Classification
Instability is best described by direction, cause and structural abnormality rather than by one acronym.
Common patterns:
- traumatic anterior instability with structural injury
- atraumatic instability with capsular laxity or muscle-patterning abnormality
- posterior instability
- multidirectional instability
Shoulder instability can be classified by:
- direction: anterior, posterior, multidirectional
- mechanism: traumatic versus atraumatic
- frequency: first episode versus recurrent
- structural damage
- presence of generalized laxity
The clinical problem is instability causing symptoms, not laxity alone.
First-time traumatic anterior dislocation
Assessment includes:
- mechanism
- age and activity
- previous instability
- axillary nerve function before and after reduction
- radiographs before/after reduction where appropriate
Associated lesions may include:
- Bankart lesion
- Hill-Sachs defect
- greater-tuberosity fracture
- rotator-cuff tear, particularly in older patients
Recurrence risk
Younger patients involved in contact or overhead sport have a higher recurrence risk after traumatic anterior dislocation. Bone loss on the glenoid or humeral head further changes risk and treatment.
Imaging
- radiographs for acute injury
- CT for glenoid/humeral bone loss
- MRI or MR arthrogram for labral and soft-tissue pathology
Plain radiographs should identify fracture, glenoid morphology and humeral-head lesions.
CT is useful for quantifying glenoid bone loss and characterising bony defects.
MRI or MR arthrography can define labral and capsular pathology.
Treatment
Non-operative
Appropriate for many first dislocations and for atraumatic/multidirectional instability:
- short period of comfort immobilisation when required
- progressive range restoration
- rotator-cuff and scapular rehabilitation
- proprioception and kinetic-chain work
Operative
Indications depend on recurrence, structural lesions, bone loss, sport and patient goals.
Options include:
- arthroscopic or open labral repair/capsular stabilisation
- remplissage for selected engaging Hill-Sachs lesions
- glenoid bone augmentation when clinically significant bone loss makes soft-tissue repair unreliable
Atraumatic muscle-patterning problems are primarily rehabilitation disorders; surgery is rarely first-line.
Traumatic anterior instability
Common structural lesions include:
- anteroinferior labral injury
- Hill-Sachs lesion
- glenoid bone loss
- capsular injury
Recurrence risk is influenced by age, sport, activity, bone loss and soft-tissue damage.
Examination
Assess:
- apprehension rather than pain alone
- relocation response
- anterior/posterior translation
- generalized hypermobility
- rotator cuff and scapular control
- axillary nerve function after acute dislocation
In recurrent instability, determine the position and activity that trigger episodes.
Bone loss and bipolar lesions
The interaction between glenoid bone loss and a Hill-Sachs defect is central. A humeral defect that engages the anterior glenoid rim under functional loading has a different recurrence risk from a contained defect.
Concepts such as the glenoid track help integrate bipolar bone loss into surgical planning.
Operative options
Soft-tissue stabilisation may be appropriate when bone loss is limited and tissue quality is suitable.
Bony procedures may be required when there is:
- substantial glenoid bone loss
- failed previous soft-tissue repair
- high-risk bipolar lesion
- other structural reasons that make isolated labral repair unreliable
Multidirectional instability
This often has different biology and should usually begin with prolonged rehabilitation focused on:
- scapular control
- rotator cuff
- proprioception
- movement pattern retraining
Surgery is reserved for carefully selected patients who fail structured rehabilitation.
Posterior instability
Posterior instability may follow trauma or repetitive loading and can be missed. Examination and imaging should assess posterior labrum, glenoid morphology and reverse Hill-Sachs lesions where relevant.
FRCS synthesis
The exam answer should progress from direction and cause → structural lesion → bone loss → patient risk profile → procedure. Avoid treating all recurrent instability with the same operation.