannot be reduced to a Bankart lesion, a positive apprehension test or a loose capsule.

Successful management requires integrating:

mechanism + laxity + structural damage + bone loss + motor control + recurrence risk + sport demands + psychological readiness.

A structurally damaged shoulder may still require extensive neuromuscular rehabilitation.

A highly lax shoulder may require no treatment if it is asymptomatic.

And a shoulder that repeatedly subluxates may sometimes have a predominantly functional motor-control problem rather than a lesion that surgery can correct.

The most useful principle is therefore to classify first, quantify the structural risk, restore dynamic control, and return the athlete according to functional criteria rather than time alone.