Posterior instability

Posterior dislocation

epidemiology

·      rare (2% of acute dislocations)

·      often missed - may be diagnosed

·      within 1 wk (25%)

·      after 1- 6 wks (25%)

·      after 6 wks - 6 mths (25%)

·      after 6 mths (25%)

aetiology

·      usually due to major trauma

·      MVA

·      seizures

·      ECT

·      electrocution

·      alcohol-related injuries

clinical
History

·      of injury

·      pain and stiffness

Examination

·      loss of ER

·       internal rotation deformity of 40o

radiology
Plain x-ray

·      AP x-ray

·      light-bulb sign (head like light bulb)

·      may see fracture lesser tuberosity

·      axillary x-ray

·      diagnostic

·      may see reverse Hill-Sachs lesion

CT san

·      confirms dislocation

·      quantifies humeral head defect

treatment

·      depends on

·      duration of dislocation

·      size of humeral head

Reduction

Indications

·      duration < 6 wks AND

·      defect < 20%

Technique

·      general anaesthetic

·      traction

·      may require open reduction

Stabilisation

Indications

·      duration < 1 yr AND

·      defect 20-50%

Technique

·      McLaughlin procedure

·      lesser tuberosity with attached subscapularis transferred into reverse Hill-Sachs lesion

·      renders defect an extra-articular problem

Hemiarthroplasty

Indications

·      duration > 1 yrs AND/OR

·      defect > 50%

Technique

·      placed in neutral cf. retroversion

·      to decrease incidence of posterior instability

Recurrent posterior subluxation

·      usually subluxation rather than dislocation

·      rarely requires reduction

aetiology

·      ligamentous laxity

·      trauma

·      repetitive microtrauma (common)

·      macrotrauma (uncommon)

·      occasionally there is history of trauma

·      commonly associated with multidirectional instability

·      posterior only - 20%

·      posterior and inferior - 20%

·      posterior, inferior and anterior - 60%

pathogenesis

·      capsular laxity

·      reverse Bankart lesion (detachment posterior labrum)

·      reverse Hill-Sachs lesion (defect in anterior humeral head)

·      increased retroversion of humeral head

·      posterior glenoid deficiency

clinical
History

·      pain and instability with arm in

·      forward flexion

·      adduction

·      internal rotation

Examination

·      tenderness posterior joint line

·      positive posterior apprehension test

·      may be

·      positive sulcus sign

·      positive anterior apprehension test

·      increased AP drawer

·      patient may be able to voluntarily dislocate shoulder

·      signs of ligamentous laxity

treatment

·      similar to multidirectional instability

Nonoperative

·      prolonged initial physical therapy for all patients

Operative

Indications

·      failed nonoperative treatment

·      major instability posterior

Technique

·      options

·      posterior capsular shift

·      reverse Putti-Platt

·      reverse Bristow

·      glenoid osteotomy

·      posterior capsular shift

·      posterior approach

·      T-incision in capsule

·      posteroinferior capsule shifted superiorly

·      labral detachment reattached if present

Multidirectional instability

definition

·      introduced as a concept by Neer & Foster in 1980

·      since then, recognised as much more common problem that is often misdiagnosed

·      requires instability in at least 2 planes

·      symptomatic inferior instability with

·      anterior and/or posterior instability

epidemiology

·      most patients athletic

·      sometimes seen in sedentary individuals

·      average age 24 yrs

·      15-54 yrs

aetiology

·      three aetiological factors in  varying combinations

·      inherent ligamentous laxity > 50%

·      repetitive overuse and capsular stress

·      one or more episodes of significant trauma < 50%

pathology

·      main pathology is increased joint volume due to enlarged inferior axillary capsular pouch

·      usually is collagen abnormality secondary to ligamentous laxity

Clinical
History

·      shoulder pain, fatigue and feeling of shoulder "slipping down" while carrying heavy loads

·      impingement type pain with overhead activities

·      anterior and/or posterior instability with arm in respective provocative position

·      transitory numbness of hand and arm

·      instability of other joints

Examination

·      sulcus sign

·      increased anterior and posterior translation

·      signs of generalised ligamentous laxity

radiology

·      traction x-rays

·      patient erect with 5-10 kg in each hand

·      shows inferior subluxation of humeral head

differential diagnosis

·      of inferior displacement of the humeral head

·      torn superior rotator cuff

·      suprascapular nerve palsy

·      deltoid atony (eg. CVA)

·      deltoid palsy

Treatment
Nonoperative

·      initially aimed at shoulder strengthening

·      aimed at strengthening 3 parts of deltoid, rotator cuff and scapular stabilisers

·      specific programme using Therabands and pulleys

·      combined with education programme

·       successful in 90% of cases

·      should persist for at least 12 months

·      allows evaluation of results of exercises

·      allows repeated assessment of patient for voluntary subluxation and psychiatric problems

·      allows repeated assessment of shoulder for direction of instability

Operative

Principles

·      should never operate on patient with voluntary instability

·      surgery for MDI less successful than surgery for unidirectional instability

·      standard stabilisation procedures not very successful for MDI

·      pathology not corrected and inferior instability remains

·      may displace head to opposite side in fixed subluxed position leading to arthritis

·      Neer recognises four surgical errors

·      surgery on voluntary dislocator with emotional problems will fail

·      shoulder may be loose but asymptomatic and pain is due to other cause (eg. AC arthritis, cervical radiculopathy)

·      standard surgery for unidirectional dislocations will fail as above

·      may be incomplete surgical correction of all elements of instability

·      Neer & Foster proposed inferior capsular shift

·      principle is to detach capsule from neck of humerus and shift it to the opposite side of the calcar to obliterate the inferior pouch

Indications

·      involuntary instability

·      failure of nonoperative programme for 12 months

·      persisting severe pain, instability or parasthesiae

Technique

·      performed anteriorly or posteriorly depending on main direction

·      EUA performed first to confirm diagnosis

·      standard deltopectoral approach

·      subscapularis detached

·      arm externally rotated

·      vertical incision at musculotendinous junction 2 cm from lesser tuberosity

·      upper 3/4 divided and lower 1/4 left intact to protect anterior circumflex humeral vessels

·      holding sutures placed in medial part of muscle to prevent retraction

·      medial muscular part peeled from underlying capsule

·      lateral tendinous part separated from capsule

·      cleft between superior and middle glenohumeral ligaments closed

·      T-shaped opening made in capsule

·      vertical incision laterally along articular margin of humeral head)

·      transverse incision in midline of capsule between middle and inferior glenohumeral ligaments

·      inferior capsular flap developed by detaching reinforced part of capsule containing inferior glenohumeral ligament from inferior aspect of neck of humerus as far as possible (to 6 o’clock)

·      joint inspected and Bankart lesion repaired if present

·      inferior capsular flap pulled superiorly and sutured to stump of subscapularis tendon and capsule remaining on humerus

·      tension on flap aimed at eliminating inferior pouch and reducing posterior capsular redundancy

·      superior flap drawn down over inferior flap and sutured down while arm in no flexion and 10-30o of external rotation

·      subscapularis tendon brought over and reattached to normal location

·      arm immobilised in Velpeau sling

·      Neer uses position of neutral flexion-extension and 10 degrees of external rotation with light plastic splint from wrist to middle part of arm and around waist with elbow bent at 90 degrees

·      maintained for 6 weeks

·      then active assisted exercises commenced

·      isometric exercises for deltoid and rotator cuff started at 8 weeks

·      resistive exercises added at 12 weeks

·      lifting more than 10 kg and participation in sports prohibited for 9 months and until strength normal compared with other side

Results

·      generally has satisfactory outcome

·      90% of patients satisfied with result

·      no significant loss of ROM