Review Article
Acute Traumatic Posterior Shoulder Dislocation Abstract Dominique M. Rouleau, MD Jonah Hebert-Davies, MD C. Michael Robinson, MD
From the Department of Orthopaedic Surgery, University of Montreal, Sacred Heart Hospital of Montreal, Montreal, ON, Canada (Dr. Rouleau and Dr. Hebert-Davies), and the Royal Infirmary of Edinburgh, Edinburgh, UK (Dr. Robinson). Dr. Rouleau or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of Smith & Nephew; has received research or institutional support from DePuy, KCI, Smith & Nephew, Stryker, Synthes, and Zimmer; and has received nonincome support (such as equipment or services), commercially derived honoraria, or other non–researchrelated funding (such as paid travel) from Arthrex. Dr. Robinson or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of and serves as a paid consultant to Acumed. Neither Dr. Hebert-Davies nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article. J Am Acad Orthop Surg 2014;22: 145-152 http://dx.doi.org/10.5435/ JAAOS-22-03-145 Copyright 2014 by the American Academy of Orthopaedic Surgeons.
March 2014, Vol 22, No 3
Posterior shoulder dislocation occurs rarely and is challenging to manage. The mechanisms of trauma are varied, which complicates diagnosis. Missed or delayed diagnosis and treatment can have serious deleterious effects on shoulder function. All cases of suspected posterior shoulder dislocation require a high level of suspicion and appropriate imaging. Identification of associated injuries, such as fractures and rotator cuff tears, is important to guide treatment. In the acute setting, most patients are treated with closed or open reduction with additional soft-tissue or bony procedures. Patients treated in a delayed fashion for persistent instability may require additional procedures, including arthroplasty.
F
irst described in 1838 by Sir Astley Cooper,1 traumatic posterior dislocations of the shoulder represent an unusual and challenging clinical problem. These injuries account for 2% to 5% of all shoulder dislocations.1-3 Anterior glenohumeral dislocation is 15.5 to 21.7 times more common than posterior dislocation.4 Seizures, high-energy trauma, and electrocution are associated with a much greater risk of posterior dislocation.1,2,5 Diagnosis is missed or delayed in up to 79% of patients.2,3,6 The authors of one study suggested that systematic evaluation of AP and Velpeau radiographs in an emergency department resulted in dislocation being missed in only 10 of 112 patients.4 In patients who present following seizure, electric shock, or trauma, a high index of suspicion for posterior shoulder dislocation should be maintained, and appropriate physical and radiologic examinations should be performed to confirm the diagnosis.7 This is particularly important in the setting of seizure, in which medical treatment combined with reduced
nociceptive sensitivity following convulsions may make it difficult for the treating physician to detect the injury.8 Early identification of these dislocations reduces morbidity and facilitates treatment.3
Anatomy of the Shoulder The shoulder is relatively unconstrained, allowing an extreme range of motion. Joint stability is provided by both static and dynamic elements,9 which allows the joint to maintain a large degree of freedom while remaining concentric.
Static Stabilizers Bony congruity is achieved with the concavity of the glenoid; this is further increased due to asymmetric deposition of cartilage, with the peripheral articular surface being thickest.10,11 The glenoid labrum increases the depth and width of the joint approximately twofold.12 Loss of the labrum decreases translational resistance by 20%.13 The three glenohumeral ligaments are discrete capsular fibrous bands
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Acute Traumatic Posterior Shoulder Dislocation
pectoralis and latissimus dorsi muscles overpower the weak external rotators (ie, infraspinatus, teres minor) and cause internal rotation of the shoulder, displacing the humeral head superiorly and posteriorly against the acromion and medially against the glenoid fossa, resulting in posterior dislocation.8,16 Adequate muscle contraction strength of the infraspinatus and teres minor and major can cause humeral neck fracture. In a recent systematic review, posterior dislocations were found to occur after trauma in 67% of cases, after seizure in 31%, and after electrocution in 2%.4
Figure 1
Classifications
Illustration of the dynamic and static stabilizers of the shoulder. IGHL = inferior glenohumeral ligament, MGHL = middle glenohumeral ligament, SGHL = superior glenohumeral ligament
that provide stability to the shoulder in various positions. The coracohumeral ligament and superior glenohumeral ligament provide little anterior resistance, but they help prevent posterior translation in the flexed, adducted, and internally rotated shoulder.12,14 The inferior glenohumeral ligament is the main stabilizer against posterior dislocation. The posterior band of the inferior glenohumeral ligament restricts posterior displacement with the arm in abduction12 (Figure 1).
Dynamic Restraints Dynamic stabilizers include all shoulder muscles that create a concavity compression force across the joint. Balance between anterior and posterior forces allows the humeral head to remain centered in the glenoid.9
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Posterior dynamic restraints of the shoulder include the rotator cuff, the biceps tendon, and the deltoid.12 The subscapularis provides the greatest opposition to posterior translation.12 The biceps tendon increases posterior stability, mostly in external rotation.
Mechanisms of Injury Several different mechanisms have been proposed for posterior dislocation. Direct high-energy trauma with the shoulder in adduction, flexion, and internal rotation is the most frequent cause of posterior dislocation.2,15 Posterior shoulder dislocation may also be caused by seizures or electrocution.8 Dislocation due to seizure is the result of unbalanced contraction of the shoulder muscles.16 In adduction, internal rotation, and flexion, the
Several classification systems exist to describe posterior shoulder dislocations, but none has been established as a clear standard. Detenbeck17 first separated dislocations based on type: acute, chronic (dislocated .3 weeks), or recurrent (traumatic or atraumatic). Heller et al18 developed a system based on an extensive literature review and included different parameters: traumatic or atraumatic, acute or persistent, or recurrent voluntary. Others have classified dislocations as acute (,6 weeks) or chronic (.6 months) and have separated pure dislocations from fracture-dislocations (ie, any associated humeral fracture except a reverse Hill-Sachs lesion).19 Robinson and Aderinto19 also classified humeral head defect as small (,25%), medium (25% to 50%), and large (.50%). Classification of the humeral head defect is extremely important for planning eventual surgical treatment. Classifications of posterior recurrent instability and atraumatic posterior instability are beyond the scope of this article.20
Clinical Evaluation Physical examination is particularly important in acute posterior shoulder
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Figure 2
A, AP radiograph of the shoulder with the trough line visible (arrow). This is representative of the anterior humeral head impaction. B, Axillary radiograph demonstrating posterior dislocation with a significant reverse Hill-Sachs lesion. C, AP radiograph demonstrating the lightbulb sign (arrows).
dislocations because patients may be unable to provide an adequate clinical history. On visual inspection, the shoulder often is in internal rotation, with a prominent coracoid process and posterior fullness in the axilla.1,3,21 Physical examination may reveal a springy or soft end point or a block to external rotation,1-3,21,22 as well as the subtler sign of diminished supination of the forearm.6 Specific instability examinations such as the jerk test, posterior load-and-shift test, or the posterior drawer test can be useful in patients with chronic instability. However, these tests are rarely useful in the acute setting.
Imaging To minimize the risk of missing a posterior glenohumeral dislocation, the evaluation should include standard AP and Velpeau radiographs.1-4,21 An axillary view is useful to evaluate associated head impaction (ie, reverse Hill-Sachs lesion) and glenoid rim fractures.21 A Velpeau view is acceptable if the patient is unable to achieve sufficient abduction. Other indirect signs that can be seen on standard radiographs include the lightbulb sign, loss of the half-moon sign, and the trough line23 (Figure 2). March 2014, Vol 22, No 3
CT is particularly useful for preoperative assessment of associated fractures and quantification of reverse Hill-Sachs impaction1,3,21,24,25 (Figure 3). Thin-slice axial CT is the best imaging modality for defining the humeral head bone defect as part of the articular surface.24 Capsulolabral and rotator cuff evaluation on MRI is essential in cases without associated fracture7 (Figure 4). Posterior labral lesions, such as reverse Bankart lesions, posterior labrocapsular periosteal sleeve avulsions, and posterosuperior tears, are found in up to 58% of patients.26 In cases of irreducible dislocation, MRI can identify the responsible structure, which most commonly is a torn rotator cuff, avulsed capsule, or biceps tendon.26
Associated Injuries Isolated posterior dislocations of the proximal humerus are rare, and associated injuries often are missed or diagnosed in a delayed fashion.7 Historically, bony and soft-tissue injuries were thought to occur in 49% of dislocations,21 but a recent systematic review indicated that up to 65% of dislocations had associated bony or
Figure 3
Axial CT scan demonstrating severe humeral head impaction, that is, reverse Hill-Sachs lesion. The extent of glenoid fracture or bone loss dictates management.
soft-tissue injuries.7 Simple or multiple fractures were present in 34% of shoulders, with the most common site being the neck (55%), followed by the lesser (42%) and greater (23%) tuberosities.7 Lesser tuberosity fractures are particularly important because they influence treatment. In these cases, it is important to enter the joint through the fracture rather than perform a subscapularis tenotomy. Reverse Hill-Sachs lesions of varying size are seen in up to 86% of
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Acute Traumatic Posterior Shoulder Dislocation
Figure 4
Axial T1-weighted magnetic resonance arthrogram of a right shoulder demonstrating a posterior Bankart lesion. The rotator cuff is also assessed on this view.
patients.26 Bone defects are common, with significant reverse HillSachs lesions found in 29% of shoulders7 and posterior rim fracture seen in approximately 5% of shoulders.4 The frequency and significance of these defects can increase with delayed or chronic presentation.5 Rotator cuff tears are found in 13% of patients evaluated with MRI; however, the odds ratio of finding a tear is 4.6 times higher in the absence of an associated fracture or reverse Hill-Sachs lesion.7 Thus, in the patient with a dislocation but without concomitant fracture on CT, a focused rotator cuff physical examination and MRI evaluation are strongly suggested. Nerve palsy secondary to posterior glenohumeral dislocation is rare, occurring in ,1% of injuries.7 The axillary nerve is the most commonly injured.
Management Nonsurgical Definitive treatment options for posterior shoulder dislocations are varied, and the decision must be individualized to each patient. In the elderly
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low-demand patient, chronic posterior dislocation can be tolerated provided pain is minimal and anterior elevation is sufficient for activities of daily living.27,28 This treatment option has been dubbed supervised neglect.28,29 Nonsurgical treatment also may be appropriate in patients with cognitive impairment or other severe medical comorbidities. Closed reduction can be attempted in the presence of an acute dislocation in an elderly low-demand patient with a reverse Hill-Sachs lesion measuring ,20%. Recurrent dislocation or failed reduction warrants a discussion with the patient and family about definitive treatment. In an active and independent patient, the goal of treatment of acute and chronic dislocations is to restore shoulder stability and mobility. Isolated closed reduction is reserved for acute posterior instability with a reverse Hill-Sachs lesion of #20% that is stable after reduction. Careful imaging evaluation should be done prior to any reduction maneuver to avoid displacing a neck fracture. In the presence of suspected fracture, an urgent CT scan should be obtained before reduction. An attempt at closed reduction of posterior shoulder dislocation requires complete sedation to allow gentle manipulation. Forceful manipulations often cause humeral head fractures, which increases the chance of osteonecrosis and has an adverse effect on prognosis. In a series of 112 patients, 33% of shoulders were successfully reduced using in-line gentle traction.4 The Stimson technique is a passive method used to manage acute posterior dislocation without associated neck fracture or a significantly engaged reverse Hill-Sachs lesion. The patient is positioned prone on a table with the arm in abduction over the side and with 5 to 10 lb placed in the hand.30 Muscle spasms can eventually be overcome with the weight to allow for spontaneous reduction.
Another method of closed reduction involves manipulating the shoulder into adduction, anterior flexion, and internal rotation. This is followed by longitudinal traction and anteriorly directed pressure on the humeral head. As the humeral head is felt to translate anteriorly, progressive external rotation and extension is done. Caution is required at this stage because initiating rotation before humeral head translation may cause humeral head fracture. Residual instability following closed reduction with the arm in the neutral position warrants surgical management provided the patient is medically fit to undergo anesthesia.
Surgical Open Reduction Following unsuccessful closed reduction, open reduction can be done through either an anterior or a posterior approach. The approach is determined based on preoperative planning. Isolated open reduction can be successful in acute dislocations with reverse Hill-Sachs lesions measuring ,20%. An anterior approach is done via a standard deltopectoral incision, where the humeral head lies deeper than usual. Initially, the rotator interval is opened to allow the introduction of a finger into the glenohumeral joint to aid in manual reduction of the shoulder. In cases in which the shoulder is not reducible through an open rotator interval alone, a formal arthrotomy is necessary. Management of the subscapularis is crucial and is dictated by associated fractures. The two options are peeling of the subscapularis and lesser tuberosity osteotomy. In the setting of persistent posterior dislocation, locked internal rotation limits access to the subscapularis. The long head of the biceps is useful in identifying the lateral margin; frequently, the subscapularis tendon lies beneath the conjoined tendon.
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mended to prevent contact between the grafted zone and the glenoid.
Figure 5
formed approximately 1 cm deep to the bicipital groove in the sagittal plane. A second cut is made from the rotator interval in the coronal plane from the reverse Hill-Sachs lesion medially to the groove laterally. This cut is possible only if the rotator interval is open. Careful manipulation of the lesser tuberosity is required to prevent fragmentation.
Posterior Open Bankart Procedure Irreducible posterior shoulder dislocations or persistent instability after closed reduction without a significant reverse Hill-Sachs lesion (#20%) can be managed with a posterior approach to achieve reduction, followed by posterior Bankart repair33 (Figure 7). A posterior longitudinal incision is made medial to the deltoid border in line with the posterior joint. Inferior dissection must be done carefully to prevent injury to the axillary nerve. The deltoid is lifted with a retractor, after which the infraspinatus is visualized and transverse tenotomy is performed in line with the capsule. The posterior labrum and capsule are repaired in a standard fashion. Alternatively, the approach can be done through a longitudinal split between the infraspinatus and teres minor. This approach allows excellent exposure of the labrum complex without posterior tendon tenotomy. The interval between these muscles is not always obvious. Typically, it can be found 2 cm inferior to the scapular spine. It is harder to see the separation at the tendinous portion, and a longitudinal tenotomy is usually necessary. Alternatively, on palpation, the humeral head is usually felt deep to the infraspinatus, whereas the inferior portion of the teres minor feels soft on palpation.
Anterior Approach and Bone Grafting Significant acute reverse Hill-Sachs lesions (20% to 40%) can also be addressed with disimpaction and bone grafting or allograft (Figure 6). The ideal patient for these techniques is young, with good healing potential. Following fracture disimpaction, an iliac crest bone graft can be inserted under the cartilage for support.32 Postoperative use of an external rotation splint for 4 weeks is recom-
Arthroscopic Posterior Bankart Repair Arthroscopic posterior Bankart repair is an option for acute reducible dislocations with little or no humeral head impaction (,20%) and with persistent instability. The arthroscope is introduced through the anterior portal, and a posterolateral portal is used for suture anchor placement. A posterosuperior portal is used for suture management. The posterior portion of the acromion may prevent vertical
A, Axial (top) and AP (bottom) illustrations of a shoulder with a reverse Hill-Sachs lesion. The AP view illustrates a modified McLaughlin procedure, which is done through a transsubscapularis approach. B, Axial (top) and AP (bottom) illustrations of the shoulder following suture of the subscapularis tendon into the defect with the help of suture anchors and subsequent repair of that approach through the tendon.
The McLaughlin Procedure For patients with reverse Hill-Sachs lesions of #20% and with persistent instability following reduction, the subscapularis can be either lifted off the lesser tuberosity and transposed into the defect with transosseous sutures after reduction as originally described by McLaughlin2 or sutured into the bed of the defect.31 The circumflex vessels are preserved inferiorly by maintaining a small sleeve of tendon attached to its original site. Modified McLaughlin Procedure In the presence of a significant reverse Hill-Sachs lesion (20% to 40%), the lesser tuberosity can be osteotomized to access the joint and eventually transposed to the bone defect after joint reduction.21 This is known as the modified McLaughlin procedure (Figure 5). The osteotomy is perMarch 2014, Vol 22, No 3
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Figure 6
A, Axial CT scan of a left shoulder with significant humeral head impaction. B, Axial CT scan of the same patient 3 months after an allograft was implanted into the deficit. C, Axial CT scan of a different patient with a similar injury 3 months after fracture disimpaction.
Figure 7
Illustration of the skin landmarks used in the posterior approach (represented by the dashed line) used to manage irreducible posterior shoulder dislocation or persistent instability after closed reduction in the absence of a significant reverse Hill-Sachs lesion. Access to the joint is achieved either through infraspinatus tenotomy or between the infraspinatus and the teres minor.
positioning of suture anchors, and the surgeon must have at the ready a variety of suture passers to accommodate the anatomy in this area. Arthroplasty In the presence of massive humeral head impaction (.40%) in patients aged
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,55 years or in patients who are not good candidates for graft incorporation, hemiarthroplasty is a good option to address both instability and the articular surface deficit.33 In order to prevent postoperative dislocation, the humeral head must be positioned in normal retroversion (#20°). In more severe cases of residual instability, the posterior labrum can be repaired before prosthesis implantation. Through an anterior approach, the humeral head is excised and the humeral cut is oriented parallel to the glenoid, leaving 1 to 2 cm of joint space to visualize the posterior labrum. Use of a laminar spreader and gentle lateral traction can improve visualization. In a right shoulder, the first glenoid anchor is positioned at the 7-o’clock position and the second at the 9-o’clock position. The anchor is placed at the edge of the cartilage at a 45° angle to the joint surface. A free 2/3 circular needle is usually sufficient to pass the anchor suture through the posterior labrum and capsule. Following repair of the labrum, the hemiarthroplasty can be performed as usual. A treatment algorithm is shown in Figure 8.
Rehabilitation Regardless of management type, the shoulder is braced in 20° of external rotation and abduction for 4 weeks to aid healing of the posterior capsule. Pendulum exercises and elbow range of motion three times per day are encouraged. At 4 weeks, unlimited progressive range of motion is initiated as well as isometric posterior rotator cuff strengthening. Noncontact sports are allowed 3 months after reduction or surgery, and contact sports are permitted 4 to 6 months postoperatively.
Results Approximately 18% of patients experience recurrent instability in the first year following acute posterior dislocation.4 Risk factors for recurrence are age ,40 years, seizure, and large reverse Hill-Sachs lesion (.1.5 cm3). Persistent functional impairment has been noted 2 years after the initial trauma, even without recurrent instability.4 Activities that require significant internal rotation may be particularly difficult. Typically, patients with persistent symptoms present with either
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Figure 8
Treatment algorithm for the surgical management of acute posterior shoulder dislocation.
subjective or objective posterior instability and a painful shoulder. On physical examination, apprehension is seen with the shoulder in adduction and forward elevation. Most patients will present additional symptoms with a posteriorly directed translational force of the humerus. Compensatory scapular winging can be seen with anterior shoulder elevation.9 For these patients, imaging should include magnetic resonance arthrography of the shoulder. Treatments include all modalities of nonsurgical treatment as well as surgical management of refractory cases. PosMarch 2014, Vol 22, No 3
terior capsular plication and posterior Bankart repair have been reported to improve both function and pain.34
Summary Posterior shoulder dislocation is a relatively uncommon pathology, with several typical modes of presentation. Dislocation often goes undiagnosed in the acute setting in patients who present following seizure, electric shock, or high-energy trauma. Thus, particular attention is required to diagnose the injury in these patients. Imaging stud-
ies should always include an axillary or equivalent radiograph. CT and MRI are both useful to diagnose associated injuries, which are much more frequent than previously thought. Treatment is individualized to each patient based on timing of presentation, size of the reverse Hill-Sachs lesion, and the presence of associated injuries (ie, fracture, rotator cuff tear, glenoid bone loss). Younger patients are treated with soft-tissue management with or without a bony procedure, whereas older patients may require arthroplasty to maintain stability.
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References Evidence-based Medicine: Levels of evidence are described in the table of contents. In this article, reference 4 is a level II study. Reference 7 is a level III study. References 2, 3, 6, 8, 15, 16, 21, 22, 24, 26, 27, 29, and 31 are level IV studies. Reference 28 is level V expert opinion. References printed in bold type are those published within the past 5 years. 1. Kowalsky MS, Levine WN: Traumatic posterior glenohumeral dislocation: Classification, pathoanatomy, diagnosis, and treatment. Orthop Clin North Am 2008;39(4):519-533, viii. 2. McLaughlin HL: Posterior dislocation of the shoulder. J Bone Joint Surg Am 1952;24(3): 584-590. 3. Hatzis N, Kaar TK, Wirth MA, Rockwood CA Jr: The often overlooked posterior dislocation of the shoulder. Tex Med 2001;97(11):62-67. 4. Robinson CM, Seah M, Akhtar MA: The epidemiology, risk of recurrence, and functional outcome after an acute traumatic posterior dislocation of the shoulder. J Bone Joint Surg Am 2011;93(17):1605-1613. 5. Hawkins RJ: Unrecognized dislocations of the shoulder. Instr Course Lect 1985;34: 258-263. 6. Rowe CR, Zarins B: Chronic unreduced dislocations of the shoulder. J Bone Joint Surg Am 1982;64(4):494-505. 7. Rouleau DM, Hebert-Davies J: Incidence of associated injury in posterior shoulder dislocation: Systematic review of the literature. J Orthop Trauma 2012;26(4):246-251. 8. Goudie EB, Murray IR, Robinson CM: Instability of the shoulder following seizures. J Bone Joint Surg Br 2012;94(6): 721-728. 9. Tjoumakaris FP, Bradley JP: Posterior shoulder instability, in Galatz LM, ed: Orthopaedic Knowledge Update: Shoulder and Elbow 3. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2008, pp 313-320.
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10. Matsen FA III: Letter: The biomechanics of glenohumeral stability. J Bone Joint Surg Am 2002;84(3):495-496. 11. Halder AM, Kuhl SG, Zobitz ME, Larson D, An KN: Effects of the glenoid labrum and glenohumeral abduction on stability of the shoulder joint through concavitycompression: An in vitro study. J Bone Joint Surg Am 2001;83(7):1062-1069. 12. Levine WN, Flatow EL: The pathophysiology of shoulder instability. Am J Sports Med 2000;28(6):910-917. 13. Lippitt S, Matsen F: Mechanisms of glenohumeral joint stability. Clin Orthop Relat Res 1993;(291):20-28. 14. Curl LA, Warren RF: Glenohumeral joint stability: Selective cutting studies on the static capsular restraints. Clin Orthop Relat Res 1996;(330):54-65. 15. Robinson CM, Akhtar A, Mitchell M, Beavis C: Complex posterior fracturedislocation of the shoulder: Epidemiology, injury patterns, and results of operative treatment. J Bone Joint Surg Am 2007;89(7): 1454-1466. 16. Shaw JL: Bilateral posterior fracturedislocation of the shoulder and other trauma caused by convulsive seizures. J Bone Joint Surg Am 1971;53(7):1437-1440. 17. Detenbeck LC: Posterior dislocations of the shoulder. J Trauma 1972;12(3):183-192. 18. Heller KD, Forst J, Forst R, Cohen B: Posterior dislocation of the shoulder: Recommendations for a classification. Arch Orthop Trauma Surg 1994;113(4):228-231. 19. Robinson CM, Aderinto J: Posterior shoulder dislocations and fracturedislocations. J Bone Joint Surg Am 2005;87(3):639-650. 20. Millett PJ, Clavert P, Hatch GF III, Warner JJ: Recurrent posterior shoulder instability. J Am Acad Orthop Surg 2006;14(8):464-476. 21. Hawkins RJ, Neer CS II, Pianta RM, Mendoza FX: Locked posterior dislocation of the shoulder. J Bone Joint Surg Am 1987; 69(1):9-18. 22. Walch G, Boileau P, Martin B, Dejour H: Unreduced posterior luxations and fracturesluxations of the shoulder: Apropos of 30 cases [French]. Rev Chir Orthop Reparatrice Appar Mot 1990;76(8):546-558. 23. Cisternino SJ, Rogers LF, Stufflebam BC, Kruglik GD: The trough line: A
radiographic sign of posterior shoulder dislocation. AJR Am J Roentgenol 1978; 130(5):951-954. 24. Wadlington VR, Hendrix RW, Rogers LF: Computed tomography of posterior fracture-dislocations of the shoulder: Case reports. J Trauma 1992;32(1):113-115. 25. Zissin R, Morag B, Apter S, Rubinstein Z: Bilateral posterior glenohumeral fracturedislocation: CT appearance. Isr J Med Sci 1990;26(1):55-57. 26. Saupe N, White LM, Bleakney R, et al: Acute traumatic posterior shoulder dislocation: MR findings. Radiology 2008; 248(1):185-193. 27. Loebenberg MI, Cuomo F: The treatment of chronic anterior and posterior dislocations of the glenohumeral joint and associated articular surface defects. Orthop Clin North Am 2000;31(1):23-34. 28. Cicak N: Posterior dislocation of the shoulder. J Bone Joint Surg Br 2004;86(3): 324-332. 29. Bühler M, Gerber C: Shoulder instability related to epileptic seizures. J Shoulder Elbow Surg 2002;11(4):339-344. 30. Court-Brown CM, McQueen MM, Tornetta P III: Shoulder girdle, in Tornetta P III, Einhorn TA, eds: Orthopaedic Surgery Essentials: Trauma. Philadelphia, PA, Lippincott, Williams and Wilkins, 2006, pp 68-88. 31. Spencer EE Jr, Brems JJ: A simple technique for management of locked posterior shoulder dislocations: Report of two cases. J Shoulder Elbow Surg 2005;14(6):650-652. 32.
Begin M, Gagey O, Soubeyrand M: Acute bilateral posterior dislocation of the shoulder: One-stage reconstruction of both humeral heads with cancellous autograft and cartilage preservation. Chir Main 2012;31(1):34-37.
33. Matsen FA III, Titelman RM, Lippitt SB, Rockwood CA Jr, Wirth MA: Glenohumeral instability, in Rockwood CA Jr, Matsen FA III, Wirth MA, Lippitt SB, eds: The Shoulder, ed 3. Philadelphia, PA, Saunders Elsevier, 2004, vol 2, pp 655-794. 34. Bottoni CR, Franks BR, Moore JH, DeBerardino TM, Taylor DC, Arciero RA: Operative stabilization of posterior shoulder instability. Am J Sports Med 2005; 33(7):996-1002.
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Acute Traumatic Posterior Shoulder Dislocation Abstract Dominique M. Rouleau, MD Jonah Hebert-Davies, MD C. Michael Robinson, MD
From the Department of Orthopaedic Surgery, University of Montreal, Sacred Heart Hospital of Montreal, Montreal, ON, Canada (Dr. Rouleau and Dr. Hebert-Davies), and the Royal Infirmary of Edinburgh, Edinburgh, UK (Dr. Robinson). Dr. Rouleau or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of Smith & Nephew; has received research or institutional support from DePuy, KCI, Smith & Nephew, Stryker, Synthes, and Zimmer; and has received nonincome support (such as equipment or services), commercially derived honoraria, or other non–researchrelated funding (such as paid travel) from Arthrex. Dr. Robinson or an immediate family member is a member of a speakers’ bureau or has made paid presentations on behalf of and serves as a paid consultant to Acumed. Neither Dr. Hebert-Davies nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article. J Am Acad Orthop Surg 2014;22: 145-152 http://dx.doi.org/10.5435/ JAAOS-22-03-145 Copyright 2014 by the American Academy of Orthopaedic Surgeons.
March 2014, Vol 22, No 3
Posterior shoulder dislocation occurs rarely and is challenging to manage. The mechanisms of trauma are varied, which complicates diagnosis. Missed or delayed diagnosis and treatment can have serious deleterious effects on shoulder function. All cases of suspected posterior shoulder dislocation require a high level of suspicion and appropriate imaging. Identification of associated injuries, such as fractures and rotator cuff tears, is important to guide treatment. In the acute setting, most patients are treated with closed or open reduction with additional soft-tissue or bony procedures. Patients treated in a delayed fashion for persistent instability may require additional procedures, including arthroplasty.
F
irst described in 1838 by Sir Astley Cooper,1 traumatic posterior dislocations of the shoulder represent an unusual and challenging clinical problem. These injuries account for 2% to 5% of all shoulder dislocations.1-3 Anterior glenohumeral dislocation is 15.5 to 21.7 times more common than posterior dislocation.4 Seizures, high-energy trauma, and electrocution are associated with a much greater risk of posterior dislocation.1,2,5 Diagnosis is missed or delayed in up to 79% of patients.2,3,6 The authors of one study suggested that systematic evaluation of AP and Velpeau radiographs in an emergency department resulted in dislocation being missed in only 10 of 112 patients.4 In patients who present following seizure, electric shock, or trauma, a high index of suspicion for posterior shoulder dislocation should be maintained, and appropriate physical and radiologic examinations should be performed to confirm the diagnosis.7 This is particularly important in the setting of seizure, in which medical treatment combined with reduced
nociceptive sensitivity following convulsions may make it difficult for the treating physician to detect the injury.8 Early identification of these dislocations reduces morbidity and facilitates treatment.3
Anatomy of the Shoulder The shoulder is relatively unconstrained, allowing an extreme range of motion. Joint stability is provided by both static and dynamic elements,9 which allows the joint to maintain a large degree of freedom while remaining concentric.
Static Stabilizers Bony congruity is achieved with the concavity of the glenoid; this is further increased due to asymmetric deposition of cartilage, with the peripheral articular surface being thickest.10,11 The glenoid labrum increases the depth and width of the joint approximately twofold.12 Loss of the labrum decreases translational resistance by 20%.13 The three glenohumeral ligaments are discrete capsular fibrous bands
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Acute Traumatic Posterior Shoulder Dislocation
pectoralis and latissimus dorsi muscles overpower the weak external rotators (ie, infraspinatus, teres minor) and cause internal rotation of the shoulder, displacing the humeral head superiorly and posteriorly against the acromion and medially against the glenoid fossa, resulting in posterior dislocation.8,16 Adequate muscle contraction strength of the infraspinatus and teres minor and major can cause humeral neck fracture. In a recent systematic review, posterior dislocations were found to occur after trauma in 67% of cases, after seizure in 31%, and after electrocution in 2%.4
Figure 1
Classifications
Illustration of the dynamic and static stabilizers of the shoulder. IGHL = inferior glenohumeral ligament, MGHL = middle glenohumeral ligament, SGHL = superior glenohumeral ligament
that provide stability to the shoulder in various positions. The coracohumeral ligament and superior glenohumeral ligament provide little anterior resistance, but they help prevent posterior translation in the flexed, adducted, and internally rotated shoulder.12,14 The inferior glenohumeral ligament is the main stabilizer against posterior dislocation. The posterior band of the inferior glenohumeral ligament restricts posterior displacement with the arm in abduction12 (Figure 1).
Dynamic Restraints Dynamic stabilizers include all shoulder muscles that create a concavity compression force across the joint. Balance between anterior and posterior forces allows the humeral head to remain centered in the glenoid.9
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Posterior dynamic restraints of the shoulder include the rotator cuff, the biceps tendon, and the deltoid.12 The subscapularis provides the greatest opposition to posterior translation.12 The biceps tendon increases posterior stability, mostly in external rotation.
Mechanisms of Injury Several different mechanisms have been proposed for posterior dislocation. Direct high-energy trauma with the shoulder in adduction, flexion, and internal rotation is the most frequent cause of posterior dislocation.2,15 Posterior shoulder dislocation may also be caused by seizures or electrocution.8 Dislocation due to seizure is the result of unbalanced contraction of the shoulder muscles.16 In adduction, internal rotation, and flexion, the
Several classification systems exist to describe posterior shoulder dislocations, but none has been established as a clear standard. Detenbeck17 first separated dislocations based on type: acute, chronic (dislocated .3 weeks), or recurrent (traumatic or atraumatic). Heller et al18 developed a system based on an extensive literature review and included different parameters: traumatic or atraumatic, acute or persistent, or recurrent voluntary. Others have classified dislocations as acute (,6 weeks) or chronic (.6 months) and have separated pure dislocations from fracture-dislocations (ie, any associated humeral fracture except a reverse Hill-Sachs lesion).19 Robinson and Aderinto19 also classified humeral head defect as small (,25%), medium (25% to 50%), and large (.50%). Classification of the humeral head defect is extremely important for planning eventual surgical treatment. Classifications of posterior recurrent instability and atraumatic posterior instability are beyond the scope of this article.20
Clinical Evaluation Physical examination is particularly important in acute posterior shoulder
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Figure 2
A, AP radiograph of the shoulder with the trough line visible (arrow). This is representative of the anterior humeral head impaction. B, Axillary radiograph demonstrating posterior dislocation with a significant reverse Hill-Sachs lesion. C, AP radiograph demonstrating the lightbulb sign (arrows).
dislocations because patients may be unable to provide an adequate clinical history. On visual inspection, the shoulder often is in internal rotation, with a prominent coracoid process and posterior fullness in the axilla.1,3,21 Physical examination may reveal a springy or soft end point or a block to external rotation,1-3,21,22 as well as the subtler sign of diminished supination of the forearm.6 Specific instability examinations such as the jerk test, posterior load-and-shift test, or the posterior drawer test can be useful in patients with chronic instability. However, these tests are rarely useful in the acute setting.
Imaging To minimize the risk of missing a posterior glenohumeral dislocation, the evaluation should include standard AP and Velpeau radiographs.1-4,21 An axillary view is useful to evaluate associated head impaction (ie, reverse Hill-Sachs lesion) and glenoid rim fractures.21 A Velpeau view is acceptable if the patient is unable to achieve sufficient abduction. Other indirect signs that can be seen on standard radiographs include the lightbulb sign, loss of the half-moon sign, and the trough line23 (Figure 2). March 2014, Vol 22, No 3
CT is particularly useful for preoperative assessment of associated fractures and quantification of reverse Hill-Sachs impaction1,3,21,24,25 (Figure 3). Thin-slice axial CT is the best imaging modality for defining the humeral head bone defect as part of the articular surface.24 Capsulolabral and rotator cuff evaluation on MRI is essential in cases without associated fracture7 (Figure 4). Posterior labral lesions, such as reverse Bankart lesions, posterior labrocapsular periosteal sleeve avulsions, and posterosuperior tears, are found in up to 58% of patients.26 In cases of irreducible dislocation, MRI can identify the responsible structure, which most commonly is a torn rotator cuff, avulsed capsule, or biceps tendon.26
Associated Injuries Isolated posterior dislocations of the proximal humerus are rare, and associated injuries often are missed or diagnosed in a delayed fashion.7 Historically, bony and soft-tissue injuries were thought to occur in 49% of dislocations,21 but a recent systematic review indicated that up to 65% of dislocations had associated bony or
Figure 3
Axial CT scan demonstrating severe humeral head impaction, that is, reverse Hill-Sachs lesion. The extent of glenoid fracture or bone loss dictates management.
soft-tissue injuries.7 Simple or multiple fractures were present in 34% of shoulders, with the most common site being the neck (55%), followed by the lesser (42%) and greater (23%) tuberosities.7 Lesser tuberosity fractures are particularly important because they influence treatment. In these cases, it is important to enter the joint through the fracture rather than perform a subscapularis tenotomy. Reverse Hill-Sachs lesions of varying size are seen in up to 86% of
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Acute Traumatic Posterior Shoulder Dislocation
Figure 4
Axial T1-weighted magnetic resonance arthrogram of a right shoulder demonstrating a posterior Bankart lesion. The rotator cuff is also assessed on this view.
patients.26 Bone defects are common, with significant reverse HillSachs lesions found in 29% of shoulders7 and posterior rim fracture seen in approximately 5% of shoulders.4 The frequency and significance of these defects can increase with delayed or chronic presentation.5 Rotator cuff tears are found in 13% of patients evaluated with MRI; however, the odds ratio of finding a tear is 4.6 times higher in the absence of an associated fracture or reverse Hill-Sachs lesion.7 Thus, in the patient with a dislocation but without concomitant fracture on CT, a focused rotator cuff physical examination and MRI evaluation are strongly suggested. Nerve palsy secondary to posterior glenohumeral dislocation is rare, occurring in ,1% of injuries.7 The axillary nerve is the most commonly injured.
Management Nonsurgical Definitive treatment options for posterior shoulder dislocations are varied, and the decision must be individualized to each patient. In the elderly
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low-demand patient, chronic posterior dislocation can be tolerated provided pain is minimal and anterior elevation is sufficient for activities of daily living.27,28 This treatment option has been dubbed supervised neglect.28,29 Nonsurgical treatment also may be appropriate in patients with cognitive impairment or other severe medical comorbidities. Closed reduction can be attempted in the presence of an acute dislocation in an elderly low-demand patient with a reverse Hill-Sachs lesion measuring ,20%. Recurrent dislocation or failed reduction warrants a discussion with the patient and family about definitive treatment. In an active and independent patient, the goal of treatment of acute and chronic dislocations is to restore shoulder stability and mobility. Isolated closed reduction is reserved for acute posterior instability with a reverse Hill-Sachs lesion of #20% that is stable after reduction. Careful imaging evaluation should be done prior to any reduction maneuver to avoid displacing a neck fracture. In the presence of suspected fracture, an urgent CT scan should be obtained before reduction. An attempt at closed reduction of posterior shoulder dislocation requires complete sedation to allow gentle manipulation. Forceful manipulations often cause humeral head fractures, which increases the chance of osteonecrosis and has an adverse effect on prognosis. In a series of 112 patients, 33% of shoulders were successfully reduced using in-line gentle traction.4 The Stimson technique is a passive method used to manage acute posterior dislocation without associated neck fracture or a significantly engaged reverse Hill-Sachs lesion. The patient is positioned prone on a table with the arm in abduction over the side and with 5 to 10 lb placed in the hand.30 Muscle spasms can eventually be overcome with the weight to allow for spontaneous reduction.
Another method of closed reduction involves manipulating the shoulder into adduction, anterior flexion, and internal rotation. This is followed by longitudinal traction and anteriorly directed pressure on the humeral head. As the humeral head is felt to translate anteriorly, progressive external rotation and extension is done. Caution is required at this stage because initiating rotation before humeral head translation may cause humeral head fracture. Residual instability following closed reduction with the arm in the neutral position warrants surgical management provided the patient is medically fit to undergo anesthesia.
Surgical Open Reduction Following unsuccessful closed reduction, open reduction can be done through either an anterior or a posterior approach. The approach is determined based on preoperative planning. Isolated open reduction can be successful in acute dislocations with reverse Hill-Sachs lesions measuring ,20%. An anterior approach is done via a standard deltopectoral incision, where the humeral head lies deeper than usual. Initially, the rotator interval is opened to allow the introduction of a finger into the glenohumeral joint to aid in manual reduction of the shoulder. In cases in which the shoulder is not reducible through an open rotator interval alone, a formal arthrotomy is necessary. Management of the subscapularis is crucial and is dictated by associated fractures. The two options are peeling of the subscapularis and lesser tuberosity osteotomy. In the setting of persistent posterior dislocation, locked internal rotation limits access to the subscapularis. The long head of the biceps is useful in identifying the lateral margin; frequently, the subscapularis tendon lies beneath the conjoined tendon.
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mended to prevent contact between the grafted zone and the glenoid.
Figure 5
formed approximately 1 cm deep to the bicipital groove in the sagittal plane. A second cut is made from the rotator interval in the coronal plane from the reverse Hill-Sachs lesion medially to the groove laterally. This cut is possible only if the rotator interval is open. Careful manipulation of the lesser tuberosity is required to prevent fragmentation.
Posterior Open Bankart Procedure Irreducible posterior shoulder dislocations or persistent instability after closed reduction without a significant reverse Hill-Sachs lesion (#20%) can be managed with a posterior approach to achieve reduction, followed by posterior Bankart repair33 (Figure 7). A posterior longitudinal incision is made medial to the deltoid border in line with the posterior joint. Inferior dissection must be done carefully to prevent injury to the axillary nerve. The deltoid is lifted with a retractor, after which the infraspinatus is visualized and transverse tenotomy is performed in line with the capsule. The posterior labrum and capsule are repaired in a standard fashion. Alternatively, the approach can be done through a longitudinal split between the infraspinatus and teres minor. This approach allows excellent exposure of the labrum complex without posterior tendon tenotomy. The interval between these muscles is not always obvious. Typically, it can be found 2 cm inferior to the scapular spine. It is harder to see the separation at the tendinous portion, and a longitudinal tenotomy is usually necessary. Alternatively, on palpation, the humeral head is usually felt deep to the infraspinatus, whereas the inferior portion of the teres minor feels soft on palpation.
Anterior Approach and Bone Grafting Significant acute reverse Hill-Sachs lesions (20% to 40%) can also be addressed with disimpaction and bone grafting or allograft (Figure 6). The ideal patient for these techniques is young, with good healing potential. Following fracture disimpaction, an iliac crest bone graft can be inserted under the cartilage for support.32 Postoperative use of an external rotation splint for 4 weeks is recom-
Arthroscopic Posterior Bankart Repair Arthroscopic posterior Bankart repair is an option for acute reducible dislocations with little or no humeral head impaction (,20%) and with persistent instability. The arthroscope is introduced through the anterior portal, and a posterolateral portal is used for suture anchor placement. A posterosuperior portal is used for suture management. The posterior portion of the acromion may prevent vertical
A, Axial (top) and AP (bottom) illustrations of a shoulder with a reverse Hill-Sachs lesion. The AP view illustrates a modified McLaughlin procedure, which is done through a transsubscapularis approach. B, Axial (top) and AP (bottom) illustrations of the shoulder following suture of the subscapularis tendon into the defect with the help of suture anchors and subsequent repair of that approach through the tendon.
The McLaughlin Procedure For patients with reverse Hill-Sachs lesions of #20% and with persistent instability following reduction, the subscapularis can be either lifted off the lesser tuberosity and transposed into the defect with transosseous sutures after reduction as originally described by McLaughlin2 or sutured into the bed of the defect.31 The circumflex vessels are preserved inferiorly by maintaining a small sleeve of tendon attached to its original site. Modified McLaughlin Procedure In the presence of a significant reverse Hill-Sachs lesion (20% to 40%), the lesser tuberosity can be osteotomized to access the joint and eventually transposed to the bone defect after joint reduction.21 This is known as the modified McLaughlin procedure (Figure 5). The osteotomy is perMarch 2014, Vol 22, No 3
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Acute Traumatic Posterior Shoulder Dislocation
Figure 6
A, Axial CT scan of a left shoulder with significant humeral head impaction. B, Axial CT scan of the same patient 3 months after an allograft was implanted into the deficit. C, Axial CT scan of a different patient with a similar injury 3 months after fracture disimpaction.
Figure 7
Illustration of the skin landmarks used in the posterior approach (represented by the dashed line) used to manage irreducible posterior shoulder dislocation or persistent instability after closed reduction in the absence of a significant reverse Hill-Sachs lesion. Access to the joint is achieved either through infraspinatus tenotomy or between the infraspinatus and the teres minor.
positioning of suture anchors, and the surgeon must have at the ready a variety of suture passers to accommodate the anatomy in this area. Arthroplasty In the presence of massive humeral head impaction (.40%) in patients aged
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,55 years or in patients who are not good candidates for graft incorporation, hemiarthroplasty is a good option to address both instability and the articular surface deficit.33 In order to prevent postoperative dislocation, the humeral head must be positioned in normal retroversion (#20°). In more severe cases of residual instability, the posterior labrum can be repaired before prosthesis implantation. Through an anterior approach, the humeral head is excised and the humeral cut is oriented parallel to the glenoid, leaving 1 to 2 cm of joint space to visualize the posterior labrum. Use of a laminar spreader and gentle lateral traction can improve visualization. In a right shoulder, the first glenoid anchor is positioned at the 7-o’clock position and the second at the 9-o’clock position. The anchor is placed at the edge of the cartilage at a 45° angle to the joint surface. A free 2/3 circular needle is usually sufficient to pass the anchor suture through the posterior labrum and capsule. Following repair of the labrum, the hemiarthroplasty can be performed as usual. A treatment algorithm is shown in Figure 8.
Rehabilitation Regardless of management type, the shoulder is braced in 20° of external rotation and abduction for 4 weeks to aid healing of the posterior capsule. Pendulum exercises and elbow range of motion three times per day are encouraged. At 4 weeks, unlimited progressive range of motion is initiated as well as isometric posterior rotator cuff strengthening. Noncontact sports are allowed 3 months after reduction or surgery, and contact sports are permitted 4 to 6 months postoperatively.
Results Approximately 18% of patients experience recurrent instability in the first year following acute posterior dislocation.4 Risk factors for recurrence are age ,40 years, seizure, and large reverse Hill-Sachs lesion (.1.5 cm3). Persistent functional impairment has been noted 2 years after the initial trauma, even without recurrent instability.4 Activities that require significant internal rotation may be particularly difficult. Typically, patients with persistent symptoms present with either
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Figure 8
Treatment algorithm for the surgical management of acute posterior shoulder dislocation.
subjective or objective posterior instability and a painful shoulder. On physical examination, apprehension is seen with the shoulder in adduction and forward elevation. Most patients will present additional symptoms with a posteriorly directed translational force of the humerus. Compensatory scapular winging can be seen with anterior shoulder elevation.9 For these patients, imaging should include magnetic resonance arthrography of the shoulder. Treatments include all modalities of nonsurgical treatment as well as surgical management of refractory cases. PosMarch 2014, Vol 22, No 3
terior capsular plication and posterior Bankart repair have been reported to improve both function and pain.34
Summary Posterior shoulder dislocation is a relatively uncommon pathology, with several typical modes of presentation. Dislocation often goes undiagnosed in the acute setting in patients who present following seizure, electric shock, or high-energy trauma. Thus, particular attention is required to diagnose the injury in these patients. Imaging stud-
ies should always include an axillary or equivalent radiograph. CT and MRI are both useful to diagnose associated injuries, which are much more frequent than previously thought. Treatment is individualized to each patient based on timing of presentation, size of the reverse Hill-Sachs lesion, and the presence of associated injuries (ie, fracture, rotator cuff tear, glenoid bone loss). Younger patients are treated with soft-tissue management with or without a bony procedure, whereas older patients may require arthroplasty to maintain stability.
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