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Dr Andrew GraingerLeeds Teaching Hospitals

� What do we mean by microinstability?� What problems does it cause?

� Internal Impingement� What structures are important?� What do we find on imaging?

� Results from chronic/repetitive trauma to capsular structures� Responsible for maintain

a centred humeral head on the glenoid

� Overhead athletes commonly affected

�

� Potential sites of involvement:� Biceps and pulley mechanism� Rotator interval� Biceps root and superior

labrum� Rotator cuff

Structural Damage

Micro-Instability

� Important mechanisms include internal impingement� Damage to the rotator interval appears to be important

� Impingement of the rotator cuff and joint capsule/labrum on the glenoid or between the glenoid and humerus

� Descriptions remain confused

� Microinstability plays an important role

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LHB

CH Lig.� Rotator Interval� Space between Supraspinatus and Subscapularis� Contains

� Biceps Tendon SGHL.

� 90 degree pivot in the neutral position

� Biceps pulley mechanism maintains the stability of the biceps� Prevents medial

subluxation

LHB

CH Lig.�Rotator Interval

�Space between supraspinatus and subscapularis

�Contains - Long head biceps (LHB)- Coracohumeral lig (CHL)- Superior GH lig (SGHL)

SGHL.

� Pulley mechanism� Superior glenohumeral ligament� Coracohumeral ligament

� With biceps� Stabilises shoulder against superior translation

Stabilises biceps tendon

� Arises from base of coracoid

� Covers rotator interval� Blends

� Laterally with Supraspinatus

� Medially with Subscapularis

�Coalescent sling stabilizes

LHB

Modified from Weishaupt et al. Invest Radiol 1999; 34(7)4:63

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3

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� CHL and SGHL form sling prevents medialisation of the biceps

� CHL and capsule bridges bicipital groove� SST and SUB contribute

� Ultrasound

� MRI

� MRA

� Aspects of interval shown on all three standard planes� Sagittal oblique most useful

� Ho. Magn Reson Imaging Clin N Am 1999;7:23� Presence of contrast causing distension greatly helps

� Particularly for Sup GH Ligament� Chung et al. J Comput Assist Tomogr 2000;24:738

� Common� 16% of patients in one series� Usually associated with Rotator Cuff tearing� Frequently due to extension of ant supraspinatus tear

� May be due to chronic repetitive injury� Anterosuperior Impingement

� Often called �Hidden Lesion� as difficult to identify on arthroscopy

� Result – LHB instability (laxity → dislocations)

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� Subluxation of LHBT on axial image� Low sensitivity but highly specific (close to 100%)

� Displacement of LHBT on Sagittal Oblique� Sensitivity around 80%, Specificity >90%

� SGHL Disruption� Sensitivity 80 – 90%, Specificity around 80%

� Biceps tendinopathy� Relatively sensitive and specific (variability between

observers)

Schaeffeler et al. Radiology 2012; 264:504

� Occurs in position of horizontal adduction and internal rotation

� Anterior superior cuff impinges on anterosuperior glenoid� Undersurface of subscapularis� Rotator interval� Undersurface of supraspinatus

� Gerber & Sebesta. J Shoulder Elbow Surg 2000;9:483

Type Injury

1 Pulley lesion. Supraspinatus and Subscapularis Intact

2 Pulley lesion + partial Supraspinatus tear

3 Pulley lesion + partial Subscapularis tears4 Pulley lesion + partial Supraspinatus and

Subscapularis tears

Hebermeyer et al. J Shoulder Elbow Surg 2004; 13:5

� Cardinal sign – Medial subluxation of biceps tendon� Pattern of injury determines whether superficial, within

or deep to subscapularis

� Cardinal sign – Medial subluxation of biceps tendon� Pattern of injury determines whether superficial, within

or deep to subscapularis

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� Cardinal sign – Medial subluxation of biceps tendon� Pattern of injury determines whether superficial, within

or deep to subscapularis

� Cardinal sign – Medial subluxation of biceps tendon� Pattern of injury determines whether superficial, within

or deep to subscapularis

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� Recognise the association between� Rotator interval

disruption� Biceps subluxation

� Tears of subscapularis� Tears of supraspinatus� Superior Labrum

� SLAC Lesion: Superior Labrum, Anterior Cuff

� Superior Labrum Anterior to Posterior� Tears of Superior Labrum known as SLAP lesions

Biceps

Superior GH Lig

Middle GH Lig

Ant Inferior GH LigPost Inferior GH Lig

� May occur in isolation� Young throwing athletes

� Repetitive Injury� Maybe part of aging process� Important to distinguish from variants

� Vary in degree� Minor fraying at the biceps anchor� Extended tears involving other labral and capsular

structures� Many different types defined, but….� Originally 4 types described� Assessed the extent and morphology of the labral and

biceps anchor tear� This classification is the one your surgeon will know

� Type 1� Fraying and degenerative

change at biceps anchor� No frank tear� Probably age related

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� Type 2� Tear of superior labrum

and biceps from underlying glenoid

� Most common type found arthroscopically

� Bucket Handle Type Tear

� Bucket handle tear extending into biceps anchor

� Large number described� Represent extension of the

tear� Inferior labrum (ant or post)� Middle GH Ligament

� Large number described� Represent extension of the

tear� Inferior labrum (ant or post)� Middle GH Ligament

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� First type of internal impingement described� Posterosuperior cuff contacts posterosuperior glenoid in ABduction and External Rotation (ABER) position

Walch G. J Shoulder Elbow Surg. 1992:1;238

� Jobe et al� Injury to cuff, labrum and

bone� Seen in throwers and

overhead athletes� Tennis� Gymnastics� Swimmers

� Due to increased frequency or force of activity

Jobe. Curr Orthop Prac 1996; 330:98

� Is it simply a case of impingement?

� Peel-back mechanism resulting from hyper-external rotation� Hyper-twisting of rotator

cuff� Hyper-twisting of biceps� Posterior traction on

superior labrum

Morgan et al. Arthroscopy 1998;14:553Burkhart et al. Arthroscopy 1998;14:637

Posterior

Volunteer positioned in 0.5-T open MR imager.

©2007 by Radiological Society of North America Gold et al. Radiology 2007;244:815

� Contact between cuff and posterosuperior glenoid is shown to be a normal phenomenon on the basis of MRI and arthroscopic studies

1) Posterior Cuff� Classically posterior supraspinatus and

anterior infraspinatus2) Posterosuperior Labrum

� Classically type II SLAP but posterior in location (IIB)

3) Bone Changes

1 2

2

3

� Posterosuperior labral tear� Classically type II SLAP but

posterior in location (IIB)

Biceps

Anterior

Type II SLAP

Type IIB SLAP Type IIA SLAP

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� Microinstability is caused by and causes structural damage� Superior labrum� Rotator Interval� (Rotator cuff)

� Role of internal impingement in the mechanism� Rotator interval damage� Cuff damage� SLAP Tears