The Shoulder Girdle

Additional Sequences ●● ABER (abduction external rotation) view:9 the shoulder is positioned with the palm behind the head, usually

combined with MR arthrography (Fig. 1.2) giving the advantage of: ●● optimal demonstration of the anterior band of the inferior glenohumeral ligament (IGHL), which is placed

under tension ●● a statistically significant increase in sensitivity for Perthes lesions of the glenoid labrum compared with

MR arthrography in the neutral position10 ●● detection of a posterosuperior labral peel back lesion, an injury described in the overhead throwing

●● ADIR (adduction internal rotation) view: performed by placing the palm behind the back: ●● aids in identification of certain anterior labral abnormalities,14 including Bankart lesions in first time

shoulder dislocation due to displacement of the labrum in internal rotation15 ●● FADIR (f lexion adduction internal rotation) view: performed by placing the arm across the chest with

the hand on the contralateral shoulder and the palm facing outwards: ●● may increase diagnostic confidence in characterising postero-inferior labral abnormalities16

volume averaging ●● isotropic resolution allows multi-planar reconstruction after single image acquisition, potentially

eliminating the need to acquire the same sequence in different planes ●● long acquisition and post-processing times have been prohibitive for incorporation into routine clinical

practice: recent technical advances, including higher field MR systems, high-resolution dedicated multichannel coils, and pulse sequences with shorter acquisition times have made 3D imaging more feasible

●● to date, has found greatest clinical use in the evaluation of articular cartilage

●● may also improve confidence in assessing small curved structures, such as the proximal biceps tendon and curved portions of the labrum19

●● reported to show similar accuracy to conventional imaging in assessing rotator cuff and labral tears, with potentially faster imaging time20,21

●● 3D MR arthrography may be a promising substitute to computed tomography (CT) as a method for assessing bony Bankart lesions and glenoid bone loss22

●● involves the intravenous injection of gadolinium (at a concentration of 0.1 mmol/kg) followed by 10-15 minutes of shoulder exercise, resulting in enhancement of areas of synovitis or hypervascular repair tissue, and following diffusion of contrast into the joint space over time, produces a hyperintense joint effusion: ●● the arthrographic effect is reliant upon the permeability of the synovial membrane, which may be

increased in inflammatory conditions such as arthritis or infection, as well as by prior surgery23 ●● coronal oblique, sagittal oblique and axial FS T1W SE sequences are performed, together with a coronal

oblique FS T2W FSE /STIR sequence ●● indirect MR arthrography is reported to show high accuracy and sensitivity in the detection of labral

abnormalities at 1.5T24 ●● the major disadvantage is the lack of joint distension ●● other factors that can lead to suboptimal indirect arthrographic imaging include synovial fibrosis, premature

scanning time or extravasation25

●● involves intra-articular injection of 12-15 ml saline under fluoroscopic control, following confirmation of intra-articular position by initial injection of 1-2 ml iodinated contrast medium

●● coronal oblique, sagittal oblique and axial imaging with FS T2W FSE sequences are performed ●● advantages: potential cost saving by eliminating gadolinium, improved allergy safety, and allows for a

reduction in imaging time as FS T1W sequences need not be performed ●● disadvantages: does not differentiate between native and injected joint fluid since both appear hyperintense:

●● image resolution may be relatively poor compared to FS T1W SE images as used in direct gadolinium MR arthrography

●● involves intra-articular injection of 12-15 ml dilute gadolinium/saline mixture (at a concentration of 1-2 mmol/l29) to distend the joint capsule and outline the intra-articular structures

artefacts;31 however, this beneficial effect has not been observed in all studies32 ●● indications include: shoulder instability, evaluation of the labrocapsular complex, rotator cuff and

post-surgery ●● injection is performed under fluoroscopic control using an anterior, rotator interval (RI) or posterior

approach, or with ultrasound guidance for which a posterior approach appears to be preferential:33 ●● the anterior approach may result in damage to, or inadvertent extravasation of contrast material within,

the subscapularis muscle/tendon (Fig. 1.3a), the subdeltoid bursa (Fig. 1.3b), the IGHL or the anterior glenoid labrum

may be preferential for the assessment of anterior instability ●● when performed under fluoroscopic guidance, initial intra-articular position is confirmed by injection of

1-2 ml iodinated contrast medium ●● imaging should be performed within 30 minutes of injection

●● coronal oblique, sagittal oblique and axial FS T1W SE sequences (Fig. 1.4a) and/or PDW FSE sequences (Fig. 1.4b) are obtained, resulting in hyperintense joint fluid

●● differentiates injected from native bursal fluid since the latter remains hypointense on FS T1W SE sequences ●● addition of a coronal oblique FS T2W FSE/STIR sequence allows assessment of:

●● bursal fluid (Figs 1.5a, b) and extra-articular cystic lesions (Figs 1.5c, d) ●● the superior surface of the tendon (Figs 1.5e, f ), signal abnormality within the tendon and bone oedema

(Fig. 1.5g) ●● the ABER (Fig. 1.2) or ADIR positions may be added to the standard MR sequences

●● the rotator cuff: comprises the supraspinatus, infraspinatus, teres minor and subscapularis muscles/tendons ●● the supraspinatus muscle: arises from the supraspinatus fossa of the scapula (Figs 1.6a, b) and inserts laterally

via two different tendons (Figs 1.6c, d):40 ●● the main tendon forms in the mid-substance of the muscle and lies progressively more anteriorly within

the muscle belly as it forms the anterior half of the supraspinatus portion of the rotator cuff (Fig. 1.6d) ●● the more posterior part of the muscle forms a much shorter aponeurosis that is about 2 cm in length,

merging anteriorly with the main supraspinatus tendon and posteriorly with the infraspinatus tendon (Fig. 1.6d)

●● the footprint insertion of supraspinatus is triangular in shape and located at the anteromedial aspect of the superior facet of the greater tuberosity, just posterior to bicipital groove (Fig. 1.6c)

●● in approximately 50% of cases, an aponeurotic extension of the supraspinatus tendon can be identified on axial images at the level of the bicipital groove, anterolateral to the long head biceps tendon (LHBT) (Fig. 1.6e)41

●● the musculotendinous junction lies within a 15° arc of the 12 o’clock position above the humeral head (Fig. 1.6c)

●● it is innervated by the suprascapular nerve (C5 and C6) ●● the infraspinatus muscle: arises from the infraspinatus fossa of the scapula (Figs 1.6b and 1.7a) and inserts

via its tendon onto a relatively large footprint,37 which is trapezoidal in shape and located at the anterolateral portion of the superior facet, as well as the entire middle facet of the greater tuberosity, just posterior to the supraspinatus tendon (Figs 1.7b-d): ●● it has a multi-pennate configuration with multiple tendons converging to the musculotendinous junction

(Fig. 1.7e)

●● the infraspinatus tendon may be fused with the teres minor tendon, and the inferior margin also blends with the joint capsule

●● it is innervated by the distal fibres of the suprascapular nerve, after it has passed into the infraspinatus fossa through the spinoglenoid notch

●● the rotator cable: also known as the humeral semi-circular ligament, is a slender fibrous band coursing along the undersurface of the supraspinatus and infraspinatus tendons perpendicular to their fibres, and is continuous with the coracohumeral ligament anteriorly:42 ●● it is thought to absorb the compressive and tensile stresses produced by the supraspinatus and infraspinatus

tendons, thereby stress-shielding the thinner, avascular crescent of distal tendon fibres which extend lateral to the cable43

●● it appears on MRI as a thin hypointense band running deep to the supraspinatus and infraspinatus tendons on coronal oblique (Fig. 1.8a) and sagittal oblique (Fig. 1.8b) images

●● it is seen in 74% of MR images, with a mean (± standard deviation; SD) distance of the cable from the medial margin of the enthesis of 1.33 ± 0.27 cm, a mean width of the cable of 1.24 ± 0.31 cm, and a mean thickness of 0.19 ± 0.05 cm44

●● the teres minor muscle: arises from the middle third of the lateral border of the scapula (Fig. 1.6b) and inserts via its tendon onto the inferior facet of the greater tuberosity (Figs 1.7d, 1.9): ●● the muscle is adherent to the posterior joint capsule, and is innervated by the axillary nerve (C4-C5)

●● the subscapularis muscle: arises from the anterior surface of the scapula (Fig. 1.6b) and inserts via multiple tendons into the lesser tuberosity (Figs 1.7d, 1.10a): ●● the medial-lateral dimension of the normal tendon footprint has a mean value of 18 mm

●● superficial fibres extend to the greater tuberosity and contribute to the transverse humeral ligament, which forms the roof of the bicipital groove

●● deeper fibres, together with fibres from supraspinatus, pass under the biceps tendon forming the floor of the biceps tendon sheath, thereby stabilising the biceps tendon

●● the muscle is divided into 9 bellies (Fig. 1.10b), and the most inferior may insert directly onto the humerus, distal to the remaining insertion onto the lesser tuberosity

●● occasionally a belly may insert onto the coracoid process ●● it is innervated by the upper and lower subscapular nerves (C5-C7)

●● the deltoid muscle (Figs 1.11a-c): originates from the lateral clavicle, acromion and scapular spine and has a common insertion into the deltoid tubercle on the humeral shaft: ●● it is the strongest abductor of the glenohumeral joint and is innervated by the axillary nerve (C4-C5)

●● the teres major muscle: originates from the posterior surface of the inferior angle of the scapula (Fig. 1.11d) and inserts on the medial aspect of the intertubercular groove of the proximal humerus (Fig. 1.11e): ●● it is an internal rotator, adductor and extensor of the humerus and is innervated by the subscapular nerve (C5-C7)

●● the coracobrachialis muscle (Figs 1.12a, b): originates together with the short head of biceps from the tip of the coracoid process, and inserts onto the anteromedial surface of the humeral shaft: ●● it is a flexor and adductor of the glenohumeral joint, and is innervated by the musculocutaneous nerve (C5-C7)

●● the triceps muscle (Fig. 1.13): the long head of triceps originates from the infraglenoid tubercle and inferior labrum, and inserts together with the two humeral heads into the olecranon process of the ulna: ●● it acts as an extensor and adductor of the glenohumeral joint, and is innervated by the radial nerve (C6-C8)

●● the supraspinatus and infraspinatus tendons are optimally assessed on coronal and sagittal oblique images ●● the normal rotator cuff tendon (RCT) is uniformly hypointense on all pulse sequences ●● increased signal intensity (SI) in the tendon on short time echo (TE) sequences may be a normal finding due

to:47,48 ●● magic angle effect, which results in increased SI of the supraspinatus tendon on T1W, PDW FSE and FS

PDW FSE images just medial to its insertion into the greater tuberosity (Figs 1.14a, b): ● it is reported with a prevalence of 5%, may be reduced by external rotation of the arm48 and disappears

on T2W FSE images ●● interdigitation of muscle fibres with the tendon at the musculotendinous junction, particularly if the

shoulder is imaged in internal rotation (Fig. 1.14c) ●● the subscapularis, infraspinatus and teres minor muscles/tendons are optimally assessed on axial and sagittal

oblique sequences: ●● the subscapularis tendon has a normal striated pattern on axial images with coronal and sagittal oblique

PDW/T1W SE images demonstrating multiple tendons (Fig. 1.10b)

The Coraco-acromial Arch Normal Anatomy ●● the coraco-acromial (CA) arch: comprises a combination of bony and ligamentous structures beneath which

the RCT runs ●● bony: the anterior acromion and acromioclavicular (AC) joint, which are optimally assessed on a combination

of coronal (Fig. 1.15a) and sagittal oblique images (Fig. 1.15b) ●● ligamentous: CA ligament, which extends from the superior surface of the coracoid process to the under

surface of the anterior acromion, being optimally assessed on sagittal oblique T2W/PDW FSE images (Fig. 1.16a), but also seen on coronal images (Fig. 1.16b): ●● its thickness at the acromial insertion varies, but is normally less than or equal to 1.5 mm49

acromial shape, but are inferior to the combination of two sagittal oblique slices obtained at the lateral acromial edge and just lateral to the AC joint51

●● low-lying acromion: defined on coronal oblique images when the antero-inferior tip of the acromion lies inferior to the plane of the distal clavicle (Fig. 1.18): ●● may also be due to AC joint separation or instability

●● os acromiale: the acromion develops from three ossification centres which fuse at ~25 years:

●● an os acromiale represents an unfused ossification centre of the anterior acromion and is optimally demonstrated on axial (Fig. 1.19a) and sagittal (Fig. 1.19b) images, but is also identified on coronal oblique images (Fig. 1.19c)

acromiale from the normal acromial apophysis, which typically has an arched interface with lobular margins, and marrow changes are uncommon (Fig. 1.19d)52

●● primary external impingement: results from abnormalities of the CA arch that cause mechanical compression on the rotator cuff and subacromial bursa

●● secondary external impingement: results from instability or rotator cuff dysfunction, and is due to excessive superior translation of the humeral head: ●● often described in multi-directional instability, or glenohumeral micro-instability in the young overhead

throwing athlete (not associated with previous anterior dislocation) ●● commonest in older patients in combination with primary external impingement ●● also seen in scapulothoracic instability: abnormal scapular motion and scapulothoracic rhythm resulting in

dynamic narrowing of the CA outlet (the CA arch is anatomically normal) ●● clinical features: shoulder pain provoked by anterior elevation/abduction and abolished by the subacromial

injection of local anaesthetic (impingement test) ●● stages: pathological:

●● 1 – oedema and haemorrhage of the bursa ●● 2 – tendinosis and fibrosis ●● 3 – subacromial spurring and full-thickness rotator cuff tear (FTRCT)

●● clinical: ●● 1 – the tendon appears normal at MRI ●● 2 – partial-thickness rotator cuff tear (PTRCT) ●● 3 – FTRCT with subacromial abnormality

●● aetiological factors: reduction of the subacromial space may be due to: ●● inferior osteophyte/capsular thickening from an osteoarthritic AC joint ●● subacromial spur formation, especially if >3 mm

● the presence of a step deformity at the junction of an os acromiale and the acromion is reported to significantly increase the risk for rotator cuff tears55

●● malunion of a greater tuberosity fracture ●● MRI findings:

●● the CA arch: ● inferior osteophyte/capsular thickening from an osteoarthritic AC joint (Figs 1.20a, b) ● subacromial spur indenting the rotator cuff: appears as a low SI structure arising from the inferior

acromion, but if mature and ossified, contains marrow fat SI (Fig. 1.20c) ● os acromiale: inferior osteophytes (Fig. 1.20d) or step-off deformity at the junction of an unstable os

acromiale and the acromion (Fig. 1.20e): – occasionally degenerative changes may be seen at the pseudarthrosis manifest by osteophytes and

marrow oedema (Fig. 1.20f, g) ● type 3 acromial morphology (Fig. 1.17c) ● a thickened CA ligament (Fig. 1.20h) ● a malunited greater tuberosity fracture (Fig. 1.20i) ● a reduced acromio-humeral distance (≤7 mm) can be associated with impingement pain in the absence

● an abnormal amount of fluid is present when bursal thickness is greater than 3 mm (Fig. 1.21a), which is associated with loss of the SD fat stripe on coronal T1W SE images

● other features suggestive of bursitis include fluid medial to the AC joint (Fig. 1.21b), or in that part of the bursa anterior to the humerus (Fig. 1.21c)

●● RCT: shows abnormalities of SI and morphology (tendinosis/tendinopathy) due to a combination of degeneration and intrasubstance tears:

● SI: focal (Figs 1.22a, b) or diffuse (Figs 1.22c, d) increased SI on T1W/PDW FSE images, which does not reach fluid SI on T2W images

● morphology: thickened with poorly-defined margins, or attenuated

●● PSII: is defined as contact between the deep surface of the RCT and posterosuperior glenoid rim with the arm in the ABER position, and is typically seen in overhead throwing athletes

●● clinically: it produces posterosuperior shoulder pain in the late cocking or early acceleration phase of the throwing action, and may be associated with anterior instability

with posterior extension (Fig. 1.23b) ●● articular-side tear at the supraspinatus-infraspinatus junction (the posterior RI) (Fig. 1.23b) ●● cystic changes of the posterior superior glenoid rim (Fig. 1.23a) ●● humeral head oedema (Fig. 1.23c), subcortical humeral head cysts (Fig. 1.23b) or osteochondral lesions

of the posterolateral greater tuberosity (Fig. 1.23d) ●● laxity of the anterior capsule and thickening of the posterior capsule

●● RCT tears: are most commonly a sequela of chronic subacromial impingement and typically occur in middle aged/elderly patients, often resulting in a painful arc and weakness of arm elevation: ●● less commonly, they are the result of acute trauma (~8%), in which case the differential diagnosis includes

an occult, non-displaced fracture of the greater tuberosity

●● RCT tears also occur in children and adolescents, often consisting of tear patterns associated with repetitive microtrauma in overhead athletic activities, or with single traumatic events,65 and they often coexist with labral tears

●● RCT tears: are classified according to the depth of tendon involved (full-thickness or partial-thickness) and the size of the tear

●● duration, aetiology and size of RCT tears all influence treatment decisions ●● the supraspinatus tendon is reported to be involved in 95% of all cuff tears, either in isolation or in

combination with other tendon tears66

Full-thickness RCT Tear (FTRCT) ●● FTRCTs: involve the complete vertical depth of the tendon with subclassification being based on size:

●● small: <1 cm ●● medium: 1-3 cm ●● large: 3-5 cm ●● massive: >5 cm in maximal dimension

●● FTRCTs: typically begin in the leading edge of the supraspinatus tendon (Figs 1.24a, b): ●● they may extend posteriorly to involve infraspinatus (Fig. 1.24c) and very rarely extend to the superior

aspect of teres minor ●● they may extend anteriorly to involve the superior margin of the subscapularis tendon (Fig. 1.24d),

thereby also involving the rotator cable: ● in a cable-deficient rotator cuff, tears may not be limited by the protective effect of the cable and could

more easily propagate in both the anteroposterior (AP) and transverse planes42,67 ●● isolated tears of infraspinatus: are rare (Figs 1.25a, b), although full-thickness tears of infraspinatus and

teres minor may occur following posterior dislocation ●● massive tears: involving the supraspinatus and infraspinatus tendons may be associated with tendon

retraction and muscle atrophy, which will be associated with poor function following cuff repair: ● patients with massive cuff tears may be candidates for reverse total shoulder arthroplasty because of

glenohumeral joint osteoarthritis (OA) ● in the presence of massive cuff tears, careful evaluation of deltoid integrity is required, as an associated

deltoid tear could preclude such surgery68 ●● full-thickness delamination tears: are FTRCTs that show horizontal retraction of either the bursal or

articular surface of the tendon, appearing as thickening of the torn retracted edge, and/or internal splitting of the tendon:69

● they most commonly involve the supraspinatus tendon, and typically the articular-side of the cuff

●● MRI findings: ●● FTRCTs are optimally assessed on a combination of coronal oblique FS PDW/T2W FSE/STIR sequences

(long axis of tendon) and sagittal oblique T2W FSE sequence (short axis of tendon) ●● discontinuity of the tendon is the most specific sign with focal increased SI in the tendon equivalent to

water on T2W FSE/STIR images (Fig. 1.26a) or PDW FSE images (Fig. 1.26b) ●● on T1W images, RCT tears are not reliably differentiated from tendinosis, since both result in

intermediate tendon SI ●● the size of a tear is assessed in coronal (long axis) and sagittal (short axis) planes ●● on sagittal images, the supraspinatus tendon accounts for the anterior 2.5 cm of cuff from the bicipital

groove, so that posterior extension beyond this indicates involvement of infraspinatus (Fig. 1.24c) ●● the tendon margins may be well-defined and sharp (Fig. 1.26c) or atrophic (Fig. 1.26d)

●● with chronic cuff tears, the gap may be filled with reactive fibrous tissue appearing of intermediate SI on T1W, PDW and T2W FSE sequences:

● a clue to the presence of a cuff tear is abnormal morphology, with loss of normal superior convexity, being seen in ~10% of cases (Fig. 1.26e)

●● tendon retraction is present if the musculotendinous junction lies greater than 15° medial to the superior aspect of humeral head on coronal images (Fig. 1.27a)

●● with massive cuff tears, the humeral head migrates superiorly and articulates with the under surface of the acromion, resulting in ‘cuff arthropathy’ (Figs 1.27a, b)

●● delamination tears appear as FTRCTs with further proximal retraction of the articular or bursal-side of the tendon (Fig. 1.27c)

●● reported MRI sensitivity, specificity and accuracy for FTRCTs is excellent:53,70 ● sensitivity 92.1%, specificity 92.9%, accuracy 92-97%

●● PTRCTs: involve only part of the vertical depth of the tendon, most occurring on the articular-side ●● PTRCTs are subclassified as follows:

●● superior surface: involving only the bursal-side of the RCT ●● inferior surface: involving only the articular-side of the RCT ●● intrasubstance (interstitial tears): involving the tendon substance with no communication to the tendon surface

●● it occurs in the anterior cuff at the tendon-bone interface, as opposed to the critical zone and is seen in a younger patient group (mean age ~31 years)

●● it is referred to in the arthroscopic literature as the PASTA lesion (partial articular-side supraspinatus tendon avulsion)

●● a distinct type of PTRCT is a concealed interstitial delamination (CID): ●● it is a focal interstitial tear at the supraspinatus footprint and is distinguished from a PASTA/reverse

PASTA lesion by the absence of a surface component ●● although less common than PASTA lesions, CID lesions are more prevalent than previously thought,

accounting for up to a third of all footprint lesions75 ●● MRI findings:

●● a focal fluid-filled area of cuff disruption, either on the bursal-side of the cuff (Figs 1.28a, b), on the articular-side of the cuff (Figs 1.28c, d) or within the central zone of the tendon substance without surface extension (Fig. 1.28e)

●● a PAINT lesion appears as a focal articular-side PTRCT with extension into the tendon substance (Figs 1.29a, b) ●● rim-rent tears appear as articular-side discontinuity of tendon fibres with a linear, transverse area of fluid

SI at the tendon-bone interface, involving supraspinatus (Fig. 1.29c) or infraspinatus (Figs 1.29d, e): ●● reverse PASTA lesions appear as bursal-side discontinuity of fibres with linear fluid SI at the tendon-bone

interface (Fig. 1.29f)

●● a CID tear appears as focal intrasubstance fluid SI at the tendon-bone interface with intact tendon fibres on both the articular and bursal sides (Fig. 1.29g)

fibrovascular tissue, and may not appear of fluid SI76

MR Arthrography of Rotator Cuff Tears2,77 ●● direct gadolinium MR arthrography, improves the differentiation of small FTRCTs from PTRCTs and

improves assessment of tear size78 ●● indirect MR arthrography: in the ABER position significantly improves the detection of PTRCTs of

the supraspinatus tendon79 ●● MR arthrography at 3T:

●● shows significant improvement in sensitivity for detection of partial articular-side supraspinatus tears (98%) compared to conventional 3T MRI (92%)80

●● 100% sensitivity compared with 95% for conventional 3T MRI in detection of FTRCTs of supraspinatus, since some FTRCTs may be missed on conventional MRI due to fibrosis simulating an intact tendon81

●● MRI findings: ●● on direct gadolinium MR arthrography, the under-surface of the normal supraspinatus tendon is smooth

to its lateral insertion into the greater tuberosity (Fig. 1.30a)

●● an articular-side PTRCT appears as: ● contrast imbibition part way into the substance of the tendon (Fig. 1.30b) with irregularity of

the undersurface of the tendon ● the majority occur at the critical zone, 1 cm medial to the tendon insertion ● the accuracy and specificity of MR arthrography is reported as 91% and 96% respectively82

●● a bursal-side PTRCT appears as: ● a partial-thickness fluid-filled defect in the superior surface of the tendon on T2W FSE/STIR

sequences (Fig. 1.5e) or irregularity of superior tendon surface: – they are not appreciated on T1W SE FS images (Fig. 1.5f)

●● an interstitial tear (including a CID) appears as: ● partial-thickness defect which is of fluid SI on T2W FSE/STIR sequences, contained within

the substance of the tendon without reaching the tendon surface (Fig. 1.30c) ● in the CID, the fluid SI reaches the bone-tendon interface (Fig. 1.30d) ● interstitial tears are not appreciated on FS T1W SE images

●● a PAINT lesion: can be distinguished from an interstitial tear due to extension of injected contrast material into the tear on FS T1W SE images (Fig. 1.30e)

●● FTRCT: appears as a focal (Fig. 1.31a) or diffuse (Fig. 1.31b) contrast-filled gap through the whole thickness of the tendon, with injected gadolinium seen in the SA-SD bursa (Figs 1.31b, c)

●● the subcoracoid space: is located between the coracoid process and the lesser tuberosity of the humeral head and contains the subscapularis tendon and muscle, the middle glenohumeral ligament (MGHL), the LHBT (Fig. 1.32) and the subcoracoid bursa

●● subcoracoid (anterior/coracohumeral) impingement: results from chronic compression of the subscapularis tendon/LHBT between the coracoid process and lesser tuberosity, and is a relatively uncommon cause of anterior shoulder pain

●● clinically: it produces anterior shoulder clicking/pain referred to the upper arm, which is maximal on adduction, internal rotation and forward flexion and is relieved by injection of local anaesthetic into the subcoracoid region83

●● aetiological factors: include reduced coracohumeral distance (CHD), when the coracoid tip lies close to the scapular neck due to idiopathic (developmental), post-surgical or post-traumatic causes: ●● a far lateral projection of the coracoid tip (Fig. 1.33a) ●● a massive rotator cuff tear resulting in static anterior subluxation of the humeral head

●● CHD: is measured between the tip of the coracoid process and lesser tuberosity, being reduced in internal rotation and forward elevation: ●● using cine MRI, the mean CHD in asymptomatic individuals is 11 mm in maximal internal rotation,

reducing to 5.5 mm in symptomatic patients84 ●● using MRI in the conventional external rotation position:85 females are found to have a CHD which is 3 mm

on average less than males: ●● sex-adjusted CHD of 10.5-11.5 mm is significantly related to subcoracoid impingement, but has a poor

predictive value (sensitivity 79-84%, specificity 44-59%) ●● the mean CHD in asymptomatic individuals is 15.5 mm, reducing to 11.2 mm in symptomatic patients86

●● MRI findings: ●● subcoracoid impingement is best imaged in internal rotation on axial images ●● reduced CHD: the mean CHD in symptomatic individuals is 5.5 mm in maximal internal rotation ●● subscapularis tendinopathy/tendinosis: the tendon lesion typically occurs 1-2 cm medial to the lesser

tuberosity insertion: ● the tendon appears hyperintense with an abnormal morphology (irregular contour, swollen or thinned)

(Fig. 1.33b) ●● subscapularis tears: may be full-thickness, but are more commonly partial articular-side tears

(Fig. 1.33c)87

●● additional features include: subcoracoid bursal distension (Fig. 1.33b), abnormalities of the long head biceps and cystic changes in the lesser tuberosity (Figs 1.33c, d)

●● the shape of the coracoid process (round, tear-drop, oval) and the morphology of the lesser tuberosity (smooth, protuberant) are not related to the presence of subcoracoid impingement85

●● rarely, a non-united or malunited fracture of the coracoid process (Figs 1.33e, f )

●● ASII: a rare condition resulting from impingement of the LHBT with the anterosuperior glenoid rim: ●● it is possibly predisposed to by a partial deep surface tear of the subscapularis tendon and/or the

biceps pulley (see later: common humeral insertion of the superior glenohumeral and coracohumeral ligaments)

●● tears of the anterior supraspinatus tendon may also be associated ●● aetiology of the biceps-pulley lesion may be degenerative (especially in repeated overhead activity),

or traumatic ●● clinically: it results in anterior shoulder pain maximal in internal rotation and forward flexion

●● MRI findings: ●● partial tear of the deep surface of the subscapularis tendon ●● contact between the subscapularis insertion and the anterosuperior glenoid rim ●● an associated biceps-pulley lesion is often seen, which can vary in appearance (see later)

●● AII: is a rare condition resulting from contact between the rotator cuff, which has a partial articular-side tear, and the superior labrum anterior to the biceps anchor ●● clinically: it presents as subacromial impingement, but since treatment differs significantly, the two

conditions must be differentiated on MRI ●● MRI findings:

●● absence of findings associated with classical subacromial impingement ●● an articular-side PTRCT is always seen at arthroscopy ●● fraying and detachment of the anterosuperior labrum is seen in 60%

●● subscapularis tears: are uncommon, with 2-8% of supraspinatus tendon tears involving the subscapularis muscle: ●● the incidence of subscapularis involvement increases with the size and chronicity of supraspinatus tears92

●● conversely, the majority of subscapularis tears (69%) are extensions of supraspinatus tendon tears: ●● 27% are PTRCT and 73% FTRCT, while 67% are limited to the cranial one-third of the tendon

●● isolated tears: can occur secondary to acute abduction-external rotation trauma, in acute anterior shoulder dislocation, or in elderly patients with recurrent anterior dislocation

●● partial thickness subscapularis tendon tears are strongly associated with fluid-like SI within the tendon on more than one imaging plane93

●● subscapularis tears are associated with: ●● reduced CHD:94 mean CHD for subscapularis tears is 5.0 +/− 1.7 mm and in controls is 10.0

+/− 1.3 mm ●● LHBT abnormalities: subluxation/dislocation in 49% and rupture in 7% ●● compensatory hypertrophy of the teres minor muscle95

●● MRI findings: ●● poorly-defined tendon contour with increased SI on PDW/T2W FSE/T2W GRE images

(Figs 1.34a, b) ●● thickening of the distal tendon and tendon discontinuity (Figs 1.34a, b)

●● partial-thickness articular sided tearing:39 may be diagnosed if the footprint attachment appears narrower than expected on axial images at the level of the superior tendon fibres (but not at the level of the RI)

●● complete tear: discontinuity (Fig. 1.34c) or retraction of the tendon from the lesser tuberosity (Fig. 1.34d)

●● effusion in the subscapularis recess and/or subcoracoid bursa (Figs 1.34a, c) ●● fluid-like SI within the tendon on more than one plane (Figs 1.34a, b) ●● additional findings:

● fatty infiltration/atrophy of the subscapularis muscle +/− hypertrophy of teres minor (Fig. 1.34e) ● subluxation/dislocation of LHBT (Fig. 1.34d) ● cysts within the lesser tuberosity can be seen, although are non-specific

●● grade 0: normal tendon, homogeneously hypointense (Fig. 1.35a) ●● grade 1: fraying and SI increase in the cranial portion of the tendon (Fig. 1.35b) ●● grade 2: tear of the cranial portion of the tendon, while the inferior portion remains attached to the lesser

tuberosity ●● grade 3: a complete tear, with medial tendon retraction ●● MR arthrography may also show extension of contrast medium deep to the tendon onto the surface of

the lesser tuberosity (Fig. 1.35c) ●● sensitivity and specificity with the combination of sagittal and axial images is reported as 91% and 86%

respectively

●● subchondral humeral head cysts: can be seen at various locations, being identified in 70% of patients, 7 times more commonly in the posterior humeral head than the anterior head

●● anterior cysts: ●● occurring at the insertion of the supraspinatus and/or subscapularis tendons appear to be associated with

RCT, being demonstrated in 28% of cases ●● a cyst within the lesser tuberosity is associated with a subscapularis tear in 92%99

●● posterior cysts: located in the bare area of the anatomical neck (posterosuperior aspect of the head/neck) are not related to cuff disease, but may represent a degenerative/ageing phenomenon

●● humeral head geodes: may also be seen in the absence of cuff pathology

●● MR findings: ●● cysts show low/intermediate SI on T1W/PDW FSE images and hyperintensity on T2W/STIR and FS

images (Fig. 1.33c) ●● anterior cysts are located in the lesser tuberosity (Figs 1.33c, d) or greater tuberosity (Fig. 1.36a) ●● cysts may be single or multiple (1-3) and are typically 2-4 mm in size ●● 94% of all humeral head cysts communicate with the joint, as demonstrated by MR arthrography

(Figs 1.35c and 1.36b) ●● geode: well-defined lesion with fluid SI characteristics, a hypointense sclerotic margin and a thin

extension to the articular surface (Figs 1.36c, d)

●● AC joint cysts: occur due to leakage of glenohumeral joint fluid through a massive complete cuff tear into a degenerate AC joint

●● clinically: they present as a painless pseudotumour of the shoulder in middle aged/elderly patients ●● MRI findings:

●● typical SI characteristics of fluid on T1W/PDW (Fig. 1.37a) and T2W/STIR images (Fig. 1.37b) ●● cyst size is reported to range from 1.5 to 6 cm (mean 3.27 cm) ●● AC joint OA is invariable and the inferior AC joint capsule is ruptured, allowing extension of joint fluid

and injected contrast at MR arthrography to enter the cyst (geyser sign) ●● an extensive RCT, with/without tendon retraction is typically seen (Fig. 1.31a)

●● intramuscular cysts: represent a collection of joint fluid within a fascial sheath or the substance of a rotator cuff muscle, but do not extend to either the bursal or articular surface

●● they have a prevalence of ~1% and may be a useful secondary sign of rotator cuff tear, occurring equally with FTRCTs or PTRCTs

●● however, ~24% of intramuscular cysts occur in the absence of a tear ●● most cysts are located in the infraspinatus muscle (~52%), the supraspinatus muscle (~31%) or rarely in

subscapularis or teres minor ●● MRI findings:

●● the cysts are elongated, running along the length of the muscle and measuring 2-4 cm in their long axis and ~2 cm in cross-section

●● they show fluid SI on T1W, PDW (Fig. 1.38a) and T2W images (Fig. 1.38b) and may be either unilocular or multi-locular

●● a small tail may communicate with the tear (Fig. 1.38c) and the cyst will often fill with gadolinium on direct MR arthrography (Figs 1.38d, e)

Fatty Infiltration and Atrophy of Rotator Cuff Muscles ●● cuff muscle atrophy: is associated with massive FTRCTs, often with tendon retraction ●● fatty infiltration: is an associated process to muscle atrophy, both being seen with increasing patient age,

even in the absence of a rotator cuff tear: ●● fatty infiltration can be graded using a 5-point semi-quantitative scale: 0, normal; 1, some fat streaks;

2, fatty degeneration of less than 50%; 3, fatty degeneration of 50% (equal fat and muscle); and 4, fatty infiltration of more than 50%

●● with increasing severity of supraspinatus tears, the prevalence of substantial fatty infiltration (grade ≥2) significantly increases103

●● moderate supraspinatus fatty infiltration appears on average 3 years after onset of symptoms of a cuff tear, and severe fatty infiltration at an average of 5 years104

●● supraspinatus:105 muscle atrophy is optimally assessed on the sagittal oblique view at the base of the medial aspect of the coracoid process, referred to as the ‘Y-view’ (Fig. 1.39a): ●● supraspinatus muscle atrophy may be calculated as the occupation ratio (R):

● R = the ratio between the cross-sectional area of the supraspinatus muscle belly and the cross-sectional area of the supraspinatus fossa

● the mean R in controls and patients with degenerative cuffs is reported as 0.7 and 0.62 (no significant difference), but in patients with FTRCTs is 0.44

●● severe atrophy: may demonstrate a positive ‘tangent’ sign,106 positive when the supraspinatus muscle does not extend above a line joining the cranial margins of the scapular body and scapular spine on the Y-view (Fig. 1.39b)

● a positive tangent sign is seen at an average of 4.5 years after onset of symptoms of a cuff tear104 and is a useful predictor of whether a tear will be irreparable107

●● supraspinatus atrophy: associated with a FTRCT is commonly asymmetric,108 being significantly more common on the superficial (fascial) side of the tendon compared to the deep (bony) side of the tendon (Fig. 1.39c):

● the deep portion of the muscle more commonly undergoes fatty infiltration ● asymmetric atrophy does not result in a change in position of the tendon within the supraspinatus fossa

●● infraspinatus:109 reported in 4.3% of shoulder MRI studies (Fig. 1.39d) and confined to infraspinatus in 20% of these: ●● associated infraspinatus tendon tears are seen in 53% of cases, while an anterior FTRCT is present in 90%

of cases ●● infraspinatus muscle atrophy can occur with an intact infraspinatus tendon

●● isolated teres minor atrophy:110 is seen in 5.5% of shoulder MRI studies, most commonly in males at a mean age of 60 years (Figs 1.39e, f )

Chondral Defects of the Glenohumeral Joint ●● chondromalacia: of the humeral head or glenoid fossa is reported with a frequency of 29% in patients

undergoing arthroscopy for subacromial impingement

●● MRI findings: ●● diagnosed with MR arthrography as surface irregularity or partial/full-thickness contrast filled defects of

the articular cartilage, and more commonly involves the humeral head ●● MR arthrography is reported to have an accuracy of 65-77% for humeral lesions and 65-67% for glenoid

lesions

●● calcific tendinopathy: of the RCT results from deposition of hydroxyapatite crystals as part of hydroxyapatite deposition disease (HADD), and is a condition of unknown aetiology

●● ~80% of cases involve the supraspinatus tendon and the condition may be bilateral ●● HADD: may also involve the subscapularis tendon, origins of the long and shorts heads of biceps (adjacent

to the supraglenoid tubercle and coracoid tip respectively), the pectoralis major tendon insertion into the anterior proximal humeral shaft113 and less commonly, other tendons and bursae around the shoulder

●● clinically: it presents with acute onset or chronic pain over the lateral shoulder and upper arm, usually in the 4th-6th decades of life, but children can also be affected114

●● pathologically: 5 phases of the disorder are described: ●● 1st: the silent (asymptomatic) phase, in which crystals are deposited in the RCT (most commonly at the

critical zone of supraspinatus) ●● 2nd: the mechanical phase, with increasing size of crystal deposition and rupture into the tendon substance

(Figs 1.40a, b), and subsequently deep to the subacromial bursa (sub-bursal rupture) or into the bursa (intrabursal rupture) (Figs 1.40c, d)

●● 3rd: adhesive periarthritis, a chronic stage in which inflammation secondary to the extruded calcifications results in fibrosis of the peritendinous soft tissues and chronic symptoms, and may be associated with spontaneous rupture of the degenerated tendon

●● 4th: intraosseous loculation, an infrequent complication where the extruded calcific material erodes into the greater tuberosity to produce a subcortical cyst (Fig. 1.40e)

●● 5th: dumbbell loculation, resulting from compression of the semi-solid sub-bursal calcifications by the CA ligament, causing a dumbbell configuration

●● MRI findings: ●● calcification appears as focal areas of low SI or signal void on all pulse sequences (Figs 1.40a, b),

often ~1 cm from the tendon insertion ●● tendon oedema and SA-SD bursitis may be seen on FS PDW/T2W/STIR sequences (Figs 1.40a, b) ●● rarely, may be associated with cortical erosion of the humerus,115 appearing as a subcortical cyst

(Fig. 1.40e) with surrounding marrow oedema ●● CT may be of value in demonstrating cuff calcification associated with humeral head erosion (Fig. 1.40f)

●● rotator cuff strain: describes a post-traumatic condition occurring typically in patients under 40 years age ●● myotendinous junction strain:119 is a distinct subgroup of cuff strains in which the injury is located medial to

the distal tendon fibres, often with an intact tendon attachment: ●● the majority (80%) of myotendinous junction injuries represent strains, with tendon tearing in this

location being uncommon ●● the infraspinatus is more commonly affected (50%) than supraspinatus (31%), subscapularis (25%) or teres

minor (19%) ●● MRI findings:

●● distal rotator cuff strain: appears as focal increased tendon SI, typically in the posterior aspect of the supraspinatus tendon, with adjacent increased humeral head marrow SI, presumed to represent bone bruising (Figs 1.41a, b)

●● myotendinous junction strain: manifests as increased SI surrounding the myotendinous junction, while fluid-like SI partially involving the myotendinous junction is indicative of a tear

●● the RI: is a triangular space in the anterosuperior aspect of the shoulder with the following boundaries: ●● superior: the leading edge of supraspinatus (Fig. 1.42a) ●● inferior: the cranial margin of subscapularis (Fig. 1.42a) ●● base: located medially and formed by the coracoid process ●● apex: located laterally and formed by the transverse humeral ligament (THL) (Fig. 1.42b)

●● the THL: cadaveric studies suggest that the THL is not a distinct anatomical structure, but rather is formed by the continuation of superficial fibres of the subscapularis tendon across the bicipital groove, which then insert into the greater tuberosity, with lesser contributions from the longitudinal fibres of supraspinatus and the coracohumeral ligament (CHL)

●● the RI: contains the LHBT as it enters the bicipital groove, which is covered by the rotator interval capsule (RIC): ●● the RIC represents that part of the glenohumeral joint capsule that bridges the supraspinatus and

subscapularis muscles ●● it functions as a passive stabiliser, limiting excessive motion including postero-inferior glenohumeral

translation122

●● the superior glenohumeral (SGHL): is a constant structure arising from the supraglenoid tuberosity or superior labrum: ●● it enters the RI from its medial aspect and then courses laterally parallel to the LHBT ●● its lateral attachment may be into the lesser tuberosity, bicipital groove or with the CHL

●● the CHL: is a well-developed structure, which is present in over 90% of individuals, arising outside the glenohumeral joint from the lateral aspect of the base of the coracoid process (Figs 1.42a and 1.43): ●● as it runs laterally, it appears inseparable from the capsule, spanning over the RI superficial to the SGHL ●● distally, the CHL forms 2 major bands:

● a larger lateral band, which inserts onto the greater tuberosity and anterior border of the supraspinatus tendon

● a smaller medial band, which crosses the LHBT to insert into the lesser tuberosity and superior fibres of subscapularis, contributing to the THL

●● the CHL is normally surrounded by fat (Figs 1.42a and 1.43) ●● the ‘biceps reflection pulley’: is formed by the SGHL, the CHL and some fibres from the subscapularis

tendon:123 ●● it surrounds and stabilises the LHBT as it enters the bicipital groove, and injuries to this region are termed

‘pulley lesions’ ●● the anatomy of the RI is optimally assessed on direct MR arthrography with oblique sagittal (Figs 1.44a, b)

and axial sequences

●● clinically: the manifestations of a RI lesion are non-specific, including chronic shoulder pain and multidirectional instability

●● injuries to the RI: may be caused by repetitive or forceful overhead throwing actions in athletes, occupational injuries from repetitive overhead labour, acute injuries from falls on the outstretched hand, or following acute antero-inferior dislocation of the humeral head: ●● injuries to the lateral RI/biceps pulley have been termed ‘hidden lesions’, since they may not be identified

at arthroscopy ●● the various structures of the RI may be injured in isolation or in combination ●● pulley lesions:125 are reported in ~7% of cases at arthroscopy and may occur in the absence of LHBT or rotator

cuff pathology (in ~32% of cases)126 ●● they may contribute to anterosuperior internal impingement (see earlier)

●● MRI findings: ●● acute injury: thickening, irregularity and heterogeneous increased SI of the CHL and RIC, with oedema

and haemorrhage in the RI (Figs 1.45a-c) ●● complete rupture of the CHL may lead to non-visualisation (Fig. 1.45d) ●● chronic injury: irregular thickening and scarring of the CHL (Figs 1.45e, f ) and RIC (Fig. 1.45g), and

synovitis within the RI ●● LHBT injury: (see later) ●● biceps-pulley lesions: acute injuries or repetitive microtrauma may result in tears of the pulley (including

CHL and SGHL) and associated subluxation of the LHBT ●● subcoracoid bursal fluid may be associated with rotator cuff and interval tears,127 and the identification of

fluid in this bursa should prompt a thorough assessment of the RI ●● associated injuries include:

● tears of the leading edge of the supraspinatus tendon immediately prior to its insertion into the greater tuberosity

● tears of the superior distal margin of subscapularis and SLAP lesions (see later) ●● MR arthrography findings:

●● abnormalities of the superior border of the subscapularis tendon, which may involve the medial component of the biceps pulley

●● extracapsular contrast extension through a ruptured RIC, with injected contrast seen in the subcoracoid space (Fig. 1.45h), around the CHL (Fig. 1.45i) and SGHL, or over the superior aspect of the humeral tuberosities

●● LHBT subluxation/dislocation (Fig. 1.34d) relative to the bicipital groove is highly specific, but insensitive

●● LHBT displacement caudally and/or anteriorly relative to the subscapularis tendon on oblique sagittal images is reported to have a high sensitivity and specificity for the presence of a pulley lesion128

●● the reported sensitivity and specificity of MR arthrography is ~90%

●● the biceps brachii muscle: is composed of two heads, the short head and long head ●● the short head: arises from the anterior aspect of the coracoid process (Figs 1.46a, b) ●● the LHBT: arises from the supraglenoid tubercle and superior labrum (biceps-labral complex), with some

fibres also arising from the base of the coracoid process ●● the LHBT has an intracapsular and an extracapsular portion:

●● the proximal LHBT is an intracapsular, but extrasynovial structure which extends from its origin, running deep to the RCT to enter the bicipital groove via the RI

●● as the distal intra-articular portion of the LHBT exits the glenohumeral joint, its position is stabilised by the biceps reflection pulley (see above)

●● rarely, the intracapsular portion of LHBT may be absent, in which case it arises from the bicipital groove ●● MRI findings:

●● the LHBT is hypointense on all pulse sequences ●● the biceps-labral complex is optimally demonstrated on coronal oblique and axial direct MR arthrography

(Figs 1.47a, b) ●● the tendon runs obliquely over the humeral head deep to supraspinatus (Fig. 1.47a) ●● it is identified within the RI on sagittal oblique images between the humeral head and RIC (Figs 1.44a, b)

and is covered in the bicipital groove by the THL, seen optimally on axial images (Fig. 1.42b) ●● a small amount of fluid within the tendon sheath is normal, as the glenohumeral joint and tendon sheath

are in direct communication

●● tenosynovitis and tendinosis: together with delamination and rupture (see later), may represent the natural history of progressive degeneration of the LHBT, and are associated with rotator cuff disease in the majority of cases

●● MRI findings: ●● tendon thickening or attenuation is reported to be specific, but insensitive in diagnosing tendinopathy ●● fusiform tendon enlargement is reported to occur primarily at the entrance to the bicipital groove

(Figs 1.48a, b) ●● synovial adhesions (Fig. 1.48c) and non-communicating effusion of the tendon sheath (Fig. 1.48d)

suggest tenosynovitis ●● intrasubstance fluid SI clefts indicate longitudinal partial-thickness LHBT tears (Fig. 1.48e)

●● displacement of the LHBT: is associated with tears of the subscapularis muscle and biceps reflection pulley, and LHBT tendinosis may arise in the presence of subluxation

as 67%, 90%, 86% and 75%, respectively ●● MRI findings:

●● subluxation: the tendon lies on the medial ridge of the bicipital groove, optimally shown on axial imaging (Fig. 1.49a)

●● dislocation: the tendon lies anterior to the medial humeral head and the bicipital groove is empty (Figs 1.49b, c)

●● a defect in the subscapularis apparatus may allow intra-articular entrapment of the LHBT, resulting in incomplete dislocation:

● MRI shows the LHBT lying within a partially disrupted subscapularis tendon (Fig. 1.49d) ●● extra-articular dislocation of the LHBT anterior to the subscapularis tendon occurs if the CHL and

anterior supraspinatus tendon are torn, but the subscapularis tendon remains intact (Fig. 1.49e) ●● morphological abnormalities: predisposing to instability include an obtuse angle of the intertubercular

sulcus (Fig. 1.49f) and a flattened LHBT

●● causes of LHBT rupture: include a chronic tear of the leading edge of the supraspinatus tendon allowing impingement of the uncovered LHBT with the under-surface of the acromion

●● LHBT ruptures:135 are associated with supraspinatus tears in 96% of cases, infraspinatus tears in 35% of cases and subscapularis tears in 47% of cases: ●● there is a significant association between supraspinatus and subscapularis tears and LHBT rupture, but not

with teres minor tears ●● acute traumatic rupture is rare

●● partial (Fig. 1.48e) or full-thickness tears of the LHBT tendon are diagnosed on conventional MRI with a sensitivity, specificity and accuracy of 52%, 86% and 79%135

●● MRI findings: ●● an empty bicipital groove containing chronic scar tissue (Figs 1.50a, b) ●● associated RCT tears and/or SLAP lesion

●● a rare form of internal impingement, in which the intra-articular portion of the LHBT is hypertrophied (hourglass lesion) relative to the cross-sectional diameter of the bicipital groove, resulting in impingement as it enters the groove

●● clinically: it presents with tenderness along the groove and loss of the final 20°of passive elevation ●● MRI findings:

●● hypertrophy of the intra-articular portion of the LHBT, but a normal appearance of the tendon in the bicipital groove (Fig. 1.51)

●● shoulder bursae: may be classified as communicating and non-communicating ●● communicating include: the subscapularis, subcoracoid and peribicipital bursae ●● non-communicating include:

●● the SA-SD bursa ●● the coracoclavicular ligament bursae: variably present between the conoid and trapezoid parts of the

coracoclavicular ligament ●● a bursa superior to the AC joint ●● a bursa adjacent to the inferior tip of the scapula (see later) ●● a bursa between the scapula and ribs (scapulothoracic – see later) ●● various bursae adjacent to the insertion sites of the latissimus dorsi, teres major and pectoralis major

muscles

●● the SA-SD bursa: consists of 2 interconnected portions: ●● the SA bursa: which is located inferior to the acromion and CA ligament, superior to the RCT and RI and

extends medially as far as the AC joint ●● the SD bursa: which is located between the lateral aspect of the humeral head and the deltoid muscle ●● both communicate with each other, but not with the glenohumeral joint ●● the normal bursa is delineated by a fat stripe seen on coronal oblique T1W/PDW FSE images

(Fig. 1.52)

●● the subscapularis bursa: represents an anterior extension of the glenohumeral joint between the SGHL and the MGHL

●● it is located between the scapular blade and the subscapularis muscle (Fig. 1.53a), sometimes extending above the subscapularis tendon to lie beneath the base of the coracoid process (Fig. 1.53b)

●● the subcoracoid bursa: lies between the anterior surface of the subscapularis tendon and the coracoid process and may communicate with the SA-SD bursa

●● isolated subacromial fluid:142 may be associated with subacromial impingement and supraspinatus tendinosis, FTRCT or bursal-side PTRCT (Fig. 1.21) and instability, or in asymptomatic patients following rotator cuff repair

●● primary bursitis: may result from rheumatoid arthritis and tuberculous (TB) synovitis, possibly with rice body formation (see Chapter 7), a non-specific response to chronic synovial inflammation143,144

●● MRI findings: ●● ‘rice body’ bursitis: a distended bursa containing multiple small T2W hypointense ‘rice bodies’ ●● subscapularis bursal fluid: may be normal or may be associated with non-specific glenohumeral joint

effusions: ● isolated fluid in the subscapularis bursa may be seen with subacromial impingement

●● subcoracoid bursal fluid:140 is reported in 0.6% of patients undergoing shoulder MRI: ● the subcoracoid bursa may be confused with the subscapularis bursa ● isolated or predominant subcoracoid effusions (Figs 1.54a, b) are considered abnormal, causes

including anterior RCT tears and RI tears127

●● glenohumeral joint stability: is provided by a combination of static and dynamic factors, with the joint capsule and labroligamentous complex playing a major role in static stabilisation

●● the joint capsule: extends from the glenoid rim to the anatomical neck of the humerus ●● the anterior capsule:146 has 3 types of capsular insertion:

●● type 1: inserts into the base of the glenoid labrum (Fig. 1.55a) ●● type 2: inserts into the scapular neck (Fig. 1.55b) ●● type 3: inserts further medially into the scapula, at the transition between the neck and body (Fig. 1.55c)

●● the relationship of types 2 and 3 to instability is unclear, and they may be acquired following previous anterior dislocation

●● the posterior capsule: always inserts into the posterior glenoid rim (Fig. 1.55c) ●● the inferior capsule: in the axillary region the capsule may be partially fused to the tendon of the long head of

triceps at its origin from the infraglenoid tubercle ●● capsular recesses include:

●● the subscapularis: anterior to the scapular blade and deep to the subscapularis muscle (Figs 1.53a, b) ●● the axillary: between the anterior and posterior bands of the IGHL (Figs 1.56a, b) ●● the intertubercular/peribicipital: surrounds the LHBT (Figs 1.56a, b)

●● the glenohumeral ligaments (GHL): represent discrete capsular bands and comprise the superior (SGHL), middle (MGHL) and inferior (IGHL)

●● the SGHL: arises from the supraglenoid tubercle adjacent to the LHBT, extending anterolaterally to merge with the CHL in the RI (Fig. 1.44b) prior to its insertion between the supraspinatus and subscapularis tendons just superior to the lesser tuberosity: ●● the SGHL confers some stability to the shoulder in adduction and helps prevent inferior subluxation ●● it is identified at MR arthrography in 98% of cases, being seen on axial (Fig. 1.57a) and sagittal oblique

(Fig. 1.57b) images as a thick band arising from the supraglenoid tubercle, adjacent to the LHBT and running parallel and medial to the coracoid process to insert at the RI

●● anatomical variants of SGHL: include a common origin with the LHBT (Fig. 1.57c) or MGHL ●● thickening of the SGHL may be associated with absence or underdevelopment of the MGHL

●● the MGHL: most commonly arises from the anterosuperior labrum, extending inferolaterally, deep to the anterior capsule and subscapularis muscle to blend into the capsular sheath of the subscapularis, and thereby insert into the lesser tuberosity inferior to the SGHL: ●● the MGHL limits anterior translation when the arm is externally rotated and moderately abducted ●● it is seen on axial (Fig. 1.58a) and sagittal (Fig. 1.58b) MR/MR arthrography images as a hypointense

band between the anterior labrum and subscapularis muscle ●● anatomical variations of the MGHL are common but these differences in morphology are not thought to

affect glenohumeral stability:151 ● variable origin: from the scapular neck (Fig. 1.59a) or a combined origin with the SGHL (Fig. 1.59b)

or IGHL

● variable insertion: may blend with the subscapularis tendon prior to insertion into the humerus (Fig. 1.58b)

● variable thickness (Figs 1.59c, d) ● the MGHL is absent in 8-30% of cases,38 resulting in a large opening between the joint cavity and

subscapularis recess ● rarely, the MGHL may be duplicated or have a longitudinal split ● the Buford complex: has a reported prevalence of 1.5-6.5%, and comprises the association of

a thickened cord-like MGHL and an absent anterosuperior labrum (Figs 1.59e, f ) ●● the IGHL has three components:

●● the anterior band: originates at the 2-4 o’clock position on the labrum (Figs 1.60a, b) ●● the posterior band: originates at the 7-9 o’clock position on the labrum (Fig. 1.60c) ●● the axillary pouch: a diffuse thickening of the capsule between the anterior and posterior bands

(Figs 1.56a, b) ●● it extends from the labrum to insert into the humeral neck (Figs 1.60a-d) ●● the IGHL is thought to be vital in preventing anterior dislocation of the shoulder joint, especially in 90°

abduction and full external rotation, being lax with the shoulder adducted152 ●● it becomes taut in the ABER position (Fig. 1.2) and contributes most to passive stabilisation ●● if it is attached to a labrum that is torn from the glenoid rim, the IGHL becomes incompetent and

the shoulder becomes unstable

●● the spiral GHL:153 also termed the fasciculus obliquus, arises from the infraglenoid tubercle of the glenoid rim and long head of triceps: ●● it forms a tight communication with the MGHL, extending to fuse with the posterocranial margin of the

subscapularis tendon, with which it inserts into the lesser tuberosity ●● it appears on MR arthrography as a thin hypointense band in the anterior capsule, lying deep to

the subscapularis tendon (Fig. 1.61)

●● the glenoid labrum: is a fibrous/fibrocartilaginous structure, which attaches to the glenoid rim ●● anatomical portions of the labrum, when viewed en-face can be described as a clock face:

●● superior: 12 o’clock ●● anterior: 3 o’clock ●● inferior: 6 o’clock ●● posterior: 9 o’clock

●● the labrum: serves as an anchor for the origin of the LHBT and GHLs, and also deepens the glenoid articular surface, thereby acting as a passive stabiliser to the glenohumeral joint: ●● compared with the anterosuperior labrocapsular complex, the antero-inferior labrocapsular complex is

more important in shoulder stability ●● the anterior and posterior labrum: are optimally assessed on axial images, appearing as hypointense,

triangular structures separated from the underlying bony glenoid by a thin intermediate SI layer of articular hyaline cartilage: ●● the anterior labrum is typically pointed and is larger than the posterior labrum (Fig. 1.62a) ●● the anterior labrum may also be rounded or blunted (Fig. 1.62b), especially with the shoulder imaged in

a degree of internal rotation (Fig. 1.62c) ●● variations in the MR appearance of the arthroscopically normal labrum include:156

●● increased linear or globular SI in 30% (Fig. 1.62d), due to a combination of fibrovascular tissue, eosinophilic/mucoid degeneration, synovialisation or ossification/calcification

●● deformed or fragmented in 12% ●● complete separation from the glenoid rim in 2% and complete absence in 2%

●● the mean size of the labrum is: ●● 3.8 × 3.3 mm anteriorly at the level of the subscapularis bursa ●● 6.1 × 5.6 mm anteriorly at the inferior portion of the glenoid rim

●● however, considerable variation in normal labral size is reported, therefore size alone is of limited diagnostic utility

●● the glenohumeral joint: is formed by the humeral head and glenoid articular surface of the scapula ●● the central portion of the glenoid articular surface is devoid of hyaline cartilage, being termed the ‘bare area’

(Figs 1.63a, b) and should not be mistaken for a cartilage defect ●● glenoid version:

●● in 75% of cases, the glenoid articular surface has a mean retroversion of 5-7° (Fig. 1.63c) ●● increased retroversion is a significant risk factor for posterior instability, each 1° increase in retroversion

resulting in 17% increased risk of posterior shoulder instability158 ●● in 25% of cases, the glenoid articular surface has a mean anteversion of 2-10° ●● glenoid anteversion and glenoid hypoplasia may predispose to glenohumeral instability

●● variations occur in the shape of the postero-inferior glenoid rim, which can be demonstrated by MRI;159 the different types assessed on the most caudal axial MR image which demonstrates glenoid articular cartilage and include: ●● a normal triangular shape, seen in 28% of cases ●● a ‘lazy-J’ shape, describing a rounded margin, seen in 59% of cases (Fig. 1.63d) ●● a ‘delta’ shape, describing a sharply angulated margin, seen in 13% of cases, commonly associated with

thickened hyaline cartilage and posterior labrum (Fig. 1.63e) ●● such glenoid dysplasia (glenoid hypoplasia, posterior glenoid rim deficiency) may predispose to posterior

labral tears and posterior instability:160 ●● moderate-to-severe dysplasia is significantly associated with the presence of posterior labral tears

compared to normal or mildly dysplastic posterior glenoid rims

●● glenohumeral instability: may be classified by its aetiology (traumatic, atraumatic and micro-instability), and its direction (uni-directional or multi-directional)

●● traumatic instability: is the commonest, typically being uni-directional (~95% anterior, ~3-5% posterior) and usually follows a single episode of dislocation, which may then become recurrent: ●● it is referred to by the acronym TUBS: Traumatic, Uni-directional, Bankart, Surgery

●● atraumatic instability: is typically multi-directional and commonly seen in individuals with congenital hypermobility syndromes: ●● it is referred to by the acronym AMBRI: Atraumatic, Multi-directional, Bilateral, Rehabilitation,

Inferior capsular shift (if surgery required) ●● micro-instability: a condition that is typically seen in the overhead athlete:

●● it is referred to by the acronym AIOS: Acquired, Instability, Overstress, Surgery

Traumatic Anterior Instability ●● traumatic anterior instability: follows an episode of anterior subcoracoid dislocation, classically due to a fall on

the outstretched hand in a person younger than 35-40 years of age: ●● in older patients, dislocation may result in an acute RCT tear, avulsion fracture of the greater tuberosity or

a tear of the subscapularis muscle and anterior capsule ●● stability of the glenohumeral joint depends upon both dynamic and static factors ●● dynamic stabilisers: include the rotator cuff muscles, LHBT, pectoralis major, latissimus dorsi and peri-

scapular muscles ●● static stabilisers: include the bony glenoid and hyaline cartilage, the fibrocartilaginous glenoid labrum,

the GHLs and the joint capsule ●● pathological lesions associated with anterior traumatic instability consist of a variable combination of soft

tissue and bony injuries

●● the soft-tissue Bankart lesion: represents a complete avulsion of the antero-inferior glenolabral complex (the antero-inferior labrum and anterior band of the IGHL) from the scapula and rupture of the scapular periosteum

●● it is the commonest injury, seen in ~74% of patients following anterior dislocation ●● during anterior dislocation or subluxation, traction on the IGHL is transmitted to the labrum, which may be

partially torn or completely detached from the glenoid rim ●● MRI findings:

●● increased SI at the glenolabral junction (Fig. 1.64a) (where the labrum shows focal detachment from the glenoid rim but remains contiguous with the anterior band of the IGHL) or an irregular, small or absent antero-inferior labrum (Fig. 1.64b)

certainty of acute Bankart lesions15 ●● MR arthrography findings:

●● an avulsed antero-inferior labrum with sublabral contrast in contact with a bare anterior glenoid rim (Fig. 1.64c)

●● linear contrast medium extending into the labrum indicating a labral tear (Fig. 1.64d) ●● a blunted labrum, resulting in an altered labral contour

●● ALPSA:169 anterior labroperiosteal sleeve avulsion, also termed the ‘medialised Bankart lesion’, represents an avulsion of the anterior scapular periosteum with the attached antero-inferior glenoid labrum (Fig. 1.65a): ●● it indicates chronic instability, rarely occurring after a single dislocation ●● rarely, the ALPSA lesion occurs in an anterosuperior location (Fig. 1.65b)170 ●● typically scars down in an inferior and medially displaced location, with MR arthrography demonstrating

a deficient antero-inferior glenoid rim and focal soft-tissue thickening along the glenoid neck, 5-15 mm medial to the glenoid rim, which has been termed the GLOM lesion (glenoid labral ovoid mass) (Figs 1.65c, d)

●● the Perthes’ lesion:171 represents a tear of the antero-inferior labrum from its osteochondral attachment, but not from its periosteal sleeve: ●● MR arthrography demonstrates contrast undercutting the antero-inferior labrum (Fig. 1.66a) ●● it may be difficult to diagnose on standard MRI sequences, particularly when the torn labrum remains

close to the glenoid rim in its normal anatomical location (Fig. 1.66b) ●● detection of the Perthes’ lesion is improved with arthrography in the ABER position (Fig. 1.66c)

compared to conventional MR arthrography, due to the tension provided by the IGHL on the labrum10 ●● glenolabral articular disruption (GLAD):172 caused by impaction of the humeral head against the antero-

inferior glenoid, and is usually a stable lesion resulting in anterior shoulder pain: ●● consists of a superficial tear of the antero-inferior labrum, which remains firmly attached to the anterior

scapular periosteum

●● an adjacent glenoid articular cartilage injury in the antero-inferior quadrant of the glenoid fossa, which may take the form of a cartilaginous flap tear or a depressed osteochondral injury (Fig. 1.67a)

●● the GLAD lesion is best imaged with MR arthrography, which shows extension of contrast material into the labral tear and a cartilage defect (Fig. 1.67b)

●● humeral avulsion of the glenohumeral ligament (HAGL):145,173-175 represents an isolated tear of the anterior IGHL from its humeral attachment rather than its labral attachment, usually associated with a severe dislocation: ●● it is reported in 7.5-9.4% of patients with anterior dislocation, usually in male patients involved in contact

sports (e.g. rugby) or those with 1st time dislocation over the age of 35 years

●● associated injuries include a tear of the subscapularis tendon insertion and dislocation of the LHBT ●● the capsular defect at the humeral attachment can result in a pseudopouch adjacent to the normal axillary

pouch, with fluid extending along the humeral neck into the quadrilateral space ●● up to 20% are associated with avulsion of bone from the humerus, referred to as a bony HAGL (BHAGL) ●● an associated Bankart lesion may rarely occur, giving rise to a ‘floating AIGHL’ lesion176 ●● in the acute setting, MRI demonstrates inhomogeneity or frank disruption of the anterior capsule at

the humeral insertion, with fluid anterior to the shoulder (Figs 1.68a, b) ●● in the chronic setting, HAGL lesions are more difficult to detect due to potential scarring down of

the IGHL to the humerus ●● MR arthrography may show a ‘J-shaped’ configuration to the anterior IGHL (in a right shoulder; reversed

‘J’ in a left shoulder), rather than the normal ‘U-shape’ on coronal images and extravasation of contrast through the capsular defect (Fig. 1.68c), which is fairly specific for IGHL rupture

●● rarely, a HAGL lesion may involve the axillary pouch of the IGHL rather than its anterior band, a finding that has been reported in volleyball players and baseball pitchers177

●● non-classifiable injuries:163 injuries that cannot be classified into the above categories at arthroscopy, typically in the setting of chronic anterior instability and reported in ~20% of cases:169 ●● MRI/MR arthrography demonstrate a swollen IGHL complex without clear distinction between the

labrum, IGHL and scapular periosteum (Fig. 1.69) ●● MR arthrography is able to classify the various types of antero-inferior labroligamentous injuries with

sensitivity of 96%, specificity of 80% and accuracy 95%178

Injury to Other Anterior Soft-tissue Structures ●● the anterior capsule: may be stripped from the scapular neck (Fig. 1.70a):

●● capsular injury in the absence of a Bankart lesion manifests as capsular thickening with adjacent increased SI (Fig. 1.70b)

●● MR arthrography may show elongation of the inferior and antero-inferior capsule in recurrent anterior dislocation179 (Fig. 1.70c)

●● the subscapularis tendon:90,180 in recurrent anterior dislocation undergoes tendinosis and tearing notably of its middle and inferior thirds: ●● thinning and elongation of the tendon has also been described (Fig. 1.70d) ●● the mean thickness and cross-sectional area of the subscapularis tendon in affected shoulders is 6.5 mm and

388.6 mm2 respectively, compared to 8.5 mm and 547.9 mm2 in unaffected shoulders

●● the Hill-Sachs deformity (Broca lesion): represents an impaction fracture of the posterolateral humeral head against the antero-inferior glenoid rim during anterior dislocation, and may be cartilaginous or osteocartilaginous: ●● its incidence based on arthroscopy following 1st time anterior dislocation is reported as at least 25%, with

nearly 100% prevalence following repeated dislocations ●● the lesions may range from a shallow, mainly chondral defect, to a deep osteochondral lesion ●● those defects that involve less than a third of the humeral head circumference are regarded as

prognostically insignificant ●● larger lesions, particularly if orientated parallel to the glenoid, are more likely to result in repeated

subluxation and dislocation ●● the bony Bankart lesion: represents an avulsion fracture of the antero-inferior rim of the glenoid during

anterior dislocation: ●● large fractures (>7 mm fragment width or >20-30% of total glenoid surface area) may result in recurrent

instability and preclude arthroscopic repair ●● MRI findings:

●● the Hill-Sachs lesion: appears as a defect in the posterolateral humeral head, and is best identified on axial images at or just above the level of the coracoid process (Fig. 1.71a), at this level the humeral head is normally round:

● the lesion fills with contrast at MR arthrography (Figs 1.71b, c)

● a Hill-Sachs defect must be differentiated from the normal humeral groove on the posterolateral aspect of humerus,183 which arises >2 cm from the top of the humeral head

● the Hill-Sachs deformity lies in a more cephalad position, usually in the top 2 cm of the humeral head ● an acute lesion may be associated with bone bruising (Fig. 1.71d), while purely cartilaginous lesions

are difficult to identify184 ● large lesions may engage the glenoid rim, reproducing symptoms of instability ● the ‘engaging Hill-Sachs lesion’ extends into the articulating surface of the humeral head, resulting in

apprehension, subluxation or even dislocation in the ABER position185 ● MRI has a sensitivity, specificity and accuracy of 97%, 91% and 94%, respectively, for the detection of

Hill-Sachs lesions ●● the bony Bankart lesion: is best identified on axial images through the inferior glenoid (Figs 1.72a, b):

● a fracture that results in the AP glenoid dimension above the mid-glenoid notch being greater than that below, as assessed on sagittal oblique images (Fig. 1.72c), is considered clinically relevant

● MRI and MR athrography using the ‘circle method’ have been reported to be accurate in estimation of glenoid bony defects when compared with 3D-CT:186,187 – T1W sagittal images with an ‘en-face’ view of the glenoid are required with a slice thickness of 1-2 mm;

a vertical line bisecting the glenoid along its long axis is drawn from the supraglenoid tubercle – the inferior portion of the glenoid contour can be approximated as a true circle, ensuring that the

centre of the circle overlays the vertical line; the percentage bone loss along the glenoid width can thereby be estimated

●● posterior dislocation: is uncommon and usually results from violent muscle contraction associated with an epileptic fit or electric shock, but may also result from recurrent microtrauma, as seen in swimmers and throwers etc.