Anterior Shoulder Dislocation

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Introduction

The shoulder is the most commonly dislocated joint in the body with almost half of these injuries occurring during sport or recreation activities.1The decision to treat conservatively or refer a patient for surgery following a shoulder dislocation is an important one as recurrence rates, pain, quality of life and return to full function for work or sporting activity are all considerations. The efficacy of traditional approaches of immobilisation and physiotherapy compared to surgical intervention have been challenged by results of trials of early surgical intervention.2

Objective

Following a shoulder dislocation the clinician may be required to advise a patient regarding surgical intervention a s a means of stabilising the joint, reducing the risk of recurrence, or improving pain or function associated with instability. Surgical treatments are viewed in context of their relationship to the various anatomical injuries associated with shoulder dislocation. The use of imaging and functional testing to assess an individual’s injury and guide treatment recommendations will be discussed.

Background

The incidence of shoulder dislocation is between 23.1 and 23.9 per 100,000 person years.1,3The distribution of data is not spread evenly throughout with male patients more likely to be younger (median age 30) with sporting activity as the mechanism of injury; and female patients more likely to be older (median age 49) with fall as mechanism of injury. 

The vast majority of the literature for both conservative and surgical treatment methods has focused upon the sub-group of young male athletes with either a proven, or a high likelihood of a Bankart’s lesion.4-10Patients who sit outside of this subgroup may present, including older patients, or those with recurrent instability.

The literature shows that young male patients who partake in demanding physical activity have a much greater rate of recurrence and this has led to age and activity based recommendations when considering surgery over conservative management.2,11Recurrence rates by age show higher rates in the young (<23 50%, 23-29 <25%, 30-40 <25%)12and lower rates in the elderly (0-10%).13This has been thought to be due to the high proportion of Bankart’s lesions in the young although humeral head and glenoid bony injury clearly play major roles in ongoing instability.  

As an individual patient’s injuries may not strictly follow age demographics this literature review analyses the incidence of the various anatomical types of injuries associated with shoulder dislocation.

Functional testing for shoulder instability and rotator cuff strength should be performed in all patients during assessment, prior to surgery and throughout rehabilitation.14-16

Imaging options for acute or chronic shoulder instability include plain radiography, ultrasound, computed tomography (CT) magnetic resonance imaging (MRI) and MR arthrography. 

Review

Soft tissue injuries:

Bankart’s lesion (Figure 1) – a capsule-labral complex avulsion from the scapular periosteum which occurs with impaction of the humeral head against the anteroinferior glenoid labrum with the humerus in abduction. This lesion occurs in one third of cases overall with rates of up to 90% in younger patients in some studies.7,11In one study of older patients (>40) with recurrent instability no patients displayed a Bankart’s lesion.17It has a strong association with recurrent dislocations.11Bankart’s lesion is classically a soft tissue avulsion injury but may also involve a fracture of the anteroinferior glenoid rim, sometimes called a “bony Bankart’s” which is noted at rates up to 32% in recurrent shoulder instability.18Anterior labral periosteal sleeve avulsion (ALPSA) is a Bankart variant in which the avulsed periosteum does not rupture, with the labrum/ligament complex rotating inferiorly and healing in a more medial position. It is associated with recurrent instability following primary dislocation and arthroscopic Bankart’s repair.11,19A Perthes lesion is a Bankart variant comprising of an undisplaced avulsion of the labrum with an intact periostium, this is seen in 6.6% of cases.11,20

The glenoid labral articular disruption (GLAD) lesion is a labral tear with an associated articular cartilage lesion. This is more often associated with pain than instability. Humeral avulsion of glenohumeral ligaments (HAGL) occurs during hyperabduction and external rotation and is seen in 0.2% of dislocation cases. This injury is difficult to approach arthroscopically and may require open surgery.11,20

The superior labrum anterior and posterior (SLAP) lesion is a lesion of the superior labrum which includes the “anchor” of the biceps tendon to the labrum.21The lesion can occur with either a compressive injury to the shoulder from a fall with outstretched arm, or as an overuse injury in throwing athletes. SLAP lesions are noted in 3.4% of dislocation cases and may be a further cause of instability. 11

Rotator cuff injuries are seen in 6.2 – 7.5%of cases.11Injury to the rotator cuff, usually supraspinatus, is seen more commonly in older patients (31.7%). When subscapularis is ruptured, there may be an associated displacement of the long head of biceps.22Rotator cuff tears have a more significant role in recurrent instability in older patients, one case series noting subscapularis and anterior capsule rupture at the lesser tuberosity in older patients with recurrent instability.17

Bone injuries:

Hill Sach’s lesion is a compression fracture in the postero-superior humeral head which impacts the glenoid rim during dislocation. This is seen in 24.6-76% of cases, with up to 100% in recurrent instability. Both the size and the exact position of the lesion contribute to ongoing instability with the presence of significant bony defects having a negative effect on the recurrence of instability following arthroscopic repair.23-26

Glenoid or humeral head osseous loss is also associated with recurrent instability following arthroscopic Bankart’s repair. There is currently not enough evidence to provide a clear guideline for the optimal techniques for glenoid and humeral head reconstruction but the contribution of bony defects towards instability must be considered prior to surgery.19,27,28

Greater tuberosity fractures occur in 7.5% of cases, are not thought to contribute to chronic instability and are actually associated with lower rates of recurrence.11,13

Conservative management:

Standard conservative management consists of immobilisation in the position of internal rotation for 2-6 weeks followed by physiotherapy.29,30Studies examining the role of external rotation immobilisation have shown contradictory results.10,31Positioning the humerus in external rotation is designed to appose the traumatically separated segments of the Bankart’s lesion. MRI studies have demonstrated better positioning between the detached labrum and underlying bone.32,33Clinical studies showing the efficacy of external rotation positioning have shown both positive10and no change findings31. Of note, the Itoi trial did not attempt to demonstrate a Bankart’s lesion either with imaging or functional testing, relying on an age profile. Duration of ER immobilisation in the setting of a Bankart’s lesion has shown coaptation of the lesion between 3 and 5 weeks.34

Surgical options

Open surgery

The open approach may be considered over arthroscopy in the presence of large bony defects, HAGL lesions, and multi-directional instability.20,27,28,35Rates of recurrent instability and functional scores are similar between open and arthroscopic techniques but a high long term risk of arthropathy must be considered with open surgery.4,36,37

Arthroscopic lavage

Only one RCT has been performed comparing arthroscopic lavage to conservative management. This showed a reduction in recurrence rate in the lavage group (13%) compared to the conservative group (43%).38

Arth and repair

Surgical options

Arthroscopic Stabilization:

Only 2 RCTs were found which compared early arthroscopic stabilization surgery versus conservative immobilization and physiotherapy.7,8,39One other study directly comparing surgical vs non-surgical techniques was presented only as a conference abstract with limited details,9other trials compared an arthroscopic technique to general rates of outcome measures with conservative management rather than as part of the trial.40The demographics of the patients in the 2 RCTs studies mirrored the specific sub-group expected to benefit most from early surgery. Recurrence rates were examined at 18 months7and 36 months.8Table 1

Table 1 – Data from RCTs comparing surgical vs conservative approaches to primary ASD

Bottoni8

Kirkley7

Number

24 (11 operative group)

40 (20 operative group)

Age

18-20 (mean age 22.4)

<30 (mean 22.4)

Sex

100% male

75% male

Sporting mechanism

67% (or 79% if “military training” included)

79%

Imaging

MRI

Injury

100% had Bankart’s lesion

All but 2 had bankarts lesions 18/20 (90%)

Chronic Instability/Recurrence rate conservative group

6/9 (75%)

11/19

Chronic Instability/Recurrence surgical group

1/9 (11.1%)

5/19

Complications

nil

1 septic joint

The rate of recurrent instability following arthroscopic Bankart repair at 10 years ranged from 3.4 to 35%.19The group most likely to suffer recurrence of instability were young (<22), male and sports competitors. One study comparing recurrence rates between arthroscopic and open surgeries on patients with confirmed Bankart’s lesions showed higher recurrence rates following arthroscopic repair.6

Mean age was 20ish bottoni kirkley wintzell 

Data for displaced vs non-displaced lesion

Discussion

The majority of research into shoulder dislocations focuses upon treatment of the most common group, the young male athlete, which accounts for up to half of all cases. Research into early stabilisation of shoulders in tis group has been shown to reduce chronic instability. This has resulted in age based recommendations which, given the range of injury types and their impact upon chronic instability is simplistic, relying upon the expectation of a Bankart’s lesion in this population. Extrapolation of the benefits of surgery outside of this population is clearly not possible and further research into instability is required to optimise management of all patients.

In Kirkley’s study 2 patients (10%) of the target group underwent arthroscopic intervention and were subsequently found to have no Bankart’s lesion. MRI performed prior to surgery confirming both the presence and type of lesion is preferable in order to guide surgical planning. Patients with chronic instability would also benefit from pre-operative estimation of bony lesions as well as MRI/MRA which has been shown to correlate well with intra-operative labral findings.8

There are no RCTs for surgery vs non-surgery in older adults. Injury types contributing to instability in older patients included a much lower proportion of Bankart’s lesions, and higher rates of rotator cuff injury.  This injury distribution could be appropriately imaged to assess the likely causes of instability in these patients which may be more suited to open repair or aggressive physiotherapy then an arthroscopic approach.

Various attempts have been made to categorise instability types with reference to the likelihood of surgical success (Table 2). They should be taken in the context that injuries occur in a spectrum rather than necessarily in isolation, the addition of subgroups to the Polar groups recognising the complexity of measuring the interacting effects of different levels of trauma (from none to traumatic dislocation) and abnormal muscle patterning (See figure X).41,42

Table 2 – Classification of shoulder instability.

Anterior instability42

Polar Groups41

TUBS – Traumatic, Unidirectional, Bankart lesion, responds to Surgery

I – traumatic structural instability (Bankart’s lesion and unidirectional anterior instability)

AMBR – Atraumatic, Multidirectional, may be Bilateral, responds to Rehabilitation

II – atraumatic structural instability

III – atraumatic non-structural instability (muscle patterning disorders/habitual)

Figure X – Stanmore classification of the polar groups: triangle model showing subgroup classification.

Predictive modelling for chronic instability following shoulder dislocation has been attempted and this approach may have utility in predicting who may best be referred for surgery.43However this particular model did not factor in injury type, relying upon demographic data. There is currently no prospective evidence that we can predict chronic shoulder instability based upon initial MRI and clinical tests. Information gained from a combination of functional testing and imaging may well help guide predictions of chronic instability as well as directing specific physiotherapy programs, but there is a dearth of prospective data in these areas. 

For the clinician faced with the prospect of assessing a patient with acute or chronic instability symptoms the following practical approach is proposed. Patients may be more or less likely to have specific injury patterns based upon age or mechanism but the assessment need not be restricted by pre-determined group allocation. A 3-week assessment would be appropriate following a primary dislocation.

Imaging

Evaluation of injury pattern may require more than one imagine modality. MRI/MRA is preferable for capsulo-labral and rotator cuff injuries, CT is best for 3-dimensional analysis of bony lesions, US provides functional information on rotator cuff injuries. The imaging modalities chosen will depend upon accessibility, cost and specific case characteristics (including functional assessment). 

Functional testing

a) Glenohumeral instability testing - unidirectional anterior instability versus multidirectional instability.

b) Rotator cuff strength testing.

Further management will then be guided by the results of imaging and functional tests. Additional factors include requirements for rapid return to high level of activity, pain, premorbid medical and injury conditions, physiotherapy and rehabilitation regime compliance. If multi-directional instability is noted then the specific injury constellation and patient factors need to be considered with any surgical approach.

Injury type and functional assessment

Treatment plan

Capsulolabral lesion with unidirectional anterior instability

Refer for surgery

Displaced capsulolabral lesion with functionally stable joint testing

Conservative management with progressive physiotherapy and regular reassessment for stability. 

Consider surgery based upon specific type of lesion and other risk factors for chronic instability such as a significant Hill Sach’s lesion. 

Consider surgery if a rapid return to high-level activity is required, or there is significant pain or loss of function.

Undisplaced capsulolabral lesion and functionally stable

Conservative management with tailored physiotherapy program.

Subscapularis tear with associated biceps tendon displacement

Consider surgery due to high risk of instability, especially if associated with significant Hill Sach’s lesion

Partial rotator cuff tears or full supraspinatous tear

Conservative management depending upon the age, premorbid state and ability to undertake an aggressive physiotherapy program.

Example case 1 – a 30 year old athlete with recurrent dislocations and unidirectional anterior instability.  This patient should have an MRI/MRA to evaluate the presence and type of capsule-labral lesion and CT to assess for size and position of Hill Sach’s lesion, or bony glenoid rim injury. This would then assist surgical planning within a spectrum from simple arthroscopic Bankart’s repair to open repair including bone grafting.

Example case 2 – a 50 year old female who presents with multidirectional instability and significant rotator cuff weakness following a shoulder dislocation during a social tennis game. This patient should have an US/MRI to assess for presence and extent of rotator cuff injury, CT to assess for bony contribution to instability. In the absence of a full subscapularis tear or major bone loss this patient would likely benefit from a tailored physiotherapy regime with review at 3 months.

Conclusion

Recent recommendations for surgery versus conservative management following shoulder dislocation are based around age and activity with outcome measures focused upon recurrence rates, and function etc.  Injury specific analysis of operative intervention in displaced/undisplaced, or unstable/stable joints is currently incomplete and future prospective research in these areas would be welcomed. The current literature may result in over-interpretation of the indications for surgical referral in young patients who either do not have a capsulo-labral lesion, or who have an undisplaced lesion with the potential for healing and joint stability with conservative management. A tailored approach to the patient is proposed, with decision for surgical referral based upon injury type (imaging showing capsulo-labral lesion, rotator cuff tear and bone lesions) and function (clinical tests showing unidirectional anterior glenohumeral joint instability). Predictive modelling may provide more accurate treatment algorithms but would need to incorporate specific injury types in order to improve accuracy for individual cases, especially for those patients outside of the young male athlete subgroup.

1  Zacchilli, M. A., Zacchilli, M. A. & Owens, B. D. Epidemiology of Shoulder Dislocations Presenting to Emergency Departments in the United States. Journal of bone and joint surgery. American volume92, 542-549, doi:10.2106/JBJS.I.00450 (2010).

2  G, H. H. H., Handoll, H. H. G., Almaiyah, M. A. & Rangan, A. Surgical versus non-surgical treatment for acute anterior shoulder dislocation. Cochrane database of systematic reviews, CD004325, doi:10.1002/14651858.CD004325.pub2 (2004).

3  Leroux, T., Chahal, J., Wasserstein, D., Mahomed, N. & Austin, P. Epidemiology of Primary Anterior Shoulder Dislocation Requiring Closed Reduction in Ontario, Canada. The American journal of sports medicine42, 442-450, doi:10.1177/0363546513510391 (2014).

4  Bottoni, C. R., Smith, E. L., Moore, J. H. & Berkowitz, M. J. Arthroscopic Versus Open Shoulder Stabilization for Recurrent Anterior Instability. The American journal of sports medicine34, 1730-1737, doi:10.1177/0363546506288239 (2006).

5  Fabbriciano, C.et al.Arthroscopic versus open treatment of Bankart lesion of the shoulder: a prospective randomized study. Arthroscopy20, 456-462 (2004).

6  Sperber, A., Hamberg, P., Karlsson, J., Swärd, L. & Wredmark, T. Comparison of an arthroscopic and an open procedure for posttraumatic instability of the shoulder: A prospective, randomized multicenter study. Journal of Shoulder and Elbow Surgery10, 105-108, doi:http://dx.doi.org/10.1067/mse.2001.112019(2001).

7  Kirkley, A., Griffin, S., Richards, C., Miniaci, A. & Mohtadi, N. Prospective Randomized Clinical Trial Comparing the Effectiveness of Immediate Arthroscopic Stabilization Versus Immobilization and Rehabilitation in First Traumatic Anterior Dislocations of the Shoulder. Arthroscopy15, 507-514, doi:10.1053/ar.1999.v15.015050 (1999).

8  Bottoni, C., R., Arciero, R. A., Harpstrite, J. K., Rooney, R. C. & Wilckens, J. H. A Prospective, Randomized Evaluation of Arthroscopic Stabilization Versus Nonoperative Treatment in Patients with Acute, Traumatic, First-Time Shoulder Dislocations. The American journal of sports medicine30, 576-580 (2002).

9  Sandow, M. J. & Liu, S. H. Acute arthroscopic bankart repair for initial anterior shoulder dislocation: A prospective clinical trial. Journal of Shoulder and Elbow Surgery5, S81, doi:http://dx.doi.org/10.1016/S1058-2746(96)80364-8(1996).

10  Itoi, E.et al.A new method of immobilization after traumatic anterior dislocation of the shoulder: a preliminary study. Journal of Shoulder and Elbow Surgery12, 413-415, doi:http://dx.doi.org/10.1016/S1058-2746(03)00171-X(2003).

11  Longo, U. G., Loppini, M., Rizzello, G. & Ciuffreda, M. Management of Primary Acute Anterior Shoulder Dislocation: Systematic Review and Quantitative Synthesis of the Literature. Arthroscopy30, 506-522, doi:10.1016/j.arthro.2014.01.003 (2014).

12  Hovelius, L.et al.Recurrences after initial dislocation of the shoulder. Results of a prospective study of treatment. The Journal of Bone & Joint Surgery65, 343-349 (1983).

13  Beeson, M. S. Complications of shoulder dislocation. The American Journal of Emergency Medicine17, 288-295, doi:http://dx.doi.org/10.1016/S0735-6757(99)90127-4(1999).

14  Hill, A. M.et al.The clinical assessment and classification of shoulder instability. Current Orthopaedics22, 208-225, doi:http://dx.doi.org/10.1016/j.cuor.2008.02.006(2008).

15  Beaudreuil, J.et al.Contribution of clinical tests to the diagnosis of rotator cuff disease: A systematic literature review.Joint Bone Spine76, 15-19, doi:http://dx.doi.org/10.1016/j.jbspin.2008.04.015(2009).

16  Yuen, C. K., Mok, K. L. & Kan, P. G. The validity of 9 physical tests for full-thickness rotator cuff tears after primary anterior shoulder dislocation in ED patients. The American journal of emergency medicine30, 1522-1529, doi:10.1016/j.ajem.2011.12.022 (2012).

17  Neviaser, R. J. & Neviaser, T. J. Recurrent instability of the shoulder after age 40.Journal of Shoulder and Elbow Surgery4, 416-418, doi:http://dx.doi.org/10.1016/S1058-2746(05)80032-1(1995).

18  Fujii, Y., Yoneda, M., Wakitani, S. & Hayashida, K. Histologic analysis of bony Bankart lesions in recurrent anterior instability of the shoulder. Journal of Shoulder and Elbow Surgery15, 218-223, doi:http://dx.doi.org/10.1016/j.jse.2005.06.006(2006).

19  Randelli, P., Pietro, R. & Ettore, T. Primary anterior shoulder dislocation in young athletes: fix them. Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA17, 1404, doi:10.1007/s00167-009-0950-6 (2009).

20  Pope, E. J., Ward, J. P. & Rokito, A. S. Anterior shoulder instability: a history of arthroscopic treatment. Bull NYU Hosp Jt Dis69, 44-49 (2011).

21  Snyder, S. J., Karzel, R. P., Del Pizzo, W., Ferkel, R. D. & Friedman, M. J. SLAP lesions of the shoulder. Arthroscopy: The Journal of Arthroscopic & Related Surgery26, 1117-1117 (2010).

22  Berbig, R., Weishaupt, D., Prim, J. & Shahin, O. Primary anterior shoulder dislocation and rotator cuff tears. Journal of Shoulder and Elbow Surgery8, 220-225, doi:http://dx.doi.org/10.1016/S1058-2746(99)90132-5(1999).

23  Bushnell, B. D., Creighton, R. A. & Herring, M. M. Bony Instability of the Shoulder. Arthroscopy: The Journal of Arthroscopic & Related Surgery24, 1061-1073, doi:http://dx.doi.org/10.1016/j.arthro.2008.05.015(2008).

24  Burkhart, S. S. & De Beer, J. F. Traumatic glenohumeral bone defects and their relationship to failure of arthroscopic Bankart repairs: Significance of the inverted-pear glenoid and the humeral engaging Hill-Sachs lesion. Arthroscopy: The Journal of Arthroscopic & Related Surgery16, 677-694, doi:http://dx.doi.org/10.1053/jars.2000.17715(2000).

25  Hovelius, L.et al.Ten year prognosis of primary anterior dislocation of the shoulder in the young. Journal of Shoulder and Elbow Surgery4, Supplement 1, S4, doi:http://dx.doi.org/10.1016/S1058-2746(95)80033-6(1995).

26  Ochoa Jr, E. & Burkhart, S. S. Bone Defects in Anterior Instability of the Shoulder: Diagnosis and Management. Operative Techniques in Orthopaedics18, 68-78, doi:http://dx.doi.org/10.1053/j.oto.2008.07.003(2008).

27  Beran, M. C., Donaldson, C. T. & Bishop, J. Y. Treatment of chronic glenoid defects in the setting of recurrent anterior shoulder instability: A systematic review. Journal of Shoulder and Elbow Surgery19, 769-780, doi:http://dx.doi.org/10.1016/j.jse.2010.01.011(2010).

28  Lynch, J. R., Clinton, J. M., Dewing, C. B., Warme, W. J. & Matsen Iii, F. A. Treatment of osseous defects associated with anterior shoulder instability. Journal of Shoulder and Elbow Surgery18, 317-328, doi:http://dx.doi.org/10.1016/j.jse.2008.10.013(2009).

29  Brukner, P. Brukner and Khan's Clinical Sports Medicine. 4th edn,  1161 (McGraw-Hill, 2012).

30  Smith, G. C. S., Chesser, T. J. S., Packham, I. N. & Crowther, M. A. A. First time traumatic anterior shoulder dislocation: A review of current management. Injury44, 406-408, doi:http://dx.doi.org/10.1016/j.injury.2013.01.001(2013).

31  Finestone, A., Milgrom, C., Radeva-Petrova, D. R. & Rath, E. Bracing in external rotation for traumatic anterior dislocation of the shoulder. Journal of bone and joint surgery. British volume91, 918-921, doi:10.1302/0301-620X.91B7.22263 (2009).

32  Hart, W. J. & Kelly, C. P. Arthroscopic observation of capsulolabral reduction after shoulder dislocation. Journal of Shoulder and Elbow Surgery, 134-137 (2005).

33  G, H. H. H., Handoll, H. H. G., Hanchard, N. C. A., Goodchild, L. & Feary, J. Conservative management following closed reduction of traumatic anterior dislocation of the shoulder. Cochrane database of systematic reviews, CD004962, doi:10.1002/14651858.CD004962.pub2 (2006).

34  Scheibel, M., Scheibel, M., Magosch, P., Kuke, A. & Nikulka, C. How Long Should Acute Anterior Dislocations of the Shoulder Be Immobilized in External Rotation? The American journal of sports medicine37, 1309-1316, doi:10.1177/0363546509331943 (2009).

35  Speer, K. P., Pagnani, M. & Warren, R. F. Arthroscopic anterior shoulder stabilization: 2-5 year follow-up using a bioabsorbale TAC. J. Shoulder Elbow Surg.4, Supplement 1(1995).

36  Hovelius, L. & Saeboe, M. Neer Award 2008: Arthropathy after primary anterior shoulder dislocation–223 shoulders prospectively followed up for twenty-five years. Journal of Shoulder and Elbow Surgery18, 339-347, doi:http://dx.doi.org/10.1016/j.jse.2008.11.004(2009).

37  Netto, N. A. Treatment of Bankart Lesions in Traumatic Anterior Instability of the Shoulder: A Randomized Controlled Trial Comparing Arthroscopy and Open Techniques. Arthroscopy28, 900-908, doi:10.1016/j.arthro.2011.11.032 (2012).

38  Wintzell, G.et al.Arthroscopic lavage reduced the recurrence rate following primary anterior shoulder dislocation A randomised multicentre study with 1-year follow-up. Knee Surgery7, 192-196, doi:10.1007/s001670050146 (1999).

39  Kirkley, A., Kirkley, A., Griffin, S., Richards, C. & Mohtadi, N. Prospective Randomized Clinical Trial Comparing the Effectiveness of Immediate Arthroscopic Stabilization Versus Immobilization and Rehabilitation in First Traumatic Anterior Dislocations of the Shoulder. Clinical journal of sport medicine7, 242, doi:10.1097/00042752-199707000-00052 (1997).

40  DeBerardino, T. M., Arciero, R. A., Taylor, D. C. & Uhorchak, J. M. Prospective evaluation of arthroscopic stabilization of acute, initial anterior shoulder dislocations in young athletes. Two- to five-year follow-up. Am J Sports Med29, 586-592 (2001).

41  Lewis, A., Kitamura, T. & Bayley, J. I. L. (ii) The classification of shoulder instability: new light through old windows! Current Orthopaedics18, 97-108, doi:http://dx.doi.org/10.1016/j.cuor.2004.04.002(2004).

42  Matsen Iii, F. A., Thomas, S. C. & Rockwood Jr, C. A. The Shoulder (2nd ed).  600, 921 (Saunders, W.B., 1990).

43  Mather Iii, R. C., Orlando, L. A., Henderson, R. A., Lawrence, J. T. R. & Taylor, D. C. A predictive model of shoulder instability after a first-time anterior shoulder dislocation. Journal of Shoulder and Elbow Surgery20, 259-266, doi:http://dx.doi.org/10.1016/j.jse.2010.10.037(2011).