Shoulder Update Anatomy

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Shoulder Update

SHOULDER INSTABILITY

Classification andAnatomic Considerations

The clinical definition of shoulder instabilityis slipping of the humeral head out of theglenoid socket during activities causingsymptoms. Instability varies from subluxationto dislocation. Patients may be classified intotwo broad categories: traumaticunidirectional anterior-inferior instability witha Bankart lesion (referred to by the acronymTUBS traumatic, unidirectional, Bankart,surgical) and AMBRI (atraumatic,

multidirectional, bilateral instability) [4,5,6].This classification primarily applies to theyounger patient. TUBS patients are usuallysurgical candidates if the dislocation isrecurrent while AMBRI patients are usuallynot [4,5,6].

The usual dislocation occurs during a fall onthe outstretched externally rotated, abductedarm (FOOSH fall on an outstretchedhand). These patients (post traumatic) fit intothe TUBS category and usually have acapsulolabral disruption (Bankart or Bankartvariation lesion) and imaging beyond plain

films is usually not requested as the patientsare initially treated conservatively. There is agrowing tendency to image the first timedislocator to document the type of lesionresulting from the trauma. There aretraumatic episodes where the patients feelthat their shoulder popped out andrelocated but the dislocation was difficult todocument clinically and not documentedradiographically. Some of these episodesrepresent true dislocations and some aresevere subluxations [5]. Imaging may berequired in these patients to document thedamage done and to plan further therapy. In

the older patient as the spectrum of lesionsresulting are generally quite different than atypical capsulolabral disruption (Bankartlesion) [7,8].

The anatomic causes of recurrentdislocation are varied. The cause ofinstability in these patients may behypermobility or laxity perhaps due tostretching of the supporting structures fromoveruse and reliable standards of normalhave not yet been defined with imaging.

Recurrent instability in TUBS patients isanterior-inferior resulting from previousdislocation. In order to understand the causeof recurrent instability it is useful to considerthe stabilizing structures of the shoulder as aunit the anterior capsular mechanism

consisting of the capsule and capsularligaments (glenohumeral ligaments), the

glenoid labrum, subscapularis muscle andtendon. The most important structurestabilizing the shoulder and limitinggross anterior-inferior subluxations anddislocations is the inferior glenohumerallabral-ligamentous complex (IGHLC)[1,9]. The ligament itself is a thickening ofthe inferior capsule and is lax when thehumerus is in the neutral position, allowingnormal shoulder motion. The ligamentouscomplex becomes taut in abduction andexternal rotation (ABER), and stabilizes thejoint at the end range of shoulder movement

in this. The threshold of restraint of thisligamentous complex is exceeded during adislocation which leads to tears and/orstretching of the inferior glenohumeral-labral complex. This in turn may lead tolaxity and symptomatic instability [10].

The anterior capsular mechanismcomponents are all important stabilizingstructures [1,9] and any or all of thesestructures may be injured afterdislocation thus leading to a spectrum ofabnormalities that may be shown withMR imaging. Usually, especially in theyounger patient, a labral ligamentousavulsion (Bankart lesion) results.

It is critically important to know the history ofthe patient before the imaging examinationis interpreted as the spectrum of lesionsdiffers depending upon the age of thepatient and mechanism of injury. Thesefactors must be kept in mind for theradiologist to consider the type of lesionsthat may result in continued instability.Sometimes neither the patient nor theorthopedist knows for certain what the exactmechanism of injury was and whether thepatient dislocated or not. Is the injury of a

repetitive nature? These are all importantquestions. We ask our technologists to askhistorical questions and document these onthe intake requisition for additionalinformation.

TECHNIQUE CONSIDERATI-

ONS: WHY ASK FOR WHICH

TYPE OF MR STUDY?

The technique of magnetic resonanceevaluation employed is dependent upon theclinical history. Conventional MRI allowsdirect visualization of most of the importantanatomical structures of the shoulder. Forinstance, in the older patient where rotatorcuff disease is suspected, conventional MRI

is indicated. The limitation of conventionalMRI is that small intra-articular structures

such as the glenoid labrum, glenohumeralligaments and articular surface of the rotatorcuff can be difficult to evaluate in theabsence of a joint effusion.

MR arthrography improves the diagnosticaccuracy of the examination [10,11,12] butthis controversial and with new gradientsand high resolution scans it is often notnecessary to perform MR arthrography.However in the chronic instability patientwhere healing (fibrosis andresynovialization) may obscure the truelesion to MRI, MR arthrography especially

with ABER imaging may be helpful. Theanterior capsule will fold on itself in theneutral position and become closely appliedto the anterior labrum in the absence of ajoint effusion. Additionally, the MRIphenomenon magic angle artifact affectsthe collagenous tissues present in theshoulder joint especially in the anterior-inferior region of the glenoid and in thecritical zone of the rotator cuff. These are thetwo areas of the shoulder where accurateimaging is essential and arthrography maybe helpful [10,13,14,15]. In the youngerpatient with chronic (healing andresynovialization) recurrent instability, MRIarthrography is often the method of choiceto help avoid a misdiagnosis [10,13,14,16].

Placing stress on the stabilizing structures ofthe shoulder may bring out an otherwiseundetected lesion. Abduction and externalrotation stresses the inferior glenohumerallabral-ligamentous complex and opens upsome partially healed or healed andincompetent labral ligamentous attachmentsto the underlying glenoid. MR arthrographyutilizing the standard position should becoupled with imaging in the abducted

externally rotated (ABER) position foradequate visualization of this region inproblem cases [15,16,18].

INSTABILITY LESIONS

Subluxation

Abduction external rotation injury resultingin a subluxation of the shoulder may result ina partial tear of the capsule, labrum or bothor stretch the capsule. These lesions maylead to repeated subluxation. Theseabnormalities may be difficult to diagnoseby conventional MRI and MR arthrography ishelpful to demonstrate the lesion.Subluxation resulting from a stretchedcapsule in the absence of a labral tear is a

Shoulder Update

Phillip F.J. Tirman


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Shoulder Update

diagnosis of exclusion as no reproducibleimaging criteria have been developed tocharacterize this abnormality.

Posttraumatic

Anterior Dislocation

The types of lesions that occur after anteriordislocation can be conveniently divided intotwo broad categories based upon thepatients age at time of first dislocation. MRarthrography helps in the evaluation of theyounger patient with glenohumeralinstability.

THE YOUNGER PATIENT

ADOLESCENCE FOR

FORTY YEARS

The Bankart LesionDamage to the anterior inferior glenoidlabrum and inferior glenohumeral ligament(labral-ligamentous complex) is the mostcommon injury after anterior shoulderdislocation in the younger age group[19,20,21]. Typically these patients have alabral-ligamentous avulsion with a disruptedscapular periosteum (Bankart lesion).TheBankart lesion represents a detachment ofthe inferior glenohumeral labral-ligamentous complex from the anteriorinferior glenoid with or without a fracture ofthe bony glenoid. Conventional MRI findingsinclude labral/ capsular tear seen asincreased signal intensity through thesubstance of the labrum. If the dislocationwas recent, an effusion is often be presentand one may visualize detachment orpulling away of the labral-ligamentouscomplex. Usually the tear is large enough toinvolve not only the labrum where theanterior band of the inferior glenohumeralligament inserts but also the mid andsometimes superior anterior labrum as thetear dissects upward. This lesion is usually

visualized using conventional(nonarthrographic) technique especially inthe acute setting. There is often surroundingsoft tissue edema in the region and bonemarrow edema or fracture may be presentincreasing the likelihood of detection. In thechronic case, healing of the lesion may takeplace which involves fibrosis andresynovialization. If the lesion does not healcorrectly, the patient will continue to beunstable. If the lesion heals or partiallyheals, it is difficult to fully demonstrate usingconventional MRI and MR arthrography

including the ABER position is helpful.

Bankart Variation Lesions:

Avulsion with an Intact

Pre Post

Pre and Post arthrography Bankart lesion in a difficult case. Because of the lack of joint fluid in this

case, the avulsed labrum was difficult to see before arthrography

Periosteum

The Bankart lesion results in a disruptedscapular periosteum. Perthes described alabral ligamentous avulsion where thescapular periosteum remained intact butwas stripped medially creating a potential

space of variable size anterior and medial tothe scapula between the scapula andstripped periosteum [22].This variant hasbeen termed the Perthes lesionr. Thelabrum may reapproximate its normalposition and partially heal and resynovializein place. In this situation, the scapularperiosteal anchor may be incompetent andresult in recurrent instability. Perthesrecommended a finger probe at surgery touncover this lesion as it may be occult at firstinspection [22]. This has potential dramaticimplications for imaging as well. The lesion

may appear deceptively normal on standardMR imaging and MR arthrography[15,18,23].

Since the labral ligamentous avulsion mayreapproximate its normal position duringhealing/ resynovialization, anatomic closureof the labrocapsular tear results. Thisphenomenon may prevent contrast materialfrom entering the potential tear and make itinvisible to conventional MRI and potentiallyto arthroscopy. If the labrum has partiallyhealed, it may regain normal signal intensity.In this situation imaging in the ABER positionsignificantly increases lesion detection[15,18,22,23]. Adding ABER imaging to thestudy protocol results in a significantincrease in lesion detection overconventional MR arthrography obtained inthe neutral position [18]. The MRI findings ofa Perthes lesion ranges from normal (falsenegative study) to those seen with a Bankartlesion, to visualization of the torn, detachedlabrum and periosteum.

Another variation of the labrocapsulardisruption is termed the anteriorlabroligamentous periosteal sleeve avulsionlesion (ALPSA) described by Nevaiser in

1993. The ALPSA lesion is an avulsion of the

anterior inferior glenoid labrum with anintact scapular periosteum where the labral-ligamentous complex rolls up in a sleevelike fashion and becomes displacedmedially and inferiorly. Using this analogy,the labrum/ligament is the shirtcuff and theperiosteum is the long sleeve where one rollsthe sleeve up as on a hot day. The ALPSAhas also been termed a medialized Bankartlesion emphasizing the characteristic that thelesion is tacked down in a mediallydisplaced location [17]. The labrum andcapsule will not heal in an anatomic positionas a result [17]. The shoulder may heal byfibrosis and granulation tissue heaping upover the displaced labral-ligamentouscomplex and then the region isresynovialized [17]. The lesion may becomedifficult to identify in the chronic state to thearthroscopist [17]. Awareness of the

possibility of the lesion is desirable becausethe surgery to correct an ALPSA lesion isdifferent than a typical Bankart lesionrepair[17]. MRI arthrography helps delineatethe anterior inferior region to bestadvantage demonstrating the ALPSA lesionalerting the surgeon to probe the region anddiscover the potentially occult abnormality.

PATIENTS OVER FORTY

Rotator Cuff Tears

The clinical presentation of an older patientafter first-time anterior glenohumeraldislocation may be confusing andmisleading. These patients are oftendiagnosed with axillary neuropraxia, nervetear, or rotator cuff (supraspinatus)disruption [7,8]. Awareness of themechanism of injury and correlation withradiological findings is desirable so that thecorrect diagnosis can be made, allowing forappropriate treatment and avoidance ofcontinued anterior instability. The injuriesoccurring to the older patient can be roughlydivided into [7,8,21]. According to the

orthopedic literature, one third of patients


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will tear the supraspinatus tendon [7,8,21]and another third will suffer a fracture of thegreater tuberosity (essentially a cuff-tuberosity avulsion or large Hill-Sachsfracture although we and others have foundthat greater tuberosity fractures can occur inany age group [7,8,21]. The final one thirdwill avulse the subscapularis and anteriorcapsule from the humerus [7,8,21].Thislatter subset may result in continued anteriorinstability as the glenohumeral capsule andsubscapularis tendon together areconsidered important anterior stabilizingstructures. This is generally considered asurgical lesion whereas the fracture may betreated conservatively. The supraspinatustear may be treated conservatively orsurgically depending on the size of the tear

and the clinical symptoms. MRI potentiallymay play a pivotal role in distinguishingbetween the lesions and direct patienttherapy. The MRI findings depend upon theinjury sustained and in general,conventional technique in these patients will

suffice.

OTHER ANTERIOR

INSTABILITY ABNORMALITIES

Avulsion of the IGHLC from the humerus[24,25,26] has also been described(Humeral Avulsion of the GlenohumeralLigament HAGL) resulting fromdislocation. MR arthrography helps with thediagnosis. Arthrographic findings includevisualization of contrast materialextravasating from the joint through thecapsular disruption at its humeralinsertion.The inferior glenohumeral ligamentmay tear in its mid substance. This is felt tobe rare or at least is rarely diagnosed with

imaging and may also be an arthrographicdiagnosis.

Posterior Instability

Posterior instability results from excessiveforce directed at the shoulder when the arm

Perthes: note normal appearing ABER: note tear

labrum

is adducted and internally rotated. This is theposition of function of the posterior capsule(the posterior portion of the inferiorglenohumeral ligament). When the arm isadducted and internally rotated, theposterior capsule is tight and injury in thisposition leads to dysfunction of the capsuleand labrum with resultant posteriorinstability. These instability lesions carry thefamiliar eponyms associated with anteriorinstability except with the word reverse isadded to them. A reverse Bankart lesionrefers to a labrocapsular disruption of theposterior labrum resulting from a posteriorlydislocated humerus. The resultant impactionfracture of the anterior-superior humerus isknown as a reverse Hill Sachs lesion. MRIfindings include visualization of thelabral/capsular tear, bony injury to theposterior glenoid and an anterior humeral

injury (lesser tuberosity). The subscapularismay partially or completely tear.

Multi-Directional Instability

Imaging is often not employed in cases ofmulti-directional instability, except when thediagnosis is in question or the multi-directional instability is a cause of shoulderpain but is not suspected as the cause. Inthis patient with instability of unknowncause, imaging may be helpful. Also MRmay be used in the patient with

multidirectional instability to rule outconventional causes of the instability such asa labral abnormality.

Non instability Anterior

Labral Abnormalities

If an injury occurs that results in a tornlabrum the patient may or may not beunstable as a result. Pappas described afunctional instability of the shoulder causedby damage confined to the glenoid labrum[27] which may result from such an injury.

The lesion may result in mechanical lockingof the joint due to torn labral fragmentsbetween the articulating surfaces. While thepatient suffers from anterior shoulder pain,they are not unstable in the classical senseand therefore the term instability issomewhat misleading. MR arthrographymay help define the lesion. Similarly,Neviaser described the GLAD lesion(Glenolabral Articular Disruption) whichrefers to a partial labral tear associated withan articular (hyaline) cartilage divot [28]. Hepostulated the injury resulted from a forcedadduction injury [28]. Again the lesion is

found in a stabile patient, may be subtle,and may be mistaken for an instability lesionby the radiologist. MR arthrography helpsdefine the lesion to best advantage.

ALPSA Lesion. Note the medially displaced labral ligamentous attachment on this ABER image. Note

that the humeral head is also subluxed anteriorly seen only on the ABER view in this patient.


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Anatomic variations of the labrum maymimic an anterior labral abnormality. Thisvariation occurs in the anterior superiorquadrant where the labrum may bedetached or absent and be normal [29,30].

A detached labrum is referred to as asublabral hole and an absent labrum is

termed a Buford complex as the absentlabrum is found in combination with a cord-like middle glenohumeral ligament. Thehistory of the patient is critical asdifferentiation between an anatomicvariation and an isolated anterior superiorlabral injury is difficult.

Superior Labral

Abnormalities

Synder described superior labral tearsanterior and posterior to the attachment of

the biceps tendon to the supraglenoidtubercle [31]. These lesions are not thoughtof as being associated with classicalinstability when they are by themselves even

though the biceps tendon may be animportant anterior stabilizer [32] Snyderdescribed 4 types ranging from fraying andfragmentation to a bucket handle tear [31].MR arthrography may lift the torn labrumfrom the attachment to the glenoid, andshow insinuation of contrast material into

the torn biceps anchor. In the case of thebucket handle variety of SLAP lesion,contrast may help define the fragment bylifting it from the remainder of the tornbiceps anchor. Care must be taken to avoidinterpreting a sub labral hole from a SLAPlesion. Good communication between theorthopedist and the radiologist is helpful inavoiding this potential pitfall. Beltran andTuite have described findings associated withSLAP lesions including high signal on shortTE sequences oriented away from theglenoid and also high signal on T2 weighted

images within the substance of the labrum.

GLENOID LABRAL CYSTS

It has been shown that cysts about theshoulder joint are often associated withlabral tears and with instability [33] In thisway they are analogous to meniscal cysts ofthe knee which originate with tears of themeniscus. Cysts in the posterior and anteriorparalabral region are associated withposterior and anterior instability respectively[33] Those cysts seen superiorly areassociated with SLAP lesions and may ormay not be seen with instability [33]. MRIfindings include visualization of a cysticstructure usually but not always intimatelyrelated to a labral tear. Occasionally at

Subscapularis avulsion after anterior disloaction. Note the torn avulsed tendon and dislocated biceps

tendon which may mimic a tron detached labrum.

arthrography, the cyst may demonstratecommunication with the joint. Cysts mayarise from a region of age relateddegeneration and or dehiscence. Unlike theusual case of the knee meniscal cyst, in theshoulder the tears may completely orpartially heal preventing communication

with the joint. This accounts for detection oflabral cysts in locations associated withinstability in patients that are currentlystabile. Arthroscopic evaluation of thesepatients usually demonstrates evidence ofprior capsulolabral disruption with fibroushealing.

The cyst may cause problems secondary tomass effect. If the cyst arises from a break inthe integrity of the posterosuperior joint (a

HAGL lesion. Note the torn edematous IGHLC

avulsed from the humerus.

Posterior and anterior labral tear in a patient withmultidirectional instability

common location) it may extend into thespinoglenoid notch, posterior to the scapulabetween the scapular spine and the glenoid.The suprascapular nerve passes through thisnotch and may be compressed, resulting ina denervation syndrome. The suprascapularnerve innervates the supraspinatus,infraspinatus and provides some pain fibersto the shoulder joint. Therefore, denervationresults in weakness in those muscles andpain simulating impingement syndromewhich may accompany a rotator cuff tear.MRI may be the only method capable ofrevealing the true cause of symptoms inthese cases.

CONCLUSIONS AND

RECOMMENDATIONS

Suggested Indications for Conventional

MRI

1) Insidious onset of shoulder pain

especially in the over forty age group.2) Impingement

3) Trauma including dislocation in theover forty age group.


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4) Initial evaluation of a patient withsuspected suprascapular nervedysfunction.

5) AC joint evaluation

6) Suspected muscle dysfunction(i.e. deltoid).

Suggested Indications for MRIArthrography

1) Chronic recurring instability especially if damage to the IGHLC issuspected and other studies areinconclusive.

2) Evaluation of labral cysts to determinethe patency of a suspected cyst labral tear communication.(CT arthrography may be helpful)

3) Biceps anchor visualization.

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[2] Snyder SJ. Arthroscopic Evaluation and Treat-ment of Shoulder Instability. In: Snyder SJ, ed.Shoulder Arthroscopy. New York: McGraw - Hill,1994: 179-214.

[3] O'Brien SJ, Warren RF, Schwartz E. AnteriorShoulder instability. Orthopedic Clinics of NorthAmerica 1987; 18:395-408.

[4] Silliman J, Hawkins R. Current concepts andrecent advances in the athletes shoulder. ClinSports Med 1991; 10:693-705.

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physical diagnosis of instability of the shoulder.Clin Orthop Rel Res. 1993; 291:7-19.

[6] Lippitt S, Harryman D. Diagnosis andmanagement of AMBRI syndrome. TechniquesOrthop 1991; 6:61-73.

[7] Neviaser RJ, Neviaser TJ, Neviaser JS.Concurrent rupture of the rotator cuff and anteriordislocation of the shoulder in the older patient. JBone Joint Surg [Am] 1988; 70(9):1308-11.

[8] Neviaser RJ, Nevaiser TJ, Nevaiser JS. Anteriordislocation of the shoulder and rotator cuffrupture. Clin Orthop and Rel Res 1993; 291:103-106.

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Surg 1950; 32-A(2):370-380.[10] Tirman PFJ, Stauffer AE, Crues JV, Turner RM,Schobert WE, Nottage WM. Saline MRarthrography in the evaluation of Glenohumeralinstability. Arthroscopy 1993; 9(5):550-569.

[11] Flannigan B, Kursunoglu-Brahme S, Snyder S,

Slap lesion (arrows). Note high signal in biceps

anchor.

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[12] Hodler J, Kursunoglu-Brahme S, Flannigan B,

Snyder SJ, Karzel RP, Resnick D. Injuries of thesuperior portion of the glenoid labrum involvingthe insertion of the biceps tendon: MR imagingfindings in nine cases. American Journal ofRadiology 1992; 159:565-568.

[13] Palmer WE, Brown JH, Rosenthal DI. Labral-ligamentous complex of the shoulder: evaluationwith MR arthrography. Radiology 1994; 190:645-651.

[14] Palmer WE, Caslowitz PL. Anterior shoulderinstability: diagnostic criteria determined fromprospective analysis of 121 MR arthrograms.Radiology 1995; 197(3):819-25.

[15] Tirman PFJ, Applegate GR, Flannigan BD,Stauffer AE, Crues JVI. Shoulder MR Arthrography.MRI Clinics 1993; 1(1):125-142.

[16] Tirman PFJ, Bost FW, Garvin GJ, et al.Posterosuperior glenoid impingement of theshoulder: Findings at MR imaging and MRarthrography with arthroscopic correlation.Radiology 1994; 193(2):431-436.

[17] Neviaser TJ. The anterior labroligamentousperiosteal sleeve avulsion lesion: A cause ofanterior instability of the shoulder. Arthroscopy1993; 9(1):17-21.

[18] Cvitanic O, Tirman PFJ, Feller JF, Stauffer AE,Carroll K. Can abduction and external rotation ofthe shoulder increase the sensitivity of MRarthrography in detecting anterior glenoid labraltears? AJR 1996; IN PRESS

[19] Bankart ASB. The pathology and treatment of

reccurent dislocation of the shoulder joint. Br JSurg 1938; 26:23-29.

[20 Bankart ASB. Recurrent or habitual dislocationof the shoulder joint. Br. Med. J. 1923; 2:1132-133.

[21] Bigliani LU, Pollock RG, Soslowsky LJ, FlatowEL, Pawluk RJ, Mow VC. Tensile properties of theinferior glenohumeral ligament. J Orthop Res1992; 10:187-197.

[22] Perthes G. ber Operationen bei habitallerSchulterluxation. Deutsch Z Chir 1906; 85:199-227.

[23] Feller JF, Tirman PFJ, Steinbach LS, Zucconi F.Magnetic resonance imaging of the shoulder:Review. Seminars in Roentgenology 1995; XXX(3):

224-239.[24] Stoller DW, Wolf EM. The Shoulder. In: StollerDW, ed. Magnetic Resonance Imaging in Ortho-paedics and Sports Medicine. Philadelphia: J.B.Lippincott, 1993: 511-632.

[25] Wolf E. Arthroscopic management of

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Association of North America Annual Meeting,

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[26] Wolf EM, Cheng JC, Dickson K. Humeral

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glenoid labrum. Am. J. Sports Med. 1983; 11(5):

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[28] Neviaser TJ. The glad lesion: Another cause

of anterior shoulder pain. Arthroscopy 1993; 9(1):22-23.

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Steinbach L, Cox I. The Buford complex - A

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166:869-873.

[30] Williams MM, Synder SJ, Buford D. The

Buford complex-The cord like middle

glenohumeral ligament and absent anterosuperior

labrum complex: A normal anatomic

capsulolabral variant. Arthroscopy 1994;10(3):241-247.

[31] Snyder SJ, Karzel RP, Del Pizzo W, Ferkel RD,

Friedman MJ. SLAP lesions of the shoulder.

Arthroscopy 1990; 6(4):274-279.

[32] Rodosky M, Rudert M, Harner C, Luo L, Fu F.

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[33] Tirman P, Feller J, Janzen D, Peterfy C,

Bergmen A. Association of glenoid labral cystswith labral tears and glenohumeral instability:

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Radiology 1994; 190(3):653-658.

Glenoid Labral Cyst. Note the inferior cyst.

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