- See:
Fracture Dislocation: /
Anterior Instability
- Discussion:
- posterior dislocation is rare & should raise possibility of
seizure as
cause, other causes include an electric
shock or ECT without muscle relaxants;
-
mechanism:
- axial loading of the adducted, internally rotated arm;
- because the internal rotator muscles are approx twice as powerful as
the exernal rotator muscles, a
sudden
contraction (such as from a seizure or shock) will cause the humeral head to
dislocate;
- involuntary recurrent posterior subluxation may be associated w/ high
forces generated during follow thru
phase of various sports activities;
- this develops as humerus is in adduction, flexion, and internal
rotation, & maximal contractions of
subscapularis
and deltoid;
- see
throwing injuries of shoulder
- voluntary dislocation:
-
Electromyography in voluntary posterior instability of the shoulder
-
risk factors:
- reverse Bankhart (detachment of posterior labrum);
- defect of the anterior portion of the humeral head (
reverse
Hill Sachs)
- increased retroversion of the humeral head or retroversion of the
glenoid;
- posterior glenoid deficiency;
- note that posterior dislocation is distinguished from recurrent posterior
instability (this is associated with
generalized laxity and is only associatted with
a documented posterior dislocation in about 23% of cases);
- posterior instability is often associated with
multidirectional instability;
- Physical Exam:
- 3 types of the posterior instability may be found:
- unidirectional
- bidirectional (inferior and posterior instability)
-
multidirectional (anterior, inferior, and posterior):
- references:
- Recurrent posterior instability (subluxation) of the
shoulder.
- Recurrent posterior shoulder instability. Diagnosis and
treatment.
-
posterior apprehension test:
- posterior translation stress is applied to the arm which is placed
in flexion, adduction, and internal rotation;
- w/ frank dislocation, pt usually presents with arm adducted and internally
rotated, and attempts at abduction
and external rotation are painful;
- inability to externally rotate in neutral position;
- inability to supinate;
- the coracoid process appears prominent;
- w/ chronic undreduced dislocation, exam may resemble
frozen shoulder;
-
Radiographs:
-
Reverse Hill Sach Lesion
- compression fracture of the anteromedial portion of the humeral head
is produced by the posterior cortical
rim of the
glenoid;
- references:
- Excessive retroversion of the glenoid cavity. A cause of
non-traumatic posterior instability of the shoulder
-
Closed Reduction:
- Non Operative Treatment:
- indicated for defects less than 20%;
- involves strengthening of the external rotators (infraspinatus);
- Operative Treatment: Arthroscopic Options: (see
anterior reconstruction)
- posterior capsule imbrication: (see
arthroscopic knots)
-
rotator interval lesion
- accessory posterior portal:
- created 2 cm inferior to the posterolateral acromial angle;
- this is about 1 cm lateral to a standard posterior glenohumeral
portal
- improves access to the posteroinferior aspect of the glenoid labrum
and capsule;
- posterior band of the inferior glenohumeral ligament is identified;
- goal is to shift the posterior capsule approximately 1 cm
superior, opposing the shifted the capsule to the
labrum (assumming no labral tear);
- superiormost suture was placed at the level of the biceps insertion (see
slap repair)
- labral pathology:
- incomplete stripping / separation without displacement
- marginal crack / incomplete avulsion
- chondrolabral erosion / loss of contour
- flap tear
- references:
-
Management of
the failed posterior/multidirectional instability patient
-
Posterior
instability of the shoulder following thermal capsulorrhaphy for
multidirectional instability.
-
Arthroscopic
posteroinferior capsular plication and rotator interval closure after Bankart
repair in patients
with traumatic anterior
glenohumeral instability.
-
A
biomechanical analysis of shoulder stabilization: posteroinferior glenohumeral
capsular plication.
-
Posterior
shoulder instability secondary to reverse humeral avulsion of the glenohumeral
ligament.
-
Arthroscopic
management of posterior instability: evolution of technique and results
-
Four-quadrant
approach to capsulolabral repair: an arthroscopic road map to the glenoid
-
Arthroscopic Technique for the Evaluation and Treatment of Posterior Shoulder
Instability
-
Arthroscopic Posterior Labral Repair and Capsular Shift for Traumatic
Unidirectional Recurrent
Posterior Subluxation of the Shoulder
- Open Surgical Treatment Options:
- Postero-Inferior Capsular Shift: (Bigliani et al JBJS
1995 and B Fuchs MD et al. JBJS)
- posteroinferior aspect of capsule is shifted superiorly;
- lateral position;
-
posterior approach to the shoulder:
- oblique incision across the scapular spine starting at
posterolateral apsect of the acromion;
- oblique incise gives nicer scar than verticle scars;
- deltoid is split no more than 5 cm below acromion (deltoid may be
split from the scapular spine to
enhance
exposure);
- careful with axillary nerve:
-
The
posterior branch of the axillary nerve: an anatomic study
-
controversies: deep dissection:
- infraspinatus split approach:
- references:
- Posterior capsulorrhaphy through
infraspinatus split for posterior instability.
Dreese J, Tech Shoulder Elbow Surg 2005;6:199-207.
- Infraspinatus muscle-splitting incision in
posterior shoulder surgery: An anatomic and
EMG study. Am J Sports Med 1994;22:113-120.
- identify the interval between the infraspinatus and the
teres minor (infraspinatus is cut and tagged for
later closure);
-
capsule
- identify the underlying capsule and clear it from
the overlying musculature;
- Bigliani et al: capsule is incised 1 cm medial to labral
edge (carefult not to injure axillary nerve);
- Fuchs et al:
- posterior aspect of the capsule is then incised
horizontally at the midglenoid level, from the site
of the glenoid attachment to the site of the humeral attachment.
- capsule is then incised vertically about 5 mm medial
to its attachment on the humerus
(avoid axillary nerve injury);
- T-shaped incision yielded a superior flap and an
inferior flap.
- shoulder is dislocated posteriorly and sequential
examination of the joint is carried out from
anterior to posterior;
- labrum is examined and is repaired if torn;
- capsule is shifted vertically and imbricated;
- superior flap is shifted inferiorly and fixed to the
lateral rim of the capsule
- inferior flap is shifted superiorly and fixed
superiorly to the lateral capsule;
-
outcomes:
- in the study by B Fuchs MD et al. JBJS, the authors
reviewed 26 consecutive shoulders which
had recurrent, voluntary posterior subluxation of the shoulder;
- subjective results were excellent for sixteen shoulders,
good for eight, and fair for two;
- instability recurred in six (23 percent) of the 26
shoulders;
- capsular shift references:
- Shift of the posteroinferior aspect of the capsule for
recurrent posterior glenohumeral instability.
- Capsulorrhaphy with a staple for recurrent posterior
subluxation of the shoulder.
- Shift of Posteroinferior Aspect of Capsule for Recurrent
Posterior Glenohumeral Instability;
Bigliani MD JBJS. Vol 77-A, No 7. Jul 1995.
- Post-Inferior Capsular Shift for Treatment of Recurrent,
Voluntary Posterior
Subluxation of Shoulder. Fuchs JBJS Vol 82-A. Jan 2000. p 16.
- McLaughlin Procedure:
- involves transfer of lesser tuberosity w/ its attached
subscapularis tendon into the defect;
- indicated for defects more than 20% but less than 40% of the joint
surface;
-
disadvantages: can limit internal rotation of
shoulder;
-
Arthroscopic Fixation of the Subscapularis Tendon in the Reverse Hill-Sachs
Lesion for
Traumatic Unidirectional Posterior Dislocation of the Shoulder.
- Allograft Reconstruction: (see
allograft menu)
- involves insertion and fixation of a shaped piece of allograft into
the defect;
- indicated for patients w/ greater than 40% defect in the humeral
head who have recurrent posterior
instability;
- advantages: prevents posterior dislocation w/o limiting internal
rotation;
-
technique:
- use anterior
approach to the shoulder;
- cryopreserved femoral head
allograft is
shaped to fit into humeral head defect so that outer
spherical femoral surface is congruent w/ humeral surface;
- grafts are fixed to the humeral head w/ a 3.5 mm cancellous
lag screws;
- references:
- Recurrent posterior dislocation of the shoulder: treatment
using a bone block.
-
Treatment of
locked chronic posterior dislocation of the shoulder by reconstruction of the
defect
in the humeral
head with an allograft
- Allograft Reconstruction of Segmental Defects of the
Humeral Head for the Treatment of
Chronic Locked Posterior Dislocation of the Shoulder.
C. Gerber M.D. and S.M. Lambert. JBJS Vol. 78-A, March,
1996.