Posterior Instability

Definition

 

Patients usually complain of subluxation rather than dislocation

- rarely requires reduction

 

Different entity to acute posterior dislocation usually

 

Epidemiology

 

Rare

 

Aetiology

 

1.  Ligamentous laxity > 50%

- commonly associated with MDI

- posterior only 20%

- posterior & inferior 20%

- posterior / inferior & anterior 60%

 

2.  Trauma

 

A.  Repetitive microtrauma 

- common

 

B.  Macro-trauma 

- uncommon

- seizures

- electrocution

- ECT

- alcohol related injuries

- MVA

 

Pathogenesis

 

1.  Capsulo- ligamentous

 

A.  Reverse Bankart lesion 

- uncommon

- detached posterior labrum < 10%

 

B.  Capsular laxity

- much more common

 

C.  Posterior IGHL avulsion

- reverse HAGL

 

2.  Bony

 

A.  Humeral Head Defects  

- reverse Hill-Sachs lesion 

- defect in Ant humeral head

- seen in traumatic dislocations / chronic posterior dislocation

- can make humerus unstable

- compared with anterior Hill-Sachs which rarely does

 

CT Humeral Head Defect

 

B.  Posterior glenoid deficiency

- seen in traumatic / chronic dislocations

 

Posterior Glenoid DeficiencyPosterior Glenoid Deficiency Sagittal

 

C.  Humeral head / glenoid retroversion

 

Shoulder Posterior Instability Glenoid Retroversion

 

History

 

Must exclude voluntary dislocator

 

History of ligamentous laxity / other problems

 

Examination

 

Must assess for

- MDI / Ligamentous Laxity

- voluntary dislocator

 

Tender posterior joint line 

- fairly specific for OA rather than instability

 

ROM

- loss of ER (in locked posterior dislocation)

 

Ligamentous laxity

 

Sulcus sign

- indicates MDI

 

Anterior apprehension

- indicates MDI

 

Posterior stress test 

- supine

- adduct, forward flex and IR arm

- posterior force

- apprehension test

 

Load and Shift / Posterior Drawer

 

Altchek Grading

 

Grade 0       No translation

Grade 1+     Up to glenoid rim

Grade 2+     Beyond rim with spontaneous reduction

Grade 3+     Translation beyond rim without spontaneous reduction

 

CT

 

1.  Define extent of Hill Sach's lesion

 

2.  Glenoid bone defect

 

3.  Glenoid version

 

Posterior Instability Glenoid Retroversion

 

MRI

 

Posterior bankart lesion

 

Shoulder MRI Posterior Labral Tear

 

Posterior labral cysts

 

Shoulder Posterior Labral Tear with Cysts0001Shoulder Posterior Labral Tear with Cysts0002Shoulder Posterior Labral Tear with Cysts0003

 

Management

 

Non-operative

 

Not infrequently little functional problems

 

Prolonged initial physical treatment for all patients

- minimum 12 months

- treat similar to MDI patients

- Matson & Rockwood 80-90% success rate

 

Operative

 

Indications

- failed non-operative management

- moderate to severe disability

 

Contra-Indications

- MDI

- voluntary dislocator

- ligamentous laxity

- minimal functional impairment

 

Pathology

 

1.  Posterior Bankart lesion

 

Options

- arthroscopic / open reconstruction

 

Posterior Labral Tear

 

Failure / Bony Block Revison

- posterior approach

- detach infraspinatous

- expose capsule

- divide capsule medial to glenoid

- take 2 cm long x 1 cm thick iliac crest

- secure to glenoid with 2 x small fragment screws

- reattach capsule lateral to bony block

 

Failed Posterior Arthroscopic Shoulder Stabilisation0001Failed Posterior Arthroscopic Shoulder Stabilisation0002Shoulder Posterior Bony Block0001Shoulder Posterior Bony Block0002

 

2.  Capsular laxity

 

Options

- posterior capsular shift arthroscopic or open

- reverse Putti-Platt

 

Open capsular plication

 

Bigliani and Flatow July 1995

- 35 patients

- If primary operation 23 of 24 successful

- 89% stable at 5 yrs

 

Reverse Putti-Platt

 

Technique

- posterior approach

- posterior imbrication of IS & Tm 

- combine with posterior capsule imbrication

- shorten tendon 1cm = 20°

- limit IR to 20o

 

3.  Humeral Head Defect

 

Humeral Head Anterior Hill Sachs CT

 

1.  HS < 25% 

- leave

 

2.  HS > 25%

- transfer SSC + LT (McLaughlin)

- OC allograft

 

3.  HS > 40%

- hemiarthroplasty / TSR (older patient)

- OC allograft (younger patient)

 

4.  Posterior Glenoid Defects

 

Option

- posterior glenoid bone graft

 

Posterior Glenoid Bone BlockPosterior Bone Block CT

 

Results

 

Meuffels etal JBJS Br 2010

- 18 year follow up of 11 patients treated with posterior bone block

- 36% had had recurrent dislocation

- half would not have the surgery again

- all had evidence of OA

 

5.  Retroverted Glenoid Version / Static Posterir Shoulder Subluxation

 

Issue

- posterior shoulder subluxation > 65%

- shoulder OA

- young age

- glenoid osteotomy

 

Static Posterior Shoulder SubluxationGlenoid Retroversion SPSSSPSS MRISPSS Calculation

 

Option

- posterior opening wedge glenoid osteotomy

- rarely indicated & technically hard

 

Indication

- congenital retroversion of glenoid > 30o

 

Technique

- only 5 mm medial to glenoid rim otherwise injure SS nerve

- must prevent penetration of glenoid

 

Complications

- anterior impingement of subscapularis on coracoid causing pain

- anterior subluxation of humeral head