- See:
Fracture Dislocation:
- 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
-
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):
-
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;
- Closed Reduction:
- Non Operative Treatment:
- indicated for defects less than 20%;
- involves strengthening of the external rotators (infraspinatus);
- Surgical Treatment Options:
- 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;
- 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);
-
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;
- 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 the humeral head defect so that the outer spherical femoral
surface is congruent with the humeral surface;
- grafts are fixed to the humeral head w/ a 3.5 mm cancellous lag screws;
- 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.
Recurrent posterior instability (subluxation) of the shoulder.
Rotational osteotomy of the humerus for posterior instability of the shoulder;
Recurrent posterior shoulder instability. Diagnosis and treatment.
Posterior subluxation of the glenohumeral joint.
Capsulorrhaphy with a staple for recurrent posterior subluxation of the shoulder.
Recurrent posterior dislocation of the shoulder: treatment using a bone block.
Excessive retroversion of the glenoid cavity. A cause of non-traumatic posterior instability of the shoulder
Locked posterior dislocation of the shoulder.
Shift of the posteroinferior aspect of the capsule for recurrent posterior glenohumeral instability.
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.
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.
Shift of the Posteroinferior Aspect of the Capsule for Recurrent Posterior Glenohumeral Instability;
L.U. Bigliani MD, R.G. Pollock MD, S.J. Mcilveen MD, D.P. Endrizzi MD, andE.L. Flatow MD. JBJS. Vol 77-A, No 7. Jul 1995.
Posterior-Inferior Capsular Shift for the Treatment of Recurrent, Voluntary Posterior Subluxation of the Shoulder.
B Fuchs MD et al. JBJS Vol 82-A. Jan 2000. p 16.
Arthroscopic Fixation of the Subscapularis Tendon in the Reverse Hill-Sachs Lesion for Traumatic Unidirectional Posterior Dislocation of the Shoulder.
