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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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� 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
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� 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