Posterior shoulder dislocation
Posterior dislocation of the shoulder is rare, accounting for less than 2% of shoulder dislocations.
May be bilateral in up to 15% of cases.
During posterior dislocation, an osteochondral impression fracture (also termed an encoche fracture or a reverse Hill-Sachs lesion) is produced on the anterior aspect of the humeral head as it impacts on the posterior aspect of the glenoid.
Posterior dislocations are still being missed.
The terminology dislocation is a slight misnomer in reality it is a subluxation because some of the articular surface of the humeral head is in contact with the glenoid and some behind it, often with an impression defect in the humeral head.
Treatment is determined by the size of the defect and the duration of the dislocation.
In his review article Cicak suggested 3 weeks as the cut off for chronic dislocations, Robinson suggested 6 weeks and acknowledged that it is a continuum, the longer the dislocation the larger the defect becomes the harder treatment becomes.
Posterior fracture dislocations are a separate entity from pure posterior dislocations. (see posterior fracture dislocation)
Although the humeral head and the glenoid are both normally retroverted with respect to their long axes, the scapula is protracted on the chest wall. Consequently, in its normal position of function, the shoulder is protected from posterior dislocation by the strong buttressing action of the posterior aspect of the glenoid.
Excessive posterior translation is also prevented by anterior constraints that contribute to capsuloligamentous stability. These include the rotator interval capsule, the superior and middle glenohumeral and coracohumeral ligaments, and the subscapularis tendon.
The relative contribution of these structures to stability varies with the position of the shoulder.
Stability also depends on coordinated glenohumeral and scapulothoracic
There is some evidence to suggest that posterior capsular tears will heal spontaneously following relocation of the shoulder.
Blood supply of humeral head
The humeral head has a segmental blood supply, mainly derived from the ascending branch of the anterior circumflex humeral artery. There is a risk of osteonecrosis after fracture dislocations through the anatomical neck, although if the fracture extends below the articular surface medially, the head may be perfused by intact posteromedial vessels.
The dislocation may be caused by:
In seizures and electric shocks, spasm in the strong internal rotators (latissimus dorsi, pectoralis major, subscapularis and teres major) overpower the weak external rotators (infraspinatus and teres minor).
The main symptom is loss of movement of the involved shoulder, particularly external rotation
Clinical findings may be subtle. The arm is held in internal rotation and adduction. Classically external rotation is limited, abduction and forward elevation is limited to between 80° and 100° (scapulothoracic movement).
Rowe and Zarins described a test in which there is inability to supinate the forearm when the arm is flexed forwards because of the internal-rotation deformity of the shoulder.
The coracoid process may be more prominent anteriorly and the humeral head palpable posteriorly.
Standard views of the shoulder are:
CT is useful to evaluate the size of the defect in the humeral head and associated glenoid changes. It may also detect radiographically occult anatomical neck fractures and reveal evidence of degenerative joint disease.
Magnetic Resonance Imaging
Magnetic Resonance Imaging is not routinely necessary because soft-tissue injury is very rare in posterior dislocation of the shoulder.
Ultrasound can be used to differentiate anterior from posterior dislocations but as yet has not replaced standard radiographs.
Treatment depends on :
Size of defect:
Despite the obvious deformity of the shoulder and loss of rotation, a chronic posterior dislocation can be surprisingly well tolerated, especially in elderly patients. There is usually little pain and enough forward elevation may be regained to allow the performance of many activities of daily living. Gerber recommends “supervised neglect” for elderly patients who have limited demands on the affected shoulder, an acceptable functional range of movement and a normal contralateral shoulder. Non-operative treatment must be considered for patients with uncontrolled fits or in any patient unable to comply with a postoperative rehabilitation programme.
Closed reduction may be attempted IF:
Method of reduction
After successful reduction, stability of the shoulder is assessed. If it is stable in internal rotation, the arm is immobilised in neutral rotation for 3 weeks. If unstable, the shoulder is immobilised with the arm at the side and in external rotation of 20° for six weeks.
If closed reduction is unsuccessful, open reduction is performed under the same general anaesthetic.
Small defect: (defect < 25% of humeral head)
In an irreducible dislocation with a defect of less than 25% of the humeral head an open reduction via a deltopectoral approach can be used.
If the shoulder is unstable with the arm in internal rotation, transfer the upper one-third of the tendon of subscapularis to the defect using transosseous non-absorbable sutures. The suture knot should be behind the bicipital groove. After this procedure the shoulder is usually stable and the arm is immobilised at the side in slight external rotation for 3-4 weeks.
Medium defect: (defect 25-50% of humeral head)
If the impression fracture of the humeral head is between 25% and 50%, an open reduction and transfer of the lesser tuberosity is recommended.
McLaughlin described the transfer of subscapularis for a defect of between 20% and 40%. The tendon of subscapularis is secured into the defect through drill holes in the bone.
Hughes and Neer modified this method by osteotomising the lesser tuberosity with the attached subscapularis.
The advantages of transfer of the lesser tuberosity are better bony filling of the humeral head and more secure reinsertion of the subscapularis.
Other options for the treatment of a defect between 25% and 50% is rotational osteotomy of the humerus and reconstruction using autograft or allograft.
Rotational osteotomy of the humerus.
The defect is filled with allograft from the femoral head which is contoured to fit the segmental defect and to restore the sphericity of the head.
The graft is fixed with cancellous screws.
This procedure has given similar results to those of transfer of subscapularis without altering the normal anatomy of the proximal humerus.
This procedure should be used in patients with good bone quality of the residual head and with no osteoarthritis.
Osteochondral autograft of the humeral head may be used in patients with a medium or large anteromedial articular impression defect as may occur with bilateral acute posterior dislocation. After removing the humeral head from the contralateral shoulder during hemiarthroplasty, the articular segment of the head is fashioned into a well-fitting osteochondral autograft and fixed into the impression defect of the head with Herbert screws.
Large defect: (defect >50% of humeral head)
In patients with an impression fracture involving more than 50% of the articular surface or when the humeral head is very soft and not viable hemiarthroplasty is indicated.
It is important to decide before surgery whether to transfer the lesser tuberosity or to perform an arthroplasty. If the latter is the case it is important not to perform an osteotomy of the lesser tuberosity. If an osteotomy is performed reconstruction of the tuberosity must be carried out with the potential problems of malunion or nonunion.
Reduction can be very difficult if the defect is large and the duration of the dislocation is more than 6 months.
It is important to release the soft tissues around the shoulder and to reduce the shoulder slowly.
Retroversion of the humeral component should be decreased from approximately 35° to 20°. Excessive anteversion is not required, nor is plication of the posterior capsule. If there is a concern regarding the stability of the humeral component, the arm is immobilised in external rotation of 10° to 20°.
This may occur following closed relocation or be due to failure of
an adjunctive surgical stabilization procedure.
Osteonecrosis of the humeral head has been reported following simple dislocation, but it is more frequently encountered following internal fixation of an anatomic neck fracture-dislocation.
The risk of osteonecrosis increases with the degree of fracture displacement and the extent of involvement of the tuberosities.
Osteonecrosis may be associated with satisfactory function if an anatomic reconstruction has previously been achieved.
Symptomatic patients are usually treated with an arthroplasty.
Posttraumatic Degenerative joint disease
Posttraumatic degeneration of the glenohumeral joint is relatively uncommon after posterior dislocation, but when it occurs the severity of the arthrosis is usually worse than that following anterior dislocation. If symptoms are severe enough to warrant treatment, a shoulder arthroplasty is usually performed.
Joint Stiffness and Functional Incapacity
Persistent shoulder stiffness and functional incapacity after a simple dislocation are associated with:
The key physical sign is fixed internal rotation of the arm.
The axillary view is essential for diagnosis and to estimate the size of the anteromedial defect of the humeral head.
‘Supervised neglect’ can be considered in a patient with limited disability and low functional expectations.
Closed reduction should be attempted if the defect is less than 25% of the articular surface and the duration of the dislocation is less than 3 weeks.
Open reduction should be carried out for an irreducible dislocation with a defect of less than 25%.
If the shoulder is unstable after open reduction transfer of the upper one-third of the tendon of subscapularis to the defect using transosseous non-absorbable sutures should be performed.
Transfer of the lesser tuberosity remains the operation of choice in patients with a defect of between 25% and 50% of the articular surface.
Hemiarthroplasty of the shoulder should be performed in patients with an impression fracture involving more than 50% of the articular surface or when the humeral head is very soft and not viable.
Total shoulder arthroplasty should be performed in patients with considerable erosion of the glenoid.
see (look and learn - shoulder /proximal humerus)
Clough, T.M.; Bale, R.S. Bilateral posterior shoulder dislocation: the importance of the axillary radiographic view. European Journal of Emergency Medicine. 8(2):161-163, June 2001.
Ogawa, Kiyohisa MD; Yoshida, Atsushi MD; Inokuchi, Wataru MD; Posterior Shoulder Dislocation Associated with Fracture of the Humeral Anatomic Neck: Treatment Guidelines and Long-Term Outcome. Journal of Trauma-Injury Infection & Critical Care. 46(2):318-323, February 1999
Goodrich, J. Allan; Crosland, Edward; Pye, Jacque. Acromion Fracture Associated With Posterior Shoulder Dislocation. Journal of Orthopaedic Trauma. 12(7):521-523, September/October 1998
Posterior dislocation of the shoulder with ipsilateral humeral shaft fracture: a very rare injury; Injury, Volume 28, Issue 2, March 1997, Pages 150-152; S. Naresh, J. A. Chapman and T. Muralidharan
Goodrich, J. Allan; Crosland, Edward ; Pye, Jacque; Acromion Fracture Associated With Posterior Shoulder Dislocation. Journal of Orthopaedic Trauma. 12(7):521-523, September/October 1998.
Munting, T.; de Beer, M. A.; Vrettos, B. C. MISSED POSTERIOR DISLOCATIONS OF THE SHOULDER. Journal of Bone & Joint Surgery - British Volume. 85-B SUPPLEMENT II:142, 2003.
Last updated 11/04/2005