- 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.
- Shoulder Arthroplasty:
- Complications of Posterior Dislocation:
- fractures of the posterior glenoid rim (occurs anteriorly directed forces that push humeral head out posteriorly);
- frx of proximal humerus (upper shaft, tuberosities, and head);
- recurrent posterior instability;
The treatment of posterior subluxation in athletes.
Posterior subluxation of the glenohumeral joint.
Locked posterior dislocation of the shoulder: Treatment using rotational osteotomy of the humerus. P Keppler et al. J. Orthop. Trauma. Vol 8. 1994. p 286-292.
Chronic unreduced dislocations of the shoulder. CR Rowe and B Zarins. JBJS-A. 1982. 64-A. p 494-505.
Rotational osteotomy of the humerus for posterior instability of the shoulder;
Locked posterior dislocation of the shoulder.
