Head of the humerus is displaced posteriorly with respect to the glenoid fossa.
Incidence -2-4% of shoulder dislocation.
Most commonly missed dislocation
Based on etiology
1.Sprains to posterior shoulder joint
2.Acute posterior subluxation of joint
3.Acute posterior dislocations
4.Recurring posterior subluxations and dislocations
5.Unreduced posterior (locked, persistent, or fixed) dislocations.
B) Atraumatic problems
1. Voluntary or habitual posterior subluxation or dislocation
2. Involuntary posterior subluxation or dislocation
3. Congenital or developmental posterior subluxation or dislocation
Classification based on anatomic position of the dislocation
A) Subacromialmost commonest 98%
Mechanism Of injury
1.Direct force –
A direct thrust applied to the anterior shoulder like during boxing.
2.Indirect force --More common.
A strain of combined adduction, flexion and internal rotation is the cause. It may also result from violent muscular contraction by electrical shock or convulsive seizures.
The combined strength of the internal rotators simply over powers the external rotators.
Clinical features :
1.H/o fall with arm in adducted internally rotated position or electric shock or seizures.
2.Shoulder is held in the sling position (adduction and internal rotation).
3.Abduction and external rotation are limited.
4.Posterior prominence of rounding of the shoulder,
5.prominent coracoid process
6.Flattening of anterior aspect of shoulder
1. Fractures of the posterior glenoid rim and the proximal humerus(upper shaft, tuberosity and head).
2. Reversed-Hill sach lesion-impaction fracture of anteromedial aspect of the humeral head
3. Avulsion of subscapularis
4. Comminuted fracture of proximal humerus.
5. Neurovascular injuries and cuff tears.
6. Recurrence -mainly seen in
(a)Atraumatic posterior dislocation
(b) Large bone defects of humerus/glenoid.
Closed reduction :
•To be done under short GA with the patient supine, traction should be applied to the adducted arm in the line of the deformity, along with a gentle lifting of the head back into the glenoid fossa.
•Care should be taken not to force the arm into external rotation; if the head is locked posteriorly on the glenoid rim, the forced rotation could produce a fracture of the head or shaft of the humerus.
•If the head is locked on the posterior glenoid, distal traction on the arm should be combined with lateral traction on the upper arm.
•A folded towel or soft roller bandage can be used by an assistant to apply the lateral traction. In locked posterior dislocations, reduction may be facilitated by gently internally rotating the humerusto stretch out the posterior capsule and cuff musculature before reduction is attempted.
OPEN REDUCTION :
1. Major displacement of an associated lesser tuberosity fragment or a major fragment off the posterior glenoid.
3. Open dislocation
4. Unstable reduction.
The anterior deltopectoral approach is used, the subscapularis is released either by lesser tuberosity osteotomy or by direct incision.
After reduction, the humeral head defect may be rendered extra-articular by filling it with the subscapularis tendon or the lesser tuberosity.
If the humeral head defect involves more than 30% of the articular surface, prosthetic replacement may be indicated.
•Me Laughlin operation : Specific indication for this is the presence of an anteromedial humeral head defect so large that a stable reduction cannot be achieved. Subscapularis is detached from the lesser tuberosity; the shoulder is reduced and the subscapular tendon is transferred into the head defect
•Neer’s modification : Neer modified this operation by transferring the lesser tuberosity with the tendon into the defect. The added fragment of lesser tuberosity helps filling the space in the defect and it is simpler to perform because lesser tuberosity can be secured into the defect with a bone.