Imaging of Glenohumeral Instability - NationalRad

Imaging of glenohumeral instability 163many as 95% of all dislocations occur in the anterior directionand are not associated with a specific sport. In theyounger patient (age 35 years) the most common lesionassociated with an anterior subluxation event is a Bankartlesion (injury of the anterior-inferior labrum) or one of theBankart variants discussed below. 15 In the older patient population(age 35 years) the rotator cuff becomes the “weaklink” rather than the labrum and patients in this older agegroup experiencing a first-time dislocation are more likely tosustain a tear or avulsion of the rotator cuff tendon or possiblyan avulsion fracture of the greater tuberosity. 16In the patient presenting with an anteriorly dislocated humeralhead, the arm is often fixed in slight abduction andexternal rotation. The humeral head may be palpated in ananteromedial position, beneath the coracoid process. Followingreduction, an untreated Bankart lesion will lead to recurrentinstability rates that approach 80%-90%. The patientoften complains of pain and a feeling of apprehension duringabduction and external rotation of the upper arm. Associatedinjuries include an impaction fracture of the posterosuperiorhumeral head (Hill-Sachs lesion), osseous or cartilaginousinjury of the anterior-inferior glenoid rim, or possibly astretching-type injury (neuropraxia) of the axillary nerve. Inthe patient with recurrent subluxation or continued signs ofapprehension, the treatment of choice is surgical repair of thespecific lesion of instability.Radiographic FindingsAssociated With Anterior InstabilityAn anterior dislocation of the humeral head is easily detectedon conventional radiographs. The AP radiograph will demonstrateinferior and medial displacement of the humeralhead into the subcoracoid location and an anterior dislocationis often referred to as a subcoracoid dislocation (Fig. 4A).The axillary and Scapular Y views will also demonstrate anteriordislocation, but are rarely necessary to establish thediagnosis. Once the humeral head is reduced, signs of previousdislocation include flattening of the posterolateral aspectof the humeral head (Hill-Sachs lesion) or a fracture of theanterior-inferior glenoid rim (osseus Bankart lesion) (Fig. 4Band C). The Hill-Sachs lesion is best depicted on the Strykernotch view or on an AP radiograph with the humeral head ininternal rotation. 17 The osseous Bankart lesion is best depictedon the West Point view (modified axillary view). 18 Inolder patients, an avulsion injury of the greater tuberositymay indicate a previous anterior dislocation.Figure 3 Abduction external rotation (ABER) imaging. (A) Normal patientpositioning for ABER imaging. The patient is supine, hand placed behindhead with arm in maximum abduction external rotation. A dual-coil configurationused. (B) A coronal scout is obtained and the ABER images areprescribed off the scout images along the long axis of the humeral shaft. (C)ABER image shows the taut anterior band of the inferior glenohumeralligament (short arrows) and the normal-appearing anterior inferior labrum(long arrow). (Color version of figure is available online.)Computed Tomography FindingsAssociated With Anterior InstabilityComputed tomography (CT) imaging is helpful in detectingand delineating the extent of osseous involvement. In particular,sagittal reconstruction images through the glenoid fossawill demonstrate the size and number of fragments of anosseous Bankart lesion. The size of the osseous fragmentshould be reported along with the number of osseous fragmentsand the extent of displacement of fragments. In addition,an estimation regarding the percentage of the face of the

164 T.G. Sanders, M. Zlatkin, and J. Montgomeryglenoid that is involved should be reported (using the sagittalimaging plane). Extensive bony deficiency of the anteriorinferiorglenoid rim has been referred to as the inverted pearappearance (Fig. 5), and bone graft material may be requiredas a part of the reconstruction if the bony deficiency is greaterthan 30% of the face of the glenoid. 19MR FindingsAssociated With Anterior InstabilityConventional MR imaging and direct MR arthrography areboth excellent techniques for detecting the extent of softtissueinjury after an anterior subluxation event. Direct MRarthrography has the added benefit of creating joint distention,which may increase the conspicuity of a subtle or nondisplacedlabral lesion, which will fill with high signal intensitygadolinium. The presence of gadolinium in the joint alsoallows the use of T1-weighted imaging to evaluate the labrum,which is a higher signal-to-noise image than the T2images typically required to detect labral pathology whenusing conventional MR imaging. The main disadvantage ofdirect MR arthrography is that it is minimally invasive andrequires the presence of a physician to perform the intraarticularinjection. The use of direct MR arthrography may beespecially beneficial in the evaluation of subtle lesions thatcan occur in the overhead athlete.Numerous Bankart variants have been described, eachdemonstrating a slightly different MR appearance with somevariations requiring a slightly different surgical repair technique.Therefore, knowledge of the various lesions and anFigure 4 Radiographic findings associated with anterior dislocation.AP radiograph (A) shows anterior dislocation of the humeralhead (long arrow) relative to the glenoid fossa (short arrow).The humeral head is positioned medial and inferior inposition. West-Point view (B) shows a small osseous Bankartlesion. True AP view of the glenohumeral joint (C) shows a smallosseous Bankart lesion (short arrow) and a large Hill-Sachs defect(long arrow).Figure 5 Osseous defect of the glenoid rim CT imaging. Sagittal CTreconstruction through the glenoid fossa demonstrates a large osseousdefect (arrows), indicating a Bankart lesion after anterior dislocation.The inverted pear appearance of the glenoid fossa indicatessignificant bone loss likely requiring bone graft to regain postoperativestability of the glenohumeral joint.

Imaging of glenohumeral instability 165accurate description of the instability lesion can be beneficialin obtaining optimal surgical results.Fibrous Bankart LesionA tear of the anterior-inferior glenoid labrum. This is themost common lesion after an anterior subluxation event. 15The labral fragment is often displaced and stripped awayfrom the adjacent glenoid. The axial imaging plane is theprimary plane for detecting Bankart lesion and MR imagingmay demonstrate an irregular fluid or contrast collection extendinginto the substance of or deep to the labrum with orwithout abnormal morphology of the labrum. 20,21 The adjacentmedial scapular periosteum is often stripped from theadjacent bone or possibly completely disrupted, resulting ina displaced labral fragment (Fig. 6). The location and extentof a labral tear should be described using either the quadrantsof the glenoid as reference points or using the numbers of theface of the clock as reference points. The coronal imagingplane may also demonstrate fluid or contrast extending intothe substance of the anterior-inferior labrum and this hasbeen described as the double axillary pouch sign (Fig. 7).Perthes LesionA nondisplaced tear of the anterior-inferior glenoid labrum. 22The medial scapular periosteum remains intact in this Bankartvariant holding the labrum in near anatomic position(Fig. 8A). A chronic Perthes lesion may resynovialize or scarback down in place making this lesion difficult to detect onconventional MR imaging. This is the 1 lesion in which directMR arthrography with stress ABER imaging may be particularlyuseful in detecting an otherwise occult lesion of instability14 (Fig. 8B).Figure 7 Double axillary pouch sign, anterior labral tear in the coronalimaging plane. Coronal MR arthrographic image (A) shows thenormal-appearing anterior-inferior labrum (short arrow). CoronalMR arthrographic image (B) shows the double axillary pouch sign, acontrast collection (long arrow) located between the glenoid rimand torn anterior labrum (short arrow).Figure 6 Bankart lesion, MR imaging. Axial T2-weighted imagethrough the glenohumeral joint reveals a tear (long arrow) of theanterior inferior labrum (short arrow). Intermediate signal is seenextending completely beneath the labrum indicating a tear andcomplete detachment of the labrum.Anterior LabroligamentousPeriosteal Sleeve Avulsion LesionAnterior labroligamentous periosteal sleeve avulsion injury(medialized Bankart lesion) (Fig. 9) is a variant of the Bankartlesion in which the medial scapular periosteum remains intactand pulls the torn labral fragment in a medial direction. 23These lesions are easily detected in the acute setting, but maybe more difficult to detect in the chronic setting when themedialized labral fragment has scarred down to the adjacent

166 T.G. Sanders, M. Zlatkin, and J. Montgomeryimages, while the sagittal imaging plane is usually best suitedfor demonstrating the size and extent of the lesion (Fig. 10).Marrow edema of the glenoid as seen on MR imaging is usuallya very minor component of the abnormality. CT imaging,especially in the sagittal imaging plane can be helpful indepicting the extent of osseous abnormality and in detectingthe number of fracture fragments. The face of the glenoid asviewed in the sagittal imaging plane has been described ashaving a pear-shaped appearance. Loss of significant bonestock along the anterior-inferior margin has been describedas the inverted pear appearance of the glenoid (Fig. 5). This isimportant to describe as a bony deficiency of more than 30%of the face of the glenoid will likely require a bone graftprocedure to regain normal stability in the postoperative setting.19Glenolabral Articular Disruption LesionGlenolabral articular disruption 24 lesion most often resultsfrom an impaction of the humeral head against the face of theglenoid, resulting in a nondisplaced tear of the anterior-inferiorlabrum with an associated chondral injury of the inferiorglenoid (Fig. 11). 25 Often there is no history of a frank dislocation,and the patient typically presents with shoulder painbut only minimal signs of instability on physical examination.Surgical treatment includes labral repair or debridementcoupled with debridement of the chondral lesion.Humeral Avulsion of theGlenohumeral Ligament LesionHumeral avulsion of the glenohumeral ligament 26,27 lesionresults from an anterior dislocation or subluxation event andresults in a tear or avulsion of the anterior band of the inferiorFigure 8 Perthes lesion (nondisplaced labral tear). Axial (A) andABER (B) MR arthrographic images demonstrate a collection of contrast(long arrow), extending partially beneath the anterior inferiorlabrum (short arrow). The medial scapular periosteum (arrowheads) remains intact holding the labrum in near anatomic position.glenoid. In the chronic setting, these lesions may requireadditional surgical debridement of the fibrosis and scar tissuebefore completing the Bankart repair.Osseous Bankart LesionFracture of the anterior-inferior glenoid rim that accompaniesa tear of the glenoid labrum. These lesions may be difficultto detect on both radiographs and MR imaging. On MRimaging, the cortex of the anterior glenoid margin should bethoroughly evaluated in all 3 imaging planes. Disruption orirregularity of the cortex may be seen on axial and coronalFigure 9 ALPSA lesion (anterior labroligamentous periosteal sleeveavulsion), medialized Bankart. Axial MR arthrographic image demonstratesthe torn anterior-inferior labrum (long arrow) pulled in amedial direction by an intact medial scapular periosteum (shortarrow).

Imaging of glenohumeral instability 167band of the inferior glenohumeral ligament can be seen at theexpected humeral attachment site. In the acute setting, therewill be adjacent soft-tissue edema and when performing directMR arthrography, contrast will often be seen leakingthrough the capsular defect.Batter’s ShoulderThis term has been used to describe a subluxation event ofthe glenohumeral joint that occurs when a baseball batter“swings and a misses” a pitch. When a powerful batter swingsa bat and misses the ball, tremendous forces are transmittedacross the glenohumeral joint and can result in a subluxationevent of the leading shoulder, (usually the nondominant ornonthrowing shoulder for a baseball player, unless the playeris a switch-hitter). We have seen numerous cases in our practicewith this exact mechanism of injury leading to a first-timesubluxation event resulting in immediate onset of disablingshoulder pain. We have seen both anterior and posteriorsubluxation events occurring with this exact mechanism ofinjury and in each case resulting in either a Bankart or “reverse”Bankart variant, often with an associated Hill-Sachs or“reverse” Hill-Sachs lesion, typically resulting in disablingpain and instability of the involved glenohumeral joint (Figs.13 and 14). Surgical repair is usually required for the patientto return to a preinjury level of play. This mechanism ofinjury has been reported in several professional baseball playersand is often a season-ending injury.Figure 10 Osseous Bankart lesion. Axial T2-weighted image (A) andcoronal T1-weighted image (B) demonstrate a minimally displacedosseous Bankart lesion (short arrow). The axial image shows an areaof cortical step-off (long arrow), while the coronal image demonstratesa low signal intensity line indicating the fracture through theglenoid.glenohumeral ligament from the level of its humeral attachment(Fig. 12). There is no age predilection for this lesion.This lesion is difficult to detect using the standard arthroscopyportals, and it is therefore very important to alert thesurgeon to the possibility of this lesion preoperatively so thepotential lesion can be adequately evaluated at the time ofsurgery. A missed HAGL lesion has been reported as a commoncause for a failed shoulder reconstruction after anteriordislocation. On MR imaging, a disruption of the anteriorFigure 11 GLAD lesion (glenolabral articular disruption). Axial T2-weighted MR image with fat saturation demonstrates a nondisplacedtear of the anterior-inferior glenoid labrum with a smalladjacent full-thickness chondral defect involving the anterior-inferiorglenoid articular surface (arrow).

168 T.G. Sanders, M. Zlatkin, and J. Montgomerywith a misdiagnosis rate that approaches 50%. In the properclinical setting, a high index of suspicion is paramount inestablishing the correct diagnosis.Classically, posterior dislocations are associated with seizureor electrical shock; however, posterior instability withoutfrank dislocation has also been shown to be associatedwith numerous sporting activities. The typical patient withposterior instability is male, with age 20-30 years who participatein an overhead activity, such as a throwing, weight-Figure 12 HAGL lesion (humeral avulsion of the glenohumeral ligament).Coronal MR arthrographic image shows a complete avulsionof the anterior band of the inferior glenohumeral ligament (longarrow) from the humeral neck. Contrast (short arrow) is seen extendingthrough the capsular defect into the adjacent soft tissues.Lesions of Instability in the OlderPatient With a First Time DislocationWhile the Bankart variants are the most common lesionsoccurring in young patients after a first-time dislocation,first-time dislocators aged more than 35 years rarely presentwith a Bankart lesion. In the older patient population, therotator cuff becomes the “weak link” and patients usuallypresent with either a tear or avulsion of the supraspinatustendon, avulsion of the subscapularis tendon, or an avulsionfracture of the greater tuberosity. 16 Tears of the supraspinatusor subscapularis tendons are treated surgically, while a nondisplacedavulsion fracture of the greater tuberosity is usuallytreated nonsurgically. Radiographs usually depict avulsionfractures of the greater tuberosity, but these lesions may occasionallybe occult radiographically. In these cases, MR imagingwill differentiate a surgical rotator cuff lesion from anonsurgical occult nondisplaced fracture of the greater tuberosity.Even in the setting of an avulsion fracture, MR imagingwill sometimes demonstrate a concurrent rotator cuff lesionthat will benefit from surgical repair.Posterior InstabilityPosterior glenohumeral subluxation events occur less commonlythan anterior subluxation events, accounting for approximately3% of all glenohumeral dislocations. 28 Posteriorsubluxation of the humeral head most often occurs becauseof a posteriorly directed force with the arm flexed, adducted,and maximally internally rotated. Posterior dislocations arecommonly missed at the time of initial clinical presentationFigure 13 Batter’s shoulder. Axial (A) and coronal (B) MR arthrographicimages of a professional short stop who experienced acuteonset of pain of his loading shoulder after a swing and a miss at apitch. Follow-up MR arthrography revealed a large osseous Bankartlesion (arrows), indicating an anterior subluxation event.

Imaging of glenohumeral instability 169A patient with an acute posterior shoulder dislocation presentswith pain and has a tendency to hold the shoulder ininternal rotation and adduction. On physical examination theremay be loss of the normal rounded contour of the anteriorshoulder and a slight posterior bulge. With posterior glenohumeralinstability there can be voluntary posterior subluxation ofthe shoulder and pain when positioning the arm in the vulnerableposition of flexion, internal rotation, and adduction.Figure 14 Batter’s shoulder. (A) A 26-year-old baseball player heard apop and experienced immediate onset of pain when he swung at andmissed a pitch. T2-weighted axial image shows a reverse Bankart lesion(tear posterior labrum) (short arrow) and a small reverse Hills-Sachslesion (long arrow) with subcortical marrow edema, indicating a posteriorsubluxation event. (B) An 18-year-old baseball player heard a popand experienced immediate onset of pain after a swing and a miss at apitch. Axial T2-weighted MR image shows a reverse Bankart lesion(short arrow), and a reverse Hill-Sachs contusion (long arrow) indicatinga posterior subluxation event. The anterior-inferior labrum wasnormal. Arrowheads indicate the normal MGHL.lifting, gymnastics, swimming, or racquet sports. Posteriorinstability can also be seen in individuals who participate inrepetitive contact sports, such as football linemen who experiencerecurring trauma with the arm in the vulnerable positionof flexion, adduction, and internal rotation. 29Radiographic FindingsAssociated With Posterior InstabilityWhile the presence of an anterior dislocation is usually quiteobvious on standard radiographic views of the shoulder, radiographicfindings in the patient with posterior dislocationcan be much more subtle and easily overlooked on AP radiographs,often delaying the diagnosis of posterior dislocation.Standard radiographic projections of the glenohumeral jointafter acute trauma should include the AP view, and a lateralview, such as the axillary or scapular Y view, to adequatelyevaluate for evidence of a posterior dislocation. 2During posterior dislocation, the humeral head most oftendislocates straight posteriorly, which can make diagnosis onan AP radiograph of the shoulder rather difficult. There areseveral subtle radiographic findings, which when present onthe AP radiograph should raise concern for a possible posteriordislocation. The first clue is that the humeral head willappear to be in the same position on both the internal andexternal rotation views of the shoulder. This occurs becausethe humeral head is locked in internal rotation at the time ofposterior dislocation and the patient is unable to externallyrotate the humeral head. Another subtle clue may be theslight lateral positioning of the humeral head relative to theglenoid resulting in a slight gap on the AP radiograph referredto as the “rim” or “empty notch” sign (widening of the glenohumeraljoint 6 mm). Alternatively, the humeral head maybe slightly medially positioned resulting in an overlap of themedial cortex of the humeral head and the glenoid fossa.Finally, a posterior dislocation can result in an impaction ofthe anterior aspect of the humeral head against the posteriorglenoid rim, resulting in a “reverse” Hill-Sachs impactionfracture. On the AP radiograph, this will appear as a scleroticvertical line paralleling the medial humeral head cortex referredto as the “trough line” sign (Fig. 15A). All of these APradiographic signs are subtle and unreliable; therefore, it iscrucial to obtain a lateral radiograph if posterior subluxationis suspected clinically or on the basis of radiographic findingson the AP view. 2 Options include an axillary view orscapular Y view and posterior dislocation is obvious onthese views as the humeral head will be sitting posterior tothe glenoid (Fig. 15B).CT Findings AssociatedWith Posterior InstabilityCT imaging can be very helpful in defining the extent ofosseous involvement after a posterior subluxation event. Flatteningof the anterior medial aspect of the humeral headindicates a reverse Hill-Sachs impaction type fracture, while a

170 T.G. Sanders, M. Zlatkin, and J. Montgomeryfracture along the posterior margin of the glenoid rim denotesa reverse osseous Bankart lesion. CT can also be helpfulin the acute or subacute setting demonstrating a persistentlocked posterior dislocation or partial subluxation. 2MR Findings AssociatedWith Posterior InstabilityMR imaging will demonstrate the reverse Hill-Sachs and reverseBankart lesions similar to CT imaging, but in addition,can detect the presence or absence of subcortical marrowedema, which will help in determining the acuity of the lesion.MR imaging will also depict associated soft-tissue injuriesafter posterior dislocation (Fig. 15C). 30Reverse Bankart LesionPosterior dislocation is often associated with a tear of theposterior glenoid labrum (Fig. 14). The tear is often nondisplacedand seen on MR imaging as high signal fluid or contrastextending into the substance or deep to the posteriorlabrum. A labral fragment may also be detached or displaced.A “reverse” osseous Bankart and or “reverse” Hill-Sachs lesionmay also be present (Fig. 15C).Reverse HAGLPosterior dislocation can also result in a tear of the posteriorband of the inferior glenohumeral ligament referred to as the“reverse HAGL” lesion. The presence of a small osseous avulsionfracture associated with the reverse HAGL lesion is referredto as the “reverse bony HAGL” (Fig. 16). ReverseHAGL lesions have also been described secondary to repetitivemicrotrauma in athletes without a frank posterior dislocation.30,31 Injuries of the teres minor muscle or tendon canoccasionally accompany a reverse HAGL lesion. Soft-tissueedema may be seen within the substance of the muscle indicatinga grade I muscle strain or contusion, or in severetrauma, a partial or full-thickness avulsion of the teres minortendon may occur. The presence of an isolated teres minormuscle injury should prompt a thorough search for the presenceof a reverse HAGL lesion.Figure 15 Locked posterior dislocation. Thirty-seven years-oldfell off son’s dirt bike and landed on left arm. AP view of theshoulder (A) obtained in the Emergency Department demonstratesa sclerotic line (arrows) paralleling the medial cortex ofthe humeral head, representing the trough sign, the radiographicsign indicating a reverse Hill-Sachs lesion. Scapular Y view (B)demonstrates posterior subluxation of the humeral head (longarrow) relative to the center of the glenoid fossa (short arrow).Axial T2-weighted MR image (C) obtained after initial radiographs,shows a posterior locked dislocation of the humeral headwith a reverse Hill-Sachs lesion (arrow).Bennett LesionGlenohumeral instability is a common entity in the overheadthrowing athlete. These athletes are predisposed to chronictraction injuries of the posterior band of the inferior glenohumeralligament that occur during the deceleration phase ofthrowing. The Bennett lesion is an extra-articular posteriorcapsular avulsion injury that may be associated with a posteriorlabral tear, posterior undersurface rotator cuff tear, andposterior subluxation of the humeral head. Calcification occurswithin the posterior capsule at the site of avulsion injury.On MR imaging, the Bennett lesion appears as an area of lowsignal abnormality due to the mineralization within the capsuleat the site of avulsion possibly with associated thickeningof the capsule or pericapsular edema (Fig. 17). CT and radiographywill show a crescentlike area of abnormal mineralizationalong the posterior margin of the osseous glenoid atthe level of the posterior capsular attachment. Patients with a

Imaging of glenohumeral instability 171of throwing. The motion of throwing has been broken downinto separate components which include1. Wind-up phase2. Early cocking phase3. Late cocking phase4. Acceleration phase5. Deceleration phase6. Follow-through phaseCurrent understanding of the biomechanics of throwing suggeststhat the majority of injuries occur either during the latecocking phase with the arm positioned in maximum abductionand external rotation or because of the tremendousforces that are generated across the glenohumeral joint duringthe acceleration and deceleration phases of throwing. 34,35The term “dead arm” has been coined to describe a pathologiccondition in which a throwing athlete is unable to continue tothrow with the same accuracy or control because of pain orbecause of a subjective unease in the shoulder. Our understandingof the pathophysiology of the dead arm in throwingathletes has evolved considerably in the past 30 years andwhile debate and research continues on this topic in theorthopedic community, it is clear that optimal treatment ofthe various lesions associated with throwing is predicatedupon not only an accurate identification of the lesion but alsoupon a thorough understanding of the pathophysiology leadingto these injuries. 34,35 Three theories now dominate theorthopedic community with regard to instability associatedwith pain in the throwing athlete. These include (1) extrinsicimpingement-instability overlap, (2) intrinsic impingement,and (3) GIRD.Figure 16 Reverse HAGL lesion. Coronal (A) and axial (B) MR arthrographicimages through the shoulder demonstrate a completeavulsion (long arrows) of the posterior band of the inferior humeralligament from the humeral neck. Contrast (short arrows) is seenextending through the capsular defect into the adjacent soft tissuesalong the posterior aspect of the glenohumeral joint.Bennett lesion experience pain during the late cocking phaseand acceleration phase of throwing. 32,33Lesions of InstabilityAssociated With ThrowingThe biomechanics of throwing have been studies extensivelyin an attempt to understand and prevent the disabling lesionsthat are often associated with the repetitive overhead activityFigure 17 Bennett lesion. Axial T2-weighted MR image in an 18-year-old pitcher with shoulder pain demonstrates a thick bandlikearea of low signal abnormality (short arrow) indicating an area ofossification, associated with an extra-articular avulsion of the posteriorcapsule. Pericapsular edema (long arrows) is also noted.

172 T.G. Sanders, M. Zlatkin, and J. MontgomeryExtrinsic Impingement-InstabilityOverlap (Secondary Impingement)In 1990, Jobe first put forth the theory that repetitive throwingor overhead activity results in stretching of the anteriorcapsule and the anterior support structures of the glenohumeraljoint resulting in subtle anterosuperior migration of thehumeral head during the late-cocking and early-accelerationphases of throwing. 36 This migration of the humeral headresults in extrinsic impingement of the rotator cuff against theundersurface of the osseous outlet. Extrinsic impingementinstabilityoverlap syndrome is thought to differ from thestandard theory of extrinsic impingement as the impingementresults from humeral head migration secondary to instabilityof the glenohumeral joint rather than resulting froman anatomic variation or a pathologic lesion of the osseousoutlet (secondary impingement). Radiographs are usuallyunremarkable. MR imaging may demonstrate cuff tendinosisinvolving either the supraspinatus or the infraspinatus tendonand if a rotator cuff tear is present, it is usually small andpartial-thickness in nature involving the articular side of thetendon. MR arthrography may be more sensitive in detectinga small partial-thickness rotator cuff tear in the young throwingathlete resulting from secondary impingement. Extrinsicimpingement-instability overlap is still widely accepted as asource of pain in the throwing athlete and is usually treatedwith anterior capsular tightening with a reported 50% returnrate to preinjury level of performance after surgery. 34Internal ImpingementJobe and Walsh later put forth the theory of internal impingementto explain the dead arm syndrome in certain throwingathletes. This theory differs slightly from the extrinsic impingement-instabilityoverlap theory described above. Withintrinsic impingement, the primary cause of the lesion isagain thought to be anterior capsular stretching resultingfrom repetitive microtrauma to these structures during thelate-cocking and early-acceleration phases of throwing. Ininternal impingement, however, the lesions rather than resultingfrom an extrinsic impingement, occur because of theimpingement of the undersurface of the posterior cuff betweenthe posterior aspect of the greater tuberosity and theposterosuperior labrum. 34 This theory of internal impingementput forth by Jobe and Walsh further supported the ideaof anterior capsular stretching as the primary lesion in throwingathletes. However, the anatomic lesions differed slightlywith the lesions of internal impingement primarily seen astendinosis and partial thickness articular-sided tears of theposterior cuff combined with posterior superior labral tears.Radiographs again are usually normal but subtle nonspecificfindings of sclerosis and subchondral cysts of the posterioraspect of the greater tuberosity may be seen on AP radiographsand the Grashey view may demonstrate subtle inferiorsubluxation of the humeral head associated with anteriorcapsular laxity. MR imaging typically demonstrates somecombination of 4 abnormalities (Fig. 18). These include (1)tendinosis and or partial thickness-articular sided tearing ofthe posterior cuff, (2) abnormal signal or a frank tear of theFigure 18 Internal impingement. A 24-year-old professional baseballpitcher demonstrates changes in internal impingement. Coronal (A)and axial (B) MR arthrographic images demonstrate fraying, irregularityand a tear of the posterior superior labrum (short arrows),tendinosis and partial thickness articular sided tearing of the infraspinatustendon (long arrows), and subcortical cystic changesand marrow edema of the greater tuberosity (arrowheads).posterosuperior labrum, (3) marrow edema and or subcorticalcystic change within the posterior aspect of the humeralhead, and finally (4) internal impingement seen on ABERimaging. The presence of abnormalities of the posterior cuffcombined with an abnormality of the superior labrum in thesymptomatic overhead athlete appears to be most sensitivewith regard to the diagnosis of internal impingement. 37-39The presence of subcortical marrow changes in the greater

Imaging of glenohumeral instability 173tuberosity is most variable, while the presence of internalimpingement of the posterior cuff between the greater tuberosityand the posterosuperior labrum on ABER imaging is theleast specific MR finding with regard to internal impingement.These lesions of the posterior cuff and superior labrumcan be quite subtle and the use of direct MR arthrography canimprove detection of these lesions in the young overheadathlete with symptoms of internal impingement.The theory of internal impingement put forth by Jobe andWalsh further supported the idea that the primary lesion ofthe “dead arm” is that of anterior capsular stretching injuryresulting from the repetitive microtrauma of throwing. Treatmentof internal impingement is again anterior capsular reconstructionor tightening with as many as 50% of overheadathletes returning to preinjury level of pitching after surgery.Glenohumeral InternalRotation Deficit DisorderGIRD is the most recent theory put forth by Dr Burkhart inthe early 1990s regarding the pathophysiology of the “deadarm” syndrome and still remains controversial in some cornersof the orthopedic community. 34,35 This theory suggeststhat the primary lesion in many overhead athletes is not astretching of the anterior capsule but rather scarring andfibrosis of the posterior capsule or tightening of the posteriorcuff musculature secondary to repetitive overhead activity.This new theory suggests that the primary lesion is one ofposterior capsular tightness rather than anterior capsular laxitythat lead to the various lesions of the labrum and rotatorcuff in the “dead arm” syndrome. It is theorized that posteriorcapsular scarring or posterior muscle tightness pulls the humeralhead in a posterior direction, shifting the humeral head“point of contact” on the face of the glenoid in a posterosuperiordirection during the late-cocking phase of throwing. This resultsin a loss of internal rotation of the glenohumeral joint to less than180° when compared with the nonthrowing arm.In GIRD, it is theorized that the posterior capsular scarringor posterior muscle tightening results from repetitive traumato the posterior shoulder during the late cocking phase ofthrowing. This results in a cascade of injuries, beginning witha posterosuperior shift of the “point of contact” of the humeralhead on the glenoid face during the late cocking phaseof throwing. Loss of internal rotation of the glenohumeraljoint of the throwing arm ensues and as a result, during thelate cocking phase of throwing, abnormal twisting rotationalforces are applied to the anchor of the long of the bicepstendon and a peel back injury occurs to the posterior superiorlabrum during the acceleration phase of throwing resulting ina tear of the posterosuperior labrum. These changes in theposterior capsule and posterosuperior labrum are often seenin conjunction with changes of the posterior cuff resultingfrom internal impingement.Radiographs are usually normal and there are still onlyspotty reports in the literature regarding MR findings associatedwith GIRD (Fig. 19). The most commonly reported findingsinclude a focal area of thickening or fibrosis of the posteriorcapsule immediately adjacent to the glenoid attachment. Also,Figure 19 GIRD (glenohumeral internal rotation deficit disorder). An18-year-old baseball pitcher with clinical findings of glenohumeralinternal rotation deficit disorder. Axial proton-density image (A)demonstrates marked thickening (arrows) of the posterior capsule.(B) Coronal T2-weighted image also shows signs of internal impingementwith tendinosis of the infraspinatus tendon (long arrows)and signal alteration within the posterosuperior labrum (shortarrow).the changes in internal impingement including abnormalities ofthe posterior cuff and greater tuberosity are seen. Finally, a peelback or avulsion-type lesion of the posterior superior labrummay be seen. 40Preventive treatment for GIRD includes posterior capsule/muscle stretching exercises after each pitching outing, whichhas been shown to decrease the incidence of GIRD in the highly

174 T.G. Sanders, M. Zlatkin, and J. MontgomeryMiscellaneousLesions of InstabilityParalabral CystsParalabral cysts of the shoulder have been described as analogousto parameniscal cysts of the knee and most often occurin conjunction with a labral tear and demonstrate a highassociation with glenohumeral joint instability. They typi-Figure 20 Paralabral cyst with compression of the suprascapularnerve. (A) Axial T2-weighted image demonstrates a tear (short arrow)of the posterior labrum with an associated paralabral cyst (longarrow) dissecting into the spinoglenoid notch posteriorly. SagittalT2-weighted image (B) shows the paralabral cyst (long arrow) dissectinginto the spinoglenoid notch posteriorly. There is diffuseedema (short arrows) isolated to the infraspinatus muscle indicatingneurogenic edema associated with a compression of the suprascapularnerve at the level of the spinoglenoid notch.competitive overhead athlete. Once a labral lesion occurs, treatmentincludes superior labrum anterior posterior repair of thepeel back lesion rather than debridement and rotator cuff debridementor repair as needed. Early results suggest a 70%-80%return to preinjury level of activity. 34,35Figure 21 Axillary nerve neuropraxy. Coronal T2-weighted imagewithout fat saturation (A) and coronal STIR (B) images in a patientafter anterior dislocation of the shoulder who complains of pain andshoulder weakness. There is diffuse edema present throughout theteres minor (short arrows) and deltoid (long arrows) muscles, indicatingneurogenic edema associated with a stretching injury of theaxillary nerve.

Imaging of glenohumeral instability 175Axillary Nerve NeuropraxyThe axillary nerve is the shortest branch of the brachialplexus and traverses the quadrilateral space adjacent to theposterior humeral circumflex artery. Anterior dislocation ofthe glenohumeral joint can result in a stretching type injuryof the axillary nerve, leading to denervation of the teres minormuscle and less commonly the deltoid muscle. Loss of deltoidmuscle function may mimic rotator cuff pathology onphysical examination. MR imaging can be very helpful indetecting signs that suggest a previous stretching-type injuryof the nerve (Fig. 21). In the acute setting, as in compressivetype lesions of the nerve, the denervated muscle will demonstratediffuse edema, while in the chronic setting, fatty infiltrationand atrophy of the muscle will occur. 43Figure 22 Recurrent Bankart lesion after labral repair. Axial MR arthrographicimage through the shoulder demonstrating contrast(long arrow) extending deep to the anterior-inferior labrum indicatinga recurrent tear after previous labral repair. Short arrow indicatesa suture anchor. Arrowheads indicate a recurrent tear of theanterior scapular periosteum.cally occur because of extrusion of fluid through a tear of thelabrum. They can be small and focal or quite large dissectinginto various spaces adjacent to the joint. They are best detectedon T2-weighted images with fat saturation, this beingone of the main reasons that most shoulder protocols includeat least 1 T2-weighted sequence, even with shoulder MRarthrography. They may communicate with the joint space,but only rarely fill with contrast during direct MR arthrography.MR imaging usually depicts an oval or multiseptated fluidfilled mass on T1- and T2-weighted images. The lesion maydissect into the suprascapular notch or into the spinoglenoidnotch resulting in compression of the suprascapular nerve(Fig. 20). Rarely, a paralabral cyst may dissect into the quadrilateralspace, resulting in compression of the axillary nerve.Nerve compression can result in denervation of the musclesenervated by the affected nerve. In the acute setting the musclewill demonstrate diffuse edema, at this point the muscleand nerve damage is still considered reversible. In thechronic setting muscle edema is replaced by fatty atrophy/fatty infiltration of the involved muscle. At this point thenerve and muscle damage is considered irreversible. Compressionof the suprascapular nerve at the level of the suprascapularnotch results in denervation of both the supraspinatusand infraspinatus muscles, while compression of thenerve at the level of the spinoglenoid notch results in isolateddenervation of the infraspinatus muscle, as the branch to thesupraspinatus muscle has already been given off. Compressionof the axillary nerve generally results in denervation ofthe teres minor and sometimes the deltoid muscle. 41,42Surgical Treatment forGlenohumeral InstabilitySeveral procedures have been developed using indirect surgicaltechniques to correct glenohumeral instability. Theseprocedures rather than repair the torn labrum, attempt toprevent recurrent instability through indirect means. Some ofthese procedures include a staple capsulorrhaphy (DuToitand Roit repair), subscapularis manipulation (Putti Platt andMagnuson Stack procedure) and repositioning of the coracoidprocess (Bristow procedure). With advances in arthroscopictechniques, these indirect repair procedures are onlyrarely performed today and are mainly of historical interest,although occasionally a patient will present for imaging whohas undergone one of these procedures years ago.Figure 23 Artifact associated with hardware from prior osseous Bankartrepair. Axial MR arthrographic image demonstrates markedartifact (arrow) obscuring much of the anatomy of the anterior inferiorglenohumeral joint. This artifact is associated with a screwthat was used to repair an osseous Bankart lesion.

176 T.G. Sanders, M. Zlatkin, and J. Montgomerywith a screw, may result in severe artifact obscuring visualizationof the labrum on subsequent MR imaging (Fig. 23). Inthese cases CT arthrography may better delineate the appearanceof the postoperative labrum in suspected cases of reinjury.Figure 24 CT imaging appearance after a Laterjet procedure. AxialCT image through the glenohumeral joint after a Laterjet procedure(bone graft procedure to repair an osseous Bankart lesion). A largescrew (long arrow) holds the bone graft (short arrow) in place. Thesize of the screw shows why MR imaging often demonstratesmarked susceptibility artifact after repairs of an osseous Bankartlesion.Direct repair techniques usually consist of debridementand or suturing of the torn labrum using suture anchorsplaced within the glenoid to reattach the torn labral fragment.Osseous Bankart lesions may be repaired using a screw toreaffix the bone fragment or may require use of allograftmaterial to correct a bony deficit of the osseous glenoid. Anengaging Hill-Sachs lesion may also require the use of bonegraft material to repair a large Hill-Sachs defect.Following labral repair, suture anchor artifact is often seenwithin the osseous glenoid adjacent to the site of labral repair.In some cases, this artifact may be severe enough to partiallyobscure the repaired labrum, but in most cases, the artifact isminimal and does not prevent adequate evaluation of thelabrum. The normal postoperative labrum may appearblunted or irregular in appearance. MR findings suggesting arecurrent tear include a detached or displaced labral fragmentor fluid undermining the labrum (Fig. 22). Recurrenttears may occur in an area of previous repair or may extendbeyond the site of repair to involve adjacent labral tissue thatwas normal at the time surgery. The use of direct MR arthrographymay help in the evaluation of the postoperative labrum.44,45Surgical repair of an osseous Bankart lesion is usually performedif the original bony defect involves more than 30% ofthe face of the glenoid. 46 If there is a single large bone fragment,a screw may be adequate to repair the fractured glenoid(Fig. 23). If the bone fragment is comminuted, this may requiredebridement and placement of graft material (Laterjetprocedure) (Fig. 24). Repair of an osseous Bankart lesionFigure 25 Hardware artifact after arthroscopic Bankart repair. AxialMR arthrographic image (A) of a patient with continued pain afterarthroscopic repair of a Bankart lesion demonstrates artifact associatedwith a prior Bankart repair. An area of prominent susceptibilityartifact (arrow) is suspicious for a proud suture anchor. The patientwas taken to the CT scanner immediately after the MR examination.Axial CT image (B) through the shoulder demonstrates a proudsuture anchor (arrow) as the source of continued pain.

Imaging of glenohumeral instability 177MR Imaging Appearanceof Postoperative ComplicationsPostoperative complications after shoulder reconstructionfor instability can include displaced or loosening of hardwareor suture anchor devices (Figs. 25 and 26). MR arthrographymay be helpful in detecting the intra-articular location ofdisplaced hardware, some of which is nonradiopaque, andtherefore occult on radiographs. 44 Osteolysis or osteomyelitiscan also occur adjacent to hardware resulting in loosening orfluid signal adjacent to the hardware or screws. Postoperativesynovitis may result in a large joint effusion and maymimic postoperative infection on MR imaging, which willpresent with a large joint effusion, synovial thickening,and enhancement with administration of intravenous gadolinium(Fig. 27).Acute chondrolysis of the glenohumeral joint refers to arapid onset of widespread chondrocyte death occurring overa short interval of time. This is a devastating complicationthat has been reported with increasing frequency after arthroscopicreconstruction of the glenohumeral joint in youngindividuals for shoulder instability. The patient typically presentswith rapid onset of shoulder discomfort and a painfuldecreased range of motion, which usually occurs within thefirst 6-12 months after shoulder reconstruction. Treatment issupportive with the patient often eventually requiring jointarthroplasty for severe glenohumeral osteoarthritis. The exactetiology remains unclear, but there is evidence to suggestthat acute chondrolysis may be related to the use of thermalprobes or Marcaine pumps at the time of surgery, and mostsurgeons now avoid the use of these ancillary techniques inan attempt to avoid this devastating complication. Other suggestedetiologies include an unknown infectious agent orimmune response to bioabsorbable material.Preoperative imaging usually demonstrates normal symmetricjoint space on radiographs and normal articular cartilageon MR imaging (Fig. 28A). At the time of onset of symptomsin the postoperative patient, radiographs usually depictsevere glenohumeral joint space narrowing and minimal subchondralsclerosis without other signs of osteoarthritis (Fig.Figure 26 Hardware complication after shoulder surgery. CoronalT2-weighted image shows a displaced tack (arrow) within the axillarypouch as a source of continued shoulder pain after surgery.Figure 27 Osteomyelitis and septic arthritis after rotator cuff repairand superior labral debridement. Coronal T1-weighted (A) and T2-weighted (B) images demonstrate marrow edema (short arrows)surrounding a suture anchor in the humeral head and a small complexjoint effusion (long arrow) in this patient who developed osteomyelitisand septic arthritis after a rotator cuff repair and superiorlabral debridement.

178 T.G. Sanders, M. Zlatkin, and J. Montgomery28B). In the acute stages of chondrolysis of the glenohumeraljoint, MR imaging shows diffuse chondral loss on both sidesof the glenohumeral joint. Minimal subchondral marrow signalchanges are noted. There is usually a paucity of jointeffusion (Fig. 28C), unlike in a postoperative septic jointwhich usually presents with a large complex joint effusion.Even in suspected cases of acute chondrolysis, septic arthritisshould be considered in the differential diagnosis with appropriateculture of joint fluid. In most cases of acute chondrolysis,no infectious agent is ever identified. 47ConclusionsGlenohumeral instability is a very complex and challengingtopic both for the clinician and the imager. Numerous subtlelesions can be detected on radiographs, CT, and MR imagingand a thorough understanding of not only the anatomy of theglenohumeral joint but the pathophysiology of these injuriesis essential to adequately diagnose and treat the various lesionsof instability.Figure 28 Acute chondrolysis of the glenohumeral joint after Bankartrepair. Preoperative AP radiograph of the shoulder (A) demonstratesa normal glenohumeral joint space (arrows). AP radiographof the shoulder approximately 6 months after surgery (B)demonstrates marked narrowing the glenohumeral joint space(arrows) in this patient who began experiencing progressive onsetof pain and decreased range of motion. Axial T2-weightedimage (C) shows complete loss of the normal articular cartilageon both sides of the glenohumeral joint (long arrows) with subchondralmarrow edema (short arrow). Note the paucity of jointfluid which can be a useful MR imaging sign to help differentiateacute chondrolysis from a postoperative septic arthritis.References1. Kroener K, Lind T, Jensen J: The epidemiology of shoulder dislocations.Arch Orthop Trauma Surg 108:288-290, 19892. Sanders TG, Jersey SL: Conventional radiograph of the shoulder. SeminRoentgenol 40:207-222, 20053. Merrill V: Shoulder girdle, in Ballinger PW (ed): Merrill’s Atlas of RadiographicPositions and Radiographic Procedures, Vol I (ed 6). StLouis, MO, Mosby, pp 101-150, 19864. Loredo R, Longo C, Salonen D, et al: Glenoid labrum: MR imaging withhistologic correlation. Radiology 196:33-41, 19955. Bencardino JT, Beltran J: MR imaging of the glenohumeral ligaments.Radiol Clin North Am 44:489-502, 20066. Tirman PF, Steinbach LS, Feller JF, et al: Humeral avulsion of theanterior shoulder stabilizing structures after anterior shoulder dislocation:demonstration by MRI and MR arthrography. Skeletal Radiol 25:743-748, 19967. Wolf E, Chang J, Dickson K: Humeral avulsion of the glenohumeralligaments as a cause of anterior shoulder instability. Arthroscopy 11:600-607, 19958. Kaplan PA, Bryans KC, Davick JP, et al: MR imaging of the normalshoulder: variants and pitfalls. Radiology 184:519-524, 19929. Legan JM, Burkhard TK, Goff WB II, et al: Tears of the glenoid labrum:MR imaging of 88 arthroscopically confirmed cases. Radiology 179:241-246, 199110. Yeh L, Kwak S, Kim Y, et al: Anterior labroligamentous structures of theglenohumeral joint: correlation of MR arthrography and anatomic dissectionin cadavers. AJR Am J Roentgenol 171:1229-1236, 199511. Tirman PFJ, Feller JF, Palmer WE, et al: The Buford complex—a variationof normal shoulder anatomy: MR arthroscopic imaging features.AJR Am J Roentgenol 166:869-873, 199612. Williams MM, Snyder SJ, Buford D: The Buford complex—the cordlikemiddle glenohumeral ligament and absent anterosuperior labrum complex:a normal anatomic capsulolabral variant. Arthroscopy 10:241-247, 199413. Cvitanic O, Tirman PJF, Feller JF, et al: Using abduction and externalrotation of the shoulder to increase sensitivity of MR arthrography inrevealing tears of the glenoid labrum. AJR Am J Roentgenol 169:837-844, 199714. Wischer TK, Bredella MA, Genant HK, et al: Perthes lesion (a variant ofthe Bankart lesion): MR imaging and MR arthrographic findings withsurgical correlation. AJR Am J Roentgenol 178:233-237, 200215. Bankart A: The pathology and treatment of recurrent dislocation of theshoulder joint. Br J Surg 26:23-29, 1938

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